Part 1 of this article reviewed the issues involved in recycling GRP and discussed the use of mechanical grinding. In Part 2 we consider thermal and chemical processes, and future developments.
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."
| ... If successful, this could create a new market for recycled glass fibres to be sold in direct competition with virgin chopped glass fibres. |
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.”
| ... 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. |
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. ♦
Further information
Stella Job is a Knowledge Exchange Expert for the Materials Knowledge Transfer Network (KTN). The Materials KTN is funded by UK Government’s Technology Strategy Board to support innovation and research in materials science. Contact stella.job@materialsktn.net. To keep in touch with Materials KTN activities in this area, join the Composite End of Life subgroup on _connect.
This article was published in the September/October 2013 issue of Reinforced Plastics magazine.
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