Recycling of Carbon Fibers from CFRP Waste by Microwave Thermolysis

Abstract

With the growth of the use of carbon fiber-reinforced polymer (CFRP) in various fields, the recovery of carbon fibers from CFRP waste is becoming a significant research direction. In the present work, degrading epoxy resin and recycling carbon fibers from CFRP waste by microwave thermolysis and traditional thermolysis were studied. The carbon fibers were successfully recovered by thermolysis under an oxygen atmosphere in this study. The properties of the recovered carbon fibers were characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and Raman spectroscopy. The result shows that using microwave thermolysis to recover carbon fibers from CFRP waste is an attractive prospect. Compared to the traditional method, the reaction time was reduced by 56.67%, and the recovery ratio was increased by 15%. Microwave thermolysis is faster, more efficient, requires less energy, and obtains cleaner recovered carbon fibers than those recovered using traditional thermolysis.Processes 2019, 7, 207 2 of 12 including mechanical processes [14,15], chemical methods [4,[16][17][18][19][20], and thermal technology [3,[21][22][23]. However, long carbon fibers are difficult to obtain using a mechanical process, and their mechanical properties are seriously damaged with this technique [24,25]. Liu et al. [13], Yildirir et al. [19], and Hyde et al. [20] have investigated recycling carbon fibers from CFRP using different solvents under subcritical or supercritical conditions. These methods are expensive, difficult to industrialize, and produce large amounts of liquid waste and hazardous gases [1]. Yang et al. [3], López et al. [22], and Ye et al. [23] have studied thermolysis methods of recovering carbon fibers from CFRP. The pyrolysis process is not very economical, producing multiple hazardous gases and depositing char on the carbon fiber surfaces [1,19,25]. Therefore, research to develop new methods of recovering carbon fibers from CFRP has begun.Microwave heating is gradually being used more often in the area of material processing due to its advantages of rapid, uniform, and selective heating [26]. Microwave heating is the process of coupling materials with microwaves, absorbing electromagnetic energy and transforming it into heat within the material volume, in which the heat is generated from the inside to the entire volume [27][28][29]. Therefore, the microwave method can treat uniform samples due to its features of volumetric and internal heating [30,31]. Yingguang Li et al. [32,33] have reported curing of CFRP by microwave energy, and CFRP can absorb microwave energy and be heated effectively. This study provides a great reference for microwave applications in the preparation and recovery of CFRP. Long Jiang et al. [34] reported that microwave irradiation is a flexible, easy-to-control, efficient method to recover high-value carbon fibers, and recovered carbon fibers could be directly used as reinforcement in new polymers (Polypropylene and nyl...

Carbon Fiber Composites Application and Recycling in Kazakhstan and Neighboring Countries

“…However, currently, several research works are carried out to investigate the implementation of more cost-effective and efficient ways of CFRP recycling. For example, some authors propose using CFRP in the production of eco-efficient cementbased materials [12], and others study microwave thermolysis claiming to be more efficient compared to conventional thermolysis [21].…”

Special Issue on “Microwave Applications in Chemical Engineering”

“…At present, a variety of technologies for carbon fiber recovery from carbon fiber reinforced epoxy composites have been proposed. In Deng's paper [7], the degradation of epoxy resin in the CFRP waste and the recycling of carbon fiber were studied by microwave thermolysis and traditional thermolysis respectively. The effects of reaction temperature and reaction time on the recovery of carbon fiber were studied, and the properties of carbon fiber were characterized to compare the characteristics of the two methods.…”

Recovery of Carbon Fibre from Waste Prepreg via Microwave Pyrolysis

“…The authors also proposed the mechanism of microwave separation, whereby the fibre was first heated via the antenna effect by microwave irradiation to gasify the resin, and then gasified resin was further decomposed by spark glow plasma between carbon fibres. Deng et al [ 18 ] compared carbon fibres recycling via microwave thermolysis and traditional thermolysis under a pure oxygen atmosphere and found 450 °C to be the optimum temperature. They also reported that microwave thermolysis saved 57% reaction time and increased recovery ratio by 15% compared to conventional thermolysis.…”