Hong Pi

The Effect of High Intensity UV Irradiation on Color Behavior of Poly(Vinyl Chloride)

A detailed study of color change in poly(vinyl chloride) (PVC) sheets due to high intensity ultraviolet (UV) irradiation was undertaken, focusing on the first 50 h of change. Color changes were monitored with a Datacolor check spectrophotometer and compared with a set of controls. Measurements were taken after 1, 3, 5, 10, 15, and 20 h of irradiation, then at 10 h intervals for the next 40 h. Further measurements were conducted at 100, 240, and 480 h. Data were analyzed using the reflectance spectra (350–800 nm) as well as the CIE (International Commission on Illumination) L* a* b* color values (L*, a*, and b* are lightness value, redness-greenness value, and yellowness-blueness value, respectively) and the total color change (ΔE). The majority of color changes were found to occur within the first 50 h. After 50 h, the color change slowed and began to reverse toward 480 h. Surface microstructure properties, such as morphology, surface tension and oxidized products, were characterized to allow a comparison of sensitivity between the color monitoring methods and a comprehensive understanding of the color change. The results show that color evolution was attributable to the competition between the formations of polyene sequences (dehydrochlorination reaction) and their subsequent oxidation (photobleaching), which was slightly different from the behavior under a xenon arc lamp. According to the color behavior and the microstructure analysis a general scheme accounting for the mechanism of ageing behavior of PVC under high intensity UV irradiation is proposed.

Influence of ultraviolet absorbers on the ultraviolet-irradiation behaviour of rigid poly vinyl chloride

The effects of ultraviolet absorbers (UVAs) on the UV-irradiation behaviours of rigid PVC were studied through Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. In addition, the absorption behaviours of these UVAs in non-polar and polar solvents were characterised and the solution photolysis experiments of these UVAs in ethanol were investigated in the absence and presence of a free radical initiator during the UV irradiation. The results showed that the protection efficiency to photo-degradation of PVC was in the following order: 2,4,6-tri(2-hydroxy-4-butoxylphenyl)-1,3,5-triazine (U3) > 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methyl phenol (U2) > 2-hydroxy-4-n-octoxy-benzophenone (U1). This protection efficiency was related to the chemical structures of the UVAs, especially the intermolecular hydrogen bond (IMHB). In a polar solution, such as dimethyl sulfoxide, the absorption corresponding to the IMHB of U3 was intact, while that of U1 disappeared. The free radical initiator weakened the intensity of the absorption, accelerating the destruction of the IMHB.

Characteristics and Kinetics of Thermal Degradation of Fluoroether Rubber

ABSTRACT An advanced, heat-resistant fluoroether rubber (FM-20) was subjected to dynamic thermogravimetric analysis (TGA) in the air atmosphere. The results suggested that its thermal degradation process can be divided into two parts. As the heating rate increased, the initial decomposition temperature and degradation temperature would move to higher ranges. The apparent activation energy of thermal decomposition, calculated by the Kissinger, Friedman and Flynn-Wall-Ozawa methods were 209, 240, and 211kJ/mol, respectively. Furthermore, the probable thermal degradation mechanism was also analyzed by the Coats-Redfern method. As a result, the most reasonable thermal degradation mechanism of FM-20 was g (α) = α3/2