A proton exchange membrane prepared by radiation grafting of p-styryltrimethoxysilane into PTFE membrane

Abstract

A proton exchange membrane ( PEM ) was produced by simultaneous radiation grafting of pstyryltrimethoxysilane ( StSi ) into polytetrafluoroethylene ( PTFE ) membranes, followed by sulfonation, hydrolyzation and condensation. The effects of solvent, absorbed dose, absorbed dose rate and monomer concentration on the degree of grafting (DOG) were studied. Toluene was chosen for its higher boiling point and giving a higher DOG with acceptable mechanical strength. DOG increased with increasing the absorbed dose and monomer concentration and changed little with the absorbed dose rate at 10-43 Gy·min-1. Monomer concentration of < 3 mol · L-1 was better for reducing the copolymer. The degree of sulfonation ( DOS ) was as high as 92% -97% at DOG > 23% , making the properties of the PEM rely much on the DOG. Scanning electron microscopy ( SEM ) gave imagines of radiation grafting happened through the surface to the centre of the membrane. The ion exchange capacity ( IEC) , water uptake, dimension expansion and proton conductivity grew up with the increase of DOG for more hydrophilic -SO3H,-Si-O-Si- crosslinking structure, and Si-OH groups were incorporated in the PEM. In addition, proton conductivity got better with temperature increase due to the good water uptake. Most of the grafted membranes exhibited lower methanol permeability than Nafion®.The prepared PEM in this work showed a good combination of high IEC (1.53 mmol·g-1) , dimension stability (dimension changed less than Nafion®117 at 90°C ) ,acceptable water uptake ( <63% at 90°C) and proton conductivity (1.5 × 10 -2 S · cm-1 at 90° and DOG 72.5%), and low methanol permeability (0.82 × 10-6cm2·s -1 at DOG 50.1%). PTFE, Styryltrimethoxysilane, Radiation grafting, Proton exchange membrane.