STUDY ON THE COMPOSITES OF COLLOIDAL SILICA AND POLY(VINYL ALCOHOL) MODIFIED WITH A SMALL AMOUNT OF SILANOL GROUPS

First, the mixtures of colloidal silica dispersion and aqueous solutions of silane-containing PVA were investigated in terms of gellation. The gellation was apt to take place with an increase in silane content, and in degree of polymerization of silane-containing PVA, and with the decrease in particle size of colloidal silica. The gellation was observed to be more favorable in neutral pH range and in the equal amounts of the both components. The gellation was estimated to occur between the silanol groups in the surfaces of colloidal silica particles and the silanol groups in PVA, followed by mutual reaction or agglomeration of the the reacted particles. Second, the properties of the films obtained from casting the aqueous mixtures were investigated. The films composed of silica and silane-containing PVA were transparent, while those composed of silica and conventional PVA were opaque. These phenomena show the agglomeration of silica particles during the film formation in the case of conventional PVA, where there does not exist the strong interaction between both materials differing from the former case. The experiments of degree of swelling of the films in water reveal the cross linking of silane-containing PVA caused by silica. The structure of the crosslinked portion seemed to be C-O-Si. Mechanical properties of the composite films showed almost no lowering at 80-degrees-C, whereas those of conventional PVA films as well as those of silane-containing PVA films lowered significantly. The phenomenon was attributed to the increase of glass transition temperature of silane-containing PVA induced with crosslinking.