Life cycle assessment of biocomposite material substitutions in window frames to implement circular design approach

Abstract

The construction sector is under increasing pressure to reduce embodied environmental impacts and support circular economy objectives through material-efficient and low-carbon design strategies. This study evaluates the environmental performance of component-level biocomposite substitutions in wood–aluminum window frames using a cradle-to-grave Life Cycle Assessment (LCA) in accordance with ISO 14040/44. Five scenarios were assessed for 1 m² of window: a baseline wood–aluminum frame (SC1), substitution of aluminum cladding (SC2), PVC glass holders (SC3), and Zamak handles (SC4) with a recycled polypropylene (rPP) + 30 wt% bleached softwood kraft pulp (BSKP) biocomposite, as well as a combined substitution scenario (SC5). The assessment was performed in LCA for Experts using the ecoinvent v3.11 database and the ReCiPe 2016 midpoint (H) method. Global warming potential (GWP), acidification, fossil resource depletion, and human toxicity were evaluated. Results identified aluminum as the dominant environmental hotspot in the baseline scenario. Aluminum substitution achieved the largest environmental improvements, reducing GWP from 47.5 to 28.8 kg CO₂-eq/m² and fossil depletion from 16.3 to 9.3 kg oil-eq/m². The combined substitution scenario (SC5) showed the best overall environmental performance, lowering GWP to 28.5 kg CO₂-eq/m², corresponding to a 40% reduction compared with the baseline. PVC and Zamak substitutions individually resulted in smaller improvements due to their limited material contribution but reinforced the overall benefits when combined. Sensitivity analyses demonstrated the importance of recycled polymers, low-carbon aluminum pathways, and end-of-life management assumptions. Mechanical recycling of rPP-based biocomposite components further reduced the GWP of SC5 to 23.9 kg CO₂-eq/m², while the environmental advantages of the substitution scenarios remained robust even when energy recovery credits from incineration were excluded. Overall, the findings highlight the potential of component-level biocomposite substitution to support circular design of window and reduce the embodied environmental impacts of window manufacturing.