Process and Applications Development for Recycled Mixed-Stream Composites

Abstract

The goal of this IACMI Phase II Technical Collaboration Project was to establish the viability of producing affordable, recycled composite parts, which were produced from fibers with the properties in the range of those reclaimed through the controlled pyrolysis technology demonstrated in Phase I [1]. For the purpose of this report, we use the terms “recovered carbon fiber” (rCF) and “recovered glass fiber” (rGF) as the material reclaimed from controlled pyrolysis. This fiber recycling technology utilizes the inherent energy in composites for fuel and preserves the structural value of glass fiber (GF) and carbon fiber (CF) for reuse. It can also be used for recycling other waste streams at the same facility, thus spreading capital risk and recovery across multiple industries and achieving economy of scale. A second goal to be addressed was the viability of using recycled fibers as reinforcing materials in additive manufacturing applications. The project scope was to evaluate and validate demonstration of recycled composite parts and preforms that show the potential for successful business cases built around recycled composite products. The ultimate vision of the Phase II project is to enable widespread adoption of recycled materials throughout the U.S. and contribute significantly to the Institute’s technical goal of 80% composite recycling in five years. The American Composites Manufacturers Association (ACMA) led the project, with participation from the University of Tennessee (UT), South Dakota School of Mines and Technology (SDSMT), LyondellBassell, Owens Corning (OC), and CHZ Technologies (CHZ). This report summarizes the scope, experimental methods, and results of the following activities: Characterization of materials recovered from pilot scale pyrolysis unit Preforming of Recycled Composites Fibers: Part A – Bulk Molding Compound (BMC) Production and Preliminary Molding Part B - Composite Thermoplastic Compounding Part C – 3D Printable Resin Development Expanded Techno-Economic Analysis (TEA) and Life Cycle Assessment (LCA) of rCF and rGF Recycled Composite Demonstration Part Fabrication Part A – Automotive Vehicle Part Molding Part B – Big Area Additive Manufacturing (BAAM) Composite Development and Test Part Analyses In addition, the report presents the benefits, commercialization, accomplishments, conclusions, and recommendations of the potential for recycled parts using rCF and rGF. In the experimental portion, the following significant results were obtained: Overall, this project proved the potential of recycling fibers in various composite applications recovered using the pyrolysis route at up to 20% substitution of virgin glass and carbon fiber. Additional work should focus on removal of char and tighter control of the thermal history of the recycled fibers. In BMC compounds, supplementing the rGF with just a low level (10-20%) of virgin fiber, maintains a moldable compound with little property loss in flexural and tensile strength. In low density polyethylene (LDPE)/rGF composites (comingling process), following a post-pyrolysis process to remove the surface char, good fiber/resin dispersion was observed throughout the composite in several test parts. This suggests that wet-lay manufacturing may be an ideal pathway for forming composite intermediates from rGF. In PA6/recycled CF composites (DiFTS process), at fiber loadings of just 30 wt%, the flex strength reaches about 250 MPa and the tensile strength 180 MPa, suggesting commercial value. In 3D printed resin development, compared to neat ABS, the compression-molded rGF/acrylonitrile butadiene styrene (ABS) composite showed a 20% higher tensile strength and a 110% higher Young’s modulus, proving the reinforcing effect of rGF. Recycled demonstration composite parts were produced with rGF and rCF, using various resins and processes, and compared to those made with virgin fibers, with favorable results: Seat back rest Battery tray part John Deere door panel Submersible device generated using 3D printable composite feedstock material Finally, the TEA/LCA presented several business cases toward IACMI’s goal of 80% recycling. This project created a new, valuable knowledge base around conventional pyrolysis that can be built upon to spur new advances. Two companies are actively pursuing commercialization of controlled pyrolysis systems: A commercial pyrolysis unit has been permitted and site prep started in Youngstown, OH by CHZ Technologies, Inc to process tires which is anticipated to be in operation by early 2023. Testing is in process for electronic scrap, treated railroad ties/utility poles, and other materials. Funding for a further demonstration system dedicated to composites is being pursued with a combination of public and private support. In a separate development, a pyrolysis-based process is now being scaled up in Knoxville, TN by Carbon Rivers LLC to focus on recovery of fiberglass from wind blades and other composite materials. While this company uses a different pyrolysis process from the one examined in this study, the technoeconomic and lifecycle assessment frameworks and identification of key differentiating limitations in conventional pyrolysis have supported the value proposition of this new process as it moves towards commercialization with composites industry partners.