Thermal treatment of carbon fibre reinforced polymers (Part 1: Recycling)

Abstract

The increasing use of carbon fibre reinforced polymers requires suitable disposing and recycling options, the latter being especially attractive due to the high production cost of the material. Reclaiming the fibres from their polymer matrix however is not without challenges. Pyrolysis leads to a decay of the polymer matrix but may also leave solid carbon residues on the fibre. These residues prevent fibre sizing and thereby reuse in new materials. In state of the art, these residues are removed via thermal treatment in oxygen containing atmospheres. This however may damage the fibre's tensile strength. Within the scope of this work, carbon dioxide and water vapour were used to remove the carbon residues. This aims to eliminate or at least minimize fibre damage. Improved quality of reclaimed fibres can make fibre reuse more desirable by enabling the production of high-quality recycling products. Still, even under ideal recycling conditions the fibres will shorten with every new life-cycle due to production-based blending. Fibre disposal pathways will therefore always also be necessary. The problems of thermal fibre disintegration are summarized in the second part of this article (Part 2: Energy recovery).

A review on the recycling of waste carbon fibre/glass fibre-reinforced composites: fibre recovery, properties and life-cycle analysis

“…Methods such as chemical treatment [26,58] and post-heating the fibres result in reducing the char formation, but only to a certain extent [1]. Recent studies have used carbon dioxide (CO 2 ) and water vapours to remove the char formation from CFRP [59]. Also, oxidising the fibre surface will result in the formation of an oxygen-rich surface, improving the adhesive nature of the fibre with resins [60].…”

Analysis of Factors Affecting the Properties of Recycled Carbon Fiber and Materials on its Basis

“…При термическом извлечении волокна из ПКМ наблюдается меньшее снижение прочности на растяжение, чем при нагревании на воздухе чистых углеродных волокон (без матрицы) [3]. Пиролиз ведет к образованию пироуглерода на поверхности волокон, что ухудшает дальнейшую адгезию с новой матрицей [6]. Пиролиз углеродного волокна при температуре выше 1300°C позволяет полностью удалить пироуглерод с поверхности, получить идеально чистые волокна с высокоактивированной поверхностью, но их прочность значительно снижена по сравнению с прочностью первичного волокна.…”

“…Для удаления пироуглерода, оставшегося на поверхности волокна после пиролиза, используется термическая обработка в газовой фазе, содержащей кислород (что, однако, может приводить к потере прочности на растяжение). В качестве альтернативы иногда рассматривается возможность использования диоксида углерода и паров воды вместо кислорода для обработки волокон [6].…”

Alkali-Activated Mortars Modified by Epoxy-Carbon Fiber Composites Wastes

“…A large quantity of scraps is generated during production and, at present, these scraps are discarded. The recovery of bare fibers is either energy consuming (pyrolysis of the matrix) [3,4] or involves the dissolution of the epoxy matrix through complex chemical reactions [5,6]. The direct reuse of the scraps has been proposed for other types of composites, such as in the formulation of alkali-activated mortars (AAMs).…”