Matthew Korey

To enable re-use, recycled fiber-filled thermoplastics may require intermediate processing, such as twin-screw compounding. These intermediate processes can introduce additional processing-induced degradation and performance variability. This study evaluated the recyclability of carbon-fiber-reinforced acrylonitrile butadiene styrene (CF-ABS) through ten consecutive pilot-scale extrusion cycles to determine the primary degradation mechanism as a function of lifetime and to quantify the impact on mechanical performance. Chemical analysis revealed that the ABS matrix remained chemically robust throughout repeated extrusion cycles, whereas optical microscopy showed that fiber breakage was significant. Fiber length exponentially decayed with repeated cycles, with the decay rate stabilizing between the 3rd and 5th cycle, resulting in a 62% reduction in weight-averaged fiber length from C0 to C10. The reduction in fiber length was found to govern both the rheological and mechanical behavior of the composite material. Viscosity and storage modulus decreased with decreasing fiber length while tan(δ) and elongation at break increased, shifting toward values characteristic of neat ABS and indicating a transition from fiber-dominant to matrix-dominant behavior. The tensile strength decreased 35% after the 10th cycle, and its decay behavior correlated with the decay rate of the measured fiber length. This correlation enabled the development of a simple analytical model to predict tensile strength, which predicted tensile strength more accurately than the Kelly–Tyson model (RMSE of 38 reduced to 3.5) and required fewer experimentally derived inputs. Overall, this study demonstrated that fiber breakage, rather than chemical degradation of the ABS matrix, dictates performance of recycled CF-ABS.

Large-format additive manufacturing is among the fastest and most energy efficient routes to large polymer parts, yet its dominant feedstocks, carbon- and glass-fiber-reinforced petroleum-based polymers are costly, energy-intensive, and reliant on imported materials. This review summarizes a multiyear collaboration between Oak Ridge National Laboratory and the University of Maine to displace these feedstocks with composites derived from domestic forest products, advancing U.S. manufacturing competitiveness through an abundant, renewable, and locally sourced supply chain. Integrating the University of Maine’s expertise in forest-derived composites and cellulose-based feedstocks with Oak Ridge National Laboratory’s large-scale printing capabilities, the partnership has enabled the fabrication of large components from bio-derived, recyclable, and locally sourced materials. These materials deliver performance sufficient for a defined class of semi-structural and tooling applications while offering decisive advantages in cost (target <$3/lb), embodied energy (a reduction from ~317 to ~57 MJ/kg for representative feedstocks), and end-of-life recyclability. These material advances were enabled by, and in turn drove, parallel progress in the manufacturing platform itself: among the world's largest-scale printing systems, operated with the precision, speed, and closed-loop process control, underpinned by process modeling, required to print challenging bio-based feedstocks reliably, together with a 500 lb/hr extruder and multiplexing extrusion technology that push deposition rate toward high-volume production economics. This article reviews the materials systems, processing challenges, demonstration parts, and scale-up opportunities associated with this program, with emphasis on sustainability, manufacturability, and application relevance.

Plastics such as polyamides (PAs) possess unique physicochemical properties that make them indispensable in modern society. However, their energy‐intensive production and challenging end‐of‐life management highlight the urgent need for efficient recycling or remanufacturing solutions. Enzymatic depolymerization offers a promising route toward circular recycling, yet remains constrained by limited enzyme characterization, lack of validation under industrially relevant conditions and substrates, and overall performance. Here, we optimized the reaction conditions for three recently discovered nylon‐degrading enzymes. One of them, Nyl12, achieved product titers with PA6 and PA66 that exceed previously reported values, without enzyme engineering or substrate pretreatment. We further demonstrated the scalability of the process and its application to complex PA‐based materials used in microelectronic components. Analysis of substrate features, including surface area and particle size, revealed key parameters governing enzymatic activity and provided a framework for future pretreatment and process optimization efforts. In combination, these efforts provide a new benchmark for enzymatic nylon recycling.

Cellulosic fibers can impart many unique benefits into composite applications, such as reduced weight or structural reinforcement; however, these materials also increase hygroscopicity and decrease thermal stability, restricting broader applications. The present work adapted an experimental process for functionalizing the cellulose surface using citric acid (CA) for three fibers: a 100% cellulose bleached soft Kraft pulp (e.g., creafill) and two natural fibers with similar composition but different fiber morphology, flax fiber and banana fiber. The process uses CA with a sodium hypophosphite (SHP) catalyst to chemically functionalize fiber surfaces, and the reaction mechanism was investigated through Fourier Transform Infrared Spectroscopy (FTIR), which suggested a grafting mechanism rather than a surface-based crosslinking between neighboring sites. Functionalized fibers were compounded into polylactic acid (PLA) at 20 wt.% to better understand how this functionalization might impact critical performance properties like thermal stability, crystallization, thermal mechanical properties, and water uptake of these composites. The study demonstrated varying levels of efficacy for the functionalization of cellulosic fibers with CA/SHP and the fiber with the most open microstructure, e.g., banana fiber, exhibited the largest change in its properties with a 38% reduction in water uptake compared to untreated banana fiber composites. Parallel evaluation of the functionalization process for different fibers demonstrates the importance of fiber morphology on surface modification and can enable their use in composites by demonstrating the efficacy of this potentially low-cost, low-toxicity method for reducing hygroscopicity and improving thermal stability.

Wind turbine blades are highly engineered structures designed to face temperature extremes and high winds. However, erosion of the blade's leading edge and subsequent repair remains a significant and costly challenge for the wind energy industry. Repair of these leading edges can lead to large amounts of downtime for the turbine and significant operational inefficiencies. In this work, the strength of adhesion and healing ability of a commercially available vitrimer (Mallinda's VITRIMAX) was compared to that of a thermoplastic resin, which has previously been demonstrated in wind energy applications (Arkema's Elium) to evaluate their efficacy as surface coatings for wind turbine blades, particularly their leading edges. Vitrimers are a class of inherently reprocessable thermosets, and it was theorized that vitrimer‐based leading edge coatings could enable more robust and efficient wind turbine blades with decreased operational downtime and safer maintenance practices. It was found that the VITRIMAX adhered better to the wind blades' surfaces than both the manufacturer's paint and Elium, with increases in pull‐off strength of adhesion ranging from 24% to 83% above that of the original paint. Furthermore, the VITRIMAX adhered strongly to the underlying composite of each blade with strength of adhesion values increasing in ranges from 42% to 97% above that of the original paint. Finally, the vitrimer coating showed an 88% decrease in surface roughness compared to end‐of‐life blade materials, and initial healing demonstrations in which coatings were manually scratched and subsequently healed exhibited an ~84.5% decrease in scratch depths.

To enable re-use, recycled fiber filled thermoplastics may require intermediate processing, such as twin-screw compounding. These intermediate processes can introduce additional processing-induced degradation and performance variability. This study evaluated the recyclability of carbon fiber reinforced acrylonitrile butadiene styrene (CF-ABS) through ten consecutive pilot-scale extrusion cycles to determine the primary degradation mechanism as a function of lifetime and to quantify the impact on mechanical performance. Chemical analysis revealed that the ABS matrix remained chemically robust throughout repeated extrusion cycles, whereas optical microscopy showed that fiber breakage was significant. Fiber length exponentially decayed with repeated cycles, with the decay rate stabilizing between the 3rd and 5th cycle and resulting in fiber length reduction after the 10th cycle of 62%, using a weighted average. The reduction in fiber length was found to govern both the rheological and mechanical behavior of the composite material. Viscosity and storage modulus decreased with decreasing fiber length while tan(δ) and elongation at break increased, shifting toward values characteristic of neat ABS and indicating a transition from fiber-dominant to matrix-dominant behavior. A strong correlation between fiber-length decay and a reduction in tensile strength enabled the development of a simple analytical model, which predicted tensile strength more accurately than the Kelly-Tyson model and required fewer experimentally derived inputs. Overall, this study demonstrated that fiber breakage, rather than chemical degradation of the ABS matrix, dictates performance of recycled CF-ABS and provides an approach for predicting material properties prior to manufacturing for a range of thermoplastic composites.

Large-format additive manufacturing (LFAM) is an enabling manufacturing technology capable of producing large parts with highly complex geometries for a wide variety of applications, including automotive, infrastructure/construction, and aerospace mold and tooling. In the past decade, the LFAM industry has seen widespread use of bio-based, glass, and/or carbon fiber reinforced thermoplastic composites which, when printed, serve as a lower-cost alternative to metallic parts. One of the highest-volume materials utilized by the industry is carbon fiber (CF)-filled polycarbonate (PC), which in out-of-autoclave applications can achieve comparable mechanical performance to metal at a significantly lower cost. Previous work has shown that if this material is recovered at various points throughout the manufacturing process for both the lab and pilot scale, it can be mechanically recycled with minimal impacts on the functional performance and printability of the material while significantly reducing the feedstock costs. End-of-life (EOL) CF-PC components were processed through industrial shredding, melt compounding, and LFAM equipment, followed by evaluation of the second-life material properties. Experimental assessments included quantitative analysis of fiber length attrition, polymer molecular weight degradation using gel permeation chromatography (GPC), density changes via pycnometry, thermal performance using dynamic mechanical analysis (DMA), and mechanical performance (tensile properties) in both the X- and Z-directions. Results demonstrated a 24.6% reduction in average fiber length compared to virgin prints, accompanied by a 21% decrease in X-direction tensile strength and a 39% reduction in tensile modulus. Despite these reductions, Z-direction tensile modulus improved by 4%, density increased by 6.8%, and heat deflection temperature (HDT) under high stress retained over 97% of its original value. These findings underscore the potential for integrating mechanically recycled CF-PC into industrial LFAM applications while highlighting the need for technological innovations to mitigate fiber degradation and enhance material performance for broader adoption. This critical step toward circular material practices in LFAM offers a pathway to reducing feedstock costs and environmental impact while maintaining functional performance in industrial applications.

As the automotive industry increasingly relies on plastic components to meet fuel efficiency and emissions targets, the challenge of managing end-of-life vehicle (ELV) plastics continues to grow. Currently, more than 80% of ELV plastics in the U.S. are landfilled due to limited economic incentives and technical barriers to recycling. This study examines a mechanical recycling pathway for thermoplastic components disassembled from ELVs and assesses their usability for reintegration into new vehicle parts. Four representative materials were chosen based on material labels embedded in recovered parts and aligned with their virgin industrial equivalents: polypropylene (PP), 10% talc-filled PP (PP-T10), 20% talc-filled PP (PP-T20), and a 20% glass-/mineral-filled polyamide (PA6 + GF7 + MF13). The materials underwent shredding, drying, and injection molding before being characterized by particle size analysis, density measurement, thermal analysis (TGA, DSC), mechanical testing, and heat deflection temperature (HDT) evaluation. The results in this work indicated that minor differences in crystallinity were observed and small differences between model materials and ELV materials could have contributed to these changes. Mechanical testing revealed that neat polypropylene suffered a 15–20% reduction in stiffness and tensile strength, but talc-filled polypropylene and glass/mineral-filled nylon retained >90% of their modulus, strength, and heat deflection temperature values relative to virgin controls. Differences between virgin and ELV materials could have been attributed to use life degradation, contamination during use life, or even chemical/processing differences in model materials and ELV materials. However, these findings suggest that mechanically recycled, disassembled ELV plastics can retain sufficient structural performance to support circularity efforts in the automotive sector.