Crystallization of linear polyethylene from melt in isothermal compression
Crystallization of linear polyethylene from melt in isothermal compression
复制标题
等温压缩中线性聚乙烯熔体的结晶
DOI：
10.1002/app.1992.070440109
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
A. Galeski
中科院分区：
文献类型：
--
作者：
T. Kowalewski;A. Galeski
用自制的微型压力装置研究了线性聚乙烯的结晶和初成核。结果表明，在等温压缩过程中，线性聚乙烯熔体以恒定速率发生结晶。在最快的转换率范围内，结晶具有等压特性。发生结晶时的压力水平随着结晶温度和/或压缩率的增加而增加。在仪器中达到的最高压力下（大约），结晶具有球晶特征。600 MPa)。令人惊讶的是，在熔体压缩过程中，平均球晶尺寸、结晶度和片层厚度与结晶压力和结晶温度没有相关性，但与压缩率有很强的相关性。在250mpa以下和300mpa以上，结晶在压力下进行，确保了持续的过冷。300mpa以上的过冷度比250mpa以下的过冷度低约10℃。在250 ~ 300 MPa的压力下，观察到初生成核和球晶结晶的变化，这与晶体从正交对称到伪六方对称的转变有关。在等温熔体压缩过程中，线性聚乙烯的分子量对结晶没有明显的影响。
Crystallization and primary nucleation of linear polyethylene has been studied by means of a custom-made miniature pressure apparatus. It has been shown that during isothermal compression of linear polyethylene melt at a constant rate crystallization occurs. In the range of fastest conversion rates the crystallization assumes isobaric character. The level of pressure at which the crystallization occurs increases with the increase of the crystal-lization temperature and/or with the increase of the compression rate. The crystallization has a spherulitic character up to the highest pressure achieved in the apparatus (approx. 600 MPa). Surprisingly, there are no dependencies of average spherulite size, degree of crystallinity, and lamellae thickness on the pressure and the temperature of crystallization during melt compression, but there is a strong relation to the compression rate. Below 250 MPa and above 300 MPa the crystallization proceeds under pressure, ensuring a constant undercooling. The undercooling for the pressure above 300 MPa is approximately 10°C lower than that for the pressure below 250 MPa. For the pressure 250–300 MPa a change in a primary nucleation and spherulite crystallization has been observed that is connected with the transformation from orthorhombic to pseudohexagonal symmetry of crystals. No noticeable effect of molecular weight of linear polyethylene on crystallization during iso-thermal melt compression has been observed.