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Plastics & Elastomers
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Quality Needs Demand Enhanced Plastics Recycling Processes

Luis Roca – May 14, 2020

TAGS:  Green and Bioplastics    

Plastic RecyclingIt was estimated that the plastic consumption worldwide was 322 million tons in 2015, out of which 58 million tons were consumed in Europe that generated 25 million tons of wastes. These wastes were treated in different ways:

  • Incineration for energy recovery (39%)
  • Landfilling (31%), and
  • Recycling (30%)

These figures can be similar in other advanced economies on the planet, which gives the perspective of the scope of improvement possessed by recycling.

Recycling has been traditionally an important sector in the plastics industry due to economic and competitive issues. But, in the last few years factors such as environmental policies, circular economy and legislations are majorly driving the changes besides competitive aspects.

The European Union hopes to boost the recycling of plastics in a significant way by 2030 (400% higher than in 2015). Overall, the key challenges about recycling converge in one concept i.e. Quality. Today, technologies, policies, standards, and R&D are focused on quality improvement, thus, driving the market uptake of recycled plastics.

Explore, in detail, how different technologies that are found along the recycling value chain can be improved in order to maximize the amount of recycled plastics available for a new life.

Let’s begin with the material sorting…



Plastic Material Sorting


Most of the time, when recycling, there is a combination of different plastics that generally act as a contaminant to the one that needs to be recycled. The main cause is that its presence affects the final performance of the plastic to recycle in an important manner.

So, obtaining a pure and highly efficient separation of the material to be recovered is key to the success of subsequent steps in the value chain. It is crucial to evaluate waste or plastic products in the two phases regarding the separation of components.

On one hand, by having NIR separation equipment, it is possible to assess whether the material would be capable of being separated in a waste sorting facility, and therefore, reach the final recycler for the recovery process.

Semi-industrial NIR Optical Sortener
Semi-industrial NIR Optical Sortener


On the other hand, other possibilities can be approached focusing on separation in the recycling company sector by following a protocol given below.

  • Mills prepared from crushing various typologies of materials using mesh sizes from 1 mm to 25 mm in order to simulate the different particle sizes that are found normally.
  • Wet separation of components in the module line, enabled for washing, spinning and cyclone system for wet or dry cleaning and separation.
  • Separation of heavier materials from lighter ones using an elutriation system, where saving water can be a significant benefit. ZIG-ZAG equipment is suitable for separation sizes between 0.1 mm and 10 mm.
  • Separation of different polymers, as well as ferric and non-ferrous materials through the electrostatic and triboelectric separator, where the product is separated into the components, depending on electroconductivity in the combined field of corona discharge with the electrostatic field.

It is good to know that depending on the form, type of plastic material, bulk density and composition, there are different technologies for better plastic sorting. Some examples of less conventional wastes that can be sorted by less conventional technologies could be:

  • Foams
  • Cables
  • Injected plastic parts
  • Textiles, and
  • Cords/ropes

After these steps, the recovered materials can be subjected to different processability technologies to obtain final applications, and test specimens to analyze their final properties and processability, all this information will give valuable information about the goodness of the sorting process.


Performance Improvement: Upcycling


Traditionally, recycling has been performed in single screw extruders because the only objective was to obtain pellets. Nowadays, quality needs are demanding more improvements in this process, and thus, co-rotating twin-screw extruders are more often employed, especially when improvements on properties are required.

In each transformation phase, plastic materials undergo different decomposition and oxidation processes which diminish their mechanical properties and appearance of recycled plastic obtained, and the mechanical recycling process is no exception here. Hence, products made from recycled materials tend to have lower performance. However, this can be prevented using suitable additive systems for recycled plastics, making them suitable for use in high-performance products. This improvement is called Upcycling.

Upcycling of recycled PA with chain extenders via Co-TSE
Upcycling of Recycled PA with Chain Extenders via Co-TSE


Upcycling and Role of Additives


Upcycling could be dependent on the type of properties that recyclers want to adjust or recover during recycling. Specific additives are used in polymers to achieve desired properties added to obtain required property, such as:

  • Antioxidants and thermal stabilizers protect polymers from thermal oxidation
  • UV filters prevent photo-oxidation
  • Polymer compatibilizers for different polymers in the system that are not separable
  • Rheology modifiers adjust viscosities to new processing methods
  • Chain extenders recover molecular weight and viscosity in polyesters and polyamides
  • Impact modifiers, fillers or fibers improve when mechanical properties, when required


Polymer Devolatilization


Another key point after recycling is how clean are plastics (after bath). Post-consumer plastics normally are contaminated with food, solvents, or another type of wastes that affect the normal process of recycling. To remove these contaminations, cleaning baths are used. But in some cases, substances migrate within the polymer matrix, and a deeper process of decontamination is needed.

Volatiles can generate problems of odors, undesired migrations, processing problems or aesthetic defects in final parts. Therefore, it is mandatory to remove or minimize them.

Devolatilization system based on SC-CO2
Devolatilization System Based on SC-CO2


The process of removal of volatile substances from solid polymer is known as devolatilization. It is based on the melting in the single or twin-screw extruder of the recycled plastic with vacuum-forced devolatilization, with the help of different stripping agents that will aid to remove the undesired contaminants.

The selection of the right processing conditions in terms of pressure and selecting the appropriated stripping agent (boiling point and polarity) are crucial to remove the identified volatiles. The stripping agents can be low boiling point solvents or supercritical gasses like CO2.

Devolatilization can then increase the use of recycled plastic materials in high added-value applications, such as automotive or electronics, where the uptake of recycled plastics still has limitations due to high technical and quality specifications.


Recyclability Standards


Another challenge which is not related to technology is how to accredit that final products are made of recycled materials, or if plastic items are recyclable.

The circular economy strategy for plastics highlights the key role that standardization must play an important role to raise industry confidence in the quality of recycled plastics. The general perception is that companies increasingly demand more support on:

  • How recyclable are their products? or
  • How to demonstrate that they introduce recycled plastic materials in their products?

This point is very important since more recycled plastic will be reintroduced in the value chain. The other aspects that could be the most important include:

  • Cost savings
  • Marketing, and
  • Sustainable company policies


Standardized International Certification and Ecolabeling Schemes


Today, there are some standardized international certification and ecolabeling schemes focused on recycled plastics that can generate trust across the value chain.

The Blue Angel The Blue Angel is a German ecolabel that sets high standards for environmentally friendly product design and has proven itself as a reliable communication tool for more sustainable consumption.

The Blue Angel ecolabel can be awarded to finished products made from recycled plastics (at least 80% post-consumer recycled content).


EUCertPlast EuCertPlast is a certification for recyclers that allow them to ensure their customers that they recycle post-consumer plastics according to best practices. This certification scheme relies on European standards (EN 15342-15348) and focuses on the traceability of plastic materials and on the quality of the recycled plastics.


RecyClass The RecyClass Protocol for PE Films establishes a procedure to be followed at the pilot level to assess whether the development of new material is compatible with the recycling of post-consumer PE film.

This protocol makes possible to validate the compatibility of a specific technology with a specific recycling flow and is divided into three main phases:

  • Pre-treatment
  • Pellet production, and
  • Blown film extrusion


Conclusion


All the measures and initiatives taken in order to boost the market uptake of recycled plastics can be summarized in one concept – Quality. Recyclers, we will be able to gain new markets only by improving the final quality of the recycled plastics.

Recycling Plastic Professionals – Stay Updated!


Sustainability and the handling of plastic waste is a critical topic globally. Understand how you can improve the quality of recycled PET consistently and reliably to meet the increased demand in volume. Take the Course "PET Mechanical & Chemical Recycling: Solutions and Value Addition" by Kenneth W Russell today!

PET Recycling

Contributed by: Luis Roca and AIMPLAS mechanical recycling group
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