生物工程学报  2022, Vol. 38 Issue (5): 1784-1808 |
表1(Table 1)
表2(Table 2) 表3(Table 3) 表4(Table 4) 表5(Table 5) 表6(Table 6) 表7(Table 7)
引用本文
|
塑料是三大有机合成材料之一，在各个领域应用广泛，用量与日俱增，目前，超过60%的塑料在使用后被填埋或随意丢弃[1]。以聚乙烯(polyethylene, pe) 和聚丙烯(polypropylene, PP) 为主的传统塑料在自然环境中难以分解，对生态环境构成严重威胁。为遏制传统塑料引发的一系列环境污染问题，国家发展改革委和生态环境部于2021年9月印发了“十四五”塑料污染治理行动方案的通知，提出了严格的塑料污染限期整治目标，这将推动我国生物可降解塑料进入快速发展期。
生物可降解塑料因含有易发生反应的化学键，能够在一定生物活性环境下，如好氧堆肥、水体、厌氧或土壤环境，通过微生物的作用，降解转化为二氧化碳(CO2)、甲烷(CH4) 等代谢产物。随着国家塑料污染治理工作逐步落实，生物可降解塑料替代传统塑料成为必然趋势。但生物可降解塑料种类繁多，性能各异，降解条件复杂，在不适合的处理处置条件下可能难以有效降解，进而导致环境污染，制约生物可降解塑料的开发应用。本文针对常见生物可降解塑料的性能、降解机理、降解功能微生物和功能酶以及在不同自然和受控条件下的降解情况进行系统综述。对生物可降解塑料降解机理和降解程度的系统归纳，将为生物可降解塑料废弃物的高效处理处置和彻底降解提供科学参考，对生物可降解塑料制品的全面推广具有重要意义。
1 生物可降解塑料的种类和性能生物可降解塑料可由天然高分子化合物加工而成，也可由微生物代谢或化学手段合成。天然高分子类生物可降解塑料以热塑性淀粉(thermoplastic starch, TPS) 为主，微生物代谢合成类生物可降解塑料主要是聚羟基烷酸酯(polyhydroxyalkanoate, PHA)，化学合成类生物可降解塑料包括聚乳酸(poly(lactic acid), PLA)、聚丁二酸丁二酯(poly(butylene succinate), PBS)、聚丁二酸-己二酸丁二酯(poly(butylene succinate-co-butylene adipate), PBSA)、聚对苯二甲酸-己二酸丁二酯(poly(butylene adipate-co-terephthalate), PBAT)、聚己内酯(poly(ε-caprolactone), PCL)、聚碳酸亚丙酯(poly(propylene carbonate), PPC)、聚乙烯醇(poly(vinyl alcohol), PVA) 等。以下对常见生物可降解塑料的中文名称、英文名称、英文缩写、聚合物的结构式和主要用途进行总结比较，详见表 1。
| Type | Abbreviations | Structural formulas | Application[2-3] |
| Thermoplastic starch | TPS | 
|
Packaging, shopping bags, garbage bags, mulch films, disposable tableware and disposable medical products |
| Polyhydroxyalkanoate | PHA | 
|
Tissue engineering, medical implant, controlled drug delivery system, packaging, mulch films and disposable medical products |
| Poly(lactic acid) | PLA | 
|
Packaging, shopping bags, garbage bags, mulch films, disposable tableware, disposable medical products, building materials and textiles |
| Poly(butylene succinate) | PBS | 
|
Packaging, shopping bags, garbage bags, pesticide and fertilizer sustained-release materials, mulch films and disposable tableware |
| Poly(butylene succinate-co-butylene adipate) | PBSA | 
|
Packaging, shopping bags, garbage bags and mulch films |
| Poly(butylene adipate-co-terephthalate) | PBAT | 
|
Packaging, shopping bags, garbage bags, mulch films and disposable tableware |
| Poly(ε-caprolactone) | PCL | 
|
Medical implant, controlled drug delivery system, absorbable surgical sutures and cryogenic packaging |
| Poly(propylene carbonate) | PPC | 
|
Cryogenic packaging, mulch films, foam materials, controlled drug delivery system and high barrier materials |
| Poly(vinyl alcohol) | PVA | 
|
Soluble packaging and high barrier materials and medical implant |
淀粉是应用最早的生物可降解塑料基材之一，淀粉分子间具有较强的氢键相互作用力，受热条件下流动性差，玻璃化转化温度与分解温度接近，加工成型困难。通过在淀粉中加入增塑剂，使增塑剂和淀粉之间的氢键代替淀粉分子间和分子内的氢键，可提高淀粉分子的活动能力，降低淀粉的玻璃化转化温度，从而实现淀粉的热塑成型[4]。TPS原料来源广泛，生产加工技术相对成熟，降解性能优良，与其他生物可降解塑料共混可提升共混塑料的分解能力。但TPS力学性能、热稳定性以及耐水性不足，难以单独使用。TPS商品化程度高，价格在1万元/t左右。
1.2 聚羟基烷酸酯(PHA)聚羟基烷酸酯(PHA) 是由微生物在碳源充足，氮、磷、微量元素等缺乏时，将多余碳源储存起来而合成的脂肪族聚酯。其结构式如表 1所示，m可以是1–4，短链PHA的R基团为-H、-CH3、-C2H5，包括聚羟基丁酸酯(poly(3-hydroxybutyrate), PHB)、聚羟基戊酸酯(poly(3-hydroxyvalerate), PHV) 等; 中长链PHA的R基团为-C3H7到-C13H27，包括聚羟基己酸酯(polyhydroxyhexanoate, PHH)、聚羟基辛酸酯(polyhydroxyoctanoate, PHO) 等。此外，将不同PHA单体按一定比例共聚可获得共聚酯。如聚3-羟基丁酸戊酸酯(poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV) 和聚3-羟基丁酸4-羟基丁酸酯(poly(3-hydroxybutyrate-co-4-hydroxybutyrate), P34HB)。PHA的物理性质与其分子构成和单体结构密切相关，短链PHA结晶度较高，表现出良好的刚性; 中长链PHA结晶度低，表现出良好的弹性[5]。但PHA的热降解温度和熔融温度相近，加工窗口窄，加工成型较为困难[6]。PHA商品化程度一般，根据纯度的不同，价格有较大差异，介于3–15万元/t。
1.3 聚乳酸(PLA)聚乳酸(PLA) 是由乳酸为原料制备的脂肪族聚酯。可通过微生物以玉米、小麦秸秆等为原料发酵制得乳酸后再缩合加工而成。乳酸有右旋(D-lactic acid, D-LA) 和左旋(L-lactic acid, L-LA) 2种旋光异构体，因此其均聚物有3种，其中半结晶的聚L-乳酸(poly(L-lactic acid), PLLA) 和聚D-乳酸(poly(D-lactic acid), PDLA) 分子链推拉时不易发生移动，表现出较强的刚性; 无定形的聚D-L-乳酸(poly(D, L-lactic acid), PDLLA) 分子链推拉时易发生移动，表现出较强的柔性[7]。PLA具有较好的水汽阻隔性和透明性，在制备硬质生物可降解塑料制品方面具有较大潜力，但质脆，抗冲击性较差，难以满足软包装领域的应用要求，在低于熔融温度下加工会使相对分子质量大幅下降，加工成型难度大[8]。PLA商品化程度高，价格区间在3–4万元/t。
1.4 二元酸二元醇共聚酯(PBS、PBSA、PBAT等)二元酸二元醇共聚酯包括聚丁二酸丁二酯(PBS)、聚丁二酸-己二酸丁二酯(PBSA)、聚对苯二甲酸-己二酸丁二酯(PBAT) 等，其中PBS和PBSA属于脂肪族聚酯，PBAT含有苯环结构，属于脂肪族芳香族共聚酯。
PBS由丁二酸和1, 4-丁二醇为主要原料制备。丁二酸和丁二醇可通过纤维素、淀粉、葡萄糖、果糖、乳糖等为原料发酵制得，也可通过石油资源加工获得。PBS可通过与传统塑料相似的挤出、吹塑、压模等方法进行加工，原料来源广泛，耐热性能较好，但质脆，较强的疏水性导致降解速率较慢[9]。PBSA由丁二酸、1, 4-丁二醇和己二酸为主要原料制备。PBSA共聚物中己二酸的含量会影响其热性能和力学性能。相较于PBS，PBSA的降解性能和柔韧性有所改善[10]，但脆性较大，抗冲击性较差。PBAT由对苯二甲酸、1, 4-丁二醇和己二酸为主要原料制备。其中脂肪族链段赋予PBAT良好的柔韧性和生物降解性，芳香族链段则用于提高PBAT的力学性能和加工性能。PBAT熔点和力学性能与低密度聚乙烯(low-density polyethylene, LDPE) 相似，加工温度范围广，可采用传统设备和方法进行加工，但柔韧性过高，刚性挺度不足，对氧气和水汽的阻隔性能差，降解速率慢，较难通过一些严格的降解标准[11]。二元酸二元醇共聚酯商品化程度较高，目前价格在3万元/t左右。
1.5 聚己内酯(PCL)聚己内酯(PCL) 是由ε-己内酯通过催化剂催化开环聚合制备的脂肪族聚酯。其结构中的重复单元含有运动性强的C-C键和C-O键，此结构赋予PCL较好的柔韧性和生物降解性。PCL熔点低，在室温下呈橡胶态，易热塑成型[12]，但刚性不足，60 ℃左右的低熔点限制了其高温条件下的应用。商品化程度一般，目前价格在5–7万元/t。
1.6 聚碳酸亚丙酯(PPC)聚碳酸亚丙酯(PPC) 是由CO2和环氧丙烷(propylene oxide, PO) 通过催化剂催化开环聚合制备的聚碳酸酯。PPC不易燃，具有较好的柔韧性、水汽阻隔性、生物降解性和生物相容性。但PPC是无定形聚合物，分子间作用力小，拉伸强度低，力学性能差; 主链上存在大量酯基，易水解、热解断链，热分解温度低，加工性能差[13]; 存在末端羟基，热稳定性差，在较高温度下容易发生解拉链式降解; 30–40 ℃玻璃化转化温度限制了其在高温条件下的应用[13]。PPC商品化程度一般，价格在5–8万元/t。
1.7 聚乙烯醇(PVA)聚乙烯醇(PVA) 是由醋酸乙烯合成聚醋酸乙烯后通过醇解制备的高分子聚合物，其物理化学性能很大程度上取决于醇解度。根据醇解度的不同可分为完全醇解型、部分醇解型和低醇解型。醇解度87%–88%的部分醇解型PVA具有最好的水溶性，而醇解度更高或更低的PVA水溶性均变差。PVA具有韧性、透明性、气体阻隔性和抗静电性，但易受潮，吸湿后气体阻隔性降低，加工性能变差[14]。PVA商品化程度一般，目前市场价格在1.2–2.5万元/t。
综上所述，生物可降解塑料种类繁多，性能各异，通过不同生物可降解塑料的共混改性可使共混塑料获得优良的加工性能和机械性能，满足塑料的应用要求。此外，较高的价格是制约生物可降解塑料广泛应用的瓶颈，降低其生产成本应是今后的研究重点。
2 生物可降解塑料的降解机理生物可降解塑料发生降解的本质是聚合物中化学键的断裂，通过在聚合物分子链中引入弱性化学键或易发生反应的化学键可使聚合物更易发生降解。分子链的开裂方式分为4种：分子链解聚型、分子链无规断裂型、分子链弱键分离型、分子链侧链或小分子脱出型[15]。一般来讲，聚合物通过水解作用进行解聚，产生低聚物和单体的过程是生物可降解塑料降解的限速步骤。微生物水解是细菌、真菌和藻类等天然微生物利用现有的酶，催化聚合物链发生断链，最终产生低聚物和单体的过程。但对于PLA、聚对苯二甲酸乙二醇酯、聚羧酸盐等聚合物而言，非生物水解的作用至关重要[16]。生物可降解塑料的水解通过表面侵蚀或整体侵蚀进行，整体侵蚀在聚合物表面和内部均匀发生，首先通过水在聚合物无定形区域的扩散引发水解反应，低聚物缓慢扩散到聚合物表面后逐渐溢出。表面侵蚀则从聚合物表面开始，聚合物体积减小(图 1)，表面侵蚀的速率远高于整体侵蚀[17]。当水解速度超过水扩散到主体中的速度，或当催化剂(例如，酶) 不能穿透主体聚合物时，会发生表面侵蚀，表面侵蚀是疏水和半结晶聚合物以及水解速率较快的聚合物发生降解的主要机制。当水的扩散速度超过水解反应速度时，会发生整体侵蚀[16-18]。
生物可降解塑料的降解很大程度上取决于聚合物的成分和结构。聚合物结构越接近天然聚合物越易降解，因此淀粉基、纤维素基等天然高分子类和PHA等微生物代谢合成类生物可降解塑料较易降解。只有线性链结构的脂肪族聚酯比包含苯环的芳香族聚酯易降解[3]，芳香单元较难被微生物破坏。紧密堆积的结晶区域阻碍了酶的攻击，因此聚合物无定形区域比结晶区域易分解[19]。高柔韧性的聚合物链更贴合酶的活性部位，因此具有较低熔融温度的聚合物由于其聚合物链较高的柔性而更容易被生物降解[19]。直链比含有支链和交联的聚合物易降解，因为酶较难渗透到复杂的网格结构中。亲水性强的聚合物更易降解，因为酶更易接近水溶性底物。聚合物表面越粗糙，微生物越易附着。以下根据生物可降解塑料降解过程中的不同断键机理展开具体介绍。
2.1 含糖苷键生物可降解塑料的降解包括淀粉基、纤维素基材料在内的多糖基生物可降解塑料，均通过糖苷键的断裂进行解聚，生成低聚物和单体后被微生物利用。糖苷键的水解酶多样，包括淀粉酶、纤维素酶、壳聚糖酶等，微生物酶对多糖糖苷键的降解效率通常较高。
TPS是目前常见的生物可降解塑料，其主要成分——淀粉，具有强吸湿性，水分子渗透到其结构中，使水解较易发生。淀粉分子有2个官能团在降解过程中起重要作用：易发生取代反应的-OH基团和易发生断链的C-O-C键[16]。TPS的降解速率取决于易降解的淀粉，微生物分解淀粉后，破坏TPS结构的完整性，增加微生物与剩余组分的接触面积，从而提升酶对剩余组分的可及性[20]。在好氧条件下，淀粉通过根霉、曲霉以及枯草芽孢杆菌等产生的糊精酶、麦芽糖苷酶和葡糖苷酶先后转化为糊精、麦芽糖和葡萄糖; 在厌氧条件下，淀粉在水解菌群产生的水解酶的作用下先后转化为麦芽糖和葡萄糖，葡萄糖透过细胞膜进入细胞，被完全转化。
2.2 含酯键生物可降解塑料的降解以PHA、PLA、PBS、PBSA和PCL为主的脂肪族聚酯和以PBAT为主的脂肪族芳香族共聚酯中存在不稳定的酯键，容易受到酶的攻击发生水解裂解和解聚，从而生成低聚物和单体，单体通过细胞膜进入细胞，经过β-氧化，最终在有氧条件下产生CO2和H2O，在厌氧条件下产生CH4。脂肪族聚酯和脂肪族芳香族共聚酯的水解解聚如图 2、图 3所示[21]。
聚酯酯键的水解酶包括脂肪酶、酯酶、蛋白酶、角质酶和PHA解聚酶等，它们具有不同的底物偏好和界面活性，催化酯键断裂形成醇和羧酸，例如，蛋白酶倾向降解α-酯键，PHB解聚酶倾向于降解β-酯键，脂肪酶则倾向于降解γ-ω酯键[17, 22]。酶对生物可降解塑料的水解主要分为2步：酶吸附于聚合物的活性位点; 由疏水结构域结合位点和催化位点诱导键的酶促水解断裂，将不同大小的低聚物释放到周围介质中[23]。在这些水解酶中，脂肪酶不溶于水，倾向于水解长链和油水界面的底物，Tokiwa等[24]报道称脂肪酶可水解含有较多亚甲基的聚酯酯键，如PCL、PBS、PBSA和聚丁二酸乙二酯(poly(ethylene succinate), PES)，但难降解具有高熔点(Tm) 的旋光性聚合物，如PHB和PHV。此外，对沿碳主链有较多侧链的聚合物活性较低[25]。酯酶溶于水，优先水解短链脂肪酸，对水溶性底物更活跃。角质酶来自α/β水解酶超家族酶，是丝氨酸酯酶，同时具备脂肪酶和酯酶的部分特性[3]，具有广泛的底物特异性。相对于酯酶，角质酶可水解脂质; 与脂肪酶相比，角质酶不受界面相互作用的影响，可更有效地水解疏水性底物[3]。蛋白酶也被称为肽酶，在广泛的pH和温度范围内表现出稳定性和活性，蛋白酶对PLA的降解至关重要。Reeve等[26]报道称来自林伯氏白色念球菌(Tritirachium album Limber) 的蛋白酶K不能裂解PLA的D-立体异构体，因此认为蛋白酶K识别PLA的L-乳酸单位。PHA解聚酶通常由较低分子量的多肽组成，其催化中心类似于脂肪酶催化中心，但它们的活性位点在空间排列上有差异[25]。目前已知的PHA解聚酶没有脂肪酶活性，若底物为具备ω-羟基酸(ω-hydroxyacids) 的聚合物，如聚4-羟基丁酸酯(poly(4-hydroxybutyrate), P4HB) 和聚6-羟基己酸酯(PCL)，一些脂肪酶具备PHA解聚酶活性[27]。
不同的水解酶对不同生物可降解塑料起作用。PHA的水解酶主要是PHA解聚酶，水解产物因PHA类型而异，PHB水解生成3-羟基丁酸，PHBV水解产生3-羟基丁酸和3-羟基戊酸，P34HB水解生成3-羟基丁酸和4-羟基丁酸。PHA解聚酶对短链PHA的解聚作用显著，中长链PHA的侧链结构较多，影响解聚酶与酯键的结合[17]。
除蛋白酶外，脂肪酶、酯酶和角质酶也对PLA的降解起作用，使其水解为不同链长的乳酸低聚物(n=2–13) 和单体[3, 28]。PLA的水解通过酯键的随机断裂发生，断链优先发生在非结晶区域。PLA断链后，羧基端基起催化作用，以自催化和自维持的方式影响PLA的水解(图 4)[18]。自催化效应使PLA在分子结构内部发生整体侵蚀的速率快于在其表面发生的表面侵蚀的速率。分子内部水解产生的低聚物缓慢向聚合物边界游离并溢出，聚合物中心的低聚物仍被包裹，从而限制了同化速率[18]。PLA的水解速率受温度和pH值的影响，通过高温水解(> 55 ℃)降低分子量后，生物降解可更快地进行[29]。此外，酸性和碱性条件也可促进PLA的水解，在碱性条件下，PLA通过酯键的无规断裂水解生成丙交酯后再转化为乳酸; 在酸性条件下，PLA通过链段酯键断裂直接水解为乳酸[17]。
PBS和PBSA在脂肪酶、酯酶、角质酶的催化作用下发生水解，PBS水解为1, 4-丁二醇(1, 4-butanediol, B)、丁二酸(succinic acid, S)、SB、SBS、BSB和SBSB为主的水溶性单体和低聚物[30]。PBSA生成B、S和己二酸(adipic acid, A) 3种单体以及3种单体以酯键相互连接而成的低聚物。PBSA中己二酸单元比1, 4-丁二醇单元降解快，而丁二酸单元更难降解[31]，己二酸的加入降低了PBSA的结晶度，无定形区域松散结构的增多，使其更易被生物降解[19]。PBAT在酯酶、角质酶的催化下发生水解，水解产物除B、A、和对苯二甲酸(terephthalic acid, T) 3种单体外，还含有BA、BT、ABA、BTB、TBT、ABT等低聚物，PBAT的降解首先发生在BA连段，BT链段较难降解[32]，相对于PBS，PBAT中对苯二甲酸的添加，降低了酶对其中酯键的可及性，使PBAT的降解速率下降[33]。在酶解过程中，含3个以上酯键的低聚物与酶的亲和力强，降解速度快，因此水解产物主要为含1–3个酯键的单体和低聚物[30]。
PCL可在脂肪酶、酯酶、蛋白酶、角质酶、几丁质酶等的催化下发生水解[3]。其水解产物主要是6-羟基己酸的单体、二聚体、三聚体和四聚体的混合物[34]。此外，PCL较高的结晶度和较强的疏水性，使其水解较困难，相对于结晶区域，PCL无定形区域可更有效地降解[35]。
2.3 含碳酸酯键生物可降解塑料的降解聚碳酸酯的降解主要以碳酸酯键断裂的方式进行，聚碳酸酯比聚酯更耐酸水解，易发生碱水解，但在碱性条件下，聚碳酸酯的降解速率比聚酯慢。造成这种现象的一个原因可能是这两种聚合物中碳原子和氧原子的电负性差异。聚碳酸酯中的羰基碳原子比相应聚酯中的羰基碳原子更亲电，聚碳酸酯中的羰基碳原子在碱性条件下更易受到氢氧根离子的攻击，导致聚碳酸酯在水解产生羧基后，进一步被催化裂解为羟基并释放CO2[33]。以PPC为代表的聚碳酸酯的解聚见图 5。
|
|
| 图 5 脂肪族聚碳酸酯的解聚机制 Fig. 5 Depolymerization of aliphatic polycarbonates. |
| |
由环氧化合物和CO2制备的聚碳酸酯，例如聚碳酸亚乙酯(poly(ethylene carbonate), PEC) 和聚碳酸亚乙酯-丙酯共聚酯(poly (ethylene- co-propylene carbonate), PEPC)，在根霉脂肪酶的催化作用下可发生降解生成简单的二元醇[36]。Suyama等[37]采用水解聚酯的酶，研究其对聚碳酸四亚甲基酯(poly(tetramethylene carbonate), PTC) 的水解作用，研究结果表明，水解PTC的酶包括：柱状假丝酵母(Candida cylindracea) 合成的胆固醇酯酶、假单胞菌(Pseudomonas sp.) 合成的脂蛋白脂肪酶以及由染色粘性菌(Chromobacterium viscosum) 和少根根霉(Rhizopus arrhizus) 合成的脂肪酶。
2.4 含多羟基生物可降解塑料的降解PVA链结构中含有多个羟基，微生物降解发生在PVA相邻的2个羟基处，其降解途径主要有两种[38]，一种是通过次生醇氧化酶(secondary alcohol oxidases, SAO) 氧化PVA，使PVA的2个相邻羟基形成β-二酮结构，然后在β-二酮水解酶(β-diketone hydrolase, BDH) 的水解作用下，β-二酮的不稳定C-C键发生断裂。当β-二酮两侧的碳链长度不同时，水解裂解发生在碳链长度较短的一侧，从而在较长段和较短段分别生成甲基酮和羧酸，水解产生的低聚物和单体进入细胞通过β-氧化三羧酸循环进行代谢。图 6总结了由SAO和BDH两种酶参与的PVA代谢。另一种途径是通过氧化PVA的1个羟基，形成β-羟基酮后，通过醛缩酶反应在β-羟基酮处断裂C–C键，生成甲基酮和醛，其中吡咯喹啉醌(pyrroloquinoline quinone, PQQ) 依赖性的PVA脱氢酶(PVA dehydrogenase, PVA-DH) 及其载脂酶(apoenzyme) 分别参与羟基氧化和醛缩酶型裂解，粪产碱杆菌(Alcaligenes faecalis) KK314被报道通过这种途径降解PVA[39]。此外产生apoPVA-DH的鞘氨醇盒菌(Sphingopyxis sp.) 113P3 (曾用名：假单胞菌Pseudomonas sp. 113P3、鞘氨醇单胞菌Sphingomonas sp. 113P3) 对PVA的代谢途径相对特殊，水解过程不形成β-二酮和β-羟基酮，这种菌株存在一种不同于BDH的周质氧化PVA水解酶(oxiPVA hydrolase, OPH)，这种酶对单酮和二酮没有活性[40]。PVA-DH属于胞内酶，PVA必须进入细胞周质后才能通过第二种途径进行降解，细胞外的SAO可能有助于PVA解聚到合适大小，使其被周质间隙吸收[40]。
目前，多数生物可降解塑料属于聚酯，其生物降解主要通过酯键的水解断裂发生，影响酯键断裂的因素众多，需要对生物可降解塑料降解机理进行系统研究，完全掌握生物可降解塑料的降解规律及特点，为实现生物可降解塑料的快速完全降解奠定基础。
3 生物可降解塑料的降解微生物降解生物可降解塑料的菌株包括中温细菌、高温细菌和真菌，存在于堆肥、淡水、海洋、厌氧和土壤等多种自然环境中，分泌不同的酶，具有不同的最适作用条件和对生物可降解塑料的降解效率。功能微生物和功能酶的高效利用对加速生物可降解塑料的降解具有重要意义。表 2总结了生物可降解塑料的降解微生物和功能酶。
| Enzymes | Strains | Properties | Source | Types of plastic degraded | References |
| Lipase | Acidovorax delafieldii BS-3 | Gram-negative bacterium; 30 ℃a | Soil | PBS, PBSA | [41] |
| Aspergillus niger MTCC 2594 | Fungus; pH 7.0, 37 ℃ | – | PLA, PCL | [42] | |
| Burkholderia cepacia PBSA-1 |
Gram-negative bacterium; 37 ℃a | Activated sludge | PBSA | [43] | |
| Burkholderia sp. | Gram-negative bacterium; pH 8.0, 30 ℃a | – | PCL | [44] | |
| Lactobacillus plantarum MTCC 4461, Lactobacillus brevis MTCC 4460, and their co-culture | Gram-positive bacterium; pH 8.1, 37 ℃a | – | PCL | [35] | |
| Paenibacillus amylolyticus TB-13 | Gram-positive bacterium; pH 10.0, 50 ℃ |
Soil | PDLLA, PBS, PBSA, PCL; not degrade PHBV | [45] | |
| Pseudomonas aeruginosa PBSA-2 | Aerobic, Gram-negative bacterium; 37 ℃a |
Cultivating soil | PBSA | [43] | |
| Pseudomonas sp. | Aerobic, Gram-negative bacterium; pH 7.0, 35 ℃a |
– | PTC | [37] | |
| Pseudomonas sp. DS04-T | Aerobic, Gram-negative bacterium; pH 8.0, 50 ℃ |
Activated sludge | PLLA | [46] | |
| Rhizopus arrhizus | Fungus; pH 7.0, 30 ℃a | – | PLLA, PCL | [47] | |
| Rhizopus arrhizus | Fungus; pH 5.6, 37 ℃a | – | PEC, PEPC | [36] | |
| Rhizopus oryzae | Fungus; pH 8.0, 30 ℃a | – | PCL | [44] | |
| Sphingobacterium sp. S2 | Gram-negative bacterium; pH 6.0, 40 ℃ |
Compost | PLA | [48] | |
| Streptomyces sp. SCM_MKPN-8 | Gram-positive bacterium; pH 7.0, 30 ℃a |
Agricultural soil | PLA, PBS | [49] | |
| Esterase | Alcanivorax borkumensis ABO2449 | Aerobic, Gram-negative bacterium; pH 9.5–10, 30–37 ℃ |
Seawater and marine sediments |
PDLLA, PCL, PHBV, PBSA, PES; not degrade PHB, PBS, PDLA, PLLA | [28] |
| Bacillus sinithii PL 21 | Gram-positive bacterium; pH 5.5, 60 ℃ | Compost | PLLA | [50] | |
| Brevundimonas sp. MRL-AN1 |
Aerobic, Gram-negative bacterium; pH 6.0–8.0, 30–37 ℃ | Soil | PCL, PES, PLA, PHB, PHBV | [51] | |
| Candida cylindracea | Gram-positive bacterium; pH 7.0, 35 ℃a |
– | PTC | [37] | |
| Leptothrix sp. TB-71 | Aerobic, Gram-negative bacterium; 30 ℃a |
Soil and freshwater | PBSA, PCL, PES; not degrade PLA, PBS, PHBV | [52] | |
| Ralstonia sp. MRL-TL | Aerobic, Gram-negative bacterium; pH 7.0, 50 ℃ |
Hot spring | PCL, PES, PLLA, PHB, PHBV | [53] | |
| Rhodopseudomonas palustris RPA1511 | Gram-negative bacterium; pH 9.5–10, 55–60 ℃ |
– | PDLLA, PCL, PBSA; not degrade PHB, PHBV, PBS, PES, PDLA, PLLA | [28] | |
| Roseateles depolymerans TB-87 | Aerobic, Gram-negative bacterium; pH 9.0, 30 ℃ |
Freshwater | PBS, PBSA, PCL, PBST; not degrade PLA | [32] | |
| Thermobifida alba AHK119 | Gram-positive bacterium; pH 6.0, 45–55 ℃ |
Compost | PBSA, PBAT, PCL | [54] | |
| Cutinase | Aspergillus oryzae RIB40 | Fungus; pH 9.0, 35–55 ℃ | PBS, PBSA | [55] | |
| Clostridium sp. | Anaerobic, Gram-positive bacterium; pH 7.0, 35 ℃a | Anaerobic sewage sludge | PCL | [56] | |
| Cryptococcus sp. S-2 | Yeast; pH 8.0, 30 ℃a | Air | PLA, PBS, PCL, PHB | [44] | |
| Fusarium moniliforme | Fungus; pH 9.0–10.0; 22 ℃b | – | PCL | [34] | |
| Fusarium solani wild-type strains 77-2-3 and ATCC 38136 | Fungus; pH 9.0–10.0, 22 ℃b | – | PCL | [34] | |
| Thermobifida fusca DSM 43793 | Gram-positive bacterium; pH 6.0–7.0, 65–70 ℃ | PBAT, PCL; not degrade PHB |
[57] | ||
| Protease | Actinomadura keratinilytica T16-1 | Gram-positive bacterium; pH 10.0, 70 ℃ |
Forest soil | PLLA, PDLLA | [58-59] |
| Amycolatopsis sp. SCM_MK2-4 | Gram-positive bacterium; pH 7.0, 30 ℃a | Agricultural soil | PLA, PCL | [49] | |
| Amycolatopsis sp. SCM_MK3-3 | Gram-positive bacterium; pH 7.0, 30 ℃a | Agricultural soil | PLA | [49] | |
| Laceyella sacchari LP175 | Aerobic, Gram-positive bacterium; pH 9.0, 60 ℃ |
Forest soil | PLLA | [60] | |
| Streptomyces sp. SCM_MKPN-9 | Gram-positive bacterium; pH 7.0, 30 ℃a | Agricultural soil | PLA, PBS | [49] | |
| Tritirachium album Limber | Fungus; pH 8.0, 30 ℃a | – | PLLA, PDLLA | [44] | |
| PHA depolymerases | Aspergillus fumigatus 76T-3 | Fungus; pH 6.4, 55 ℃ | Soil of hot springs | PHB, PES, PBS | [61] |
| Bacillus sp. IBP-VN2; Enterobacter sp. IBP-VN Enterobacter sp. IBP-VN1; Enterobacter sp. IBP-VN4; Enterobacter sp. IBP-VN5; Gracilibacillus sp. IBP-VN3 | Natural seawater; pH 7.0–7.5, 27–30 ℃a | Tropical coastal waters | PHB, PHBV | [62] | |
| Clostridium botulinum | Anaerobic, Gram-positive bacterium; pH 6.8, 37 ℃b | Anaerobic sewage sludge | PHB, PHBV | [56] | |
| Pseudomonas fluorescens GK13 | Aerobic, Gram-negative bacterium; pH 9.5, 40 ℃ | Activated sludge | PHO | [63] | |
| Pseudomonas lemoignei LMG 2207 |
Aerobic, Gram-negative bacterium; pH 8.0, 37 ℃b | Soil, compost | PHB, PHV | [64] | |
| Streptomyces sp. AF-111 | Aerobic, Gram-positive bacterium; pH 7.0–8.0, 35–55 ℃ |
Sewage sludge treatment plant | PHBV | [65] | |
| SAO and BDH |
Pseudomonas sp. | Aerobic, Gram-negative bacterium; pH 7.0, 30 ℃a |
– | PVA | [38] |
| PVA-DH | Alcaligenes faecalis KK314 | Gram-negative bacterium; pH 7.5, 30 ℃a |
River water | PVA | [39] |
| Sphingopyxis sp. 113P3 | Gram-negative bacterium; pH 7.2, 37 ℃ |
Activated sludge | PVA | [40] | |
| a: the experimental conditions for the activity of the enzyme; b: pH and temperature are optimum condition and experimental condition for the activity of the enzyme, respectively. The others are the optimal conditions for the activity of the enzyme. | |||||
降解PHA的菌种多样，已在多种环境中被分离出来。约90%能够降解淀粉的微生物具有降解短链PHA的能力，但不能降解大分子量和复杂的中长链PHA[5]。Tseng等[66]对大约341株嗜热放线菌在50 ℃条件下进行筛选，其中有31株可同时分解PHB、PCL和PES，这些菌株属于小双孢菌属(Microbispora) (25.8%)、马杜拉放线菌属(Actinomadura) (12.9%)、高温放线菌属(Thermoactinomyces) (9.7%)、链霉菌属(Streptomyces) (48.4%) 和糖单孢菌属(Saccharomonospora) (3.22%)。与好氧降解相比，PHB和PHBV的厌氧降解更快。Abou-Zeid等[56]鉴定出2株降解PHB和PHBV的菌株，它们与肉毒杆菌Clostridium botulinum的16S rRNA表现出94.9%的序列同源性。当以分离的单一菌株作为接种物时，37 ℃条件下经75 h降解，PHB粉在不控制pH时，pH会由7.0下降至4.8，而降解率停留在75%;若控制pH维持在6.8左右，约90%的PHB粉在50 h内被降解。此结果说明，若以单一菌株作为接种物，系统的稳定性较难维持。此外，真菌也可降解PHA，包括子囊菌门Ascomycota、接合菌亚门Zygomycotina、担子菌纲Basidiomycetes和半知菌纲Deuteromycetes[5]。Kim等[67]通过在28、37和60 ℃条件下开展实验，分离出来自农场土壤和活性污泥的多株PHB降解真菌，其中烟曲霉(Aspergillus fumigatus) LAR 9分布最广，在3个温度下均可降解PHB; 简青霉(Penicillium simplicissimum) LAR 13对PHB的降解率最高，27 ℃条件下经28 d降解后，降解率达到64.5%。
3.2 PLA的降解微生物PLA降解微生物大多来自芽胞杆菌科(Bacillaceae)、小单孢菌科(Micromonosporaceae)、假诺卡氏科(Pseudonocardiaceae)、链孢囊菌科(Streptosporangiaceae)、高温放线菌科(Thermoactinomycetaceae)和高温单孢菌科(Thermomonosporaceae)[68]。Satti等[68]从堆肥中分离出了4株PLA水解菌(金黄杆菌(Chryseobacterium sp.) S1、鞘氨醇杆菌(Sphingobacterium sp.) S2、铜绿假单胞菌(Pseudomonas aeruginosa) S3和S4)，它们在中温条件下对PLA具有较高的降解率。此研究证明了在30 ℃左右的中温条件下，微生物对PLA的解聚作用。其中Sphingobacterium sp. S2表现出脂肪酶活性，此酶的最高比活性达260 U/mg[48]，在土壤中额外投加此菌株后，显示出对PLA膜矿化率的显著增加[69]。Hajighasemi等[28]报道了来自泊库岛食烷菌(Alcanivorax borkumensis) ABO2449和沼泽红假单胞菌(Rhodopseudomonas palustris) RPA1511菌株的PDLLA降解活性酯酶。在35 ℃条件的36 h内，RPA1511的活性酯酶对PDLLA的降解率达到40%，而ABO2449对PDLLA的降解率高达90%。Hanphakphoom等[60]从来自森林土壤的嗜热放线菌高温放线糖莱斯菌(Laceyella sacchari) LP175中证明了PLA降解蛋白酶对PLLA降解的促进作用，此酶的比活性高达328 U/mg。此外，真菌被证明具有分解PLA的能力。来自隐球菌(Cryptococcus sp.) S2的纯化角质酶可有效降解PLA和其他聚酯，如PBS和PCL。在30 ℃条件下，此酶分别在60、5和30 h内将PLA、PBS和PCL降解完全，但在该条件下，PHB仅部分降解[44]。
3.3 二元酸二元醇共聚酯的降解微生物对于二元酸二元醇共聚酯系列(PBS、PBSA、PBAT等)，不含芳香单元的PBS和PBSA的降解性能明显优于含芳香单元的共聚酯。Hayase等[31]从土壤中分离的短小芽胞杆菌(Bacillus pumilus) 1-A菌株，在30 ℃条件下14 d内对PBS的降解率达到90%，对PBSA的降解率高达100%，而对PBAT的降解率不高(4.8%)。Lee等[43]从活性污泥中分离出2株PBSA降解菌，洋葱伯克霍尔德菌(Burkholderia cepacia) PBSA-1和Pseudomonas aeruginosa PBSA-2。在37 ℃条件下，2株菌株均通过产生脂肪酶使PBSA在40 d后达到78%的降解率。Nakajima- Kambe等[52]报道了来自纤毛菌(Leptothrix sp.) TB-71菌株的PBSA降解酯酶。在30 ℃条件下，3 d内该菌株对PBSA的降解率介于96%–100%之间，对PES的降解率达到100%，5 d内对PCL的降解率达到43%。此外，通过琼脂平板的透明圈和液体培养基的澄清现象，Maeda等[55]证实了真菌米曲霉(Aspergillus oryzae) RIB40在30 ℃条件下，5 d内对PBS和PBSA的显著降解。从此真菌中分离纯化的角质酶对PBS、PBSA和PLA的比活性分别为0.42 U/mg、11 U/mg和0.067 U/mg。此酶以醇和羧酸作为识别位点，对底物的亲和性取决于碳链长度。
对于脂肪族芳香族共聚酯，Shah等[32]从淡水中分离出1株脂肪族芳香族共聚酯分解菌，Roseateles depolymerans TB-87，其产生的酯酶，对PBA、PBSA、聚对苯二甲酸-丁二酸丁二酯(poly(butylene succinate-co-terephthalate), PBST) 和PCL等均具有分解作用。Kleeberg等[70]从高温堆肥中分离出20多株脂肪族芳香族共聚酯降解菌株，嗜热放线菌发挥了突出作用，似乎主导最初的降解步骤，其中菌株褐色热单孢菌(Thermomonospora fusca) K13g和K7a-3对共聚酯的降解率比普通堆肥微生物高20倍。Kleeberg等[57]从褐色嗜热裂孢菌(Thermobifida fusca) DSM 43793 (曾用名：Thermomonospora fusca DSM 43793) 中纯化出具有高度脂肪族芳香族共聚酯水解活性的嗜热水解酶，该酶在pH 6.0–7.0，温度65–70 ℃时活性最高，酶的特性介于酯酶和脂肪酶之间，可能是一种角质酶。Witt等[71]利用上述菌株Thermomonospora fusca DSM 43793在55 ℃条件下开展降解实验，PBAT在22 d内的降解率高达99.9%。此外，真菌也参与PBAT的降解。Trinh等[72]在中温条件下(30 ℃) 评估了29种细菌和真菌对PBAT的降解效果，这些菌株大多分离自土壤。降解21 d后，2株细菌(枯草芽孢杆菌(Bacillus subtilis) ATCC 6051和ATCC 21332) 和3株真菌(黑曲霉(Aspergillus niger) ATCC 16888、淡紫拟青霉(Paecilomyces lilacinus) ATCC 200182和嗜松青霉(Penicillium pinophilum) ATCC 9644) 使共聚酯膜出现视觉变化。
3.4 PCL的降解微生物PCL降解菌在自然界中存在较多，Khan等[35]报道称短乳杆菌(Lactobacillus brevis) MTCC4460、植物乳杆菌(Lactobacillus plantarum) MTCC4461和它们的混合菌群可通过产生脂肪酶降解PCL。37 ℃条件培养10 d，PCL膜的质量损失分别在MTCC4461的脂肪酶浓度为5 mg/mL以及MTCC4460和MTCC4461混合菌群的脂肪酶浓度为10 mg/mL时达到最高，为60%和50%。从温泉水中分离的嗜热劳尔氏菌(Ralstonia sp.) MRL-TL[53]和从土壤中分离的短波单胞菌(Brevundimonas sp.) MRL-AN1[51]可能通过生产PCL降解酯酶作用于PCL。Ralstonia sp. MRL-TL菌株在50 ℃条件下，10 d内降解了超过60%的PCL膜; Brevundimonas sp. MRL-AN1菌株在37 ℃条件下，10 d内降解了超过80%的PCL膜。Abou-Zeid等[56]从厌氧污泥中分离了2株中温PCL降解菌，它们与Clostridium botulinum的16S rRNA表现出91.7%的序列同源性，可能是梭菌属新种，其分泌的PCL降解酶可能是角质酶，但降解速率不高，在37 ℃条件下，最大降解速率仅0.14 mg/周。Chua等[73]从土壤中分离了嗜热菌株热紫链霉菌(Streptomyces thermoviolaceus subsp. thermoviolaceus) 76T-2，并从培养基上清液中纯化出2种PCL解聚酶，其中1种具有几丁质酶活性。在40–50 ℃温度范围内，PCL可在6 h内被纯化的76T-2菌株完全降解。真菌在PCL的降解中显示出重要作用。真菌菌株粉红螺旋聚孢霉(Clonostachys rosea) 16G[74]和草酸青霉(Penicillium oxalicum) DSYD05及其突变株DSYD05-1[75]均表现出对PCL的分解潜力。在28 ℃条件下，Clonostachys rosea 16G菌株对PCL膜的降解率在30 d内达到52.91%，对淀粉基购物袋的降解率在16 d内达到100%。而Penicillium oxalicum DSYD05-1的解聚酶具有广泛的底物特异性，除PCL外，还可降解PHB和PBS，但不能降解PLA，在28 ℃条件下，该菌株在9 d内对PCL薄膜降解完全，降解过程分为3个阶段，在第1阶段，薄膜质量缓慢下降; 第2阶段，薄膜的降解速度迅速增加，薄膜快速失重可能与PCL无定形区域的快速降解有关; 在最后一个阶段，质量下降放缓，可能是由于剩余的结晶区降解较慢。
3.5 PVA的降解微生物降解PVA的菌种大多是假单胞菌属(Pseudomonas) 或鞘氨醇单胞菌属(Sphingomonas)，还包括其他一些革兰氏阴性细菌(Alcaligenes faecalis和γ-变形菌门γ-proteobacteria)、革兰氏阳性细菌(巨大芽孢杆菌(Bacillus megaterium)、解淀粉类芽孢杆菌(Paenibacillus amylolyticus)、微杆菌(Microbacterium barkeri) 和委内瑞拉链霉菌(Streptomyces venezuelae)) 和真菌(分解木质素的白腐菌和褐腐菌、青霉菌)[38]。根据代谢过程中的主要水解酶，产生SAO的菌种包括Pseudomonas sp. O-3、泡囊假单胞菌(Pseudomonas vesicularis) PD、Pseudomonas sp. VM15C和Sphingopyxis sp. PVA3;产生PVA-DH的菌种有Pseudomonas sp. VM15C、Sphingopyxis sp. 113P3和Alcaligenes faecalis KK314[38]。
目前分离出部分具备高效降解生物可降解塑料的功能微生物和功能酶，但在产品生产和废弃物处理处置过程中，实际应用的案例较少，应重视对降解功能微生物和功能酶的开发应用，通过生物强化等手段，提高生物可降解塑料的分解速率和程度，减轻环境压力。
4 生物可降解塑料在不同环境条件下的降解生物可降解塑料的降解与微生物的种类和数量以及温度、湿度、氧含量、pH值、降解持续时间、紫外辐射等环境因素有关[2, 76-77]。在一定温度范围内，酶活性会随温度的升高而增强，合适的湿度和pH是微生物生存的关键，含氧量决定了微生物的种类。例如，PBAT仅可在好氧条件下达到较高的降解率[78]，而PLA在较高的温度下进行非生物水解降低分子量后进而开始生物降解[77, 79]。生物可降解塑料种类繁多，降解环境多变，降解条件复杂，影响因素众多，系统归纳总结生物可降解塑料在好氧堆肥、淡水、海水、厌氧和土壤环境中的降解周期和程度对其使用后的处理处置具有重要意义。
4.1 生物可降解塑料在好氧堆肥条件下的降解生物可降解塑料的好氧堆肥分为家庭堆肥和工业堆肥，分别采用(28±2) ℃和(58±2) ℃。相对于家庭堆肥，工业堆肥条件下微生物对生物可降解塑料的分解更加有效，有利于提高其降解速率和程度。为了使微生物保持良好的生物活性，需要为其生长繁殖提供适宜的条件，如湿度(50%–60%)、氧气浓度(超过5%) 和碳氮比(20︰1–40︰1)。在低温好氧堆肥条件下TPS和PCL可在3个月内完成分解，而PLA、PBS较难降解。升高温度有利于提高生物可降解塑料的分解速率，高温条件下的降解性能：PHB > PCL > PLA > PBSA > PBS > PBAT。表 3详细总结了生物可降解塑料在好氧堆肥条件下的降解情况。
| Type | Shape | Conditions | Biodegradation period (d) | Biodegradation indicator | Biodegradability (%) | References |
| TPS | Film | 28 ℃, home composting | 90 | CO2 produced | 90 | [77] |
| PHA | ||||||
| Film (PHB) | 58 ℃, industrial composting | 45 | CO2 produced | 100a | [77] | |
| Film (PHB) | 58 ℃ | 110 | CO2 produced | 79.9 | [80] | |
| Film (PHB) | 55 ℃, 70% humidity | 28 | CO2 produced | 80 | [81] | |
| Film (PHO) | 28 ℃, home composting | 365 | CO2 produced | 22 | [77] | |
| Film (PHO) | 58 ℃, industrial composting | 124 | CO2 produced | 100a | [77] | |
| PLA | Film | 28 ℃, home composting | 365 | CO2 produced | < 20 | [77] |
| Film | 58 ℃, industrial composting | 75 | CO2 produced | 100a | [77] | |
| Film | 58 ℃ | 8 | Weight loss | 100 | [82] | |
| Film | 55 ℃, 70% humidity | 28 | CO2 produced | 70 | [81] | |
| Film | 58 ℃, 60% humidity | 30 | Weight loss | 60 | [83] | |
| Sheet | 58 ℃ | 120 | CO2 produced | 85.8 | [84] | |
| PBS | Film | 28 ℃, home composting | 365 | CO2 produced | < 20 | [77] |
| Film | 58 ℃, industrial composting | 207 | CO2 produced | 92a | [77] | |
| Film | 58 ℃, 50%–55% humidity | 90 | CO2 produced | 60.7 | [85] | |
| Powder | 58–65 ℃, 50%–55% humidity | 160 | CO2 produced | 90 | [86] | |
| PBSA | Film | 58 ℃, 50%–55% humidity | 90 | CO2 produced | 92.1 | [85] |
| PBAT | Film | 58 ℃, industrial composting | 90 | CO2 produced | 50–60 | [78] |
| Sheet | 58 ℃ | 120 | CO2 produced | 23.7 | [84] | |
| PCL | Film | 28 ℃, home composting | 88 | CO2 produced | 91 | [77] |
| Film | 58 ℃, industrial composting | 45 | CO2 produced | 100a | [77] | |
| a: biodegradability is expressed based on the comparison with cellulose. | ||||||
在水体环境中，因微生物的种类和数量、营养物质、温度、溶解氧量等存在较大差异，生物可降解塑料的降解情况会有所不同，评估生物可降解塑料在水体环境的降解情况相对复杂，需要充分考虑上述影响因素。目前在水体条件下开展的生物可降解塑料的降解研究通常采用两种条件，接种外源微生物和控制温度的受控条件以及不接种外源微生物和不控制温度的自然条件，两种不同条件下生物可降解塑料的降解情况有明显差异，相对于受控条件，生物可降解塑料在缺乏营养物质和微生物的自然条件下降解速率通常较慢。在淡水条件下，TPS、PHA和PVA可较快实现分解，PBS、PBSA和PPC分解情况次之，PLA较难分解。在海水条件下，TPS和PHA可较快完成分解，PCL和PBS次之，PLA和PBAT较难分解。表 4和表 5详细总结了生物可降解塑料在淡水和海水条件下的降解情况。
| Type | Shape | Conditions | Biodegradation period | Biodegradation indicator | Biodegradability | References |
| TPS | Film | 21 ℃ | 28 d | CO2 produced | 94%a | [77] |
| PHA | Film (PHB) | 21 ℃ | 56 d | CO2 produced | 90%a | [77] |
| Film (PHB) | 25 ℃ | 365 d | Weight loss | 8.5% | [87] | |
| Film (PHO) | 21 ℃ | 56 d | CO2 produced | 51%a | [77] | |
| PLA | Film | 21 ℃ | 56 d | CO2 produced | Not significant | [77] |
| Film | 25 ℃ | 365 d | Weight loss | < 2% | [87] | |
| Film | 28 ℃ | 21 d | Weight loss | 4.5% | [88] | |
| PBS | Film | 21 ℃ | 56 d | CO2 produced | 3%a | [77] |
| Film | 25 ℃ | 80 d | O2 consumed | 31% | [89] | |
| Film | Before modification, inoculated with soil suspension | 50 d | Weight loss | 11% | [90] | |
| Film | After modification, inoculated with soil suspension | 50 d | Weight loss | 8% | [90] | |
| PBSA | Film | Before modification, inoculated with soil suspension | 50 d | Weight loss | 16% | [90] |
| Film | After modification, inoculated with soil suspension | 50 d | Weight loss | 9% | [90] | |
| PCL | Film | 30 ℃ | 28 d | Weight loss | 7.6% | [91] |
| Film | 21 ℃ | 56 d | CO2 produced | 52%a | [77] | |
| Film | 25 ℃ | 365 d | Weight loss | < 2% | [87] | |
| PPC | Film | 28 ℃ | 21 d | Weight loss | 9.5% | [88] |
| PVA | Wastewater containing PVA | 20–25 ℃, biological aerated filter | 24 h (HRTb) | PVA removal | 64.4% | [92] |
| Wastewater containing PVA | 20–25 ℃, biocontact oxidation reactor | 30 h (HRT) | PVA removal | 74.5%–81.3% | [92] | |
| Wastewater containing PVA | 25 ℃, aerobic membrane bioreactor | 9 h (HRT) | PVA removal | 100% | [92] | |
| a: biodegradability is expressed based on the comparison with cellulose; b: hydraulic retention time (HRT). | ||||||
| Type | Shape | Conditions | Biodegradation period (d) | Biodegradation indicator | Biodegradability | References |
| TPS | Film | 30 ℃ | 28 | CO2 produced | 92%a | [77] |
| PHA | Film (PHB) | 30 ℃ | 43 | CO2 produced | 89%a | [77] |
| Film (PHB) | 25 ℃ | 14 | BOD removal | 80% | [93] | |
| Film (PHB) | 21 ℃, static incubation | 49 | Weight loss | 99% | [94] | |
| Film (PHB) | 12–22 ℃, dynamic incubation | 90 | Weight loss | 30% | [94] | |
| Film (PHBV) | 21 ℃, static incubation | 49 | Weight loss | 99% | [94] | |
| Film (PHBV) | 12–22 ℃, dynamic incubation | 90 | Weight loss | 30% | [94] | |
| Film (PHO) | 30 ℃ | 56 | CO2 produced | 38%a | [77] | |
| PLA | Film | 30 ℃ | 56 | CO2 produced | 7%a | [77] |
| Film | 25 ℃ | 365 | Weight loss | < 2% | [87] | |
| Sheet | Natural seawater | 364 | Weight loss | Not significant | [95] | |
| PBS | Film | 30 ℃ | 56 | CO2 produced | 21%a | [77] |
| Sheet | Natural seawater | 364 | Weight loss | < 2% | [95] | |
| PBAT | Sheet | Natural seawater | 364 | Weight loss | < 2% | [95] |
| PCL | Film | 25 ℃ | 365 | Weight loss | < 2% | [87] |
| Film | 30 ℃ | 56 | CO2 produced | 80%a | [77] | |
| Film | 25 ℃ | 70 | Weight loss | 25% | [96] | |
| Sheet | Natural seawater | 364 | Weight loss | 32% | [95] | |
| a: biodegradability is expressed based on the comparison with cellulose. | ||||||
在厌氧降解过程中，生物可降解塑料主要通过胞外酶的作用使长链聚合物转化为低聚物和单体，随后，低聚物和单体进入细胞，被胞内酶进一步分解。具有苯环的脂肪芳香族共聚酯在此条件下难以实现完全分解，通过进一步的好氧处理或将消化物施用于土壤，可实现最终的生物分解。厌氧消化产生的CH4可被集中收集，作为清洁能源高效利用，且沼液残渣可作为有机肥料用于农业生产，相对于好氧降解有更多优势。在中温厌氧消化条件下，TPS和短链PHA可在较短的时间内完成降解，降解性能：PHB > TPS > PHBV > PVA，PLA、PCL、PBS和PBAT较难分解; 高温厌氧条件对生物可降解塑料的降解更加有效，PLA和PCL的降解速率加快，而PBS和PBAT依旧较难降解，降解速率：PHB > TPS > PLA > PCL。表 6详细总结了生物可降解塑料在厌氧条件下的降解情况。
| Type | Shape | Conditions | Biodegradation period (d) | Biodegradation indicator | Biodegradability | References |
| TPS | Film | 35 ℃, aqueous anaerobic | 56 | Biogas produced | 99%a | [77] |
| Film | 52 ℃, high-solids anaerobic | 127 | Biogas produced | 73% | [77] | |
| PHA | Film (PHB) | 35 ℃, aqueous anaerobic | 56 | Biogas produced | 100%a | [77] |
| Film (PHB) | 37 ℃ | 70 | Weight loss | 23% | [56] | |
| Film (PHB) | 37 ℃, incubated sludge | 9 | Weight loss, biogas produced | 100%, 100%c | [56] | |
| Powder (PHB) | 35 ℃, untreated | 40 | Biogas produced | 67% | [97] | |
| Powder (PHB) | 35 ℃, alkaline-thermal pretreated | 40 | Biogas produced | 91% | [97] | |
| Powder (PHB) | 37 ℃ | 9 | Biogas produced | 90% | [98] | |
| Film (PHB) | 52 ℃, high-solids anaerobic | 127 | Biogas produced | 83% | [77] | |
| Powder (PHB) | 55 ℃ | 14 | Biogas produced | 90% | [99] | |
| Film (PHBV) | 37 ℃ | 70 | Weight loss | 22.5% | [56] | |
| Film (PHBV) | 37 ℃, incubated sludge | 42 | Weight loss, biogas produced | 60%, 29%c | [56] | |
| Film (PHO) | 35 ℃, aqueous anaerobic | 56 | Biogas produced | 6.5%a | [77] | |
| Film (PHO) | 52 ℃, high-solids anaerobic | 127 | Biogas produced | 5% | [77] | |
| PLA | Film | 35 ℃, aqueous anaerobic | 56 | Biogas produced | Not significant | [77] |
| Film | 35 ℃ | 39 | Biogas produced | 8.6% | [100] | |
| Film | 35 ℃ | 28 | Biogas produced | Not significant | [91] | |
| Powder | 37 ℃ | 277 | Biogas produced | 29%–49% | [98] | |
| Film | 52 ℃, high-solids anaerobic | 80 | Biogas produced | 80% | [77] | |
| Powder | 55 ℃ | 75 | Biogas produced | 75% | [99] | |
| Powder | 55 ℃ | 60 | Biogas produced | 90% | [79] | |
| PBS | Film | 35 ℃, aqueous anaerobic | 56 | Biogas produced | Not significant | [77] |
| Film | 35 ℃ | 100 | Biogas produced | 2% | [89] | |
| Film | 52 ℃, high-solids anaerobic | 127 | Biogas produced | 12% | [77] | |
| Film | Natural anaerobic landfill | 90 | Weight loss | Not significant | [89] | |
| PBAT | Film | 35 ℃ | 39 | Biogas produced | 5.9% | [100] |
| Film | 37 ℃ | 126 | Biogas produced | 2.2% | [101] | |
| Film | 55 ℃ | 126 | Biogas produced | 8.3% | [101] | |
| PCL | Film | 35 ℃, aqueous anaerobic | 56 | Biogas produced | 2.5%a | [77] |
| Film | 35 ℃ | 28 | Weight loss | Not significant | [91] | |
| Film | 37 ℃, methane sludge | 70 | Weight loss | 7.6% | [56] | |
| Film | 37 ℃, sewage sludge | 42 | Weight loss, biogas produced | 30%, 16%c | [56] | |
| Powder | 37 ℃ | 277 | Biogas produced | 3%–22% | [99] | |
| Film | 52 ℃, high-solids anaerobic | 127 | Biogas produced | 85% | [77] | |
| Powder | 55 ℃ | 50 | Biogas produced | 80% | [99] | |
| PVA | PVA-14 000b | 27 ℃, river sediment | 125 | TOCd removal | 60% | [102] |
| PVA-2 000b | 27 ℃, river sediment | 125 | TOC removal | 85% | [102] | |
| PVA-14 000b | 27 ℃, anaerobically treated activated sludge | 175 | TOC removal | 60% | [102] | |
| PVA-2 000b | 27 ℃, anaerobically treated activated sludge | 175 | TOC removal | 35% | [102] | |
| Wastewater containing PVA | 32–34 ℃, anaerobic baffle reactor | 2 (HRT) | PVA removal | 80% | [92] | |
| a: biodegradability is expressed based on the comparison with cellulose; b: 14 000 and 2 000 represent the number-average molecular weight of PVA; c: biodegradability is expressed as weight loss and produced biogas, respectively; d: total organic carbon (TOC). | ||||||
生物可降解塑料可被土壤中的多种微生物分解，如芽孢杆菌属、假单胞菌属、链球菌属和葡萄球菌属[2]，其降解情况受土壤条件的影响，如土壤中的微生物种类和数量、土壤含水率和土壤酸碱度。此外，当大量生物可降解塑料投加到土壤中时，生物分解过程会消耗土壤中的氧气，产生代谢产物，对土壤环境造成干扰。TPS、短链PHA、PCL和PPC可在土壤条件下较快分解，降解性能：PHB > TPS > PCL > PPC，PLA、PBS和PBAT分解较慢。表 7详细总结了生物可降解塑料在土壤条件下的降解情况。
| Type | Shape | Conditions | Biodegradation period (d) | Biodegradation indicator | Biodegradability | References |
| TPS | Film | 25 ℃ | 136 | CO2 produced | 95.5%a | [77] |
| PHA | Film (PHB) | 25 ℃ | 136 | CO2 produced | 100%a | [77] |
| Film (PHB) | Natural soil | 180 | Weight loss | 64.3% | [103] | |
| Film (PHB) | Natural soil, 15 cm depth | 365 | Weight loss | 98%, 46%b | [104] | |
| Pellet (PHB) | Natural soil, 15 cm depth | 365 | Weight loss | 55%, 28%b | [104] | |
| Film (PHBV) | Natural soil, 15 cm depth | 365 | Weight loss | 61%, 14%b | [104] | |
| Pellet (PHBV) | Natural soil, 15 cm depth | 365 | Weight loss | 35%, 8%b | [104] | |
| Film (PHO) | 25 ℃ | 136 | CO2 produced | 6%a | [77] | |
| PLA | Film | 25 ℃ | 136 | CO2 produced | Not significant | [77] |
| Sheet | 30% humidity | 98 | Weight loss | 10% | [105] | |
| Powder | 25 ℃, 60% humidity | 28 | Total soil carbon removal | 13.8% | [106] | |
| Powder | 25 ℃, 60% humidity | 28 | Weight loss | Not significant | [106] | |
| PBS | Film | 25 ℃ | 136 | CO2 produced | Not significant | [77] |
| Film | 25 ℃, 60% humidity | 28 | Weight loss | 1.2% | [106] | |
| Powder | 25 ℃, 60% humidity | 28 | Total soil carbon removal | 16.8% | [106] | |
| PBAT | Film | 27 ℃ | 365 | CO2 produced | 20%–30% | [78] |
| PCL | Film | 25 ℃ | 136 | CO2 produced | 92%a | [77] |
| Film | 28 ℃, 60% humidity, soil and landfill leachate | 60 | Weight loss | 89.7% | [107] | |
| Film | 28 ℃, 60% humidity, soil | 60 | Weight loss | 22% | [107] | |
| PPC | Film | Natural soil, 15 cm depth | 150 | Weight loss | 39.7% | [108] |
| a: biodegradability is expressed based on the comparison with cellulose; b: biodegradability in two tropical soils with different weather conditions and microbial communities. | ||||||
综上所述，生物可降解塑料降解条件复杂，影响因素众多，在不同环境条件下的分解情况存在较大差异。此外，由于实验条件、环境、操作和接种物等的不同，生物可降解塑料的降解情况在文献报道中也存在一定差别，难以对它们进行明确的比较衡量。综合看来，除TPS和PHB外，生物可降解塑料在自然和受控条件下分解速率依旧较慢，较难实现彻底分解，随意丢弃到自然环境将引发环境积累问题，生物可降解塑料的处理处置问题可能制约行业发展。未来需要重视生物可降解塑料的降解研究，采用生物强化、预处理等措施突破其降解慢的瓶颈，为实现生物可降解塑料的快速彻底降解寻找出路。
5 讨论与展望中国作为塑料生产和消费第一大国，塑料废弃物处理压力巨大，以PE、PP为代表的传统塑料在自然条件下极难分解，对生态环境构成严重威胁。研发、制备和应用生物可降解塑料是促进生态、经济与社会可持续发展的必然要求，具有广阔的发展潜力和市场空间。然而，目前对于生物可降解塑料的研究大多集中在改善其机械性能和加工性能方面，而关注降解的系统研究或详细综述较少。
迄今为止，研究人员已筛选出一些高效降解生物可降解塑料的功能微生物并纯化出功能酶，评估了生物可降解塑料在不同环境条件下的降解性能，但对于生物可降解塑料的研究仍存在以下问题：(1) 多数生物可降解塑料降解速率缓慢，难以满足目前资源化处理技术(好氧堆肥、厌氧消化) 对降解周期的要求，制约行业发展，生物可降解塑料的降解速率和程度亟待提高。(2) 虽然目前筛选出了多株生物可降解塑料降解功能菌并纯化了功能酶，但大多停留在实验室开发阶段，使用功能微生物和功能酶对降解过程进行生物强化的案例较少。(3) 针对生物可降解塑料在自然和受控条件下的降解研究文献不多，所用方法和条件各异，造成报道的结果差别较大，对生物可降解塑料的科学应用不利。此外，共混改性的生物可降解塑料以及其内部的化学添加剂，如增容剂、扩链剂、增塑剂、阻燃剂、杀菌剂、色素等对降解的影响也有待深入研究。(4) 标准规范亟待完善。目前有关部门大多仅采用好氧堆肥标准作为决定生物可降解塑料能否上市的仲裁标准，因此生物可降解塑料在其他环境条件下的降解性能难以有效保障，无法合理制定废弃物的处理处置策略。(5) 生物可降解塑料价格相对昂贵，机械性能不高。生物可降解塑料的价格普遍高于传统PE塑料，如何在保证较高生物可降解性能的前提下，降低生产成本、提升机械性能，需要深入研究，不同材质的生物可降解塑料产品需要进一步研究和开发。
针对上述问题，可从以下几个方面开展研究：(1) 针对生物可降解塑料降解缓慢的问题，一方面可从产品入手，在生产过程中添加功能酶或真菌孢子，当生物可降解塑料废弃后，酶或真菌在合适的湿度、温度、含氧量等条件下发挥作用; 另一方面针对废弃生物可降解塑料的处理处置过程，通过投加适合该环境条件的功能微生物或复合菌系进行生物强化，有利于实现高效彻底降解。(2) 重视生物可降解塑料的降解研究，在同一工作条件下开展系统实验，对不同生物可降解塑料的降解性能进行科学评价和全面比较，完全掌握生物可降解塑料的降解规律及特点，明确添加剂对其降解的影响，合理运用添加剂。(3) 对于生物可降解塑料产品，上市前应参照标准充分评估其在不同环境下的降解性能，并明确标注降解的环境条件，为其废弃后的处理处置提供建议和指导，减少环境积累，有关部门应参照国家标准严格把控产品质量，规范市场准入。(4) 深入研究生物可降解塑料的改性方法和加工技术，提升生物可降解塑料的机械性能; 研发原料生产新方法，提高技术和制造成熟度，降低生物可降解塑料生产成本。对生物可降解塑料的降解机理和降解程度的系统掌握，将为生物可降解塑料废弃物的高效处理处置和彻底降解提供科学指导，推动生物可降解塑料制品全面而广泛的应用。
| [1] |
Geyer R, Jambeck JR, Law KL. Production, use, and fate of all plastics ever made. Sci Adv, 2017, 3(7): e1700782. DOI:10.1126/sciadv.1700782
|
| [2] |
Folino A, Karageorgiou A, Calabrò PS, et al. Biodegradation of wasted bioplastics in natural and industrial environments: a review. Sustainability, 2020, 12(15): 6030. DOI:10.3390/su12156030
|
| [3] |
Satti SM, Shah AA. Polyester-based biodegradable plastics: an approach towards sustainable development. Lett Appl Microbiol, 2020, 70(6): 413-430. DOI:10.1111/lam.13287
|
| [4] |
严海彪, 胡慧, 金科. 淀粉基塑料制备与降解性能的现状与进展. 塑料, 2020, 49(5): 96-101. Yan HB, Hu H, Jin K. Progress in preparation and degradation of starch-based plastics. Plastics, 2020, 49(5): 96-101 (in Chinese). |
| [5] |
Meereboer KW, Misra M, Mohanty AK. Review of recent advances in the biodegradability of polyhydroxyalkanoate (PHA) bioplastics and their composites. Green Chem, 2020, 22(17): 5519-5558. DOI:10.1039/D0GC01647K
|
| [6] |
Turco R, Santagata G, Corrado I, et al. In vivo and post-synthesis strategies to enhance the properties of PHB-based materials: a review. Front Bioeng Biotechnol, 2020, 8: 619266.
|
| [7] |
Hobbs SR, Parameswaran P, Astmann B, et al. Anaerobic codigestion of food waste and polylactic acid: effect of pretreatment on methane yield and solid reduction. Adv Mater Sci Eng, 2019, 2019: 4715904.
|
| [8] |
Nofar M, Sacligil D, Carreau PJ, et al. Poly(lactic acid) blends: processing, properties and applications. Int J Biol Macromol, 2019, 125: 307-360. DOI:10.1016/j.ijbiomac.2018.12.002
|
| [9] |
Xu J, Guo BH. Poly(butylene succinate) and its copolymers: research, development and industrialization. Biotechnol J, 2010, 5(11): 1149-1163. DOI:10.1002/biot.201000136
|
| [10] |
Puchalski M, Szparaga G, Biela T, et al. Molecular and supramolecular changes in polybutylene succinate (PBS) and polybutylene succinate adipate (PBSA) copolymer during degradation in various environmental conditions. Polymers, 2018, 10(3): 251. DOI:10.3390/polym10030251
|
| [11] |
张婷, 张彩丽, 宋鑫宇, 等. PBAT薄膜的制备及应用研究进展. 中国塑料, 2021, 35(7): 115-125. Zhang T, Zhang CL, Song XY, et al. Research progress in preparation and applications of PBAT films. China Plast, 2021, 35(7): 115-125 (in Chinese). |
| [12] |
Mahmoud Salehi AO, Heidari Keshel S, Sefat F, et al. Use of polycaprolactone in corneal tissue engineering: a review. Mater Today Commun, 2021, 27: 102402. DOI:10.1016/j.mtcomm.2021.102402
|
| [13] |
刘小文, 潘莉莎, 徐鼐, 等. 聚碳酸亚丙酯共混改性研究进展. 化工进展, 2010, 29(5): 901-908, 975. Liu XW, Pan LS, Xu N, et al. Advances in blending of poly(propylene carbonate). Chem Ind Eng Prog, 2010, 29(5): 901-908, 975 (in Chinese). |
| [14] |
Aslam M, Kalyar MA, Raza ZA. Polyvinyl alcohol: a review of research status and use of polyvinyl alcohol based nanocomposites. Polym Eng Sci, 2018, 58(12): 2119-2132. DOI:10.1002/pen.24855
|
| [15] |
张敬勋. 聚碳酸亚丙酯在膜制品中的应用研究[D]. 青岛: 青岛科技大学, 2017. Zhang JX. Application research of poly(propylene carbonate) for film products[D]. Qingdao: Qingdao University of Science & Technology, 2017 (in Chinese). |
| [16] |
Kasirajan S, Ngouajio M. Polyethylene and biodegradable mulches for agricultural applications: a review. Agron Sustain Dev, 2012, 32(2): 501-529. DOI:10.1007/s13593-011-0068-3
|
| [17] |
Haider TP, Völker C, Kramm J, et al. Plastics of the future? The impact of biodegradable polymers on the environment and on society. Angew Chem Int Ed Engl, 2019, 58(1): 50-62. DOI:10.1002/anie.201805766
|
| [18] |
Elsawy MA, Kim KH, Park JW, et al. Hydrolytic degradation of polylactic acid (PLA) and its composites. Renew Sustain Energy Rev, 2017, 79: 1346-1352. DOI:10.1016/j.rser.2017.05.143
|
| [19] |
Díaz A, Katsarava R, Puiggalí J. Synthesis, properties and applications of biodegradable polymers derived from diols and dicarboxylic acids: from polyesters to poly(ester amide)s. Int J Mol Sci, 2014, 15(5): 7064-7123. DOI:10.3390/ijms15057064
|
| [20] |
Shah AA, Hasan F, Hameed A, et al. Biological degradation of plastics: a comprehensive review. Biotechnol Adv, 2008, 26(3): 246-265. DOI:10.1016/j.biotechadv.2007.12.005
|
| [21] |
Al-Itry R, Lamnawar K, Maazouz A. Improvement of thermal stability, rheological and mechanical properties of PLA, PBAT and their blends by reactive extrusion with functionalized epoxy. Polym Degrad Stab, 2012, 97(10): 1898-1914. DOI:10.1016/j.polymdegradstab.2012.06.028
|
| [22] |
Ghosh SK, Pal S, Ray S. Study of microbes having potentiality for biodegradation of plastics. Environ Sci Pollut Res, 2013, 20(7): 4339-4355. DOI:10.1007/s11356-013-1706-x
|
| [23] |
Numata K, Abe H, Doi Y. Enzymatic processes for biodegradation of poly(hydroxyalkanoate)s crystals. Can J Chem, 2008, 86(6): 471-483. DOI:10.1139/v08-004
|
| [24] |
Tokiwa Y, Calabia BP. Review Degradation of microbial polyesters. Biotechnol Lett, 2004, 26(15): 1181-1189. DOI:10.1023/B:BILE.0000036599.15302.e5
|
| [25] |
Kumar A, Gross RA, Jendrossek D. Poly(3-hydroxybutyrate)-depolymerase from Pseudomonas lemoignei: catalysis of esterifications in organic media. J Org Chem, 2000, 65(23): 7800-7806. DOI:10.1021/jo000814y
|
| [26] |
Reeve MS, McCarthy SP, Downey MJ, et al. Polylactide stereochemistry: effect on enzymic degradability. Macromolecules, 1994, 27(3): 825-831. DOI:10.1021/ma00081a030
|
| [27] |
Jaeger KE, Steinbüchel A, Jendrossek D. Substrate specificities of bacterial polyhydroxyalkanoate depolymerases and lipases: bacterial lipases hydrolyze poly(omega-hydroxyalkanoates). Appl Environ Microbiol, 1995, 61(8): 3113-3118. DOI:10.1128/aem.61.8.3113-3118.1995
|
| [28] |
Hajighasemi M, Nocek BP, Tchigvintsev A, et al. Biochemical and structural insights into enzymatic depolymerization of polylactic acid and other polyesters by microbial carboxylesterases. Biomacromolecules, 2016, 17(6): 2027-2039. DOI:10.1021/acs.biomac.6b00223
|
| [29] |
Hamad K, Kaseem M, Yang HW, et al. Properties and medical applications of polylactic acid: a review. Express Polym Lett, 2015, 9(5): 435-455. DOI:10.3144/expresspolymlett.2015.42
|
| [30] |
Kitakuni E, Yoshikawa K, Nakano K, et al. Biodegradation of poly(tetramethylene succinate-co- tetramethylene adipate) and poly(tetramethylene succinate) through water-soluble products. Environ Toxicol Chem, 2001, 20(5): 941-946.
|
| [31] |
Hayase N, Yano H, Kudoh E, et al. Isolation and characterization of poly(butylene succinate-co- butylene adipate)-degrading microorganism. J Biosci Bioeng, 2004, 97(2): 131-133. DOI:10.1016/S1389-1723(04)70180-2
|
| [32] |
Shah AA, Eguchi T, Mayumi D, et al. Purification and properties of novel aliphatic-aromatic co-polyesters degrading enzymes from newly isolated Roseateles depolymerans strain TB-87. Polym Degrad Stab, 2013, 98(2): 609-618. DOI:10.1016/j.polymdegradstab.2012.11.013
|
| [33] |
Artham T, Doble M. Biodegradation of aliphatic and aromatic polycarbonates. Macromol Biosci, 2008, 8(1): 14-24. DOI:10.1002/mabi.200700106
|
| [34] |
Murphy CA, Cameron JA, Huang SJ, et al. Fusarium polycaprolactone depolymerase is cutinase. Appl Environ Microbiol, 1996, 62(2): 456-460. DOI:10.1128/aem.62.2.456-460.1996
|
| [35] |
Khan I, Ray Dutta J, Ganesan R. Lactobacillus sps. lipase mediated poly(ε-caprolactone) degradation. Int J Biol Macromol, 2017, 95: 126-131. DOI:10.1016/j.ijbiomac.2016.11.040
|
| [36] |
Zhou M, Takayanagi M, Yoshida Y, et al. Enzyme-catalyzed degradation of aliphatic polycarbonates prepared from epoxides and carbon dioxide. Polym Bull, 1999, 42(4): 419-424. DOI:10.1007/s002890050484
|
| [37] |
Suyama T, Tokiwa Y. Enzymatic degradation of an aliphatic polycarbonate, poly(tetramethylene carbonate). Enzym Microb Technol, 1997, 20(2): 122-126. DOI:10.1016/S0141-0229(96)00084-1
|
| [38] |
Kawai F, Hu XP. Biochemistry of microbial polyvinyl alcohol degradation. Appl Microbiol Biotechnol, 2009, 84(2): 227-237. DOI:10.1007/s00253-009-2113-6
|
| [39] |
Matsumura S, Tomizawa N, Toki A, et al. Novel poly(vinyl alcohol)-degrading enzyme and the degradation mechanism. Macromolecules, 1999, 32(23): 7753-7761. DOI:10.1021/ma990727b
|
| [40] |
Klomklang W, Tani A, Kimbara K, et al. Biochemical and molecular characterization of a periplasmic hydrolase for oxidized polyvinyl alcohol from Sphingomonas sp. strain 113P3. Microbiology (Reading), 2005, 151(pt 4): 1255-1262.
|
| [41] |
Uchida H, Shigeno-Akutsu Y, Nomura N, et al. Cloning and sequence analysis of poly(tetramethylene succinate) depolymerase from Acidovorax delafieldii strain BS-3. J Biosci Bioeng, 2002, 93(2): 245-247. DOI:10.1016/S1389-1723(02)80022-6
|
| [42] |
Nakajima-Kambe T, Edwinoliver NG, Maeda H, et al. Purification, cloning and expression of an Aspergillus niger lipase for degradation of poly(lactic acid) and poly(ε-caprolactone). Polym Degrad Stab, 2012, 97(2): 139-144. DOI:10.1016/j.polymdegradstab.2011.11.009
|
| [43] |
Lee SH, Kim MN. Isolation of bacteria degrading poly(butylene succinate-co-butylene adipate) and their lip A gene. Int Biodeterior Biodegrad, 2010, 64(3): 184-190. DOI:10.1016/j.ibiod.2010.01.002
|
| [44] |
Masaki K, Kamini NR, Ikeda H, et al. Cutinase-like enzyme from the yeast Cryptococcus sp. strain S-2 hydrolyzes polylactic acid and other biodegradable plastics. Appl Environ Microbiol, 2005, 71(11): 7548-7550. DOI:10.1128/AEM.71.11.7548-7550.2005
|
| [45] |
Akutsu-Shigeno Y, Teeraphatpornchai T, Teamtisong K, et al. Cloning and sequencing of a poly(DL-lactic acid) depolymerase gene from Paenibacillus amylolyticus strain TB-13 and its functional expression in Escherichia coli. Appl Environ Microbiol, 2003, 69(5): 2498-2504. DOI:10.1128/AEM.69.5.2498-2504.2003
|
| [46] |
Wang ZY, Wang Y, Guo ZQ, et al. Purification and characterization of poly(L-lactic acid) depolymerase from Pseudomonas sp. strain DS04-T. Polym Eng Sci, 2011, 51(3): 454-459. DOI:10.1002/pen.21857
|
| [47] |
Tsuji H, Kidokoro Y, Mochizuki M. Enzymatic degradation of biodegradable polyester composites of poly(L-lactic acid) and poly(ε-caprolactone). Macromol Mater Eng, 2006, 291(10): 1245-1254. DOI:10.1002/mame.200600276
|
| [48] |
Satti SM, Abbasi AM, Marsh TL, et al. Statistical optimization of lipase production from Sphingobacterium sp. strain S2 and evaluation of enzymatic depolymerization of poly(lactic acid) at mesophilic temperature. Polym Degrad Stab, 2019, 160: 1-13. DOI:10.1016/j.polymdegradstab.2018.11.030
|
| [49] |
Penkhrue W, Khanongnuch C, Masaki K, et al. Isolation and screening of biopolymer-degrading microorganisms from northern Thailand. World J Microbiol Biotechnol, 2015, 31(9): 1431-1442. DOI:10.1007/s11274-015-1895-1
|
| [50] |
Sakai K, Kawano H, Iwami A, et al. Isolation of a thermophilic poly-L-lactide degrading bacterium from compost and its enzymatic characterization. J Biosci Bioeng, 2001, 92(3): 298-300. DOI:10.1016/S1389-1723(01)80266-8
|
| [51] |
Nawaz A, Hasan F, Shah AA. Degradation of poly(ε-caprolactone) (PCL) by a newly isolated Brevundimonas sp. strain MRL-AN1 from soil. FEMS Microbiol Lett, 2015, 362(1): 1-7.
|
| [52] |
Nakajima-Kambe T, Toyoshima K, Saito C, et al. Rapid monomerization of poly(butylene succinate)-co- (butylene adipate) by Leptothrix sp.. J Biosci Bioeng, 2009, 108(6): 513-516. DOI:10.1016/j.jbiosc.2009.05.018
|
| [53] |
Shah AA, Nawaz A, Kanwal L, et al. Degradation of poly(ε-caprolactone) by a thermophilic bacterium Ralstonia sp. strain MRL-TL isolated from hot spring. Int Biodeterior Biodegrad, 2015, 98: 35-42. DOI:10.1016/j.ibiod.2014.11.017
|
| [54] |
Hu XP, Thumarat U, Zhang X, et al. Diversity of polyester-degrading bacteria in compost and molecular analysis of a thermoactive esterase from Thermobifida alba AHK119. Appl Microbiol Biotechnol, 2010, 87(2): 771-779. DOI:10.1007/s00253-010-2555-x
|
| [55] |
Maeda H, Yamagata Y, Abe K, et al. Purification and characterization of a biodegradable plastic-degrading enzyme from Aspergillus oryzae. Appl Microbiol Biotechnol, 2005, 67(6): 778-788. DOI:10.1007/s00253-004-1853-6
|
| [56] |
Abou-Zeid DM, Müller RJ, Deckwer WD. Degradation of natural and synthetic polyesters under anaerobic conditions. J Biotechnol, 2001, 86(2): 113-126. DOI:10.1016/S0168-1656(00)00406-5
|
| [57] |
Kleeberg I, Welzel K, VandenHeuvel J, et al. Characterization of a new extracellular hydrolase from Thermobifida fusca degrading aliphatic-aromatic copolyesters. Biomacromolecules, 2005, 6(1): 262-270. DOI:10.1021/bm049582t
|
| [58] |
Sukkhum S, Tokuyama S, Tamura T, et al. A novel poly(L-lactide) degrading actinomycetes isolated from Thai forest soil, phylogenic relationship and the enzyme characterization. J Gen Appl Microbiol, 2009, 55(6): 459-467. DOI:10.2323/jgam.55.459
|
| [59] |
Panyachanakul T, Kitpreechavanich V, Tokuyama S, et al. Poly(DL-lactide)-degrading enzyme production by immobilized Actinomadura keratinilytica strain T16-1 in a 5-L fermenter under various fermentation processes. Electron J Biotechnol, 2017, 30: 71-76. DOI:10.1016/j.ejbt.2017.09.001
|
| [60] |
Hanphakphoom S, Maneewong N, Sukkhum S, et al. Characterization of poly(L-lactide)-degrading enzyme produced by thermophilic filamentous bacteria Laceyella sacchari LP175. J Gen Appl Microbiol, 2014, 60(1): 13-22. DOI:10.2323/jgam.60.13
|
| [61] |
Jung HW, Yang MK, Su RC. Purification, characterization, and gene cloning of an Aspergillus fumigatus polyhydroxybutyrate depolymerase used for degradation of polyhydroxybutyrate, polyethylene succinate, and polybutylene succinate. Polym Degrad Stab, 2018, 154: 186-194. DOI:10.1016/j.polymdegradstab.2018.06.002
|
| [62] |
Volova TG, Boyandin AN, Vasiliev AD, et al. Biodegradation of polyhydroxyalkanoates (PHAs) in tropical coastal waters and identification of PHA-degrading bacteria. Polym Degrad Stab, 2010, 95(12): 2350-2359. DOI:10.1016/j.polymdegradstab.2010.08.023
|
| [63] |
Schirmer A, Jendrossek D, Schlegel HG. Degradation of poly(3-hydroxyoctanoic acid)[P(3HO)] by bacteria: purification and properties of a P(3HO) depolymerase from Pseudomonas fluorescens GK13. Appl Environ Microbiol, 1993, 59(4): 1220-1227. DOI:10.1128/aem.59.4.1220-1227.1993
|
| [64] |
Mergaert J, Schirmer A, Hauben L, et al. Isolation and identification of poly(3-hydroxyvalerate)-degrading strains of Pseudomonas lemoignei. Int J Syst Bacteriol, 1996, 46(3): 769-773. DOI:10.1099/00207713-46-3-769
|
| [65] |
Akbar S, Hasan F, Nadhman A, et al. Production and purification of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) degrading enzyme from Streptomyces sp. AF-111. J Polym Environ, 2013, 21(4): 1109-1116. DOI:10.1007/s10924-013-0600-4
|
| [66] |
Tseng M, Hoang KC, Yang MK, et al. Polyester-degrading thermophilic actinomycetes isolated from different environment in Taiwan. Biodegradation, 2007, 18(5): 579-583. DOI:10.1007/s10532-006-9089-z
|
| [67] |
Kim MN, Lee AR, Yoon JS, et al. Biodegradation of poly(3-hydroxybutyrate), Sky-Green® and Mater-Bi® by fungi isolated from soils. Eur Polym J, 2000, 36(8): 1677-1685. DOI:10.1016/S0014-3057(99)00219-0
|
| [68] |
Satti SM, Shah AA, Auras R, et al. Isolation and characterization of bacteria capable of degrading poly(lactic acid) at ambient temperature. Polym Degrad Stab, 2017, 144: 392-400. DOI:10.1016/j.polymdegradstab.2017.08.023
|
| [69] |
Satti SM, Shah AA, Marsh TL, et al. Biodegradation of poly(lactic acid) in soil microcosms at ambient temperature: evaluation of natural attenuation, bio-augmentation and bio-stimulation. J Polym Environ, 2018, 26(9): 3848-3857. DOI:10.1007/s10924-018-1264-x
|
| [70] |
Kleeberg I, Hetz C, Kroppenstedt RM, et al. Biodegradation of aliphatic-aromatic copolyesters by Thermomonospora fusca and other thermophilic compost isolates. Appl Environ Microbiol, 1998, 64(5): 1731-1735. DOI:10.1128/AEM.64.5.1731-1735.1998
|
| [71] |
Witt U, Einig T, Yamamoto M, et al. Biodegradation of aliphatic-aromatic copolyesters: evaluation of the final biodegradability and ecotoxicological impact of degradation intermediates. Chemosphere, 2001, 44(2): 289-299. DOI:10.1016/S0045-6535(00)00162-4
|
| [72] |
Tan FT, Cooper DG, Marić M, et al. Biodegradation of a synthetic co-polyester by aerobic mesophilic microorganisms. Polym Degrad Stab, 2008, 93(8): 1479-1485. DOI:10.1016/j.polymdegradstab.2008.05.005
|
| [73] |
Chua TK, Tseng M, Yang MK. Degradation of poly(ε-caprolactone) by thermophilic Streptomyces thermoviolaceus subsp. thermoviolaceus 76T-2. AMB Express, 2013, 3(1): 8. DOI:10.1186/2191-0855-3-8
|
| [74] |
Urbanek AK, Rymowicz W, Strzelecki MC, et al. Isolation and characterization of Arctic microorganisms decomposing bioplastics. AMB Express, 2017, 7(1): 148. DOI:10.1186/s13568-017-0448-4
|
| [75] |
Li F, Yu D, Lin XM, et al. Biodegradation of poly(ε-caprolactone) (PCL) by a new Penicillium oxalicum strain DSYD05-1. World J Microbiol Biotechnol, 2012, 28(10): 2929-2935. DOI:10.1007/s11274-012-1103-5
|
| [76] |
Bátori V, Åkesson D, Zamani A, et al. Anaerobic degradation of bioplastics: a review. Waste Manag, 2018, 80: 406-413. DOI:10.1016/j.wasman.2018.09.040
|
| [77] |
Narancic T, Verstichel S, Reddy Chaganti S, et al. Biodegradable plastic blends create new possibilities for end-of-life management of plastics but they are not a panacea for plastic pollution. Environ Sci Technol, 2018, 52(18): 10441-10452. DOI:10.1021/acs.est.8b02963
|
| [78] |
Anunciado MB, Hayes DG, Astner AF, et al. Effect of environmental weathering on biodegradation of biodegradable plastic mulch films under ambient soil and composting conditions. J Polym Environ, 2021, 29(9): 2916-2931. DOI:10.1007/s10924-021-02088-4
|
| [79] |
Yagi H, Ninomiya F, Funabashi M, et al. Anaerobic biodegradation tests of poly(lactic acid) under mesophilic and thermophilic conditions using a new evaluation system for methane fermentation in anaerobic sludge. Int J Mol Sci, 2009, 10(9): 3824-3835. DOI:10.3390/ijms10093824
|
| [80] |
Weng YX, Wang XL, Wang YZ. Biodegradation behavior of PHAs with different chemical structures under controlled composting conditions. Polym Test, 2011, 30(4): 372-380. DOI:10.1016/j.polymertesting.2011.02.001
|
| [81] |
Tabasi RY, Ajji A. Selective degradation of biodegradable blends in simulated laboratory composting. Polym Degrad Stab, 2015, 120: 435-442. DOI:10.1016/j.polymdegradstab.2015.07.020
|
| [82] |
Arrieta MP, López J, Rayón E, et al. Disintegrability under composting conditions of plasticized PLA-PHB blends. Polym Degrad Stab, 2014, 108: 307-318. DOI:10.1016/j.polymdegradstab.2014.01.034
|
| [83] |
Mihai M, Legros N, Alemdar A. Formulation-properties versatility of wood fiber biocomposites based on polylactide and polylactide/thermoplastic starch blends. Polym Eng Sci, 2014, 54(6): 1325-1340. DOI:10.1002/pen.23681
|
| [84] |
Intaraksa P, Rudeekit Y, Siriyota P, et al. The ultimate biodegradation of the starch based biodegradable plastics. Adv Mater Res, 2012, 506: 327-330. DOI:10.4028/www.scientific.net/AMR.506.327
|
| [85] |
赵剑豪, 王晓青, 曾军, 等. 聚丁二酸丁二醇酯及聚丁二酸/己二酸-丁二醇酯在微生物作用下的降解行为. 高分子材料科学与工程, 2006, 22(2): 137-140. Zhao JH, Wang XQ, Zeng J, et al. Studies on biodegradation behavior of poly(butylene succinate) and poly(butylene succinate-co-butylene adipate) by microorganisms. Polym Mater Sci Eng, 2006, 22(2): 137-140 (in Chinese). DOI:10.3321/j.issn:1000-7555.2006.02.035 |
| [86] |
Anstey A, Muniyasamy S, Reddy MM, et al. Processability and biodegradability evaluation of composites from poly(butylene succinate) (PBS) bioplastic and biofuel co-products from Ontario. J Polym Environ, 2014, 22(2): 209-218. DOI:10.1007/s10924-013-0633-8
|
| [87] |
Bagheri AR, Laforsch C, Greiner A, et al. Fate of so-called biodegradable polymers in seawater and freshwater. Glob Challenges, 2017, 1(4): 1700048. DOI:10.1002/gch2.201700048
|
| [88] |
王淑芳, 陶剑, 郭天瑛, 等. 脂肪族聚碳酸酯(PPC)与聚乳酸(PLA)共混型生物降解材料的热学性能、力学性能和生物降解性研究. 离子交换与吸附, 2007, 23(1): 1-9. Wang SF, Tao J, Guo TY, et al. Thermal characteristics, mechanical properties and biodegradability of polycarbonates/poly(lactic acid) (PPC/PLA) blends. Ion Exch Adsorpt, 2007, 23(1): 1-9 (in Chinese). DOI:10.3321/j.issn:1001-5493.2007.01.001 |
| [89] |
Cho HS, Moon HS, Kim M, et al. Biodegradability and biodegradation rate of poly(caprolactone)-starch blend and poly(butylene succinate) biodegradable polymer under aerobic and anaerobic environment. Waste Manag, 2011, 31(3): 475-480. DOI:10.1016/j.wasman.2010.10.029
|
| [90] |
王磊. PBS及其共聚物的丁二酰氯扩链及降解研究[D]. 西安: 陕西科技大学, 2012. Wang L. Study on degradation and chain extender of PBS and PBS-based polyester[D]. Xi'an: Shaanxi University of Science & Technology, 2012 (in Chinese). |
| [91] |
Massardier-Nageotte V, Pestre C, Cruard-Pradet T, et al. Aerobic and anaerobic biodegradability of polymer films and physico-chemical characterization. Polym Degrad Stab, 2006, 91(3): 620-627. DOI:10.1016/j.polymdegradstab.2005.02.029
|
| [92] |
李功松, 陈小光, 汪彩华. 含PVA废水处理工艺探讨. 工业水处理, 2019, 39(10): 20-25, 31. Li GS, Chen XG, Wang CH. Discussion on treatment process of wastewater containing PVA. Ind Water Treat, 2019, 39(10): 20-25, 31 (in Chinese). DOI:10.11894/iwt.2019-0889 |
| [93] |
Tachibana K, Urano Y, Numata K. Biodegradability of nylon 4 film in a marine environment. Polym Degrad Stab, 2013, 98(9): 1847-1851. DOI:10.1016/j.polymdegradstab.2013.05.007
|
| [94] |
Thellen C, Coyne M, Froio D, et al. A processing, characterization and marine biodegradation study of melt-extruded polyhydroxyalkanoate (PHA) films. J Polym Environ, 2008, 16(1): 1-11. DOI:10.1007/s10924-008-0079-6
|
| [95] |
王格侠, 黄丹, 张维, 等. 典型生物降解聚酯在海水中的降解性能. 功能高分子学报, 2020, 33(5): 492-499. Wang GX, Huang D, Zhang W, et al. Degradation performance of typical biodegradable polyesters in seawater. J Funct Polym, 2020, 33(5): 492-499 (in Chinese). |
| [96] |
Tsuji H, Suzuyoshi K. Environmental degradation of biodegradable polyesters 1. Poly(ε-caprolactone), poly[(R)-3-hydroxybutyrate], and poly(L-lactide) films in controlled static seawater. Polym Degrad Stab, 2002, 75(2): 347-355. DOI:10.1016/S0141-3910(01)00240-3
|
| [97] |
Benn N, Zitomer D. Pretreatment and anaerobic co-digestion of selected PHB and PLA bioplastics. Front Environ Sci, 2018, 5: 93. DOI:10.3389/fenvs.2017.00093
|
| [98] |
Yagi H, Ninomiya F, Funabashi M, et al. Mesophilic anaerobic biodegradation test and analysis of eubacteria and archaea involved in anaerobic biodegradation of four specified biodegradable polyesters. Polym Degrad Stab, 2014, 110: 278-283. DOI:10.1016/j.polymdegradstab.2014.08.031
|
| [99] |
Yagi H, Ninomiya F, Funabashi M, et al. Thermophilic anaerobic biodegradation test and analysis of eubacteria involved in anaerobic biodegradation of four specified biodegradable polyesters. Polym Degrad Stab, 2013, 98(6): 1182-1187. DOI:10.1016/j.polymdegradstab.2013.03.010
|
| [100] |
Ren YN, Hu J, Yang MR, et al. Biodegradation behavior of poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT), and their blends under digested sludge conditions. J Polym Environ, 2019, 27(12): 2784-2792. DOI:10.1007/s10924-019-01563-3
|
| [101] |
Svoboda P, Dvorackova M, Svobodova D. Influence of biodegradation on crystallization of poly(butylene adipate-co-terephthalate). Polym Adv Technol, 2019, 30(3): 552-562. DOI:10.1002/pat.4491
|
| [102] |
Matsumura S, Kurita H, Shimokobe H. Anaerobic biodegradability of polyvinyl alcohol. Biotechnol Lett, 1993, 15(7): 749-754. DOI:10.1007/BF01080150
|
| [103] |
Jain R, Tiwari A. Biosynthesis of planet friendly bioplastics using renewable carbon source. J Environ Health Sci Eng, 2015, 13: 11. DOI:10.1186/s40201-015-0165-3
|
| [104] |
Boyandin AN, Prudnikova SV, Karpov VA, et al. Microbial degradation of polyhydroxyalkanoates in tropical soils. Int Biodeterior Biodegrad, 2013, 83: 77-84. DOI:10.1016/j.ibiod.2013.04.014
|
| [105] |
Wu CS. Preparation, characterization, and biodegradability of renewable resource-based composites from recycled polylactide bioplastic and sisal fibers. J Appl Polym Sci, 2012, 123(1): 347-355. DOI:10.1002/app.34223
|
| [106] |
Adhikari D, Mukai M, Kubota K, et al. Degradation of bioplastics in soil and their degradation effects on environmental microorganisms. J Agric Chem Environ, 2016, 5(1): 23-34.
|
| [107] |
de Campos A, Marconato JC, Martins-Franchetti SM. The influence of soil and landfill leachate microorganisms in the degradation of PVC/PCL films cast from DMF. Polímeros, 2012, 22(3): 220-227.
|
| [108] |
杨晓庭, 吴景贵, 李建明, 等. 半干旱地区土壤中PPC地膜与普通地膜的降解特征研究. 环境科学与技术, 2020, 43(11): 45-53. Yang XT, Wu JG, Li JM, et al. Study on degradation characteristics of PPC plastic film and ordinary plastic film in semi-arid soil. Environ Sci Technol, 2020, 43(11): 45-53 (in Chinese). |
