The Primary Studies On HPC/PVA Thermosensitive Membranes

Thermosensitive membranes are defined as some kind of membrane that can change their flux, retention level and porosity rapidly and reversibly in response to a variation in environmental temperature. They are expected to be ’chemical valve’, and widely used in many fields such as separation and purification, artificial organs, controlled drug delivery, bionics, and so on.Among many membrane materials, hydroxypropyl cellulose （HPC） is a kind of cellulose ether with advantages of thermosensitivity, bio-degradation, good bio-compatibility and innocuity, which can be applied in the field of bio-pharmacy. While poly（vinyl alcohol） （PVA） is the world’s largest volume synthetic polymer produced for its excellent film-forming property, bio-compatibility and low market price. In this investigation, HPC and PVA were chosen to prepare blending membranes. The influences of blending composition and membrane-forming conditions on the membrane structure and performance such as flux, porosity and retention level were discussed. The study of swelling kinetics and phase transition temperature indicated thermosensitivity of HPC/PVA blending membrane.Theoretical calculation based on thermodynamics theory showed good compatibility of HPC/PVA blends system in certain blending ratio. The results were consistent with the testing of FT-IR, polarized light microscope and viscosity measurements. The more PVA contained, the better compatibility HPC/PVA blends system had.The conformation transformation of six-member-ring of glucose in HPC macromolecular chains occurred due to the temperature variation, which resulted in the expansion of the whole macromolecular chains, and the changes of the internal structure of blend membranes. The LCST of HPC/PVA blends system changed to a lower value with the increasing content of PVA. While temperature below LCST, the swelling ration decreased with the increase of HPC, which was due to the swelling process mainly controlled by relaxation process of polymer chains. The experimental data suggested that the structure and properties of the blend membranes were affected by the solution concentration, conditions of coagulation bath etc. With the increase of solution concentration, the flux and porosity of HPC/PVA membranes decreased, but retention level of albumin bovine increased. With the increaseing amount of HPC, the flux and average pore size increased. With the different coagulation bath temperature, the structure and performance of blending membrane changed accordingly.Finally we measured the interaction parameters of glycerol-H₂O, HPC/PVA-H₂O systems and HPC/PVA-glycerol systems by the methods of freezing point depression and equilibrium swelling respectively. Flory-Huggins’s polymer solution theory was employed to calculate bimodal line and spinodal line, as well as to plot the ternary phase diagrams of HPC/PVA-H₂O-glycerol system with H₂O as solvent and glycerol as nonsolvent by the method of Matlab computer program.This paper is an exploratory study, and it can provide some theory reference for commercial production of the HPC/PVA thermosensitive blend membranes.