UNVULCANISED

Mention may here be made of the fact that natural unvulcanised rubber is poly-isoprene (2-methylbutadiene) ... 

Tables 5.4 and 5.5 predict that unvulcanised natural rubber (8 = 16.5) will be dissolved in toluene (8 = 18.2) and in carbon tetrachloride (8 = 17.5) but not in ethanol (8 = 26.0), all values being in units ofMPa. This is found to be true. Similarly it is found that there is a wide range of solvents for polystyrene in the solubility parameter range 17.2-19.7 MPa. ...

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers. 

Such chemical cure methods have been used for many years but, due to the inherent hazards of flammability and toxicity of the system, are not accepted in several countries. Also, if all the exposed working surfaces have not been properly treated, unvulcanised areas may occur which would rapidly deteriorate when the lining is put into service. 

The lining sheet is prepared by calendering in thin plies up to 1 mm in thickness, followed by combining the individual layers on the calender to form a finished sheet, usually between 3 mm and 6 mm thick. Alternatively, lining sheet can be manufactured by the roller die process in which the sheet is extruded and then passed through rollers to give the finished thickness. Extrusion is also used for the preparation of unvulcanised rubber tubes suitable for lining pipes up to 200 mm in diameter. 

In principle, any type of sample can be analysed by SEC provided that it can be solubilised and that there are no enthalpic interactions between sample and packing material. By definition then, this technique cannot be carried out on vulcanisates and even unvulcanised fully compounded rubber samples can present problems due to filler-rubber interactions. The primary use of SEC is to determine the whole MWD of polymers and the various averages (number, viscosity, weight, z-average) based on a calibration curve and to allow qualitative comparisons of different samples. Many commercial polymers have a broad MWD leading to strong peak overlap in the chromatography of complex multicomponent systems. 

Moore [231] has used hybrid MS/MS (EBQQ geometry El spectra) for the direct analysis of DODPA in unvulcanised rubber. Particular advantages of the technique are ... 

Unreacted free sulfur can be determined to ISO 7269 1995 — Rubber — Determination of free sulfur. Three methods for the determination of free sulfur in vulcanized rubber are detailed two versions of the copper spiral method and the sodium sulfite method. The copper spiral methods are also applicable, subject to limitations, to unvulcanised rubber. The technique of DSC can detect non-reacted rubber curatives such as residual peroxides. 

The rubber in unvulcanised filler-rubber mixes which is insoluble in a usual rubber solvent. Bonding Agent... 

Bound rubber in an unvulcanised carbon black-rubber mix. It results from the production of free radicals in the mastication of rubber these radicals attach themselves chemically to the particles of carbon black and form a proportion of carbon gel which is insoluble in the usual rubber solvents. 

Rubber which is deliberately rendered electrically conductive by the inclusion in the unvulcanised mix of certain types of carbon black. Conductive rubber for use in, e.g., aircraft tyres has a resistivity below about 105 to 107 ohm-cm. The changeover from the use of channel blacks to oil-based furnace blacks has conferred a degree of conductivity (sometimes unwanted) on many black rubber products, and it should no longer be assumed that any black rubber is a good electrical insulator. See Antistatic Rubber. 

A calendering process in which hot soft unvulcanised rubber compound is applied to a fabric. The cloth passes between the bottom and middle bowls of a three-bowl calender it travels at the speed of the bottom bowl and the faster middle bowl shears the rubber into the pores of the fabric. 

A plain weave cotton fabric filled with a starchy substance to give it a glossy, non-adherent surface. It was formerly much used to preserve a fresh tacky surface on unvulcanised mbber (tyre, tube and belt repair patches) but has been almost completely superseded by polyethylene film. Holofol... 

A process for making hollow mbber articles from a single sheet of calendered unvulcanised mbber. The surface of the sheet is semi-vulcanised and the application of a swelling agent causes the sheet to split thus forming the hollow article, the vulcanisation of which is completed thereafter. Homo polymer... 

A textile material used to prevent the tacky surfaces of unvulcanised rubber from adhering. The liner is often treated to permit easy release from the rubber. 

Melvin M. Mooney is best known for the development of an instrument for determining the plasticity (viscosity) of unvulcanised elastomers. 

An instrument which determines the viscosity of unvulcanised elastomers by measuring the resistance of the rubber to the shearing action resulting from the motion of a rotor in the centre of the test piece (BS 903-A58). 

General name for mixtures of liquid hydrocarbons obtained from petroleum, coal tar or shale, used as solvents for unvulcanised rubber. 

A term used to describe the toughness and elasticity of unvulcanised, unmasticated elastomers. Mastication reduces nerve, and, if the process is continued long enough, may destroy it altogether. See Dead Milled. 

Also termed softener and processing aid. A compounding ingredient which facilitates processing by making the unvulcanised compound more plastic, aids in the incorporation... 

A convenient term for the rheological properties of an unvulcanised elastomer (see Rheology). It has been defined as the susceptibility to, and retentivity of deformation , and also the degree of flow which takes place under given conditions of temperature and pressure . The use of the term viscosity is a more appropriate description. Plasticity Retention Index... 

Unvulcanised rubber in the form of granules. It is used for dissolving in hot bitumen for making the surfaces of so-called rubberised roads Power Factor... 

Indicates the ability of an unvulcanised rubber compound to accept the heat history required in processing without risk of scorching. 

Unvulcanised natural rubber which has been cooled quickly while under tension. In this condition it behaves like a relatively inextensible fibrous material. 

The process of roughening the surface of vulcanised rubber preparatory to applying a layer of unvulcanised rubber as in tyre re-treading, conveyor-belt repairing, etc. 

The degree to which a raw elastomer or unvulcanised compound returns to its original dimensions on the removal of an applied stress which has caused deformation. Die swell in extrusions and increase of thickness of calendered sheet are examples of recovery. 

The fitment of a new wearing surface to a worn pneumatic tyre. The operations comprise rasping to remove the remaining old tread, solutioning, fitment of unvulcanised tread and, finally, curing in a suitable press or autoclave. 

A term which generally applies to vulcanised rubber unfit for any other use than reclaiming or grinding to crumb rubber. In the rubber factory scrap may also refer to unvulcanised trimmings which can be reprocessed. 

The time during which an unvulcanised rubber compound (e.g., tyre, tube and belting repair materials) or a vulcanised rubber product will remain usable when stored under normal atmospheric conditions of temperature and humidity. 

Change in dimensions of an unvulcanised rubber (calendered sheet or extruded section) on cooling from the processing temperature. Also the volume contraction of a moulded rubber product on cooling from vulcanising temperature. See Coefficient of Thermal Expansion (Volumej. Shrinking... 

The process of controlled, gentle warming of unvulcanised calendered sheet rubber to reduce its anisotropy and prevent subsequent distortion of articles made from the sheet and cured by embedding in chalk in open steam. 

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