How to used a waste rubber?

Regenerated rubber is often popularly known as reclaim rubber in the tires and rubber industry. This is becoming more and more popular with the increase in natural rubber and synthetic rubber prices. Regenerated rubber is a product obtained from waste and worn out vulcanized scrap. Use of reclaim rubber is already established in automotive tires, butyl tube. Energy recovery is one of the important processes of tires reclaim. Tires (once the steel wire is removed) have a relatively high specific heat value, as compare to coal. Worldwide energy recovery makes up one of the largest uses of reclaim tires. Test suggests that the use of waste tires as a substitute for coal result in lower emissions of nitrogen and sulfur. There has been a significant amount of reclaim tires used in cement kilns.

The rubber industry worldwide has focused mainly on the disposal of waste rubber rather than recapturing the economic value of the resources incorporated in the waste, historically the uses for waste rubber have been of low economic value, resulting in a low volume of recycling and stockpiling of tires. Tires are consider as the most visible of waste rubber product and their accumulation is increasing at an alarming rate worldwide.

There is an enormous potential for reclaim and reuse of rubber in developing countries. Whether rubber tires are reused, reprocessed, or used for making article for human use, the end result is there is less waste and less degradation of these materials which could cause harmful effects in our environment.

In Asian countries there has been a culture to reuse and to recycle all materials. Other than making reclaim rubber, scrap tires parts have also been used in shoe soles, slippers and in washers. Worn out tread have been nicely stripped off and used on the wheel of bull carts. Sidewalls of a tires are stripped off and knitted nicely with steel wire to make mats, mattresses and flooring products. Worn out bladders have been used in making flower garden and so on.

There is tremendous potential for the application of rubber crumb (powder rubber) in the construction of road. Crumb rubber may be used as : Fill material , In asphalt(wet and dry), As a crack sealant and in repair membranes.

Recycled rubber storage

Recycled rubber from whole tires into chips and crumbs can generate heat up to 115 *C in the ambient grinding process. This can on storage without sufficient cooling lead to spontaneous combustion. The presence of iron in the natural rubber compounds can catalyze the oxidation process, causing rubber degradation. This degradation is accelerated with heat. During grinding processing generation of crumbs and storage, volatiles and hot fumes may be generated.

Thus the recycled rubber must be sufficiently cooled, either by water or air to avoid spontaneous combustion. Rubber crumbs should be stored at ambient temperature in dry areas but not in tin sheds or tin roof warehouses.

Relate Topic

Evaluation of recycled rubber in compounds.

Evaluation of recycled rubber in compounds

Recycled rubber is blended with virgin rubber compound in two ways

1. The total elastomer content from the virgin compound plus recycled rubber is kept at 100 phr (part per hundred rubber)
2. The recycled rubber ia added on top of the virgin compound , where the total elastomer content becomes more than 100 phr.

Researcher found that at more than 20 phr natural rubber reclaim, tensile strength are higher when reclaim rubber is added on the top of 100 phr than when elastomer content of the blend is constant at 100 phr.

The amount of recycled rubber used in a rubber compound must be optimized. Experiments can be used to determine the effect of varying amount of recycled rubber on desired properties.

The natural rubber compound containing 30 phr recycled rubber had shorter scorch time , higher cure rate, and lower maximum torque than the control compound with no recycled rubber.

In the case of virgin rubber compound was mixed , cure and cryogenically ground. The ground recycled rubber was added to the virgin rubber compound at different levels. It appears that 5 phr ground butyl rubber content is the optimum level. At 10 and 15 phr tensile properties and air permeability are reduced significantly.

Recycled Rubber Techniques

Recycled rubber is defined as recyclable , vulcanized rubber that has been processed to give particulates or orther forms of different shapes size and size distributions.

Techniques are used to generate recycld rubber

Reclaiming

This is done by a chemical digestion process. Aryl sulfides and other chemicals are added to rubber , and then the mixture is chemically digested. Over the years, there have been significantly decreases in use of reclaim rubber.

Ground Rubber

Vulcanized scrap rubber is first reduced to approximately 2.5 cm by 2.5 cm to 5 cm by 5 cm chips by shredding. This material is further reduced in size by use of ambient grinding mills. The finer particle size needed, the longer the rubber must be milled. Multiple grinds reduce the particle size. Any fiber is removed by air and metal is removed by magnetic seperation. The heat generated in this process can degrade rubber if the product is not cooled properly before storage or shipping.

Cryogenic Ground Rubber

This process , small rubber chips or crumb rubber , 10 to 20 mesh are cooled by chiller using liquid nitrogen and then put through a grinding mill. For finer particle, multiple cooling and grinding are usually needed. Little heat is generated in the process, thereby decreasing degradation of the rubber. All fiber and steel are separated by freeze-grinding to give a higher yield of usable product.

Wet Ground Rubber

Ground rubber is produced by passing a water suspension of rubber particle through a flour-grinding type mill.

Devulcanization Process

In sulfur-accelelator vulcanization of diene rubbers,sulfur-sulfur bonds are formed. Devulcanization is the reverse process in which either via external energy or by addition of chemicals some of the sulfur-sulfur bonds are broken. There may also be cleavage of some C-S and C-C bond in these process.The resulting devulcanized rubber can be compound as is , or mixed with virgin rubber and recured. Chemical devulcanization involves addition of certain accelerators and sulfur to the crumb rubber on the mill or in Banbury.

Relate Topic

Evaluation of recycled rubber in compounds.