RECLAIM RUBBER (RUBBER RECLAIMATION UNIT)

Reclaimed or Re-generated rubber is the product resulting from the treatment of ground vulcanized scrap rubber tires, tubes and miscellaneous waste rubber articles by the application of heat and chemical agents, followed by intense mechanical working. The regenerated rubber has almost the original plasticity of virgin rubber, permitting the same to be compounded, processed and re-vulcanized or reused.

In reclaiming of scrap vulcanized rubber, the scrap is normally ground and is then treated with the application of heat, chemical peptizers and is then intensely worked upon mechanically to partially de-vulcanize (break the bonds between rubber polymer chains) the rubber component. This partially de-vulcanized product is commonly called reclaimed or re-generated rubber and can be compounded, processed and re-vulcanized much like virgin rubber. The availability and processing characteristics of suitable scrap sources has dictated the types of reclaim produced. Reclaimed rubber has become widely accepted as a raw material which possesses processing and economic characteristics that are of great value in the compounding of natural and synthetic rubber compounds.

Re-generated or Reclaimed rubber is produced by partial de-vulcanization of rubber granulate obtained from end-of-life tyres and other rubber products. The regenerated rubber has almost the original plasticity of virgin rubber, permitting the same to be compounded, processed and re-vulcanized or reused.

Regeneration can occur either by breaking the existing cross links in the vulcanized rubber (partial de-vulcanization) or by promoting scission of the main chain of the polymer (breakage of C-C bonds) or a combination of both processes.

Partial De-vulcanization means selective cleavage or breakage of Disulphide (S-S) chemical bonds (see: Figure below) leading to the separation of natural rubber polymer chains using heat, mechanical shear force and assisted by peptizers (like process oil & pine tar oil) and reclaiming agent (like Disulphides). The de-vulcanization is partial i.e. some and not all Disulphide (SS) chemical bonds are broken. The main mechanism of de-vulcanization is by means of thermal – oxidative degradation and high shear force acting on the material.

Figure: Vulcanized Natural Rubber (with Sulphur)

By the application of heat and chemical agents followed by intense mechanical working to ground vulcanised scrap or worn out rubber tires, tubes and waste rubber articles, a substantial regeneration on devulcanisation of the rubber compound to its original plastic state is effected, thus permitting the product to be compounded, processed and revulcanised. Reclaiming is essentially depolymerisation and misnomerically called “devulcanisation” although combined sulphur is not removed. By this depolymerisation, the reclaimed rubber shows decreased resistance to deformation at ordinary temperature; thus losing its elastic nature and become less resistant to compression, stretching or swelling. Reclaimed rubber was born because a secondary source of rubber was urgently needed. Entire rubber industry was growing so fast in the early days and there was no enough crude rubber to substantiate the demand. Reclaim rubber soon become indispensable. Apart from this, tire pose a disposal problem and therefore utilized as basic raw material in the form of ground vulcanised waste (crumb rubber) or converted to reusable state-reclaimed rubber.

Because of short break-down and mixing time, the power consumption during break-down and mixing, low temperature required in calendering and extrusion, non-critical calendering temperature penetration to fabric, tack improvement, minimising sulphur bloom, forming of uncurved stock, low swelling and shrinkage on extrusion and calendering, low thermoplasticity, high rate of cure and cheaper rubber/filler are important considerations in the mind of the compounder in deciding upon regular use of reclaim for low cost, energy, conservation and efficient processing steps even with new generation polymers to achieve desired optimum properties. Reclaimed rubber is primarily used in the manufacture of cycle tyres, Rickshaw tyres, Battery Boxes, Automobile tyres and other moulded rubber goods.