A team from the University of Sydney's School of Civil Engineering has designed a method to improve the recycling of carbon fiber reinforced polymer (CFRP) composites, the findings of which are published in the Journal of Cleaner Production. CFRP composites are found in a wide range of industrial parts and products, including wind turbines, airplanes, cars, ships, sports equipment, laptops, and cell phones. Unfortunately, the materials are largely non-biodegradable and often end up in landfills or incinerators, where they emit greenhouse gases into the atmosphere. Additionally, a lack of effective recycling of CFRPs also means that new composites are produced with higher demand, a process that also emits greenhouse gases.
"We embarked on the project with the aim of producing high grade, low-cost structural materials made from recycled carbon fiber composites, for use in industries from aerospace and automotive through to sporting goods and renewable energy and construction, " says lead researcher on the study, Dr. Ali Hadigheh.
"Until now, it has been impossible to continuously recycle products made of carbon fibers. Given that most recycling involves shredding, cutting or grinding, fibers are worn out, decreasing a future product's viability. This presents a huge challenge and threat to our environment, as it has led to the production of virgin carbon fiber which contributes significantly to greenhouse gas emissions. To combat this issue and to support a true circular economy, we developed an efficient and cost-effective method for recycling carbon fiber, which is present in tablets through to BMWs.”
The method involves two steps: first, pyrolysis, to break down the material with heat; and second, oxidation. During the thermal decomposition of the CFRPs, the chemical reactions in the composites separate the fibers from the rest of the material, preserving them for later recovery.
"What makes our method so successful is that we have added specific parameters -- such as temperature, heating rate, atmosphere or time spent being oxidized and heated -- that preserve the functionality of carbon fiber," explains Dr. Hadigheh.
The method demonstrated it was effective at preserving fibers that maintain 90% of their original strength. If widely introduced to applicable industries, it could have significant implications for reducing greenhouse gas emissions from fiber-reinforced polymer production.
"The 2016 Australian National Waste Report concludes that the use of composite materials is creating future challenges to recycling. Plainly put, if we do not develop efficient and cost-effective methods to recycle carbon fiber composites, we risk damaging the environment significantly," Dr. Hadigheh concludes.