关于混有二氧化钛氧化镁在PVC门窗型材中的可用性研究外文资料翻译.doc

附　录 PAGE 16 PAGE 9 外文资料翻译 A study on usability of magnesium oxide with titanium dioxide in PVC door and window profiles 1. Introduction Polyvinyl chloride is among the most widely used synthetic organic polymer materials. Plasticized polyvinyl chloride compositions are widely encountered as, for instance,vinyl sheet goods and as objects formed from plastisols.Polyvinyl chloride is commercially available in a variety of grades, some of which are suitable for preparing rigid,plasticizer-free compositions for extrusion . For plastics, prolonged exposure to the sun’s electromagnetic radiation in the ultraviolet (UV) region can lead to photooxdiation and degradation of physical properties, often manifested by color change and embrittlement. Similarly,the UV component of ordinary fluorescent lighting can degrade polymers and many of the additives used with them. The effective UV radiation that does reach the earth’s surface extends from about 290–400 nm. This range happens to include the highest energy component UV band, and the segment around 300 nm, which is the most distractive to plastics. Some man-made high-energy radiation sources mercury arc lamps, xenon arcs, carbon arcs, and various sun-lamps can emit radiation at wave lengths below 290 nm and these can degrade plastics even more severely than natural sun light. Hence, they are often used for accelerated testing of plastics. The energy content of UV radiation in the 290–400 nm can rupture most of the chemical bonds present in polymer structures. Not all the polymers are equally affected by UV radiation, and some have a degree of resistance, otably polymethyl methacrylates and fluorocarbons. Others, that in their pure forms could be expected to be resistant to UV, are degraded because of contaminants present that act as sites for UV energy absorption. Absorption of radiation energy by polymer produces molecular excitations: if the level of absorbed energy is high enough, it can activate a chemical reaction wh