Life Cycle Assessment of a Hybrid Poly Butylene Succinate Composite
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Poly butylene succinate (PBS) is a biodegradable plastic polymer that has physical and mechanical properties similar to common petroleum plastics like polypropylene (PP) and polyethylene (PE). PBS may be produced from petroleum or bio-based feedstocks, or by a hybrid combination of petroleum and bio-based resources. Producers are reducing content of petroleum components used for the production of PBS, and by doing so are seeking potential environmental performance improvements. In this study, “hybrid” PBS refers to the production of PBS polymer from bio-based succinic acid (SAC) sourced from sorghum and petroleum-based 1, 4-butanediol (BDO). Given its biodegradability, PBS is commercially used for compostable bags and agricultural mulching film applications. A recent study in Ontario identified composite materials made with PBS blended with natural fibres like switchgrass (SG) as promising for applications in automotive products. Such novel composite materials are touted as potential bio-based alternatives to conventional petroleum-based plastics. Of the few studies that have considered the environmental performance of PBS materials, none have assessed the potential environmental impacts of a hybrid PBS composite. Therefore, this study undertook a life cycle assessment (LCA) of SG reinforced hybrid PBS composite (hybrid composite). LCA is an environmental management technique that is used to assess environmental aspects (inputs and outputs) and potential environmental impacts of a product or service throughout its life cycle. The analysis considered a cradle-to-gate system boundary and evaluated eleven environmental performance indicators. The environmental performance of the hybrid composite was compared to a conventional glass fibre (GF) reinforced polypropylene (PP) composite (baseline composite), a material that is widely used in automotive components. Results showed that the production of the hybrid composite in comparison to the baseline composite decreased potential impact for most of the assessed indicators: cumulative energy demand by 40%, waste heat by 23%, global warming potential by 35%, smog by 2%, carcinogens by 54%, non-carcinogens by 172%, respiratory effects by 22% and ecotoxicity by 45%. Increases in the values of impact indicators were apparent for ozone depletion, acidification, and eutrophication by 43%, 16%, and 322%, respectively. Analysis revealed that dominant influences on results were not related directly to the bio-based make-up. Rather, the biggest influence on the environmental performance of composite production were the sources of heat used in petroleum-based materials, the energy mix in electricity for bio-based materials, the type of reinforcing fibre and the co-product treatment methodology used. The study helps fill a gap in knowledge regarding bio-based chemicals and hybrid biodegradable plastic composites, and points to opportunities for future research on feedstocks for industrial composite materials. The importance of this study is that it helps to identify the environmental strengths and weaknesses associated with the production of the hybrid composite specifically, and bio-based materials more generally. It points to alternative material substitution options for use in the automotive industry. In this study, life cycle assessment exemplifies multidisciplinary methodologies, which seek to traverse the boundaries between the social and natural sciences and disciplines to support more sustainable policy decisions for a bio-economy. The systematic nature and the widely applicable consequences of this LCA study have the potential to contribute to industrial and business management, and reach the public policy arena in an effort to drive environmental and social change.