Recycled Composites Research Articles

BUILDING MATERIAL FROM WASTE

This paper proposes an alternative recycling method to divert commingled post-consumer plastics away from dump sites through the production of an environmentally safe construction material. The engineering and service properties of the proposed new recycled plastic waste composite was evaluated and presented. The test results revealed that the new material is suitable for use as pedestrian and light traffic paving brick. The compressive strength was 7.25% higher than the ASTM limit. The composite material exhibited a high modulus of rupture compared to clay bricks and industrial floor bricks indicating its potential for use in structural service requirements. The abrasion resistance of the composite material was 70% higher than the Egyptian standard limit for cement tiles. The composite material exhibited very low density and water absorption rate in comparison to cement tiles and paving units. In addition, the material showed high chemical resistance to acidic and alkaline attack allowing for its use as industrial flooring. Other service conditions were also investigated.Ce document propose une autre méthode de recyclage pour éloigner des décharges les plastiques mélangés, déjà utilisés, par production d’un matériau de construction écologique. On a évalué et présenté les propriétés d’ingénierie et de service du nouveau composite de déchet plastique recyclé que l’on propose. Les résultats de l’évaluation ont révélé que le nouveau matériau était approprié pour utilisation comme brique de pavage pour piéton et pour trafic léger. La résistance à la compression était 7.25% plus élevée que la limite d’ASTM. Le matériau composite exhibait un module de rupture élevé en comparaison avec les briques en limon et les briques pour planchers industriels, indiquant son potentiel pour utilisation en construction. La résistance à l’abrasion du matériau composite était 70% plus élevée que la limite de la norme égyptienne pour les carreaux de ciment. Le matériau composite exhibait une très faible densité et un très faible taux d’absorption d’eau en comparaison avec les carreaux de ciment et les unités de pavage. De plus, le matériau montrait une grande résistance à l’attaque chimique acide et alcaline, permettant son utilisation comme revêtement de sol industriel. On a également investigué d’autres conditions de service.

Recycling of Polymeric Matrix Composites

This work brings up the issue of the recycling of residues made of polyester reinforced glass fibres (PRGF), as well as the involved recycling technology. The future PRGF growth projections have led to an increased attention of the post-consumed products. For PRGF, it is observed that three recycling routes are available: mechanical, chemical or energy recovery. The mechanical recycling is attained by means of grinding a material, which has characteristics that allow its reuse. This paper deals with powder technology processing of residues, by reviewing the available technologies and processes aiming the PRGF recycling.

Design and Function of Lignin-Based Recyclable Composites

Through the phase-separation system composed of phenols and concentrated acid, the phenol components are selectively hybridized into C1-positions of phenylpropane units of native lignin to give 1, 1-bis(aryl)propane-type linear polymers (lignophenols) quantitatively. Lignophenols have unique properties such as high phenolic activity and obvious phase transition. Furthermore, the functionality of lignophenols was able to be controlled using the intramolecular switching function: Under alkaline condition, C1-phenols in lignophenols nucleophilically attack adjacent C2 as switching devices, followed by the cleavage of aryl ether linkages. In ligno-p-cresol and ligno-2, 4-dimethylphenol with similar switching functionality and structural characteristics, ligno-p-cresol was highly hydroxymethylated (HM) on the cresolic nucleus to give network-living pre-polymer. On the other hand, ligno-2, 4-dimethylphenol having reactive sites mainly on the terminal unit gave linear-living pre-polymers. The structures of polymerized lignophenols were controlled by mixing ratio of HM-ligno-p-cresol and HM-ligno-2, 4-dimethylphenol or by the hybridization ratio of p-cresol and 2, 4-dimethylphenol in lignophenols followed by hydoxymethylation. The resulting polymer chains were cleaved at the switching points to give low molecular weight subunits by the switching function. Recyclable composites were prepared by the combination of cellulose and HM-lignophenol (the mixing ratio of HM-ligno-p-cresol to HM-ligno-2, 4-dimethylphenol was 1:0, 1:1, 0:1, respectively). The composites had glossy surfaces and looked like wood. The dimensional stability of composites was improved significantly with increasing mixing ratio of HM-ligno-p-cresol to HM-ligno-2, 4-dimethylphenol. Using the switching functionality of lignophenol, the composites were re-separated into lignophenols with low molecular weight and cellulose.

Morphology/behavior relationship and recyclability of composites based on PP/EPDM blends and short aramid fibers

AbstractThe effect of short aramid fibers on the mechanical behavior of polypropylene (PP) and ethylene‐propylene‐diene (EPDM) and their blends has been investigated by means of an experimental design. The results have shown that aramid fibers are very effective reinforcing agents for composites when the continuous phase of the matrix is constituted by PP, so sensible increments in tensile modulus and strength are obtained as fiber content in the composites increases. An optimal matrix composition and fiber content has been observed that produced high abrasion resistance compounds. However, the abrasion resistance of very rich EPDM matrices is hardly affected by fibers content. The addition of fibers to EPDM rich (>50%) matrices gives rise to a sensible decrease of the impact strength of this polymer. However, at PP contents above 50% in the polymer matrix, an increase of impact strength is observed at fiber percentages in the composites above 10%. The different behavior of the fibers depending on matrix type can be attributed to a better affinity of these fibers for PP matrix. Morphological studies of the composites have been carried out by scanning electron microscopy. Finally, the price and recyclability of these materials have been analyzed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2474–2484, 2002

THERMOPLASTIC, FLEXIBLE, AND RECYCLABLE COMPOSITES, DESIGN, PREPARATION, AND CHARACTERIZATION

Glass fiber reinforced composites based on thermosets are the traditional materials used for many applications due to their good mechanical properties. The non-recyclability of these materials has led to the necessity to develop thermoplastic composites and industrial processes for their manufacture [1]. The present paper deals with the preparation of thermoplastic pre-pregs unidirectionally reinforced with Twarn® and their mechanical characterization.

THERMOPLASTIC, FLEXIBLE, AND RECYCLABLE COMPOSITES, DESIGN, PREPARATION, AND CHARACTERIZATION

THERMOPLASTIC, FLEXIBLE, AND RECYCLABLE COMPOSITES, DESIGN, PREPARATION, AND CHARACTERIZATION

Hard Metals in New Orleans

Recent progress in the recycling and recovery of polyurethane and polyurethane composites is reviewed. The various types of polyurethane waste products, consisting of either old recycled parts or production waste, are generally reduced to a more usable form, such as flakes, powder or pellets, depending on the particular type of polyurethane that is being recycled. The various recycling technologies for material and chemical recycling of PU materials have greatly contributed to improve the overall image regarding the recyclability of polyurethanes in recent years, by far the most important being regrinding and glycolysis. These technologies open an emerging, effective and economic route for recycling polyurethane rigid foams and composite. Polyurethane foam in automotive seating has been successfully recycled using regrind technology. Glycolysis of polyurethanes can be economically acceptable, but still requires more development in order to tolerate more contamination in the post-consumer material. Current technologies can recover the inherent energy value of polyurethanes and reduce fossil fuel consumption. Energy recovery is considered the only suitable disposal method for recovered material for which no markets exist or can be created. Increasing waste-to-energy and other thermal processing activities involving gasification, pyrolysis and two-stage combustion has contributed for the disposal of significant amounts of scrap PU without many difficulties. It is concluded that many of the plastic feedstock recycling processes appear to be technically feasible and robust enough to warrant further development in the future.

Recycling of Metal Matrix Composites

Fundamental ideas of recycling of metal matrix composites are introduced. Two fundamentally different ways for separating reinforcements from the matrix metal exist. One is the mechanical method and another is the chemical method. In this report the separation of fibers in an aluminum matrix composite is demonstrated by a chemical method.

Recycling of Metal Matrix Composites

Fundamental ideas of recycling of metal matrix composites are introduced. Two fundamentally different ways for separating reinforcements from the matrix metal exist. One is the mechanical method and another is the chemical method. In this report the separation of fibers in an aluminium matrix composite is demonstrated by a chemical method.

Functionality controllable polymers derived from native lignin.

Through the phase-separation system, the functionality controllable lignin-based polymers (lignophenols) with 1, 1-bis (aryl) propane units were synthesized. Ligno-p-cresol with the reactive sites on the Cl-cresolic and the terminal phenolic units were hydroxymethylated (HM) to give network-type polymers by heating. On the other hand, ligno-2, 4-dimethylphenol with reactive sites only on the terminal phenolic units gave linear-type polymers. The polymerization of lignophenols could be controlled by mixing HM-ligno-p-cresol and HM-ligno-2, 4-dimethylphenol. Under alkaline conditions, the resulting polymers were depolymerized effectively to small fragments by the switching function (nucleophilic attack of C1-phenolic nuclei to C2). The recyclable composites with high dimensional stability were prepared by the combination of cellulose and HM-lignophenols. Using the switching function of lignophenols, the composites were re-separated into lignophenols and cellulose.

Tertiary Recycling of Automotive Plastics and Composites

The use of engineering plastics and composites in automotive applications is increasing to achieve weight reductions and the accompanying performance increases. These materials are difficult to recycle using conventional technologies because they are contaminated with metals and paints or are cross-linked polymer structures. A novel tertiary recycling process is being developed as an economical means for recycling scrap automotive plastics and composites. Early development work on this process for recycling scrap aerospace composites and electronics shows that it can convert a variety of polymers and composites into low-molecular-weight hydrocarbons at temperatures near 300'C. The hydrocarbons produced can then be reused as chemicals, fuels, or monomers. Metal, glass, fillers, and fibers are separated from the hydrocarbons during the process and can be reclaimed for reuse. Initial feasibility studies have shown that the proposed catalytic conversion process is effective for recycling plastics and composites used in automotive parts. This process does not require presorting of plastic wastes and allows fibers and fillers to be reclaimed for reuse. Conversion products from recycling sheet molding compounds (SMC), auto shredder residue (ASR), and scrap mixtures of automotive plastic body panels show that commercial recycling plants based on the catalytic conversion process should be an economical alternative to landfilling.

Characterization of mixed fiber nylon composites incorporating composite scrap

AbstractRecycling of engineering thermoplastics and their composites represents both a challenge and an opportunity in today's material science. A study on nylon 6,6 based composites with mixed glass‐fiber and carbon‐fiber reinforcement, including nylon composite scrap in their formulation, is reported. Several formulations were prepared by injection molding and were characterized by stress‐strain‐measurements, impact testing, simultaneous differential thermal analysis and thermogravimetry (DTA‐TG), density measurements and scanning electron microscopy (SEM). No dependence on mechanical properties due to increasing amounts of scrap in the composites was found up to 10.4 wt%. The generated recycled composites generally showed lower mechanical properties as compared with the virgin composite because of a poor matrix‐fiber adhesion.

Recycling of aluminum matric composites

Separation of matrix metals in composites was tried on alumina short fiber-reinforced aluminum and 6061 alloy composites and SiC whisker-reinforced 6061 alloy composite for recycling. It is possible to separate molten matrix metals from fibers in the composites using fluxes that are used for melt treatment to remove inclusions. About 50 vol pct of the matrix metals was separated from the alumina short fiber-reinforced composites. The separation ratio of the matrix from the SiC swisker-reinforced 6061 alloy composite was low and about 20 vol pct. The separation mechanism was discussed thermodynamically using interface free energies. Since the flux/fiber interface energy is smaller than the aluminum/fiber interface energy, the replacement of aluminum with fluxes in composites takes place easily. Gases released by the decomposition of fluxes act an important role in pushing out the molten matrix metal from the composite. The role was confirmed by the great amount cavity formed in the composite after the matrix metal flowed out.

Recycling of aluminum matrix composites

Separation of matrix metals in composites was tried on alumina short fiber-reinforced aluminum and 6061 alloy composites and SiC whisker-reinforced 6061 alloy composite for recycling. It is possible to separate molten matrix metals from fibers in the composites using fluxes that are used for melt treatment to remove inclusions. About 50 vol pct of the matrix metals was separated from the alumina short fiber-reinforced composites. The separation ratio of the matrix from the SiC whisker-reinforced 6061 alloy composite was low and about 20 vol pct. The separation mechanism was discussed thermodynamically using interface free energies. Since the flux/fiber interface energy is smaller than the aluminum/fiber interface energy, the replacement of aluminum with fluxes in composites takes place easily. Gases released by the decomposition of fluxes act an important role in pushing out the molten matrix metal from the composite. The role was confirmed by the great amount cavity formed in the composite after the matrix metal flowed out.

Interfaces in repair, recycling, joining and manufacturing of polymers and polymer composites

A basic set of 10 thermoset polymer–polymer interfaces has been identified to play a vital role in the technical and economic aspects of composite manufacturing (RIM/RTM, compression molding, autoclave lamination), recycling, repair, welding, and joining of polymer composites. Knowledge of the chemical interactions and molecular connectivity at these interfaces and their influence on processability and mechanical properties of the polymers and polymer composite is essential, and has been the focus of this research. Presented in this report are the results of an exploratory study performed to understand the interactions at the polymer–polymer interface and their influence on the interfacial fracture toughness of a thermoset vinyl ester, which is widely used in liquid molding applications. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 775–785, 1999

Interfaces in repair, recycling, joining and manufacturing of polymers and polymer composites

A basic set of 10 thermoset polymer–polymer interfaces has been identified to play a vital role in the technical and economic aspects of composite manufacturing (RIM/RTM, compression molding, autoclave lamination), recycling, repair, welding, and joining of polymer composites. Knowledge of the chemical interactions and molecular connectivity at these interfaces and their influence on processability and mechanical properties of the polymers and polymer composite is essential, and has been the focus of this research. Presented in this report are the results of an exploratory study performed to understand the interactions at the polymer–polymer interface and their influence on the interfacial fracture toughness of a thermoset vinyl ester, which is widely used in liquid molding applications. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 775–785, 1999

Recycling of polymeric composites

For material recycling, composites have to be separated into their components, as only non-mixed raw materials can grant high quality standards. A combined mechanical and subsequent electrostatic separation can be classified as highly economic because it is a dry treatment. This is demonstrated on wire scrap. The separated copper and synthetic materials are obtained in a high degree of purity. Chemical disaggregation of composites has been worked out with medicinal blister packs and beverage packs. Two methods of separation were used: separating the plastic-aluminium composite by dissolving the plastic material or dissolving the adhesive that bonds together the plastic and aluminium. To demonstrate the technical feasibility of the processes, a pilot plant with a capacity of up to 25 tons of blister pack material per year was built. Chemical separation with non-problematic aqueous media was demonstrated with flocked plastics. When integrating composites into chemical processes, questions concerning material specification as well as preparation and chemical utilization must be answered. Mechanical preparation of appropriate raw materials has been exemplified by mixed packing waste, carpet-floor waste, and synthetic material from electrical waste. After the raw materials were analyzed and studies of their quantity and compositions were made, their possible re-use as raw material within a chemical process has been elaborated.

Manufacturing and Recycling of A380Al/SiC<SUB>(p)</SUB> Composites

The melting and degassing equipment and the process used in the production of particulate aluminum matrix composites is proposed. Also presented is the successful preparation of A380/80 μm SiC particulate aluminum alloy composites, where SiC particulate was evenly dispersed throughout an aluminum alloy matrix and a die cast chain wheel had very little porosity. In addition, recycling equipment for particulate aluminum matrix composites was designed. The old material and new material of these composites are mixed in ratios of 1:1, 2:1, and 3:1 by weight. After the first, second, and third recyclings, it was found that the amount of porosity and inclusion is much less for recycled composites. In addition, from composition analysis, it was found that the Si content increases with an increase in the amount of old materials and recycling times. From tensile strength tests, it was found that tensile strength and elongation are the same for new materials and composites with old material to new material weight ratios of 1:1 and 2:1 for the first to the third recyclings. However, tensile strength and elongation decrease for composites with an old material to new material weight ratio of 3:1 for the first to the third recyclings, in particular for material of the third recycling. If Si was added before the recycling process, though the formation of Al3C4 and Si crystal could be constrained, it would have no significant effect on the increase of elongation.

Recycling of polypropylene-based composites

The potential of recycling polypropylene-based composites by means of a dissolution process was investigated. The composites were dissolved in an appropriate solvent, and subsequently the polymer solution, containing the fibers in suspension, was filtrated for recovery of the reinforcing agent and of the polymer matrix. Different amounts of hot solvent were employed for washing during filtration, to vary the polymer content remaining on the fibers. The recycled fibers were incorporated in the same polymer matrix, but of virgin quality. The results on the tensile and impact performance of these second generation composites were compared to those of the base material containing unused fibers. It becomes evident that a significant increase of the tensile modulus and strength occurs as the polymer phase deposited on the fibers increases. However, it appears that this interphase alteration has a negative effect on the Izod impact strength. The overall behavior is discussed in terms of fiber dispersion aspects and fiber/matrix adhesion. © 1997 John Wiley & Sons, Inc. Adv in Polym Techn16; 313–322, 1997

Ultrasound Devulcanization of SBR: Molecular Mobility of Gel and Sol

Abstract In an effort to support the recycling of rubbery polymers and composites, 1H NMR relaxation and pulsedgradient spin echo diffusion measurements have been performed on virgin and unfilled vulcanized strene-butadiene rubber (SBR), and networks after various extents of devulcanization using an ultrasound technique. The NMR methods recognize unentangled light molecules (e.g. sol), but do not distinguish between unattached entangled large molecules and chemical network segments. Devulcanization generates additional sol with a wide mass distribution, thus increasing both sol and gel mobility, but decreasing sol mean diffusivity. The latter effect is accounted for by the increasing mean sol molecular mass but also by the increasing glass transition temperature, which is related to main-chain stiffening seen in our earlier 13C NMR experiments. In addition to improving the molecular-level understanding of devulcanization, this study provides guidance for the optimization of the devulcanization parameters.