Recycled Composites Research Articles

Stress distribution in carbon fiber-reinforced epoxy composites under the supercritical condition

The recycling of carbon fiber-reinforced resin matrix composites is attracting more and more attentions, and many mechanical, chemical, and energy recycling methods have been proposed. Among those methods, supercritical solvent recycle technique has been developed recently. Hygrothermal treatment was applied first to the composites before the supercritical process. Numerical simulation method was used to carry out the calculation of the thermal stress, peel stress, and interfacial shear stress under both the hygrothermal and supercritical conditions, to identify the mechanism of structural damage of composites. It shows that the hygrothermal treatment reduced both the critical pressure and temperature, and accelerated the structural damage of composites under the supercritical condition. The temperature and pressure simultaneously impacted the mechanics performance of composites, while the temperature was the dominant factor to destroy the composites' structure. And, potential damage areas were located in the free end with two failure types mainly: interfacial debonding failure and stratified destruction. POLYM. COMPOS., 36:961–968, 2015. © 2014 Society of Plastics Engineers

The effect of recycling number on the mechanical, chemical, thermal, and rheological properties of PBT/PC/ABS ternary blends: With and without glass‐fiber

The recycling possibilities of poly(butylene terephthalate)/polycarbonate/acrylonitrile–butadiene–styrene (PBT/PC/ABS) ternary blend with and without glass‐fiber content were investigated using repeated injection molding process. In this study, PBT/PC/ABS ternary blends were reprocessed at five times and the results were presented after each recycling process. The recycling possibility of PBT/PC/ABS ternary blend was evaluated by measuring the mechanical, chemical, thermal, and rheological properties. Mechanical properties were determined by the tensile strength, yield strength, strain at break, elastic modulus, impact strength, flexural strength, and flexural modulus. Chemical and thermal properties were evaluated by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, and scanning electron microscopy. Rheological properties of the ternary blends were studied by melt flow index measurement. From the results, it was found that mechanical properties of recycled composites were better than virgin PBT/PC/ABS ternary blends. POLYM. COMPOS., 35:2074–2084, 2014. © 2014 Society of Plastics Engineers

Progress in Recycling of Composites with Polycyanurate Matrix

Thermoset based composites are used increasingly in industry for light weight applications, mainly for aircraft, windmills and for automobiles. Fiber reinforced thermoset polymers show a number of advantages over conventional materials, like metals, especially their better performance regarding their strength-to-weight ratio. However, composite recycling is a big issue, as there are almost no established recycling methods. The authors investigate the recyclability of polycyanurate homo- and copolymers with different recycling agents under different conditions. Also the influence of the recycling process on the most important reinforcement fibers, i.e. carbon-, glass-, aramid-, and natural-fiber is investigated. The authors find that: the recycling speed is not only dependent on the temperature, but also is significantly influenced by the particular recycling agents and the polycyanurate formulation. Hence, the stability against the recycling media can be adjusted over a broad range by adjusting the polymer composition. Furthermore, the authors find that the inorganic reinforcement fibers (carbon and glass) are almost unaffected by neither recycling agent at either temperature. Aramid-fibers degrade, depending on the particular recycling agent, from slightly up to extremely strong. This leaves one with the possibility to find a combination of matrix resin and recycling agent, which does not affect the aramid-fiber significantly. In the case of natural fibers, the dependence on the particular recycling media is very strong: some media do not affect the fiber significantly; others reduce the mechanical properties (tensile strength and elongation at break) significantly, and still others even improve both mechanical properties strongly. From the Recyclate, the authors synthesize and subsequently characterize a number of new polyurethane thermosets (foamed and solid samples) with different contents of recyclate, exhibiting Tg in the range of 60°C to 128°C.

Chemical recycling of carbon fibers-reinforced phenolic resin composites by phenol in subcritical conditions

In this work, a composite prepared with a phenolic matrix and reinforced with carbon fibers was subjected to degradation by phenol under subcritical conditions. Phenol was able to solubilize the resin matrix under relatively mild conditions (T ≤ 390 °C, P < 0.5 MPa) without altering the carbon fibers, as confirmed by scanning electron microscopy and by mechanical characterization of the fibers recovered after heat treatment.

Up-cycling end-of-use materials: Highly filled thermoplastic composites obtained by loading waste carbon fiber composite into fluidified recycled polystyrene

Carbon fibers reinforced epoxy resins are used in a wide range of applications, such as automotive and aerospace industry. Because of their thermosetting nature, recycling at the end of the life cycle is a difficult issue. However, lack of recyclability poses environmental concerns to the use of these composite materials. In this article, a sustainable, cost-effective technological approach aiming at recycling postconsumer carbon fibers reinforced thermosets (CFRT) is proposed. Composites containing 50 and 70 wt% of CFRT particles were prepared by incorporating the filler fraction into a fluidified postconsumer expanded polystyrene matrix. A cold mixing approach consisting in the use of a low boiling solvent as a binder to guarantee the dispersion homogeneity on micro- and macroscopic level was set up. For comparison, analog composites were also prepared through melt mixing process. Morphological, mechanical, and thermal analyses allowed to prove the effectiveness of the cold mixing approach and to evaluate the influence of particle size on the performance of new recycled composites. Thermogravimetric analysis and thermal conductivity tests of samples highlighted further peculiarities of the cold mixing process. The approach proposed is an effective recycling technology for CFRT and could be extended to other postconsumer materials. POLYM. COMPOS., 35:1621–1628, 2014. © 2013 Society of Plastics Engineers

Thermal regeneration of recyclable reduced graphene oxide/Fe3O4composites with improved adsorption properties

BACKGROUND Graphene was chosen as magnetic adsorbent because of its unique size and structure. Much effort has been made to prepare magnetic graphene-based composite materials with Fe3O4, however, regeneration of the magnetic adsorbent has been ignored. In this study, a simple thermal regeneration method was proposed with the advantages of low cost, environment-friendly and no secondary pollution. The effectiveness of thermal recovery in reduced graphene oxide (RGO)-Fe3O4 recyclable composites (RGFs) was tested. The evolution of structure, morphologies, magnetic properties, and recyclability of RGFs were characterized. RESULTS The results show that equilibrium data were best described by the Sips isotherm model, with a maximum monolayer adsorption capacity of 228.64 mg g−1 at 25°C. Adsorbed methylene blue was removed from contaminated RGFs through a simple thermal recovery method (calcination at ∼300°C in air). Meanwhile, RGO sheets remained stable, and the Fe3O4 transformed to magnetic γ-Fe2O3, rather than nonmagnetic α-Fe2O3, which enables magnetic separation of RGFs. CONCLUSION Compared with other similar reported adsorbents, RGFs exhibited excellent adsorbability and recyclability without obvious performance degradation using the proposed thermal regeneration procedure. © 2013 Society of Chemical Industry

Low-velocity impact response and compression after impact assessment of recycled carbon fiber-reinforced polymer composites for future applications

The influence of recycling on the impact damage resistance of recycled carbon fiber-reinforced polymer (CFRP) composites was investigated using low-velocity impact and compression after impact (CAI) tests. The relationships among load, force, and time were analyzed to gain insight into the damage characteristics of three types of composite laminate: virgin CF-reinforced polymer (V-CFRP), recycled CF-reinforced polymer (R-CFRP), and treated recycled CF-reinforced polymer (TR-CFRP). Special emphasis was placed on evaluating the extent of damage and the residual mechanical properties as affected by three different fiber surface states. Substantial differences were noted in the shape, area, and damage mode of impact using ultrasonic c-scanning, photography, and scanning electron microscopy (SEM). V-CFRP indicated significant improvement in impact damage resistance in the form of less damage, higher residual strength, and greater shear failure angle. Damage resistance was improved up to 80% of V-CFRP by surface cleaning while R-CFRP is 50% of V-CFRP. Shear failure angle of 16° was attained from R-CFRP and it was increased to 24° when the recycled fibers were cleaned. The result of SEM showed that there was less delamination of TR-CFRP compared with R-CFRP. This work proves that the low-velocity impact response of recycled composites can rival that of virgin composites, while providing a basis for future applications of recycled carbon in many fields. POLYM. COMPOS., 35:1494–1506, 2014. © 2013 Society of Plastics Engineers

Tensile Strength and Water Absorption Behavior of Recycled Jute-Epoxy Composites

Recycled natural fi bers and biopolymers with sustainable, eco-friendly, and biodegradable properties are receiving increased attention. The moisture absorption and swelling of natural fi ber composites adversely infl uence their mechanical properties and applications. In this research, bio-based epoxy polymers that are reinforced with recycled woven jute fabrics were subjected to water immersion tests in order to study the effect of water absorption on their mechanical and geometrical properties. For comparison, petroleum-based epoxy polymers that are reinforced with new woven jute fabrics were also subjected to the same tests. The effect of fi ber percentage on water absorption, thickness swelling, and volume swelling was measured as a function of immersion time. It was observed that water absorption and swelling behavior were higher in bio-based epoxy than in petroleum-based epoxy composites. The stress decreased and the strain increased after water immersion in both composites. However, the rates of change in stress and strain were much more signifi cant for composites made with bioepoxy.

The influence of micromechanical properties and reinforcement architecture on the mechanical response of recycled composites

Technologies for recycling carbon–fibre composites are now becoming mature, so a key challenge is to establish applications for the recycled products. This paper aims to further our understanding on the mechanical response of recycled composites, so as to guide the optimisation of recycling processes and support their use in non-critical structural components. This work thoroughly characterises three recycled composites and analyses the relations between fibre and interfacial properties, reinforcement architecture, and macroscopic mechanical response. An unequivocal relationship between the architecture of a recycled composite and its fracture toughness is established; this proves that fibre bundles are not necessarily a recycling defect, but can actually toughen the material by at least up to an order of magnitude without significantly reducing stiffness or strength.

Tensile Properties of Aminosilane Treated Rice Husk/ Recycled PVC Composite

Rice husk is an agricultural waste produced in bulk quantity as a part of rice milling. There have been many approaches in utilizing rice husk as fillers in polymer composite. However, recycled PVC has not been reported to be used in PVC/rice husk composites yet. In this research, a good interfacial interaction between rice husk and recycled polyvinylchloride has been achieved by incorporation of aminosilane as coupling agent. The aminosilane treated recycled polyvinyl chloride was mixed with rice husk and then fabricated by using hot compression moulding. Three different ratio of rice husk to recycled polyvinyl chloride were used which is 65/35, 55/45 and 45/55 as shown in Table 1. The positive effect of rice husk reinforcement as well as surface treatment has been reflected in the improved tensile properties of the resulting polyvinyl chloride based composite. However, flexural stress of the treated composite drops with increasing filler percentage. The incorporation of aminosilane as coupling agent increases the tensile stress of 45 wt% of rice husk significantly. Scanning electron microscopy has been used to understand the failure mechanisms of aminosilane modified rice husk filled recycled polyvinylchloride composites. The findings can be used to increase the effort in recycling rice husk and PVC.

Mechanical characterization of sisal fiber-reinforced recycled HDPE composites

The increasing awareness of the environment protection has contributed to concerns regarding alternative procedures for recycling of plastic wastes. Since chemical processes are high cost, energy and often environment harmful, thermo-mechanical techniques of recycling rises as a good alternative. This research deals with mechanical characterization of thermo-mechanical recycling of composites based on recycled high density polyethylene (HDPE) from post-consumed motor-oil plastic containers as matrix and natural fibers (sisal) as reinforcement. The composites were made by extrusion and then melt blended in a compression mold. The sisal fibers do not contribute to increase tensile strength. As fiber content increases loss of ductility is observed.

The Influence of Processing and the Polymorphism of Lignocellulosic Fillers on the Structure and Properties of Composite Materials-A Review.

Cellulose is the most important and the most abundant plant natural polymer. It shows a number of interesting properties including those making it attractive as a filler of composite materials with a thermoplastic polymer matrix. Production of such composite materials, meeting the standards of green technology, has increased from 0.36 million tons in 2007 to 2.33 million tons in 2012. It is predicted that by 2020 their production will reach 3.45 million tons. Production of biocomposites with lignocellulosic components poses many problems that should be addressed. This paper is a review of the lignocellulosic materials currently used as polymer fillers. First, the many factors determining the macroscopic properties of such composites are described, with particular attention paid to the poor interphase adhesion between the polymer matrix and a lignocellulosic filler and to the effects of cellulose occurrence in polymorphic varieties. The phenomenon of cellulose polymorphism is very important from the point of view of controlling the nucleation abilities of the lignocellulosic filler and hence the mechanical properties of composites. Macroscopic properties of green composites depend also on the parameters of processing which determine the magnitude and range of shearing forces. The influence of shearing forces appearing upon processing the supermolecular structure of the polymer matrix is also discussed. An important problem from the viewpoint of ecology is the possibility of composite recycling which should be taken into account at the design stage. The methods for recycling of the composites made of thermoplastic polymers filled with renewable lignocellulosic materials are presented and discussed. This paper is a review prepared on the basis of currently available literature which describes the many aspects of the problems related to the possibility of using lignocellulosic components for production of composites with polymers.

Mechanical properties of eco-friendly recycled polymer composites: a comparative study of theoretical and experimental results

This study discusses the influence of incorporation of natural fiber on the performance of recycled polypropylene composites. Composites consisting of polypropylene (PP) and sisal fiber were prepared through mixing and compression process, in various proportions. The surface modification of the fibers has been carried out, using various chemical treatments. Mechanical properties of the systems have been evaluated. A comparative study has been conducted between the theoretical as well as experimental results using various suitable models. The impact of treatment of the fibers on the thermal and flammability properties has also been investigated. The interfacial properties have been interpreted from scanning electron micrographs (SEM).

Degradation of phenol by using magnetic photocatalysts of titania

Magnetic TiO2 (MT) composites were prepared and applied to degrading phenol, which is one of the listed priority pollutants. The effects of heat treatment under preparation on the photocatalytic activity of MT composites have been investigated by varying the soaking time under a constant final temperature of 823 K. The total organic carbon and ring-remaining intermediates of o-DHB, p-DHB and 1,4-BQ in solution were detected during the photodegradation of phenol. All the resulting MT composites were the single-phase anatase and magnetite judged by X-ray diffraction patterns. The calcination of the as-prepared particles was proven to be extremely crucial to the photocatalytic activity. The best condition of heat treatment was found to be soaking time of 2 h at T = 823 K due to the good performance of photocatalytic activity, stable magnetic property, and reusability over three times. The results lead to the conclusion that recyclable MT composites prepared in this study, which belonged to the category of recyclable green materials, exhibit good photocatalytic activity to degrade phenol so as to possess applicable potential for the degradation of refractory organics in the aqueous solution. Furthermore, the environmental and health impacts were reduced as MT composites were applied in the treatment of water pollution.

Low combustible polypropylene/flax/magnesium hydroxide composites: mechanical, flame retardation characterization and recycling effect

Natural fibre-reinforced polymer composites are nowadays receiving considerable attention, especially in the automobile and civil engineering industries. Reduction in flammability characteristics besides retention of their excellent mechanical properties will ensure wider market for these composites. Polypropylene matrix was reinforced with 30 and 50 wt% of flax fibres. Magnesium hydroxide was added at different levels of 0, 20 and 30 wt% in order to investigate the flammability resistance behaviour. Thermal and thermomechanical tests were carried out in order to evaluate new and recycled composites. Limited oxygen index was improved to more than 27 with 50 wt% flax/30% magnesium hydroxide, although very slow burning rate in the horizontal test condition was achieved with 30/30, 50/20 and 50/30 wt% for flax/magnesium hydroxides. Regarding the UL94 test, no sample passed vertical burn test. Recycling of these composites was investigated and showed 4 and 10% decrease in strength and stiffness, respectively. Recycling experiments on 50/30 system showed an effect of 5% limited oxygen index decrease after reprocessing for two cycles.

Recycling of fiber-reinforced composites and direct structural composite recycling concept

Fiber-reinforced polymer composites are engineered materials commonly used for many structural applications because of the high strength-to-weight and stiffness-to-weight ratios. Although the service life of these materials in various applications is usually between 15 and 20 years, these often keep the physical properties beyond this time. Recycling composites using chemical, mechanical, and thermal processing is reviewed in this article. In this review of carbon, aramide, and glass fiber composites, we provide, as of 2011, a complete view of each composite recycling technology, highlight the possible energy requirements, explain the product outputs of recycling, and discuss the quality (fiber strength) of recyclates and how each recyclate fiber could be used in the market for sustainable composite manufacturing. This article also includes the new concept of ‘direct structural composite recycling’ and the use of these products in the same or different applications as low-cost composite materials after small modifications.

Effects of Temperature and Flue Gas Recycle on the SO2 and NOx Emissions in an Oxy-fuel Fluidized Bed Combustor

Oxy-fuel combustion consists in burning a fuel with a mixture of nearly pure oxygen and a CO2-rich recycled flue gas resulting in a product flue gas from the boiler containing mainly CO2 and H2O.In this work, the effect of combustion temperature and flue gas recycle composition on pollutant emissions and on the sulfation process, in order to optimize the SO2 retention in circulating fluidized beds (CFBC), were analyzed.The experimental work was carried out with an anthracite coal in a 3 kWth continuous bubbling fluidized bed (BFB) combustor operating in oxy-fuel conditions. It was found that in oxy-combustion conditions in BFB an increase of combustor temperature produced an increase on NO emission and a decrease in the CO and N2O emissions. The optimum temperature to reach the highest sulphur retention was at 900-925°C.Flue gas recirculation was simulated by mixing different gases (CO2, SO2, NO, and steam) in different concentrations. It was observed that SO2 recycle produced an increase on the sulfur retention as a consequence of the higher SO2 concentration existing in the bed. About 65% of the recycled NO was reduced to N2, being the NO converted to N2O lower than 5vol.%. Wet recycle produced an important reduction on NO emission in comparison with dry recycle.

Microstructure and Mechanical Properties of Dual Matrix Aluminium-Fly Ash Composites Processed via Cryomilling, Cold Compaction and Hot Extrusion

Abstract AA6061/Al alloy chips of different size and fly ash particles have been recycled using the solid state process. The effect of chip size and fly ash content on the microstructure, mechanical and wear properties of the recycled AA6061/Al two phase composites were investigated. Microstructural characterization revealed a uniform distribution of fly ash particles in recycled composites with fine chips and a good interface between fly ash particulates and AA6061/Al two phase matrixes. According to mechanical and wear results, the incorporation of fly ash particles in the AA6061/Al two phase matrix caused reasonable increase in hardness, compressive strength, and wear resistance. On the recycled composites fine chips, the destructive action of the steel ball was very limited compared to that of the Al 2O3 ball.

Mozliwosci recyklingu i utylizacji materialow polimerowych i wyrobow kompozytowych

The paper describes the methods of recycling of polymer composites in Europe and Poland, with a particular focus on duroplastic composite materials reinforced with glass or carbon fibres. The ways to solve the problems connected with composite recycling as well as the existing European Community regulations in this area have been discussed.

Recycled blocks with improved sound and fire insulation containing construction and demolition waste

The environmental problem posed by construction and demolition waste (C&D waste) is derived not only from the high volume produced, but also from its treatment and disposal. Treatment plants receive C&D waste which is then transformed into a recycled mixed aggregate. The byproduct is mainly used for low-value-added applications such as land escape restoration, despite the high quality of the aggregate. In the present work, the chemical composition properties and grading curve properties of these aggregates are defined. Furthermore, the resulting recycled concrete with a high proportion of recycled composition, from 20% to 100% replacement of fine and coarse aggregate, is characterized physically and mechanically. An environmental study of the new construction material when all aggregates are substituted by C&D waste shows a low toxicity level, similar to that of other construction materials. The new material also has improved properties with respect to standard concrete such as high fire resistance, good heat insulation, and acoustic insulation.