Page 127 - CW E-Magazine (26-11-2024)

Point of View

Recycled PET demand set to receive a boost with

clearance for food use

The utility of plastics, including as a means of packaging, is unquestionable, and the material stands out in comprehensive analyses as a
sustainable material compared to several other options. Despite this, the issue of plastics waste is a matter of great concern, including in India
where streets and water bodies are littered with indiscriminately disposed wastes. There is a sense of urgency to tackle this problem, which
is not surprising considering the world produces and consume several million tonnes of plastics, and a considerable portion is in short-lived
packaging applications. Today, global, regional, national and local efforts are ongoing to tackle this issue, and the responsibility of action is
being pinned on resin producers, convertors that transform it into myriad formats, and fast-moving consumer goods companies that use them
to package their products.

There is no denying that only a small chunk of plastics produced is recycled. This is rising, but not as fast as consumption, which implies
that the total quantum ending up in landfills is growing. This has caused several NGOs to question the commitment of the plastics industry,
but that is unfair. It will take coherent and collaborative efforts of all stakeholders – including governments and local municipal bodies – to
make a significant impact.

PET – a versatile & eminently recyclable plastic
Part of the problem with plastics recycling stems from the fact that they are an array of materials with varying chemical constitution,
application and ease of recycling. No surprise then that the rates of recycling of the individual polymer classes vary. A standout in plastics
recycling – with the highest recycling rate globally and in India – is polyethylene terephthalate (PET), a polyester. The principal application
for PET (aside of fibre) is for packaging of drinks, especially carbonated soft drinks (CSD) and water. Other uses include packaging of food,
pharmaceuticals & agrochemicals and for making sheets. While growth in CSD markets has petered out in the western world – largely due
health concerns – consumption for health drinks and water continues to see above-average growth.

In India too, PET is the packaging material of choice for water, juices, CSDs, vegetable oils etc. Packaging of edible oils, in particular, has
shown significant increase in the last decade, thanks to PET’s excellent barrier properties (especially to oxygen), tamper-evidence, ease of
handling, eco-friendliness, and cost-effectiveness.
The high recycling rates for PET bottles in India – 85-90%, with the caveat that this is largely bottle-to-fibre – is for several reasons. For
one, these bottles are easy to pick out from mixed plastics waste as they have an easily recognisable form. Unlike plastic thin films, which
have much less economic value, PET bottles are economically more attractive to pick and divert for recycling. They are also more amenable to
sorting (removing labels, caps, etc.) and cleaning – two essential steps to produce quality recyclate. Unlike most other polymers, PET bottles
contain no additives, simplifying recycling and avoiding contamination of recyclate on this count.
Mechanical recycling
In the mechanical recycling systems now deployed at scale in India, the bottles are shredded, cleaned and reprocessed by extrusion into
lower-value, typically non-packaging applications such as polyester fibres for textile applications. In the Indian context, the large and growing
market for polyester fibre – unlike in much of the developed world where this is a mature use with little growth – makes this a viable route
for recycling.

In the past, finished products from recycled PET (r-PET) face discoloration (yellowing) and intrinsic viscosity drops due to impurities in
flakes and influence of recycling process conditions. These factors narrowed usage to low value-added applications. But that has now changed,
thanks to a slew of process innovations such as cold high speed friction cleaning, ultrafine filtration, low shear and low temperature rise during
extrusion, laser spectroscopy for sorting, infra-red heating leading to uniform crystallisation, etc. Nevertheless, mechanical recycling does
result in downcycling of polymer properties.

Chemical recycling
This can be overcome with chemical recycling in which the polymer is broken down to its constituent monomers or other intermediates,
which are then purified and used – just as virgin material – in polymerisation.
There are three main methods in PET chemical recycling, depending on the added hydroxyl-bearing molecule: glycol for glycolysis; methanol
for methanolysis; and water for hydrolysis. While several versions of the technology have been developed and some are commercially offered,
efforts are ongoing to develop more intricate processes such as fermentation (Carbios), microwave-assisted depolymerisation (Gr3n), glycolysis
using ionic liquids (Ioniqa Technologies), ambient condition depolymerization (Loop Industries), etc.

Chemical Weekly November 26, 2024 127

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