Effects of nucleating agents on crystallization behavior and mechanical properties of high-fluid polypropylene

摘要

The effects of organic aluminum phosphate (NA-21) and rare earth organic coordination compounds (WBG), serving as α, β nucleating agents, on crystallization and mechanical properties of high-fluid polypropylene (PP) have been investigated. As determined by differential scanning calorimetry, the isothermal crystallization temperature of PP increased from 126.5 to 137.7℃ and 133.6℃with NA-21 and WBG, respectively. The two endothermal melting peaks of PP blending with WBG indicated the transformation of β-crystal. The wide-angle X-ray diffraction pattern and melting behavior of PP blending with WBG testified that a high proportion of β-crystal, which was more than 70%, was induced, while the crystal-phase of PP modified with NA-21 had little change. The mechanical properties of nucleated PP were tested by tensile testing machine and izod pendulum impact tester. A dramatic increment of impact strength, as high as 191%, was obtained for PP with the introduction of WBG, comparing to 132% by NA-21 addition. The impact fracture surfaces were observed by scanning electron microscope; the resistance of crack growth of nucleated PP was better than that of pure PP. Although flexural strength of PP improved in both scenarios, the influence of nucleators on yield strength of PP differed. Yield strength of PP increased by 8.5% when using 0.2 wt% NA-21, but decreased by 6% when using WBG at the same content. Therefore, WBG, a novel β-nucleator, played an essential role in enhancing impact strength of PP.