Recycled Composites Research Articles

Recycling of Carbon Fiber Reinforced Composite Polymers-Review-Part 1: Volume of Production, Recycling Technologies, Legislative Aspects.

The paper presents the current volume of international production and global markets of carbon fiber reinforced polymer composites, also regarding the potential development trends. Examples were provided on how to effectively recycle carbon fiber reinforced polymer composites. Legally binding legislation in the EU on polymer composite recycling was given.

Composite Material Recycling Technology—State-of-the-Art and Sustainable Development for the 2020s

Recently, significant events took place that added immensely to the sociotechnical pressure for developing sustainable composite recycling solutions, namely (1) a ban on composite landfilling in Germany in 2009, (2) the first major wave of composite wind turbines reaching their End-of-Life (EoL) and being decommissioned in 2019–2020, (3) the acceleration of aircraft decommissioning due to the COVID-19 pandemic, and (4) the increase of composites in mass production cars, thanks to the development of high volume technologies based on thermoplastic composites. Such sociotechnical pressure will only grow in the upcoming decade of 2020s as other countries are to follow Germany by limiting and banning landfill options, and by the ever-growing number of expired composites EoL waste. The recycling of fiber reinforced composite materials will therefore play an important role in the future, in particular for the wind energy, but also for aerospace, automotive, construction and marine sectors to reduce environmental impacts and to meet the demand. The scope of this manuscript is a clear and condensed yet full state-of-the-art overview of the available recycling technologies for fiber reinforced composites of both low and high Technology Readiness Levels (TRL). TRL is a framework that has been used in many variations across industries to provide a measurement of technology maturity from idea generation (basic principles) to commercialization. In other words, this work should be treated as a technology review providing guidelines for the sustainable development of the industry that will benefit the society. The authors propose that one of the key aspects for the development of sustainable recycling technology is to identify the optimal recycling methods for different types of fiber reinforced composites. Why is that the case can be answered with a simple price comparison of E-glass fibers (~2 $/kg) versus a typical carbon fiber on the market (~20 $/kg)—which of the two is more valuable to recover? However, the answer is more complicated than that—the glass fiber constitutes about 90% of the modern reinforcement market, and it is clear that different technologies are needed. Therefore, this work aims to provide clear guidelines for economically and environmentally sustainable End-of-Life (EoL) solutions and development of the fiber reinforced composite material recycling.

Influence of lignin structure change during extrusion on properties and recycling of lignin‐polyethylene thermoplastic composites

AbstractKraft lignin has been widely investigated for the production of composite plastics by blending with different synthetic polymers. In the present study, softwood kraft lignin‐polyethylene (PE) composites are produced by extrusion. The change in lignin structure during the extrusion has been investigated and the influences of the lignin structure change on the properties and recyclability of the composites have been investigated. Extrusion reduces the content of functional groups in lignin (especially aromatic OH group) and decreases its glass transition temperature, but increases its weight‐average molecular weight and polydispersity index. In the lignin‐PE composites, lignin and PE only blend at the macroscopic level and there is no intermolecular interaction between them. Because extrusion reduces Tg and particle size of lignin, a lower temperature is needed to reprocess the lignin‐PE composites. These recycled composites have similar thermal properties, but enhanced mechanical properties. This work shows that lignin can be used as a potential component to reduce the usage of synthetic polymers, thus partially eliminating white pollution.

Influence of chemical treatment on the recycling of composites before pyrolysis

Recycling of carbon fibers is one of the upcoming global research topics in composite engineering. This work investigates the influence of chemical treatment on the recovery of carbon fibers from carbon fiber reinforced plastic before pyrolysis. The chemical pretreatment was achieved using a zinc chloride/ethanol solution. The pyrolysis process was conducted in a sliding furnace. The effect of such pre-treatment on thermal degradation behaviour was determined by a thermogravimetric analyser (TGA). An original sample was also investigated for benchmarking. After the thermal pyrolysis process, the fiber tensile properties were measured using a single fiber tester. The surface functional groups and graphitization degree recovered carbon fiber were characterized using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The surface morphology of recycled carbon fibers was investigated by SEM. Pristine carbon fibers were also included in the study for benchmarking. During the pyrolysis process, the devolatilisation temperature of the pre-impregnated prepregreduced by around 40-50°C and the peak temperature was 40-50°C lower compared to that of the original prepreg. The chemical pre-treatment process reduces the pyrolysis temperature compared to the conventional pyrolysis process. After pyrolysis in nitrogen with a small amount of air, loose carbon fibers were recovered, and their surface was clean. The similar surface functional groups and the decrease of degree of graphitization were detected on the recycled carbon fiber.

Experimental analysis of recycled thermoplastic material

The large number of plastics that are disposed of today in our surroundings are mostly undegradable and need imperative ways of recycling the thermoplastics like bottles, polythenes, etc. As chemical solutions to this problem are in general expensive and hazardous to the ecosystem as well so, A possible and sustainable solution is the recycling of such materials by a technique called thermo-mechanical recycling. This paper takes into consideration the thermo-mechanical recycling of plastic bottles and other thermoplastic composites which are disposed of after use. In this technique the collected waste ‘thermoplastics’ will be sent through several stages where it undergoes a cleaning process after which the waste material undergoes crushing in small fine particles and then granules are made out of the crushed waste material after this process silica colloidal additives are added to the granules while molding to restore it’s mechanical properties, thermal stability, and recyclability so that the recycled plastics can be further used in engineering applications and to ensure its physical properties after recycling some test has to be conducted like stiffness, machinability, shear stress, energy-absorbing property while impact, molding property, etc.

Sustainable Sandwich Composites Manufactured from Recycled Carbon Fibers, Flax Fibers/PP Skins, and Recycled PET Core

European union end of life vehicle directive mandates the use of more sustainable/recyclable materials in automotive industries. Thermoplastics matrix-based composites allow recyclability of composites at the end of life; however, their processing technology is more challenging than thermoset composites. Manufacturing process and mechanical testing of sustainable sandwich composite made from sustainable materials: flax, recycled carbon fiber, polypropylene, and recycled PET foam are presented in this article. High pressure compression molding with adhesive thermoplastic polymer film was used for manufacturing sandwich composite skin. The recycled PET foam core was integrated/joined with the skin using a thermoplastics adhesive film. A three-point bending test was conducted to compare the flexural properties. The results show that such sustainable sandwich composites will be an excellent material for truck side panel to operate in adverse wind/storm conditions. The sustainable sandwich composite can potentially be an excellent candidate for the fabrication of light-duty, lightweight, and low-cost engineering structures in automotive industry to meet the EU end of life requirements.

Reprintable Polymers for Digital Light Processing 3D Printing

Abstract3D printing is becoming a disruptive technology and shows great potential for various practical applications. Specially, digital light processing (DLP) 3D printing demonstrates advantages in high resolution and high efficiency. However, extensive production of infusible and insoluble thermosets in DLP printing causes serious resource waste and environmental problems after its disposal. Herein, a reprintable linear polymer is reported for repeatable DLP printing. Taking advantage of the dissolution of linear polymer in its monomer, printed objects can be recycled into liquid resin and reprinted via the same DLP. Polymerization kinetics and printing resolution of recycled resins and mechanical properties of reprinted polymers retain identical as the original. The thermoplastic nature of linear polymer endows 3D objects with welding and reshaping property. Recyclable composites are also successfully fabricated, and sustainable usage of high‐value fillers comes true. This strategy helps to address environmental issues arising from unprocessable thermosets and may contribute to an efficient materials recycling.

Recycling of polymeric composites from industrial waste by pyrolysis: Deep evaluation for carbon fibers reuse

The use of polymeric composite on transport applications as reinforcement material has been increased due to the low fuel consumption when replacing heavier materials. It is estimated that 170,000 tons of polymeric composites will be discarded by 2025, and recycling processing for carbon fibers recovery is required to save primary energy and reduce waste. Among the current techniques, pyrolysis processing has been most effective. On the other hand, innovation must maintain the structure for reuse since physical and mechanical properties are important for recycled materials. For this reason, the goal of the present study was the recycling of polymeric composite by pyrolysis. The recovered carbon fibers were analyzed in SEM and EDS to verify surface defects compared with virgin carbon fibers. The effect of temperature, time, and atmosphere were investigated. Results showed that at 550 °C for 1 h, it was possible to obtain free carbon fibers from the polymeric matrix. After the pyrolysis process in this condition, the fibers had no pores, material fracture, and carbonization. This paper contributes to the widening and systematizing knowledge on effectiveness and understanding polymeric composites recycling for carbon fiber recovery, maintaining its structure for reuse.

Recycling of Wood-Polymer Composites in Relation to Substrates and Finished Products

Nowadays, the aim is to minimize the impact of a product or service on the environment in all phases of its life cycle. In particular, this applies to those in which the impact is greatest. One of the techniques that allow comprehensive assessment of the environmental impact of manufactured products is Life Cycle Assessment (LCA). With this method, an environmental declaration is made for the products obtained. WPC composites can be made in a sustainable way, without wasting any material and without altering. WPC composites can be made in a sustainable way, without wasting any material and without altering. Composites with wood fillers may be competitive to materials with inorganic fillers. Wood-polymer composites can be produced from original natural raw materials. They can also be obtained as a result of recycling, where either wood or polymers come from the recyclate. It is also possible to use both components from recovery. Another way is to use WPC as a future raw material. Research on the utilization of waste from such materials is also conducted in a number of research centres, taking material recycling as the basic direction, and technical products are manufactured from the obtained recyclate.

Opportunities for Recycling of Fiber-Reinforced Plastics Under Technical, Economic and Social Aspects

Fiber-reinforced composite plastics have been in extensive use across various industries. Owing to their properties of being lightweight materials with high strength to weight ratio; durability; stiffness; resistance to corrosion, wear, impact and fire, makes them suitable for applications in mechanical, construction, automobile, aerospace, marine and many other manufacturing industries. But this growing application of has also led to a research into the recycling and reuse of FRP composites and its recyclates. FRP recyclates have been found to be useful in various industries and also lower environmental pressure. This paper draws upon this opportunity of FRP recycling and studies its technical, economic and social aspects. The paper aims to develop an understanding to the dearth of recycling procedures available and thus highlights the importance of focused research in this area.

The influence of the recycled wood proportion in particle boards to the tool life of milling tools

ABSTRACT The main factor influencing tool life in particleboard machining is mineral content, and therefore the aim of this investigation is to study the issue and evaluate the tool lifetime by machining different particleboards Also, the change of the mineral content of particle boards over a time frame of 30 years and the geographic origin of the boards should also be taken in account. For this purpose, the mineral content was determined on 600 samples which were produced between 1989 and 2018 in different countries. The influence of the mineral content to tool lifetime was examined with cutting tests at a special series of industrially produced boards with known recycled wood composition. Machining conditions and cutting material have been the same during the investigation. A comparison of the amount of recycled wood which is used in production of particleboard showed a higher mineral content for an increasing proportion of recycled wood, and thereby also an increased wear on the tools.

Recyclable epoxy systems for rotor blades

The global energy demand is largely met by power generated from fossil fuels (Thermal Power plants) and nuclear means (Nuclear Power plants). Even though both these technologies have been used for decades, they have huge environmental impact and severe sustainability issues with depleting fossil fuel and serious concerns about the spent nuclear rods disposal. With growing awareness of impact on the environment and finding a sustainable solution for power generation, wind energy offers a lasting solution that addresses both issues, however it is still not truly sustainable as the primary materials used for manufacturing of rotor blades are non-recyclable. A new revolutionary technological solution has been invented where in, the epoxy thermoset can be recovered as thermoplastic and the reinforcement in composite can be re-used, making it a first of its kind in the thermoset industry segment. The Recyclable Epoxy Systems for rotor blades provide a path breaking solution that enables recycling of epoxy thermoset, recovery and re-use of the reinforcement and the matrix in a fibre reinforced composite. Leveraging from the proprietary Recyclamine® platform technology, series of recyclable epoxy systems are developed for wet lay-up and infusion processes to meet the requirements for both on-shore and off-shore rotor blades, including next generation rotor blades. The systems are characterized by determining process and performance properties and found to provide distinct advantages in comparison to the conventional non-recyclable epoxy systems. The recycling of composites made from recyclable epoxy systems is successfully demonstrated by low energy solvolysis followed by recovery of the reinforcement and epoxy matrix as thermoplastic. The recovered reinforcement and epoxy thermoplastic are re-used to make composite and representative thermoplastic object respectively, deriving value from the waste and closing the loop to make the wind energy industry sustainable for a circular economy.

Upgrading and reuse of glass fibre recycled from end-of-life composites

The value of recycled glass fibres is significantly reduced due to the loss of fibre strength and surface functionality that occurs during recycling. Results are presented from the ReCoVeR project on the regeneration of the strength of thermally conditioned glass fibres. Thermal recycling of end-of-life glass fibre reinforced composites or composite manufacturing waste delivers fibres with virtually no residual strength or value. Composites produced from such fibres also have extremely poor mechanical performance. Data is presented showing that a short hot alkali treatment of glass fibres which have been heat treated at typical composite recycling temperatures can more than triple their strength and restore their ability to act as an effective reinforcement in second life composite materials. Glass fibre recovered from fluidised bed recycling of composite materials exhibited much greater levels of mechanical abrasion damage. However, the strength of these fibres could also be increased to levels required in composite reinforcement by longer or more aggressive alkali treatment. The implications of these results for real materials reuse of recycled glass fibres as replacement for pristine reinforcement fibres are discussed.

Perceptive removal of toxic azo dyes from water using magnetic Fe3O4 reinforced graphene oxide–carboxymethyl cellulose recyclable composite: Adsorption investigation of parametric studies and their mechanisms

A magnetic FGC composite was prepared using Fe3O4 particles and graphene oxide–carboxymethyl cellulose which were blended as the source materials. The adsorptive interactions of FGC matrix with dye molecules like Congo Red (CR), Acid Red 1 (AR1) and Reactive Red 2 (RR2) were examined and explained through various analytical techniques. The optimum conditions for the adsorption of dyes include the initial concentration of dyes (50 mg/L), volume of dyes (50 mL), adsorbent dosage (100 mg) and solution pH (3-6). In these conditions, the FGC showed extreme adsorption efficiency of 45.09, 47.32 and 46.21 mg/g for the removal of CR, AR1 and RR2 dye molecules, respectively. The Freundlich isotherm data shows better fit for dye molecules adsorption. The thermodynamic results confirmed the endothermic and spontaneous nature in adsorption. The mechanism of CR, AR1 and RR2 dyes adsorption on FGC composite follows the interactions such as electrostatic attraction, hydrogen bonding, π−π stacking, and surface complexation. The FGC composite was regenerated over 65% after five consecutive cycles using an aqueous 0.1 M NaOH solution. The FGC composite showed an enhanced adsorption capacity for the removal of toxic azo dyes. Hence, the prepared composite could be used as a potential adsorbent for the removal of dye molecules from contaminated water.

From aviation to aviation: Environmental and financial viability of closed-loop recycling of carbon fibre composite

By 2050, the aviation sector is expected to generate about 500,000 tonnes of accumulated carbon fibre reinforced plastic waste from the production and end-of-life phase. In this study, aircraft interior applications of recycled carbon fibre (rCF) replacing virgin glass fibre are examined over the full life cycle in terms of environmental and financial viability. The viability of rCF for closed-loop aviation applications are demonstrated across rCF conversion (papermaking; fibre alignment) and composite manufacture (compression moulding; injection moulding)The results show that rCF composites, especially aligned rCF composites, give reasonable environmental (4–31%) and cost reductions (5–31%) relative to virgin glass fibre composites.

Enhanced Resistance to Fire of the Bark-Based Panels Bonded with Clay

The aim of this study was to investigate the flammability of ecologically friendly, 100% natural larch and poplar bark-based panels bonded with clay. The clay acted as a fire retardant, and it improved the fire resistance of the boards by 12–15% for the surface and 27–39% for the edge of the testing specimens. The thermal conductivity was also analyzed. Although the panels had a density ranging from 600 to 900 kg/m3, thermal conductivity for the panel with a density of 600 kg/m3 was excellent, and it was comparable to lightweight insulation panels with much lower densities. Besides that, the advantage of the bark clay boards, as an insulation material, is mostly in an accumulative capacity similar to wood cement boards, and it can significantly improve the climatic stability of indoor spaces that have low ventilation rates. Bark boards with clay, similar to wood cement composites (wood wool cement composites and wood particle cement composites), have low mechanical properties and elasticity. Therefore, there their use is limited to non-structural paneling applications. These ecologically friendly, 100% natural and recyclable composites can be mostly used with respect to their thermal insulation, acoustics and fire resistance properties.

Carbon nanotube filler enhances incinerated thermoplastics-induced cytotoxicity and metabolic disruption in vitro

BackgroundEngineered nanomaterials are increasingly being incorporated into synthetic materials as fillers and additives. The potential pathological effects of end-of-lifecycle recycling and disposal of virgin and nano-enabled composites have not been adequately addressed, particularly following incineration. The current investigation aims to characterize the cytotoxicity of incinerated virgin thermoplastics vs. incinerated nano-enabled thermoplastic composites on two in vitro pulmonary models. Ultrafine particles released from thermally decomposed virgin polycarbonate or polyurethane, and their carbon nanotube (CNT)-enabled composites were collected and used for acute in vitro exposure to primary human small airway epithelial cell (pSAEC) and human bronchial epithelial cell (Beas-2B) models. Post-exposure, both cell lines were assessed for cytotoxicity, proliferative capacity, intracellular ROS generation, genotoxicity, and mitochondrial membrane potential.ResultsThe treated Beas-2B cells demonstrated significant dose-dependent cellular responses, as well as parent matrix-dependent and CNT-dependent sensitivity. Cytotoxicity, enhancement in reactive oxygen species, and dissipation of ΔΨm caused by incinerated polycarbonate were significantly more potent than polyurethane analogues, and CNT filler enhanced the cellular responses compared to the incinerated parent particles. Such effects observed in Beas-2B were generally higher in magnitude compared to pSAEC at treatments examined, which was likely attributable to differences in respective lung cell types.ConclusionsWhilst the effect of the treatments on the distal respiratory airway epithelia remains limited in interpretation, the current in vitro respiratory bronchial epithelia model demonstrated profound sensitivity to the test particles at depositional doses relevant for occupational cohorts.

Additive Re-Manufacturing of Mechanically Recycled End-of-Life Glass Fiber-Reinforced Polymers for Value-Added Circular Design.

Despite the large use of composites for industrial applications, their end-of-life management is still an open issue for manufacturing, especially in the wind energy sector. Additive manufacturing technology has been emerging as a solution, enhancing circular economy models, and using recycled composites for glass fiber-reinforced polymers is spreading as a new additive manufacturing trend. Nevertheless, their mechanical properties are still not comparable to pristine materials. The purpose of this paper is to examine the additive re-manufacturing of end-of-life glass fiber composites with mechanical performances that are comparable to virgin glass fiber-reinforced materials. Through a systematic characterization of the recyclate, requirements of the filler for the liquid deposition modeling process were identified. Printability and material surface quality of different formulations were analyzed using a low-cost modified 3D printer. Two hypothetical design concepts were also manufactured to validate the field of application. Furthermore, an understanding of the mechanical behavior was accomplished by means of tensile tests, and the results were compared with a benchmark formulation with virgin glass fibers. Mechanically recycled glass fibers show the capability to substitute pristine fillers, unlocking their use for new fields of application.

Composite of TiO2 nanoparticles and carbon nanotubes loaded on poly(methyl methacrylate) nanofibers: Preparation and photocatalytic performance

Carbon nanotubes (CNTs) are widely used in the preparation of composite functional materials with improved performance due to their unique electrical, mechanical properties and one-dimensional nanostructure. In this paper, the composite of TiO2 nanoparticles and acid-treated carbon nanotubes distributed on poly(methyl methacrylate) (PMMA) nanofibers was fabricated by sequential treatments of electrospinning, hydrothermal synthesis and freeze-drying. The resulting ternary composite of TiO2/CNTs/PMMA, which is featured with a specific surface area of 83.2 m2/g, effectively photodegraded a series of dyes, such as methyl blue, Rhodamine B, Sulforhodamine B and methyl orange (MO). In particular, complete degradation of MO (10 mg/L, 100 mL) was accomplished with TiO2/CNTs/PMMA (20 mg) in 40 min under UV irradiation. Moreover, the high photocatalytic activity of the ternary composite, which is superior to that of TiO2/PMMA, did not deteriorate during consecutive photodegradation tests up to ten runs. The photocatalytic mechanism of TiO2/CNTs/PMMA has been explored. The desirable high photocatalytic activity, excellent stability and easy recyclability of the ternary composite is attributed to the introduction of CNTs and the electrospun PMMA nanofiber support.

3D Printing and Solvent Dissolution Recycling of Polylactide-Lunar Regolith Composites by Material Extrusion Approach.

The in situ resource utilization of lunar regolith is of great significance for the development of planetary materials science and space manufacturing. The material extrusion deposition approach provides an advanced method for fabricating polylactide/lunar regolith simulant (PLA/CLRS-1) components. This work aims to fabricate 3D printed PLA–lunar regolith simulant (5 and 10 wt.%) components using the material extrusion 3D printing approach, and realize their solvent dissolution recycling process. The influence of the lunar regolith simulant on the mechanical and thermal properties of the 3D printed PLA/CLRS-1 composites is systematically studied. The microstructure of 3D printed PLA/CLRS-1 parts was investigated by scanning electron microscopy (SEM) and X-ray computed tomography (XCT) analysis. The results showed that the lunar regolith simulant can be fabricated and combined with a PLA matrix utilizing a 3D printing process, only slightly influencing the mechanical performance of printed specimens. Moreover, the crystallization process of PLA is obviously accelerated by the addition of CLRS-1 because of heterogeneous nucleation. Additionally, by using gel permeation chromatography (GPC) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) characterization, it is found that the 3D printing and recycling processes have a negligible influence on the chemical structure and molecular weight of the PLA/CLRS-1 composites. As a breakthrough, we successfully utilize the lunar regolith simulant to print components with satisfactory mechanical properties and confirm the feasibility of recycling and reusing 3D printed PLA/CLRS-1 components via the solvent dissolution recycling approach.