Butyralization of poly(vinyl alcohol) under supercritical carbon dioxide for a humidity-resistant adhesive to glass substrates

Poly(vinyl butyral) (PVB) is widely accepted as an adhesive for glass substrates within the automobile windows. In this work, we suggested and performed butyralization of poly(vinyl alcohol) (PVA) under supercritical carbon dioxide (sc-CO2) and investigated not only the structure and mechanical properties of the obtained PVB but also its adhesion properties under various conditions, comparing this PVA with other PVBs prepared in the solution and swollen states. The conversion ratio of butyralization under sc-CO2 was larger than that in the swollen state and lower than that in the solution state and exhibited a sufficient material performance as the adhesive for glass substrates. The Young’s modulus and tensile strength of PVB under sc-CO2 were higher than those of the other PVBs. The mechanical properties of the PVB prepared under sc-CO2 have no correlation to the modification ratios because sc-CO2 penetrated into the amorphous region of the PVA and preferentially modified its hydroxyl groups. Furthermore, the adhesive strengths of all the obtained PVBs increased, and under a high-humidity atmosphere, the adhesive strength of the PVB prepared under sc-CO2 was the largest. The humidity resistance of the PVB adhesive prepared under sc-CO2 was proven. Poly(vinyl butyral) (PVB) is accepted as an adhesive to glass substrates. The PVB was prepared through butyralization of poly(vinyl alcohol) under supercritical carbon dioxides. The Young’s modulus and tensile strength of the PVB prepared under supercritical carbon dioxides were higher than those of the PVBs in the preparation method in solution and swollen states. In addition, the PVB under supercritical carbon dioxide possessed higher adhesive strength to glass substrates even under high humid condition, compared with the other PVBs.