Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, CH-1700, Fribourg, Switzerland.
Adv Mater. 2019 Apr;31(14):e1807212. doi: 10.1002/adma.201807212. Epub 2019 Jan 24.
A new concept for the design of self-toughening thermoplastic polymers is presented. The approach involves the incorporation of plasticizer-filled microcapsules (MCs) in an intrinsically rigid and brittle matrix polymer. The intriguing adaptability that this simple tactic enables is demonstrated with composites composed of a poly(lactic acid) (PLA) matrix and 5-20% w/w poly(urea-formaldehyde) (PUF) MCs that contained hexyl acetate as plasticizer. At low strain (<1.5%), the glassy PLA/MC composites remain rigid, although the intact MCs reduce the Young's modulus and tensile strength by up to 50%. While the neat PLA shows brittle failure at a strain of around 2.5%, the composites yield in this regime, because the MCs rupture and release their plasticizing cargo. This effect leads up to 25-fold increase of the elongation at break and 20-fold increase of the toughness vis-à-vis the neat PLA, while the impact on modulus and ultimate stress is much smaller. Ballistic impact tests show that the self-toughening mechanism also works at much higher strain rates than applied in tensile tests and the operating mechanism is corroborated through systematic thermomechanical studies that involved dynamic mechanical testing and thermal analysis.
提出了一种设计自增韧热塑性聚合物的新概念。该方法涉及在固有刚性和脆性基体聚合物中加入增塑剂填充微胶囊（MCs）。用聚乳酸（PLA）基体和 5-20wt%w/w 的含有己酸乙酯作为增塑剂的聚脲甲醛（PUF）MCs 组成的复合材料证明了这种简单策略所具有的适应性。在低应变（<1.5%）下，玻璃态 PLA/MC 复合材料仍然保持刚性，尽管完整的 MCs 使杨氏模量和拉伸强度降低了多达 50%。尽管纯 PLA 在应变约为 2.5%时表现出脆性破坏，但在该区域复合材料会屈服，因为 MC 会破裂并释放其增塑剂。与纯 PLA 相比，这种效应使断裂伸长率增加了 25 倍，韧性增加了 20 倍，而对模量和极限应力的影响要小得多。弹道冲击试验表明，自增韧机制在比拉伸试验更高的应变率下也能起作用，并且通过涉及动态力学测试和热分析的系统热机械研究证实了其工作机制。
