Study On Modification Of Cinnamic Acid-grafted Poly(vinylidene Fluoride) And Preparation Of Microfiltration Membranes

Poly(vinylidene fluoride) (PVDF) is a widely used material in membranes. Despite its popularity as a membrane material, the hydrophobic nature of PVDF often results in serious membrane fouling, and thus a low permeation flux in aqueous separation system. To solve this problem, in this work, polymers PVDF-g-P(CA) was designed and synthesized in an attempt to promote the hydrophilicity of the PVDF and the ability of fouling resistance.In this study, Cinnamic acid (CA)-graft-poly(vinylidenefluoride) (PVDF) polymers were synthesized for the first time via free radical polymerization using benzoyl peroxide (BPO) as initiator in a N,N-dimethylformamide (DMF) solution. Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and thermo gravimetric analysis (TG) of the grafted polymers showed that the CA side chains were grafted onto the PVDF backbone. Contact angle measurements indicated that the contact angle of modified PVDF reduced from 88°to 54°, which revealed that the hydrophilicity ability of PVDF was remarkably improved after the introduction of hydrophilic material.The change of graft ratio was relevant to not only free radical reaction mechanism, but also diffusion movement of monomer. For this graft polymerization system, the optimum time is 10 h, the suitable temperature is 70℃, amount of CA is 5% and a appropriate used amount of the initiator is 5% of the monomer mass.Microfiltration membranes were prepared from PVDF and the PVDF-g-P(CA) polymer with poly(vinyl pyrrolidone) (PVP) as the pore former by the tape casting method. The morphology of the membranes was studied by scanning electron microscope (SEM). The membranes cast from the DMF solution of PVDF-g-P(CA) had a greater pore size distribution (600-700nm) and higher porosities than those of the pristine PVDF. The modified membranes were characterized through water flux measurement and fouling-resistant experiment. The flux of the modified PVDF was 81 L/(m2·h), which increased by 16 L/(m2·h) over the pure PVDF. The adsorption amount of bovine serum albumin (BSA) on the modified membrane decreased. The BSA solution permeation of modified membrane increased. The results indicate the PVDF membranes have the better fouling resistance and filtration performance through the grafting of CA.The effects of various factors, during the preparation of PVDF membranes were examined, including a suitable pore former, temperature raising rate, environment humidity and the concentration of pore former. Only under optimum condition can a good quality membrane be made.