定义Definition
聚乙烯是乙烯加聚得到的热塑性塑料，重复单元为 –CH₂–CH₂–，是全球产量最大的塑料。按密度和结构分为低密度聚乙烯（LDPE）、线型低密度聚乙烯（LLDPE）和高密度聚乙烯（HDPE），还有超高分子量聚乙烯（UHMWPE）。
Polyethylene is the thermoplastic made by addition polymerisation of ethylene, with the repeat unit –CH₂–CH₂–, and the plastic produced in the largest amount worldwide. By density and structure it is low-density (LDPE), linear low-density (LLDPE) or high-density (HDPE), with ultra-high-molecular-weight polyethylene (UHMWPE) as a special grade.
结构与性能Structure and properties
LDPE 用高压自由基法生产，含大量长短支链，结晶度约 40–50%，密度 0.910–0.925 g/cm³，柔软透明，用于薄膜。HDPE 用齐格勒或菲利普斯催化剂在低压下生产，支链很少，结晶度可达 70–80%，密度 0.941–0.965 g/cm³，坚硬，用于瓶、管和箱。聚乙烯化学惰性好、耐低温、电绝缘性优良，但耐热性较差（熔点约 105–135 °C）。
LDPE, made by high-pressure radical polymerisation, has many long and short branches, about 40–50% crystallinity and a density of 0.910–0.925 g/cm³; it is soft and clear and used for film. HDPE, made at low pressure with Ziegler or Phillips catalysts, has few branches, up to 70–80% crystallinity and a density of 0.941–0.965 g/cm³; it is rigid and used for bottles, pipes and crates. Polyethylene is chemically inert, tough in the cold and an excellent insulator, but its heat resistance is limited (melting at about 105–135 °C).
发现与发展Discovery and development
1898 年冯·佩希曼加热重氮甲烷时偶然得到聚亚甲基。1933 年英国帝国化学工业公司（ICI）的吉布森和福西特在高压下研究乙烯与苯甲醛反应时，意外得到白色蜡状聚合物，1939 年投产，二战中用作雷达电缆绝缘材料。1953 年齐格勒发现常压下的钛-铝催化剂，1951 年菲利普斯石油公司发现铬催化剂，使 HDPE 成为可能。1970 年代 LLDPE、1990 年代茂金属聚乙烯相继出现。
In 1898 von Pechmann obtained polymethylene by chance while heating diazomethane. In 1933 Gibson and Fawcett at ICI, studying ethylene and benzaldehyde under high pressure, unexpectedly got a white waxy polymer; production began in 1939, and it insulated radar cables in the Second World War. Ziegler's titanium–aluminium catalyst of 1953 and Phillips Petroleum's chromium catalyst of 1951 made HDPE possible. LLDPE followed in the 1970s and metallocene polyethylene in the 1990s.
用途与环境Uses and environment
全球年产约 1.1 亿吨，用于购物袋、食品包装膜、农膜、奶瓶、水管、电缆护套和玩具。UHMWPE 纤维强度极高，用于防弹衣和缆绳；UHMWPE 块材用于人工关节。聚乙烯在环境中几乎不降解，是海洋塑料垃圾和微塑料的主要来源之一。
World output is about 110 million tonnes a year, used for shopping bags, food film, farm film, milk bottles, water pipes, cable jackets and toys. UHMWPE fibre is extremely strong and goes into body armour and ropes, and solid UHMWPE into artificial joints. Polyethylene hardly degrades in the environment and is a major source of marine plastic litter and microplastics.
反应Reactions
LDPE：150–300 MPa，150–300 °C，O₂ 或过氧化物引发；HDPE：常压到数 MPa，50–100 °C，齐格勒-纳塔或铬催化剂。
LDPE: 150–300 MPa, 150–300 °C, oxygen or peroxide initiator; HDPE: atmospheric to a few MPa, 50–100 °C, Ziegler–Natta or chromium catalysts.
与 1-丁烯共聚得到 LLDPE
Copolymerising with 1-butene gives LLDPE
化学性质Chemical properties
耐酸、碱、盐溶液，常温下不溶于任何溶剂，在热的二甲苯或十氢萘中溶解。
Resists acids, bases and salt solutions; insoluble in all solvents at room temperature, but dissolves in hot xylene or decalin.
燃烧时火焰上黄下蓝，滴落并有石蜡气味：(CH₂)ₙ + 1.5n O₂ → n CO₂ + n H₂O。
Burns with a yellow-tipped blue flame, dripping and smelling of paraffin: (CH₂)ₙ + 1.5n O₂ → n CO₂ + n H₂O.
年表Timeline
- 1898
冯·佩希曼得到聚亚甲基
Von Pechmann obtains polymethylene
- 1933
ICI 发现高压聚乙烯
ICI discovers high-pressure polyethylene
- 1939
LDPE 工业化
LDPE goes into production
- 1953
齐格勒发明低压法
Ziegler invents the low-pressure process
- 1963
齐格勒与纳塔获诺贝尔化学奖
Ziegler and Natta receive the Nobel Prize in Chemistry