Effects of rare earth nucleating agent WBG-Ⅱ on crystallization behaviors of isotactic polybutene-1
Rare earth nucleating agent WBG-Ⅱ was selected and melt blended into isotactic polybutene-1(iPB-1).The effects of WBG-Ⅱ on crystallization behaviors and crystalline structures of iPB-1 were stud-ied by differential scanning calorimetry(DSC),wide angle X-ray diffractometer(WAXD)and polarizing microscope(POM).The results showed that incorporation of WBG-Ⅱ into iPB-1 does not affect the melt as-crystallized crystal form of form Ⅱ but with increasing crystallization temperature Tc,peak,melting point Tm,Ⅱ and crystallinity Xc,Ⅱ of iPB-1 form Ⅱ,especially at a low WBG-Ⅱ content.With more WBG-Ⅱ in-corporated,the Tc,peak,Tm,Ⅱ and Xc,Ⅱ all increased slowly to a plateau,showing a decreasing promotion effect on iPB-1 melt crystallization.Under the same isothermal crystallization temperature Tc,incorpora-tion of WBG-Ⅱ resulted in shorter half crystallization time t1/2 and higher spherulite radius growth rate G,proving the promotion effect on iPB-1 melt as-crystallization into form Ⅱ.With Tc increasing,the promo-tion effect weakens.For iPB-1 melt crystallization into form Ⅱ,the random coils of iPB-1 in the melt needs to transit into 11/3 helices.The promotion effect of WBG-Ⅱ on iPB-1 crystallization into form Ⅱ means WBG-Ⅱ incorporation favors the transition from random coils to 11/3 helices of iPB-1,resulting a needed critical cooling rate øc to avoid iPB-1 crystallization while cooling a melt to the glass transition tem-perature Tg.The enhanced iPB-1 chain conformation adjustment ability weakens the"strong melt"charac-teristics of iPB-1.The results would shed lights on understanding of polymer crystallization as well as on research and development of iPB-1 nucleating agents.
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