Recycled Carbon Fiber Research Articles

Effect of Silane Coupling Agent on the Properties of Recycled Carbon Fibers Reinforced Bio-based Epoxy Composites

In this work, the effect of a silane coupling agent on the mechanical behavior of recycled carbon fiber reinforced bio-based epoxy composites was studied. For this purpose, the surface of the recycled carbon fiber was treated with 3-aminopropyltriethoxysilane (APS) agent at the concentrations in the 0–8 wt.% range. Dynamic mechanical analysis and characterization of the tensile and flexural properties were performed to observe the mechanical behavior of the specimens, and the morphology of the fracture surface after mechanical testing was also studied by scanning electron microscopy. It was found that the glass transition temperature and the tensile and flexural strengths of the composites increased with an addition of a suitable amount of the silane agent (< 4 wt.%), which was attributed to the cross-linking and curing reaction between the amino groups of APS and the epoxy matrix that improved the interfacial bonding. Thus, an appropriate concentration of the silane coupling agent can improve the mechanical properties of recycled carbon fiber reinforced bio-based epoxy composites.

Microstructural changes and mechanical performance of cement composites reinforced with recycled carbon fibers

In recent years, efforts have been made to utilize recycled carbon fibers (RCFs) into the cement composites. However, limited information is available on the interaction of these recycled fibers with the host cement matrix. Therefore, this study aims to provide a better understanding of the influence of milled recycled carbon fibers (RCFs) on cement composites. For this purpose, six different fiber volume fractions ranging from 0.25% to 1.5%, at an increasing rate to 0.25%, were selected to develop fiber-reinforced cement composites, and a comprehensive research study was conducted to investigate the effect of RCFs on strength improvement, microstructure, crystalline phase change, and hydration products of cement composites over time. The X-ray diffraction analysis, FTIR, and thermogravimetric analysis revealed that RCFs promote the growth of hydration products by providing inert nucleation sites without any additional chemical reaction. The degree of hydration and chemically bound water was increased by 6.64% and 1.59%, respectively, when 1.5% by volume of RCFs were added to the cement composites. The reinforcing effect was most obvious with the addition of 1% by volume of RCFs, by which the flexural and compressive strengths were increased by 82% and 47%, respectively. This study revealed that RCFs have a great potential to be utilized as reinforcement into the cement composites.

Elucidation of damage factors to recycled carbon fibers recovered from CFRPs by pyrolysis for finding optimal recovery conditions

The purpose of this study is to further the search for the optimal conditions for the recovery of recycled carbon fiber (rCF) from epoxy matrix CFRP by thermal decomposition. We revealed that an oxidizing atmosphere was required to recover rCF. By investigating the strength reduction of CF after the heat treatment (hCF), it was demonstrated that significant strength reduction occurred at 600 °C. The damage also depended on the treatment temperature and time because of the oxidative decomposition of the fiber surface. By comparing the virgin CF, hCF and rCF, it was demonstrated that the strength reduction of the rCF was caused not only by the thermal oxidative decomposition but also by its interaction with the resin. Additionally, the time required to recover rCF differs depending on the treatment temperature and the degree to which each effect on the CF in CFRP depended on the location of the CF. At low temperatures, recovery time was longer, and the differences in strength between rCF recovered from the inner and outer layers were large. although CF recovery was quick at high temperatures, but the strength was significantly lower because of the effect of the interaction with the resin.

Mechanical properties and foaming behavior of polypropylene/elastomer/recycled carbon fiber composites

AbstractResearch on lightweight products for transportation industry, to address fuel efficiency and lower carbon footprint, has attracted great attention due to public environmental awareness. Polymer composites containing carbon fiber are boosted by automotive original equipment manufacturers (OEMs) as a replacement for steel. However, their high cost has generated interest to find cost‐effective alternatives. In this report, a recycled carbon fiber and an elastomer are introduced to polypropylene impact copolymers to modify matrix properties in terms of strength and toughness. Fractography analysis is carried out to elucidate the failure mechanisms governing the mechanical performance of the compatibilized carbon fiber reinforced thermoplastic polyolefin (TPO) composites. The results suggest that for the TPO composites, toughened by an ethylene‐1‐octene copolymer, the complex interplay of intrinsic and extrinsic toughnesses in impact resistance is predominantly governed by the presence of the fibers. Incorporating 20 wt% recycled carbon fibers into the matrix resulted in an improvement of the heat distortion temperature (HDT) by 100 °C, and ~ 3.5 and ~ 11.5 times enhancements in tensile strength and stiffness, respectively. Moreover, microcellular foams with expansion ratios higher than 11 and 5 were achieved for the neat samples and reinforced composites, respectively, confirming the foamability of composites with such a high carbon fiber content.

Multifunctionality of polymer composites based on recycled carbon fibers: A review

Carbon fiber reinforced polymers (CFRP) offer outstanding lightweight potential and can play a key role for modern energy and mobility concepts. However, production of carbon fibers is energy- and cost-intensive, while at the same time waste rates of common manufacturing technologies are quite high and repair possibilities for damaged parts still limited. Therefore, holistic recycling approaches are urgently required in order to reach acceptable cost-efficiency and sustainability. What makes the recycling so challenging, is the fact that true recycling, i.e. re-usage of fibers in high-performance composites, requires preservation of a high fiber length and enabling of accurate fiber orientation. This generates a trade-off between the best possible exploitation of the fiber properties and the effort to minimize the recycling costs. Hence, this paper does not only give a brief overview of technologies to recover carbon fibers from waste and to process them to new CFRP components. In addition, different approaches are presented, that exploit the specific characteristics of semi-finished products based on recycled carbon fibers, in order to achieve process- or material-related multifunctionality. This includes quasi-plastic deformation behavior (enables deep-drawing or curved tow placement), improved surface quality through reduced fiber print-through, robust resin impregnation through supersaturated nonwovens, and high energy absorption.

Reinforcing potential of recycled carbon fibers in compatibilized polypropylene composites

Materials that are low cost and lightweight are essential for future automotive and aerospace industries. While carbon fibers have been shown to achieve high mechanical properties for high-end applications, their high cost has generated interest to find cost-effective alternatives. The recent advances in recycling carbon fibers has created an opportunity to develop low cost composite materials. Using a maleic anhydride grafted polypropylene (MA-g-PP), the interfacial adhesion between the polypropylene (PP) matrix and the recycled carbon fibers is greatly improved. The integration of 20 wt% recycle carbon fibers result in 2.4 times, 4.9 times, and 5.7 times enhancements in tensile strength, notched Charpy impact strength, and flexural modulus, respectively. This enhancements in mechanical properties are significantly higher than those reported in previous works. The addition of recycled carbon fibers also increases the heat deflection temperature (HDT) of the neat PP sample, indicating the higher resistance of the composite samples at high temperature. This work demonstrates the great potential of the recycled carbon fibers in manufacturing cost-effective and high-performance PP composites.

Life cycle assessment and energy intensity of CFRP recycling using supercritical N-butanol

Recycling carbon fiber reinforced polymer (CFRP) waste is unavoidable for the sustainable manufacturing and cost reduction of CFRP products. Supercritical fluid technology is an emerging chemical method for recycling CFRP waste, but its energy intensity and environmental implication are limited understanding. In this paper, the energy intensity and environmental impact of supercritical fluid technology were quantitatively assessed in CFRP recycling process. Then, the life cycle assessment (LCA) method was used to analyse the life cycle environmental impact of CFRP in two scenarios, scenario (a) using conventional waste disposal method, while scenario (b) with CFRP waste recycling process. The results show that the energy consumption of CFRP waste recycling is 49.21 MJ/kg using the supercritical n-butanol method, which is far lower than that of virgin carbon fiber production (286 MJ/kg). Scenario (b) with CFRP waste recycling has a lower impact than scenario (a) at nine environmental impact categories, including a 26% reduction of global warming potential. Besides, the energy consumption of the supercritical n-butanol method is 31% lower than that of the steam thermolysis method (71.64 MJ/kg) in recycling 1 kg of CFRP waste, which validates that the supercritical n-butanol method is a potential strategy for recycling CFRP waste.

Development of Carbon Fiber-Reinforced Thermoplastics for Mass-Produced Automotive Applications in Japan

The application of carbon fiber-reinforced thermoplastics (CFRTPs) for automotive mass production is attracting increasing attention from researchers and engineers in related fields. This article presents recent developments in CFRTPs focusing on the systematic development of lightweight CFRTP applications for automotive mass production. Additionally, a related national project of Japan conducted at the University of Tokyo is also introduced. The basic development demands, the specific requirements of CFRTPs for lightweight applications in automotive mass production, and the current development status and basic scientific outputs are discussed. The development of high-performance CFRTPs (chopped carbon fiber tape-reinforced thermoplastics (CTTs)) and functional CFRTPs (carbon fiber mat-reinforced thermoplastics (CMTs)) is also introduced. The fabrication process control of CTTs is evaluated, which demonstrates the extreme importance of the mechanical performance. The ultralight lattice, toughened structures, and orientation designable components of CMTs provide a flexible multi-material solution for the proposed applications. Moreover, highly efficient carbon fiber recycling technology is discussed, with recycled carbon fibers exhibiting outstanding compatibility with CFRTPs. A cost sensitivity analysis of carbon fiber and CFRTPs is conducted to guarantee the feasibility and affordability of their application. This article also discusses the trends and sustainability of carbon fiber and CFRTPs usage. The importance of the object-oriented optimal development of CFRTPs is emphasized to efficiently exploit their advantages.

Biobased High-Performance Epoxy Vitrimer with UV Shielding for Recyclable Carbon Fiber Reinforced Composites

A novel biobased epoxy vitrimer (Gte-VA) with desirable mechanical properties was synthesized from glycerol triglycidyl ether (Gte) and an imine-containing hardener (VA), which was also a biobased ...

Ultrafast carbon nanotubes growth on recycled carbon fibers and their evaluation on interfacial shear strength in reinforced composites

The global demand for products manufactured with carbon fibers (CFs) has increased in recent years; however, the waste generated at the end of the product lifetime has also increased. In this research, the impact of the addition of carbon nanotubes (CNTs) on the interlaminated resistance of recycled carbon fibers (RCFs) was studied. In this work, a recycling process of the composite material was applied via thermolysis to obtain the CFs, followed by the growth of CNTs on their surface using the Poptube technique. The recycling temperature were 500 °C and 700 °C; and ferrocene and polypyrrole were used to grow CNTs on CFs surface. CNTs were verified by Raman spectroscopy and scanning electron microscopy (SEM). Finally, to determine the interlaminar resistance, a double cantilever beam (DCB) test was performed. The results indicate that with Poptube technique, CNTs can be grown on RCFs using both impregnations. Thermolysis recycling process at 500 °C allowed CFs without resin residues and without visible damage. The DCB tests showed a decrease in the fracture resistance in mode I loading of 34.9% for the polypyrrole samples and 29.3% for the ferrocene samples compared with the virgin carbon fibers (VCFs) samples with a resistance of 1052.5 J/m2.

Recycling of Carbon Fiber-reinforced Epoxy Resin-based Composites Using a Benzyl Alcohol/Alkaline System

High-efficiency recycling of carbon fiber-reinforced epoxy resin-based composites is difficult because of their three-dimensional network structure. In this article, a benzyl alcohol/alkaline system was used to recycle carbon fiber-reinforced epoxy resin-based composites cured by an anhydride. The degradation rate, mechanical properties and degradation mechanism of the recycled carbon fiber were determined by gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy, liquid chromatography-mass spectrometry, scanning electron microscope and X-ray photoelectron spectroscopy. The experimental results indicated that there were two steps in benzyl alcohol/K3PO4 degradation system. The first was transesterification by benzyloxy selective attack to give small-molecule esters. Then the esters were saponified by the alkaline materials. After degradation, the stratification of resin and benzyl alcohol occurred, which was conducive to their separation. The optimal degradation time was 40 min under the weight ratio of alkaline material to benzyl alcohol of 1:10, atmospheric pressure, and temperature of 195 °C and the decomposition efficiency exceeded 90 %. A clean carbon fiber surface was obtained with an oxygen content comparable to that of the original carbon fiber. The tensile strength of the recycled carbon fiber was above 90 % of the original value.

UV-Assisted 3D Printing of Polymer Composites from Thermally and Mechanically Recycled Carbon Fibers

Despite the growing global interest in 3D printed carbon fiber reinforced polymers, most of the applications are still limited to high-performance sectors due to the low effectiveness–cost ratio of virgin carbon fibers. However, the use of recycled carbon fibers in 3D printing is almost unexplored, especially for thermoset-based composites. This paper aims to demonstrate the feasibility of recycled carbon fibers 3D printing via UV-assisted direct ink writing. Pyrolyzed recycled carbon fibers with a sizing treatment were firstly shredded to be used as a reinforcement of a thermally and photo-curable acrylic resin. UV-differential scanning calorimetry analyses were then performed to define the material crosslinking of the 3D printable ink. Because of the poor UV reactivity of the resin loaded with carbon fibers, a rheology modifier was added to guarantee shape retention after 3D printing. Thanks to a customized 3D printer based on a commercial apparatus, a batch of specimens was successfully 3D printed. According to the tensile tests and Scanning Electron Microscopy analysis, the material shows good mechanical properties and the absence of layer marks related to the 3D printing. These results will, therefore, pave the way for the use of 3D printed recycled carbon fiber reinforced polymers in new fields of application.

Life cycle energy and greenhouse gas emissions implications of using carbon fiber reinforced polymers in automotive components: Front subframe case study

Vehicle lightweighting benefits consumers through fuel savings, manufacturers through a more fuel-efficient vehicle portfolio, and the environment through reduced fossil fuel use and lower emissions. Vehicle components can be lightweighted by replacing conventional materials with alternatives such as aluminum or composites. However, lightweight materials come with their own set of environmental and economic challenges. Often, manufacturing of lightweight materials requires more energy than for conventional materials such as steel. Understanding the net energy and environmental benefits of lightweighting requires life cycle assessment with a large enough system boundary to prevent shifting of impacts and to ensure a fair comparison between different material options. Life cycle assessments of carbon fiber composite parts are hampered by substantial uncertainties in the energy needed for their production and recycling and the vehicle fuel consumption benefits. The present study addresses these deficiencies using a detailed vehicle fuel consumption model and industrially relevant carbon fiber production data and component design. The front subframe case study considered illustrates the challenges associated with achieving life cycle energy and greenhouse gas savings using carbon fiber. The base case with no powertrain resizing, secondary weight savings, or recycled carbon fiber and with 160,000 miles vehicle lifetime has no energy or emission benefits. When powertrain resizing, secondary weight savings, carbon fiber recycling, and increased vehicle lifetime travel were considered, energy and greenhouse gas benefits were found.

Carbon fibers recovery from CFRP recycling process and their usage: A review

Carbon fiber is a popular polymer reinforcing material for forming carbon fiber reinforced polymer composites (CFRP) as a construction material under high loading. The use of this composite has spread in various fields of technology with a quite large production volume annually. Consequently, when the life span of the composite has run out it will leave composite waste and brought up CFRP recycling cases as a dare for scientists and engineers. Research on carbon fiber reclamation from CFRP materials has been carried out with the main purpose of taking and reusing carbon fiber. Several CFRP recycling methods have been investigated in laboratories and applied successfully to business but the capacity of production is not comparable with the addition of CFRP composite waste each year. High recycling energy is one of the main reasons constrained this waste recycling business. Recycled carbon fiber (r-CF) also shows a decrease in performance compared to virgin carbon fiber (v-CF) with a varied distribution of degradation according to the recycling method applied. However, reuse of r-CF in the form of short fibers in a composite materials under medium and low loads has been thoroughly tested and applied with promising results as a reinforcement for new composites

Processing and properties of long recycled-carbon-fibre reinforced polypropylene

Recycled carbon fibres have been employed as a reinforcement material for the synthesis of polypropylene-based thermoplastic matrix composites with different fibre/resin ratios (10, 20 and 30%) by means of injection moulding. A thorough study of their mechanical properties including tensile, impact and bending tests, as well as fibre distribution and orientation and chemical behaviour was conducted. The stiffness and strength of the composites increased linearly with the fibre fraction in a ratio of 180 and 0.9 MPa/% Vf respectively. The distribution and alignment of the fibres in the injection flow contributed to the improvement of the mechanical behaviour of the composite. In addition, changes in the fibre orientation were found along the injected sample, which emphasised the importance of temperature control during injection on the alignment of the fibres. However, even though the addition of a coupling agent improved the fibre/matrix adhesion, the unremarkable impact results reveal that future efforts in long recycled-carbon-fibre reinforced thermoplastic composites should be directed to enhance interface performance.

Catalyst-free malleable, degradable, bio-based epoxy thermosets and its application in recyclable carbon fiber composites

Carbon fiber reinforced composites (CFRCs) are a kind of most potential materials due to the high strength-to-weight ratio, excellent fatigue and corrosion resistance. However, the vast majority of CFRCs prepared from carbon fiber and thermosetting matrices are difficult to be recycled and depend on limited fossil resources. Here, for the first time, we reported fully bio-based catalyst-free epoxy vitrimers for CFRCs. The epoxy vitrimers exhibited excellent malleability and could be reprocessed by compression molding. Outstanding degradability was also achieved, which enabled multiple recovery of CF from their CFRCs without damage. In addition, CFRCs regenerated from multiple recovered CF exhibited insignificant differences from the original CFRCs. This work will provide an effective method for the sound development of CFRCs from both economic and environmental aspects.

Optimisation of CFRP composite recycling process based on energy consumption, kinetic behaviour and thermal degradation mechanism of recycled carbon fibre

Abstract Pyrolysis is a thermo-chemical method to recover clean fibres from carbon fibre reinforced polymer (CFRP) composite waste under oxygen-free conditions. To ensure the recovery quality and economic efficiency of reclaimed fibres, thermal decomposition of CFRP needs to be guided by the kinetic analysis. This paper investigates the kinetic behaviour of CFRP thermal decomposition at temperatures of up to 800 °C. A thermo-gravimetric method is used to monitor the thermal decomposition of CFRP samples during the pyrolysis process. The activation energies (E) required for different conversion fractions (α) are evaluated based on five different kinetic models: four Arrhenius-type model-free methods (Friedman, OFW, KAS and Starink) and one curve fitting method (Coats-Redfern). Pyrolysis of CFRP composite wastes show that the process consists of two stages, where majority of the polymer matrix (55%) is removed in the first stage of reaction. During stage one and up to 425 °C, lower heating rates successfully lead to higher conversion fractions with lower activation energies. Moreover, by investigating physical characteristics of the recycled fibres using scanning electron microscopy (SEM) and conversion kinetics of the recycling process, it is shown that pyrolysis of the composite remains efficient until 425 °C and an oxidation process up to 550 °C is required to achieve high quality recycled carbon fibre (rCF) products. The outcomes of this research contribute to optimisation of process variables and development of highly efficient and cost effective CFRP recycling method using pyrolysis technique.

Heterogeneous Thermoset/Thermoplastic Recycled Carbon Fiber Composite Materials for Second-Generation Composites

With an increase in the use of carbon fiber composites in the aerospace and automobile industry a collateral issue of what to do with end-of-life carbon fiber composites has risen. In this study, we successfully developed a second-generation composite using a heterogenous mixture of thermoset and thermoplastic recycled carbon fiber composites (CFCs). The recovered vinyl ester and epoxy CFCs (thermosets) were characterized using thermogravimetric analysis. Adhesive performance was evaluated through double lap shear tests by melt-bonding a thermoplastic polyether ether ketone (PEEK) CFC to either the thermoset epoxy or vinyl ester CFC. The waste carbon fiber composites were also mechanically milled and classified through screening techniques. The resulting milled materials were used to form and produce composite panels through high temperature compression molding. The influence of particle size and platen temperature were evalauted through mechanical testing. Results indicate that melt-bonding with the vinyl ester/CFC exhibited significantly higher lap shear strength values than that between epoxy/CFC and PEEK. Findings also show that adding thermoset CFCs to the thermoplastic system (PEEK) enhanced the flexural properties of composites.

Development of recycled polypropylene-based sustainable composites with recycled carbon fibre/Kenaf fibre hybrid reinforcements

Recycled carbon fibre (RCF) and Kenaf fibre (KF) have been used as reinforcement materials in combination with recycled polypropylene (RPP) matrix to manufacture a sustainable composite. Maleic anhydride grafted polypropylene (MAPP) has also been used as a compatibilizer to modify the interface between fibres and matrix composites, resulting in improved composite strength and thermal resistance. After modified with MAPP, the recycled carbon fibre was combined with KF fiber to improve the KF/RPP composite properties such as mechanical and thermal stability. The results were indicated that the mechanical properties of RCF/RPP composite was improved with increasing of MAPP when MAPP added 8 Wt. %, these reached a Maximum of 77.6 MPa and 271.4 MPa, respectively. When the RCF combined with the KF hybrid composite, the mechanical strength of the hybrid composite was improved with the amount of RCF. The DSC results showed that the MAPP could reduce the Tc of RPP and increase the crystallization degree. The hybrid composite presented that the crystallization degree was increased with the increment of RCF content. The DMA results showed that the RCF can influence the β translation of RPP.

Life Cycle Primary Energy Demand and Greenhouse Gas Emission benefits of vehicle lightweighting with recycled carbon fibre

Recycled carbon fibre (rCF) is a potential material for sustainable vehicle lightweighting but its realistic environmental impacts are still unclear. In this study, a Life Cycle Assessment (LCA) investigates the primary energy demand (PED) and global warming potential (GWP) of using rCF reinforced Polyamide 66 (PA66) for a side-view mirror bracket, in comparison with its conventional cast aluminium counterpart. Results indicate that using rCF+PA66 with 40wt% rCF in the US can achieve around 13% and 34% reduction in the PED/GWP of the cradle-to-gate phases and the use phase, respectively. Scenario analysis is also carried out to understand the impact of geographical setting and fibre content in rCF+PA66. It shows that replacing aluminium with 40wt% rCF+PA66 in the EU saves 31.5% and 29.7% more cradle-to-gate PED and GWP, respectively, than in the US. A higher reduction of 43.4% and 41.2% in the cradle-to-grave PED and GWP compared to aluminium can be achieved by increasing fibre mass fraction.