Porous and non-porous cellulose membranes have been produced using a novel solvent system. The membranes were made from cellulose alone or blended with another polysaccharide. Porous cellulose membranes had pore sizes around 200 nm while blended membranes were around 1000 nm. Characterization found the cellulose-only membrane had a cellulose II crystal structure while the blended membrane was amorphous. The blended membrane absorbed more water and had improved strength and flexibility compared to cellulose-only membranes.
![Cellulose - Polysaccharide Membranes Cast from a Novel Green Solvent System Eugene F. Douglass 1 , Richard Kotek 1 , Richard Venditti 2 , Joel Pawlak 2 1 Department of Textile Engineering Chemistry & Science, North Carolina State University, Raleigh, NC 27695-8301 2 Department of Forest Biomaterials, North Carolina State University, Raleigh, NC 27695-8005 Introduction: A new solvent system was developed in previous work 1 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 membranes 210 ± 42 nm mean pore sizes Figure 3 - Micro-porous cellulose/polysaccharide membranes 1000 ± 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 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 systems 3 . The water absorbance tests shows that the added polysaccharide improves the water absorbency of the membrane, while improving the tensile strength and failure strain %. ,[object Object],[object Object],[object Object],[object Object],SEM micrographs of Membrane Cross Sections Table 2 - Porous membrane water absorbance tests 24 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 2 θ angles for Cellulose I are 15,17 and 23 3 . These are present in this data. Typical 2 θ angles for Cellulose II are 12, 20 and 22 3 . 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. Cellulose membrane type Tensile Modulus (GPa) Failure Stress (MPa) Failure Strain (%) NMMO non-porous 2 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 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](https://image.slidesharecdn.com/acspostermarch2010kotek-12948582433966-phpapp01/85/ACS-Poster-1-320.jpg)
