Rubber compound viscosity

The curing is carried out either freely using hot or steam or in a mold that is only partially filled with the molding compound. Synthetic rubbers, particularly SBR, are preferred as they allow precise control over level of viscosity required for obtaining consistent product quality. The sponge and expanded rubber products include carpet backing, sheets, profiles, and molding. 

Scorch resistance is frequently measured by the time at a given temperature required for the onset of cross-link formation as indicated by an abrupt increase in viscosity. The Mooney viscometer is usually used. FuUy compounded, unvulcanized rubber is contained in a heated cavity. Embedded in the rubber is a rotating disc. Viscosity is continuously measured (by the torque required to keep the rotor rotating at a constant rate) as a function of time. The temperature is selected to be characteristic of rather severe processing (extrusion, calendering, and so on). 

Compound viscosity has a profound effect on processes in rubber manufacturing systems. This is certainly true for rubber injection moulding, where plasticised material must pass through narrow pathways, under pressure, to reach the mould. 

Plasticisers used in rubbers are materials, which have the effect of reducing compound viscosity, thus making the material more plastic during processing. These materials also function to control physical properties such as hardness and low-temperature flexibility. Plasticisers have an influence on many other properties and thus must be selected in order to provide the overall property profile for the end product. Basic types available are as described in the following sections. 

Butyl rubbers, unlike many other rubbers, do not break down easily during the normal mixing process in the mill. The compound viscosity can be controlled by selection of the proper grade of butyl rubber, the type of carbon black and the type and loading level of oil. Relatively high loading levels of paraffinic or naphthenic oils are employed for typical butyl applications, such as inflatable seals, tubes or sealing bladders and solid body items. 

Mooney viscosity measurement of the plasticity or viscosity of an uncompounded or compounded, unvulcanized rubber seal material, by means of the Mooney shearing disk viscometer. 

Fatty-acid soaps have some inherent characteristics which make them more acceptable as a means of reducing compound viscosity than do chemical peptizers. Because of their fatty-acid soap base they could eliminate or reduce the need for added fatty acid activators, and considerably reduce the stickiness of low-viscosity natural rubber masterbatches. They can be used in a number of applications where conventional chemical peptizers could cause contamination problems, e.g. in the food industry. They must, however, be used in considerably higher dosages than chemical peptizers. 

Mathematical models of the internal mixing process for the on-line prediction of rubber compound viscosity and viscoelastic properties were developed on the basis of multiple linear regression and artificial neural networks. The models gave high levels of accuracy when applied to predicting the properties of SBR and NR/SBR/ polybutadiene compounds produced using mixers of three different sizes. 9 refs. 

Cure Characteristics. Methods of natural rubber production and raw material properties vary from factory to factory and area to area. Consequentiy, the cure characteristics of natural mbber can vary, even within a particular grade. Factors such as maturation, method and pH of coagulation, preservatives, dry mbber content and viscosity-stabilizing agents, eg, hydroxylamine-neutral sulfate, influence the cure characteristics of natural mbber. Therefore the consistency of cure for different grades of mbber is determined from compounds mixed to the ACSl formulation (27). The ACSl formulation is as follows natural mbber, 100 stearic acid, 0.5 zinc oxide, 6.0 sulfur, 3.5 and 2-mercaptobenzothiazole (MBT), 0.5. 

Oxidized castor oils are excellent nonmigrating, nonvolatile plasticizers (qv) for ceUulosic resins, poly(vinyl butyral), polyamides, shellac, and natural and synthetic mbber (see Rubber, natural). The high viscosity products are also used as tackifiers in gasket compounds and adhesives (qv) because of good oil and solvent resistance. They also serve as excellent pigment grinding media and as a base for inks (qv), lubricating oils, and hydrauHc oils (62). 

In order to "cure" or "vulcanize" an elastomer, ie, cross-link the macromolecular chains (Fig. 2), certain chemical ingredients are mixed or compounded with the mbber, depending on its nature (4,5). The mixing process depends on the type of elastomer a high viscosity type, eg, natural mbber, requires powerhil mixers (such as the Banbury type or mbber mills), while the more Hquid polymers can be handled by ordinary rotary mixers, etc (see Rubber... 

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