Abstract

Abstract

In the last decade, a great effort has been made to achieve a transition from the current linear economy to a circular economy. This transition also affects the composites sector, which, due to the intrinsic complexity of recycling, requires the implementation of recovery and remanufacturing processes that will be technically, economically and environmentally feasible. This challenge was addressed within the FiberEUse project, in which one of the working lines was based on waste recycling from wind and aeronautical sectors. Both glass and carbon fiber were recovered by pyrolysis. Subsequently, the recycled fiber was treated and processed with thermoplastic matrices used in automotive applications. The technologies used and the results obtained throughout the value chain, from the waste to the part, are presented in this paper. Formulations with different recycled fibers, with and without sizing treatments and with different matrices, were manufactured by compounding-injection. These materials were mechanically analysed and tested with the aim of selecting three formulations. The reinforced materials were validated in three real automotive prototypes: a pedal bracket, a front-end and a cowl top support. As a result, the prototypes were manufactured, tested and validated by the automotive companies.

Abstract

Abstract

The growing utilization of carbon fiber reinforced polymers (CFRP) in industry involves the generation of high quantities of this kind of waste. This tendency has fomented the investigation of different alternatives to recycle CFRP waste with the aim of reclaiming the carbon fibers, a material with high specific economic value. Among the alternatives, pyrolysis is the only one runnig at commercial scale nowadays. This process consists on heating the waste in an inert or oxygen-poor atmosphere, which causes the decomposition of the polymeric resin of the material and consequently the reclamation of the carbon fibers. The resin decomposes into organic vapors, which are normally incinerated and released to the atmosphere. The objective of this paper is to present the economic and energy benefit of a method for treating the vapors coming from the resin decomposition, through which high value chemicals can be obtained, avoiding the vapors incineration and emission. By means of this recently patented method a gas fraction with a higher energetic content than that of the vapors without treatment can be obtained. Besides, this gaseous fraction contains high quantities of hydrogen, which could be separated and sold. The commercialization of this hydrogen could increase 6 times the economic value of the gaseous fraction compared to the gas fraction without treatment.

Abstract

Due to the rapid growth in the use of composite materials, environmental concerns have become an increasingly influential topic, making recyclability of composite materials a key issue. Furthermore, several related European laws have been passed to minimize the environmental impact of composites (EU 2000/53/CE [1], 2000/76/EC [2], 2004/35/EC [3]). Caused by the high energetic requirements and the huge amount of composite materials used in the manufacturing process, recycling supposes a reduction of a 70% in the costs and 98% in the energy demanded [4].

Once the fibers are obtained through pyrolysis, with a high retention of mechanical properties, the next step is the manufacturing process by injection using a thermoplastic polymeric matrix of polypropylene, a polymer widely used in the composite industry. For that purpose, a study of the compatibility of the fiber with the maleic anhydride polypropylene at different relations -10, 20 and 30%- has been carried out.

In order to enhance the mechanical properties, a combination of homopolymer polypropylene, maleic anhydride polypropylene and recycled carbon fibers is studied through the production of a masterbach composed of maleic anhydride polypropylene and carbon fibers, followed by the addition of the homopolymer polypropylene.

Once the pellets are obtained, they are injected. The samples injected are analyzed in terms of fiber distribution by scanning electron microscopy and tomography, thus the mechanical properties are evaluated through tensile, impact and bending tests, to determine the optimum fiber/resin ratio.

Abstract

Las fibras de carbono y de vidrio que se encuentran en los residuos que se generan en los sectores industriales que fabrican o utilizan materiales compuestos reforzados con fibra pueden recuperarse a través del tratamiento térmico. Este tratamiento consiste en el calentamiento del material en atmósfera inerte (pirólisis) hasta la temperatura suficiente para que se descomponga la resina polimérica y la posterior oxidación de los productos carbonosos generados en esta descomposición en presencia de aire. El resultado de este tratamiento es la eliminación completa de la resina y la recuperación de las fibras, que mantienen buenas propiedades físico-químicas. En este trabajo se ha utilizado el diseño estadístico de experimentos para determinar la influencia que tienen las tres variables de operación principales involucradas en la recuperación de fibras por tratamiento térmico (temperatura de pirólisis, temperatura de oxidación y tiempo de oxidación) sobre el rendimiento de eliminación de resina polimérica. La estrategia experimental utilizada ha sido el diseño factorial completo 2k, donde k=3, las variables de operación estudiadas. El método se ha aplicado a residuos procedentes del sector eólico y del sector aeronáutico, tanto de piezas curadas como pre-pregs caducados, y reforzadas con fibra de carbono y fibra de vidrio. Con los resultados obtenidos en la experimentación con termobalanza se ha determinado la importancia relativa de las variables estudiadas para cada una de las muestras y se han definido las ecuaciones matemáticas que permiten predecir el rendimiento de eliminación de resina en función del valor que tomen estas variables.

Abstract

Due to the rapid growth of the composite market, several European laws have emerged to minimize their environmental impact (EU 2000/53 / EC, End of life vehicles), as well as to make rational use of landfills (EU 1999/31 / EC). For example, in the aeronautical sector, composites can reach 50% by weight of the aircraft. Consequently, recyclability is a key issue. The objective of this work is the study of the recycling techniques of carbon fiber composites with thermoset polymer matrix in order to obtain fibers with similar properties to the original ones. In this way, the fibers could be reused in new composites by themselves or together with flass fibers in the manufacture of new hybrid composite materials. By this hybridization, materials with properties far superior to the GFRP would be obtained, but at much lower cost than the original CFRP. Therefore, this recycling and reprocesing strategies provides great economical attractiveness.  The main objective of the project is to study and optimize the recyclability of cured carbon fiber / epoxy prepregs for use in hybrid materials. Starting from a pyrolysis in a controlled atmosphere reactor, followed by a oxidation, carbon fibers with properties similar to virgin fibers are obtained, with a loss less than 20% of the tensile strength. An evaluation of the different parameters of the recycling process has been carried out in order to optimize the procedure. The characterization of the fibers includes tensile tests, scanning electron microscopy and Raman spectroscopy.

Abstract

Los bio-FRP (polímeros reforzados con fibras) que utilizan fibras naturales como refuerzo y resinas procedentes de fuentes renovables se utilizan cada vez más en sectores como aviación, construcción o deporte, ya que son una tecnología clave para reducir el impacto ambiental gracias a su favorable combinación de propiedades mecánicas y bajo peso (lo que reduce el consumo de combustible y las emisiones de CO2 a la atmósfera). Sin embargo, el uso generalizado de los FRP y los bio-FRP ha provocado dificultades en la gestión de los residuos, ya que las matrices poliméricas suelen ser resinas termoestables que tienen una estructura molecular reticulada que supone un reto para las tecnologías de reciclaje convencionales. A pesar de todas las ventajas de estos biocomposites, no se han encontrado soluciones eficaces para la gestión del fin de vida (EoL) cuando se convierten en residuos. Esto es más pronunciado en el caso de los biocomposites, un nuevo material que, a diferencia de los composites convencionales, no contiene fibras de carbono con un alto valor de mercado. En la búsqueda de nuevas soluciones para el reciclaje de biocomposites, el proyecto ELIOT revisa las actuales tecnologías de reciclaje de composites para analizar las alternativas más viables en cuanto a rendimiento medioambiental, económico, de recursos y técnico. Posteriormente, las tecnologías más prometedoras se adaptarán a las características de los biocomposites y se probarán a escala de laboratorio. Finalmente, este proyecto desmostrará la viabilidad técnica a escala preindustrial de 2 métodos EoL para 2 biocomposites objetivo, respectivamente, incluyendo su validación en términos de sostenibilidad del ciclo de vida.