Comparative life cycle assessment of one-step and two-step injection molding compounding for manufacturing recycled glass fiber/polypropylene composites

Despite advances in fiber-reinforced polymer recycling, few studies have assessed the environmental impacts of manufacturing processes and their compatibility with recycled composites. This study presents a comparative Life Cycle Assessment (LCA) of a conventional compounding plus granulation and injection molding process, and an innovative one-step injection molding compounding (IMC) for the cleaner production of composites using virgin and recycled polypropylene reinforced with mechanically recycled glass fibers. Two LCA perspectives, manufacturing and component, differ in functional unit, system boundaries, and material modelling. The manufacturing perspective evaluates cradle-to-grave processing impacts per geometrically identical item, while the component perspective includes raw material acquisition and end-of-life treatment of the component compared at equal tensile strength. Both perspectives show that IMC reduces environmental impacts across all 16 EF3.1 impact categories for all material combinations. Infrastructure and energy use are major contributors in the manufacturing perspective, while manufacturing accounts for roughly half of total impacts in the component perspective considering a passive use phase. Results are sensitive to processing waste and mass variations based on process-induced differences in composite quality. The strength-based equivalence applied here is simplified and should be adapted for industrial design contexts. Material modelling approaches, the zero-burden approach or the Circular Footprint Formula, influence virgin polypropylene impacts but provide comparable results for recycled materials. This deviation from previous findings may be case-specific, highlighting uncertainties in the formula's parameters, which require region- and market-specific evaluation. The study also discusses implications of IMC's low technological readiness and experimental setup, providing insights for other assessments considering scale effects. • Recycled materials from post-industrial organosheet and post-consumer packaging waste. • LCA methodological choices from manufacturing and component perspectives. • Reduction of environmental impacts due to one-step injection molding compounding. • Further research on specific field of application and industrial upscaling required.