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.