Degradable Packaging and Bag Questions & Answers

One key factor is the energy required to make various materials; some are summarized in the table below:
Material Energy for production MJ/kg.
Polylactic acid (PLA) 69
Polyhydroxy alkanoates 89
Polyethylene 29 (as well Addiflex®)
Paper ~ 600
It is apparent from this table that materials such as PLA, although made from annually renewable resources consume considerable resources in their manufacture. Furthermore paper, often touted as a better environmental option than plastic film, is no such thing. Partly because of the energy required the cost of PLA and PHA products are multiples of the equivalent PE product.

1) Why are you doing this?

We follow the principles of the waste hierarchy of: reduce, reuse, recycle, and discard, as closely as possible. We encourage the end-user to use the bags at least twice. However, we know that many packaging items and carrier bags end up being thrown away or are re-used at home (in waste paper bins, for example) and then discarded, ultimately ending up in landfill. This is why we decided to mitigate the impact they have on the environment by making them degradable.

2) What are the environmental benefits of using degradable bags?

Normal plastic degrades very, very slowly. As it was invented less than 100 years ago, we still don’t know how long it might take to totally break down: possibly hundreds of years. That means that standard plastic packaging application or bags take up space in precious landfill sites.

The bio – degradation reduces the enourmous waste volume from 100 % down to 15 % tto 20 % as the plastic is converted into CO2, Water and Biomass.

3) What are degradable packaging films or carrier bags made of?

Normal plastic packaging and bags are made from HDPE (high-density polyethylene), LDPE (low-density polyethylene), colouring and chalk. To make them degradable, all we have done is include trace amounts of a special additive. This additive causes the films to oxidise, meaning that the structure of the plastic is attacked by oxygen causing it to disintegrate more rapidly (i.e. it acts as a catalyst, speeding up a process that happens extremely slowly naturally).

Chalk (or calcium carbonate) is added as a natural, mineral modifier to the polyethylene during the film producing process in order to minimise the use of plastic, speed up the production process and improve the physical strength of the bag.

4) How long does it take?

The additive has a built-in time release, which has been set to activate approximately 12 months after the film is made. This allows plenty of time for the packaging films to be shipped to stores, given away at tills and used by the customer – possibly more than once – before the degradation process begins.

The amount of time it takes for the degradable film to disappear depends on how it is disposed of: it can take as little as 6 weeks but will typically take a couple of years. Estimates suggest that a standard, non-degradable plastic bag would take hundreds of years to disintegrate – if ever.

5) How does the additive work?

It is a thermo-oxidation system, which means that once the additive is activated, the presence of oxygen causes the packaging film to disintegrate. Heat, sunlight and stress (i.e. movement) trigger and accelerate this process.

If all four are present – for instance a bag stuck in a tree being buffeted by the wind during summer – it can degrade in as little as 6 weeks. However, as long as there is oxygen, “thermal” degradation can occur at any temperature (even at less than 0oC, although it may take several years).

6) And if there isn’t any oxygen?

The packaging film will not degrade. This is a big advantage over biodegradable materials that, in the absence of oxygen, begin anaerobic decomposition, the product of which is methane – a greenhouse gas 20 times more damaging than CO2.

7) What exactly happens – and what is left – when the packaging film or the bag degrades?

The system we are using is a two step process: initially there is a chemical process where oxygen attacks the carbon chains in the HDPE, turning long chains into smaller and smaller chains which now incorporate oxygen in their chemical make-up. At this point, the plastic has all been turned into organic functional groups (ketones, carboxylic acids, alcohols etc) which attract water. These transformations (smaller chains, and the presence of oxygen and water) create the conditions for a potential second stage: microbial digestion.

If microorganisms are present (as they will be in compost or landfill) then these small fragments will be included in their trophic chain, as food. These fragments therefore decompose further into simple elements: carbon dioxide, water and biomass (biomass is just the organic waste of microbe cells).

This process is similar with the degradation of the lignin in the wood

8) Are they, therefore, biodegradable?

If the conditions are right and microbes are present – such as in active landfill or in a maintained compost – then, yes, the carbon chains do indeed biodegrade.

9) So will it disintegrate in my kitchen drawer?

Eventually, yes, but you can keep reusing it until you notice that the plastic is becoming brittle. At that point, one should discard it.

10) You say the process releases CO2 but, as it is a greenhouse gas, isn't it bad for the environment?

CO2 is unavoidably created in all natural breakdown processes. The alternative is to keep the carbon locked up as plastic but that means the bag lasts hundreds of years.

11) So what happens in a typical landfill site?

Landfills vary – if they are well maintained and active (compost plants are being turned over) then the packaging film or bags will rapidly disappear. Estimates suggest that carrier bags take up as much as 1% of landfill space so by making ours degradable we are freeing up a considerable amount of space. Carrier bags are often recycled in the home as bin liners so a secondary benefit is that any contents of a sealed plastic bag will also be released to degrade.

12) I heard the degradable additive is a heavy metal – doesn’t that mean it pollutes the environment?

Not in AddiFlex.
The active substances in the additive are metal salts that are not classified as heavy metals.
The metals used are essential parts of the minerals used in living systems (like our own bodies).

13) Can you put them in domestic compost heaps?

We would not advise this, simply because a home compost does not usually create enough heat to cause the breakdown to occur quickly. While it will eventually disintegrate, the lower temperature means it could take several years.

14) Why not using PLA bags (polylactic acid) made from substances like cornstarch?

At present, PLA is considerably more expensive to produce than polyethylene, and requires more energy to make at the outset. Similarly, most, if not all, cornstarch comes from genetically modified corn crops and we are against the use of GM. Balancing these considerations, we have decided that degradable plastic currently makes the best sense both for our business and the environment. We will review this as the technology improves, and costs come down.

Also, if PLA cornstarch bags were put into our carrier bag recycling units at high volumes, it would contaminate the waste stream, making recycling impossible.

We do not support littering but as the majority of the packaging applications and carrier bags do not end in a controlled way of disposal, the way to make the bags degradable helps the environment.