Life cycle assessment of carbon fiber-reinforced polymer composites

The use of carbon fiber-reinforced polymer matrix composites is gaining momentum with the pressure to lightweight vehicles; however energy intensity and cost remain major barriers to the wide-scale adoption of this material for automotive applications. This study determines the relative life cycle benefits of two precursor types (conventional textile-type acrylic fibers and renewable-based lignin), part manufacturing technologies (conventional SMC and P4), and a fiber recycling technology. A representative automotive part, i.e., a 30.8-kg steel floor pan having a 17% weight reduction potential with stringent crash performance requirements, has been considered for the life cycle energy and emissions analysis. Four scenarios-combinations of the precursor types and manufacturing technologies-are compared to the stamped steel baseline part. The analysis finds the lignin-based part made through P4 technology to offer the greatest life cycle energy and CO(2) emissions benefits. Carbon fiber production is estimated to be about 14 times more energy-intensive than conventional steel production; however, life cycle primary energy use is estimated to be quite similar to the conventional part, i.e., 18,500 MJ/part, especially when considering the uncertainty in LCI data that exist from using numerous sources in the literature. The sensitivity analysis concludes that with a 20% reduction in energy use in the conversion of lignin to carbon fiber and no energy use incurred in lignin production since lignin is a by-product of ethanol and paper production, a 30% reduction in life cycle energy use could be obtained. A similar level of life cycle energy savings could also be obtained with a higher part weight reduction potential of 43%.