Acrylic acid (AA) and sodium styrene sulfonate (SSS) were grafted onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) membranes by preirradiation method

and a humidity sensing membrane with strong acid and weak acid groups was prepared.Grafting was carried out by using γ-ray from 60Co at room temperature.Thermal and chemical properties of the grafting membranes were investigated.Infrared spectroscopy analysis of the grafting membrane confirmed the existence of sulfonate and carboxylic acid groups in the grafting membranes.The thermal behavior of grafting membranes was evaluated by TGA

and the results show that the higher the grafting yield is

the higher the char residue

which indicates that the branch chains including —SO3Na and —COOH provide catalytic impetus to the charring.The degree of crystallinity of grafting membranes containing —SO3Na and —COOH groups decreased with the increase of the grafting yield.The static contact angle with water of the grafting membrane decreases meanwhile the hydrophilicity of the grafting membrane increases with increasing the grafting yield.The electrical response properties of the grafting membrane to humidity was examined

too.The resistive of the grafting membrane changes linearly by 3 orders of magnitude over almost the whole humidity range (5%～98%RH).Furthermore

the grafting membrane exhibits a quick response (absorption:less than 1 min; desorption:less than 2 min) and small hysteresis (less than 3%RH).The FEP-AA+SSS membrane can be a promising approach to the development of new humidity sensitive materials with good sensing characteristics.