The everyday use of garments, workwear, towels or bed sheets leads to the end of the lifecycle of the materials even if their maintenance is carried out correctly if not perfectly. Still, the decline of the material cannot be avoided. What happens to the materials whose lifecycle ended?
The concept of recycling is acquiring more and more importance. With time, it has become one of the primary points in every new technological and scientific development. One of the main obstacles translates to dealing with secondary raw materials comparable to virgin materials on the performance level which decreases, in the recycled products, often due to contamination, treatments and additives.
Over the last years, the interest in material recycling has increased. It refers to the majority of the industrial sectors including textile sector. It has led to the increase in the re-use and recycling of textiles due to the development of new processes of textiles recycling in particular. The problems tackled in the recycling phase are constituted by the difficulties in removing the finishing chemical agents such as the “flame retardant” and water repellency. Let us take cotton recycling as an example. The presence of finishing processes for easy maintenance of the fabric reduces the solubility in the solvent used in the Lyocell method; as a result, before the process, cotton is washed with acid and alkali solutions to remove the chemical substances. Another problem is the type of a chemical link between the colorants and the fiber that affects the recovery and the recycling of the material. Nevertheless, it was possible to demonstrate the removal of various colorant classes through the use of ozone to degrade the dye molecules or through the use of supercritical fluids. Other factors that strongly influence textile recycling are low prices, the volume and availability of virgin materials; these factors have limited the capacity to integrate the recycling processes as consolidated and profitable operations of textile recycle from the economical point of view. The available options for textile recycling are limited. As a matter of fact, the majority of current recovery systems for the post-consumption waste mainly include the mechanical “down-cycling” processes. What is more, current technology can lead to 75% loss of the material value after the first recycling process. Still, it has been forecast that the development in the technological field, promoted by the research for eco-sustainability will contribute to the increase in feasible options leading to the decrease in costs, impact and the reduction of the loss of the material value. Actually, still today, there are many different textile productive sites all over the world that are developing or have developed the productive processes of recycled textiles and waste recovery on all the levels of textile production chain.
Types of recycling
There are four types of approach as far as textile recovery goes: re-use, mechanical process, chemical process, energy recovery. Re-use consists of the material recycling in its original form for the equal value of the material recycled.
Mechanical processes take advantage of the material modification through specific operations that physically stimulate the material which changes the chemical-physical properties of the treated material.
Chemical processes use chemical agents for pyrolysis, hydrolysis, separation and depolymerization to separate the elements that the material is constituted of until the initial material is obtained.
Energy recovery is carried out by converting the material into energy through the use of incinerators.
Among the above processes, the most applied ones in the textile recovery sector are the mechanical and chemical methods.
The processes lead to obtaining different final products due to the removal or non-removal of some incompatible or dangerous substances present in the waste to be recycled.
During the mechanical recycling phase, chemical substances added and present in the material will remain in the final products due to the low effect of the process at the molecular level; in case dangerous chemical substances are present, this will lead to the potential health and environmental problems during the production phase and the use of the recycled product. The mechanical process comprises techniques that take advantage of physical characteristics of fibers the textile is made of. Synthetic fibers are harder than natural fibers which will result in the use of different machines for the same type of a process. First, the textile is cut, then it is shred with the use of a carder or a garnett, for natural and synthetic fibers respectively. In the process, the textile material is open and brought back into the fiber state through mechanical stress applied by toothed rolls. The fibers obtained this way are spun and wound again with the possibility of adding the virgin material. Apart from grinding, synthetic fibers can be recycled by extrusion. Synthetic fiber is first grinded and granulated, then it undergoes the extrusion through the melting of polymer chips.
In case of chemical recycling, a great portion of the material elements is eliminated by the processes of leaching, degradation, distillation and separation; this results in fewer risks of the dangerous substances transfer to the recycled product. They however, need to be treated and/or removed from the means with which they have been separated. From this point of view, the post-industrial products turn out to be less problematic as long as the producers provide the necessary information on the composition and the chemical substances present. On the contrary, the post-consumption waste is not subjected to controls which leads to the lack of information on the presence of the contaminants that could invalidate the recovery and recycling processes as well as the best type of the recycling process to be used. Chemical process modifies the textile material through the use of chemical agents that can dissolve it or modify its chemical structure partially or completely. In the chemical process, fabrics are first dissolved in solvents, then they can be reprecipitated or, as in the majority of cases, wet spun. Also, in this case, synthetic fibers can be processed in an alternative way. As a matter of fact, the polymers the fabric is made of can be depolymerized until the initial monomers are obtained that can still be further polymerized to obtain the material that presents the same chemical-physical properties as the virgin material.
Mixed fabrics, problems and emerging solutions
The illustrated processes appear simple and highly performing in case of monomaterial fabrics. Yet, the majority of garments are multimaterial therefore, the recycling of such fabrics turns out to be quite problematic as it is necessary to separate the fibers. To solve the problem, the developed processes for the recycling of mixed textiles take advantage of the existing chemical-physical differences of the constituent fibers. The mechanical separation process consists of selective degradation by undermining the less resistant fiber through thermal processes. The products of degradation are then removed by the use of a solvent. This process has been developed in few cases, mainly to separate nylon from elastane by undermining elastane that leads to the consequent loss of the material.
Chemical products instead, are more frequently used in the separation of fibers constituted by different materials. As a matter of fact, through these processes, it is possible to solve, degrade or depolymerize, in case of synthetic materials, the purposely selected fiber which will lead to obtaining a mix containing separate textile constituents.
The problems translate to the development of future, better performing, new technologies with less impact in order to reduce the waste and the environmental impact. In this context, some companies are turning to the concept of monomaterial that can be disassembled and assembled again through mechanical processes thus, avoiding the use of chemical compounds. The concepts developed through the use of this new, end of a lifecycle ideology can be withdrawn from the producers directly, washed, grinded, then melted and destined to produce the components of a new product. This “closed cycle” ideology implies some interesting insight on one of the methods on the implementation and the circular economy increase, more and more present in textile sector today. As a matter of fact, it is technically easier and more sustainable economically to recycle materials that even if complex, are constituted by a single material, and that the post-consumption recovery and recycling are possible as long as the consumers are thoroughly informed on how to manage the end of a lifecycle materials.
Dott. Daniele Piga, Ph.D.
Area Ricerca e Innovazione Multisettoriale/Multi-Sector Research and Innovation Area
Centro Tessile Cotoniero e Abbigliamento Spa
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