Mechanical properties of polyvinyl acetate incorporated with silica-gel by sol-gel process

Abstract

A vinyl acetate-vinyl triethoxysilane copolymer with molar ratio 9:1 was incorporated with silica-gel by the sol-gel process. Tetraethoxysilane (TEOS) and methyl triethoxysilane (MTES) were used as silicon alkoxides. Hybrid films of the copolymer prepared from TEOS were rigid and the film mixed with 60 wt% of TEOS was brittle. On the other hand, films from MTES were softer than those from TEOS. MTES could be mixed with the copolymer until 80 wt% obtaining free-standing films. The tensile strength of hybrid film from TEOS increased as the amount of TEOS increased and had a maximum (48 MPa) at 50 wt% of TEOS. In the case of MTES, the strength increased rapidly with MTES content, keeping almost the same value (43 MPa) from 20 to 80 wt% of MTES. The dynamic viscoelastic properties of the hybrid films were measured. The dynamic modulus of hybrid film from TEOS was higher than that from MTES above Tg. A broad tan6 peak was observed at about 80-90 °C for the TEOS hybrid, while the tan8 peak of the hybrid from MTES appeared at 70-80 °C and was sharper than that of the TEOS hybrid. The methyl group in MTES decreased the modulus and Tg of the hybrid.