Various zeolites (4A, Y, 13X) and related fillers (molecular sieves and coal fly ash) were used to prepare PLA composites and to assess their degrading effect on the polyester matrix under different processing conditions, at various zeolite/filler loadings. In this objective, untreated fillers, as well as washed and thermally activated zeolites, were used. PLA–zeolite composites were produced by melt-blending step followed by the evaluation of rheological information and molecular and thermal characteristics. The degradation of PLA during the preparation and processing of PLA–zeolite composites, or due to the presence of fillers, was evidenced by specific analyses (SEC, DSC, TGA, TG-FTIR). PLA degradation was mainly dependent on the nature of zeolite, filler loading, and thermal and processing history. The results of the study suggest that a stronger degradation effect is obtained by the addition of zeolite 4A into PLA (at loading of 5–10%) with respect to other zeolites (e.g., 13X and Y). It was also revealed the key roles of the temperature and residence time (as parameters in melt-mixing process), free alkalinity level, and water uptake in determining the ultimate characteristics of composites. The washing and thermal activation pretreatments of fillers have diminished in some cases the degradation of PLA matrix. Finally, the study also highlights the zeolite grades capable of being used to produce new PLA composites with competitive properties and those that could be of interest to improve PLA recycling by pyrolysis.

中文翻译：

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熔融共混制备的聚乳酸-沸石复合材料的热降解

使用各种沸石（4A、Y、13X）和相关填料（分子筛和粉煤灰）制备 PLA 复合材料，并评估它们在不同加工条件下、不同沸石/填料负载下对聚酯基体的降解效果。在这个目标中，使用了未经处理的填料以及洗涤和热活化的沸石。PLA-沸石复合材料通过熔融共混步骤生产，然后评估流变信息以及分子和热特性。在 PLA-沸石复合材料的制备和加工过程中，或由于填料的存在，PLA 的降解通过特定分析（SEC、DSC、TGA、TG-FTIR）得到证实。PLA 降解主要取决于沸石的性质、填料负载以及热和加工历史。研究结果表明，相对于其他沸石（例如 13X 和 Y），将沸石 4A 加入 PLA（负载量为 5-10%）可获得更强的降解效果。还揭示了温度和停留时间（作为熔体混合过程中的参数）、游离碱度和吸水量在决定复合材料的最终特性方面的关键作用。在某些情况下，填料的洗涤和热活化预处理减少了 PLA 基质的降解。最后，该研究还重点介绍了能够用于生产具有竞争力的新型 PLA 复合材料的沸石等级，以及那些可能有助于通过热解改善 PLA 回收利用的沸石等级。