| Chitosan (CS) is an N-deacetylated product of chitin that is one of the most abundant polysaccharides in nature and has good physical, biological and biodegradable properties. It is readily processable into membranes from aqueous acid solutions. The membranes obtained by chitosan and its blend have been reported to be suitable for various applications. In many cases of such applications, it is necessary to have an open porous structure. In this work, we've developed a novel method to prepare chitosan base porous membrane. It consists of casting a suspension of CS/counterpart polymer blend solution, removing the solvent by evaporation, neutralization, and dissolving the counterpart polymer by hot water afterward.Three kinds of water soluble polymers (i.e. polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG)) were chosen as the counterpart polymers. Results showed that there are more or less interactions between CS and the counterpart polymers. In the CS/counterpart polymer blends, the crystalline structure of each component is destroyed upon blending. The compatibility between CS and PEG is much worse than the other two blend pairs. Phase separation occurred in case of CS/PEG blend system. Hence, their blends had poor mechanical properties.The pore structure induced by this method is controlled by the compatibility of CS and the counterpart polymers. The pore size reflects the phase size and phase continuity of the blend. No pore structure was induced in the case of CS/PVP due to their molecule level miscibility and the strongest interaction. Highly porous membranes with good water permeability were prepared from CS/PEG blend membranes for its phase-separated structure caused by the poor compatibility. The compatibility and membrane structure of CS/PVA is in between of them. The asymmetric structure obtained from CS/PVA blend membrane was mainly because its surface state during blend membranes preparation.The pore structure and hence the properties of the membrane can also be controlled by altering the molecular weight of PEG. It is well known that thepermeability of a porous material is determined by its pore size and porosity. The highest water permeability of the extracted CS/PEG20000 can be attributed to its biggest pore size and high porosity. And the high water permeability of the extracted CS/PEG2000 blend membranes can be mainly attributed to its highest porosity. The low water permeability of the other three cases (PEG4000, PEG6000, and PEG10000) indicated that they have relatively small pore size and low porosity.To prevent dissolution in acidic solution, CS membranes were crosslinked. The PEG embedded within the CS/PEG semi-IPN has been extracted effectively by hot water to induce porous structure. The content of PEG and the crosslinking agent has a significant effect on the pore structure. The pore size was in sub-mireometer level (<3um). Hence, it is help to the availability of a large range of pore sizes provides more flexibility to submit to a wider spectrum of applications, especially for those that require pore size in sub-micrometer level. The membrane is pH sensitive, exhibiting reversibility and rapid response in swelling to pH changes. The swelling ratio oscillated between ca. 120 to ca. 220 when pH was alternated between 3.2 and 11. It also has fairly well mechanical strength both in dry and swollen state. Thus, it was expected as potent candidates for biomedical use as environmental pH condition altered.
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