Influence of injection molding process parameters on the mechanical properties of polypropylene and polyethylene parts

Abstract

Polypropylene (PP) and high-density polyethylene (HDPE) are the most common polymers in modern industrial plastic part production. Both materials can be easily shaped through injection molding, which is one of the most widespread processing methods for polymer materials. When manufacturing parts from PP and HDPE, it is necessary to achieve the required mechanical characteristics that depend on processing parameters (melt temperature, tool temperature, cooling time, etc.). This paper presents research on the impact of tool temperature on the tensile strength of injection-molded test specimens made from PP and HDPE. Since both materials contain amorphous and crystalline phases, changes in the ratio of phases are possible depending on the tool temperature, which leads to mechanical properties (tensile strength) changes. In the experimental assessment of tensile strength for polypropylene (PP) and high-density polyethylene (HDPE) specimens, conducted at varying tool temperatures (20°C, 50°C, and 80°C), notable disparities in tensile strength values were observed. These variations were attributed to alterations in the crystalline phase content within the materials, instigated by disparate cooling rates resulting from utilizing distinct tool temperatures.