Material's life cycle does not end when it is no longer used: its disposal can be a more complicated issue than its production, bringing up questions of ecological impact.
In this research, we studied methods of plastic recycling and the production of new items from the reclaimed matter.
Technically, almost every plastic can be recycled: however, it is not always economically and environmentally sound. The quality of the material decreases and the amount of energy required for transportation, preparation, and treatment of plastic can be too high.
There are types of plastic that are recycled fairly easily: for instance, colorless bottle plastic (PET) is shredded into granules that are then melted to produce new items. For many other kinds, the recycling process is more challenging.
Problems appear when the material is contaminated, either with additives or with the product that it held before. In this case, the material needs to be heated, losing its aesthetic qualities or consuming too much energy.
This inability to recover the material to its initial state pushes manufacturers to invent other methods of reusing plastics.
Making them parts of composites or using downgraded materials, companies and researchers look for solutions that draw attention to waste and help to reduce landfills and the cost of production of new items.
In the mechanical approach, plastics are first shredded into small granules. Ground, plastics form transparent or colored particles that can be used for the production of the same packaging or for all sorts of objects made of reclaimed materials, like clothing, bags, or furniture.
Matter can also be treated this way when it is to be used as a foundation for composite materials, like tires forming crumbles used for covering asphalt on playgrounds and athletic fields.
Whenever it is possible, plastic is then melted. It can be mixed with virgin material to increase its durability lost during heating or used unadulterated. In the latter case, the plastic might be utilized where it needs to be less rigid: clothing might be made of reclaimed PET instead of bottles.
Another way to treat the material is chemical. More energy-efficient, this type of technology is still developing, but there are already some kinds of materials that are recycled this way.
Influenced by solvent or enzymes that destroy chemical connections, plastic is turned into a liquid feedstock and then extracted from it.
With heat and pressure, reclaimed plastic is turned into new items. One way to do it is to create a composite material that includes recycled plastic together with other components, often serving as a binder.
Shredded plastic can be drenched with rubber or another plastic to reduce the amount of virgin material used in the production. There are sneakers and household items already made with this approach, yet it still stays experimental and limited in its reach.
Plastic can be used independently as well. In our project, we imagined several ways of how reclaimed material can form structures and patterns for something novel. The first of them is similar to the technique described previously, but the plastic granules are the main ingredient here, used with little additives.
Pressed, glued, or melted together, they form a material that can be more or less uniform, depending on how many colors and types of plastic were mixed. In the finished product, the granular structure can be either accentuated for the purpose of decoration, like in furniture, or be less obvious and more functional.
A method utilized in PET recycling is based on pulling threads out of liquified plastic. Fibers that result from this process have properties similar to polyester and are used to produce a variety of textile products, from weightless shopping bags to thicker rugs and shoes.
Reclaimed material can also be turned into sheets for vacuum forming. This method of production is widely spread, as it is cheap and time-saving, however, recycled plastic is not yet used on an industrial scale and is mostly a part of home laboratories of enthusiasts who experiment with their own vacuum machines.
Another technique that we imagined to be applied to recycled materials is SLS printing. It uses directed laser beams to melt plastic granules precisely where it is needed to form intricate shapes and structures.
The technology itself is still finding its way into industrial-scale production, so there are no examples of consumer goods being made from recycled material with SLS, however, there are efforts to create sustainable material for this method.
Probably, with the rise of SLS popularity, there will be more new materials, as it was with 3D printers, for which filaments from recycled plastic are already available.
Igor Sordokhonov, Maxim Zhestkov
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