酚醛树脂增容聚甲醛/丁腈橡胶共混物的力学性能与结晶形态

STUDY ON MECHANICAL PROPERTIES AND CRYSTALLITE OF POLYACETAL/NITRILE BUTADIENE RUBBER BLENDS COMPATIBILIZED WITH VOVOLAK

考察了热塑性酚醛树脂 ( Novolak)增容聚甲醛 ( POM) /丁腈橡胶 ( NBR)共混物的力学性能、断裂形貌和结晶形态。研究发现 ,POM与 NBR共混后由于不相容而导致共混物力学性能下降 ;共混物中添加 Novolak后 ,在 NBR含量为 4 0 %时发生“脆 -韧”转变 ;其中 NBR- 2 6对 POM的增韧效果最佳。断裂形貌考察表明 ,POM/ NBR共混物的断裂面呈脆性断裂特征 ;而添加 Novolak后 ,共混物断裂面呈现延性断裂并出现丝状牵伸物。对共混物结晶形态观察发现 ,POM/ NBR共混物中 POM易形成大球晶 ,这是导致共混物缺口冲击强度下降的重要原因 ;而在共混物中添加 Novolak后 ,Novolak通过与 POM分子链间的相互作用 ,改变了 POM分子链固有的规程和排列方式 ,从而改变了 POM的结晶形态 。

The mechanical properties, fracture morphology, and crystallite of polyacetal(POM) and nitrile butadiene(NBR) blends compatibilized with Novolak were investigated. It is found the POM and NBR are immiscible system, and the interface adhesion and compatibilization of POM and Novolak in blends can be improved by addition of Novolak. As a result, Izod impact strength of blends increases remarkblely. The impact fracture surface showed a tough morphology for POM/NBR/Novolak blends and brittle one for POM/NBR blends. The crystallite morphology of the blends under polarized light microscopy demonstrated that the size of spherulites of POM/NBR blends was so large as to increase the brittleness of blends. The size of spherulites of blends could be sharply reduced by mixing with Novolak, which suggested that Novolak could diminish the inner stress concentration in blends and improve the toughness of blends.