LEE GOETZ ART RAGAUSKAS

Transcription

1 Cellulose Based Hydrogels and Absorbents LEE GETZ ART RAGAUSKAS

2 Hypothesis Cellulosics can be crosslinked with poly (methyl vinyl ether-co-maleate) (PMVEMA) poly ethylene glycol (PEG) and will exhibit enhanced water absorbing properties

3 bjective 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

4 Superabsorbent Polymers What are they? Materials with the ability to absorb and retain large volumes of solutions (water and aqueous most commonly) Common commercial SAPs Crosslinked Poly(acrylic acid)

5 Superabsorbent Actions

6 Cellulose based hydrogels/films Development of biofriendly products Agricultural 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

7 Background US Patent Poly (methyl vinyl ether-co-maleate) (PMVEMA) and Polyol Modified Cellulosic Fiber, Barcus et al Sept. 17, 1991 Donated Patent Crosslinking Agents Used: Poly (methyl vinyl ether-comaleate), Polyethylene glycol Pulp: CTMP, Kraft HW & SW, bleached & unbleached

8 My Program Look at fundamental chemistry Water 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

9 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 C ( 6 min). The crosslinked fibers are wetted and washed with (1) water, (2) caustic, (3) water and dried.

10 Reaction heat

11 Crosslinked Pulps ECF Pine Kraft Water Absorbency (g/g) Water Absorbency Values - Pine Fiber Milled Pine Whole Fiber Pine Crosslinked Pine Pulp (2x) Crosslinking agent charge

12 Crosslinked Pulps ECF Birch 0.5 x PMVEMA Reacted Birch Pulp 2 x PMVEMA

13 CP/MAS 13 C NMR of Crosslinked Pulps Birch Pulp Crosslinked Birch Pulp Pine Pulp Crosslinked Pine Pulp

14 Cellulose Whiskers From Microcrystalline cellulose (MCC) to Cellulose AFM Whiskers (CNW) Cross Polarized Light MCC Centrifuge Dialyze against H 2 64% H 2 S 4 MCC & H 2 (chilled) MCC, H 2 S 4 & H 2 (65 C 130 min) Centrifuge Dialyze against PEG

15 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

16 FT-IR of Crosslinked Whiskers 1724 cm cm cm -1 50CNW Film 50CNW Film treated with 0.1 M NaH

17 CP/MAS 13 C NMR of Crosslinked Whiskers H H H H H H H H H H H H H H H H H H H CNW only 50CNW film PMVEMA only Estimated Shift Projections

18 Water Sorption of Crosslinked Whiskers Timed absorption 1000 Water uptake (g/g,%) PMA-PEG/CNW25 PMA-PEG/CNW50 PMA-PEG/CNW Time(min) 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

19 Mechanical Properties of Crosslinked Whiskers 54% Relative Humidity Stress, MPa PMA-PEG/CNW100 PMA-PEG/CNW75 PMA-PEG/CNW50 PMA-PEG/CNW Strain, % The strength and E-modulus improved and strain decreased with increased CNW. 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 Stress, MPa % CNW Film 2% RH 54% RH 92% RH Strain, % The strength and E- modulus decreased and strain increased with increased relative humidity.

20 SEM of Crosslinked Whiskers 25% CNW Film Cut 25% CNW Film Tensile Test Fractured

21 Behavior of Crosslinked Materials in Water Crosslinked pulp fibers dry, then wetted 0.5 g SAP ml 21.5 ml ml Crosslinked whisker films dry, then wetted

22 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)

23 TGA of Crosslinked Whiskers 1 0 and 100% NCC Film Derivative Weight 0-100% NCC Film Degradation 0,9 100% NCC Film Derivative Weight, (%/ C) 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0% NCC Film Temperature, C Weight Percent, % % NCC Film 75% NCC Film 50% NCC Film 25% NCC Film 0% NCC Film 25-75% NCC Film Derivative Weight 80 Derivative Weight, (%/ C) 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 75% NCC Film 50% NCC Film 25% NCC Film 0, Temperature, C Temperature, C Thermogravimetric Analysis (TGA) TA TGA mg samples conditioned at 54% relative humidity were heated from room temperature to max temperature of 700 C at 10 C/min.

24 DMTA of Crosslinked Whiskers 0,6 0,5 0,4 0,3 Tan Delta PMA- PEG/CNW25 Tan Delta PMA- PEG/CNW50 Tan Delta PMA- PEG/CNW Storage Modulus PMA-PEG/CNW25 Storage Modulus PMA-PEG/CNW50 Storage Modulus PMA-PEG/CNW75 0, , 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

25 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

26 Future Work Vary PMVEMA, PEG, CNW ratios Water sorption cycling Manuscripts in preparation Thesis (Dec./2008)

27 Acknowledgements Institute of Paper Science and Technology, Georgia Tech fellowship support NSF IREE