Precise Engineering of Sustainable Fiber Composites Comprising Biobased or Valorized Matrices and Solid Components: A Perspective.

Long-fiber composites play a significant role in a wide range of applications across industrial sectors, including automotive, construction, energy, aerospace, and marine. Current trends point to sustainable solutions that use environmentally friendly materials, reduce waste, rely on renewable energy sources, and adopt circular manufacturing. Reusing, valorizing, and upcycling ensure an optimal approach to economically rational solutions connected to environmentally friendly procedures. Long-fiber composite materials contain multiple functional components beyond solid-phase filament reinforcement, including a continuous binding resin (matrix), solid-phase particle fillers, separators, and functional additives. From a sustainability standpoint, the long-fiber reinforcements and the binding matrix are key components, as they account for the majority of a composite's total weight. This work summarizes, describes, and evaluates several approaches to valorizing, circulating, and reusing either the fiber or the matrix composite content. The sustainability aspect can be enhanced by circulating composite products, modifying and reusing functionalized resins, incorporating natural fibers as alternatives to fossil-based ones, or engineering novel, partly or fully biobased matrices as substitutes for currently used petroleum resins. The primary aim of this work is to provide a comprehensive and critical evaluation of the numerous strategies reported in the available literature and to determine the most promising sustainable strategies.