弹性体共混改性对聚甲醛结晶行为及力学性能的影响

Influence of Blending Elastomers on the Crystallization Behavior and Mechanical Properties of Polyoxymethylene

本文采用不同弹性体——热塑性聚氨酯(TPU)和聚乙烯弹性体乙烯-辛烯共聚物(POE)对聚甲醛(POM)进行增韧改性,研究了纯POM、POM/TPU (85/15)、POM/POE (85/15)三种体系的结晶行为和微观结构演变对材料力学性能的影响。结果表明,由于纯POM在结晶过程中能够形成较大的球晶,球晶边缘无定形区分子耗尽而形成微孔,这些微孔结构导致POM具有较差的缺口冲击强度。弹性体的加入可显著提高POM的结晶速率并大幅减小其球晶尺寸,因此有效减少了微孔数量,从而增加POM的韧性。比较而言,POM/TPU (85/15)的抗冲强度提升更为明显,主要原因在于二者良好的相容性和形成的大量细小球晶;而对于POM/POE体系,二者相容性差,且两者界面对球晶形貌起到了限制作用,因此降低了机械性能。

In order to improve the toughness of polyoxymethylene （POM）, two elastomers, namely thermoplastic polyurethane （TPU） and polyolefin elastomer （POE, ethylene-octane copolymer）, were blended. The influence of crystallization behavior and microstructure evolution on the mechanical properties of pure POM, POM/TPU （85/15） and POM/POE （85/15） blends were examined. Large size spherulites of pure POM was found under polarizing microscope and a large number of micron-scale voids exist on the fracture surface of pure POM, which might be the main contribution to its poor notch impact strength. The voids as the defects of the material tend to form at the edge of the spherulites during the cooling or at the late stage of isothermal crystallization. Blending of the elastomers could significantly accelerate the crystallization rate of POM while reducing the size of the spherulites, which will reduce the number of voids and thus improve the toughness. For POM/TPU 85/15 blend, good compatibility between the two components and the large number of fine crystals coherently determine its significantly improved toughness and better tensile strength. While the poor compatibility between POM and POE with the interface restricted spherulite morphology make it exhibits discounted mechanical properties.