The influence of ultraviolet (UV)-irradiation on the photodegradation mechanism of different average degrees of polymerization (DP) of poly(vinyl) chloride (PVC) with UV-irradiation time was investigated by viscosity-average molecular weight determination, UV-vis spectroscopy, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), contact angle measurement, and scanning electron microscopy (SEM). PVC films with different DP (800, 1000, 1300, 3000) were prepared by solution casting. It was carried out exposing specimens to a xenon-arc light source with a spectral irradiance of 0.68 W/(m 2 nm) at 638C. It was found that the photodegradation mechanism of the lower DP of PVC (DP ¼ 1000) was different from the higher DP of PVC (DP ¼ 3000). This was because the lower DP of PVC was a homopolymer, while the higher DP of PVC was often produced by copolymerizing with a certain quantity of crosslinking agent (e.g., DAP and DAM). UVvis and FTIR spectroscopy studies provided some results concerning the structure of the irradiated PVC, and the carbonyl index and CÀ ÀCl index were induced to study the process of PVC photodegradation with different DP. TGA showed that the degradation temperatures of different weight loss increased with the irradiation time. The surface morphology of the irradiated polymer films with different DP was observed by contact angle measurement and SEM.

The influence of UV absorber (Chimassorb81) on the photodegradation mechanism of different average degrees of polymerization (DP) of poly (vinyl chloride) (PVC) with UV-irradiation time was investigated by viscosity-average molecular weight determination, UV-vis spectroscopy, FTIR, contact angle measurement, and scanning electron microscopy (SEM). The PVC films with different DP (1000 and 3000), which contained 0.3 or 0.5 phr Chimassorb81, were prepared by solution casting. It was carried out by exposing specimens to xenon-arc light source with a spectral irradiance of 0.68 W/(m 2 nm) at 638C. It is found that the Chimas-sorb81 is efficient photostabilizer for PVC with different DP. Although the Chimassorb81 delays the photodegradation of PVC, it does not influence the photodegradation mechanisms of PVC with different DP. The main photodegradation reaction for the lower DP of PVC is dehydrochlorination in the initial stage of UV-irradiation, and then the crosslinking and chain scission reactions occurred after long irradiation. However, the main reaction of the higher DP of PVC is not dehydrochlorination but crosslinking and chain scission in the initial stage of UV-irradiation. The results of carbonyl index, CÀ ÀCl index, contact angle measurement, and SEM also show that the photostability of Chimassorb81 is more effective for the higher DP of PVC, especially in the presence of higher concentration of Chimassorb81.

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A bilayer structure with polydopamine (PDA) transition layer and 3-glycidyl ether oxy-propyl trimethoxy silane (GOPTS) hydrolysiscondensate strengthened layer on the surface of ultra-high molecular weight polyethylene (UHMWPE) fiber is prepared to improve the damage resistance of composites and more efficient stress transmission in composites. PDA is covered on the surface of UHMWPE fiber and then GOPTS is hydrolyzed and condensed to form inorganic -O-Si-O-with epoxy groups on the PDA layer. In addition, the surface activated nano-SiO 2 is dispersed in the epoxy resin to increase the strength of the matrix resin. The results show that the interfacial shear strength (IFSS), the impact strength, the flexural strength and flexural modulus of UHMWPE-PDA-GOPTS/EP-SiO 2 increase by 99.1%, 54.1%, 76.8%, and 36.6% respectively compared with unmodified UHMWPE/EP. The chemical compositions of the treated fiber surface are characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (ATR-FTIR). With the help of the scanning electron microscopy, the interface failure and reinforcement mechanism of the composites are further explored due to UHMWPE fiber shear yield deformation, UHMWPE fiber fracture, matrix resin cracking and the relative sliding friction between the fiber and matrix.