Quality of raw materials

A VIEW FROM A SYNTHETIC RUBBER PRODUCER

There are three contributing factors which, between them, determine both the efficiency of the mixing process and the quality of the mixed compound. These are:

•The quality of the raw materials used;

•The degree of control of the mixing process: and

•The test methods used to assess both raw material quality and the degree of mixing of the compound.

This article will deal with one of these factors.

There has been a significant change in emphasis towards high quality and consistency of products in the rubber industry during the 1980s. This change was instigated by the end-user, especially the automotive industry, and was transmitted by the processor back to the producers of the raw materials.

The major raw materials of the rubber industry are, in addition to the rubber itself, carbon black, other fillers, oils and various chemicals. For each of the categories the processors have to establish the minimum requirements for suppliers.

Many rubber processors today have in place a supplier accreditation system, or audit, whereby raw material suppliers’ plants, processes, laboratories and quality systems can be assessed against objective standards. This type of close communication between suppler and processor generates confidence that the guaranteed quality is being provided and, eventually, leads to reduction, even elimination, of incoming raw material testing and minimization of inventories. It also enables development of specifications and standards that are both right for the customer, and feasible for the producer.

3. Make up the plan to the text.

4. Give a brief summery of the text.

Text D

1. Read the text and choose the most suitable title out of the given ones:

a) Chemical Constitution of Rubber.

b) Chemical Reactions of Rubber.

c) The Molecular Weight of Rubber.

From the moment of its introduction into Europe the unusual nature and properties of rubber attracted the attention of chemists. A knowledge of the structure assumed an added importance as a first step towards ultimate synthesis; indeed an account of natural rubber and its chemistry is indispensable as a logical approach to the problems of the so-called modern synthetic rubbers.

Faraday made combustions of rubber and found the composition to correspond to C₅ H₈ – a formula which has since been confirmed.

An important contribution to the elucidation of the rubber hydrocarbon was later made and a ring formula for rubber was put forward. The existence of the long chains of molecules has been verifiedby X-ray examination.

Raw rubber disso1ves incompletely in ethyl ether and this fact serves to distinguish between the sol fraction and the gel fraction is insoluble. The hydrocarbon in Hevea rubber latex just taken from the tree has a very broad molecular - weight distribution; it ranges from several million down to below 100,000.

The molecular weight of raw rubber is lower than that of fresh latex, but may be as high as 460,000. The decrease in molecular weight from the latex state to the raw rubber state is due to the breakdown of the polymer, which occurs in the creping and sheeting operations. When the rubber is compounded, the milling which is necessary for proper distribution of sheeting the chemicals throughout the mass, results in an additional decrease in molecular weight.

2. Write out:

a) the key word and terms;

b) the sentences expressing the main idea of each paragraph.

Дата добавления: 2014-10-17