The recycling of textile floor coverings is on the agenda for almost 10 years not only for the industry but also for the regulative authorities. Already in 1993 the carpet industry represented by GUT and its members agreed in the so called "Vaals Declaration" that the development of concepts for economical and ecological viable disposal and recycling systems for textile floor coverings would be an important task for the industry.
At that time it was already stated that landfill of carpet waste under ecological criteria is one of the worst solutions. If landfill is not an option for the future methods and strategies for the recycling of post consumer carpet waste as well as production waste has to be developed. After the "Vaals Declaration" had been published within the carpet industry and the suppliers industry a discussion started to find out, whether an intelligent combination of materials could support recycling processes. Besides the discussion on heavy metals and other materials, filler-free (chalk) and 100 % polyamide carpets were suggested. But taking into account the interests of the different industry groups like fibre and dyestuff producers it could clearly be estimated that proposals like a "Filler Free 100% Polyamide Carpet" would directly lead to conflicts. Nothing the despite such suggestions were seriously discussed for some time.
Therefore GUT decided to co-ordinate its activities with the European organisations of the suppliers industry like EATP, CIRFS, EPDLA and ETAD. Besides the problem of choosing the right materials for "recyclable carpets" questions of logistics and transportation had to be solved. When looking at the European carpet market one has to realise that different types of carpet are produced and sold in different markets. In the end a specific type of carpet produced somewhere in Belgium, after its lifetime, will be found in household waste either in Southern Germany or in Middle England in pieces may be not larger than a few square meters. This means that the big challenge we have to face is fighting against a thermodynamic principle, which can be expressed in three simple words: "Entropy Always Wins!"
Realising this, the collection, identification and separation of carpet waste into well-defined raw materials becomes the crucial part in the whole discussion on carpet recycling. This situation at that time was one of the basic arguments of those who preferred a direct incineration of carpet waste in municipal waste incineration plants, whereas others stated that carpets could lead to higher and harmful emissions from these incineration plants and therefore other ways than incineration had to be found.
After the "Vaals Declaration" was published, there were still more questions than answers. Nevertheless this was the initiation of a number of national and international research projects dealing with carpet recycling in the one or the other way. The results and the consequences of these research projects on actual and future carpet recycling strategies are summarised in the following paragraphs.
Incineration of Carpet Waste
In the early 90's waste incineration, mainly for political reasons, was not regarded as an ecological or environmental friendly alternative to landfill. Even incineration under energy recovery aspects, for a long time, was not accepted by the regulative bodies. There was no information available on the environmental influence of carpets burned in municipal waste incineration plants. What is the fate of heavy metals from dyes? Does polyamide lead to higher NO-emissions? Are dioxins formed and emitted? Do ashes contain harmful substances? These were questions without answers, and only industry statements were available, not accepted by the authorities or by NGO like Greenpeace. Therefore GUT decided to investigate the environmental fate of incinerated carpets.
The report comes to the statement that the co-combustion of carpet waste in modern municipal waste incineration plants does not lead to any negative influences to the environment.
Besides the co-combustion of carpet waste it was also investigated whether shredded and palletized carpets could be used as the solely fuel in fluidised bed reactors for energy recovery. At the University in Aachen TFI investigated the behavior of carpets compared with other solid fuels like coal or brown coal. The results showed that the calorific value of carpet waste depends strongly on its composition. Whereas carpets made of natural fibres like wool have low calorific values of about 19 MJ/kg and Polyamide carpets already have 26 MJ/kg, Polypropylene carpets have a calorific value of 42MJ/kg. At that time (1995) most carpets had a foam backing and the calorific value of the carpet waste is strongly influenced by the amount of inorganic filler present, sometimes more than 55 mass% of the total carpet. But during the tests it could be shown that the filler also has a positive aspect.
The RECAM Project
Besides these research projects with the aim to show that the incineration of carpets either in municipal incineration plants or in special designed reactors for the energy recovery does not lead to environmental problems, the RECAM project was started in 1996 to figure out whether a complete recycling system for all materials in carpets could be an environmentally friendly and economically acceptable alternative to energy recovery. Looking to its overall composition, carpet waste contains a lot of valuable raw materials, such as polymers (PA6, PA66, PET, PP), natural fibres (wool), and inorganic fillers (CaC03). The challenge was to develop a system that not only gives a technical possibility to reuse these materials (either as a material, a chemical feedstock, or as energy), but which also is better for the environment and less depletion of non-renewable natural resources), and economically acceptable. The latter means that the costs of the system may be higher than present day land filling costs, but can be competitive on the longer term with the costs of MWI's.
Furthermore it was shown that wool carpet waste could be recovered for use in so-called nonwovens. The resulting mats (with a high or low density) can be used for insulating purposes and carpet underlay. Nylon 6, nylon 66 and polypropylene can be recycled mechanically to engineering plastics. Because of the different carpet colours involved, the recycled material can only be used in dark-colored engineering plastic applications. For these applications, the shredding and grinding necessary in order to separate the fibres from the carpet backing is very expensive.
Certain kinds of carpet wastes are unsuitable for mechanical or chemical recycling. Face fibre materials other than PA6, PA66, PET, PP, and wool are not recognised by the NIR identification tools. Sorting carpet waste into 6 differentiated piles (5 mono streams and one 'unknown' pile) is already complicated (manual as well as automated sorting). Not only less-common face fibre types (e.g. cotton, acrylics) end up in the 'unknown' category. Also blends (wool/PP, PA6/PA66, etc. in various ratios) are found in the market. It is impracticable to develop recovery technology for these streams. The amounts available for each type are too small, and the effort to accomplish a separation into reusable (mono) materials is simply not worth. Another material stream that is unsuitable for further chemical or mechanical recycling is the SBR/chalk fraction that comes from the process that separates face fibre and backing. This is necessary to obtain e.g. a pure PA 6 material for mechanical recycling purposes. Although in theory it could be reused as filler in carpet backing, this is technically & economically not feasible. But
the incineration studies showed that all these waste streams can in principle is used as secondary fuels in cement kilns and incinerators.
An LCA-study showed that there is a large environmental benefit when the complete RECAM system can be implemented. The environmental load of RECAM is for each of the investigated parameters in the LCA (abiotic depletion, green house potential, human toxicity, Eco-toxicity (aquatic), acidification, nitrification, photochemical oxidation, and land use) at least about 50% better than environmental load of the existing situation (70% landfill, 30% MWI's). Although the technical results of the RECAM project were very positive none of the partners could give any answer on economic question. Only by experience it could be estimated whether some technical feasible recycling routes were unacceptable under economic aspects. The back to feedstock process for polypropylene fibres for instance is so expensive that the overall benefit is doubtful. Wool fibres from recycled carpets as base material for insulating mats is technical also feasible, but is there a market for woolen insulating mats. The same questions have to be asked for Polyester and PA66 recovered from old carpets. Is there a market and what will the price?
Nevertheless for one of the carpet fibre materials this question was answered positive. PA6 carpet fibres were regarded as being a technical, ecological and economical interesting source for back to feed stock recycling activities. This was the reason why DSM and Allied decided to start up their "Evergreen Nylon 6 Recycling Program" in Augusta (USA), and the Polyamid 2000 plant was build in Premnitz, Germany near Berlin. Both plants use carpet waste as their raw material input. Whereas Evergreen only accepts PA6 carpets as input stream, PA2000 accepts all types of carpet waste, separates the PA6 and Pa66 fibres and recycles them in the way describe in the RECAM project. The main difference in the two processes is the depolymerisation techniques used for the PA6 recycling and depending on this the design of the whole plant. In the end both concepts can be compared with gold digging, but not gold, PA6 is what they are looking for. This means techniques for the identification and separation and concentration of PA6 carpets from other carpet materials is the crucial step. This is the reason why the European decided to set up the first automated carpet sorting plant near Mainz, Germany. In a three years period it was the task of this plant to deliver all data, necessary for the economic, technical and ecological evaluation. It could be shown that with very good results PA6 carpet could be separated from PA66 and other carpets. This was done in close cooperation with DSM and PA2000. The data obtained show that sorting of carpets can be done under economical aspects. But either the gate fee for the carpet waste has to be high enough or a price for the PA6 carpet waste has to be paid by those, who need the PA6 fibres as raw materials for their processes. The actual development especially on the German waste market show that gate fees are permanently decreasing, as long as landfill is a legal alternative to recycling. Therefore units like the automated carpet sorting plant in Mainz, cannot operate economically, the same is true for the Evergreen Nylon Recycling (ENR) plant. It has been temporarily suspended.
This article was originally published in the November issue of the New Cloth Market: the Complete Textile Magazine from Textile Technologists