標題:
有關發泡膠既問題。CHEM高手入！ (十萬火急)
發問:
我想問吓發泡膠(expanded polystyrene / polystyrene foam)既製造方法，係「發泡膠既製造方法」，唔係polystyrene既製造方法。 順便問吓點解1990年之前既發泡膠會損害大氣層！ 唔該詳細D！THX！
最佳解答:
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Expanded polystyrene foam (EPF) is a plastic material that has special properties due to its structure which is composed of individual cells of low density polystyrene. After polymerization of styrene is complete, the mixture,consisting of beads made up of polystyrene chains is then cooled. These beads are then washed out and dried. Uniform bead size is achieved by sorting the beads through meshes which filter out over- and undersized beads. After that, the beads of polystyrene must be expanded to achieve the proper density. This process is known as pre-expansion, and involves heating the polystyrene either with steam (the most common method) or hot air (for high density foam, such as that used for a coffee cup); the heating is carried out in a vessel holding anywhere from 50 to 500 gallons (189 to 1,892 liters). During pre-expansion, an agitator is used to keep the beads from fusing together. Since expanded beads are lighter than unexpanded beads, they are forced to the top of the vessel's cavity and discharged. This process lowers the density of the beads to three percent of their original value and yields a smooth-skinned, closed cell EPF that is excellent for detailed molding. Next, the pre-expanded beads are usually "aged" for at least 24 hours in mesh storage silos. This allows air to diffuse into the beads, cooling them and making them harder. However, during the manufacture process of polystyrene, some chemicals suchas CFCs,HCFC will be used. This kinds of pollutants will deplete the ozone layer to cause it to become thinner. More harmful UV rays therefore reach the ground.
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