This Small Business Innovation Research Phase II project will develop long fiber thermoplastic (LFT) compositions based on recycled carbon fiber. In Phase I, we demonstrated the ability to make high quality LFT formulations based on (1) waste carbon fiber and (2) composites scrap and end-of-life thermoplastic and thermoset carbon fiber composites. Mechanical properties of these composites were similar to, and in some cases superior to, those for virgin carbon fiber. In this project, we will continue to develop manufacturing capabilities to make both thermoset and thermoplastic composites. In this Phase II project, we will look at the following technical issues: (1) examining the use of new recycled fiber forms and comparing the results to prior data; (2) investigating the molding parameters associated with the "forging" of flat blanks of LFT; (3) optimizing the LFT compositions; (4) demonstrating consistent moldability and mechanical properties; and (5) demonstrating the conversion of molded LFT parts back into LFT compound to "close the loop" on recycling. This effort will feature partnerships with a not-for-profit composites laboratory and another small business, both of whom have extensive experience in developing LFTs using virgin carbon fiber.
The broader impact/commercial potential of this project includes a reduction in the amount of carbon fiber going into landfills and lower greenhouse gas emissions. Worldwide carbon fiber production is ~80 million pounds per year, with demand growing at ~15% annually. Conservatively, 20% of this fiber ends up as waste during composite manufacture (~16 million pounds/year) and is landfilled. The aerospace industry is a main consumer of this material (military aircraft, Boeing 787 and Airbus A380), but industrial, automotive, and recreational markets are also growing. However, few composite manufacturing processes are designed to work with chopped fibers, which is the primary form of recycled carbon fiber. Developing LFTs based on recycled carbon fiber will allow us to achieve "Three Shades of Green" by eliminating landfilling, reducing energy costs relative to virgin fiber, and improving sustainability. A significant business opportunity exists if manufacturing methods can be developed that use recycled fiber in the forms that are typical of reclaimed material. The potential market for composites made from recycled/reclaimed carbon fiber is more than $200 million. Finally, the amount of energy needed to recycle carbon fiber is only about 4% of that needed to make virgin fiber, reducing associated greenhouse gas emissions.
This project developed long fiber thermoplastic (LFT) compositions and injection molding compositions based on recycled carbon fiber (RCF). Most fiber-reinforced thermoplastic composites are made by (1) compounding chopped fiber with thermoplastic resin in an extruder or (2) compression molding broad goods consisting of chopped or continuous fiber with a thermoplastic matrix. Compounded thermoplastics, comprising injection molding and LFT, represent more than 80% of the overall thermoplastic composite market, mainly with fiberglass reinforcement. Injection molding and LFT have great shape forming capability and make net-shaped parts, which results in little waste of material during fabrication. We used several types of RCF in this project including: (1) IM7 fiber recovered from edge scrap from a weaving operation; (2) T800 fiber recovered from scrap prepreg; (3) AS4 fiber reclaimed from an end-of-life fighter aircraft; and (4) AS4 fiber reclaimed from thermoplastic prepreg. All of the fibers were aerospace grade: IM7 and T800 are intermediate modulus fibers; AS4 is a standard modulus fiber. This project demonstrated that RCF drawn from a wide variety of sources is a valuable raw material for making nylon (PA66), polyphenylene sulfide (PPS), and polyethersulfone (PESU)-based LFT and injection molding compounds. The mechanical properties achieved with RCF in LFT and injection molding compounds were equal or superior to those for commercial materials in all the thermoplastic systems we have studied. Further, in work conducted outside of the NSF project, we have demonstrated the fabrication of high-quality injection molding compounds based on RCF and several other polymers including polypropylene, nylon 6, polycarbonate, PEI[polyetherimide], and PEEK [poly(ether ether ketone)]. The recycled carbon fibers - whether in as-received, pyrolyzed, or regrind conditions - compounded and molded well in the PPS, PESU, and PA66 resin compositions. As an example of "closing the loop," we manufactured about 250 pounds of LFT parts in a PPS-40 wt % RCF composition. We then shredded those parts into ~1/2-inch pieces, re-compounded the material, and then molded new parts from the re-compounded LFT. We repeated this process for six generations - the original LFT composition and fiber regrinds. For each generation, we measured strength, stiffness, impact resistance, glass transition temperature, melting point, and vibrational loss behavior. We observed no systematic change in any of the properties as the number of generations increased. This behavior indicated that the PPS-40 wt% RCF LFT system is robust relative to the reuse and reprocessing of molded parts. Another example of "closing the loop" involved thermoplastic composites made from uniaxial prepreg. Composites made from uniaxial or woven continuous carbon fiber-reinforced thermoplastic resins are often touted as being "recyclable" simply by virtue of their thermoplastic resin matrix. What is often not mentioned is "how" those continuous fiber composites would be recycled. As part of this study, out-of-spec seats for a regional jet aircraft made from uniaxial carbon fiber and PPS were shredded, blended with additional PPS resin to make an LFT compound, and then compression molded into new LFT parts. The mechanical properties of those parts were excellent. This is a prime example of how continuous filament carbon fiber thermoplastic composites can be recycled into new, high quality forms. The use of carbon fiber, especially affordable RCF, in place of fiberglass reinforcements provides a path for replacing light metals like aluminum and magnesium alloys in aircraft, automobiles, and consumer electronics with injection molded or LFT molded thermoplastic parts. Several automotive OEMs are actively evaluating RCF-reinforced engineering polymers (nylon 6 and 66, PET, PBT, polycarbonate, etc.) as weight-saving approaches to replace metal parts in many different under-hood and secondary structural components. We have received inquiries from many producers of injection molding and LFT compound regarding the use of our RCF in commercial applications. We currently have over $7 million in orders booked for RCF to be used in injection molding compounds. The applications range from consumer electronics (cases for phones, tablets, and lap top computers) to automotive (various secondary structural parts) to aerospace (various parts in aircraft interiors).