Cellulose - Polysaccharide Membranes Cast from a Novel Green Solvent SystemEugene F. Douglass1, Richard Kotek1, Richard Venditti2, Joel Pawlak2

1Department of Textile Engineering Chemistry & Science, North Carolina State University, Raleigh, NC 27695-83012Department of Forest Biomaterials, North Carolina State University, Raleigh, NC 27695-8005

Introduction:A new solvent system was developed in previous work1 to make novel fibers and films from cellulose; this study is a natural continuation of that work. Cellulose and cellulose – polysaccharide blends have been dissolved and coagulated to make membranes with this system. Both microporous and nonporous membranes were produced.

Raw Materials:Cellulose from acetate-grade wood pulp is used as the prime raw material. The other raw materials dissolved in this system are common biomaterials. One specific blend is shown here. The solvent system involves an amine and a metallic salt combined in a specific optimized ratio. Figure 1 - Non-porous cellulose membranes

Figure 2 - Micro-porous cellulose membranes210 ± 42 nm mean pore sizes

Figure 3 - Micro-porous cellulose/polysaccharide membranes1000 ± 208 nm mean pore sizes

Experimental Procedure:The fibrous wood pulp (and the polysaccharide (if desired)) is dissolved in a specific optimized solvent blend (of an amine and metallic salt) at elevated temperature under a nitrogen atmosphere. Membranes are cast using a metal casting bar on PET film on a casting table, and the material is coagulated in a non-solvent to precipitate the membrane. A solvent exchange procedure is then used to extract the solvent and salt to replace with an easily removed non-hydrophilic solvent for drying purposes to retain porous morphology. The materials were then analyzed with tensile tests, SEM, WAXS and water absorbency.

Figure 4 - WAXS scans of:

a) Raw pressed cellulose pulp b) Cellulose membrane

c) Cellulose and polysaccharide blend membrane

Cellulose membrane type Tensile Modulus (GPa) Failure Stress (MPa) Failure Strain (%)

NMMO non-porous2 1.6 ± 0.6 64.9 ± 18.3 6.5 ± 1.5

ED/KSCN non-porous 1.63 ± 0.16 52.6 ± 6.9 26.2 ± 10.1

ED/KSCN porous 0.32 ± 0.09 5.79 ± 1.67 3.9 ± 1.4

ED/KSCN porous blend 0.5 ± 0.15 10.4 ± 3.9 10.0 ± 5.3

Summary:Porous and nonporous membranes from cellulose and cellulose

blended with another polysaccharide have been produced. These membranes are both strong and flexible.

These porous cellulose membranes have pore sizes around 200 nm for cellulose alone versus around 1000 nm for the cellulose blend. The resultant crystal structure for the cellulose membrane is Cellulose II, with an amorphous morphology for the blend. This amorphous nature shows the other added polysaccharide affects the former crystal structure upon swelling & dissolution and is fixed in place with coagulation. The cellulose II structure for the cellulose membrane is consistent with other solution membranes developed with other systems3.

The water absorbance tests shows that the added polysaccharide improves the water absorbency of the membrane, while improving the tensile strength and failure strain %.

References:2.Margaret W. Frey , Hester Chan , Kristen Carranco . Rheology of cellulose/KSCN/ED solutions and coagulation into filaments and films. Journal of Polymer Science Part B: Polymer Physics 2005;43(15):2013-223.Khare VP, Greenberg AR, Kelley SS, Pilath H, Roh IJ, Tyber J. Synthesis and characterization of dense and porous cellulose films. J Appl Polym Sci 2007;105(3):1228-363. Cao Y, Tan HM. Cellulose Carbohydr Res 2002;337:1291.

SEM micrographs of Membrane Cross Sections

Material Dry Mass (g) Wet Mass (g) Wet Mass Increase (%)

Cellulose Membrane 0.49 1.03 110

Cellulose /

Polysaccharide Blend

Membrane

0.93 2.89 310

Table 2 - Porous membrane water absorbance tests24 Hour DI Water Immersion Test, 25º C

Table 1 - Tensile test comparison (ASTM D882 5lb, or 250lb cell)

500x 5000x

500x

500x

5000x

5000x

Cellulose I Cellulose II

Amorphous

Analysis of SEM micrographs – Figure 1 is nonporous because when water or methanol alone is used as coagulant and then the membrane is dried, the original porous structure collapses due to strong hydrogen bonding forces pulling the structure together while it shrinks as the swelling solvent blend is removed. The solvent exchange procedure locks the pores in place (for figures 2 & 3), and removes the solvent blend without collapsing the pores.

Typical 2θ angles for Cellulose I are 15,17 and 233. These are present in this data.

Typical 2θ angles for Cellulose II are 12, 20 and 223. Clearly a shift is evident in this data.

The peaks have been shifted into one, removed or smeared with a cloud, indicating an amorphous morphology.