Life-Cycle Assessment of Laboratory-Scale Extrusion of Virgin and Recycled Polyolefins: Influence of Operating Duration on Life-Cycle Inventory Development.

Life-cycle assessment (LCA) is widely used to evaluate the environmental performance of polymer processing and mechanical recycling systems, with its reliability fundamentally dependent on the quality and representativeness of the underlying life-cycle inventory (LCI) data. Laboratory-scale extrusion is extensively employed to generate inventory data for polymer processing, plastic waste mechanical recycling, and material development; however, the influence of operating duration on representative LCI development and the resulting environmental impact assessment has received little attention. Because startup energy represents a fixed contribution to each extrusion cycle, short-duration laboratory experiments may generate non-representative life-cycle inventories, leading to systematic overestimation of specific energy consumption (SEC) and associated environmental impacts. In this study, laboratory-scale co-rotating twin-screw extrusion of commercial virgin-grade and post-consumer high-density polyethylene (HDPE) and polypropylene (PP) was investigated to develop a runtime-dependent LCI framework. Extrusion trials at 1 and 3 h were experimentally implemented, while 8 and 24 h continuous-operation cases were developed as extrapolated runtime scenarios, which were subsequently evaluated using gate-to-gate LCA to quantify climate change (CC) and cumulative energy demand (CED) associated with extrusion electricity consumption. The measured melt flow index (MFI) ranged from 0.365 to 8.497 g 10 min-1, reflecting differences in material flowability and throughput. Specific energy consumption decreased from 0.931-1.282 kWh kg-1 for 1 h operation to 0.578-0.838 kWh kg-1 for 24 h operation as fixed startup energy was distributed over a larger processed mass. Consequently, gate-to-gate climate change impacts decreased from 0.483-0.664 to 0.300-0.434 kg CO2-eq kg-1, while cumulative energy demand decreased from 10.564-14.547 to 6.559-9.509 MJ kg-1. Startup energy accounted for 36-40% of total electricity consumption during 1 h operation but less than 3% during 24 h operation, demonstrating that laboratory operating duration can substantially influence the calculated inventory under otherwise fixed modeling conditions and consequently influence calculated environmental impacts without changes in material, equipment, or processing conditions. Sensitivity analysis showed that increasing the adopted operating power from 9 to 11 kW increased SEC by approximately 13-14% at 1 h and approximately 22% at 24 h, whereas varying fixed-cycle energy by ±20% changed SEC by approximately ±7-8% at 1 h but by less than ±1% at 24 h. The results demonstrate that representative laboratory-derived extrusion inventories depend on both fixed-energy allocation and material throughput and that explicit separation of experimental observations, modeling assumptions, and extrapolated runtime scenarios can improve the transparency and comparability of polymer-processing LCI data.