Gas permeation through water-swollen sericin / PVA membranes
Silk sericin, a protein obtained from cocoons, is a highly hydrophilic macromolecular material with many hydroxyl, carboxyl and amino acid groups. Sericin has been used for cosmetics, medical, polymer materials and other applications due to its antioxidative, antibacterial, UV resistant and moisture-absorbing and -desorbing properties. On the other hand, polyvinyl alcohol (PVA) has been used as a membrane material because of its good film forming properties. In this study, sericin was blended with PVA to form membranes that are permselective to gases. Due to their hydrophilic properties a novel water-swollen sericin / PVA membrane was investigated for the gas permeation of carbon dioxide and nitrogen. Silk sericin with molecular weights 26 - 170 kDa was obtained from cocoons by extraction with water. At 95 the yield of sericin was found to be 22.8% after 9 hrs of extraction. The sericin / PVA membranes were prepared by blending sericin and PVA followed by crosslinking with glutaradehyde. After drying, the membranes were heat treated at 120 for 1 hr. The membranes containing 0 to 30.3% sericin showed that the permeability was 2.7-4.0 Barrer for O2, 1.3-2.3 Barrer for N2 and 66.5- 28.8 Barrer for CO2, corresponding to a separation factor in the range of 48.3 to 60 for CO2/N2 and 1.4 to 2.2 for O2/N2. The membranes showed a favourable selectivity for CO2/N2 separation, which is relevant to CO2 capture from flue gas for green house gas emission control. In addition, the effects of water in the membrane on the membrane properties were evaluated. It was shown that the swelling of the membranes with water tended to improve the permeability and selectivity of the membranes due to the increased free volume available for gas transport in the membrane. The water vapor sorption and desorption were also studied, and the diffusion coefficient was determined. It was found that the membrane permeability depended on the water sorption uptake in water-swollen membranes.