Influence of load variation on the melt flow rate test for polymers

Abstract

Polymeric materials are used for various purposes, ranging from the manufacture of product packaging, automotive parts, and toys to household utensils, geomembranes, and several other applications. Due to this wide variety, polymers must possess key characteristics such as mechanical strength, chemical barrier properties to prevent contamination, thermal and electrical insulation, and resistance to degradation caused by chemicals, depending on the specific product. For each desired product, there are polymers that demonstrate better capabilities based on performance or production cost. Polymers such as HDPE (High-Density Polyethylene), LLDPE (Linear Low-Density Polyethylene), and EVA (Ethylene-Vinyl Acetate) are used as raw materials in the manufacture of polymeric products, and their processing demands different machine conditions. In addition to the polymeric raw material, manufacturing utilizes additives such as dyes, flow improvers, and UV radiation protection, which influence the processing capacity of these materials. One way to evaluate this influence and control the process is through the Melt Flow Rate (MFR) test, which assesses the effect of processing temperature and applied force on polymer rheology. The melt flow test allows for the variation of force and temperature in the equipment, enabling an evaluation of these parameters on polymers in an extrusion process with a calibrated orifice. To evaluate the effect of the extrusion force on the polymers, HDPE, LLDPE, and EVA were tested in both virgin state and additive-enhanced with mineral coal, varying the applied force through the system's mass. The results indicate that the use of mineral coal increased the melt flow rate for HDPE and LLDPE compared to the virgin material; however, increasing the force reduced the difference between the virgin and additive-enhanced materials. EVA showed a characteristic reduction in fluidity with the addition of coal, and the increase in force led to an even greater decrease compared to the virgin material, from 2% (3.8 kg mass) to 13% (21.6 kg mass)