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.

Abstract. Non-isothermal crystallization and subsequent melting of three grades of ethylene-vinyl acetate copolymer were investigated by differential scanning calorimetry (DSC) technique. The DSC crystallization curves show that vinyl acetate (VAc) content has the same effect on the onset, peak and final crystallization temperatures, and these copolymers have almost the same spacing of thermal windows under identical crystallization condition. Subsequent melting DSC results suggest that EVA14 (14 wt% VAc) has the narrowest distribution of lamellar thickness and the most perfect crystals. Though the instantaneous nucleation was preferred, non-isothermal crystallization kinetics shows that EVA14 could form tridimensional crystallites, whereas EVA18 (18 wt% VAc) and EVA28 (28 wt% VAc) are prone to crystallize two-dimensionally, as a result of more noncrystallizable VAc co-monomers introduced in the crystallizable ethylene segments. The growth rate falls on the following sequence: EVA14>EVA18>EVA28. Moreover, the kinetic crystallizability G also well characterizes the variation of the non-isothermal crystallization of these EVA materials, in the view of structural impediment caused by the VAc content.

We reported herein the damp-heat aging of ethylene-vinyl acetate copolymers (EVA) with different vinyl acetate (VAc) contents simultaneously for weeks. The aging was carried out under temperature of 40 C and relative humidity of 93% in air atmosphere. The changes of copolymers' structures and properties were investigated by means of FTIR, wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) and mechanical tests. CI values derived from ATR-FTIR spectra have a decrease when aging time is 1 week and then increase during damp-heat aging process which suggests the first loss then incorporation of O¼ ¼C group. WAXD infer that the narrowing trend of FWHM and increase of crystal sizes may attribute to the melting and re-crystallization of secondary crystallization, which is also confirmed by DSC results. Mechanical tests including Shore A and Shore D hardness, modulus at 100%, tensile strength and elongation at break, are all depending on the primary crystallization and influenced little by damp-heat aging.

Multiple melting behaviors and partial miscibility of ethylene-vinyl acetate (EVA) copolymer/low density polyethylene (LDPE) binary blend via isothermal crystallization are investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). Crystallization temperature T ( C) is designed as 30, 50, 70, 80 C with different crystallization times t (min) of 10, 30, 60, 300, 600 min. The increase of crystallization temperature and time can facilitate the growth in lateral crystal size, and also the shift of melting peak, which means the completion of defective secondary crystallization. For blends of various fractions, sequence distribution of ethylene segments results in complex multiple melting behaviors during isothermal crystallization process. Overlapping endothermic peaks and drops of equilibrium melting points of LDPE component extrapolated from HoffmanWeeks plots clarify the existence of partial miscibility in crystalline region between EVA and LDPE. WAXD results show that variables have no perceptible influence on the predominant existence of orthorhombic crystalline phase structure.

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.