Recycling of carbon fiber composites in carbon-bonded alumina refractories

This study investigates the feasibility of recycling carbon fiber reinforced polymer (CFRP) composites in carbon-bonded alumina refractories. For this purpose, different procedures for pretreatment and separation of recyclable CFRP composites were examined. The influence of pretreatment, dimensions and condition of the CFRPs on physical, mechanical, and thermo-mechanical properties of carbon-bonded alumina refractories were evaluated. The CFRP fractions were classified by sieving and partly treated by means of mechanical and thermal methods. The mechanical approach describes a simple method to obtain short fibers along with a reusable fiber dust. By thermal treatment in an oxidizing atmosphere, the carbon fibers can be easily separated from the polymer matrix. Carbon-bonded alumina bricks of industry standard with CFRPs of different length and treatment and partly silicon as antioxidant were produced and compared to the respective reference without CFRPs. The addition of recycled CFRPs to carbon-bonded alumina refractories resulted in a modified microstructure consistent with open porosity and altered mechanical properties at room temperature. The microstructural change in the refractory material provoked by recycled CFRPs < 1 mm increased the high-temperature Young's modulus up to 200%. The addition of mechanically treated and short CFRPs resulted in enhanced creep resistance at high temperature. Thus, different treatment methods of CFRPs exhibit promising recycling approaches for reusing carbon composites in carbon-bonded refractories by improving thermo-mechanical properties and simultaneously operating as final repository.