Effect of different preparation methods on structure and properties of chitosan/poly-lactic acid blend porous membrane

Two kinds of blend solutions were used to prepare chitosan (CS)/poly-L-lactic acid (PLLA) blend membranes by the immersion precipitation phase inversion method. CS/PLLA blend membrane was fabricated by mixing CS-acetic acid solution and PLLA-dioxane solution, chitosan powder (CSP)/PLLA blend membrane was fabricated by mixing CSP and PLLA-dioxane solution. The membrane structure and properties were characterized by Scanning Electron Microscope, Wide Angle X-ray Diffraction, porosity, water vapor transmission rate and swelling property. The results showed that CS content in CSP/PLLA blend membrane was nearly 70 times higher than in CS/PLLA blend membrane. Two types of blend membranes took on an unsymmetrical structure with a skin layer, a microvoid sub-layer and a porous bottom surface. But CSP/PLLA blend membrane exhibited a porous skin layer, while the skin layer of CS/PLLA blend membrane was impact. The WAXD analysis revealed that PLLA and CS were amorphous in CS/PLLA blend membrane, while there were PLLA and CS crystalline in CSP/PLLA membrane, which resulted in the higher initial modulus of CSP/PLLA blend membrane. The porosity, WVTR and equilibrium swelling (Q(eq)) of CSP/PLLA blend membrane were higher than that of CS/PLLA blend membrane, especially Q(eq) . The swelling kinetics results showed that in the initial swelling, water molecules diffusion followed Non-Fickian diffusion for CS/PLLA blend membrane swelling, and the swelling of CSP/PLLA blend membrane fitted with the relaxation diffusion model. The swelling kinetics studies for whole swelling revealed that the swelling degree and the initial swelling rate of CSP/PLLA membrane were significantly higher than that of CS/PLLA membrane, although the total swelling rate of CSP/PLLA blend membrane decreased lightly.