Recycling the Un-Recyclable!

Let’s talk about bags.

If you’re like me, you used to use single use carrier bags as a throw away item. Come home with the shopping then bin the bag or use it as a bin liner. Then the 5p charge came in and the bags suddenly held value. Something that used to be a free commodity now cost actual money, this cost then went up to 10p! Now I have a drawer full of them as I keep forgetting to take them to the supermarket. Technically it’s a draw full of money I can’t spend, that I can’t do anything with as the council won’t take them in the recycling bin.

When it comes to recycling flexibles things get quite interesting. There are numerous problems when you try to recycle them but given some effort it can be achieved usually by hand sorting. This isn’t always economically viable, which is why it gets classed as “un-recyclable”.

One of the first issues is when the material arrives at a sorting centre. It’s unloaded onto a conveyor and put through a sorting system. These automated systems usually have Near-infrared spectroscopic scanners fitted. The material passes over the scanner and a pulse of air blasts it in the relevant direction. The problem is bags can tangle in the conveyor mechanism, in the fines screen or can be too light and floaty to get directed properly. Most flexibles and films get removed by an air knife which takes off anything below a certain density. Further down the line granulated plastic goes through a air elutriation process to remove films. Given the issue one bag can cause for what is a very small weight of plastic most facilities won’t accept them.

So, suppose you’ve overcome this issue by having a segregated source of flexible plastic. Your next issue is how to process the material. It can’t be fed into an extrusion line as is, it first must be finely chopped then run through an agglomerator to get a feed-able crumb. When a single bag weighs approximately 5g it takes a whopping 200,000 bags to produce 1t of crumb, this can take between one and three hours to produce. But now you have a feed-able material. Finally getting somewhere.

So, what can we make? To bastardise the great George Orwell, all bags are equal, but some are more equal than others. So, bags are comprised of different polymers depending on the manufacturing process and purpose. Most bags are made of LDPE (Low-density polyethylene) but others are made from PP (Polypropylene), LLDPE (Linear low-density polyethylene), HDPE (High Density Polyethylene) and ULDPE (ultra-low density polyethylene). The problem here is that they are not compatible and all have slightly different melting points meaning that when you melt, mix and extrude them, some parts will solidify before others when cooled. This leads to a weakened structure. For example, if you were to blow them into a film to turn them back into carrier bags you would end up with tiny spots of solid plastic forming on the film, this would cause the film to tear under the pressures of the moulding process leaving you with unusable material.

I set myself and the team here the task of recycling “the unrecyclable” and the Technical & Innovation team have been working hard to identify and classify this interesting feedstock. The R&D is still ongoing but soon this flexible waste will be recycled into new products and will mean no more shipping out of the UK and no more going to landfill.