El trabajo describe cómo, dependiendo de la naturaleza tanto de las matrices como de las fibras de refuerzo, la reutilización de este tipo de fibras debe estar dirigida hacía un tipo de procesos u otros y cómo, mediante la variación de las tecnologías, es posible dar lugar a productos con una mayor o menor orientación de las fibras. De la misma manera, el capítulo analiza algunos de los procesos de fabricación de materiales compuestos, que pueden afectar a la longitud de las fibras y por lo tanto modificar las propiedades del material final. 

De esta forma, se describen las diferentes tecnologías actualmente disponibles y en proceso de desarrollo en España para poder dar una nueva vida a las fibras de carbono y de vidrio, orientadas a retener la mayor parte de su valor añadido y propiedades, como son: reutilización en materiales compuestos termoestables, reutilización como refuerzo en materiales compuestos termoplásticos, reprocesado de la fibra (estructuras de fibra tejidas o no tejidas), reciclado de fibras que todavía estén embebidas, reciclajes específicos según la naturaleza de la fibra. 

A lo largo del texto se van recogiendo algunos de los proyectos liderados por entidades españolas con mayor relevancia en el desarrollo de las diferentes tecnologías y, además, al final del mismo se remarcan esos mismos proyectos y otros más en los que se destaca el trabajo realizado por centros, universidades y empresas españolas en el campo de la reutilización y reciclaje de fibras de carbono y de vidrio.

The synthesis of bio-epoxy monomers from vegetable oils, polysaccharides, lignin, polyphenols, and natural resins is currently the subject of interest in several research projects and scientific papers, in some cases reaching the level of product commercialization. Vegetable oils, such as linseed and soybean, and the transformation of saccharides into epoxy monomers are examples of explored options. Naturally occurring epoxy monomers derived from polyphenols from various plant sources can also be found, although their epoxidation requires the use of toxic compounds such as epichlorohydrin.

Several natural sources, such as natural rubber, resin acids, and lignin are examined as alternatives to synthesize epoxy resins of natural origin. Leutelin, recently identified in fruits and medicinal herbs, is highlighted as a promising compound to produce bioepoxy monomers.

Although initially the research focused mostly on the development of monomers of natural origin, research also extends to hardeners of natural origin, highlighting the synthesis of amines from vanillin and curing agents based on phenalkamines. The development of hardeners with reversible bonds, such as lignin imines, is also being explored, and the catalytic effect of hemp fibers in the curing of epoxy resins is highlighted.

The combination with traditional monomers or the development of recyclable resins and vitrimers with reversible bonds are current fields of interest for the development of these resins, especially in the context of their competitors of petrochemical origin.

In this context, Tecnalia has been working for years on the direct resistive heating technology in order to accelerate and optimize composite material manufacturing processes. The direct application of a current to the carbon fiber material to be processed has the advantage of avoiding the heating and cooling of the molds or other adjacent tools, obtaining the results much more quickly and efficiently than with the methods used until now. In the case, for example, of the preforming process of carbon fabrics, applying heat only to the preform allows reducing cycle times and energy consumption by more than 60% and 80% respectively. This means reducing the cost of the process related to lower energy consumption and shorter cycle time. The quality of the preforms obtained through resistive preforming is the same to that obtained through conventional hot drape forming technology and, in addition, it is a repetitive process that has been validated in industrial manufacturing environment.

The article also indicates that this direct resistive heating technology is not only applicable in carbon fiber preforming processes but could also be used in other manufacturing processes for composite material components.

Especially critical is the situation of thermostable composite materials, widely used in structural applications due to their excellent performance/weight ratio. There are different fields of research, oriented towards the search for more sustainable alternatives for these matrices so that these high mechanical performances continue to be guaranteed and that they can be transformed by conventional manufacturing processes.

Reactive thermoplastic resins are a sustainable alternative for the manufacture of recyclable, weldable and processable structural composite components by conventional manufacturing technologies (Infusion, RTM. Pultrusion, Fillament Winding)

The technologies used to reduce the size of the initial pieces substantially influence the characteristics of the final product obtained, especially if they are to be used for functional purposes in terms of electrical or thermal properties. In addition, the fibers obtained have a proportion of resin from the initial composite material, so the subsequent treatment processes of these fibers, both physical and chemical, can affect the amount of final resin present in the product, its agglomeration or its surface characteristics. 

The current challenges for these products is to find processes that allow a better quality and greater uniformity of the final properties of the short fiber, so that the products obtained present a greater added value, which allows them to compete with other current discontinuous reinforcements.

Therefore, considering the development of these new materials and the existing concerns about developing more sustainable manufacturing techniques and materials, the need arises to establish new methods for the proper identification of both the composite material waste generated and those composite materials that are recycled, i.e., those that are reused. Products can be labeled to facilitate better recovery at the end of their useful life (End of Life, EOL), especially due to the wide variety of possible material compositions in composite materials. Labeling is mandatory for certain plastic products in the automotive industry (including composite materials) according to the End-of-Life Vehicle (ELV) directive [3]. There are standards for labeling products in other sectors. Some high-value products in the aerospace and automotive industries now incorporate Radio Frequency Identification (RFID) tags for tracking product life cycle management (Product Life Management, PLM) and ensuring provenance and traceability. These tags may contain data about the material to facilitate higher-value recycling and could be linked to virtual databases that include material origin, manufacturing, and usage data throughout the entire life cycle.

Proper identification of components can also be done through the Digital Product Passport proposed as part of the ESPR (Ecodesign for Sustainable Products Regulation) [4], to maintain adequate traceability of products in terms of material technical characteristics, repair information, etc., so that consumers have a complete understanding of the materials and their environmental impact, in order to establish appropriate reuse techniques. The ESPR, in turn, aims to design components that result in more reliable, durable, reusable, repairable, easy-to-maintain, recyclable, and energy-sustainable products.

In addition, waste can be classified using EWC codes (European Waste Catalogue). This can enable proper identification of waste that may be more hazardous or waste that could be reused at the end of its first life cycle.

Therefore, this chapter aims to address, in a simple manner, those methods for identifying composite materials, both focused on the traceability of products through digital passports, and for managing the waste generated during their service life using EWC codes.

This study delves into the reuse and repurposing of polymer composites, promoting their integration within the Circular Economy to preserve material integrity and value. It showcases innovative repurposing projects in Spain and across Europe, such as transforming wind turbine blades into materials for construction, which demonstrates the feasibility of extending these materials' lifecycles. These efforts align with sustainability goals aimed at waste reduction and resource conservation. However, challenges persist, including matching waste volume and condition with market demands and scaling these practices effectively. The concept of structural re-use, turning cured composite waste into high-value, reusable products, highlights the potential of merging reuse and recycling strategies. Innovative approaches to reuse not only mitigate sustainability challenges but also foster economically viable solutions, marking a significant stride towards sustainable and efficient resource utilization in the composites sector.