Comparative thermal, biological and photodegradation kinetics of polylactide and effect on crystallization rates
Comparative thermal, biological and photodegradation kinetics of polylactide and effect on crystallization rates
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DOI：
10.1016/j.polymdegradstab.2012.12.012
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发表时间：
2013-03-01
影响因子：
5.9
通讯作者：
Alamo, R. G.
中科院分区：
文献类型：
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作者：
Santonja-Blasco, L.;Ribes-Greus, A.;Alamo, R. G.
对现有文献和目前三种主要类型聚乳酸（PLA）降解的结果进行了比较，对降解机制的细节以及影响降解的明确因素进行了比较。在220℃的等温条件下，在生物和光降解条件下，用类似于4 mol% D的聚乳酸（PLA）分析了摩尔质量的时间下降。在生物降解过程中，摩尔质量随时间的减少遵循一阶过程(M = M(o)e(-kt))，而在热降解和光降解过程中测试的样品的摩尔质量遵循二阶规律（1/M = (1/M-o) + kt）在类似降解条件下获得的文献数据也充分拟合了这些方程。这使我们可以得出结论，在三种类型的退化的主要步骤是一个随机链切除，在代数功能上有一些差异。在测试的降解条件下，降解速率遵循热>光>生物的顺序。对于等效摩尔质量，降解类型对冷结晶和熔化的影响是显著的，这表明降解不能仅仅用链断裂和摩尔质量减少的结果来解释。这一特点是特别突出的线性增长率的标本遭受生物或光降解进行比较。与同等摩尔质量的生物降解样品相比，在光降解过程中形成的酸酐基团降低了结晶速率。最大生长速率的摩尔质量依赖关系遵循幂律，生物样品的指数为1.3，光降解样品的指数为1.0，代表半纠缠系统。根据二次成核分析，生长速率的温度系数与生物和光降解样品呈线性关系，晶体的表面自由能随摩尔质量的降低从85到55 erg/cm(2)。摩尔质量表征、红外光谱和热结晶速率分析的结合被证明是评估和区分PLA结构由不同类型降解引起的宏观变化的有效策略。这项工作还强调了分析线性增长率作为揭示降解过程中特定结构变化的参数的重要性。(c) 2012 Elsevier Ltd.版权所有。
A comparison is made between available literature and present results of the three major types of polylactide (PLA) degradation giving a compiled view on the details of degradation mechanisms with relation to explicit factors affecting degradation. The temporal decrease of molar mass has been analyzed under isothermal conditions at 220 degrees C, biological and photodegradation conditions using a polylactide (PLA) with similar to 4 mol% D units. The decrease of molar mass with time during biodegradation follows a first order process (M = M(o)e(-kt)) while the molar mass of specimens tested during thermal and photodegradation follows a second order law (1/M = (1/M-o) + kt) Literature data obtained in similar degradation conditions were also adequately fitted with these equations. This allows us to conclude that the main step in the three types of degradation is a random chain excision, with some differences in the algebraic functionality. Under the degradation conditions tested, the degradation rate follows the progression thermal > photo > biological. For equivalent molar mass, the effect of degradation type on cold crystallization and melting is significant indicating that degradation cannot be explained by a solely outcome of chains breakage and molar mass reduction. This feature is especially prominent when the linear growth rates of specimens subjected to bio or photo degradation are compared. Anhydride groups that are formed during photodegradation decrease the crystallization rate compared to biodegraded specimens of equivalent molar mass. The molar mass dependence of the maximum growth rate follows a power law with exponents 1.3 for bio and 1.0 for photodegraded specimens, representative of semi-entangled systems. The temperature coefficient of the growth rate, analyzed according to secondary nucleation leads to a linear dependence for bio and photodegraded specimens, and to values of the surface free energy of crystallites that decrease from similar to 85 to 55 erg/cm(2) with decreasing molar mass. Combinations of molar mass characterization, FTIR, and thermal and crystallization rate analysis are proven useful strategies to assess and discriminate macroscopic changes of PLA structure induced by different types of degradation. This work also underlines the importance of analyzing the linear growth rates as a parameter that uncovers specific structural changes during degradation. (c) 2012 Elsevier Ltd. All rights reserved.