hydrocarbon, such as n-pentane. The formed PS beads contain 5-8% of volatile hydrocarbon. When the beads are heated in steam, they soften and volatilization of low-boiling hydrocarbon and diffusion of steam into the beads cause the beads to expand to about 40 times their original size (at this stage the beads are not fused together)/ The beads are then loaded into a mould through which steam is passed, they again expand (by a small amount) and, being enclosed in the mould, are consolidated into a block. * Properties and Applications PS (amorphous, Tg ~ 108 oC) is a hard, rigid, rather brittle material. It has relatively low softing point and does not withstand the temperature of boiling water. PS is highly transparent, transmitting about 90% of visible light; it also has a high refractive index of 1.59 which gives it particular brilliance. Since it is a
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