Development of impact-resistant polymeric materials by nano structure control

发展了评价聚合物和复合材料冲击断裂韧性的新实验技术。然后通过测试包括可生物降解聚合物和复合材料在内的各种材料来检验该技术的有效性和适应性。这些技术也被应用于这些材料，在纳米和微观水平上改变了它们的结构。对冲击断裂机理进行了研究。通过测量试样材料断裂后的动态响应和残余变形，研究了冲击断裂机理。由于聚合物的断裂韧性通常取决于材料的粘度和裂纹扩展引起的动态效应，因此分析了动态效应和非弹性效应。在影响分析中考虑了这两种影响。施加在试样上的外部功被划分为三个分量：弹性能、非弹性能和产生新断裂面的断裂能。估算了能量释放率，详细研究了冲击断裂机理。通过退火、共混和/或与不同的可生物降解材料混合来改性可生物降解聚合物和复合材料的结构。测试了试样在静载荷和冲击载荷下的断裂韧性，并利用偏光显微镜和扫描电镜观察了断口和裂纹前沿损伤区的形貌。作为控制裂纹扩展的断裂参数，利用载荷和位移图确定了能量释放率，结果表明，从纳米和微观层面控制结构可以明显提高断裂韧性。

New experimental techniques for evaluating the impact fracture toughness of polymers and composite materials were developed. The validity and adaptability of the techniques were then examined by testing the various materials including biodegradable polymers and composites. The techniques were also applied to these materials which changed their structures in the nano- and micro-scopic level. The impact fracture mechanism was then investigated.The impact fracture mechanism was studied by measuring the dynamic response and residual deformation of the specimen materials after fracture. The dynamic and non-elastic effects were analyzed, because the fracture toughness of polymers is generally dependent on both the viscosity of material and the dynamic effect due to the crack propagation. These two effects were taken into consideration in the impact analysis. The external work applied to the specimen was partitioned into three components : the elastic energy, non-elastic energy, and fracture energy for creating a new fracture surface. The energy release rate was estimated to examine the impact fracture mechanism in detail.The structures of biodegradable polymers and composite materials were modified by annealing, blending and/or mixing with different biodegradable materials. The fracture toughness of the specimens was measured under static and impact loadings, and the morphology of the fracture surfaces and damage zone ahead of the crack front were also examined using polarizing microscopy and scanning electron microscopy. As a fracture parameter that controls crack growth, the energy release rate was determined using a load and displacement diagram, and it was shown that the fracture toughness can be clearly improvable by controlling the structures by nano- and micro-scopic level.