Circular Economy
18/03/2022 | Sesotec
To move from a linear to a circular economy for plastics, all plastics must remain part of the cycle. However, in terms of recyclability, there are major differences among the various types of plastics. In this article, you can read about the recycling of polystyrene (PS) and acrylonitrile butadiene styrene (ABS) and what makes these two types of plastic different.
What is Polystyrene(PS)?
Polystyrene, or PS for short, is one of the standard plasticsand is used - either as a thermoplastic material or as foam (EPS) - in manyareas of everyday life. Above all, disposable articles made of polystyrene havebecome established in the scientific field as well as in many economic andhousehold sectors.
In its solid state, polystyrene is crystal clear, hard,impact-sensitive and electrically insulating. However, it can be colored andprinted without any problems. Its physiological harmlessness has also made theplastic attractive to the food sector as visible packaging. Other common applicationsinclude disposable drinking cups, lids with spouts for coffee cups ordisposable cutlery while yogurt cups or packaging for honey or coffee cream arealso produced from polystyrene. Polystyrene is also frequently used in industrysettings, for example for component covers, coil formers or switch knobs.
As expanded polystyrene orESP, also known as Styrofoam, polystyrene is used for the production oftake-away packaging or trays and containers for fish, meat, fruit andvegetables. Polystyrene is very cost-effective compared to other plastics. Italso has high permeability to gases and water vapor and is odorless andtasteless, which makes it ideal for food storage.
What isAcrylonitrile Butadiene Styrene (ABS)?
Acrylonitrile butadiene styrene (ABS) is the most important engineeringthermoplastic in terms of volume. It is a polymer consisting of three monomers- acrylonitrile, butadiene and styrene, whose shape can be changed as often asdesired at certain temperatures, and which is moisture- and dirt-repellent andlargely resistant to grease and oil, electrostatic charge and temperaturefluctuations. ABS is stiff, impact- and scratch-resistant and can also beeasily bonded, welded and machined. The plastic is also well suited for coatingwith polymers or metals. The main applications for ABS plastics are 40% for householdappliances and 26% for electrical and electronic (E&E) applications. ABShas also been used in the toy industry for decades: For example, well-knownbuilding blocks are molded from acrylonitrile-butadiene-styrene. In theautomotive industry, ABS is used, for example, for body parts, trim, spoilers,headlamp lights as well as various interior parts. Last but not least, 3Dprinting technology has made ABS plastic known worldwide, as the substance isone of the most widely used materials in the 3D printing process.
Recycling potential for PS and ABS
Recycling ofPS
Since the properties ofpolystyrene change only slightly even after repeated processing, it can be recycled very well.
The polystyrene used for packaging in the retail sector is collected bythe dual systems throughout Germany. In the sorting plants, hard PS can beeasily separated using near-infrared technology. Used EPS packaging containersare also well suited for mechanical recycling. They are collected separatelyand delivered to the recycling sites as a separate fraction.
Pure polystyrene ismechanically shredded and processed into high-quality recyclate, which in turnis used for the production of various everyday items such as folding boxes,furniture or clothes hangers. Alternatively, the used plastic packaging can beremelted into new products using an injection molding process.
Recycling ABS
ABS is basically very easy to recycle mechanically. The advantage of thisplastic is that, as is the case with PS, as arecyclate it retains the same properties as before the recycling process. Here,however, recyclers often face a major challenge. In the case of householdappliances or electrical scrap, after the metal fractions have been separatedin the sorting plants, what remains is a plastic mixture that not only consistsof a wide variety of plastic types, but is also contaminated by dust, wood,pieces of glass, residual metals and other impurities. The task is then toproduce clean and recyclable plastic fractions from this complex mixture. Coloralso plays a major role in the recycling process. Electronic scrap, forexample, has a particularly high proportion of black plastics, which in turnare not detected by the near-infrared technology used in sorting plants.
As a result, a largeproportion of valuable ABS ends up as waste because of the black coloring. Asolution is offered by so-called electrostatic separation technology, which canalso separate completely black material mixtures and even achieve purities ofup to 99% for ABS fractions. However, this is only possible if the electronicscrap is pre-concentrated, sorting out plastics that contain flame retardants,for example. This pre-concentration of plastics from complex material mixturesrequires a combination of dry and wet processing techniques.
Conclusion
Both PS and ABSare, in theory, readily recyclable and can be returned to the plastics cycle.While PS is already being recycled successfully to a large extent and is usedin the manufacture of new products, too much valuable ABS still ends up in thetrash. The reason for this is that ABS is mainly used for household andelectrical appliances, which are complex mixtures of materials, and recyclingcompanies often lack the right sorting technologies to sort these complex mixtures and producehigh-quality recyclate, which in turn can be used to create new products.
New E-Book: The Circular Economy - Challengesand opportunities for Recyclers and plastics processors
In this comprehensive e-book, you will gain insight into the most important factors of the Circular Economy. In particular, we look at the goal of creating a circular economy that must be profitable not only for people and the environment but also for recyclers, plastics manufacturers and processors.
