12 September 2013

Recycling glass fibre reinforced composites – history and progress

This article discusses the issues surrounding the recycling of glass fibre reinforced plastics (GRP), and reviews some of the options available today.

The world is going through a low carbon revolution and the potential for composites to reduce greenhouse gas emissions is clear. But the difficulty of recycling glass fibre reinforced plastic (GRP) is a stumbling block particularly in construction and automotive where the pressure to recycle is high.

The European Composites Industry Association (EuCIA) states that GRP is “recyclable and compliant with EU legislation,” and it is (see EuCIA issues position paper on recycling of glass reinforced thermoset composites). But at present facilities exist only in Germany to recycle, which for companies in UK, for example, is prohibitively expensive and not environmentally friendly due to the effect of transport, leaving the option only to landfill.

To what extent is GRP economically recyclable, and therefore actually being recycled? How much would it affect markets for GRP if there were fully functioning, economically sustainable, geographically widespread recycling supply chains?

Several articles in Reinforced Plastics have advised us of the development of pyrolysis based carbon fibre recycling processes and these are now commercially available in several places since the launch of Milled Carbon (nowELG Carbon Fibre) in the West Midlands, UK. But the value of carbon fibre is around ten times that of glass, so while commercialising these processes has not been easy, it has been 'easier' than finding recycling routes for GRP, despite the much smaller volumes (76,000 tonnes carbon fibre reinforced plastic compared to about 1 million tonnes GRP parts produced in Europe in 2012, according to AVK's 2012 market report).

The recycling process supported by EuCIA, and available in Germany, involves the addition of GRP waste to cement kilns. This gains value from all parts of the composite and is commercially active in Germany through the route known asCompocycle, operated by Zajons and feeding Holcim’s cement kilns. However there is still a significant gate fee for the process. In Germany regulations leave no option to landfill so the volumes of GRP waste are sufficient to justify such a process. Composite manufacturers such as Fiberline in Denmark have supported that process, being close enough to take advantage of it. But this route reduces the value of the material to that of calcium carbonate and at present is not economic compared to landfill where landfill is an option.

Cement kiln route – how does it work

Incineration of GRP is not practical since about 50-70% of the material is mineral and would be left as ash, which still needs to be landfilled. For co-processing in cement kilns, composite parts are size-reduced and mixed with other waste to feed into the kilns.

GRP typically contains E-glass, which is usually alumino-borosilicate, along with an organic resin and often calcium carbonate filler. When fed into a cement kiln the organic resin burns providing energy (about 12 MJ/kg of waste) and the mineral constituents provide feedstock for the cement clinker.

The clinker is ground to form cement. Any calcium carbonate calcines (releasing carbon dioxide) to calcium oxide, the primary component of Portland cement. Alumina and silica also have cementitious properties in an alkaline environment and are typically present in Portland cement at about 25%, and in much higher proportions in cement alternatives from fly-ash and slag. Boron, which is found in most E-glass, can cause a reduction in early strength during the setting of cement, but as long as proportions are kept low it is not considered a problem (ref: Pickering, Benson, Recovery of material and energy from thermosetting plastics, Proceedings, ECCM6 – Recycling concepts and procedures, 1993.

Mechanical grinding

Recycling of GRP by mechanical grinding has been happening for several decades. Back in the 1970s the late Wolfgang Unger was developing his proprietary Seawolf technology in Florida, US, to grind fibreglass scrap and use it for replacing rotten boat transoms or incorporate it using spray-up equipment for making bathtubs and other products.

Unger’s company is now called Eco-Wolf and is managed by his daughter SabineCorinna Unger. Eco-Wolf has recently (2011) partnered with Global Fiberglass Solutions which is seeking to build and manage facilities to collect and recycle fibreglass across the US, having developed applications such as railroad ties (railway sleepers).

ERCOM Composite Recycling GmbH was established in Germany in 1990 to recycle automotive production and post-use waste by shredding and grinding graded parts into powder, to be used in new sheet moulding compound (SMC) in proportions up to 20% (ref: George Marsh, Facing up to the recycling challenge, Reinforced Plastics, Volume 45, Issue 6, June 2001, pages 22-26). ERCOM terminated in 2004. This approach of grinding GRP to fine powder for use as filler is well established in several industries, but as with the cement kiln route, it reduces the value of the material to that of calcium carbonate, which can be purchased at very low cost (around £200/tonne). In addition, it requires a significant amount of energy input to grind the material finely. Thus apart from some in-house recycling (see below), attempts to commercialise this as a recycling route have failed.

In the UK two roof light manufacturers now recycle some of their own waste by grinding. Filon Products has invested in machinery to grind their in-house GRP waste and incorporates it into a range of products including roofing sheet, valley gutters and flat sheet for signage. They are now investigating using the recyclate in moulding compounds.

Hambleside Danelaw (HD) is similarly grinding waste, and offers a take-back scheme for products at end of life. They have been involved in trials in numerous products over the last 10 years or so. Initially they worked with Dundee University using the recyclate in foamed concrete which had some advantages, but the reduction in slump (effectively increased viscosity) meant that it did not flow easily into moulds. In 2007-2008 in the UK several trials were undertaken through the BeAware project (Built Environment Action on Waste Awareness and Resource Efficiency) to incorporate GRP waste into precast concrete and rubber products. Improvements in properties were demonstrated, but again results were not commercialised.

However HD has found that there is more value in separating off the glass fibres from the resin powder to re-use as reinforcement. They have trialled this in new glass fibre mats for valley gutters and also in thermoplastic composites. In addition to glass fibre reinforced polyester products, they manufacture building products from injection moulded polypropylene (PP) and other polymers. Adding the short glass fibres to the PP increases strength and stiffness as well as reducing the PP content and therefore the cost of the injection moulded products. They are exploring ways to widen applications and so reach a place where they can take waste from other companies to process and sell back into new products.

Under floor vent from Hambleside Danelaw. Typically made from PP, but this one is 100% recycled with glass fibres from ground GRP recyclate and in-house PP waste, resulting in a stiffer, stronger product with no increase in cost. (Picture © Stella Job.)

 

Ray Khan, Director of Quality and Environmental Standards at HD, says: “As a responsible business we feel that we have to look at a circular economy and take responsibility for the products we manufacture. We can’t keep throwing things into holes in the ground, because a) there aren’t enough holes, and b) the cost of landfill is increasing.”

Similar work has been done by Mixt Composites Recyclables (M-C-R) in France, a subsidiary of Plastic Omnium Auto Exterieur. M-C-R manufactures moulding compounds and takes back process waste from its clients which is ground and re-integrated into new compounds for automotive parts. The recyclate is finely ground to about 50 microns to replace filler.

Sébastien Masson, R&D Project Manager at M-C-R, explains that the added value is in the environmental aspect, or in respecting incentives to recycle/increase recycled content.

M-C-R also extracts longer fibres from less finely ground recyclate and sells this as a substitute for PP fibres in cement floor screeds, where the fibres limit cracking during the early setting of the cement. This has been validated in trials by CERIB (Centre d’Etudes et de Recherches de l’Industrie du Béton). They have also done some studies compounding the fibres in thermoplastics, though this is not yet commercially active.

In Belgium, Reprocover manufactures manhole covers, valve chambers and other construction products using ground thermoset industrial waste including GRP and clean waste fibres from nearby glass fibre reinforcement manufacturer, 3B-the fibreglass company. They have recently developed a bi-block railway sleeper with excellent vibration absorbing qualities which is currently undergoing detailed testing for approval to replace timber railway sleepers. Timber railway sleepers are likely to be phased out in Europe due to legislation which is expected to come into force in 2018 relating to the carcinogen effect of the creosote used to treat them, so railway companies are actively seeking alternatives. This could be a useful growth market application for waste GRP.

Thermal and chemical processes

Research into several other processes for GRP recycling has been undertaken over the years. For example, treatment of moulding compounds in a fluidised bed process was trialled at Nottingham University, UK, in the 1990s. The fibres recovered were re-used in a dough moulding compound (DMC) and properties measured.

A study in pyrolysis of GRP waste at University of Leeds, UK, in the early 2000s demonstrated that recovered glass fibres could replace up to 20 wt% of virgin glass fibre in DMC. The oil and gas generated by the pyrolysis could in principle be recovered for use as fuel and chemical feedstocks. Indeed a pyrolysis approach was developed by Danish company ReFiber for GRP in 2001-2003, where the fibres were bound with PP into insulation slabs, but this was not taken to market. Their prototype pyrolysis oven went on to be used for carbon fibre recycling for French textile recycling company Apply Carbon.

A focus of research in Japan has been on chemical breakdown of the polymers, e.g. by sub-critical water hydrolysis, where glass fibres and chemicals are recovered and re-used in new products. This approach has also been studied in Europe in the EURECOMP project involving Exeter University, Plastic Omnium and others and completed in 2012. The project demonstrated the feasibility of the process, but there is a compromise to be made regarding processing temperature, in that a higher processing temperature damaged the mechanical properties of the fibres too much, but a lower temperature led to an unacceptably long cycle time.

A useful outcome of EURECOMP was a full life cycle assessment of the process in comparison with other recycling processes. The final report summary states: “A life cycle assessment … reveals that the solvolysis process is not yet competitive with treatments like mechanical recycling or energy recovery, but can possibly be competitive with pyrolysis in terms of environmental impacts."

A common feature of most recycling processes is that the strength of glass fibres tends to be substantially reduced, though in most cases stiffness is retained at or near original. Jim Thomason at University of Strathclyde, Scotland, an expert in glass fibre sizings and formerly involved in glass fibre research at Owens Corning, is developing a way to post treat thermally reclaimed glass fibres from GRP waste in order to regenerate properties to be comparable to virgin glass fibres (ReCoVeR project). If successful, this could create a new market for recycled glass fibres to be sold in direct competition with virgin chopped glass fibres.

Activity in the UK

The Materials KTN has been involved in supporting the development of composite recycling processes in the UK since its inception. A Materials KTN workshop in February 2011 brought together stakeholders from across the UK to discuss the GRP recycling supply chain. As a result of this Sue Halliwell, Operations Manager for trade association Composites UK, took on the challenge to find funding to undertake a fuller review of the recycling situation.

Funding was obtained from WRAP (Waste & Resources Action Programme) for a Resource Efficiency Action Plan (REAP) to bring together interested parties and publish a REAP document for the composites industry. This is due to be published imminently and will highlight actions in four areas:

  • help develop commercially viable markets for GRP recyclate;
     
  • support the commercialisation of new processes for GRP and CFRP recycling;
     
  • provide consistency in the categorisation of composite wastes; and
     
  • disseminate case studies, information on best-practice and emerging technologies to the sector, particularly SMEs.

Composites UK, Materials KTN and the industry partners involved will undertake to see that those actions are carried through and the document is updated as appropriate.

So where from here?

If we look back at the history of GRP recycling it could be seen to be a list of good intentions which came to nought, or very little. Perhaps much of the activity was before its time. Erik Grove-Nielsen of Refiber, who now investigates new materials for wind turbine blade production, made a pertinent comment a few years ago: “To get into recycling fibres again, the market would have to be more secure. There has to be a ‘cry’ for the service.”

Perhaps that is exactly what is changing. As one who is in contact with people across the composites industry, there are still people who accept landfill as a solution for their waste, but more and more I find that companies are asking questions and seeking answers, even appointing people with responsibility to see that their is waste dealt with responsibly. They want their waste to be recycled, both from an economic perspective (landfill prices rising) and from an environmental perspective. It matters. Their clients think it matters, and sometimes require it in contracts.

It seems that the most economically sustainable recycling routes will involve processes and applications where the value of the recyclate is maximised. With mechanical grinding this means extracting and using the longer fibres. I watch with interest the work at University of Strathclyde to see if they can economically recycle fibres to compete with virgin.

The European End of Life Vehicles (ELV) Directive is a strong motivator for recycling and including recycled material in car parts, which is still increasing as we approach the 2015 deadline to increase recyclability to 85%. Likewise the potential for recycled timber replacement railway sleepers is an opportunity for the coarser fractions of GRP regrind. Increasing use of BREEAM (Building Research Establishment Environmental Assessment Method) is a strong driver for improving recycling and recycled content in the construction industry. Landfill bans in some countries and increased landfill taxes in others provide further momentum to recycle.

The principle of producer responsibility that the ELV enshrines extends to other industries, and in this 'green' revolution in which we find ourselves, public perception has changed dramatically in recent years and continues to change. For our children, recycling has always been part of their experience.

It is this change in perception, whether driven by economics, markets, legislation or altruism, that gives me hope that the current activities in GRP recycling will achieve more success than their predecessors in creating an economically sustainable GRP recycling supply chain. I look forward to seeing the effect this has on the market for GRP products, and the further environmental benefits that will be gained from using GRP more widely. ♦


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