cellulose based hydrogels and...

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



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)

[email protected]

Acknowledgements

Institute of Paper Science and Technology, Georgia Tech fellowship support

NSF IREE

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