Life cycle assessment of poly(lactic acid)-based green composites filled with pine needles or kenaf fibers

A cradle-to-gate life cycle assessment (LCA) study is performed on green composites made of poly(lactic acid) (PLA) filled with different amounts (10–40 vol%) of natural (lignocellulosic) fibers obtained from pine needles (PN) or kenaf fibers (KB). The impact of (i) raw material production/harvesting, (ii) transportation, (iii) fiber production, (iv) melt compounding, and (v) granulation to obtain PLA/PN and PLA/KB bio-pellets ready to be transformed into green products was assessed. Although derived from a naturally grown feedstock, PN are only slightly preferable with respect to KB due to a non-optimized pre-treatment of washing and drying performed on the pine needles at the laboratory scale. Being obtained from cultivated feedstocks, KB is more impacting in terms of toxicity indicators, mainly because of the use of fertilizers. The environmental indicators of PLA are significantly higher than those of the fibers. As a result, green composites are substantially less impacting than the pure PLA, with gains that increase with filler content (e.g.: −48% of greenhouse gas emissions and −32% of primary energy demand for green composites containing 40% of fibers). Further environmental advantages derive from the enhancement of the properties ensured by the fibers, which enable material saving with respect to the use of neat PLA at equal performance (weight reduction up to 8% at 30 wt% of KB for a stiffness-limited design).