热塑性塑料Thermoplastic

非晶态热塑性塑料（如聚苯乙烯、PMMA、聚碳酸酯）在 Tg 以上软化，通常透明；半结晶热塑性塑料（如聚乙烯、聚丙烯、尼龙、PET）在 Tg 与熔点 Tm 之间仍具一定强度，加热到 Tm 以上才熔融流动。它们可溶于适当溶剂，长期受力会发生蠕变。

Amorphous thermoplastics such as polystyrene, PMMA and polycarbonate soften above Tg and are usually transparent; semicrystalline ones such as polyethylene, polypropylene, nylon and PET keep some strength between Tg and their melting point Tm and flow only above Tm. They dissolve in suitable solvents and creep under sustained load.

1870 年赛璐珞是最早的热塑性材料之一。1930 年代起聚苯乙烯、PVC、聚乙烯、PMMA、尼龙陆续工业化，二战后迅速普及。热塑性塑料主要用注塑、挤出、吹塑、热成型和 3D 打印（熔融沉积）加工，生产效率高，边角料可以回收再熔。

Celluloid (1870) was among the first thermoplastic materials. From the 1930s polystyrene, PVC, polyethylene, PMMA and nylon were commercialised and spread quickly after the Second World War. Thermoplastics are processed by injection moulding, extrusion, blow moulding, thermoforming and fused-deposition 3D printing at high speed, and scrap can be remelted.

热塑性塑料原则上可机械回收（粉碎重熔），树脂识别码 1–6 分别为 PET、HDPE、PVC、LDPE、PP、PS。但多次重熔会导致降解，不同塑料混杂难以分离，因此实际回收率较低（全球约 9%）。化学回收（解聚回单体、热解成油）是补充途径。

Thermoplastics can in principle be recycled mechanically by shredding and remelting; resin codes 1 to 6 are PET, HDPE, PVC, LDPE, PP and PS. Repeated melting degrades them, and mixed plastics are hard to separate, so actual recycling rates are low (about 9% worldwide). Chemical recycling, depolymerising to monomer or pyrolysing to oil, is a complementary route.