THE PENNSYLVANIA STATE UNIVERSITY SCHREYER HONORS COLLEGE DEPARTMENT OF MATERIAL SCIENCE AND ENGINEERING DEVELOPMENT OF KEVLAR ARAMID NANOFIBROUS MEMBRANES FOR NANOFILTRATION SEPARATION PROCESSES NATALIE DAYRIT MAMROL FALL 2020 A thesis submitted in partial fulfillment of the requirements for a baccalaureate degree in Material Science and Engineering with honors in Material Science and Engineering Reviewed and approved* by the following: Michael Hickner Professor of Materials Science and Engineering, Chemical Engineering Thesis Supervisor Robert Allen Kimel Associate Professor of Materials Science and Engineering Associate head for Undergraduate Studies in Material Science and Engineering Honors Adviser * Signatures are on file in the Schreyer Honors College.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
THE PENNSYLVANIA STATE UNIVERSITY SCHREYER HONORS COLLEGE
DEPARTMENT OF MATERIAL SCIENCE AND ENGINEERING
DEVELOPMENT OF KEVLAR ARAMID NANOFIBROUS MEMBRANES FOR NANOFILTRATION SEPARATION PROCESSES
NATALIE DAYRIT MAMROL
FALL 2020
A thesis submitted in partial fulfillment
of the requirements for a baccalaureate degree
in Material Science and Engineering with honors in Material Science and Engineering
Reviewed and approved* by the following:
Michael Hickner Professor of Materials Science and Engineering, Chemical Engineering
Thesis Supervisor
Robert Allen Kimel Associate Professor of Materials Science and Engineering
Associate head for Undergraduate Studies in Material Science and Engineering Honors Adviser
* Signatures are on file in the Schreyer Honors College.
i
ABSTRACT
There is a critical need for sustainable and advanced separation processes to provide access to
clean water and recover or separate hazardous materials from waste streams as the global population
skyrockets and millions of people face water shortages due to contaminated water and depletion of natural
resources.
Therefore, this thesis reports two pressure-driven nanofiltration membranes for organic solvent
nanofiltration (OSN) and desalination applications with a sustainability focus. The first membrane
reported is a thin film composite (TFC) Kevlar aramid nanofibrous (KANF) membrane synthesized via a
pressure vacuum filtration and heat treatment method. This membrane utilized a green approach to create
a controllable membrane structure through a simple deposition of Kevlar aramid nanofibers (KANFs)
onto a microfiltration support membrane and subsequent heat treatment. With this method, the water
between KANFs was removed to form a nanofiltration selective layer with adjustable thickness. Proof of
concept and potential of this membrane as a viable and sustainable fabrication method is reported,
however future work must be completed before this can be considered a viable fabrication method for
OSN membranes.
The second membrane reported is a thin film composite (TFC) KANF hydrogel membrane that
used a novel approach to perform interfacial polymerization (IP) of piperazine (PIP) (0.015, 0.0175 wt%)
and trimethyl chloride (0.01 wt%) onto a Kevlar aramid nanofibrous hydrogel membrane with thickness
of the selective layer as low as 15.5 nm. This method yields superior desalination performances with an
ultrafast permeance of 52.8 and 62.9 Lm-2h-1bar-1 and a rejection of 96.4% and 93.5% for Na2SO4. This
method utilized the hydrogel as a free water phase for IP and reduces the diffusion of PIP monomers to
the interaction surface, hence resulting in an extremely thin selective layer. Overall, this membrane
outperformed current and state-of-the-art membranes with permeability nearly 3 times higher than the
average, and it reduced the fabrication steps and simplified the scalability for a green alternative
membrane technology.
ii
TABLE OF CONTENTS
LIST OF FIGURES ..................................................................................................... iii
LIST OF TABLES ....................................................................................................... iv
ACKNOWLEDGEMENTS ......................................................................................... v
Preface.......................................................................................................................... viii
Considerations in Engineering and Design..................................................................... 23 Economic Issues ..................................................................................................... 23 Environmental Issues and Sustainability ................................................................ 26 Ethical, Social, and Political Issues ........................................................................ 27 Health and Safety ................................................................................................... 29 Code of Hammurabi ............................................................................................... 30
Synthesis of Nanofibrous Hydrogel Support Saturated with PIP Monomers .......... 50 Interfacial polymerization on nanofibrous hydrogel for TFC nanofiltration membrane 51 Interfacial polymerization on conventional PSU ultrafiltration membrane for
Figure 1 Bar graph of increasing number of publications on OSN membranes ..................... 4
Figure 2 Diagram of membrane in a feed solution under a driving force ............................... 7
Figure 3 Schematic of symmetric and asymmetric membrane structures18 ............................ 8
Figure 4 Interfacial polymerization between PIP and TMC23 ............................................... 12
Figure 5 Strategy to develop greener membranes through the principles of green chemistry25 14
Figure 6 Energy consumption to concentrate 1 m3 of a dilute solution in methanol using (a) distillation and (b) membrane25 ...................................................................................... 15
Figure 7 a) Synthesis of aramid monomer (PPTA) from p-phenylene and diamineterephthaloyl chloride; (b) Homogenization of Kevlar into homogeneous KANF solution; c) Structural transformation of macroscopic aramid fibers into nanofibers; Dissolution of Kevlar with DSMO/water with KOH catalyst system (d) Splitting of PPTA threads into nanofibers to form KANF solution29 .................................................................................................... 18
Figure 8 Comparison of KANF Hydrogel to Conventional (PSU) Polymeric Membrane1 .... 21
Figure 9 Diagram of coating line for fabrication of support membrane41 ............................... 25
Figure 10 Diagram of reaction line for fabrication of thin-film composite RO membrane41 .. 25
Figure 11 Dissolution of PPTA into red and viscous KANF Solution1 .................................. 34
Figure 12 Dead end filtration equipment including a) filtration cell; b) 3-way valve; c) pressure regulator54 ...................................................................................................................... 35
Figure 13 Picture of Crossflow Filtration Unit Set Up54 ........................................................ 35
Figure 15 Schematic for vacuum assisted filtration over a microporous support for KANF membranes ..................................................................................................................... 44
Figure 16 SEM images of a) Alumina microporous support membrane; b) Alumina and KANF membrane; c) Uncoated regions on alumina support; d) PTFE microfiltration support membrane e) PTFE and KANF membrane .................................................................... 46
Figure 17 Step by step process for fabrication of hydrogel-TFC membrane1 ......................... 49
Figure 18 KANF Hydrogel post drying with super critical dryer1.......................................... 50
Figure 19 Impact of Applied Pressure on TFC KANF Membrane ......................................... 52
v Figure 20 Permeability and Rejection for Varying PIP Concentrations for the TFC KANF
Figure 25 Picture of TFC KANF Hydrogel Membrane .......................................................... 58
Figure 26 SEM images of a) the nanofibrous network of KANFs in the hydrogel membrane; b) the surface of the TFC PSU KANF hydrogel membrane ............................................... 59
Figure 27 TEM images of the thickness of the selective separation layer of the KANF TFC hydrogel membrane fabricated with PIP concentrations of: a) 0.015 wt%; b) 0.02 wt%; and c) 0.04 wt%, and d) the thickness of the freestanding membrane at PIP concentrations 60
Figure 28 AFM morphology of Hydrogel-TFC membranes synthesized from PIP concentration of 0.0175 wt% and 0.02 wt% ............................................................................................. 60
Figure 29 Water contact angle of dry nanofibrous hydrogel (72°) and Hydrogel-TFC membrane (PIP-0.015,54°) ........................................................................................................... 61
Figure 30 Surface morphology of Hydrogel-TFC membranes ............................................... 65
Figure 31 Surface morphology of PSU-TFC membranes ...................................................... 65
vi
LIST OF TABLES
Table 1 List of Materials for Experiments ............................................................................. 31
Table 2 List of Solutes for Membrane Characterization......................................................... 32
Table 3 Dyes Used for Rejection Tests .................................................................................. 32
Table 4 Roughness of TFC KANF Hydrogel membranes ...................................................... 61
vii
ACKNOWLEDGEMENTS
There are several people that I want to acknowledge for the completion of this thesis, mentorship
through my undergraduate experience, and for their unconditional support and love.
First, I would like to thank my supporting faculty, department, and advisers for giving me this
opportunity to conduct research and write a senior honors thesis. I am grateful for Dr. Hickner and his
support, research opportunities, and academic freedom to pursue my scientific interests. I would like to
thank Dr. Van der Bruggen for accepting me into his lab with a collaborative and supportive research
environment. Thank you to Dr. Kimel for supporting my application to enter the Schreyer Honor College
and pursue my research interests. I would like to thank Dr. Runt and Dr. Preeya Kuray for getting me
started in research through the NASA WISER Freshman Internship. Also, I want to give a shoutout to
Miss Meg Abplanalp for her superior advising and support.
To my mentors in this project, Dr. Shushan Yuan, Dr. Yan Zhao, and Dr. Zhaohuan Mai; I would
like to say I am incredibly grateful for your guidance, teachings, and support. I would have never been
able to complete this thesis without you. I learned so much about the scientific method, membrane science
and characterization, writing research papers and literature reviews, and persistence in experimentation.
Thank you for including me into your research efforts with an abundance of opportunities and into your
lives. I also want to thank the rest of Dr. Van der Bruggen’s lab for the excellent memories and
collaboration.
To my friends, thank you for listening to me and supporting me through every stressful and
exciting moment. It means the world to be able to share and grow through college with you.
Finally, to my family: Maria and Francis Mamrol, Alex and Jimmy Mamrol, and Virginia
Mamrol, thank you for everything; I love you very much.
viii
Preface
This thesis contains two novel major works that I completed during my undergraduate career
related to the development of Kevlar aramid nanofibrous (KANF) membranes for organic solvent
nanofiltration and nanofiltration for desalination separations. The two works that I have included are a
vacuum filtration technique and heat treatment method for KANF TFC membranes, and interfacial
polymerization technique for TFC KANF hydrogel membranes. These works were completed during a
study abroad research experience and continued with cooperation at my home university, Penn State
University.
Through the Euroscholars Research Abroad program, I was fortunate to work in Belgium at De
Katholieke Universiteit Leuven (KU Leuven) in the membrane science group led by Dr. Van der
Bruggen. During this experience, I contributed to two major works published in The Journal of Materials
Chemistry1 and The Journal of Membrane Science2 as the fourth and fifth coauthor, respectively, and
contributed as an editor to another published work in Chemical Society Reviews.3 I also recently
submitted a literature review on electro-driven membranes for Lithium recovery as a second co-author.
For this thesis, I draw upon my significant contributions to these projects and my own novel work on the
vacuum filtration and heat treatment method technique for KANF membranes.
My contributions to these projects are related to my material science and engineering area of
study with emphasis on polymeric synthesis and design for membranes. In these works, I led or co-led the
synthesis and modification of the polymer-based membrane; testing of permeability, selectivity, and
stability; and analysis of SEM/TEM, water contact angle, water uptake, surface roughness
characterization. Other characterization pertaining to these works will be mentioned in this thesis such as
XPS, zeta potential, and mechanical strength, however I was not the lead on those characterizations.
During my time at Penn State University, I worked in Dr. Hickner’s lab on 3D printing of
colorimetric sensing membranes and sensors. I would have liked to integrate the works from both
ix universities together. Although due to time constraints and the ramifications on research due to the
COVID-19 pandemic, I was unable to integrate the two works together to produce a solvent resistant 3D
printable membrane.
1
Chapter 1
Introduction
The current impact of global population growth and technological advancements is
unprecedented in significance and consequence on the environment and global resources.4 Rapid
consumption of goods and technological innovations in industrialization, manufacturing, and energy
production have increased human prosperity throughout the world.5,6 In effect, rates of infant mortality
decreased, human life expectancy increased, adult literacy increased, access to education improved, and
global food production increased faster than the population grew.7 However, this prosperity is at the
expense of the depletion of the world’s stock of natural resources, and ecological and development
models shows trends of the detrimental consequences leading to the developing ecological crisis and
widening social disparities on future generations.8
Therefore, a critically important challenge to sustain current global development is in the
advancement of green technology. “Green” technology refers to the field focused on the development of
materials and processes to reduce current society’s environmental impact. The goals of this field are
rooted in sustainability, source reduction, and innovation.9 Furthermore, there is a current push to find
green technologies to address the global drinking water crisis. The World Health Organization (WHO)
estimates that there are over one billion people who cannot access clean water. In addition, health
monitoring reports that everyday about 4000 children die from waterborne diseases as a result of water
pollution.10 Part of this problem lies in that the available drinking water is either brackish or polluted by
human activities and the discharge of effluents from industrialization.
Solvent losses account for a major proportion of organic pollution. In chemical and
pharmaceutical industries, organic syntheses typically use organic solvents as raw materials, cleaning
2 agents, and reactants with high value products that must be recovered or discarded by the end of the
process. These industries consume an excessive amount of solvents, and it has been estimated that the
annual industrial scale production of organic solvents is nearly 20 million MT (metric tons)11. The
treatment including separation, recovery, and disposal of these organic waste streams consume a lot of
energy that accounts for nearly 40-70% of both capital and operating costs in chemical processing
operations, and separation processes account for 10 to 15 percent of the world’s energy consumption.12
While the excessive consumption of nonrenewable and toxic solvents is unsustainable, solvation remains
a critical component for maintaining selectivity control, purity, safety, and improved handling for many
chemical processes.
Additionally, the use of water as a solvent in industrial applications produces wastewater streams
that become polluted due to the discharge of potential emerging pollutants (PEPs) such as toxic
chemicals, pharmaceutical by-products, heavy metals, fertilizers, sludge, and endocrine disruptors. These
pollutants can contribute to waterborne pathogens that have severe health consequences if they diffuse
into groundwater and pose serious threats to water ecology at large. PEPs require clear identification,
separation, and disposal, however according to the United States Environmental Protection Agency
(USEPA), these hazardous materials lack the regulatory standards.10 Likewise, a current issue is the
pollution of drinking water with an array of violate organic compounds and semi-volatile organic
compounds following the California forest fires. In the aftermath of the fire, toxins are released from the
plumbing systems, and damage can reside in the pipes for years.13
Another potential source of water is from brackish or brine water, domestic waste waters with
high total dissolved solids, and on-site treatment of water used in fracking treated within desalination
plants for potable use. For example, in 2015, the International Desalination Association reported there are
at least 18,426 desalination plants in over 150 countries that each day produce 86.8 million m3 or 22.9
billion gallons of water. Potential saltwater sources typically contain total dissolved solids of 1,000 to
3 3,000 mg/l in brackish water and 35,000 mg/l in open ocean. These sources also contain a variety of ions
such as sodium, calcium, magnesium, and sometimes even contain microbes.14
Conventional separation treatments such as adsorption, distillation, liquid-liquid extraction, media
filtration, and macro-porous polymer extraction can be used in the treatment of wastewater, organic waste
streams, and salt water, but are energy intensive and need improvements in separation efficiency.
Membrane separation-based processes are another technique to treat water and organic waste streams that
have a low initial investment, low costs of production and maintenance, are less energy intensive, and
produces high ratio of water quality to solute recovery. In fact, membrane based separation systems have
reported potential to decrease energy consumption by 90% to traditional methods.15 There are many
different membrane separation processes including microfiltration (MF), ultrafiltration (UF),
nanofiltration (NF), and reverse osmosis, and these processes separate out particle sizes ranging from
molecular weight cutoffs of 3,000 to 500,000 Dalton (Da), 2000-100,000 Da, 300-500 Da, and 100-200
Da, respectively. Based on the size of solvents and ions in water, nanofiltration membrane technology is
an excellent process for the highest purity in separation and recovery of small solvent molecules or
purification of brackish water.
For example, in the last 10 years, there have been an increasing amount of studies on OSN
membrane synthesis and fabrication (Figure 1), however it has yet to make an industrial breakthrough.
There are two reasons for this: the need to improve the chemical stability and maintain sustainable
scalability of the nanofiltration membranes.12 OSN membranes synthesized with ordered structures and
controllable chemical activity are ideal for this application.
4
Figure 1 Bar graph of increasing number of publications on OSN membranes
Furthermore, there is significant interest in increasing the efficiency of desalination plants
through the fabrication of membranes with faster permeance and high rejection.1 Higher efficiency
ultimately provides more water to regions with critical shortages and reduces the consumption of energy
leading to a more sustainable process. Lastly, the fabrication and life cycle of the membranes need to be
sustainable to offset any potential CO2 footprint.
Motivation of this work
There is a need for green technology for reducing solvent waste and pollution into wastewater
steams from industrial chemical processes and for increasing the efficiency of desalination plants. The
goal of this work is to address this challenge with the synthesis of “green” fabrication methods for KANF
membranes with improved solvent resistance for industrial applications and desalination performance.
There are several criteria for the KANF nanofiltration membranes to achieve this goal. First, the
criteria include using greener solvents and low toxicity chemicals for casting, coating, and crosslinking,
and reducing solvent waste in membrane production. The next criteria are minimizing energy usage in
preparation and synthesis and exploring the use of new solvent resistance materials in membrane
5 fabrication. Finally, in conjunction, this work aimed to improve membrane separation performance
against current competition
With these criteria, two novel solvent-limited fabrication techniques were developed with a high-
performance polymer, Kevlar aramid nanofibers (KANFS), to prepare OSN and desalination NF
membranes. KANFS are an emerging material for the synthesis of membranes with excellent physical
properties, high mechanical strength, and solvent resistance. The research objectives of this thesis are
summarized in two parts: First, a pressure vacuum filtration method for the fabrication of KANF
membranes synthesized by the regeneration of hydrogen bonds by a heat treatment for organic solvent
nanofiltration. Second, a KANF hydrogel assisted interfacial polymerization TFC nanofiltration
membrane for desalination of water.
Overall, the separation performance and economic efficiency of membrane-based technology for
advanced separations of solvent are highly dependent on the membrane fabrication and structure.
Therefore, it is critical to understand conventional and current membrane separation technology before
the development of novel techniques.
6
Chapter 2
Literature Review
Conventional Membrane Separation Technology
Membrane science and technology is the field of engineering for the selective transport of a target
component or separation of a mixture by a semi-permeable barrier. Mixtures or feed solutions pass
through these barriers or membranes by a driving force such as pressure, concentration, electrical
potential, or temperature. Permeate passes through the membrane via flux or permeation and is enriched
with the target components. Retentate is retained by the membrane via selectivity and is enriched with the
leftover components as shown in Figure 2. Membranes are designed to have high selectivity and high flux
or permeability towards the target specie, mechanical strength, chemical stability, low fouling in
operating conditions, and cost-effective production and maintenance.16
Other advantages of membrane-based separation are the operations are often compact, cheap, and
simple. For example, membrane technology generally costs less, is easier to operate, and have high
efficiency and performance than distillation processes. However, some limitations of membranes include
lack of long term established reliability, need for some pre- and post- treatment procedures, and lower
mechanical strength. Research and developments in membrane technology actively find solutions to
overcome these limitations, and state-of-the-art membrane technology has many markets in desalination,
food processing, sterilization, hemodialysis, and alcohol recovery.17
7
Figure 2 Diagram of membrane in a feed solution under a driving force
Membrane Structure, Properties, and Characterization
Membranes are homogenous or heterogenous, symmetric or asymmetric, porous or dense,
sometimes charged or neutral, or at times even a liquid as shown in Figure 3. Asymmetric membranes are
the most important commercial type of membranes compared to symmetric membranes. In symmetric
membranes, the structure and composition are homogenous and usually are limited in application by the
greater thickness of the separation layer and low flux. Asymmetric membranes have layered structures
that differ in porosity, pore size, or even composition from top to bottom of surface. The top layer
typically has a thin and selective layer for selectivity of target specie and higher flux across the
membrane. The bottom layer is the support for the top layer and is usually thicker as a microporous
substrate. The bottom layer does not contribute to the selectivity but needs to be compatible with the top
layer to ensure membrane stability and handling. The cross-section of membranes is identified through
scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. These
methods are used to identity the structural properties of the membrane and is very important in the overall
performance of the membrane.17
8
Figure 3 Schematic of symmetric and asymmetric membrane structures18
Other important structural properties of membranes include the surface roughness of the top layer
and thickness of the top selective layer. Surface roughness of the top layer contributes to the fouling
potential of the membrane, essentially the stability of the membrane flux over time. Greater surface
roughness may increase the effective surface area of the selective layer for higher permeability and
performance, but also increases effect of membrane fouling.19 Surface roughness is characterized by
scanning electron microscopy and atomic force microscopy. In addition, the thickness of the selective
layer is characterized by scanning electron microscopy. 20
Physical properties also greatly influence the performance of the membrane including
hydrophilicity or hydrophobicity and swelling. Depending on the application of the membrane in
wastewater or organic waste streams, hydrophilicity or hydrophobicity determines its interaction and
potentially its rate of transport across the membrane. This property is determined by the contact angle of
water or sometimes solvent on the membrane surface. Swelling is another important physical property
because the degree of swelling in an aqueous solution may impact the stability of the membrane. For
9 example, if the water uptake in a hydrogel membrane is too high, it may rupture or tear. Swelling is
measured using a simple swelling test.20
Furthermore, chemical properties play a critical role the performance of the membrane. Surface
chemistry affects the interaction of the membrane surface to the solutes in solution. Due to the Donnan
effect, the flux or rejection of the membrane may be greatly impacted by the membrane electronegativity.
Furthermore, the membrane may become fouled or clogged based on the chemical interaction with the
feed solution. The surface chemistry is measured by x-ray photoelectron spectroscopy and attenuated total
(PEEK), polyethersulfone (PES), and polydimethylsiloxane (PDMS), and polyamides (PA).26 These
polymers are solvent resistant and do not swell into solvent solutions. However, a soluble polymer
solution for membrane fabrication often uses large consumption of aggressive and often hazardous
14 solvents such as NMP, DMAC, DMF, and H2SO4. Moreover, a common way to improve polymer solvent
resistance is crosslinking. For example, OSN membranes are fabricated through an interfacial
polymerization and crosslinking process onto an ultrafiltration membrane. The process forms a highly
selective separation layer and converts the ultrafiltration into a nanofiltration membrane. However, this
process uses a large amount of solvent and crosslinking chemicals; ultimately increasing the cost and the
environmental burden in fabrication.27
Figure 5 Strategy to develop greener membranes through the principles of green chemistry25
Sustainability Assessment of OSN Membranes
The limiting factor in the application of OSN membranes is the development of a membrane that
is both stable and scalable. Research on this topic focuses on the development of novel materials,
improved membrane modules, and innovative systems.12 Meanwhile, researchers balance the scalability
and stability of OSN membranes with the sustainability of fabrication and processes, economic
competitiveness compared to downstream technology, and selectivity and productivity of solvent
recovery.25 This is achieved by using greener solvents, low toxicity materials, lower number of fabrication
steps, room temperature production, and renewable or degradable materials as shown in Figure 5.25 In
15 addition, as the advancements on the permeance of OSN membranes plateaus, more important work on
non-deal membrane module effects such as concentration polarization and pressure drop, need to be
addressed to enable bulk liquid separations in industrial settings.12 Overall, OSN membranes can have a
much lower CO2 footprint than distillation, prompting the continued research of this field. For example as
depicted in Figure 6, the energy consumption to concentrate 1 m3 of a dilute solution in methanol from
membrane filtration decreases by a factor of ten compared to distillation. 25
Figure 6 Energy consumption to concentrate 1 m3 of a dilute solution in methanol using (a) distillation and (b) membrane25
Membrane Application: Desalination by Nanofiltration
Desalination is a method used for water treatment and purification to solve the water scarcity
problem. Nanofiltration desalination is membrane separation technology that uses an applied pressure
across a semi-permeable membrane for water treatment. There is a need for faster permeance and higher
salt rejection for industrial applications of desalination membranes. One potential drawbacks of this
technology are concentration polarization of the membrane separation process and can lead to membrane
fouling. The sustainability focus of desalination membranes is aimed at reducing the energy costs and
16 increasing the water recovery. In addition, sustainable fabrication of the desalination membrane is also
important.28
Kevlar Aramid Nanofibrous Membranes
Kevlar aramid nanofibers (KANFs) are an emerging material for the fabrication of membranes
with excellent intrinsic physicochemical properties. KANFs are a class of one-dimensional organic
nanomaterials typically obtained from the dissolution of Kevlar fabric. The characteristics of this material
are high solvent resistance, high strength material, making it ideal for the synthesis of solvent resistance
membranes. This thesis is interested in adapting Kevlar membrane fabrication into a more-green route
and gain better control over the structure, and membranes of this nature were also reviewed by Y. Zhao,
Xi Li, et al.29
Structure and Synthesis of KANFs
Kevlar is the commercial name for polyparaphenylene terephthalamide (PPTA) and is a class of
synthetic polymers that form para-crystalline fibers when spun from crystalline dopes. PPTA is used for
high performance applications due to its high strength to weight ratio and gained notoriety through its
application in ballistic protective fabrics such as bulletproof vests and as a reinforcement for aerospace
components.30 This material is produced by the reaction of terephthaloyl chloride and p-
phenylenediamine in a solvent mixture of hexamethylphosphoramide and N-methylpyrroliodone to obtain
a fiber form.
Compared to traditional polymers, PPTA has a highly ordered, asymmetric chemical structure of
long molecular chains of alternating benzene rings and aramid bonds; strengthened by strong
intermolecular forces such as hydrogen bonding, π -π stacking bonds, and van der Waal forces.31 When
17 fabricated into a membrane, KANFs form strong interactions between nanofibers and matrices resulting
in high mechanical strength. KANFs differ from other nanofibers with their super intrinsic
physiochemical properties due to their ordered and asymmetric alternating nanostructure of molecular
chains and ability to hydrogen bond.29
New research on the dissolution of Kevlar (PPTA) fabric utilizes a green approach to obtain the
nanoscale version of aramid nanofibers (KANFs). This approach to dissolve Kevlar (PPTA) uses
DMSO/KOH at 70 to 90°C instead of corrosive H2SO4 in the preparation of a dope Kevlar nanofibrous
solution.27 Former methods to obtain KANFs were limited in efficiency, scalability, and controllability
due to the caustic nature of H2SO4. 32 Comparatively, the DMSO/ KOH solution breaks down PPTA in a
facile and safer manner, breaking the strong interchain bonds between fibers and deprotonation of amide
groups to form KANFs.31 In this method, the short PPTA polymer chains or nanofibers were dispersed
into the solvent with diameter of 20-30 nm, and increased the viscosity of the solution. The concentration
of KANFs in solution is adjustable from 1.0 to 6.0 wt%.The resulting KANFs membranes from phase
inversion have a large specific surface area and strong intermolecular forces due to the increase number of
functional groups such as COOH and NH2. The process for PPTA synthesis, homogenization of PPTA
into KANF solution with DMSO/KOH, structural transformation of PPTA into KANFs, and splitting of
PPTA into KANFs is shown in Figure 7.29
18
Figure 7 a) Synthesis of aramid monomer (PPTA) from p-phenylene and diamineterephthaloyl chloride; (b) Homogenization of Kevlar into homogeneous KANF solution; c) Structural transformation of macroscopic aramid fibers
into nanofibers; Dissolution of Kevlar with DSMO/water with KOH catalyst system (d) Splitting of PPTA threads into nanofibers to form KANF solution29
Key Properties
One of the main advantages of KANFs are their tunable structure that enable fabrication for
practically any application, and dense or porous membranes are attainable through a variety of techniques
that adjust the structure of the nanofibers. Furthermore, KANFs benefit from a combination of useful
properties including electrical conductivity, hydrophilicity or hydrophobicity, flexibility, mechanical
robustness, physical and chemical stability, and resistance to solvents.29
Tunable Structure
KANFs have a highly tunable structure of single PPTA polymer chains and form a dense
membrane structure with the regeneration of hydrogen bonds through a simple phase inversion and drying
process. Pore size of the resulting membranes is highly dependent on the geometry and connectivity of
19 interactions between molecules. The stronger interactions between molecules increase the strength of the
KANF membrane, but negatively decrease the flux limit. Therefore, a variety of techniques such as
physical dispersion, blending, hybridization, interpenetrating polymer networks, and MOF and COF
networks were developed to tailor the structure of KANFs to yield membranes with high separation
performance. Additionally, the characteristic NH2 and COOH groups of KANFs can be used to react with
various monomer or polymers through substitution reactions or amide condensation reactions to tune the
structure for numerous applications.29 For this thesis, the KANFs were used as dissolved without any
further modification.
Physico-Chemical Stability
The physical and chemical stability of KANFs are excellent due to their chemical structure. The
strong amide groups and hydrogen bonds between KANF molecules yield outstanding mechanical
properties and thermostability. Likewise, these intermolecular forces yield high chemical stability and
resistance to solvents. KANFs can also be prepared with physically or chemically stable polymers such as
methoxypolyethylene glycol to form uniform and stable dispersions.33
Hydrophobicity/ Hydrophilicity
KANFs can exhibit hydrophilic or hydrophobic behavior depending on chemical reactions with
other compounds on the amide bonds. For organic solvent nanofiltration membranes, hydrophobicity is
important to avoid scaling and is achieved through KANF mixtures with polyvinyl fluoride (PVDF) or
poly(dimethylsiloxane) (PDMS). 34
20 Selectivity
The size seizing effect between target molecules and ions is the most effective way for selective
separation and is crucial for resource recycling and for zero emissions targets in industry. The structure of
KANF based membranes relies on the strong and dense interactions between particles and can be tailored
for specific pore sizes and pore size distributions for selective separation of molecules or ions. Moreover,
electrostatic repulsion is another method to increase selective separation with the addition of charged
functional groups on the membrane surface.29
Design of KANF Fabricated Membranes
There are several methods for the design of KANF based membranes for precise and rapid
separations. Following the dissolution of PPTA into KANFs, additives may be added to the casting
solution before a phase inversion process to transform KANFs into KANF membranes. In the phase
inversion process, the casting solution is spread out buy a casting knife onto a glass plate in an even and
uniform manner. The glass plate is submerged into a water bath, and though an immersion phase
inversion process, the organic solvent in the membrane is rapidly replaced with water to precipitate a
dense asymmetric KANF hydrogel membrane (Figure 8). The membrane has a gel-like feel and is
removed from the water bath for drying.27 Additionally, various techniques exist such as blending,
chemical reactions, network interpenetrating, and interfacial polymerization. These techniques are
employed to adapt and modify the membrane for specific applications by selecting specific or
functionalized materials and integrating them into the membrane.29
21
Figure 8 Comparison of KANF Hydrogel to Conventional (PSU) Polymeric Membrane1
Blending is a technique that disperses compatible nanoparticles, nanosheets, nanowires, or
organic polymers and monomers into the KANF solutions. These additives can increase the flux or
selectivity of membranes and functionalize for certain applications.35–37 Chemical reactions utilize amide
hydrolysis and condensation to functionalize COOH and NH2 groups on KANFs with charged monomers
for electrochemical membrane applications. Likewise, through substitution reactions on the benzene rings
and aramid groups, the hydrophilicity or hydrophobicity of KANF based membranes is modified.38
Chemical reactions may also be initiated post phase inversion for secondary processing functionalization.
Composite KANF membranes with interpenetrating networks are formed through the addition of small
crystals, molecules, or polymers into the hydrogel. This technique is typically used for functionalization
of KANF membranes in electrolyte and fuel cells.39 Interfacial polymerization (IP) forms a thin active
layer onto a porous hydrogel support membrane, and typically uses TMC, and MPD. The latter part of
this thesis adapts KANFs hydrogels as support membranes from IP for desalination.
22 Applications of KANF Membranes
The tunable structures and adjustable composition of KANF membranes endows specific pore
size for a wide range of applications including water treatment, organic solvent nanofiltration, separation
of ions, battery separators, and proton exchange membranes.29
23
Chapter 3
Engineering Considerations
Considerations in Engineering and Design
This section evaluates the engineering considerations of this work such as economic issues,
environmental issues, sustainability, manufacturability, ethical issues, health and safety, social and
political implications, and the Code of Hammurabi.
Economic Issues
Several factors needed to be considered for the application of these membranes in industrial
settings such as the cost of materials, the cost of processing, and manufacturing technology.
Cost
To become competitive, KANF OSN and desalination membrane separation processes must be
less energetically, chemically, and operationally intensive than other traditional separation processes and
other membrane separation processes. Membrane separation technology is a continuous process that
consumes less energy and contends with conventional methods such as adsorption, absorption,
evaporation, distillation, crystallization, and chromatography. In my proposed works, the main component
of these membranes is KANFs, and unlike other technical polymers, KANFs are a lower cost material
because they are easily produced from strands of Kevlar fiber and do not need crosslinking agents or
24 additives to create 3D networks. Furthermore, the advantageous economic interest of KANF membranes
is linked to their facile fabrication. In these works, KANF membranes are processed with less solvent
intensive processes. Using less solvent reduces the costs in raw materials, additional processing steps, and
post processing steps. Furthermore, these KANF OSN and desalination membranes can be used in
existing membrane separation process technologies or adapted into a hybrid process with conventional
techniques.
There are also some hidden costs to consider such as energy costs, marketability, intellectual
property, life cycle cost, and local, state, or federal interactions. The product must yield competitive
separation performances in life cycle assessments to be implemented into industrial applications.
Likewise, the intellectual property of the membranes should be protected by patents before large scale
applications of KANF membranes at companies like Dow, Dupont, and BASF. Significant push to
implement these membranes in membranes modules at the state or private sectors must also be funded.
Start-up grants are an option to find investors.
Manufacturability and Operations
The manufacturability and implementation of these novel membranes is achievable within several
years. The deliverable products from this study has promise for economic and environmentally friendly
scalability. For example, large sheets of KANF membranes were synthesized via phase inversion as a
proof of concept.27 Furthermore, the two proposed methods for membrane fabrication can be adapted to
existing membrane fabrication module infrastructures such as the support membrane and TFC membrane
manufacturing systems. Figure 9 and 10 show schematics of a coating line membrane fabrication module
and a TFC reverse osmosis membrane fabrication module. In the support membrane module, two extra
steps of vacuum filtration and heat treatment with the novel casting solution can be added to convert the
support membrane into a nanofiltration membrane. Likewise, the TFC membrane manufacturing system
25 can be adapted with the new KANF hydrogel support. By using existing membrane manufacturing
infrastructure, the cost of manufacturing decreases. In addition, the standard module design for NF
membranes is spiral wound geometry. This module has the benefit of being compact, easy to operate, and
lower cost than other modules.40
Figure 9 Diagram of coating line for fabrication of support membrane41
Figure 10 Diagram of reaction line for fabrication of thin-film composite RO membrane41
Overall, these proposed membranes can be adapted in a profitable manner. Specifically, OSN
membranes have the potential for commercialization and have been demonstrated at a membrane unit at
ExxonMobil’s Beaumont refinery. At this refinery, approximately 11,500 m3 of lubrication oil was
processed daily and helped debottleneck existing dewaxing units resulting in reductions of 20% process
energy intensity, 20,000 tons a year in greenhouse gas emission, and four million gallons of water usage
daily, and 125 tons in violate compound emissions annually.42 The materials, fabrication of the membrane
product, or implementation of the process within different chemical separation save energy and bring
down the cost of manufacturing resulting in a higher profit margin. These membranes can be fabricated
domestically or offshore and sent to manufacturing or community locations for application.
26 Environmental Issues and Sustainability
This project is partly based in increasing the sustainability of OSN membranes for organic solvent
recovery and nanofiltration desalination membranes to decrease environmental issues and provide access
to clean water. The main material of this project is KANFs, sourced from Kevlar string from Dupont,
USA. Kevlar fiber is 100% recyclable, and can be respun into a new yarn, used as a padding for cushions
or clothing articles, pulped. However, Kevlar in its dissolved nanofiber form or as a membrane cannot be
recycled without further processing because other polymer materials are used and crosslinked networks
cannot be broken down.43 The materials and products used to fabricate these membranes do not
deteriorate for many years. Therefore, it is important to make membranes as durable as possible to
increase lifespan and avoid pollution of deteriorated membranes.
Likewise, solvent is consumed in the Kevlar dissolution and fabrication of membranes.
Therefore, leftover casting solution and solvent waste needs to be separated before disposal, and dyes
solutions for testing also need to be separated. It is important to minimize the number of materials mixed
because this post treatment separation process increases the energy consumption of the membrane
fabrication and decreases the sustainability. However, solvents that are less environmentally hazardous
are utilized such as dimethyl sulfoxide instead of the caustic sulfuric acid. In terms of chemical, thermal,
noise, particulate pollution, there are no hazardous chemical byproducts from membrane separation.
However, retentate from the membrane process needs to be recycled or disposed in a responsible manner
to avoid potential environmental issues. For example, desalination retentate disposed into the ocean
increases the salinity of the local aquatic systems resulting in significant consequences on marine life. 44
In the upcoming years, OSN and desalination membranes are increasing in public interest for
their green fabrication and separation activity. These membranes aim to reduce the population of organic
matter into water ways. The long-term goal to decrease pollution of water sources to address the grand
challenge of providing clean water globally. These membranes will most likely be used in developed
27 countries, but hopefully become more accessible to developing countries that are most at risk. As the
usage of solvent continues to increase in chemical operations, there will always be a need for sustainable
separation technology at an affordable cost. Likewise, as the global population continues to skyrocket, the
demand for water as a resources becomes more critical.
Ethical, Social, and Political Issues
Locally, based on the success of the resulting experiments, these novel membranes can be
implemented into local chemical industries to improve solvent separation and recovery and decrease
solvent pollution. Likewise, they may also be implemented into desalination plants to improve the overall
operations and production of clean water. Access to clean water has huge social implications for
communities, specifically women and girls tasked with providing clean water for their families. Obtaining
clean water from a well sourced miles away is a time consuming and often dangerous daily journey for
young girls. When communities gain access to clean water, girls can focus on education leading to huge
social change.45 Once established, these membranes can be implemented globally into different chemical
and desalination separation industries. These membranes can be effective in developed and developing
countries for organic solvent nanofiltration or desalination. However, the fabrication of these membranes
must be less environmentally detrimental than their function can negate.
Implementing these membranes into existing desalination or membrane modules should not be
difficult on a political level due to the pre-existing technology and no action of the government to
subsidize projects. However, implementation of entire desalination plants could prove more difficult.
Politically, tangible information on water costs are uncertain for communities and policy makers due to
diverse intervening economic and environmental parameters. This makes it difficult to install desalination
plants to regions of critical need. For example, there are several factors to consider when installing a
desalination plant such as technical criteria for site selection, costs of operation, time schedule, and
28 environmental influences and impacts. Sites for desalination plants are chosen based on the potable water
demand, seawater intakes and outfalls, subsoil conditions, fresh water and power availability,
accessibility, seashore line protection, local labor and infrastructure, and various regulations.46 The most
economical way for separation operations is continuous based on energy consumption and separation
efficiency, and return flows must be safely disposed of or recycled. For low income areas, the high prices
installing a desalination need to be subsidized and compared against the costs of importing fresh water to
the area.
In consideration, there are several steps to execute application of membrane separation
desalination plants to regions of critical need including information gathering, analysis, reporting, and
decision making. In a review of countries with critical water shortages, regions in China, India, Republic
of Korea, Russia, Algeria, Egypt, and Indonesia were identified, and each had unique problems.47 For
example, in China, there are 104 cities with 200 million people in northern and coastal areas that have a
critical water shortage. Freshwater sources such as the Pearl River Delta and Yangtze river are polluted
with high concentrations of Cadmium and the low-income region requires a state subsidy for separation
projects. Even in cities like Shanghai, water supply stations can charge up to US $25 per cubic meter of
water. For political consideration, it costs less money to develop water sources in these coastal cities than
build infrastructure to transport it. Likewise, in India, there is 4000 km3 of rain annually, however it is not
evenly distributed with chronic water shortages in Tamil Nadu, Andhra Pradesh, Saurashtra, and western
Rajasthan. Furthermore, ¾ of the available rainwater is lost to the sea and leaves only ¼ to be stored as
ground water. Conventional water supplies such as dams, lakes, canals, piped water need large capital
(US $1-2 x109) for water supplies of 9000-22,500 m3/d. In addition, these conventional water supplies are
contested by civilians as lands are submerged, populations uprooted, and forests destroyed. Finally,
regions in Indonesia deal with critically polluted water that cannot be used without extensive filtration.
Government funding may be somewhat challenging to secure due to corruption or opposing viewpoints,
and independent investors need to find a profitable return on clean water access.
29 It is the hope of this research projects and other research projects in this field to improve the
desalination of membrane modules to provide access to water to these critical regions. In addition, the
implementation of OSN membranes into chemical plants may improve the recovery and separation of
hazardous chemicals from waste streams and decrease the detrimental consequences of environmental
pollution and polluted water systems.
Health and Safety
Composite materials synthesized with Kevlar aramid nanofibers have potential health and safety
hazards during testing, manufacturing, and processing that may significantly affect researchers and
industrial workers. As shipped, Kevlar aramid nanofibers are chemically inert, nonhazardous in the dry
fabric form or after curing in a membrane matrix, and nonbiodegradable, but nontoxic to aquatic life.
However, machining or mechanically altering the Kevlar fibers may release airborne respirable fibrils and
dust that upon inhalation can become trapped in the deep lung and cause tissue damage.48,49 To minimize
risk of inhalation, Occupational Safety and Health Administration (OSHA) mandates the use of
respiratory protective masks with a diameter less than 3 micron in size; the size and diameter of Kevlar
aramid nanofibers is typically 8 micron.49 In this experiment, the Kevlar aramid nanofibers are dissolved
into solvent, and their dispersion and electrochemical interactions with solvent decrease the chance of
becoming airborne. Furthermore, the Kevlar aramid nanofibers must be stored properly to avoid fire and
becoming electrostatically charged. If this material catches on fire, it may release toxic or irritating gas,
and build-up of electrostatic charge may ignite nearby vapors.
Some of the chemicals and solvents used in membrane fabrication are highly or extremely
flammable. When working with membrane casting resin, precautions must be made to avoid inhalation
and skin/eye contact with the chemicals and chemical fumes. The adverse possible effects are lung
damage, fertility damage, exposure to carcinogens, and drowsiness or dizziness. To minimize risk of
30 exposure, OSHA directs the use a fume hood and proper personal protection wear. The fume hood should
be mechanically checked often to ensure proper ventilation of chemicals; glassware should be checked for
cracks; an invention kit should be on standby. At minimum, the personal protective wear should include a
lab coat, safety glasses, and cryogenic gloves when handling these solvents. Finally, chemical waste
should be selectively separated for proper and safe disposal.
Overall, the safety and health in this work and potential industrial scaling is achievable and
maintainable with workplace responsibility and engineering controls. The use of solvents and machining
of Kevlar should be minimized to reduce risk of pollution of byproducts and airborne dispersion of
nanofibers.
Code of Hammurabi
The Code of Hammurabi is effectively risk management for engineering and is an important step
to ensure to proposed technologies or projects will not negatively impact users or the community by
holding the professional accountable. Much of this assessment has already been mentioned in health and
safety. In terms of this project, membrane separation technology has facile and safe operating conditions
for users with low temperatures, relatively low pressure, and without the use of harsh chemicals such as
hydrofluoric acid.26 These novel membranes do not pose any risk of injury or death in their final inert
fabricated form. The synthesis of these membranes does use some medium risk chemicals and should be
handled with care and proper personal protection wear to avoid injury.49 Furthermore, these membranes
are rigorously tested to ensure highest separation efficiency for the greatest reduction in environmental
pollution. The retentate and permeate solution may be tested periodically to ensure the performance of the
membrane does not decrease during operation and release pollution. Overall, the risks in fabrication,
operation, and process can be effectively minimized to pose little or no danger to operators or users.
31
Chapter 4
Experimental Procedures
Materials
All materials used in the pressure vacuum filtration with heat treatment and hydrogel assisted
interfacial polymerization methods are detailed in this section in Table 1. Before use, Bulk Kevlar 69 was
dried in the oven for 12 h at 60 °C. Deionized water was used in these experiments. Solutes for membrane
characterization are listed in a separate table, Table 1. BSA was used as the solute for the OSN KANF
pressure vacuum filtration with heat treatment method. Salts and dyes were used as the solute for the
KANF hydrogel assisted interfacial polymerization TFC nanofiltration membrane for desalination of
water. The salts and dyes were tested separately with 1.0g/L of feed concentration.
Where ρ is the density of KANFs and t is the thickness of the membrane. For example, about 0.60 mg of
KANFs was needed for 100nm thick membrane. The dope solution of KANFs was 2 wt% or 20 mg/g, so
2 to 3 grams of dope solution is necessary to get the desired KANF loading and thickness of the selective
layer. To decrease the viscosity of the dope solution for dispersion over the microporous support
membrane, 15 g of solvent was added. Initial work synthesized three membranes for 100nm, 200nm, and
300 nm thick layers; the goal set as <80 nm thickness.
Vacuum Assisted Filtration
The amount of KANFs was calculated for desired thickness and dispersed into deionized water or
DMSO. For KANF and deionized water solution, 50 ml of water was used. Likewise, for KANF and
DMSO solutions, 15 ml of solvent was used. Solutions were stirred for 10 minutes using a stir bar at room
temperature. The color of the dispersant solution was yellow orange in the DMSO and clear in the water.
Figure 14 Lab assembled apparatus for vacuum assisted filtration54
The lab assembled apparatus used for vacuum filtration is like the set-up in Figure 14. The
microfiltration membrane of PTFE with a pore size of 0.2 to 0.8 μm or the alumina with a pore size of 0.2
μm was clamped between the glass vessels. During filtration, the KANF suspension is poured into the
44 top vessel along glass wall to avoid a turbulent mixture of KANFs and uneven dispersion onto the
microporous membrane (Figure 15). The bottom glass vessel is connected to the flask below via a rubber
cork to maintain vacuum pressure, and the secondary neck of the flask is connected to the vacuum source.
The removal of the solvent for phase inversion is driven by gravity and the vacuum pressure.
Figure 15 Schematic for vacuum assisted filtration over a microporous support for KANF membranes
After dispersion, the membrane was placed into the oven thermal treatment at 60℃ for 24 h for
10 minutes to regenerate OH bonds. Alternatively, the membrane was also left out to air-dry overnight to
avoid flaking the selective layer from the microporous support.
Membrane Characterization Results
Permeation, selectivity, and SEM characterization was done for the initial work on this project.
The initial permeance of PTFE was measured as a reference, and the value was 11275 (L/m2hbar).
Consequently, KANF selective layers of 100, 200, and 300 nm thickness were deposited on to the
microporous supports. Both the alumina and the PTFE support and KANF membranes failed to
selectively permeate BSA at any thickness. However, the permeance of the membranes decreased as the
45 thickness increased; for the PTFE support, permeance decreased from around by half from its original
value for a membrane thickness of 100nm. This suggested that there was the formation of a selective layer
onto the support membranes. For alumina support, the permeance and rejection was similar to the PTFE
support. Additionally, the permeance of the KANF membrane with the PTFE support decreases over time
due to compaction.
The data suggests that possibly a nanofiltration layer is selectively formed on top of the
microporous support. However, the presence of defects and flaking of the selective layer from the support
suggest incompatibility between the support and KANF materials decrease the selectivity. Future work to
modify the dispersion of the KANFs with PVOH to create less defective and higher compatibility with
the support membrane is the next step. Furthermore, the permeability decreased as the thickness of the
membrane increased, indicating that the thickness of the membrane is controlled by the calculated amount
of KANF in solution.
46
Figure 16 SEM images of a) Alumina microporous support membrane; b) Alumina and KANF membrane; c) Uncoated regions on alumina support; d) PTFE microfiltration support membrane e) PTFE and KANF membrane
A SEM image of the PTFE and alumina membranes before vacuum filtration were taken. In these
images, the PTFE had a microporous structure with pore sizes up to one nanometer in size. Similarly, the
alumina microstructure had much smaller pore sizes. The pore sizes were also equiaxed and more regular.
The following SEM images were taken at two magnification of the deposited Kevlar layer on top of the
support membranes. On both the alumina and the PTFE support, a KANF membrane layer was identified.
On alumina, the KANF layer was cracked, likely due to poor interactions between the polymer and
ceramic. Also, the KANF did not completely disperse over the alumina, confirming the poor bonding
interactions between the support and selectivity layer. On PTFE, the KANF layer was dense and evenly
dispersed. These SEM images are organized in Figure 16.
47 Chapter 6
Hydrogel Assisted Interfacial Polymerization Results and Discussion
As mentioned, the results of this section are available from this paper1, and additional discussions
are found there. I was responsible for the synthesis of membranes, testing permselectivity and rejection,
water contact angle, water uptake, and surface roughness; I did not do mechanical strength, zeta potential,
or XPS. In addition, a free-standing membrane was synthesized as a comparison against the TFC KANF
hydrogel membrane reported. As I was not responsible for this synthesis, I did not report it, however it
remains a useful comparison for data analysis.
Membrane Design Strategy
Current thin film reactions use two reactive monomers (organic diamines and acyl chlorides) that
polymerize at the interface of two immiscible liquids. Interfacial polymerization adapts this method to a
thin PA layer on top of porous UF membrane.24 However, to make this technology more competitive
against other separation methods, IP membranes need higher efficiency, lower energy consumption, and
higher permeability to process large volumes of wastewater.
There are two methods to increase effective membrane area and boost the permeability of TFC
membranes without sacrificing solute rejection. The first method is to develop TFC membranes with a
rougher PA layer to increase effective surface area and permeation. A rough PA layer is achieved by
controlling the diffusion of anime monomers in interfacial polymerization or adding filler into the surface.
However, some limitations of this method are fillers on support membrane increase the cost and
complexity of fabrication method and decrease the scalability.58 Another limitation is the increased
surface area may lead to membrane fouling on the surface and a decrease in the membrane permeation.
The other method to improve the permeation is to reduce the thickness of PA layer formed
through interfacial polymerization at the aqueous interface.24 To reduce the thickness of a PA layer, an
48 ideal interface of homogenously distributed free water and hexane is used in the diffusion of amine
monomers without the disturbance of a support membrane. This ideal interface yields a theoretical PA
layer of 10 nm, and this thin selective layer shortens the mass transfer resistance leading to higher flux.
The free aqueous -organic interface is an ideal medium for interfacial polymerization, but there are still
several limitations. For example, oil and water do not mix regularly and may disturb the water phase
leading to an unstable reaction interface. Furthermore, it is a sophisticated process to move the thin PA
layer onto the support membrane, and a lack of chemical interactions between PA layer and support
causes the PA layer to detach during crossflow filtration.59
There is interest in using a KANF hydrogel membrane as the free water interface for an ideal
interface to perform IP. Hydrogels are a crosslinked hydrophilic polymeric network that can hold large
amounts of water, making them suitable replacement for the water interface in a free water interface
reaction.60 Also, hydrogels have applications in membrane separations as the support membrane for TFC
membranes.
Overall, the goal of this research to make TFC NF membranes by conducting interfacial
polymerization on bottom surface of nanoporous KANF hydrogel. The water saturated KANF hydrogel is
a substitution for the free water phase in synthesizing free-standing membrane and enables homogenous
polymerization without disturbance of support membrane. The KANF support hydrogel membrane adds
additional mechanical support and robustness to the final membrane, and OH bonding between polymer
and amine chains helps to control the diffusion of amine monomers during interfacial polymerization.
49
Figure 17 Step by step process for fabrication of hydrogel-TFC membrane1
Figure 17 depicts the fabrication process for the hydrogel-TFC membrane; (a) casting of
KANF/DMSO (2 wt%) on a glass plate with knife; (b) immersion of glass plate with KANF solution in
water/PIP bath for phase inversion and preloading of PIP monomers in KANF hydrogel; (c) KANF
hydrogel preloaded with PIP monomers; (d) detail of nanofibrous PIP saturated structures; (e) Interfacial
polymerization with Hexane and TMC solution.
Membrane Fabrication Methods
This section details the fabrication of the KANF hydrogel saturated with PIP, interfacial
polymerization on the KANF hydrogel and conventional PSU support. Other membranes formed for this
study for comparison were interfacial polymerization at free hexane and water interface, and interfacial
50 polymerization onto a polyvinyl alcohol (PVA) based hydrogel. Details about the latter membranes are
found in the publication.
Synthesis of Nanofibrous Hydrogel Support Saturated with PIP Monomers
The nanofibrous support hydrogel was prepared through phase inversion of KANF and DMSO
dope solution (2 wt%) in a water bath preloaded with PIP monomers. This solution was spread onto a
glass plate at room temperature and humidity of 50-60% with a casting knife with a gap 200 μm. Then the
coated glass plated was immersed into deionized water to form KANF hydrogel membrane through
solvent exchange with DMSO. Furthermore, the concentration of PIP monomers dissolved in water bath
for phase inversion was (0.01 wt% to 0.04 wt%) and served to preload the hydrogel membrane. The
membrane was left in the water overnight to remove residual solvent, and its final appearance was
transparent and soft. The water content of this KANF hydrogel support membrane of 3D nanofibrous
networks was 96.5%. Figure 18 shows a cross section the hydrogel dried by a super critical dryer at a)
cross section; b) magnified cross section; c) bottom surface; d) top surface.
Figure 18 KANF Hydrogel post drying with super critical dryer1
51 Interfacial polymerization on nanofibrous hydrogel for TFC nanofiltration membrane
Since the hydrogel membrane was preloaded with PIP solution, there was no additional step
necessary to rinse and deposit PIP on surface for the interfacial polymerization. This preloading step
decreases the complexity of the fabrication by removing a step. Then to form the PA layer, a trimesoyl
chloride and n-hexane solution was poured on the porous bottom surface of the hydrogel membrane for 1
min. The solution contained 6 ml of TMC n-hexane solution with a concentration of 1 mg ml-1. Next,
excess TMC solution was dried in oven at 60 °C for 6 min, and the final IP membrane was stored in
stored in deionized water.
Interfacial polymerization on conventional PSU ultrafiltration membrane for Comparison
Interfacial polymerization of PIP and TMC monomers was also performed on a conventional
polysulfone (PSU) ultrafiltration support membrane as a comparison against the KANF hydrogel
membrane. In the fabrication process for the PSU IP membrane, the PSU ultrafiltration was wetted with
6ml PIP solution (0.01 wt%- 0.1wt%) for 5 min. The support membrane was dried gently with
compressed air to remove excess PIP. Then, a solution containing TMC and n-hexane (1 mg ml-1) was
poured on surface for 1 min. Finally, excess TMC solution dried in oven at 60 °C for 6 min and the final
membrane was storied in deionized water.
Membrane Characterization Results
The desalination performance of the TFC KANF membrane was measured by the water
permeability and rejection of salts in aqueous suspension. The TFC KANF membrane was compared
against the TFC PSU membrane and free-standing membrane to demonstrate its superior performance.
52 Other characterization methods such as SEM, AFM, water contact angle, water uptake, mechanical
strength, and zeta potential were used to explain and understand the desalination performance.
Permeability
The permeability of the TFC KANF membrane was initially evaluated with PIP concentrations of
0.0175 wt% and 0.0150wt%, and with TMC concentrations of 0.1w/v%. These values were selected from
other TFC monomer concentrations from literature.22 In this test, 1000 ppm Na2SO4 and water solution
was in the cross flow flat membrane filtration apparatus, and the impact of applied pressure was tested.
As shown in Figure 19, the flux of the membrane increased proportionally from 2 to 8 bar due to the
increased driving force of pressure. However, at higher pressure values, the rejection level of the
membrane decreased likely due to concentration polarization. Therefore, pressure values from 2 to 4 bar
had the highest rejection for the TFC KANF membrane with values at 97.1% and 96.4 for PIP
concentrations of 0.0175 wt % and 95.5% and 93.5% for PIP concentrations of 0.015 wt %. An applied
pressure of 4 bar ultimately gives the highest flux of 211.8 Lm-2h-1 (PIP 0.0175 wt %) and 251.6 Lm-2h-1
(PIP 0.015 wt %). At pressure values above 8 bar, the flux of the membrane levels off.
Figure 19 Impact of Applied Pressure on TFC KANF Membrane
2 4 6 80
100
200
300
400
500
600
Flux
(L. m
-2.h
-1)
Pressure (bar)
PIP-0.0175 wt% PIP-0.015 wt%
0
20
40
60
80
100
Reje
ctio
n (%
)
53 Then, the permeability and rejection of the TFC KANF hydrogel membrane were studied with
varying concentrations of PIP from 0.01 wt% to 0.04 wt% and a TMC concentration of 0.1 wt% (Figure
20). The amount of PIP was varied to adjust the thickness of the membrane, increase interactions between
the support and PA layer, and modify the electronegativity of the selective layer, and these modifications
ultimate influenced the permeability of the membrane. The permeability of the TFC KANF hydrogel
membrane increases from 18.3 to 62.9 Lm-2h-1bar-1 as the PIP concentration decreases from 0.04 wt% to
0.015 wt%. Furthermore, the Na2SO4 rejection decreases from 99.4% to 93.5% as the PIP concentration
decreases. At the ultrahigh permeation of 140 Lm-2h-1bar-1 at a PIP concentration of 0.01 wt%, the
rejection of Na2SO4 was too low at a value of 28%. At slightly higher concentrations of PIP (0.015 wt%),
the rejection increased to 92.5% and the permeability of water was 61 Lm-2h-1bar-1.
Figure 20 Permeability and Rejection for Varying PIP Concentrations for the TFC KANF Hydrogel Membrane
Next, the permeability of the TFC KANF hydrogel membrane, TFC polysulfone membrane, and
freestanding PA membrane was tested with varying concentrations of PIP from 0.01 wt% to 0.04 wt%
and a TMC concentration of 0.1 wt% (Figure 21).
Compared to the TFC KANF hydrogel membrane, the TFC PSU membrane had much higher
permeability, but much lower rejection. However, when the permeability was compared against the
rejection for Na2SO4, it was evident that a nanofiltration membrane was not formed until PIP
0.01 0.02 0.03 0.04
20
40
60
80
100
120
140
Perm
eabil
ity (L
/(m2 . h
. bar
))
PIP concentration (wt%)
0
20
40
60
80
100
Na2S
O 4 re
jectio
n (%
)
54 concentrations greater than 0.07 wt%. There are several reasons for the poor rejection and high
permeability of the TFC PSU membrane at lower PIP concentrations. For example, the interface of TMC/
n-hexane solution and wet PSU support are influenced by physiochemical properties such as the pore size,
hydrophilicity, and roughness of the PSU support membrane. These properties may lead to uneven
distribution and diffusion of amine monomers through the support membrane to the interface surface and
result in defected selective layer at the lower PIP concentrations. Ultimately, TFC membranes using a
PSU need a higher concentration of PIP than the KANF hydrogel to form a NF membrane for
desalination.
Likewise, when compared to the TFC KANF hydrogel membrane, the free-standing membrane
had lower permeability for all concentrations of PIP, but the rejection of Na2SO4 is above 90% for tested
PIP concentrations indicating a nanofiltration membrane was achieved. The lower permeability of the
free-standing membrane may be related to the greater thickness of the selective layer compared to the
TFC KANF hydrogel membrane, and the thickness is observed through TEM cross sections in a later
section. The TFC KANF hydrogel has strong bonds between the PIP monomers and the KANF hydrogel
and limits the diffusion of monomers to interface for the IP interaction result in lower consumption of
nearby monomers during polycondensation.
Figure 21 Permeability of TFC KANF Hydrogel membrane, TFC PSU Membrane, and Free Standing Membrane
0 0.01 0.02 0.03 0.04 0.05
0
50
100
150
200
250
300
Perm
eabi
lity
(L/(m
2 h b
ar))
PIP concentration (wt%)
PSU Freestanding KANF
55 Overall, the TFC KANF hydrogel membrane benefited from amide and OH groups in KANFs for
bonding with the PIP and limiting the diffusion of PIP to the interface of the membrane to create a defect-
free and thin selective separation layer for the optimal permeability and rejection in desalination
performance.
Selectivity and Rejection of Salts and Dyes
The rejection of salts in aqueous suspension is another important indicator of desalination
performance, only superficially mentioned in the previous section.
First, the rejection of the TFC KANF hydrogel membrane was tested using four salts including
MgSO4, MgCl2, NaCl, Na2SO4 (Figure 22). The rejection of MgSO4 and Na2SO4 salts was greater than
90% for PIP concentration as low as 0.015 wt%. The rejection of MgCl2 and NaCl was lower and likely
related to the smaller sulfate size of those ions compared to Na2SO4. Additionally, the membrane was
negatively charged and led to the higher rejection of MgSO4 and Na2SO4 salts due to the Donnan
exclusion effect and sulfate ions are removed to balance the surface charge of the membrane. The charge
of the membrane was later confirmed by the work of this paper when zeta potential curves were measured
to be negative for all pH values. The membrane is likely negatively charged due to the dissociation of
carboxylic acid groups from the hydrolysis of acyl chloride groups on the TMC monomer.61
Figure 22. Rejection of MgSO4, MgCl2, NaCl, Na2SO4 salts by the TFC KANF Hydrogel Membrane
0.01 0.02 0.03 0.04
0
20
40
60
80
100
Rejec
tion
(%)
PIP concentration (wt%)
Na2SO4 MgSO4 MgCl2 NaCl
56
To confirm the function of this membrane as a nanofiltration membrane for desalination
applications, several dyes solutions including congo red, direct red 80, direct red 23, and reactive blue 2
were filtered through TFC KANF hydrogel membranes at PIP concentrations of 0.0175 wt% and 0.015
wt%. For each dye in water, the rejection rate was over 98% for both membranes.
Then, the rejection of Na2SO4 of the TFC KANF hydrogel membrane, TFC polysulfone
membrane, and freestanding PA membrane was tested with varying concentrations of PIP from 0.01 wt%
to 0.04 wt% and a TMC concentration of 0.1 wt% (Figure 23). As the PIP concentration decreased, there
was a reduction in the rejection of each membrane. However, the TFC KANF hydrogel and the free
as low as 0.015 wt%. The drop off in rejection performance is likely due to the enlarged pore size of
membranes at lower concentrations of PIP. In contrast, the TFC PSU membrane was tested individually
and found that it did not form a nanofiltration membrane until concentration of PIP as high as 0.07 wt%.
At those concentrations of PIP, the permeability was much lower due to higher thickness resulting in poor
desalination performance.
Figure 23 Na2SO4 Rejection of TFC KANF Hydrogel Membrane, TFC PSU Membrane, and Free Standing Membrane
0.01 0.015 0.02 0.025 0.03 0.035 0.04
0
10
20
30
40
50
60
70
80
90
100
Na 2
SO4
reje
ctio
n (%
)
PIP concentration (wt%)
PSU Freestanding KANF
57 Lastly, continuous nanofiltration using Na2SO4 in aqueous solution in the cross flow filtration module
demonstrated no change over 6 hr in water flux and salt rejection (Figure 24). This desalination
performance is stable over long periods over and does not change due to membrane compression.
Figure 24. TFC KANF Membrane Desalination Performance Over 6 Hr
Compared to thirty state of the art desalination membranes from the past three years in literature,
these membranes had a superior desalination performance with the highest permeability of 62.9 Lm-2h-
1bar-1 and rejection of 92.5% for Na2SO4. Finally, as proof for scalability in industrial applications, large
pieces of TFC KANF hydrogel membranes were synthesized with dimensions of 19 cm x 35 cm.
Surface Characterizations
Several characterization methods were used to understand and explain the superior desalination
performance of the TFC KANF hydrogel membrane including SEM, TEM, water contact angle, and
water uptake. Figure 25 shows the final synthesized TFC KANF hydrogel membrane. The resulting
membrane was translucent with yellow and white tint.
0 100 200 3000
80
160
240
320Fl
ux (L
m-2
h-1
)
Time (min)
PIP-0.0175 wt% PIP-0.0150 wt%
40
60
80
100
Na 2
SO
4 re
ject
ion
(%)
58
Figure 25 Picture of TFC KANF Hydrogel Membrane
SEM
SEM images were taken to confirm the structure of the KANF hydrogel and the attachment of a
selective PA layer onto the hydrogel. Figure 26 shows a) the polymeric nanonetworks in the KANF
hydrogel, and b) the SEM surface image of the TFC KANF hydrogel membrane. As noted in Figure 26a,
the KANF hydrogel has a porous structure, and in Figure 26b, developed a highly dense surface due to IP
of PIP and TMC. The selective PA layer has a dense and smoother surface that is firmly attached to the
KANF hydrogel and indicates robust chemical interactions between the support and selective layer. High
compatibility between these layers yielded excellent membrane stability under long time periods. The
high compatibility was also proven with XPS results showing similar chemical groups and composition
between the layers, however that was not covered the scope of my work and can be found in the
supporting paper.
59
Figure 26 SEM images of a) the nanofibrous network of KANFs in the hydrogel membrane; b) the surface of the TFC PSU KANF hydrogel membrane
TEM
TEM images were taken to observe the cross-sectional regions of the TFC KANF hydrogel
membrane at different PIP concentrations and the free-standing membrane. The lowest possible thickness
achieved by IP on the KANF hydrogel yielded a crosslinked and defect free PA selective layer of 15.5nm.
From Figure 27, as the concentration of PIP was lowered from 0.04 wt% to 0.01 wt%, the thickness of the
PA selective layer decreased from 39nm to 15.5 nm. The lower thickness resulted in larger pore sizes as
the material was less densely packed to cover the same surface area as higher concentration. Furthermore,
the lower thickness improved the negative charge of the membrane resulting in higher rejection values for
salts. Compared to the free-standing membrane shown in Figure 27.d, the TFC KANF hydrogel
membrane had a lower thickness at the same PIP concentration. The TFC KANF hydrogel membrane
likely had a lower thickness due to the limited diffusion of PIP monomers through the KANF hydrogel
membrane to the interface surface, and the high compatibility of the PA layer to the KANF membrane
leading to a denser and tighter structure.
60
Figure 27 TEM images of the thickness of the selective separation layer of the KANF TFC hydrogel membrane fabricated with PIP concentrations of: a) 0.015 wt%; b) 0.02 wt%; and c) 0.04 wt%, and d) the thickness of the
freestanding membrane at PIP concentrations
AFM
The surface roughness measurements of the TFC KANF hydrogel membrane was observed and
found that the membrane was exceptionally smooth with an average of 8 nm for all concentrations of PIP
(Figure 28). The smooth surface provides less effective surface area for permeation but decreases the
effect of fouling on the surface. As the membrane already has excellent permeability, the lower surface
area is not a concern.
Figure 28 AFM morphology of Hydrogel-TFC membranes synthesized from PIP concentration of 0.0175 wt% and 0.02 wt%
The AFM measurements for this membrane are found in Table 4.
61 Table 4 Roughness of TFC KANF Hydrogel membranes
TFC KANF Hydrogel
PIPO Concentrations
(Wt%)
0.015 0.0175 0.02
Roughness (nm) 7.28 8.1 8.06
Water Contact Angle
The water contact angle was measured to determine the hydrophilicity of the membrane. The TFC KANF
hydrogel membrane had a water contact angle of 54 degrees, indicating hydrophilicity (Figure 29).
Hydrophilicity is recommendable to avoid fouling of the membrane surface.
Figure 29 Water contact angle of dry nanofibrous hydrogel (72°) and Hydrogel-TFC membrane (PIP-0.015,54°)
Water Uptake
The water uptake of the TFC KANF hydrogel membrane was 96.5 wt% which was similar to
free water phase in freestanding IP membranes.
62
Chapter 7
Conclusions and Future Work
TFC Vacuum Filtration KANF Membrane for Organic Solvent Nanofiltration
The vacuum filtration method deposited a KANF selective layer onto the support membranes of
alumina and PTFE, and the thickness of the membrane was controlled by the amount of KANF deposited
onto the surface. However, this membrane failed to selectively filter out dyes from solvent and needs
further work. Low rejection failed to yield nanofiltration results and was caused by microcracks and poor
interactions between the KANFs and support. It is also possible that the KANFs fall through the porous of
the support membrane, causing the defects in the membrane surface. Furthermore, there is no long-term
stability of the TFC KANF membrane, most likely caused by compression of the selective KANF layer
on the support membrane.
This work is in its infancy stages, but there are several techniques to improve its performance and
ultimately create a successful organic solvent nanofiltration membrane. For instance, dopamine can be
used to improve KANF and support interactions. However, dopamine is not readily available for purchase
in this country and does increase the costs of fabrication significantly. Furthermore, the membranes can
be left to airdry overnight to avoid potential peeling from the support membrane; while this increases the
time of fabrication, it may put less stress between the support and selective layer. Another method to
improve the membrane is to research different support membranes that are more compatible with KANF
selective layer, such as support membranes with similar chemical groups and composition. Additionally,
PVA or PEI can be added to the KANF dope solution to improve the flexibility of the selective membrane
layer and decrease the number of cracks or another molecule can be found that has computability with the
KANF and the support membrane to further improve compatibility. However, adding another molecule to
63 the dope solution and selective layer may lessen the effects of the heat treatment and formation of a
nanofiltration selective layer.
Once a viable dope solution and support membrane are established, a 100 nm selective KANF
layer may be deposited onto the support and subsequently heat treated to form a nanofiltration membrane.
At this point, the dope solution may be modified to decrease to content of material and therefore control
the thickness of the selective layer of the organic solvent nanofiltration membrane.
Overall, this idea has merit to conceive an organic solvent nanofiltration membrane with a
controllable thickness of the selective layer and therefore greater permeability and performance.
Additionally, this method reduces the amount of solvent used by utilizing a greener solvent DMSO as
opposed to more acidic solvents like H2SO4 and a facile heat treatment rather than additional chemicals
that need to be separated and recovered. Currently, this is not an optimal fabrication method for OSN
membranes. Although, the promising reduction in the CO2 footprint of this OSN membrane, and
potentially controllable structure and performance provide an excellent alternative to traditional
separation processes and perhaps other state of the art membranes in terms of sustainability and cost
effectiveness.
TFC KANF Hydrogel Membrane for Desalination
Interfacial polymerization of PIP and TMC monomers onto the porous bottom of a KANF
hydrogel membrane successfully fabricated a nanofiltration desalination membrane. The fabrication steps
of the synthesis were reduced by preloading (PIP) monomers into the KANF hydrogel as an aqueous
phase and reacted with trimethyl chloride and hexane to form a strong polyamide (PA) selective layer.
The resulting membranes with PIP concentrations of 0.0175 wt% and 0.015 wt% and TMC concentration
of 0.01 wt% yielded ultrafast permeance of 52.8 and 62.9 Lm-2h-1bar-1. This selective PA layer reached a
rejection of 96.4% and 93.5% for Na2SO4 and in comparison, superior desalination performance to other
64 PA TFC nanofiltration membranes.1 The superior performance is attributed to the decreased thickness of
the selective layer due to the strong interactions between the KANF hydrogel support membrane and PA
selective layer. The membrane and the support layer have similar chemical groups and composition such
as amide groups and hydrogen bonding. Moreover, no harsh solvents or crosslinking chemicals were
utilized in this fabrication process, and the process can be easily scaled up with the fabrication of large
membrane sheets.
The TFC KANF Hydrogel membrane has excellent desalination performance, but there is still
room for improvement. For example, the concentration of TMC may be adjusted to improve the charge of
the membrane surface to reject more salts or heavy metals.62 Additionally, other materials other than
KANFs and PVA may be synthesized and implemented as hydrogel support to perform IP for
desalination membranes. Likewise, monomer alternative to PIP may be used such as MPD to possibly
adjust the negative charge or thickness of the selective layer. Therefore, through the combination of size
exclusion and adjusting the electronegativity of the membrane surface, the performance of the membrane
may be improved. Alternatively, covalent organic framework materials may be added into the selective
layer during IP to increase the permeability and maintain the rejection of the membrane performance.
This membrane may also be adapted as an organic solvent nanofiltration membrane, depending on the
solvent resistance of the selective layer.
Overall, the TFC KANF hydrogel membrane is an excellent option for current desalination
systems with the potential to make operations 3x faster. Faster operations reduce the operating time and in
effect cost and energy usage, making this a green viable alternative. Furthermore, the CO2 footprint of this
membrane is reduced by the consolidation of fabrication steps, avoidance of harsh solvents, and the
ability to scale to size. For large scale manufacturing of IP TFC membranes, the current membrane
support may be replaced with the KANF hydrogel membrane to create superior desalination membranes
with a more sustainable and cost effective approach.
65 Appendix A
Surface Morphology of KANF and PSU-TFC membranes
Figure 30 Surface morphology of Hydrogel-TFC membranes
Figure 31 Surface morphology of PSU-TFC membranes
References
(1) Yuan, S.; Zhang, G.; Zhu, J.; Mamrol, N.; Liu, S.; Mai, Z.; Van Puyvelde, P.; Van Der
Bruggen, B. Hydrogel Assisted Interfacial Polymerization for Advanced Nanofiltration
Membranes. J. Mater. Chem. A 2020, 8 (6), 3238–3245.
https://doi.org/10.1039/c9ta12984g.
(2) Zhao, Y.; Wu, M.; Shen, P.; Uytterhoeven, C.; Mamrol, N.; Shen, J.; Gao, C.; Van der
Bruggen, B. Composite Anti-Scaling Membrane Made of Interpenetrating Networks of
Nanofibers for Selective Separation of Lithium. J. Memb. Sci. 2021, 618, 118668.
https://doi.org/10.1016/j.memsci.2020.118668.
(3) Yuan, S.; Li, X.; Zhu, J.; Zhang, G.; Van Puyvelde, P.; Van Der Bruggen, B. Covalent
Organic Frameworks for Membrane Separation. Chemical Society Reviews. Royal Society
of Chemistry May 21, 2019, pp 2665–2681. https://doi.org/10.1039/c8cs00919h.
The Schreyer Honors College, Penn State, University Park, PA B. S. in Material Science and Engineering, Magna Cum Laude K.U. Leuven, Leuven, Belgium Euroscholars Research Abroad Program
• Prestigious semester-long study abroad program designed for talented and highly motivated undergraduate students looking to participate in international research
London Study Tour, London and Edinburgh, U.K
• Signature travel program of Schreyer Honors College to culture politically, theoretically, ethically, religiously, socially, and philosophically through live musical theatre and drama
Graduation 2020
Spring 2019
May 2018
Pennridge High School, Perkasie, PA Salutatorian
Graduation 2016
RESEARCH EXPERIENCE
Membrane Synthesis and Fabrication Researcher in Van der Bruggen Group K.U. Leuven, Leuven, Belgium • Applied polymer synthesis, characterization, and data analysis to
develop and test membranes for organic solvent nanofiltration applications
• Won the Euroscholars Consortium Grant and Schreyer Travel Grant to perform research through Euroscholars program at K.U. Leuven
• Coauthored multiple publications on these work • Presented at Euroscholars Student Research Competition
Jan. 2019-Present
3D Printing and Membrane Synthesis Researcher in Hickner Research Group
Pennsylvania State University, University Park, PA • Employed polymer synthesis, characterization, and data analysis to
perform independent project to develop 3D-printed and color responsive ion exchange membranes for applications in heavy metal detection and filtration
• Working on a publication related to 3D polymerized colorimetric sensor for pH detection using cell phone photography
Jan. 2018- 2020
Polymer Research Assistant in Runt Research Group Pennsylvania State University, University Park, PA • Exercised polymer synthesis, characterization, and data analysis with
team of graduate students to tailor glass transition state in epoxy and polyurethane integrated networks for applications in soundproof coatings
• Won NASA WISER Freshman Grant to perform research for two semesters
• Acknowledged for my work in associated paper: Ion Transport in Pendant and Backbone Polymerized Ionic Liquids
PROFESSIONAL EXPERIENCE
Polyethylene Product Development Intern
ExxonMobil Chemical, Houston, TX • Conducted polymer research in product development of PE • Organized and prepared extrusion line operations for 7 different PE
grades and led characterization team in scientific investigation of PE thermal properties such as hot tack and sealing
• Presented findings to PE Product Development Department and intern presentations
May-Aug. 2019
Metallurgy Intern Corning Incorporated, Corning, NY • Used metallurgical engineering to complete microstructural and
surface finish study on the metals used to fabricate dies for cellular ceramic extrusion
• Optimized processing route via selected heat treatments and post-processing finishing techniques in fabrication process to increase lifespan of dies
• Presented conclusive findings to metallurgy departmental meeting and at the intern poster competition
May-Aug. 2018
Material Process and Metallurgy Engineering Intern Precision Castparts Corporation, New Hartford, NY • Practiced metallurgical sample preparation and characterization and
statistical analysis to assist senior engineers on study of the changes in mechanical properties, microstructure, and chemical composition during heat treatments for Ni-Ti alloy
• Wrote several standard operating procedures and documentation to optimize heat treatment conditions
May-Aug. 2017
PUBLICATIONS
MAJOR PUBLICATIONS: • Y. Zhao, M. Wu, P. Shen, C. Uytterhoeven, N. Mamrol, J. Shen, C. Gao, B. V. Bruggen, "Composite
anti-scaling membrane made of interpenetrating networks of nanofibers for selective separation of lithium." J. Membr. Sci., 618 (2021).
• S. Yuan, G. Zhang, J. Zhu, N. Mamrol, S. Liu, Z. Mai, P.V. Puyvelde, B.V. Bruggen, "Hydrogel assisted interfacial polymerization for advanced nanofiltration membranes." J. of Mater. Chem. A, 8[6], 3238-3245.
HONORS UNDERGRADUATE THESIS: • Mamrol, Natalie. DEVELOPMENT OF KEVLAR ARAMID NANOFIBROUS MEMBRANES FOR
NANOFILTRATION SEPARATION PROCESSES. 2020. Penn State University, Schreyer Honors Thesis.
SUBMITTED PUBLICATIONS: • Y. Zhao, N. Mamrol, W. A. Tarpeh, Y. Guo, B.V. Bruggen, "Fundamentals, fabrication, and
application of ion-selective electro-driven membranes for aqueous separations." {Submitted} • Y. Zhao, Y. Qui, N. Mamrol, E. Ortega, X. Li, J. Shao, C. Gao, B. V. Bruggen, "Membrane
bioreactors in medical wastewater treatment for epidemic prevention." {Submitted} ACKNOWLEDGED AND ASSOCIATED PUBLICATIONS:
• S. Yuan, X. Li, J. Zhu, G. Zhang, P. V. Puyvelde, B. V. Bruggen, “Covalent organic frameworks for membrane separation.” Chem. Soc. Rev., 48 2665-2681 (2019).
• P. Kuray, T. Noda, A. Matsumoto, C. Iacob, T. Inoue, M. Hickner, J. Runt, “Ion Transport in Pendant and backbone Polymerized Ionic Liquids.” Am. Chem. Soc., 52 [17] 6438-6448 (2019).
LEADERSHIP EXPERIENCE
Team Leader of Engineering Methodology and Design Team
Pennsylvania State Material Science and Engineering Competition • Led five-member team in my proposal to implement piezo-resistive
polymer composite sensors into gloves to enhance virtual reality experiences
• Highest score on my engineering pitch, high marks on white paper, and full proposal
• Reviewed engineering considerations in economic, environmental, sustainability, manufacturability, ethics, etc.
Jan.- May 2018
Executive Secretary & Relay for Life Chairperson College of Earth and Mineral Sciences Student Council • Facilitated friendly interactions between student, faculty, and
alumni; organize college wide communication, professional events, and volunteer opportunities; maintain membership involvement to support over 150 active members with purpose of fostering a diverse, educational, and communal environment for all College of Earth and Mineral Sciences undergraduate members
• Created and implemented fundraising events, organized volunteers, and raised over $3,000 for Penn State Relay for Life event to promote awareness for the American Cancer Foundation resources and survivors
Sept. 2016- 2017
TECHNICAL AND SOFT SKILLS
• Material Preparation and Characterization: 3D Printing, Differential Scanning Calorimeter (DSC), Dynamic Mechanical Analysis (DMA), and Dielectric Spectrometry, RGB Color Analysis, Tensile Testing, Polishing/Grinding/Etching, Optical Microscopy, SEM, Surface Roughness, Abrasive Saw Machining, Membrane Synthesis and Fabrication, Metal Characterization, Polymer Characterization
• Data Analysis: Origin, JMP, MATLAB, Excel • Communication: Technical reports, Research presentations, Poster presentations, Mentoring
Phi Sigma Rho: Sorority of Women Engineers Sept. 2016- Present EMS Ambassadors May 2018- Present Material Advantage Member Sept. 2016- Present Mathematics Grader
Aug 2018 – Dec 2018
DISTINCTIONS
AWARDS EMSAGE Laureate
• Awarded to Penn State College of Earth and Mineral Sciences Students with significant achievement across the broad categories of scholarship, experiential learning and global literacy, and service
Penn State Schreyer Honors College Medal • Just 5% of the undergraduate students enrolled at Penn State are members
of the Schreyer Honors College and can earn the distinction of graduating with honors from Penn State
Dean's List Salutatorian, Pennridge High School GRANTS Euroscholars Grant Award (€2500) Schreyer Travel Grant for Euroscholars Internship ($750) Schreyer Travel Grant for London Study Tour ($750) NASA PA Space Grant Research Internship Program ($1200) SCHOLARSHIPS Binder for Studies Scholarship, PSU College of EMS Scholarship J & E Teas Scholarship, PSU College EMS Scholarship AVX/Kyocera Foundation Scholarship, PSU MATSE Department Scholarship S & T Ross Trustee Scholarship, PSU Schreyer Honors College Scholarship R&M Munro Trustee Scholarship, PSU Schreyer Honors College Scholarship Michael M. and Mary Jane Coleman UG Award in the College of Earth and Mineral Science, PSU MATSE Department Scholarship State of the Art, Inc. Annual Scholarship, PSU MATSE Department Scholarship Dr. Peter B. Lake Endowed Scholarship, PSU MATSE Department Scholarship Matthew J Wilson Honors Scholarship, PSU College of EMS Scholarship Penn State Provost Award Verna M. Butterer Educational Trust Scholarship
• Annual award up to $14,000 to Bucks County demonstrated a financial need to achieve a post-secondary education in their chosen fields.