Takayama Tetsuo, Shibazaki Rin
Graduate School of Organic Materials Science, Yamagata University, Yonezawa 992-8510, Japan.
Polymers (Basel). 2023 Oct 20;15(20):4167. doi: 10.3390/polym15204167.
The molecular orientation formed by melt-forming processes depends strongly on the flow direction. Quantifying this anisotropy, which is more pronounced in polymer blends, is important for assessing the mechanical properties of thermoplastic molded products. For injection-molded polymer blends, this study used short-beam shear testing to evaluate the mechanical anisotropy as a stress concentration factor, and clarified the correlation between the evaluation results and the phase structure. Furthermore, because only shear yielding occurs with short-beam shear testing, the yielding conditions related to uniaxial tensile loading were identified by comparing the results with those of three-point bending tests. For continuous-phase PP, the phase structure formed a sea-island structure. The yield condition under uniaxial tensile loading was interface debonding. For continuous-phase PS, the phase structure was dispersed and elongated in the flow direction. The addition of styrene-ethylene-butadiene-styrene (SEBS) altered this structure. The yielding condition under uniaxial tensile loading was shear yielding. The aspect ratio of the dispersed phase was found to correlate with the stress concentration factor. When the PP forming the sea-island structure was of continuous phase, the log-complex law was sufficient to explain the shear yield initiation stress without consideration of the interfacial interaction stress.
熔体成型过程形成的分子取向强烈依赖于流动方向。量化这种在聚合物共混物中更为显著的各向异性，对于评估热塑性模塑制品的机械性能很重要。对于注塑成型的聚合物共混物，本研究采用短梁剪切试验来评估作为应力集中因子的机械各向异性，并阐明了评估结果与相结构之间的相关性。此外，由于短梁剪切试验仅发生剪切屈服，通过将结果与三点弯曲试验的结果进行比较，确定了与单轴拉伸载荷相关的屈服条件。对于连续相PP，相结构形成海岛结构。单轴拉伸载荷下的屈服条件是界面脱粘。对于连续相PS，相结构在流动方向上分散并拉长。苯乙烯-乙烯-丁二烯-苯乙烯（SEBS）的添加改变了这种结构。单轴拉伸载荷下的屈服条件是剪切屈服。发现分散相的长径比与应力集中因子相关。当形成海岛结构的PP为连续相时，对数复数定律足以解释剪切屈服起始应力，而无需考虑界面相互作用应力。
