The capability of a polymer to be molded by the injection molding process is referred to as its moldability. Injection molding technicians typically estimate moldability using a parameter known as the Melt Flow Index (MFI), but this metric can be misleading as it reflects the polymer’s ability to flow under specific conditions that may differ considerably from those encountered during injection molding. A more relevant parameter is the flow length, which represents the distance a polymer travels in a thin, cold mold cavity during the injection molding process. In this study, three types of commercial polypropylene were injection molded in cavity and the flow lengths were measured based on injection pressure and temperature. The outcomes were then compared to the polymer’s rheological properties. The findings indicate that the MFI is not a reliable indicator of polypropylene’s moldability. An empirical equation is suggested to predict polypropylene’s flow length as a function of injection pressure.

聚合物通过注射成型工艺成型的能力称为其可成型性。注塑技术人员通常使用称为熔体流动指数 (MFI) 的参数来估计可塑性，但该指标可能会产生误导，因为它反映了聚合物在特定条件下的流动能力，而这些条件可能与注塑过程中遇到的情况有很大不同。更相关的参数是流动长度，它表示注射成型过程中聚合物在薄的冷模具腔中行进的距离。在这项研究中，三种类型的商用聚丙烯在型腔中注射成型，并根据注射压力和温度测量流动长度。然后将结果与聚合物的流变特性进行比较。研究结果表明，MFI 并不是聚丙烯成型性的可靠指标。建议使用经验方程来预测聚丙烯的流动长度作为注射压力的函数。