EXTENDERS

Extenders

These are substances which are added to rubber compounds in lage quantities so that the cost of the compound can be reduced, without seriously affecting the final properties. Important among the commercially used extenders are the following.

1. Rubber reclaim

This is a product resulting from the treatment of vulcanized scrap rubber tires, tubes etc. by the application of heat and chemicals, whereby a substantial degree of devulcanisation and regeneration of the rubber compound to its original plastic and state is affected, thus permitting the product to be processed, compounded and vulcvanised. Reclaiming is essentially depolarization, the combined sulphur is not removed. Different types are available, depending upon the original type of waste rubber employed. Whole tyre reclaim (WTR) contains about 50% rubber hydrocarbon and 20-25% carbon black, the rest being plasticisers and miscellaneous ingredients. While using whole tyre reclaim for every 1 part of rubber which is being replaced, 2 parts of reclaim is added. In addition to the economic advantage, use of reclaim has other beneficial affects such as short mixing time, low power consumption, low heat development during processing, reduced swelling and shrinkage, higher cure rate, minimized reversion, good ageing etc.

2.Factice:
This is a class of elastic gums made by reacting certain vegetable oils with sulphur. Most familiars is the one used in erasers. Fictive can be blended with NR and with some synthetic rubbers is a rather high proportion and the blend will remain highly elastic. It will also be soft and suffer much loss of strength and abrasion resistance. Another way in which it is used is to increase the tolerance for liquid softeners in synthetic rubber compounds.

3.Mineral rubber
Airs blown petroleum asphalt are called mineral rubber. Products of this sort wold hand only moderate weakening effect on tensile and tear strength. But would relatively be poor in respect of resilience and heat build up and flexing.

White pigments and colours
White pigments are used in rubber compounds to which them. Its use in coloured compounds mains the colours brighter important among the common white pigments are titanium dioxide and lithophone.

Pure titanium is extracted from minerals, precipitated as the hydroxide, calcined to the oxide and ground. It is a semireinforcing filler comparable on a volume basis with zinc oxide, but is mainly used for its whitening power in tyre sidewalks, hospital accessories, floor tiles etc. And as an excellent heat resistant filler for silicone rubber. The agnate form is preferred where extreme wittiness is required. The retile form gives a rather creamier colour, but is more state at high temperatures.

Lithophone is a mixture of zinc suphide and barium sulphate, usually co precipitated in equimolecular proportions it is used mainly in cheaper white or coloured compounds as a whitening agent.