Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites 12 th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron Stabilization of polystyrene/polylactic acid cocontinuous blends by interfacial graphene Lian Bai 1 , Siyao He 2 , John W. Fruehwirth 1 , Xiang Cheng* 1 , Christopher W. Macosko* 1 1. Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis, Minnesota 55455, United States 2. Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States Reduced graphene oxide (r-GO) is known to be effective in increasing the conductivity of cocontinuous polymer blends with a lower electrical percolation threshold. However, little is known regarding the localization and dynamics of r-GO along with morphology change during annealing. In this study, we develop a facile method to stabilize the polystyrene (PS)/polylactic acid (PLA) cocontinuous blends with r-GO jammed at interface. In this method, the non-functionalized GO is premixed with PLA via solvent method, and then reduced in-situ at 210 o C to obtain a PLA/r-GO masterbatch. This masterbatch is further mixed with PS via batch melt compounding to obtain the PLA/PS/r-GO ternary nanocomposite. We observe the migration of r-GO from the PLA phase to the interface during annealing. The interfacial r-GO suppresses the coarsening of cocontinuous morphology and increases the conductivity of the filled polymer blend. Moreover, we systematically investigate the relationship between r-GO localization, rheological and conductivity change during annealing of r-GO filled PLA/PS cocontinuous blends. 1
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Stabilization of polystyrene/polylactic acid cocontinuous blends by interfacial graphene
Lian Bai1, Siyao He2, John W. Fruehwirth1, Xiang Cheng*1, Christopher W. Macosko*1
1. Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis,Minnesota 55455, United States
2. Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, United States
Reduced graphene oxide (r-GO) is known to be effective in increasing the conductivity of cocontinuous polymer blends with a lower electrical percolation threshold. However, little is known regarding the localization and dynamics of r-GO along with morphology change during annealing. In this study, we develop a facile method to stabilize the polystyrene (PS)/polylactic acid (PLA) cocontinuous blends with r-GO jammed at interface. In this method, the non-functionalized GO is premixed with PLA via solvent method, and then reduced in-situ at 210oC to obtain a PLA/r-GO masterbatch. This masterbatch is further mixed with PS via batch melt compounding to obtain the PLA/PS/r-GO ternary nanocomposite. We observe the migration of r-GO from the PLA phase to the interface during annealing. The interfacial r-GO suppresses the coarsening of cocontinuous morphology and increases the conductivity of the filled polymer blend. Moreover, we systematically investigate the relationship between r-GO localization, rheological and conductivity change during annealing of r-GO filled PLA/PS cocontinuous blends.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Covalent Modification of Bulk Carbon Nanotube Materials for Improved Tensile Properties
James S. Baker1,2 ; Michael A. Meador1
1 NASA-Glenn Research Center, Cleveland, Ohio; 2 NASA Postdoctoral Program Fellow
Carbon nanotubes (CNT) have attracted a great deal of interest as reinforcement in composite materials due to their exceptional mechanical properties. However, less than ideal tensile properties are obtained in composites using bulk CNT materials as the reinforcement. This is due in part to relatively weak inter-CNT and CNT-matrix interactions leading to poor load transfer through the material.
Our group has examined covalent functionalization of the CNT as a means to improve the tensile properties of both bulk CNT materials (sheets, yarns) and the polymer-CNT composites prepared using these functionalized CNTs. Functionalizations examined include: epoxidation (Epox-CNT), aliphatic amine (ApA-CNT), and aromatic amine (ArA-CNT). ApA-CNT functionalized sheet offered the greatest enhancement in sheet tensile properties, with a specific tensile strength of 265 MPa/(g/cm3) compared to 127 MPa/(g/cm3) for the unmodified sheet. Specific tensile modulus was increased to 4.9 GPa/(g/cm3), compared to 0.78 GPa/(g/cm3) for the unmodified material.
Carbon nanotube sheet material was used as a “drop-in” substitute for carbon fiber in the preparation of 60/40 wt% CNT/epoxy resin composites. While the tensile strength of composites using the functional CNT was not significantly improved relative to those using non-modified CNT, composites using the Epox-CNT and ArA-CNT exhibited tensile modulus improvements of 90% and 160%, respectively, relative to the non-modified composites. Strain at failure for the Epox-CNT and ArA-CNT composites was 11% and 3.6%, compared to 27% for the non-modified CNT composite. This presentation will highlight our efforts to improve the tensile properties of CNT sheet and composites obtained using these functionalized materials.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Mechanical Characterization and Modeling of Rate Dependent Toughened Structural
Adhesives
Erol Sancaktar, Gamze Sultan Bas
University of Akron, Polymer Engineering Department, Akron, USA 44325
Structural adhesives such as toughened epoxy adhesives are excellent candidates to be used as
impact-resistant adhesives and play an important part in the design of light-weight structures. They
poses energy absorption capability for the endurance of framework to be crashworthy. These
particular properties provide safer conditions for the driver and passengers against the crash effects
in case of accident of automobiles.
In this work, epoxy formulations which contain various combinations of toughening agents have
been characterized to predict rate dependent physical properties by using tensile testing with high
elongation strain gauges at rates varying between 25 and 500 mm/min crosshead rate. Hereby
tensile strength, failure strain and toughness of those structural epoxy adhesives have been
modeled as a function of loading rate by using Ludwik-type equations, and the results compared
with results obtained using Hopkinson Pressure Bar apparatus at different but high speeds
representing impact speeds.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Gluing Soft Interfaces by Nanoparticles
Zhen Cao, Andrey Dobrynin
Abstract: Using a combination of the molecular dynamics simulations and scaling analysis we studied
reinforcement of interface between two soft gel-like materials by spherical nanoparticles. Analysis of the
simulations shows that the depth of penetration of a nanoparticle into a gel is determined by a balance of
the elastic energy of the gel and nanoparticle deformations and the surface energy of nanoparticle/gel
interface. In order to evaluate work of adhesion of the reinforced interface, the potential of mean force for
separation of two gels was calculated. These simulations showed that the gel separation proceeds through
formation of necks connecting nanoparticle with two gels. The shapes of the necks are controlled by a
fine interplay between nanoparticle/gel surface energies and elastic energy of the neck deformation. Our
simulations showed that by introducing nanoparticles at soft interfaces, the work required for separation
of two gels could be 10-100 times larger than the work of adhesion between two gels without nanoparticle
reinforcement. These results provide insight in understanding the mechanism of gluing soft gels and
biological tissues by nano- and micro-sized particles.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
High Loading, Dispersion and Stabilization of MWCNT in Epoxy Prepolymers from Continuous High Shear
Reactor Processing
Brian M. Greenhoe, Jeffrey S. Wiggins1
School of Polymers and High Performance Materials, University of Southern Mississippi
118 College Drive #5050, Hattiesburg, MS 39406
Abstract
This manuscript describes a one-step continuous reaction method for preparing large volumes of multiwall carbon
nanotube (MWCNT) reinforced tetraglycidyl-4, 4’-diaminodiphenylmethane prepolymers at nanotube loading up to
26% wt/wt. The continuous reactor was designed based on a co-rotating intermeshing twin screw extruder where the
reactor barrels were modified into two sections, hot and cold zones. Hot zone temperature was set at 160 to 200 °C
and designed for the partial curing of the epoxy resin to build viscosity while the cold zone was maintained between
room temperature and 100 °C to quench the reaction and enhance MWCNT dispersion. Differential scanning
calorimetry and rheological analysis were used to demonstrate the cure conversion, glass transition temperatures,
and viscosity of epoxy prepolymers can be finely tuned through the adjustment of hot zone temperature. Optical
microscopy and transmission electron microscopy indicated that the nanotube dispersion was greatly improved at
lower cold zone temperatures due to the increased shear states imposed by an increased resin viscosity. Bulk
electrical conductivity obtained by four point probe analysis was used as an indirect qualification of dispersion state
and conductivities of up to 0.84 S/cm were obtained.
Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Failure of Tube Models to Predict the Linear Rheology of Star/Linear Blends
RYAN HALL, University of Michigan, PRIYANKA DESAI, University of Michigan,
BEOMGOO KANG, University of Tennessee, MARIA KATZAROVA, Illinois Institute of
Technology, QIFAN HUANG, University of Michigan, SANGHOON LEE, Pohang University
of Science and Technology, TAIHYUN CHANG, Pohang University of Science and
Technology, DAVID VENERUS, Illinois Institute of Technology, JIMMY MAYS, University of
Tennessee, JAY SCHIEBER, Illinois Institute of Technology, RONALD LARSON, University
of Michigan
We compare predictions of two of the most advanced versions of the tube model, namely the
“Hierarchical model” by Wang et al. (J. Rheol. 54:223, 2010) and the BOB (branch-on-branch)
model by Das et al. (J. Rheol. 50:207-234, 2006), against linear viscoelastic data on blends of
monodisperse star and monodisperse linear polybutadiene polymers. The star was carefully
synthesized/characterized by temperature gradient interaction chromatography, and rheological
data in the high frequency region were obtained through time-temperature superposition. We
found massive failures of both the Hierarchical and BOB models to predict the terminal
relaxation behavior of the star/linear blends, despite their success in predicting the rheology of
the pure star and pure linear. This failure occurred regardless of the choices made concerning
constraint release, such as assuming arm retraction in “fat” or “skinny” tubes, or allowing for a
“disentanglement relaxation” even to cut off the constraint release Rouse process at long times.
The failures call into question whether constraint release can be described as a combination of
constraint release Rouse processes and dynamic tube dilation within a canonical tube model of
entanglement interactions.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Reinforcement of Polyamide 6 with cellulose nanocrystals prepared via in-situ ring
opening polymerization: thermal, mechanical and rheological properties
Shahab Kashani Rahimi and Joshua U. Otaigbe,
School of Polymers and High Performance Materials, University of Southern Mississippi
118 College Drive, Hattiesburg, MS, USA
Novel class of polyamide 6 nanocomposites reinforced with cellulose nanocrystals were prepared by in-situ ring-
opening polymerization followed by melt extrusion with the CNC content ranging from 1-3 wt% in the matrix. The
effects of CNC content and of surface modification with organosilane coupling agent on thermal, mechanical and
melt rheological properties of these systems were systematically studied. Solid state NMR analysis confirmed the
formation of interfacial bond between the matrix and the surface of CNC through two different mechanisms namely
the re-propagation of polyamide chains through surface initiated anionic species and transamidation reaction. The
thermal analysis results revealed that the CNC significantly impeded the spherulitic crystal growth rate of the
polyamide chains that is associated with reduction in crystallinity. The surface modified CNC particles were found
to enhance the promotion of γ-type crystals which is associated with the interfacial bond formation on the particle
surface. The mechanical properties of the polyamide matrix were found to be enhanced by addition of the CNC
while the SEM images of the fractured surface showed that a significant interfacial plastic deformation occurred
when using the surface modified particles. The reinforcing effect of the CNCs is confirmed by the observed increase
in tensile modulus and strength. The melt rheological analysis showed significant changes in flow behavior of these
systems both in steady and oscillatory modes, confirming the evolution of the samples structure. This novel method
of reinforcing high-melting engineering thermoplastics by renewable cost effective cellulosic fibers through in-situ
reactive polymerization opens up a new opportunity towards development of novel functional high performance
composite materials reinforced with small fraction of environmentally-friendly fibers for a number applications
where traditional fiber-reinforced polymer composites are not useable.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Relaxation Dynamics of Nanoparticle-Tethered Polymer Chains
Sung A Kim,†, § Rahul Mangal,† and Lynden A. Archer†
†School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York
14853, United States
§Department of Chemical Engineering and Materials Science, University of Minnesota,
Minneapolis, Minnesota 55455, United States
This talk presents the relaxation dynamics of nanoparticle-tethered cis-1,4-polyisoprene (PI)
investigated using rheometry and dielectric spectroscopy. By densely grafting polymer chains to
spherical nanoparticles, this self-suspended suspension is a model platform to study the effects of
surface and geometrical confinement on the chain configuration and dynamics from the
experiments performed in bulk materials. We find that tethered polymer molecules relax more
slowly and generally form more extended chain configurations than their untethered
counterparts. At a fixed grafting density, increasing the PI molecular weight up to values close to
the entanglement molecular weight speeds up chain relaxation dynamics and decreases the
degree of chain stretching when compared to untethered chains. Decreasing the polymer grafting
density for a fixed molecular weight has the opposite effect. It dramatically slows down chain
relaxation, increases interchain coupling, and leads to a transition in rheological response from
simple fluid behavior to jammed, soft-glassy rheology. Higher measurement temperature
produces more jamming, more intense chain stretching, and speed-up of molecular relaxation at
a rate that decreases with grafting density and molecular weight. Our observations are explained
in terms of chain confinement driven by crowding between particles and the space filling
constraint on chains tethered to nanoparticles in self-suspended materials.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
VOLUMETRIC PROPERTIES AND STRAIN PERFORMANCE OF GLASSY AMORPHOUS POLYMER NETWORKS
Kyler R. Knowles, Jeffrey S. Wiggins School of Polymers and High Performance Materials, The University of Southern Mississippi
118 College Drive #5050 Hattiesburg, MS 39401
Processing carbon fiber composite laminates creates molecular-level strains in the thermoset matrix upon curing and cooling which can lead to shape deformations, micro-cracking, and other issues. The origin of these strains lies in the properties of the polymer matrix, which experiences significant changes in volume and physical state throughout the curing process. In this study, two glassy amorphous high-Tg polymer networks were formulated to be chemically-similar while differing in crosslink density. Tetraglydicyl-4,4’-diamino-diphenyl methane and diglycidyl ether of bisphenol-F were combined with 3,3’-diaminodiphenyl sulfone to examine the effect of crosslink density on key properties which dictate strain creation in composites manufacturing. Volumetric properties such as chemical shrinkage and coefficient of thermal expansion were quantified using high-pressure mercury dilatometry and thermomechanical analysis, respectively. Increased crosslink density corresponds with a decrease in both chemical shrinkage and coefficient of thermal expansion. Additionally, a non-contact, full-field strain measurement technique known as digital image correlation was used for strain analysis, allowing for observation of anelastic strain recovery after loading in compression and correlation with matrix volumetric properties.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
DNA as a Flame Retardant Additive for Low-Density Polyethylene
Parker W. Leea, Sergey A. Isarova, Jenna H. Towsleea, Kathleen M. Hoffmanb, Rick D. Davisb,
João M. Maiaa, and Jonathan K. Pokorskia,*
aDepartment of Macromolecular Science and Engineering, School of Engineering, Case Western
Reserve University, Cleveland, OH, 44106, USA bFire Research Division, Engineering Laboratory, National Institute of Standards and
Technology, Gaithersburg, MD, 20899, US
The need for alternatives to classic halogenated and metal oxide flame retardant additives
has increased in the past 40 years due to environmental concerns and high loading levels
respectively. Intumescent organic flame retardants, such as melamine polyphosphate (MPP) and
ammonium polyphosphate (APP), have been used to fill this need as they can provide flame
retardant properties at lower loading levels than metal oxides. However, there are environmental
and biological concerns over the use of MPP and APP as additives. Deoxyribonucleic acid
(DNA) has been recently shown to act as an effective flame retardant when applied as a coating
to cotton fabrics and compounded with polyethylene-co-vinyl acetate, however it has not yet
been applied to commodity thermoplastics.
This study expands the use of DNA as a flame retardant by studying the properties of
low-density polyethylene (LDPE) when compounded with DNA. LDPE is one of the most
widely used commercial thermoplastics and has very poor flame retardant performance. A
systematic study was performed on the effect of DNA loading level on flame retardant
performance with MPP used as a comparator. The compounding torque, mechanical properties,
dispersion, and biochemical properties of DNA/LDPE materials were studied to determine the
compatibility and state of DNA after compounding. The results indicate that DNA has better
flame retardant properties than MPP at lower loading levels and maintains better mechanical
properties. This study is the first to utilize DNA as a flame retardant additive with LDPE and
expands the utility and understanding of DNA during compounding with commodity
thermoplastics.
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Abstract: We study mechanical properties of polymeric nanocomposites with liquid
inclusions in polymer network matrix using molecular dynamics simulations. The
shear modulus of nanocomposite is shown to be a function of the elastocapillary
number γSL/(GNR0), where γSL is the surface tension of network/liquid interface, GN is
the shear modulus of network and R0 is the initial size of the liquid inclusion. First, in
the range of elastocapillary numbers, γSL/(GNR0) << 1, the composite shear modulus
increases with increasing this parameter value. In this interval of elastocapillary
numbers, the liquid inclusion softens the network such that the composite modulus
Gcomp is smaller than GN. This is in agreement with the classical Eshelby's inclusion
theory. However, for elastocapillary numbers, γSL/(GNR0) ≈ 1, the shear modulus of
composite is comparable to that of the network, Gcomp ≈ GN. In this range of
parameters, the surface energy gained from the deformed liquid inclusion
compensates for the elastic energy lost by replacing network with liquid. When the
elastocapillary number increases further, γSL/(GNR0) >> 1, the interfacial energy of
network/liquid interface dominates the mechanical response of the composite.
Analysis of the shape of the liquid inclusion shows that the inclusion stays spherical
under this situation. Under this situation, the liquid inclusion behaves like a
nanoparticle, acts as a stress concentrator and stiffens the network. The classical
Eshelby's inclusion theory fails to explain this phenomenon. We apply a new
continuum mechanics model of this class of nanocomposite materials to explain this
unusual mechanical response of nanocomposite materials.
Mechanical Properties of Polymeric Nanocomposites with Liquid Inclusions
Authors: Zhen Cao, Andrey Dobrynin, Heyi LiangThe University of Akron
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Oral Presentations: Mechanical – Rheological Properties of Polymers and Composites
12th National Graduate Research Polymer Conference 2016 | College of Polymer Science and Polymer Engineering at The University of Akron
Rheology and Dynamics of Spherical Motifs in Ordered Self-assembly