Delpouve Nicolas, Faraj Hajar, Demarest Clément, Dontzoff Eric, Garda Marie-Rose, Delbreilh Laurent, Berton Benjamin, Dargent Eric
University of Rouen Normandie, INSA Rouen, CNRS, GPM, 76000 Rouen, France.
Polymers (Basel). 2021 Jul 12;13(14):2285. doi: 10.3390/polym13142285.
The impact of the immersion in water on the morphology and the thermomechanical properties of a biocomposite made of a matrix of poly (lactic acid) (PLA) modified with an ethylene acrylate toughening agent, and reinforced with miscanthus fibers, has been investigated. Whereas no evidence of hydrolytic degradation has been found, the mechanical properties of the biocomposite have been weakened by the immersion. Scanning electron microscopy (SEM) pictures reveal that the water-induced degradation is mainly driven by the cracking of the fiber/matrix interface, suggesting that the cohesiveness is a preponderant factor to consider for the control of the biocomposite decomposition in aqueous environments. Interestingly, it is observed that the loss of mechanical properties is aggravated when the stereoregularity of PLA is the highest, and when increasing the degree of crystallinity. To investigate the influence of the annealing on the matrix behavior, crystallization at various temperatures has been performed on tensile bars of PLA made by additive manufacturing with an incomplete filling to enhance the contact area between water and polymer. While a clear fragilization occurs in the material crystallized at high temperature, PLA crystallized at low temperature better maintains its properties and even shows high elongation at break likely due to the low size of the spherulites in these annealing conditions. These results show that the tailoring of the mesoscale organization in biopolymers and biocomposites can help control their property evolution and possibly their degradation in water.
研究了水浸对由用乙烯丙烯酸酯增韧剂改性的聚乳酸（PLA）基体和芒草纤维增强制成的生物复合材料的形态和热机械性能的影响。虽然未发现水解降解的证据，但水浸使生物复合材料的机械性能减弱。扫描电子显微镜（SEM）图片显示，水诱导的降解主要由纤维/基体界面的开裂驱动，这表明内聚性是控制生物复合材料在水环境中分解时需要考虑的一个主要因素。有趣的是，观察到当PLA的立构规整度最高以及结晶度增加时，机械性能的损失会加剧。为了研究退火对基体行为的影响，对通过增材制造制成的PLA拉伸棒在不同温度下进行结晶，填充不完全以增加水与聚合物之间的接触面积。虽然在高温下结晶的材料中出现明显的脆化，但在低温下结晶的PLA能更好地保持其性能，甚至由于在这些退火条件下球晶尺寸较小而表现出高断裂伸长率。这些结果表明，对生物聚合物和生物复合材料中的中尺度组织进行定制有助于控制其性能演变以及可能在水中的降解。
