This paper assesses the aspects related to sustainability of polymer composites, focusing on the two main components of a composite, the matrix and the reinforcement/filler. Most studies analyzed deals with the assessment of the composite performance, but not much attention has been paid to the life cycle assessment (LCA), biodegradation or recyclability of these materials, even in those papers containing the terms “sustainable” (or its derivate words), “green” or “eco”. Many papers claim about the sustainable or renewable character of natural fiber composites, although, again, analysis about recyclability, biodegradation or carbon footprint determination of these materials have not been studied in detail. More studies focusing on the assessment of these composites are needed in order to clarify their potential environmental benefits when compared to other types of composites, which include compounds not obtained from biological resources. LCA methodology has only been applied to some case studies, finding enhanced environmental behavior for natural fiber composites when compared to synthetic ones, also showing the potential benefits of using recycled carbon or glass fibers. Biodegradable composites are considered of lesser interest to recyclable ones, as they allow for a higher profitability of the resources. Finally, it is interesting to highlight the enormous potential of waste as raw material for composite production, both for the matrix and the filler/reinforcement; these have two main benefits: no resources are used for their growth (in the case of biological materials), and fewer residues need to be disposed.

This work describes an extraction method for giant reed fibers from stems and leaves based on chemical soaking and crushing through a rolling mill. Obtained fibers, together with the shredded plant (stems + leaves), are characterized in terms of chemical composition, thermal stability, morphology, and crystallinity. Mechanical properties of fibers have also been assessed (single fiber tensile tests). The results show that the proposed method allows obtaining fibers with higher cellulose content (near 70%), good thermal stability (10% weight loss over 270°C), higher density, and better mechanical properties than other Arundo fibers previously reported in the literature. Fibers from leaves are thinner and show higher crystallinity than those from stems (72 μm vs. 157 μm, 73% vs. 67% crystallinity, respectively), although mechanical properties are similar for both (around 900 MPa for tensile strength and over 45 GPa for elastic modulus). Analysis of the microstructure shows that fibers consist of microfiber bundles, and the removal of a thin layer of non-cellulosic nature is clear; fibers provide a rougher, cleaner surface than shredded raw material.

This paper compares the mechanical properties of different natural fiber composites produced by rotational molding as a way of waste valorization from campaigns to control invasive plant species in Macaronesia. Rotomolded parts produced with polymeric matrices (polyethylene) and filled with up to 20% by weight of cellulosic fibers obtained from Arundo donax L., Pennisetum setaceum, and Ricinus communis plants were characterized in terms of tensile, flexural, and impact strength. It was found that the sieving of natural fibers allowed for their introduction in higher loadings, from 10 (for un-sieved material) to 20%; fiber size greatly affected the mechanical properties of the final parts, although some combinations were proven not to reduce the mechanical properties of the neat resin. This study is a first approach to the valorization of residues obtained from periodic campaigns of the control of invasive species performed by public authorities, usually at the local level. It is important to highlight that the main objective of this research did not focus on economically profitable activity; instead, it was focused on the reduction of wastes to be disposed from ecosystem maintenance actions and the investment of potential income into preservation policies.