Compound Viscosity

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. 

In general it is best to aim for a compound viscosity that is sufficiently low and yet remains compatible with the specifications of the component. 

For natural rubber (NR) it is preferable to use a controlled viscosity grade, rather than attempt to reduce a variable, non-controlled grade to a lower viscosity by premastication. Not only is the product less variable, it is also less expensive in terms of labour and machine utilisation. Synthetic rubbers offer a wide availability of viscosity grades and are designed to allow for ease of processing. Whatever the polymer, it is important to ensure that it has been kept dry and free from the gelling effects of sunlight. 

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Latex compound viscosity obviously forms an important aspect of dipped product manufacture. Accurate measurement by a Brookfield or similar viscometer is desirable to estabhsh the fundamental viscosity of a compound, but Flow-Cup viscometers (Ford B.3 Cup) are more commonly used for day-to-day control of latex compounds during compounding and product manufacture. It is necessary to ensure that only stainless steel flow cups are used, if the measured latex is allowed to return to the production tanks brass cups yield an unacceptable level of copper contamination, which adversely affects aging properties of products made from copper-contaminated mbber compound. 

Plasticizers (qv) are usually present at lower concentrations compared to general-purpose mbber-based compounds, because of their volatility at typical ACM service temperatures and/or their partial extractabiflty by the aggressive fluids where acryflc elastomers are employed. Other additives are therefore required to improve processibiflty. These processiag aids act as lubricating agents and enhance the release characteristics of the acryflc compound and/or reduce compound viscosity. 

Plasticizers and Processing Aids. Petroleum-based oils are commonly used as plasticizers. Compound viscosity is reduced, and mixing, processing, and low temperature properties are improved. Air permeabihty is increased by adding extender oils. Plasticizers are selected for their compatibihty and low temperature properties. Butyl mbber has a solubihty parameter of ca 15.3 (f /cm ) [7.5 (cal/cm ) ], similar to paraffinic and naphthenic oils. Polybutenes, paraffin waxes, and low mol wt polyethylene can also be used as plasticizers (qv). Alkyl adipates and sebacates reduce the glass-transition temperature and improve low temperature properties. Process aids, eg, mineral mbber and Stmktol 40 ms, improve filler dispersion and cured adhesion to high unsaturated mbber substrates. 

The purpose of this section is to explain in a qualitative way how the product quality is related to the calendering parameters. Therefore a simplified calender model is presented. The model describes the pressure buildup in the calender nip region as a function of compound viscosity, clearance, calender line speed, rolling bank height, as well as geometrical data. The general layout of a typical steel and fabric cord calender is explained by means of the result of the presented calender model. 

Apart from the effect on the crosslinking efficiency, the use of co-agents in peroxidecuring also imparts the molecular structure of crosslinks. It has been reported that coagents with two or more unsaturated moieties can be incorporated as individual molecules between two elastomer strands to form crosslinks [103-109]. In this way the crosslink structure of peroxide-cured elastomers can be altered. Thus, apart from the expected benefits, such as improved crosslinking efficiency, decreased compound viscosity and faster cure, the use of co-agents may also provide a tool for manipulating mechanical properties. 

Preparing a water-soluble additives mixture containing water, salt, antimicrobial compounds, viscosity thickeners, and water-soluble flavorings. Formula amounts of thickeners and water-soluble flavorings increase as the fat content of a spread is reduced. The water should be microbiologically potable and deionized to remove calcium, magnesium, iron, and copper. 

Steam and acid resistance in all cures Low compound viscosity in bisphenol stocks... 

The goals of these investigations were to examine the influence of the polymer structure and viscosity on the antifoam compound performance. Of particular interest was the influence of the compound viscosity on the antifoam performance at the higher temperatures typical of many foaming situations. 

Filler dispersion Compound viscosity Crumbly batches Lumpy stocks Slow mixing... 

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