Differences between Size Reduction, Reclaiming and Devulcanisation in the recycling of rubber.
We have consistently found that the rubber industry confuses itself when discussing recycled rubber. Information has started to become lost and miss-translated; people have stopped collaborating and sharing their knowledge. The purpose of this blog post is to hopefully clear up the difference between the three types; size reduction, reclaiming and devulcanisation. I have already written about both size reduction and reclaiming processes and their advantages, but feel a post about the differences between all three at once, Â is worth my time.
First of all, letâ€™s quickly discuss each process:
Recycled rubber has now become the term most associated with size reduction recycling. This is due to the fact that there has been no chemical process involved in the recycling process. It has been, exactly as named, â€śReduced in sizeâ€ť.
There are 3 main types of size reduction recycling; Ambient Grinding, Cryogenic and Wet Paste.
- Ambient grinding is grinding/tearing the rubber to the small sizes at room temperature. This is our preferred recycling technique as we firmly believe it gives not only the most economical sized reduced rubber but also the most reusable (due to its shape giving the largest surface area).
- Cryogenic is the freezing of scrap rubber using liquid Nitrogen and reducing the size literally by smashing it to pieces. This is less economical due to the amount of liquid nitrogen used per kilo of scrap rubber (1:1 Ratio). The final shape also gives a much smaller surface area as it has flat surfaces, this means less rubber can lock/bond into the rubber compound.
- Wet Paste is another grinding technique. This is where the rubber is ground while in water. This can produce finer particles than ambient grinding due to the rubber being in cooled down by the water. Unfortunately this technique is not very economical because the ground rubber almost has an affinity to the water and drying the recycled rubber is extremely hard and costly.
This is where people start to get confused. Reclaim, Rubber Reclaim, Reclaimed Rubber, as stated is a much more complicated form of recycled rubber, it has been put under a chemical process. In fact, it has been put under a complex thermochemical and mechanical process.
Rubber is first reduced in size and then mixed with oils/reclaiming agents and heat. Without getting into too much detail, this process shortens theÂ polymer chain.
- During the reclaim process small amounts of sulphur cross links may be broken â€“ but not enough to claim it as devulcanisation.
- For rubbers, such as Nitrile (NBR) which has high chemical and heat resistance, reclaim is not yet possible.
Devulcanisation is the rarest of rubber recycling, but probably has the biggest potential. It is the breaking of the sulphur cross links. Breaking these sulphur cross links means that the resulting recycled rubber is almost exactly like the starting rubber compound. The recycled rubber will contain up to 90% of the original properties. This would make it the easiest recycled rubber to reuse.
Unfortunately breaking the sulphur cross links is extremely difficult and not many devulcanisation techniques are available due to economical issues at present. Although Remould.org.uk are getting close.
Differences between Size Reduction, Reclaiming and Devulcanisation:
From the explanations above, the differences are clear.
- Size reduction has no effect on the chemical structure of the rubber.
- Reclaiming rubberÂ breaksÂ bonds within the polymer chain (and a small amount of sulphur cross-links) and therefore hasÂ an effect on the polymer chain length.
- Devulcanisation has a small amount of effect on polymer chain length but mostly gives large polymer chains which have no sulphur cross links.
- Size reduction is an additive/cheapener rather than a material for replacing rubber polymer in the rubber compound. The ratio of the original materials in the rubber compound would be the same. Larger, size reduced, rubber (rubber granules) can be used in horse arenas and playground surfaces.
- Reclaim, unlike size reduction can be used to replace some rubber polymer being added in the rubber compound. In fact, if you really wanted, reclaim could make rubber compound by adding curatives/accelerators, although the quality would be poor.
- Devulcanisation, similar to reclaim would be able to replace the rubber polymer. In fact, it would probably be able to replace nearlyÂ the entire rubber polymer and most of the compound!
- Size reduction of rubber produces, shred (for tyres only), granules and crumb.
- Reclaim is extruded into blankets on a mill.
- The best devulcanised rubber would be extruded and would be available like reclaim.
I hope this post will shed some light on the confusion between the two different types. If you have any questions feel free to leave a comment and I will get back to you ASAP.