Do fiber-reinforced polymer composites provide environmentally benign alternatives? A life-cycle-assessment-based study
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Do fiber-reinforced polymer composites provide environmentally benign alternatives? A life-cycle-assessment-based study Joost R. Duflou, Yelin Deng, Karel Van Acker, and Wim Dewulf This article summarizes the energy savings and environmental impacts of using traditional and bio-based fiber-reinforced polymer composites in place of conventional metal-based structures in a range of applications. In addition to reviewing technical achievements in improving material properties, we quantify the environmental impacts of the materials over the complete product life cycle, from material production through use and end of life, using life-cycle assessment (LCA).
Introduction Fiber-reinforced polymers (FRPs) are among the most widely produced categories of composite materials.1 Initially developed decades ago for the aerospace industry, these composites have spread to a wide range of applications, including automobiles, shipbuilding, circuit boards, construction materials, and household equipment (Figure 1). Because of their high stiffness, strength, and fatigue resistance, as well as their low density and ease of shaping, FRPs provide attractive alternatives to steel and nonferrous metals in structural applications.3 Recently, researchers have also explored bio-based FRPs, in which either the polymer matrix or the reinforcement fibers, or both, come from renewable resources.4 This article discusses the environmental impacts of transitioning from conventional materials to FRPs, as determined by life-cycle assessment (LCA). The net change depends on many processes throughout the life cycle of an envisaged application, including energy and mass flows as well as emissions and waste (Figure 2). Because FRP components are often lighter than their traditional counterparts, it is important to compare their impacts on a functionally equivalent basis.
Traditional and bio-based fiber-reinforced polymers Fiber materials The best-established FRPs are glass-fiber-reinforced polymers (GFRPs), which are used in a variety of products, including printed circuit boards, tanks and pipes, car body panels, and wind turbine blades. The high melting temperature of glass (glass-fiber production occurs at ∼1550°C) makes energy intensity the major environmental issue.5 Carbon-fiber-reinforced polymers (CFRPs) use carbon fibers that require considerable energy to produce, because they are made by pyrolysis at 1000–1400°C for high-modulus fibers or at 1800–2000°C for high-strength fibers.6 The energy expenditure has decreased, however, as production methods have evolved.7–9 One promising class of carbon fibers, carbon nanofibers, requires more energy to produce, depending on the feedstock and other details, and generally gives low yields of 15–50%.10 A major concern for nanofibers is their potential human toxicity and ecotoxicity. Although they are probably less harmful in a matrix, free particles in the nanometer size range raise health and environmental concerns because of their large surface-areato-mass ratios and their ability to penetrate biological cells.11
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