European Rubber Journal

One of the first things a new recruit learns upon joining the rubber industry is that rubber can’t be recycled. It’s a thermoset. When it’s cured, a chemical reaction takes place which changes the nature of the material forever. That’s what everyone in the rubber industry is taught, and that is what everyone knows.

Every few months an entrepreneur pops up and claims that the latest technology — whether it be crumbing or pyrolysis or something else — can produce material that can be used in rubber goods with no reduction in the properties of the vulcanisate.

We have all learned to ignore them. We know that rubber crumb is a nightmare to work with and that scrap tyres are contaminated with all kinds of unpleasant chemicals.

We might just be wrong.

Not about scrap tyres, but about post-industrial scrap.

Scrap tyres are post-consumer waste. The mix of truck tyres and high performance car tyres dramatically affects the final properties of the mix; also the granulation process affects the processing performance and then there is the risk of contamination either by engine oils or by steel fibres.

Like everyone who reads this, I have more or less written off this source of recycled material, except for kids’ playgrounds and other low-grade applications.

Behind the wheeler-dealers who process postconsumer tyres, there are a few — a very few — companies who are attempting to process postindustrial scrap.

How much scrap does the typical rubber factory produce? If you measure it by the reject rate, then typically less than 2 percent of volume.

However, the reject rate is the smallest source of scrap rubber. If a tonne of rubber compound comes out of the mixer, often only 700 kg or even less is shipped out as finished product. The other 300 kg emerges as process scrap in the form of sprue, blank stampings, edgings, grade-change products and suchlike.

We don’t count it as scrap, because it is costed in to the production process. Nevertheless, it ends up in the waste bin. For want of a better word, I’ll use the term process waste to describe this cured material.

If there were a method of reversing the curing process, would it make sense to use the process waste as an ingredient in the virgin compound? The answer, in these times of intense cost pressure, is yes — at least in theory.

There are difficulties, not least the technology of reversing the curing reaction.

Another difficulty is that adding post-processed scrap will change the properties of the compound.

This might seem to limit the options for using process waste, but those who have tried, have discovered that re-formulating is relatively easy, because the new ingredient is well defined in terms of properties and ingredients.

This post-industrial scrap does not suffer from any of the drawbacks of post-consumer tyres. The postindustrial material is well known and well-understood. It is consistent from batch to batch and from year to year. It is not granulated, but rather comes in sheet form, ready for the mill.

Mouldings and stampings made from FKM, HNBR and other technical elastomers tend to generate a lot of process waste. Because of the high value of these polymers, it makes sense for companies to research every possible way to minimise that scrap.

If I said that highly technical users of high-value elastomeric materials are at this moment, using their own vulcanised process waste in their finished products, would it help to persuade you? 

If there is a question, it is over the technique and equipment used to re-process the waste. I have in recent weeks seen two systems which claim to do this. Their customers verify that the resulting material can be used as an alternative ingredient in virgin compound.

In each case, the key element is carefully controlled mechanical stressing of the process waste. One proprietary process uses a special chemical which is said to improve the efficiency of the process, but works on a simple two-roll mill. The other uses a speciallydesigned machine to apply a specific stress regime to the materials. 

This industry has learned too well that vulcanised rubber cannot be re-used. It has had its fingers burned by charlatans — who do not understand the first thing about rubber — making outrageous claims. But now there are processes and equipment out there which, in the right circumstances can deliver highly cost-effective results.

In these difficult times, we can’t let our prejudices blind us to the possibilities.