The absorption and thermal behaviors of PET-SiO2 nanocomposite films

In this paper, to improve properties of Poly(ethylene terephthalate) (PET) in thermal stability and barrier to water, the films of PET, PET with micronmeter Silica/Polystyrene (SiO2/PS) Composites (SPET) and PET with nano-SiO2/PS composites (SNPET) are prepared and their water absorption and thermal stable behaviors are investigated. In the samples, silica load is optimized as 2 wt%, at which silica not only disperses well but also forms the tough morphology in PET as investigated by SEM. The nanoeffect and thermal degradation behaviors of SNPET are firstly presented. The water absorption experiments for the samples show that the maximum absorption water weight percentage (C.) and the pseudodiffusion coefficient (D) of water reduce with SiO2 particle size varying from 440 nm to 40 nm, and the barrier property to water of SNPET is superior to those of pure PET and SPET. At the minimum silica size of 40 nm, the C-infinity and D of SNPET approach the minimum values that are 0.946% and 7.075 x 10(-13) m(2) s(-1), respectively. Fixing SiO2 size at 40 nm, with un-modified SiO2 and modified SiO2, the core-shell SiO2/PS nanocomposite particles are more effective on keeping PET from absorbing water. With the increase in nano-SiO2 load, the C. and D of SNPET films reduce, proving that the nano-SiO2 particles can inhibit water absorption. When amorphous SNPET films are annealed at 130 degrees C, their C-infinity and D quickly decrease with the increase in annealing time, stating that the crystallized SNPET also retards the water absorption or diffusion in PET. Under oversaturated oxygen atmosphere, the C-infinity and D of amorphous PET and SNPET, and crystallized SNPET samples are higher than those of corresponding samples without flowing oxygen, showing that oxygen promotes the films to absorb water. TGA results show that SNPET keeps similar thermal degradation behavior under the conditions of with and without both water and oxygen. But SNPET is more thermally stable than PET. (c) 2006 Elsevier Ltd. All rights reserved.