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Effect of Artificial Weathering on PLA/Nanocomposite Molecular Weight Distribution

机译：人工风化对PLA /纳米复合物分子量分布的影响

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The reduction of polylactide acid (PLA) molecular weight for amorphous and semicrystalline grade nanocomposites with 5 wt% load of organomodified montmorillonite Cloisite30B (C30B) was investigated in periods of up to 360 h under artificial weathering. A correlation between artificial and natural weathering was established. The nanocomposites were prepared by mixing the C30B in PLA matrix using two stages of extrusion followed by injection molding. In addition, we also studied materials without C30B in PLA matrix prepared by a single stage of injection, as well as with two stages of extrusion followed by injection, in order to assess thermal effects. XRD (X-ray diffraction) and TEM (Transmission electron microscope) were used to determine the layer dispersion of the C30B within the PLA. An increase in the interlayer spacing of a sandwich structure corresponding to a partial exfoliation of the C30B was found, leading to the creation of small particles at nanoscale of one (1.29 nm) to eight (11.76 nm) platelets. Also, GPC (Gel permeation chromatography) was used to evaluate the molecular weight decay of neat PLA and its nanocomposites due to thermal processing and subsequent artificial weathering exposure. From thermal processing, a more significant decrease of polydispersity in amorphous PLA than in semicrystalline PLA counterparts could be observed. First order fitting of molecular weight decay of samples versus time of exposure under artificial weathering was found for all materials tested. It was observed that the addition of clay favored PLA degradation in amorphous PLA, in comparison with semicrystalline PLA in both thermal processing and artificial weathering. Moreover, a possible effect of C30B interactions with PLA chains under artificial weathering could be postulated.
机译：研究了在人工风化条件下，在长达360 h的时间内，对有机改性蒙脱土Cloisite30B（C30B）负载5 wt％的无定形和半结晶级纳米复合材料，聚乳酸酸（PLA）分子量的降低。建立了人工和自然风化之间的关系。通过将C30B在PLA基体中混合使用两个阶段的挤出，然后进行注塑成型，来制备纳米复合材料。此外，为了评估热效应，我们还研究了通过单步注射以及分两步挤出再注射制备的PLA基质中不含C30B的材料。 XRD（X射线衍射）和TEM（透射电子显微镜）用于确定PLA中C30B的层分散。发现夹层结构的层间间距增加，对应于C30B的部分剥落，导致在一个纳米级（1.29 nm）至八个（11.76 nm）血小板中形成了小颗粒。此外，GPC（凝胶渗透色谱法）用于评估纯PLA及其纳米复合材料由于热处理和随后的人工风化作用而引起的分子量衰减。通过热处理，可以观察到无定形PLA中的多分散性比半结晶PLA中的多分散性更明显。对于所有测试的材料，发现样品分子量衰减与人工风化下暴露时间的一阶拟合。观察到在热加工和人工老化中，与半结晶PLA相比，粘土的添加有利于PLA在非晶PLA中的降解。此外，可以推测在人工风化作用下C30B与PLA链相互作用的可能影响。

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