STUDIES ON ALPHA AND BETA FORMS OF ISOTACTIC POLYPROPYLENE BY CRYSTALLIZATION IN A TEMPERATURE-GRADIENT
STUDIES ON ALPHA AND BETA FORMS OF ISOTACTIC POLYPROPYLENE BY CRYSTALLIZATION IN A TEMPERATURE-GRADIENT
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DOI：
10.1002/pol.1977.180150405
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发表时间：
1977-01-01
影响因子：
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通讯作者：
GRYTE, CC
中科院分区：
文献类型：
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作者：
LOVINGER, AJ;CHUA, JO;GRYTE, CC
在高达300°C/cm的温度梯度下以低至3 μm/min的生长速率对全同立构聚丙烯（PP）样品进行区域固化。虽然β形核极其罕见，但β相很容易通过沿着取向α前沿的生长转变而引发。由于发现β相的生长速度比α相快得多，因此α到β的转变点在整个样品中发散，中断了定向α原纤维的生长。对区域固化PP的差示扫描量热法（DSC）研究表明，缓慢的生长速率、较高的温度梯度和熔体中较大的结晶度有利于β相的形成，所有这些因素都倾向于抑制成核。在1°C/min的加热速率下获得的大部分β-PP的差示热谱图显示β球晶实际熔融并重结晶成α形式。
Samples of isotactic polypropylene (PP) were zone‐solidified in temperature gradients up to 300°C/cm at growth rates down to 3 μm/min. Oriented α‐type spherulites were obtained only by nucleation. While β nucleation is extremely rare, the β phase is easily initiated by growth transformations along the oriented α front. Since the β phase was found to grow considerably faster than the α phase, the α‐to‐β transformation points diverge across the sample, interrupting growth of the oriented α fibrils. This causes subsequent nucleation to yield teardrop‐shaped α spherulites.Differential scanning calorimetry (DSC) studies of zone‐solidified PP show the β‐phase to be favored by slow growth rates, high temperature gradients, and large degrees of superheat in the melt—all of which tend to suppress nucleation. Differential thermograms of largely β‐PP obtained at a heating rate of 1°C/min show the actual melting and recrystallization of the β spherulites into the α form.