Recycled Composites Research Articles

Long-term closed-loop recycling of high-density polyethylene/flax composites

This work investigates the loss of performance and the recyclability of natural fibre composites for a long-term closed-loop process. Composites based on flax fibres and high-density polyethylene are subjected up to 50 extrusion cycles under constant processing conditions with or without maleic anhydride grafted polyethylene as a coupling agent. The results show that the addition of fibre increases the rigidity but decreases the elongation properties. The initial processing cycle leads to an important decrease of the fibre length and modification of the molecular weight distributions, thus indicating that the addition of fibre enhances chain scission and that fibre breakup mainly happens during the initial processing. The effect of recycling is much less significant, except for the mechanical properties. Negligible variations are observed for density, differential scanning calorimetry, thermogravimetric analysis, gel permeation chromatography and impact results. On the contrary, the mechanical properties are strongly affected by recycling as most of them increase with recycling. The addition of a coupling agent improves the composite properties, but this effect disappears with recycling. These trends are associated to a balance between fibre breakup and macromolecular chain scission compared to more homogeneous materials (better fibre distribution) taking place in the materials during recycling. The results show that long-term recycling of composites is possible as their overall performances remain acceptable.

Recent History, Types, and Future of Modern Caisson Technology: The Way to More Sustainable Practices

The construction of caisson breakwaters dates from ancient times (Brindisi battle and Caesarea Maritima, Roman Empire) of yore but has evolved with regards to technology and the materials available at all times (wood, gravel, and rubble mound). The growth in draught in vessels searching for deep water depths for berthing plus environmental problems have led to the 20th century facilitating the boom in vertical types and concrete caissons built in different ways (dry and floating techniques). Furthermore, structural criteria gave way to functional, environmental, and aesthetic criteria. The search for new, more efficient forms led to the construction of increasingly more complex elements including many that still require an economically viable construction system. To where will this search for new materials and forms take us? The use of composite materials could be considered, at the moment, as too expensive, but analyzing the cost with a wider approach, as Life Cycle Assessment, shows us that caissons in composite materials are cost effective and could be a solution. Furthermore, the possibility of using recyclable composites opens up big opportunities of using these materials at affordable costs. Caissons in composites or recycled composites are then a real alternative to concrete caissons. In Spain, two examples can be observed: a berthing area in Canary Island (Puerto del Rosario, South Atlantic Ocean) and a crown wall in Cartagena using polyester fiber bars (Mediterranean Sea). European policy in matters of sustainability promotes the circular economy, which means not only consider construction of caissons in recycled composites should be considered but also the comparison of all materials and construction procedures. Lastly, the calculation of the Environmental Product Declaration (EPD) should be promoted.

Methylene blue (a cationic dye) adsorption performance of graphene oxide fabricated Fe-Al bimetal oxide composite from water

AbstractGraphene oxide (GO) fabricated iron-aluminium oxide (GO@IAO) nanocomposite was synthesized with one-spot chemical reaction from emulsification of GO (1.0 g) in 0.2 L of 1.0 M mixed metal solution, which was characterized with some of the latest analytical tools aiming to assess methylene blue (MB) adsorption performance from aqueous solutions. Adsorption of MB on GO@IAO surfaces shows a steep increase from pH 3.0 to 5.0, but steepness declines at pH >5.0. The closeness of fitted kinetic data with the pseudo-second order (PSO) equation (R2 = 0.9845) compared to the pseudo-first order equation (R2 = 0.9527) confirms the adsorption process is of the PSO type. The MB adsorption equilibrium data can be described better by the Langmuir isotherm (R2 = 0.99) than the Freundlich isotherm (R2 = 0.96–0.97), inclining to the monolayer adsorption process. The Langmuir adsorption capacity of GO@IAO has been estimated to be 330.35 mg/g at 303 K. The MB adsorption is established to be spontaneous (–ΔG0 = 26.31–26.61 kJ/mol) owing to favourable enthalpy and entropy changes (ΔH0 = –23.38 kJ/mol; ΔS0= 0.01 kJ/mol/K). Both absolute and aqueous (1/1, v/v) alcohols regenerate the MB adsorbed GO@IAO up to 80–85%, indicating recyclability of composite.

A counter-intuitive heuristic for specifying the composition of recycle streams

The use of recycle streams in chemical processes is one of the oldest and most frequently applied methods for process intensification. Recycles can increase overall yields and selectivities so that losses of valuable raw materials are reduced and product quality is improved. Since a recycle stream is not a product stream with a specified purity, recycle composition is an important design optimization variable that involves trade-offs between the reaction and separation sections of the process in terms of both capital investment and energy cost.Intuition would lead the design engineer to expect that the optimum recycle composition would depend on the relative amount of recycle (per-pass conversion of reactants as reflected in the chemical equilibrium constant) and on the difficulty of separation of the reactant and product components (relative volatilities). Large recycle flowrates entail high separation costs as do difficult low-relative-volatility separations. Reducing recycle purity specifications would be expected to reduce separation costs. The purpose of this paper is to demonstrate that this is not the case. Recycle purities should be quite high in most cases. The heuristic recommended is to design for recycle impurities 0.5 to 1 mol% away from vapor-liquid equilibrium constraints.

Analysis of technologies for producing composites with polyester-glass recyclate

Abstract The aim of the article was to present selected methods for the production of layered composites in the aspect of the additive in the form of polyester-glass recyclate. The polyester-glass recyclate was obtained from the original composite material from which the ship’s hull was made in Poland in the 1980s. The article presents the technology of processing polyester-glass waste in order to obtain recyclate. The methods of manual lamination, vacuum bag method and vacuum infusion were described successively. The advantages and disadvantages of particular technologies have been presented in terms of the possibility of their use in the production of polyester-glass recycled composites. From the described and verified technologies, the vacuum bag method can be the most advantageous for composites with recyclate.

Evolution of microstructure and mechanical properties of Al-B4C composite after recycling

A remelting method was used to recycle Al-15wt.% B4C composite and the microstructure and mechanical properties of the composite were investigated before and after recycling. Scanning electronic microscope (SEM) showed that some of the particle clusters present in the original composite were broken down and the distribution of B4C in the matrix was more uniform after recycling. The interface reaction was further intensified and the protection layer coated on the surface of B4C was thicker after recycling. In addition, there were more TiB2 particles which peeled off from the surface of B4C and distributed around B4C. Al3Ti phase, which was present in the original composite, disappeared after recycling, while Al3BC phase increased markedly. Tensile test and hardness test revealed that the mechanical properties were preserved well after recycling. Therefore, it is proposed that remelting method is a feasible method for Al-B4C composite recycling.

Comparing Life Cycle Energy and Global Warming Potential of Carbon Fiber Composite Recycling Technologies and Waste Management Options

Carbon fibre reinforced polymers (CFRP) are used in increasing quantities as they have some of the best properties in terms of specific strength and stiffness of any widely available material. By 2020, annual global CFRP production is expected to be over 140,000 tonnes. However, the resulting increased quantity of CFRP waste has highlighted the need for sustainable treatment options as carbon fibre manufacture has high-energy intensity. A life cycle methodology is used to evaluate primary energy demand (PED) and global warming potential (GWP) leveraging best available literature data, process models, and experimental work. Overall results indicate that recycling scenarios are generally the environmentally preferable options over landfill and incineration. However, the relative environmental benefits of advanced recycling processes (i.e., pyrolysis, fluidised bed, and chemical recycling process) depend on the method used to determine displacement of virgin carbon fibre by recycled carbon fibre. Totally, recycling processes can achieve a representative GWP of -19 to -27 kg CO2eq. and PED of -395 to -520 MJ per kg CFRP, providing superior environmental performance to conventional composite waste treatment technologies.

Development of conductive cementitious materials using recycled carbon fibres

Conductive cementitious materials have gained immense attention in recent years owing to the possibility of achieving multifunctional materials. The usual approach has been to incorporate carbonaceous nanomaterials and/or virgin carbon fibres into cementitious matrices. This paper presents the first research devoted to the development of conductive cementitious materials using recycled carbon fibres (rCFs). Four different types of PAN-based rCFs were studied, by varying the aspect ratio and supplying characteristics, in two concrete dosages: conventional and ultra-high-performance concrete mixes. Two mixing methods—dry and wet—commonly used to fabricate fibre-reinforced concrete were considered. The results obtained in our result have shown that wet mix method achieves better workability of the mixes and good dispersion of the fibres. Furthermore, electrical resistivity values in the range of 3–0.6 Ω m were obtained for rCF contents ranging from 0.2 to 0.8% in vol. The obtained results demonstrate the possibility of using rCF to develop multifunctional cementitious materials and thus enhance the possibility of using these materials from an industrial point of view. Furthermore, new possibilities are created for the recycling of carbon fibre composites to obtain high-added-value products.

Recycling of Epoxy Thermoset and Composites via Good Solvent Assisted and Small Molecules Participated Exchange Reactions

Thermosetting polymers and composites are a class of high-performance materials with significant industrial applications. However, recycling of thermosets and their filling matters are significantl...

Energy-efficient scheduling of flexible flow shop of composite recycling

Composite recycling technologies have been developed to tackle the increasing use of composites in industry and as a result of restrictions placed on landfill disposal. Mechanical, thermal and chemical approaches are the existing main recycling techniques to recover the fibres. Some optimisation work for reducing energy consumed by above processes has also been developed. However, the resource efficiency of recycling composites at the workshop level has never been considered before. Considering the current trend of designing and optimising a system in parallel and the future needs of the composite recycling business, a flexible flow shop for carbon fibre reinforced composite recycling is modelled. Optimisation approaches based on non-dominated sorting genetic algorithm II (NSGA-II) have been developed to reduce the time and energy consumed for processing composite wastes by searching for the optimal sub-lot splitting and resource scheduling plans. Case studies on different composite recycling scenarios have been conducted to prove the feasibility of the model and the developed algorithm.

Nanoscale zero-valent iron/biochar composite as an activator for Fenton-like removal of sulfamethazine

Abstract In this work, biochar-supported nanoscale zero-valent iron (nZVI/BC) was synthesized and used as an activator for Fenton-like removal of sulfamethazine (SMT). The possible removal mechanisms in the reaction system were proposed. nZVI was mainly responsible for H2O2 decomposing to generate OH for the degradation of SMT, while BC played multiple roles, i.e., preventing nZVI aggregation, adsorbing SMT, activating H2O2, and alleviating nZVI passivation. The effects of various factors (i.e., the mass ratio of nZVI to BC, solution pH, H2O2 concentration and nZVI/BC dosage) on SMT removal were evaluated. The highest removal efficiency (74.04%) of SMT (10 mg/L) was achieved at the optimal conditions (the mass ratio of nZVI and BC = 1:5, pH = 3, H2O2 = 20 mM and nZVI/BC = 1.2 g/L). Additionally, the feasibility of recycling of nZVI/BC composites was examined. It was found that the removal efficiency of SMT decreased significantly from 74.04% to 53.28% and 38.02%, respectively, in the second and third run of experiments. X-ray diffraction analysis of the recycled composites demonstrated the gradual loss of Fe0 content after each run of experiment, which resulted in the decrease of catalytic activity of nZVI/BC composites and thus the drop of SMT removal.

Recycled wind turbine blades as a feedstock for second generation composites

With an increase in renewable wind energy via turbines, an underlying problem of the turbine blade disposal is looming in many areas of the world. These wind turbine blades are predominately a mixture of glass fiber composites (GFCs) and wood and currently have not found an economically viable recycling pathway. This work investigates a series of second generation composites fabricated using recycled wind turbine material and a polyurethane adhesive. The recycled material was first comminuted via a hammer-mill through a range of varying screen sizes, resinated and compressed to a final thickness. The refined particle size, moisture content and resin content were assessed for their influence on the properties of recycled composites. Static bending, internal bond and water sorption properties were obtained for all composites panels. Overall improvement of mechanical properties correlated with increase in resin content, moisture content, and particle size. The current investigation demonstrates that it is feasible and promising to recycle the wind turbine blade to fabricate value-added high-performance composite.

Effects of Multiple Extrusions on Structure-property Performance of Natural Fiber High-density Polyethylene Biocomposites

Detailed analysis of the effects of multiple extrusions on physical, mechanical, micro-structural as well as dynamic mechanical thermal properties of natural fiber high-density polyethylene (HDPE) composites is reported. Composite materials containing HDPE, wood flour, and Maleic Anhydride polyethylene (MAPE) were manufactured and subjected to a recycling process consisting of up to four times grinding and reprocessing under industrial conditions. A wide range of analytical methods including bending tests, modulus of elasticity, impact strength, Scanning electron microscopy (SEM), fiber length measurement, water absorption tests, and dynamic mechanical thermal analysis (DMTA) were employed to understand the effects of recycling on natural fiber-HDPE composites. The results revealed that the recycled composites had lower bending strength and modulus of elasticity values, as compared to the reference counterparts. Also, the once recycled composites showed higher impact strength. Results, as well, indicated that generally the recycled composites had lower water absorption values as compared to the reference ones. The results obtained from DMTA exhibited a decrease in storage modulus and an increase in mechanical loss factor (tan δ) for all composites subjected to recycling. Alterations in phase transition temperatures and intensities were also monitored and the possible reasons were analyzed.

Nanocellulose-montmorillonite composites of low water vapour permeability

A simple technique was developed to well disperse montmorillonite (MMT) into novel nanocellulose composites of varying MMT content (9.1–37.5 wt%). The objective was to develop nanocellulose-MMT composites of very low water vapour permeability (WVP) by increasing the composite tortuosity. The new composites are strong (strength-110 MPa), stiff (modulus-11 GPa) yet flexible. Scanning electron micrographs revealed MMT platelets to be uniformly distributed across and within the composite, creating a tortuous path restricting water molecules diffusion. WVP decreased by half, from 24.2 ± 2.7 g μm/m2 day kPa without MMT to 13.3 ± 2.0 g μm/m2 day kPa with only 16.7 wt% MMT. Further increasing the MMT content increased composite WVP, due to MMT aggregation. Two separate MMT dispersion methods were tested to break down MMT stacks and improve WVP by increasing MMT available surface area: (a) sonication, which worsened WVP, and (b) high pressure homogenization, which reduced WVP further to 6.33 ± 1.5 g μm/m2 day kPa with 23.1 wt% MMT. This is the lowest WVP reported in literature for nanocellulose-MMT composites. This study developed a recyclable composite of very low WVP. These thin, inexpensive, strong and flexible nanocellulose-MMT composites present a new and attractive option as recyclable/compostable packaging materials for large volume packing applications where water vapour protection is critical.

The review of technologies and machines destined for recycling of polymer composites

The review of technologies and machines destined for recycling of polymer composites

Some Exploitation Properties of Wood Plastic Composites Based on Recycled High Density Polyethylene and Plywood Production Residues

One type of birch wood plywood by-product: plywood sanding dust (PSD) and recycled high density polyethylene (rHDPE) composites physical mechanical properties (tensile, flexural strength and modulus, impact strength and microhardness), water resistance and fluidity of the composite melts, were evaluated. These studies showed the possibility of the usage of presented by-product as an excellent reinforcement for recycled high density polyethylene matrix. It was observed that the modulus of the tensile for unmodified rHDPE+PSD composites increased up to 2.3 times, the modulus of flexural till 4 times, but the microhardness only 1.4 times. Optimal content of the PSD in recycled high density polyethylene composites could be 50 wt. %. As a coupling agent, the maleated polyethylene (MAPE) for modifying of the rHDPE+50 wt. % PSD composite was used. Due to the MAPE additives, the improvement (30-50 %) of the investigated exploitation properties was observed, but in comparison with unmodified composites the resistance of water increased up to 3.0 times. Optimal content of MAPE in rHDPE+50 wt. % PSD composition could be 3 wt.%.

Hybrid biobased recyclable epoxy composites for mass production

Hybrid flax/carbon composites were studied in this artcle. The matrix used was developed using a sustainable green epoxy monomer cured by a novel cleavable amine. The combination of cleavable amine with green epoxy monomers led to a fully recyclable composite. The laminates were manufactured by using High Pressure Resin Transfer Molding with injection cycles down to 25 sec and cure cycles of 8 min at 120°C, followed by postcuring at 120°C for 1 h. The effect of the stacking sequence of the laminates was analyzed in terms of the tensile, flexural, and impact properties. A chemical recycling was also performed and the mechanical properties of the recovered thermoplastic measured. POLYM. COMPOS., 39:E2217–E2225, 2018. © 2017 Society of Plastics Engineers

Influence of thermal conditioning on tensile behaviour of single basalt fibres

This article presents an experimental investigation of the effects of temperature and atmosphere on the tensile behaviour of basalt fibres. The heating conditions have been chosen in order to mimic those used in thermal recycling of polymer matrix composites. The change of properties is investigated at room temperature on fibres heat-treated for 1 h up to 600 °C in air and in inert atmosphere (argon). The loss in fibre strength was found to be affected by both temperature and atmosphere with a significant strength loss occurring under the heating conditions used for high temperature incineration of polymer composites. Scanning electron images of fibre fracture surfaces after tensile tests for different environments and temperatures confirmed that failure originated from the fibre surface. The modulus of thermally-treated basalt fibres increased with conditioning temperature and these effects have been discussed in terms of decomposition of the organic sizing and structural relaxation during thermal treatment while X-ray diffraction excluded the effect of crystallization phenomena on the strength loss of basalt fibres after thermal exposure.

Thermoset composite recycling – Driving forces, development, and evolution of new opportunities

Thermoset composites represent a substantial challenge for recycling, even as composite products increase in market interest. The concept of putting all future thermoset composite products into landfills over the next decades is unlikely to continue. This paper examines the three eras in the history of thermoset product recycling, the drivers for increased recycling, and possible future trends. Technology for managing thermoset composite products at end-of-life first focused on retrieving fiber and to a lesser extent resin. Then in a second era, research focused on better utilization of recovered fiber and finally the third era is now keeping more of the original resin–fiber structure to reuse these composites. Drivers are emerging to stimulate thermoset recycling, including States with success in recycling other challenging products (tires, carpets, automobile parts, etc.) setting policy and fees to encourage recycling. The evolution of heat recovery as a thermoset recycling option in Europe is another driver. Additionally, efforts at certification of recycled fiber quality may stimulate greater reuse.

Current and potential decommissioning scenarios for end-of-life composite wind blades

Contrary to other wind turbine components such as steel towers, concrete foundations and the high value metals used in generator linings, whose end-of-life is properly described in life cycle assessment (LCA) studies, composite blades have proven to be the sustainability blind spot of wind energy systems. The reason for this is that end-of-life management of composite wind blades is a complex engineering problem which depends on the actual design of the blade, its material composition, the availability of recycling technology, legislation and requisite infrastructure, as well as the economics of the process itself—including the logistics of transportation, dismantling, etc. This paper offers a comprehensive analysis of current and potential decommissioning scenarios for end-of-life composite wind blades. Based on 40, in depth, semi-structured interviews with North American and European wind energy experts and a meta-analysis of 52 LCAs of wind energy this paper argues that over approximately the next 5 years, the wind industry will face a significant challenge: as the focus on sustainability engineering and product stewardship shifts the waste disposal responsibility to original equipment and component manufacturers, wind system LCAs may include—and may increasingly become more important in determining—end-of-life scenarios for composite blade waste. It is still too early to ascertain whether LCA will determine the future of composite wind blade recycling by either promoting or legitimizing a certain scenario over another. Nevertheless, as LCAs becoming increasingly more popular in both wind energy and composite recycling, a likely conclusion is that as more economically viable recycling options become available, LCAs will examine the decommissioning phase of used and damaged blades in more detail.