A novel poly(vinyl alcohol)/silica composite film with “spherical crystal interlocking structure” and its barrier and enhancement mechanism

Using the semi-crystalline poly(vinyl alcohol) (PVA) as the polymer matrix and silica nanoparticles (SNPs) as the reinforcing filler, composite films with excellent water vapor barrier, high tensile strength, visible light transmission and ultraviolet (UV) shielding performances were constructed via a simple heat treatment process, during which the films underwent dehydration cross-linking and isothermal recrystallization to form a "spherical crystal interlocking structure". Both the dosage and average particle size of SNPs significantly affected the barrier property, and the optimal values were 7 wt% and 15 nm, respectively. The heat treatment further improved the water resistance, mechanical strength, and barrier property to a great extent. Moreover, different theoretical models including Guggenheim Anderson de Boer (GAB), Brunauer Emmett and Teller (BET), Hailwood-Horribon (H-H) model, crystallinity model and Fick's law model were successfully used to explain the water vapor barrier mechanism. The water vapor permeability (WVP) of the optimized composite film was reduced to 2.20 × 10−12 g·m/(m2·Pa·s) at 37°C and 65% RH, while the tensile strength was increased up to 116.8 MPa. In addition, the absorption rate of ultraviolet of the film after heat treatment increased from 13% to 92.0%, while the transmittance of visible light remained above 78%.