聚丙烯结晶行为的PVT研究

通过受限液体PVT测量技术对等规聚丙烯的结晶行为进行了研究,采用PVT等压测量模式描述了不同压力场下半结晶聚合物的结晶过程.结果表明,随着压力的升高,等规聚丙烯分子链间的相互作用增强,使得等规聚丙烯分子链段更容易排入晶格中,这是结晶温度和结晶速度升高的主要因素.通过对数据拟合,建立了压力对等规聚丙烯结晶过程参数的影响公式.对Jeziorny结晶动力学模型进行改进,并研究了压力对等规聚丙烯结晶动力学的影响,结果发现,当结晶度大于0.08时,结晶动力学拟合曲线呈较好的线性,分析结果可以对结晶过程的变化机理进行合理地预测,在小于200 MPa压力环境下,等规聚丙烯的结晶生长方式仍是球晶生长模式,晶体的生长符合二维片晶生长方式,自由体积的减小是结晶速率加快的主要原因之一.

PVT STUDIES ON CRYSTALLIZATION BEHAVIORS OF iPP

The crystallization behaviors and crystallization kinetics of iPP in pressure field were investigated by confining-fluid pressure-volume-temperature(PVT) measurement technique.The absolute specific volume of the polymer can be obtained by correcting the relative volume difference with the specific volume of the confining fluid.So it was an effective method by confining-fluid pressure-volume-temperature(PVT) measurement to catch information of crystallization of semicrystalline polymers.The results revealed that molecular chain of iPP was introduced more easily into crystal lattice with powerful free energy of molecular chain improved by pressure field so as to improve the crystallization temperature and crystallization speed.Formula of crystallization temperature with pressure was found by means of data fitting.It was attempted to build a crystallization kinetics model by improving Jeziorny equation which can forecast the crystallization process of the iPP in pressure environment.The results showed that crystallization curves can be suitable for explaining some changes of the crystallization of iPP when crystallinity exceeded 0.08.Growth pattern of crystallization accorded with the behavior of 2-dimensional crystallites.Decrease of free volume was one of the main causes for the increase of crystallization rate.