Reduced-energy processing of PLA/Talc biocomposites: Comparing in-mold crystallization and IR annealing

PLA is a promising bio-based alternative to fossil-based plastics, but its slow crystallization during injection molding often requires high mold temperatures, increasing cycle time and energy demand. This study evaluates two manufacturing routes for obtaining highly crystalline PLA/talc injection-molded parts: (i) high mold temperature molding at 100 °C and (ii) low mold temperature molding at 30 °C followed by infrared post-molding annealing. The comparison integrates manufacturability, crystallinity, surface quality, thermomechanical/mechanical response, and gate-to-gate specific energy consumption. Samples molded at 100 °C with a cooling time of 35 s (HM(35)) reached a crystallinity of 54.12 ± 0.65%, whereas samples molded at 30 °C (LM) showed 25.0 ± 0.23%. A 1-min IR treatment increased the crystallinity of LM-IR to approximately 54%. Under optimized annealing utilization and similar crystallinity, LM-IR reduced specific energy consumption by about 45% relative to HM(35). Ejection force measurements showed lower ejection demand during the high mold temperature molding, while surface roughness parameters including Ra, Rz, Rv, and Rp showed lower values at 100 °C. Maximum tensile strength was 48.98 ± 0.42 MPa for LM, compared to 44.66 ± 1.44 MPa for HM(35) and 43.50 ± 0.83 MPa for LM-IR. Heat deflection temperature increased from 55.0 ± 0.2 °C for LM to 145.81 ± 0.42 °C for HM(35) and 134.6 ± 1.4 °C for LM-IR. Overall, the study provides an integrated gate-to-gate comparison of two established routes for the investigated commercial PLA/talc composite and quantifies the process-property-energy trade-offs that govern route selection in similar nucleated PLA systems.