Degradable Polymers | 可降解聚合物

📚 Degradable Polymers | 可降解聚合物

Polymers have transformed modern life, but their resistance to chemical attack creates a serious waste problem. Degradable polymers are designed to break down into smaller molecules through hydrolysis, light, or microbial action. This article reviews the main types, degradation mechanisms, and environmental implications relevant to Cambridge A-Level Chemistry.

聚合物改变了现代生活，但它们抵抗化学侵蚀的特性造成了严重的废弃物问题。可降解聚合物被设计为通过水解、光或微生物作用分解成较小分子。本文回顾与剑桥 A-Level 化学相关的主要类型、降解机制和环境影响。

1. What Are Degradable Polymers? | 什么是可降解聚合物？

A degradable polymer is a macromolecule whose chains can be broken down into smaller fragments under specific environmental conditions. The breakage usually occurs at functional groups in the polymer backbone, such as ester, amide, or glycosidic links.

可降解聚合物是一种大分子，其链在特定环境条件下可断裂成较小的片段。断裂通常发生在聚合物主链中的官能团上，例如酯键、酰胺键或糖苷键。

Degradable does not automatically mean ‘harmless’. Some polymers fragment into microplastics without full chemical breakdown, so chemists distinguish between disintegration, degradation, and mineralisation. Complete mineralisation converts the polymer into CO₂, H₂O, and biomass.

可降解并不自动意味着 ‘无害’。有些聚合物只碎裂成微塑料而未完全化学分解，因此化学家区分崩解、降解和矿化。完全矿化将聚合物转化为 CO₂、H₂O 和生物质。

2. Why Degradability Matters | 为什么可降解性很重要

Conventional addition polymers such as poly(ethene) and poly(propene) have carbon-carbon backbones that are very resistant to nucleophilic attack and enzyme-catalysed hydrolysis. They persist in landfills and oceans for decades or centuries.

传统加聚物如聚乙烯和聚丙烯具有碳-碳主链，对亲核进攻和酶催化水解非常稳定。它们在垃圾填埋场和海洋中可存留数十年甚至数百年。

Condensation polymers containing ester or amide links are more susceptible to hydrolysis. Designing polymers with such links allows controlled breakdown at the end of their useful life. This supports circular-economy goals and reduces plastic pollution.

含有酯键或酰胺键的缩聚物更容易水解。设计带有这类键的聚合物可以在使用寿命结束后实现可控分解。这支持循环经济目标并减少塑料污染。

3. Hydrolytic Degradation | 水解降解

Hydrolytic degradation occurs when water molecules attack polar functional groups in the polymer chain. For polyesters, water cleaves the ester link in a condensation reaction reverse:

水解降解发生在水分子进攻聚合物链中的极性官能团时。对聚酯而言，水使酯键断裂，这是缩合反应的逆过程：

R–COO–R’ + H₂O ⇌ R–COOH + R’–OH

The carboxylic acid product can further catalyse the hydrolysis, making polyester degradation autocatalytic. Factors such as pH, temperature, crystallinity, and hydrophilicity control the rate.

生成的羧酸产物可进一步催化水解，因此聚酯降解具有自催化特征。pH、温度、结晶度和亲水性等因素控制降解速率。

In the Cambridge specification, students are expected to recognise ester and amide links in condensation polymers and write hydrolysis equations producing monomers or smaller fragments.

在剑桥考试大纲中，学生应能识别缩聚物中的酯键和酰胺键，并写出水解生成单体或较小片段的方程式。

4. Photodegradation | 光降解

Photodegradation is initiated by ultraviolet (UV) radiation, which breaks bonds or generates reactive radicals in the polymer. Light-sensitive carbonyl groups, peroxide impurities, or added photoinitiators absorb UV energy and cause chain scission.

光降解由紫外线辐射引发，紫外线使聚合物断键或产生活性自由基。光敏羰基、过氧化物杂质或添加的光引发剂吸收紫外能量并引起断链。

Polymer chains may lose molecular mass and become brittle, allowing water and microorganisms to access the surface more easily. Photodegradable polymers are often used in agricultural mulch films and packaging that will be exposed to sunlight.

聚合物链可能失去分子量并变脆，使水和微生物更容易接触表面。光降解聚合物常用于农用地膜和暴露在阳光下的包装材料。

5. Biodegradation by Microorganisms | 微生物生物降解

Biodegradation involves enzymes secreted by bacteria or fungi. Enzymes such as esterases and lipases recognise specific links and lower the activation energy for hydrolysis. The polymer must first be fragmented into small enough pieces for cells to ingest.

生物降解涉及细菌或真菌分泌的酶。酯酶和脂肪酶等酶识别特定键并降低水解活化能。聚合物必须先碎裂成足够小的碎片才能被细胞摄取。

Under aerobic conditions, microorganisms convert the breakdown products into CO₂, H₂O, and new biomass. Under anaerobic conditions, landfill degradation can produce CH₄, a potent greenhouse gas, which may be captured for energy.

在有氧条件下，微生物将分解产物转化为 CO₂、H₂O 和新的生物质。在厌氧条件下，填埋场降解可能产生强效温室气体 CH₄，可收集用于能源。

6. Polylactic Acid (PLA) | 聚乳酸

PLA is a biodegradable polyester produced from renewable resources such as maize starch or sugarcane. Its repeating unit can be written as:

聚乳酸是一种可生物降解聚酯，由玉米淀粉或甘蔗等可再生资源生产。其重复单元可写作：

–[O–CH(CH₃)–CO]–ₙ

PLA is made by ring-opening polymerisation of lactide or by direct condensation of lactic acid. It contains chiral centres, and the ratio of L- and D-lactic acid units affects crystallinity and degradation rate.

聚乳酸通过丙交酯开环聚合或乳酸直接缩合制备。它含有手性中心，L-乳酸和 D-乳酸单元的比例影响结晶度和降解速率。

PLA degrades mainly by hydrolysis of its ester groups, not by rapid microbial attack in soil. Industrial composting at elevated temperature (about 58 °C) and high humidity is usually needed for fast breakdown.

聚乳酸主要通过酯基水解降解，而不是在土壤中快速被微生物降解。通常需要在高温（约 58 °C）和高湿度下的工业堆肥中才能快速分解。

7. Polyhydroxyalkanoates (PHAs) | 聚羟基链烷酸酯

PHAs are a family of polyesters synthesised naturally by bacteria as intracellular carbon and energy storage granules. The best-known example is poly(3-hydroxybutanoate), PHB:

聚羟基链烷酸酯是一类由细菌天然合成的聚酯，作为细胞内碳源和能量储存颗粒。最著名的例子是聚(3-羟基丁酸酯)，即 PHB：

–[O–CH(CH₃)–CH₂–CO]–ₙ

Unlike PLA, PHAs are generally biodegradable in a wider range of environments, including marine and soil conditions. Microorganisms recognise the ester bonds and produce extracellular enzymes that degrade the polymer into 3-hydroxybutanoic acid.

与聚乳酸不同，聚羟基链烷酸酯通常在更广泛的环境中可生物降解，包括海洋和土壤条件。微生物识别酯键并产生胞外酶，将聚合物降解为 3-羟基丁酸。

Production cost remains higher than conventional plastics, but fermentation using waste feedstocks and genetic engineering is reducing the cost. PHA is used for medical implants, sutures, and compostable packaging.

其生产成本仍高于传统塑料，但利用废弃原料发酵和基因工程正在降低成本。PHA 用于医用植入物、缝合线和可堆肥包装。

8. Starch-Based and Cellulose-Based Polymers | 淀粉基与纤维素基聚合物

Starch is a natural polysaccharide made of α-glucose units joined by glycosidic links. Starch-based materials are often blended with biodegradable polyesters such as PLA, polycaprolactone, or poly(vinyl alcohol) to improve mechanical properties and water resistance.

淀粉是由 α-葡萄糖单元通过糖苷键连接而成的天然多糖。淀粉基材料通常与聚乳酸、聚己内酯或聚乙烯醇等可生物降解聚酯共混，以改善力学性能和耐水性。

Cellulose, a β-glucose polysaccharide, is abundant in plant cell walls. Modified cellulose esters such as cellulose acetate are used in films and fibres. Both starch and cellulose can be broken down by glycosidase enzymes into glucose monomers.

纤维素是一种 β-葡萄糖多糖，大量存在于植物细胞壁中。改性纤维素酯如醋酸纤维素用于薄膜和纤维。淀粉和纤维素都可被糖苷酶分解为葡萄糖单体。

These natural polymers are renewable and biodegradable, but chemical modification can reduce their biodegradability. For example, highly substituted cellulose acetate degrades more slowly than cellulose itself.

这些天然聚合物是可再生且可生物降解的，但化学改性会降低其生物降解性。例如，高取代度醋酸纤维素降解比纤维素本身慢。

9. Polyglycolic Acid and Polycaprolactone | 聚乙醇酸与聚己内酯

Polyglycolic acid (PGA) has the simplest aliphatic polyester structure:

聚乙醇酸具有最简单的脂肪族聚酯结构：

–[O–CH₂–CO]–ₙ

PGA undergoes relatively fast hydrolysis because its structure is hydrophilic and lacks bulky side groups. It is widely used in absorbable surgical sutures and tissue-engineering scaffolds. The degradation product, glycolic acid, is naturally metabolised in the body.

聚乙醇酸水解较快，因为其结构亲水且没有庞大的侧基。它广泛用于可吸收手术缝合线和组织工程支架。其降解产物乙醇酸可在体内自然代谢。

Polycaprolactone (PCL) has a repeating unit with five methylene groups:

聚己内酯的重复单元含有五个亚甲基：

–[O–(CH₂)₅–CO]–ₙ

PCL degrades more slowly than PGA because the longer hydrocarbon segments are hydrophobic and reduce water penetration. PCL is used in compostable film, controlled-release drug delivery, and biodegradable implants.

聚己内酯降解比聚乙醇酸慢，因为较长的烃链段疏水，减少水渗透。聚己内酯用于可堆肥薄膜、控释药物递送和可生物降解植入物。

10. Factors Affecting Degradation Rate | 影响降解速率的因素

The rate of polymer degradation depends on both chemical structure and environmental conditions. Key factors include:

聚合物降解速率取决于化学结构和环境条件。关键因素包括

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Degradable Polymers | 可降解聚合物