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Recycling of fibre-reinforced plastics

News International-French

22 Jul 2011

Fibre-reinforced plastics (FRPs) are wonderful materials to design with. Their specific properties give them an advantage over traditional materials but the long life of polymeric composites poses serious environmental problems. FRPs, in general, are difficult to recycle due to their multiphase nature. Various recycling technologies have been proposed but none have proved economically viable. In many cases, the price of raw material produced from recycled composites is considerably higher than the prices for virgin reinforcements and fillers. Perhaps it is time for a philosophical realignment in our approach towards developing sustainable use of FRPs?

(Published on May 2005 – JEC Magazine #17)



A variety of industries including electronics, automotive, and transportation have contributed significantly to the increasing use of FRPs. Although other types of thermoset composites exist, sheet and bulk moulding compounds (SMC and BMC respectively) make up the largest portion of thermoset composite waste because of their use in high-volume applications. For example, the automotive industry has steadily increased its use of SMCs and BMCs to produce lighter, more fuel-efficient cars. The French Ministry of Economy, Finance and Industry estimates the world market for composites growing by 5.7% (in volume) per year since 1994. In 2000, output was at 7 million tonnes and estimates forecast the output of composite possibly reaching 10 million tonnes in 2006. North American accounts for approximately 47% of the world’s composite processing (3.4 million tonnes). Estimates from the Composite Fabricators Association (CFA) for Unit State have approximately 1.1 millions tonnes being shipped in the early 90s and that amount increasing steadily with 2.0 million tonnes of composite materials being shipped in 2000. The French Ministry of Economy, Finance and Industry further estimates the European market second to North America at 28% (2 million tonnes) followed by the Asian market at 23% (1.6 million tonnes). Market growth rates are estimated to be highest in Asia (7%) followed by Europe (4.5%) and the US. There is a small, 2%, market in South American with a projected yearly growth rate of more than 8%.


The end-of-life challenge

End-of-life (EoF) issues are an enormous challenge to sustaining the growth rates estimated above. Before 1970, many of the current environmental laws and regulations had not yet been fully developed or implemented. Once a product’s useful life was complete, the product was typically disposed in a landfill. That is certainly not the case today. European Union (EU) directives such as End of Life Vehicles (ELV, 2000/53/EC) require 85% of the ELV will have to be reused or recycled by 1 January 2015 with 10% incinerated with energy recovery and 5% landfill wasted. Other EU directives such as the Waste Electrical and Electronic Equipment (WEEE), Landfill (1999/31/EC) and Incineration will put similar pressure on fabricators and end-users for sustainable FRP waste management. Other countries share in this concern. The UK government policies, such as the Waste Strategy 2000, the sustainable construction strategy, and the landfill tax, could all influence the FRP industry there. In the US, approximately 14,000 nationwide landfills have been closed since 1978 due to being full, or because of environmental issues. The cost of disposal of the materials will only increase as landfills begin to fill up. The State of Minnesota calculated that 18,750 tonnes of fibre-reinforced plastics were being sent to landfills in the state each year at a cost of nearly $20 million. Cost increases can already be seen in Europe; in Germany, landfill transfer costs have increased 300% in recent years. Japan’s Recycling and Treatment Council (RTC) is so concerned about the environmental effects of unusable composites that it has commissioned a committee to address the technological and social problems regarding recycling thermoset composites wastes and, according to Kojima and Furukawa, the disposal and recycling of these composite products have “constituted a great social problem, as there is no effective reusing system for it”.


FRPs, in general, are difficult to recycle due to their multiphase nature, typically containing three or more components: fibre reinforcement, resin matrix and fillers (typically calcium carbonate, CaCO3). Recycling of thermoset FRPs presents an especially difficult challenge because once the thermoset matrix molecules are cross-linked, they cannot be melted or reformed. Thermoplastics, on the other hand, are inherently recyclable. Further, the value of the material constituents of GRP reclaimed from recycling is low. Hence there is little business (monetary) incentive to recycle.


Four classes of recycling technology

Various recycling technologies have been proposed. They can be divided into four classes: energy recovery, thermal breakdown of the matrix, chemical breakdown of the matrix, and size reduction. The potential energy recovered from unreinforced plastics can be substantial. In 1990, it was estimated that the reaction injection moulding production scrap of North America would have been the energy equivalent of 30–35 million litres of crude oil. Incineration is not a favourable method for recycling thermoset composites such as SMCs and BMCs because of their high inorganic contents (up to 70%), which significantly reduces the energy available.


Pyrolysis and fluidized beds are two thermal decomposition methods that have been used to recycle thermoset composites. Each technique removes the resin by volatilizing it with heat. The by-products are typically gases and liquids from the resin, which are used as fuels and extenders in other materials. The problem is that the high temperatures needed for these processes either degrade the properties of the glass fibres or have heating costs that approach or exceed the value of the products extracted.


Three methods for chemically recycling BMCs and SMCs have been discussed in literature: hydrolysis, glycolysis, and solvolysis. All the three methods have been successful to some extent but chemical recycling is a mixed blessing because there is often a large amount of chemical waste produced in the process. In order for a process to be environmentally viable, more materials must be recycled than the chemical waste produced. While this appears possible in laboratory conditions, larger-scale industrial chemical recycling does not seem to be feasible.


About FRPs
FRPs are attributed with six properties that give them an edge over traditional materials: longer life cycles due to high fatigue strength, increased corrosion resistance, improved fire resistance, easier design because of functional integration, possibility of complex shape, and lower weight. They can be broadly categorised according to their constituents, i.e., by fibre, glass or carbon, and their matrix, thermoset or thermoplastic. Thermoplastic FRPs currently have a higher growth rate than thermoset composites, at 9% and 3% per year respectively, but thermoset FRPs account for more than two-thirds of the market. A glass-fibrereinforced/ plastic resin matrix (GRP) morphology constitutes the bulk of thermoset FRPs in use today, primarily in the form of SMC and BMC. “High-tech” carbon fibre (CFRP) and/or thermoset plastic matrix resin morphology is concentrated in the sports and aerospace industry, which contributes much less to the overall waste volume.


Size reduction is the only method currently being used commercially to produce useful recyclate from SMC and BMC waste. A few companies in Europe, such as ERCOM, Mecelec, and Valcor, are focusing on recycling SMCs. In the US, companies such as R.J Marshal, Premix, and the now defunct Phoenix Fiberglass, have made efforts involving SMC recycling. The grinding processes employed by different recyclers involve individual technologies, but every methodology involves a series of size reduction and separation steps. The ground recyclate is added to virgin constituents to form a new FRP material.


The problem with this material is that it experiences significant reductions in stiffness and strength compared to all virgin constituent FRP. This reduction is thoroughly documented in the literature and the state-of-the-art may be reflected in work by Telfeyan as illustrated in the graph. A variety of BMCs were derived from a generic formulation of 50 wt% CaCO3 filler, 16.67wt% fibre, and 33.33wt% resin. Sets of samples with virgin fibre (VF) lengths of 3.175mm, 6.35mm, a 50/50 weight mix of 6.35mm and 12.7mm, 12.7mm, 19.05mm, and 25.4mm were made. Samples with mixtures of recyclate and virgin fibre were also made based on the generic composition. With 16.6wt% fibre, 70wt% of that was virgin fibre (lengths of 6.35 mm, 12.7 mm, and 19.05mm) and 30wt% was recyclate. A set of BMC samples with no fibre reinforcement (75wt% CaCO3 and 25wt% resin) was made for comparison. By combining varying lengths of VF and recyclate, the reduction in structural properties was mitigated but still existed.


So, what sort of philosophical realignment towards developing sustainable use of FRPs is required? Let us summarize the arguments presented thus far:
- thermosets are difficult to recycle;
- constituents recovered from the largest volume of FRP waste (GRPs) have low value;
- thermoplastics are inherently recyclable;
- carbon fibre has a higher value than glass fibre reinforcement. The higher rate of growth in thermoplastics usage gives us a hint. Although costing initially more, thermoplastic FRPs offer better recycling opportunities and thus sustainable use.


Secondly, increasing the value of virgin FRP constituents increases the value of reclaimed recyclate. The net value of reclaimed aerospace grade of carbon fibres from a thermoset matrix has been estimated a $2.50/lb. Markets have been identified for recycled carbon fibres in cellular phone and laptop computer housings made lighter in weight by use of thinner walls, for bi-polar plates in proton exchange membrane fuel cell applications, and in SMC/BMC for automobiles. Will industry and endusers voluntarily shoulder the initially higher costs for CFRP in their applications? If history (and a keen business sense) are any guide, the answer is “No”. But the point may not be one for industry to decide. Impending legislative action appears ready to force the adoption of sustainable FRP use and, at this juncture, CFRP/thermoplastics may be the only viable alternatives.