采用扫描电子显微镜(SEM)和透射电子显微镜(TEM)考察了热塑性酚醛树脂(Novolak)增容聚甲醛(POM)／丁腈橡胶(NBR)共混物的亚微相态。通过对共混物的TEM及经刻蚀后脆性断裂面的SEM观察发现,对于POM／NBR共混物,NBR在基体中呈现不规则的“海-岛”结构,由于两相不相容导致分散相NBR在基体中的分散性很差。对于POM／NBR／Novolak共混物,在NBR含量为30%时,共混物仍然呈现“海-岛”结构,但NBR在基体中的分散性有所提高;当NBR含量为40%时,NBR在基体中呈现带状网络结构相态。文中提出了Novolak增容POM／NBR共混物的增韧机制,即高含量的NBR通过Novolak的增容作用,在POM中基体形成互锁的带状网络结构;当材料受到外力冲击时,这种橡胶网络带能够终止受外力作用而在基体中产生的银纹和剪切屈服,增加了共混物的破裂能,从而使共混物的韧性得到显著提高。
The morphology of polyacetal(POM) and nitrile-butadiene(NBR) blends compatibilized with Novolak was investigated by SEM and TEM. POM／NBR(60／40) blends was found to exhibit a sea-island morphology, where NBR was the dispersed phase sea and POM was continuous phase island. Although POM／NBR／Novolak(70／30／5) blends still showed a sea-island structure, the despersion of NBR in POM matrix was improved because of the improvement of interface adhesion between two phase. The morphology of POM／NBR／Novolak(60／40／5) blends show that the ternary blends is not in a structure of sea-island but of a physical elastomer network. The elastomer network impedes the growth of craze and promotes the shear deformation of POM matrix. As a result, a large amount of impact energy can be adsorbed and the super-toughness is thus obtained, A novel toughening mechanism is proposed on the basis of this research.
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