Recycling Technology for Fiber Reinforced Plastics (FRP)
Chemical recycling technology using supercritical water
When recycling waste products, the key is how to cover the cost of treatment with the value of the recycled product. There is no better way to recycle waste products than by converting them into more valuable products. In this sense, the chemical recycling technology using supercritical water with hydrolysis is highly anticipated as a next-generation FRP treatment technology.
The Industrial Technology Research Institute of the Agency of Industrial Science and Technology, in collaboration with the Industrial Technology Center of Kumamoto Prefecture, has developed a technology to decompose phenol resin in carbon fiber reinforced plastics and recover carbon fibers by using supercritical water to which alcohol and alkali are added. Phenolic resin is persistent and only a low degradation rate of less than 20% was obtained with supercritical water alone at 380°C. However, the degradation rate increased to 65% when alkali was added under the same temperature conditions. Furthermore, when ethanol was added to the supercritical water + ethanol mixed alkaline solution, the decomposition rate increased to 93.9%, and purified carbon fiber with absolutely no plastic adhering to it was obtained.
FRP made of unsaturated polyester can be easily decomposed in a short time by supercritical water, but carbon fiber-reinforced plastic made of phenol resin is much more difficult to decompose than FRP, and no carbon fiber has ever been recovered from it. Furthermore, carbon fiber has higher added value than glass fiber, making it more valuable to recover.
Jointly developed by the Ship Technology Research Institute of the Ministry of Transport and Hitachi, Ltd.
In this system, FRP is melted at high temperature, cooled, and recycled into products, and the organic resin is decomposed with supercritical water and returned to raw materials. The supercritical water is obtained from a boiler that supplies steam, and electricity is supplied by a steam turbine and combined cycle power generation, with waste plastic pyrolysis gas used as fuel for the boiler and gas turbine. It is estimated that 4,000 tons of waste FRP and 57,600 tons of waste plastic can be processed annually, and 65.37 million kilowatts of surplus electricity can be obtained. The system is expected to be economically feasible for practical use.
Current Status and Issues of FRP Waste
FRP (Fiber Reinforced Plastics) is used in a wide range of fields, from bathtubs, septic tanks, and water tanks, which account for half of the total production volume, to construction materials, various small vessels such as pleasure boats and fishing boats, aircraft, automobiles, industrial machinery, fishing rods, tennis rackets According to the Reinforced Plastics Association, FRP is the most widely used plastic material in the world. According to the Reinforced Plastics Association, annual shipments of FRP have grown from 44,000 tons in 1968 to approximately 500,000 tons today, with an estimated 270,000 tons disposed of in 1998. Of this amount, about 10% is generated from the manufacturing process at factories. As for waste products, housing equipment (bathtubs, etc.) accounts for about 80,000 tons, industrial equipment, tanks and containers for about 30,000 tons each, and boats ships and construction materials for about 20,000 tons each. 2002 is estimated to bring the annual disposal volume to over 400,000 tons.
At present, however, FRP contains a large amount of glass, which is difficult and costly to crush and burn, and the collection and transportation costs to treatment facilities for ships and vessels are high, making recycling and treatment a bottleneck. Currently, FRP is disposed of by landfill, high-temperature incineration, or crushing, and problems such as illegal dumping and abandoned vessels have been pointed out for some time.
Development of Recycling Technology and Future Prospects
Recently, methods have been developed and put into practical use for crushed waste from factories, such as crushing it into SMC filler or using it as concrete aggregate. On the other hand, for waste from ships and other vessels, it is difficult to separate out foreign materials, and development of treatment methods using oilification and gasification is underway. However, this is still only a small part of the movement, and the development of treatment technology, recovery, and treatment systems is long awaited.
Bathtubs are being processed as a result of remodeling. Some FRP bathtubs are incinerated in kiln furnaces to be used as raw materials for cement, but as they are low in calories, they need to be mixed with other waste plastics and burned to adjust the heat value. However, the material as it is is low in calories and needs to be mixed with other waste plastics for combustion to adjust the heat value. Therefore, it is likely to become the mainstream method to reuse the material as it is for concrete aggregate, etc., taking advantage of its properties.
In August 1999, Sekisui Chemical started a test program to collect and recycle waste round bathtubs for remodeling houses in the Kinki region. The company plans to establish a recycling system by the end of FY2000, mainly in the Kinki region.
In cooperation with several major FRP bathtub manufacturers, Kubota collects defective products generated at plants mainly in the Kinki region, crushes and grinds them at recycling plants, and supplies them to its affiliated companies for reuse as cement admixture, cement product aggregate, and other products.
With assistance from the New Energy and Industrial Technology Development Organization (NEDO), the company began developing FRP bathtub recycling technology in December 1995 at a demonstration plant with a daily capacity of 5 tons built in Iga Town, Mie Prefecture, and in 1997 established technology to crush and grind FRP bathtubs and use them as aggregate to make cement tiles. In 1997, we established a technology to crush FRP bathtubs and use them as aggregate to make cement tiles. Based on the results of our demonstration research to date, we are now developing a new technology for mass-processing waste FRP bathtubs with the assistance of NEDO.
