COMPOUNDING INGREDIENT

Before making decisions on the ingredients to be used it is worthwhile taking into consideration facts about the materials available that may not be readily discovered by persons new to the industry. These factors are suggestions designed to  

It has been found, from unfortunate experience, that cutting costs through the use of a short-term buying advantage will result in unexpected results and components failing to meet zero defect targets. 

In addition to homopolymers of varying molecular and particle structure, copolymers are also available commercially in which vinyl chloride is the principal monomer. Comonomers used eommercially include vinyl acetate, vinylidene chloride, propylene, acrylonitrile, vinyl isobutyl ether, and maleic, fumaric and acrylic esters. Of these the first three only are of importance to the plastics industry. The main function of introducing comonomer is to reduce the regularity of the polymer structure and thus lower the interchain forces. The polymers may therefore be proeessed at much lower temperatures and are useful in the manufacture of gramophone records and flooring compositions. 

In the massive form poly(vinyl chloride) is a colourless rigid material with limited heat stability and with a tendency to adhere to metallic surfaces when heated. For these, and other, reasons it is necessary to compound the polymer with other ingredients to make useful plastics materials. By such means it is possible to produce a wide range of products, including rigid piping and soft elastic cellular materials. 

Other miscellaneous materials also used occasionally include fire retardants, optical bleaches and blowing agents. 

It is an observed fact that heating PVC at temperatures above 70°C has a number of adverse effects on the properties of the polymer. At processing temperatures used in practice (150-200°C) sufficient degradation may take place during standard processing operations to render the product useless. It has been found that incorporation of certain materials known as stabilisers retards or moderates the degradation reaction so that useful processed materials may be obtained. 

The choice of a stabiliser thus becomes an empirical yet systematic process. The following factors are the most important which must be considered  

Raw rubber can be either natural or synthetic. The standard grades of natural rubber are smoked sheets and pale crepe. For high grade products, first grade smoked sheets, namely RMAIX or Pale Crepe, is used. Pale Crepe is practically colourless and is preferred in products where delicate colour, extreme whiteness or transparency 

Source Percentage of rubber hydrocarbon Specific gravity Percentage sulphur 

The percentage sulphur (determined in the un-vulcanized reclaim) and the available rubber hydrocarbon are taken into consideration while evolving the compound formulation. It should be noted that reclaimed rubber is not all rubber. In arriving at the total rubber content in the rubber formulation containing reclaim, allowance must be made for its rubber content. For example in the following blend of smoked sheet and whole tyre reclaim, the total rubber content is to be considered as 100 parts instead of 125 parts as below and the proportion of other ingredients should be worked out accordingly on parts per hundred rubber (phr) basis. 

Whole tyre reclaim (rubber content-50%) - 50 parts Total -125 parts 

The rubber content should be reckoned as 75 plus 25 (RHC of 50% of 50 parts of reclaim) = 100 phr. 

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Ring stmcture and location of the aldehyde group were estabUshed by the efforts of Baeyer, Markwald, and Harries (11—14). For some time, furfural was a laboratory curiosity and a compounding ingredient of perfumes. 

In a flexible PVC compound, ingredients in the recipe are chosen based on cost and/or thein contribution to physical and other properties and performance. Typical ingredients (16,17) are stabilizers, fillers, plasticizers, colorants, and lubricants. 

D. R. Smith, ed., Rjcbber WorldMaga ne s 1995 Blue Book, Lippincott Peto, Akron, Ohio, 1995. An annual compilation of materials, compounding ingredients, machinery, and services for the mbber industry. Available on CD-ROM in combination with R. E. Ohm, ed.. The Vanderbilt RjibberHandbook, 14th ed.,1995. 

Latex Mixes. The first step in latex fabrication is to bring compounding ingredients into solution or suitable dispersion form. Most ingredients are not water soluble and it is necessary to emulsify Hquids and microdisperse soHds in water (see Latex technology). 

SBR mbber compounds are prepared in two stages the nonproductive and the productive phases. In the nonproductive phase the compound ingredients are mixed, usually in internal mixers (Banbury). The mixing time is usually short and the compound temperature is in the 160—195°C range. 

The 1978 revision was carried out in accordance with IS 1043 although the latter also deals with compounding ingredients.)... 

Acrylonitrile-butadiene rubber (also called nitrile or nitrile butadiene rubber) was commercially available in 1936 under the name Buna-N. It was obtained by emulsion polymerization of acrylonitrile and butadiene. During World War II, NBR was used to replace natural rubber. After World War II, NBR was still used due to its excellent properties, such as high oil and plasticizer resistance, excellent heat resistance, good adhesion to metallic substrates, and good compatibility with several compounding ingredients. 

NR adhesives accept a wide variety of compounding ingredients. 

R. Bond, Compound Ingredient Consistency—Its Role in Process Capability, Ninth Annual Meeting of the Polymer Processing Society, Manchester, England, April 5-8 (1993). 

The pneumatic tire has the geometry of a thin-wallcd toroidal shell. It consists of as many as fifty different materials, including natural rubber and a variety ot synthetic elastomers, plus carbon black of various types, tire cord, bead wire, and many chemical compounding ingredients, such as sulfur and zinc oxide. These constituent materials are combined in different proportions to form the key components of the composite tire structure. The compliant tread of a passenger car tire, for example, provides road grip the sidewall protects the internal cords from curb abrasion in turn, the cords, prestressed by inflation pressure, reinforce the rubber matrix and carry the majority of applied loads finally, the two circumferential bundles of bead wire anchor the pressnrized torus securely to the rim of the wheel. 

The resistant properties of a lining compound depend on the choice of polymer and the compounding ingredients added to form the final material. Thus there is a diversity of choice between the base polymers and also in various compounds based on the same polymer. The ultimate choice is usually that which will be cost effective for the environment to be resisted. 

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