Cradle-to-gate life cycle assessment of sisal/PLA biocomposite: Uncovering the dominance of transport and burden-shifting trade-offs in sustainable material design

Natural fibre-reinforced biocomposites are increasingly recognised as promising alternatives for reducing the high carbon footprint of the construction sector; however, the environmental implications of transcontinental supply chains remain insufficiently understood. This study presents a cradle-to-gate life cycle assessment of a sisal yarn-reinforced polylactic acid biocomposite plate manufactured in Denmark using sisal fibres cultivated and spun in Tanzania. Environmental impacts were assessed for a performance-based functional unit using the ReCiPe 2016 Midpoint (H) method, normalising values through a structural bending stiffness index to enable benchmarking against conventional window frame materials. Under baseline pilot-scale conditions, the biocomposite exhibited a global warming potential of 17.52 kg of carbon dioxide equivalent, with intercontinental air freight accounting for 62.53% of total emissions. Scenario optimisation involving ocean freight, 100% wind energy, and a 60:40 polylactic acid-to-sisal ratio reduced the global warming potential to 9.82 kg of carbon dioxide equivalent, a 43.97% reduction. When normalised for structural performance, the optimised biocomposite demonstrated a lower global warming potential than conventional polyvinyl chloride and aluminium window frame materials. Nevertheless, these improvements resulted in significant shifts in environmental burdens, with human non-carcinogenic toxicity increasing by 125.91% and freshwater ecotoxicity by 322.88%, primarily due to heavy fuel oil combustion during marine transport and the use of synthetic phosphate fertiliser in sisal cultivation. The findings indicate that although transcontinental sisal/polylactic acid biocomposites can offer competitive structural and climate performance, their long-term sustainability depends on holistic multi-indicator assessments and the adoption of cleaner logistics and sustainable agricultural practices to avoid transferring environmental burdens across impact categories.