Kościuszko Artur, Marciniak Dawid, Sykutera Dariusz
Department of Manufacturing Techniques, UTP University of Science and Technology, Kaliskiego 7, 85-796 Bydgoszcz, Poland.
Materials (Basel). 2020 Dec 23;14(1):22. doi: 10.3390/ma14010022.
Dimensions of the injection-molded semi-crystalline materials (polymeric products) decrease with the time that elapses from their formation. The post-molding shrinkage is an effect of secondary crystallization; the increase in the degree of polymer crystallinity leads to an increase in stiffness and decrease in impact strength of the polymer material. The aim of this study was to assess the changes in the values of post-molding shrinkage of polypropylene produced by injection molding at two different temperatures of the mold (20 °C and 80 °C), and conditioned for 504 h at 23 °C. Subsequently, the samples were annealed for 24 h at 140 °C in order to conduct their accelerated aging. The results of shrinkage tests were related to the changes of mechanical properties that accompany the secondary crystallization. The degree of crystallinity of the conditioned samples was determined by means of density measurements and differential scanning calorimetry. It was found that the changes in the length of the moldings that took place after removal from the injection mold were accompanied by an increase of 20% in the modulus of elasticity, regardless of the conditions under which the samples were made. The differences in the shrinkage and mechanical properties of the samples resulting from mold temperature, as determined by tensile test, were removed by annealing. However, the samples made at two different injection mold temperature values still significantly differed in impact strength, the values of which were clearly higher for the annealed samples compared to the results determined for the samples immediately after the injection molding.
注塑成型的半结晶材料（聚合物产品）的尺寸会随着其成型后时间的推移而减小。成型后收缩是二次结晶的结果；聚合物结晶度的增加会导致聚合物材料的刚度增加和冲击强度降低。本研究的目的是评估在两种不同模具温度（20°C和80°C）下注塑成型的聚丙烯成型后收缩值的变化，并在23°C下进行504小时的调湿处理。随后，将样品在140°C下退火24小时以进行加速老化。收缩试验结果与二次结晶伴随的力学性能变化相关。通过密度测量和差示扫描量热法测定调湿处理后样品的结晶度。结果发现，从注塑模具中取出后成型件长度的变化伴随着弹性模量增加20%，无论样品的制备条件如何。通过拉伸试验确定，由模具温度导致的样品收缩和力学性能差异通过退火消除。然而，在两个不同注塑模具温度值下制备的样品在冲击强度方面仍有显著差异，退火样品的冲击强度值明显高于注塑成型后立即测定的样品结果。
