Screening Life Cycle Assessment comparing One-step and Two-step Injection Molding Compounding using Conservative and Optimistic Scenarios

Abstract

One-step injection molding compounding (IMC) is an innovative process to manufacture short-fiber-reinforced polymer composites. The aim of combining compounding and injection molding into one process is to enhance component quality and minimize environmental impacts. In this study, a screening Life Cycle Assessment (LCA) is conducted to evaluate and compare the environmental impacts of the IMC process with standard two-step manufacturing. Two scenarios for the IMC are considered, each differing in terms of machinery requirements, energy consumption, and material usage. Mechanically recycled polypropylene and glass fiber are used, and considered in the LCA employing a simple cut-off approach without awarding credits for substituting (primary) materials. The functional unit is the composite produced via the respective process, assuming equal functionality. Inventory data are obtained from initial experiments, literature, and the ecoinvent database. The impact assessment method selected is ReCiPe2016. Results indicate that the environmental performance improvement achieved by the IMC compared to the reference process is minimal in the conservative scenario where energy and material usage can be reduced but machinery usage is increased. However, in an optimistic scenario, the IMC can reduce the impacts of composite manufacturing by 34 %. The contributions at the midpoint level vary, and metal usage and energy consumption are the main contributors in all scenarios. A variation of the energy source for manufacturing shows the dependency of environmental impacts of components produced in both processes on the geographical location of production and its electricity supply. Methodological choices, such as the definition of the functional unit and modeling of recycled materials, have a large influence on LCA results, and alternative options are discussed.