The Packaging Series: Recycled PET resin explained
October 13, 2021

What is rPET plastic? 

Not all plastics are recyclable, but polyethylene terephthalate (PET) is. With that in mind you’ve probably guessed what rPET stands for – recycled PET. You may also hear of rPET resin; a resin is a mix of organic compounds that are either solid or (usually) highly viscous and are eventually cured into solids. PET is a non-toxic synthetic resin and a type of polyester used to produce food packaging and clothing. 

Did you know that PET is the 4th most common resin in the world and its most recycled plastic? 

PET flakes 

PET is recycled using mechanical or chemical means but it also starts at a material recovery centre where the plastic is cleaned and sorted by colour and size, thankfully made more efficient by near-infrared light which detects the properties of different plastics [CITE]. Mechanical, or physical recycling, can be grinding, crushing, re-granulating and compounding PET into PET flakes. In the final step, contaminants in tiny flakes are filtered out with a liquid. Mechanical recycling is the dominant method in Europe but drops in RPET feedstock can reduce its viability. 

Melting plastic into sheets 

Polyethylene terephthalate is in a class of plastic polymers known as ‘thermoplastics’ which means that you can change the structure of the plastic at a specific temperature known as the ‘melting point’. For PET the magic number is 225C, meaning the plastic becomes pliable once it reaches that point. After sufficient melting, PET can be thermoformed into sheets. 

Bubbles forming on melted plastic.

Plastic bottle recycling  

  • Depolymerisation: 
    Plastics are polymers – a natural or synthetic material composed of smaller units of molecules, called monomers, in a repeating chain. This means that PET plastic must be separated into monomers before being reconstituted into the recycled plastic that you know. Depolymerisation could be considered an umbrella term for the other methods we will discuss.  
  • Pyrolysis: this is essentially using heat (temperatures much higher than 225C, ranging from 500C to even 900C) to change the chemical composition of PET, specifically to transform it into a liquid oil. When you think of changing an objects’ composition with heat your mind tends to go to combustion but that is where pyrolysis is different – it decomposes PET in the absence of oxygen. Since objects only burn when oxygen is supplied, there is no combustion in pyrolysis. It is because pyrolysis is endothermic (a chemical reaction that takes in heat instead of expelling it) that makes pyrolysis is an attractive option: it the most environmentally friendly method for recycling PET because it produces low volumes of combustion gases,2 and the oil produced could provide valuable energy for transportation.3  This means pyrolysis can fall into the ‘energy recovery’ category not just recycling.  
     
  • Solvent based: You may also hear it called ‘solvolysis’, except this is also an overarching term for glycolysis, hydrolysis, alcoholysis, aminolysis (no, you were not tricked into reading an alien tongue-twister) and more. ‘Lysis’ means ‘to break down’ so solvolysis is the process of breaking down a substance using a solvent; for alcoholysis the solvent is alcohol. Solvolysis is less used than mechanical recycling because the solvents needed are costly and contamination issues sometimes arise.  

RPET fabric 

If you own a T-shirt, tote bag or any other clothing made from former plastic bottles, you mostly likely have a piece of what is now considered the future of sustainable textiles. Producing recycled PET is half as carbon intensive as producing organic cotton. RPET fabric is the result of melting PET bottles and spinning it into polyester fibre or ‘yarn’.  

Where is PET recycled? 

Only 9% of the world’s virgin plastics are recycled, and the reason for that may seem absurd – finding efficient ways of collecting viable plastics for recycling is hard [Czapp]. Before plastics can be made into rPET flakes and pellets they need to be collected and transported to the facilities that transform them. And that’s where the first challenge in making recycled PET available presents itself: how to gather all the plastic. 

The COVID-19 pandemic has slowed down collection. Growth in US recycling rates have plateaued over the last five-to-six-year period, dipping to just 27.9% in 2019. Back in 2018, Europe collected twice the number of post-consumer plastic than it did in the previous year – but just under a third of it was recycled.4 PET is the most consumed plastic in Europe and in the food ingredients and agricultural sectors overall because it works well as a fibre, film and containers.  

The US Environmental Agency reported that from 1990 – 2015, plastic was the least recycled material in the US (the most recycled was paper). This outcome is largely due to chemical plastic recycling methods like depolymerisation, pyrolysis and solvolysis not being scaled up for large operations.5 With more pressure to act on the impacts of plastics and single waste plastic being banned in more nations, chemists and engineers in this field will need to work with plastics producers to make large recycling operations ubiquitous. 

Recycled PET and pollution and the circular economy 

Reusing materials is one of the core practices of a circular economy, that is an economy designed to tackle international issues, namely global warming. As more international organisations are challenged to reduce their carbon emissions, more investors are making a stake in recycled PET. In mid-2021, several major virgin plastic producers invested in RPET production facilities in the US and Australia. The European Union’s bid to reduce 55% of plastic waste by 2030 means recycling operations need to improve substantially. Still the unequal distribution of the technology for recycling across EU nations, compounded with struggles to provide high quality, cost efficient, non-contaminated recycled plastics is an ongoing challenge for the industry, but one that is being tackled by more stakeholders nonetheless.6  

For more information about the rPET market you can sign up to Czapp for free, where we share the latest analyst insights, information and data. Check out the latest article on RPET Trends October 2021.

SOURCES

  1. The Association of Plastic Recyclers, 2018, Evaluation of the Near Infrared (NIR) Sorting Potential of a Whole Plastic Article. 
  1. Osman et al, 2020, Pyrolysis kinetic modelling of abundant plastic waste (PET) and in-situ emission monitoring. 
  1. Miandad et al, 2019, Catalytic Pyrolysis of Plastic Waste: Moving Toward Pyrolysis Based Biorefineries. 
  1. Schyns Z. and Shaver M., 2020, Mechanical Recycling of Packaging Plastics: A Review. 
  1. Tullo, 2019, Plastic has a problem; is chemical recycling the solution? 
  1. European Bioplastics, 2020, Mechanical Recycling Background Jul 2020. 

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