Extrusion foaming of linear and branched polypropylenes – input of the thermomechanical analysis of pressure drop in the die

IF 1.1 4区 工程技术 Q4 ENGINEERING, CHEMICAL
C. Sandino, E. Peuvrel-Disdier, J. Agassant, P. Laure, S. Boyer, G. Hibert, Y. Trolez
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Abstract

Abstract This paper aims at a better understanding of the polypropylene (PP) physical extrusion foaming process with the objective of obtaining the lowest possible foam density. Two branched PPs were compared to the corresponding linear ones. Their shear and elongation viscosities were measured as well as their crystalline properties. Trials were conducted in a single screw extruder equipped with a gear pump and a static mixer cooler to adjust the melt temperature at the final die. The effect of decreasing this temperature on the PP foamability and on the pressure drop in the die was analyzed. The foam density of branched PPs varies from high to low values while decreasing the foaming temperature. In the same processing conditions, the foam density of linear PPs does not decrease so much, as already evidenced in the literature. The foamability transition coincides with an increase of the pressure drop in the die. The originality of the work lies in the thermomechanical analysis of the polymer flow in the die which allows the identification of the relevant physical phenomena for a good foamability. The comparison of the experimental pressure drops in the die and the computed ones with the identified purely viscous behavior points out the influence of the foaming temperature and of the PP structure. At high foaming temperature the discrepancy between experimental measurements and the computed pressure drops remains limited. It increases when decreasing the foaming temperature, but the mismatch is much more important for branched PPs than for linear ones. This difference is analyzed as a combination of the activation energy of the viscosity, the elongational viscosity in the convergent geometry of the die which is much more important for branched PPs than for linear ones, and the onset of crystallization which occurs at higher temperature for branched PPs than for linear PPs.
直链和支链聚丙烯的挤出发泡——模具中压降的热机械分析输入
摘要本文旨在更好地理解聚丙烯(PP)物理挤出发泡过程,以获得尽可能低的泡沫密度。将两种支链PP与相应的线性PP进行比较。测量了它们的剪切粘度和伸长率以及它们的结晶性能。试验在配备有齿轮泵和静态混合冷却器的单螺杆挤出机中进行,以调节最终模具的熔体温度。分析了降低该温度对PP发泡性和模具压降的影响。支化PP的泡沫密度从高到低变化,同时降低发泡温度。在相同的加工条件下,线性PPs的泡沫密度不会降低那么多,正如文献中已经证明的那样。发泡性转变与模具中压降的增加相一致。这项工作的独创性在于对模具中聚合物流动的热机械分析,这使得能够识别相关的物理现象以获得良好的发泡性。模具中的实验压降和计算压降与所确定的纯粘性行为的比较指出了发泡温度和PP结构的影响。在高发泡温度下,实验测量值和计算压降之间的差异仍然有限。当降低发泡温度时,它会增加,但失配对支链PP比线性PP更重要。这种差异被分析为粘度的活化能、模具收敛几何形状中的拉伸粘度的组合,拉伸粘度对支链PP比线性PP重要得多,并且结晶的开始发生在支链PP比线型PP在更高的温度下。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
International Polymer Processing
International Polymer Processing 工程技术-高分子科学
CiteScore
2.20
自引率
7.70%
发文量
62
审稿时长
6 months
期刊介绍: International Polymer Processing offers original research contributions, invited review papers and recent technological developments in processing thermoplastics, thermosets, elastomers and fibers as well as polymer reaction engineering. For more than 25 years International Polymer Processing, the journal of the Polymer Processing Society, provides strictly peer-reviewed, high-quality articles and rapid communications from the leading experts around the world.
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