Article
  • Study on the Pressure-Volume-Temperature Properties of Polypropylene at Various Cooling and Shear Rates

  • Pengcheng Xie*, Huaguang Yang*, Tianze Cai*, Zheng Li*, Yuelin Li*, and Weimin Yang*,**,†

  • *College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing, PRC
    **State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing, PRC

  • 다양한 냉각속도와 변형률속도에서 폴리프로필렌의 압력-부피-온도 특성에 관한 연구
Abstract

To understand the pressure-volume-temperature (PVT) properties of polymer in injection process, a dilatometer with high cooling rate (up to 25 ℃/s) and shear rate (up to 320 s-1) was developed. The working pressure and temperature of the dilatometer range from 0 to 100 MPa, and from 30 to 300 ℃, respectively. With this instrument, a crystalline polymer polypropylene (PP) was employed to study the effects of cooling rate, shear rate, pressure and their coupling effect on its PVT properties. It was demonstrated that the cooling rate showed a significant effect on the PVT properties. With the increase of cooling rate, the transition temperature of PP from melt state to crystallization decreases gradually and the temperature range of crystallization was also extended. Shear increased the transition temperature of PP from melt state to crystallization. Meanwhile, the initial temperature of shear and crystalline segment was shifted to a higher temperature region with increasing shear duration or shear rate. Above the transition temperature, the effect of shear on the PVT properties weakened gradually with increasing the initial temperature. The coupling analysis of cooling and shear processes showed that increase in cooling rate was enhanced the effect of shear on the transition temperature of PP from melt state to crystallization.


Keywords: pressure-volume-temperature properties, cooling rate, shear rate, crystallization.

Introduction

The PVT properties of polymers are usually used to describe the relationship between specific volume (V), temperature (T) and pressure (P), which offer compressibility and thermal expansion of melting or solid polymer within temperature and pressure range during injection molding process. The simulation software of injection molding usually describes the PVT property of polymer using double domain Tait equation,1 which is obtained by fitting the experimental data, in which the correctness totally depends on the accuracy of the experimental results of the PVT parameters.2
In the past decade, the researchers have been constantly investigating the influence of cooling and shear on the polymer PVT property. Results revealed that increasing cooling rate decreased the transition temperature of polypropylene (PP) while both the temperature range of transformation process and final specific volume was increased.3-8 Besides, applied shear increased the transition temperature and shifted the crystallization region to the high temperature area, and this phenomenon became more obvious with increasing pressure.9-12 It is concluded that the cooling and shear conditions can cause the offset of the PVT property curve, which cannot be ignored. Therefore, the offset of the PVT property curve caused by cooling and shear conditions will influence the precision of simulation results. This paper presents a novel PVT testing apparatus with the function of cooling and shear.13 The dynamic evolution of the PVT properties of PP was explored at high cooling and shear rate. This work provides theoretical basis for the quality control of the molding products

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  • Polymer(Korea) 폴리머
  • Frequency : Bimonthly(odd)
    ISSN 0379-153X(Print)
    ISSN 2234-8077(Online)
    Abbr. Polym. Korea
  • 2022 Impact Factor : 0.4
  • Indexed in SCIE

This Article

  • 2018; 42(2): 167-174

    Published online Mar 25, 2018

  • 10.7317/pk.2018.42.2.167
  • Received on Mar 22, 2017
  • Revised on Jul 11, 2017
  • Accepted on Oct 1, 2017

Correspondence to

  • Weimin Yang

  • *College of Mechanical and Electrical Engineering, Beijing University of Chemical Technology, Beijing, PRC
    **State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing, PRC

  • E-mail: yangwm@mail.buct.edu.cn
  • ORCID:
    0000-0001-5471-3151