Water governs the mechanical properties of poly(vinyl alcohol)

The presence of water molecules can significantly determine the macroscopic mechanical property and microscopic chain dynamics of poly(vinyl alcohol) (PVA). However, to date it has remained fully understood the molecular mechanism behind experimentally and theoretically. Herein, we systematically examine the effect of water contents on the mechanical property, glass transition, free volume, and intermolecular interactions by combining experimental and MD simulation. Our results show that the presence of water significantly reduces the mechanical strength of PVA, and only 1.8 wt% of water reduces the tensile strength by similar to 32% but notably increases the plasticity of PVA by similar to 2.5 times. Meanwhile, the inclusion of water remarkably lowers the glass transition temperature, increases free volume, and promotes the relaxation and mobility of PVA chains. This is mainly because the presence of water gives rise to both the plasticization and even lubricating effect on the PVA chains. This work unravels how water governs the mechanical performances of the PVA.