Process-level impact assessment of wood waste pre-treatments: Isolating environmental trade-offs through a gate-to-gate life cycle approach

Abstract

Pre-treatment of wood waste represents a technically necessary but often methodologically underexplored stage in the life cycle of wood–plastic composites (WPCs). This study applies an attributional, gate-to-gate life cycle assessment to quantify the environmental implications of five representative laboratory-scale conditioning routes, including three chemical compatibilization pathways (SA1–SA3), thermo-mechanical pelletization (SB) and thermo-physical thermal modification (SC). Life cycle inventories were reconstructed from experimentally reported parameter ranges documented in laboratory-scale studies, and the resulting scenarios were modelled in SimaPro. Impact assessment was performed using three complementary methods, ReCiPe 2016 Midpoint (H), EF 3.0, and Cumulative Energy Demand, to capture climate, resources, and toxicity-related burdens. Main results indicate that chemically intensive scenarios generally exhibit higher impacts than energy-driven treatments, with SA1 showing the highest values across climate, toxicity, and resource-related categories (e.g., 0.91 kg CO₂-eq, 4.09 CTUe, 2.76 Pt). SB and SC, which rely primarily on electricity and moderate heat inputs, display comparatively lower burdens, although SC shows a more intermediate profile due to its exclusive dependence on electricity. To explore whether alternative reagent choices may offer environmental advantages, a set of substitution scenarios was developed based on options documented in experimental literature. The outcomes showed divergent effects: while the replacement of acetic anhydride with maleic anhydride in SA1 lead to modest reductions in several categories, other substitutions, such as those involving citric acid, exhibited mixed effects. Results suggested that the environmental performance of “lower-severity” or bio-based reagents strongly depends on their upstream production profiles and should be evaluated on a case-by-case basis. Overall, the study highlights the relevance of conditioning steps within early-stage environmental assessment of WPC systems and emphasizes the importance of transparent boundary definition and scenario analysis when evaluating alternative pre-treatment strategies