Synthesis and barrier properties of poly(vinylidene chloride-co-acrylonitrile)/SiO₂ hybrid composites by sol-gel process

Poly(vinylidene chloride-co-acrylonitrile) (P(VDC-co-AN))/silica hybrid composite systems were successfully prepared by the sol-gel method using an appropriate coupling agent and solvent system (1:1 ratio of THF - tetrahydrofuran and NMP - N-methyl-2-pyrrolidone) to enhance their water vapor and oxygen barrier properties while maintaining their coating transparency. A silane coupling agent consisting of 3-glycidyloxypropyltrimethoxysilane (GPTMS) was used to suppress the phase separation between the P(VDC-co-AN) and inorganic SiO₂. The gas permeabilities of the hybrid composites were minimized by adding the silica component in the range of 10-20 wt%, and a thin coating at ca. 1-2 μm lowered the permeabilities of oxygen and water vapor to 2.88 × 10^-10 ml mm m^-2 s^-1 GPa^-1 and 1.12 × 10^-5 g mm m^-2 s^-1, corresponding to improvements of 94.14% and 25.38%, respectively, compared to that of the pristine PET film. The optical transmittance of the hybrid coating was over 85% in the visible range (380-800 nm) and the surface roughness was less than 86.3 nm.