LEE GOETZ ART RAGAUSKAS Cellulose Based Hydrogels and Absorbents
LEE GOETZ
ART RAGAUSKAS
Cellulose Based Hydrogels and Absorbents
Hypothesis
Cellulosics can be crosslinked with poly (methyl vinyl ether-co-maleate) (PMVEMA) – poly ethylene glycol (PEG) and will exhibit enhanced water absorbing properties
Objective
Prepare softwood and hardwood pulp based crosslinked fibers and cellulose whisker based films with a PMVEMA-PEG matrix
Characterize physical, chemical, and novel water sorption properties
Superabsorbent Polymers
What are they? Materials with the ability to absorb and retain large volumes ofsolutions (water and aqueous most commonly)
Common commercial SAPsCrosslinked Poly(acrylic acid)
Superabsorbent Actions
Cellulose based hydrogels/films
Development of biofriendly productsAgricultural applications - moisture control in arid climates
Biomedical – burn wound dressings, drug delivery
Food packaging – absorbing or delivering moisture for freshness and appearance
Personal hygiene products – diapers, etc
Background
US Patent 5049235 Poly (methyl vinyl ether-co-maleate) (PMVEMA) and PolyolModified Cellulosic Fiber, Barcus et al Sept. 17, 1991
IPST@GT Donated Patent
Crosslinking Agents Used: Poly (methyl vinyl ether-co-maleate), Polyethylene glycol
Pulp: CTMP, Kraft HW & SW, bleached & unbleached
My Program
Look at fundamental chemistryWater Absorption, Retention
Chemical Characterization (NMR, SEM, FTIR)
Degree of Crosslinking
Current interest is in new materials based crosslinking cellulosics:
SW/HW kraft fibers
Milled SW/HW kraft fibers
Whiskers
General Experimental Procedure Pulp Based Cellulosics
PMVEMA, Polyethylene glycol (MW 3350), and water (pH 2) are heated to 65 °C.
Pulp fibers are mixed (1-5 min), dried, and cured at 125 - 135°C (∼6 min).
The crosslinked fibers are wetted and washed with (1) water, (2) caustic, (3) water and dried.
Reaction
heat
Crosslinked Pulps – ECF Pine Kraft
0
50
100
150
200
250
0 0.5 1 1.5 2 2.5
Wat
er A
bsor
benc
y (g
/g)
Crosslinking agent charge
Water Absorbency Values - Pine Fiber
Milled Pine Whole Fiber Pine
Crosslinked Pine Pulp (2x)
Crosslinked Pulps – ECF Birch
0.5 x PMVEMA
Reacted Birch Pulp
2 x PMVEMA
CP/MAS 13C NMR of Crosslinked Pulps
Pine Pulp
Crosslinked Pine Pulp
Birch Pulp
Crosslinked Birch Pulp
From Microcrystalline cellulose (MCC) to Cellulose Whiskers (CNW)
Cellulose Whiskers
MCC
Centrifuge
64% H2SO4
MCC & H2O
(chilled)
MCC, H2SO4 & H2O
(65 °C 130 min)
Dialyze against H2O
Centrifuge Dialyze against PEG
AFM Cross Polarized Light
Crosslinked Whisker Sample Preparation
Whiskers + PMVEMA + PEG film Vary percentage (weight) of whiskers
Air dry in oven
Cure at 135°C for 6.5 min
Store in humidity controlled desiccators for further testing
2%, 54%, 92% relative humidity
FT-IR of Crosslinked Whiskers
50CNW Film 50CNW Film treated with 0.1 M NaOH
1724 cm-1 1538 cm-11724 cm-1
CP/MAS 13C NMR of Crosslinked Whiskers
28.9
73.2
42.8
30.4
28.9
171.2
181.7
57.1
72.929.8 45.0
63.471.7
76.574.1
110.1
78.2
75.1
73.6
45.3
68.8
73.8
73.3
60.7
47.2
76.7
19.8
30.1
28.9
72.9
45.0
30.1
28.9
72.9
44.7
57.1
173.6
181.7
57.1
173.6
181.7
57.1
171.2
36.1
180.7
14.1
67.2
69.3
70.1
70.1
69.3
67.2
171.2
44.7
36.172.9
14.128.6
57.1
180.7
181.7
173.6
56.8
35.7
44.4
21.3
181.7
181.7
11.3
OH
O
OO
O
O
O
OHOH
HO
OH
OH
OH
OHOH
O
HO O
OHOO
HO O
OHO
O
O O
OHO
O
O
OO
OOHO
HOO
HO O
O
O OH
OHO
CNW only
50CNW film
PMVEMA only
Estimated Shift Projections
Water Sorption of Crosslinked Whiskers
Timed absorption
0
200
400
600
800
1000
0 2000 4000 6000
Time(min)
Wat
er u
ptak
e (g
/g,%
) PMA-PEG/CNW25PMA-PEG/CNW50PMA-PEG/CNW75
Procedure
-1 cm diameter circular samples were immersed in distilled water and removed at appropriate time intervals relative to each film, blotted to remove surface water, weighed and replaced.
-This was repeated until equilibrium was reached
Mechanical Properties of Crosslinked Whiskers
• Tensile (Stress-Strain)– Measured with 500 N Load
Cell, on Instron 4411– A rectangular shaped strip
(60 mm long x 8 mm wide) with a 25 mm distance between the two heads, with a 5 mm/min load rate
0
1
2
3
4
5
6
7
8
9
10
0 50 100 150 200 250 300
Strain, %
Stre
ss, M
Pa
2% RH
54% RH
92% RH0
1
2
3
4
5
0 50 100 150 200 250 300
Strain, %
Stre
ss, M
Pa
PMA-PEG/CNW100PMA-PEG/CNW75PMA-PEG/CNW50PMA-PEG/CNW25
• The strength and E-modulus improved and strain decreased with increased CNW.
The strength and E-modulus decreased and strain increased with increased relative humidity.
54% Relative Humidity
50% CNW Film
25% CNW Film – Cut
SEM of Crosslinked Whiskers
25% CNW Film – Tensile Test Fractured
Behavior of Crosslinked Materials in Water
Crosslinked pulp fibers dry, then wetted…
Crosslinked whisker films dry, then wetted…0.5 g SAP + 8.5 ml 21.5 ml 136.5 ml
Comparison SEMs of Pulps
Crosslinked Birch Pulp (1:0.56:0.17 birch pulp:PVMEMA:PEG)
Crosslinked Pine Pulp
(1:0.56:0.17 pine pulp:PVMEMA:PEG)
TGA of Crosslinked Whiskers
0 - 100% NCC Film Degradation
75
80
85
90
95
100
25 75 125 175 225 275
Temperature, °CW
eigh
t Per
cent
, %
100% NCC Film75% NCC Film50% NCC Film25% NCC Film0% NCC Film
0 and 100% NCC Film Derivative Weight
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
-50 50 150 250 350 450 550 650Temperature, °C
Deri
vativ
e W
eigh
t, (%
/°C)
100% NCC Film
0% NCC Film
25 - 75% NCC Film Derivative Weight
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
-50 50 150 250 350 450 550 650Temperature, °C
Der
ivat
ive
Wei
ght,
(%/°C
)
75% NCC Film
50% NCC Film
25% NCC Film
Thermogravimetric Analysis (TGA)– TA TGA 500– 6 -10 mg samples conditioned at
54% relative humidity were heated from room temperature to max temperature of 700 °C at 10°C/min.
DMTA of Crosslinked Whiskers
– Die cut samples (38.9 mm x 5.3 mm) were loaded into the TA DMTA 800 and heated from -40°C to 200°C.
– Liquid nitrogen was used as the carrier gas because of the presence of descending peaks when starting at room temperature
0
0,1
0,2
0,3
0,4
0,5
0,6
-100 -50 0 50 100 150 200 250
Tan Delta PMA-PEG/CNW25
Tan Delta PMA-PEG/CNW50
Tan Delta PMA-PEG/CNW75
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
-60 -40 -20 0 20 40 60 80 100
Storage ModulusPMA-PEG/CNW25Storage ModulusPMA-PEG/CNW50Storage ModulusPMA-PEG/CNW75
Conclusions
Established novel size dependency of crosslinked pulp fibers and water absorbency properties
Unique benefits for SW kraft pulp fibers
First example of crosslinked cellulose whisker films that exhibit unique hydrogel properties
Demonstrated water sorption properties
Demonstrated strength properties
Future applications for managing water/humidity in packaging and for medical devices
Future Work
Vary PMVEMA, PEG, CNW ratios
Water sorption cycling
Manuscripts in preparation
Thesis (Dec./2008)
Acknowledgements
Institute of Paper Science and Technology, Georgia Tech fellowship support
NSF IREE