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

First, the mixtures of colloidal silica dispersion and aqueous solutio ns of silane-containing PVA were investigated in terms of gellation. T he gellation was apt to take place with an increase in silane content, and in degree of polymerization of silane-containing PVA, and with th e decrease in particle size of colloidal silica. The gellation was obs erved to be more favorable in neutral pH range and in the equal amount s 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 agglomeratio n of the the reacted particles. Second, the properties of the films ob tained from casting the aqueous mixtures were investigated. The films composed of silica and silane-containing PVA were transparent, while t hose composed of silica and conventional PVA were opaque. These phenom ena show the agglomeration of silica particles during the film formati on in the case of conventional PVA, where there does not exist the str ong interaction between both materials differing from the former case. The experiments of degree of swelling of the films in water reveal th e cross linking of silane-containing PVA caused by silica. The structu re of the crosslinked portion seemed to be C-O-Si. Mechanical properti es of the composite films showed almost no lowering at 80-degrees-C, w hereas those of conventional PVA films as well as those of silane-cont aining PVA films lowered significantly. The phenomenon was attributed to the increase of glass transition temperature of silane-containing P VA induced with crosslinking.