Polymer Recycling

An issue that pops up from time to time is related to the recycling of plastics… can it be done, is it economical, how do you do it and what do you get?

Let’s take a look at this subject and see what some of the issues are and what we as consumers can do about them.

First, what is a plastic? Most people understand the word “plastic” to mean something sort of light, flexible, non-rusting and maybe cheap. In the chemical world we use the word polymer, which means “many units”. Polymers are typically made from small molecules containing carbon, which are attached to one another by chemical processes to make very long chains. The chains can have other atoms such as hydrogen, oxygen and nitrogen in them as well. It is the length of these chains, and the way in which they fit with each other that give polymers their interesting and useful properties, such as resistance to water or oxygen or fuels, ability to be formed, coloured, drawn into fibres, extruded into films, act as an electrical insulator and many other applications.

Polymers generally have two main enemies: heat and ultraviolet light (sunlight). This is why your plastic lawn chair goes brittle after about three summers. The heat and UV act to break the long chains into smaller fragments. This weakens the polymer and soon it will fracture or crumble, and the object made from the polymer is no longer useable. Some things can be added to the polymer to protect it from heat and UV, such as carbon black pigment, or special compounds called antioxidants, which will extend its life.

So now we get to the recycling part. We collect water bottles, grocery bags, and margarine and yogurt tubs and put them in the blue box, but what then? All of these will have been exposed to some heat and UV and they will not be as strong as when they were made. As well, by the blue box stage they are all contaminated with labels, adhesive, and of course residue of what they contained. Another issue is that not all polymers are alike in that the items I mentioned above are all made from different polymers that cannot be combined. So, there have to be several processes: separation, cleaning and sorting, and then upgrading of some kind to make them useable.

Now, another part of the problem: many polymers are used in food packaging and medical applications, where contamination of any kind is unacceptable, and some applications such as fibre spinning require a very clean polymer. So you can already see the problem emerging: every time you recycle a polymer, you essentially downgrade a step or two. If you are making plastic municipal garbage cans or park benches, you have a lot of polymer to choose from, at a very reasonable price. Food wrap and intravenous tubing requires top quality material, and as a society we seem to want more food wrap and fewer municipal garbage cans.

Another issue is this: pick up your full blue box (without glass jars in it) and you will see it is pretty light. Waste polymer is mostly air, and until you can crush it or grind it or make it denser it takes up a lot of space for not much material, so shipping costs can be high.

So where does all this take us? Good quality waste polymer is a useful commodity and can command a high price. But it required extensive and costly sorting, cleaning and general upgrading to get there. Lower quality recycled polymer, with more contamination is of considerably less value. Our manufacturing system has incorporated economies of scale such that virgin polymers such as Styrofoam and low density polyethylene are only slightly more expensive than recycled material so there is little incentive to recycle these. PET (water bottle polymer) is of higher value and recycling these is more economical.

The grocery bag you took home from the supermarket the other day weighs about 5 grams. The recycle industry will pay about $.25/lb. for this material… so you need 100 bags to make $.25 worth of polymer for recycling, and only then if you have a truckload of it.

Used tires present a special case. Recycling rubber is already a thriving business, and most truck tires have treads made from recycled rubber. There are several ways to deal with used tires that are proven: they can be shredded and added to new rubber to make new tires and other rubber products; they can be shredded and added to paving material after the steel wire is removed; they can be added to the fuel used to fire a cement kiln, as these are fitted with effluent control; they can be heated in a vessel with a low oxygen atmosphere where the rubber breaks down into an oil-like material that can serve as fuel or be added to a crude stream. These technologies are either commercial in scale or at least proven in trials.

There is a class of polymers made from cellulose, corn waste, sawdust, and other renewable materials that we will look at in a later column.

As consumers we must demand more recycled content in the areas where it makes sense, and do as much as possible to clean, sort and recycle our polymer waste. We can influence the marketplace through our choices and our purchases. Let’s try to make reasoned choices and work to lower the amount of polymer waste we generate.