Biodegradation rate of biodegradable plastics at molecular level
Biodegradation rate of biodegradable plastics at molecular level
复制标题
DOI：
10.1016/j.polymdegradstab.2017.12.011
复制
发表时间：
2018-01-01
影响因子：
5.9
通讯作者：
Degli-Innocenti, Francesco
中科院分区：
文献类型：
--
作者：
Chinaglia, Selene;Tosin, Maurizio;Degli-Innocenti, Francesco
塑料是固体材料，生物降解发生在表面。只有表面受到生物降解的影响，而内部不应容易进行生物降解。因此，在实验室一级，生物降解率预计是测试样品表面积的函数。在其他环境条件相同的情况下，表面积越大，生物降解率越高。为了进一步探索颗粒尺寸对生物降解性的作用，将聚癸二酸丁二醇酯的塑料颗粒研磨并筛分成不同的颗粒尺寸，从而获得包括颗粒在内的具有不同比表面积（33、89、193和824 cm（2）g（-1））的四个样品。通过直接测量（颗粒）或理论估计，然后进行图像分析来评估表面积。不同的样品在土壤中进行了138天的生物降解测试。在生物降解过程的第一部分用线性回归计算的速率与各自的总可用表面积有关。通过双倒数图的线性回归（酶动力学中使用的Lineweaver-Burk方法）很好地描述了数据，该方法能够估计理论最大生物降解速率（k（max）= 97 mg C-聚合物/天（-1））。当可用表面积不限制生物降解时，k（max）可以被认为是在分子水平上对生物降解速率的估计。另一个假设是，在具有不同微生物负荷的土壤中测试的相同聚合物将显示不同的k（max）。米氏常数（K-m），即反应速率k为最大速率一半时的表面积，为1122 cm（2）。值得注意的是，如果聚癸二酸丁二醇酯可以以纳米聚合物的形式进行测试，它很可能满足经济合作与发展组织（OECD）对化学品的“快速生物降解性”标准（例如，在28天的测试中，在10天的窗口内生物降解60%）。这是第一次，固体聚合物的生物降解动力学已被估计通过使用Michaelis-Menten方法。
Plastics are solid materials where biodegradation happens on the surface. Only the surface is affected by biodegradation while the inner part should not be readily available for biodegradation. Thus, at a laboratory level, the biodegradation rate is expected to be a function of the surface area of the tested sample. The higher the surface area, the higher the biodegradation rate, all other environmental conditions being equal. In order to further explore the role of particle size on biodegradability, plastic pellets of polybutylene sebacate were milled and sieved into different particle sizes, thus obtaining four samples, pellets included, with different specific surface areas (33, 89, 193, and 824 cm(2)g(-1)). The surface areas were assessed through direct measurement (pellets) or a theoretical estimation followed by an image analysis. The different samples were tested for biodegradation in soil for 138 days. The rates calculated with a linear regression in the first part of the biodegradation process were related to the respective total available surface area. The data are well described by a linear regression of the double reciprocal plot (the Lineweaver-Burk approach used in enzymatic kinetics) that enables the estimation of the theoretical maximum'biodegradation rate (k(max) = 97 mg C-polymer day(-1)). The k(max) can be considered as an estimation of the biodegradation rate at molecular level, when the available surface area is not limiting biodegradation. An additional hypothesis is that the same polymer tested in soils with different microbial loads would display different k(max). The Michaelis constant (K-m), i.e. the surface area at which the reaction rate k is half the maximum rate, is 1122 cm(2). It is remarkable to notice that if polybutylene sebacate could be tested in a nanopolymeric form, it could very likely satisfy the Organization for Economic Co-operation and Development (OECD) criteria of "ready biodegradability" for chemicals (e.g. 60% biodegradation in a 10-day window within a 28-day test). This is the first time that the biodegradation kinetics of a solid polymer have been estimated by using the Michaelis-Menten approach.