This paper describes the history, manufacturing process and characteristics of carbon fiber. It also introduces the mechanical properties of carbon fiber reinforced plastic (CFRP) and the molding technology of CFRP. This is a molding technology that is divided into two parts : a molding method using continuous fiber and a molding method using discontinuous fiber. Although the molding method that use continuous fiber has high mechanical properties, its productivity is low. On the other hand, the molding method that uses discontinuous fiber has low mechanical properties but has high productivity.

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This paper discusses the development of carbon fiber reinforced plastic (CFRP) technology for the field of lightweight vehicles, an endeavor aimed at tackling current global environmental issues. In the development of the Lexus LFA, in which TOYOTA adopted a CFRP body, we not only improved rigidity but also achieved weight savings using the integral molding process and a more flexible design. We have now begun studying CFRP using thermoplastic resin to apply it to CFRP technologies in the mass production of vehicles. For the future production scale, we will need to develop recycling technologies for CFRP in addition to the CFRP technology itself. The key to recycling technologies will be finding out how to separate carbon fibers from CFRP keeping the costs and energy consumption at a minimum. A variety of methods have been studied up to now, including, for example burning or melting methods. We feel an effective collaborative effort is now required so that we can approach many other related issues, such as disassembling of CFRP from vehicles as well as supply chain management strategies.

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We have developed a carbon fiber reinforced plastic (CFRP) recycling technology using depolymerization of cured epoxy resin (EP) under ordinary pressure. Carbon fiber (CF) was recovered from used tennis rackets by dissolving EP with tripotassium phosphate as a catalyst and benzyl alcohol as a solvent at 200 °C for 10 h. We were able to produce non-woven fabrics with the recovered CF using a carding machine. With these fabrics we then produced recycled CRRPs and measured their mechanical properties. Their properties were nearly equal to the CFRP using commercial fresh CF non-woven fabric. At the same time, the depolymerized EP cured with acid anhydrides was analyzed with high-pressure liquid chromatography and nuclear magnetic resonance. Our results showed that the depolymerization was proceeded by a transesterification reaction to produce dibenzyl esters and bis-phenoxypropanediols, which can be used for recycled EP. We are currently investigating the application of recovered CF and depolymerized EP.

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Techniques for the decomposition and dissolubility of epoxy resin and the recovery of carbon fiber in carbon fiber reinforced plastic (CFRP) are introduced. In the case of supercritical water as a solvent, epoxy resin was decomposed into small molecules, including phenolic compounds, at 380 °C, 25 MPa with a 30 min reaction time. When supercritical methanol was used as a solvent at 270 °C, 10 MPa in 60 min, the acid anhydrate curing thermosetting epoxy resin decomposed into methanol-soluble resin, which kept the backbone structure of thermosetting epoxy resin due to the selective decomposition of the bridged structure. Furthermore amine curing thermosetting epoxy resin decomposed completely using high-temperature acetone steam at 320 °C, 1 MPa in 20 min. The tensile strengths of the recovered carbon fibers at these conditions were slightly decreased by 7-9 %, as compared to the virgin fiber. The carbon fiber sheets recovered by supercritical methanol using a bench-scale plant could be used to make a recycled CFRP by mixing virgin epoxy resin and cross-linker. The strength of the recycled CFRP was close to that of virgin CFRP.

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The incorporation of carbon fiber reinforced plastic (CFRP), being used as composite materials in automobiles and aircraft, is expected to significantly reduce transportation energy. The objective of this research is to optimize the two-staged thermal treatment system, which consists of a carbonizing furnace to decompose the plastic components in the CFRP thermally and an oxidizing furnace to burn the residual carbon on carbonized carbon fibers. Results confirmed that with the carbonizing furnace, the heat capacity of the product gases and tar after decomposition of the resin components thermally can cover the amount of heat required for CFRP pyrolysis and that the superheated steam can give an energy savings of 63 % for the small CYT-1700 (1 m³) furnace and 56 % for the large CYT-7000 (5 m³) furnace. For the oxidizing furnace, an oxidizing condition of less than 500 °C was revealed to be appropriate and it can achieve an energy savings of 33 %. This can be further improved to 48 % in stable operating conditions. In research on carbon fiber strength tests, it was confirmed that recycled carbon fiber can obtain a strength that is 80 % greater than that of virgin carbon fiber.

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A novel technology has been developed to achieve complete recovery of carbon fibers from CFRP (carbon fiber reinforced plastic) on the basis of thermal activation of oxide semiconductors (TASC). This is a new application using semiconductors at high temperatures. Here, “thermal activation” means that the semiconductor exhibits no catalytic effects at RT. The appearance of significant catalytic effects when heated in the 350-500 °C range was, however, accidentally discovered. The present finding has been applied to the complete recovery of reinforcing fibers from various FRP, and the embedded fibers have been isolated without any damage. This is a 100 %-dry process. The present technology can also be utilized to recover metals from cell phones, mold motors, etc.

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The high production cost of carbon fiber has limited the widespread application of carbon fiber reinforced plastics (CFRP) and the increasing quantity of CFRP waste in the future is of concern. The development of a high-efficiency and low-cost recycling process for CFRP waste is therefore required. In this paper, we examine the potential for carbon fiber recovery from CFRP while simultaneously modifying the fiber surface for adequate interfacial adhesion with the resin in new CFRP materials using a superheated steam (SHS) treatment. SHS treatment at over 500 °C enabled the recovery of continuous textile fibers from CFRP with polyamide 66 matrix resin, and the recovered fibers had almost the same tensile strength as the virgin fiber. On the other hand, the addition of N₂ gas to SHS was effective in suppressing degradation of the strength of virgin carbon fibers and improving the interfacial adhesion between fiber and epoxy resin.

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