可降解塑料Biodegradable plastic

这类高分子主链多含酯键等可水解基团。降解通常分两步：先由水解或酶（脂肪酶、蛋白酶、解聚酶）把长链切成低聚物和单体，再由微生物吸收代谢为 CO₂ 和 H₂O。降解速度强烈依赖温度、湿度和微生物：PLA 在工业堆肥（约 58 °C）中几个月即可降解，但在海水或常温土壤中可能需要多年。“可降解”与“生物基”不同：PBAT 是石油基但可降解，生物基聚乙烯则不可降解。

Their backbones usually contain hydrolysable links such as esters. Degradation has two stages: hydrolysis or enzymes (lipases, proteases, depolymerases) cut the chains into oligomers and monomers, which microbes then take up and metabolise to CO₂ and H₂O. Rates depend strongly on temperature, moisture and microbes: PLA breaks down within months in industrial compost at about 58 °C but may take years in seawater or cool soil. Biodegradable is not the same as bio-based: PBAT is fossil-based yet biodegradable, while bio-based polyethylene does not biodegrade.

1926 年法国巴斯德研究所的勒莫瓦涅在细菌中发现聚羟基丁酸酯（PHB）。1932 年卡罗瑟斯在杜邦合成了低分子量的聚乳酸。1990 年代嘉吉公司（后 NatureWorks）实现乳酸发酵—丙交酯开环聚合制备高分子量 PLA 的大规模生产。2020 年前后多国推出“限塑令”，推动可降解塑料快速发展。

In 1926 Lemoigne at the Pasteur Institute found polyhydroxybutyrate (PHB) in bacteria. Carothers made low-molecular-weight polylactic acid at DuPont in 1932. In the 1990s Cargill, later NatureWorks, commercialised high-molecular-weight PLA made by fermenting lactic acid and ring-opening polymerisation of lactide. Plastic restrictions adopted by many countries around 2020 drove rapid growth.

可降解塑料用于购物袋、快递袋、一次性餐具、农用地膜、3D 打印耗材和可吸收手术缝线。争议在于：许多产品只在工业堆肥条件下降解，混入普通回收体系会降低再生料质量；“氧化降解”塑料只是碎裂成微塑料，并非真正生物降解，已被欧盟禁止。

They are used for shopping and courier bags, disposable tableware, agricultural mulch film, 3D-printing filament and absorbable surgical sutures. Debates centre on the fact that many products degrade only in industrial compost and contaminate conventional recycling streams, while 'oxo-degradable' plastics merely fragment into microplastics and are not truly biodegradable; the EU has banned them.