Rubber processing

Processing help Cross-linker Increases cure rate Modifies cure system Diminishes degradation Reinforcement Mixing aid 

If a smooth finish is desired, a calender is used to process at the end of the processing cycle. A calender is a set of pressurized rollers usually made of chilled cast iron but sometimes steel. The calender is heated and operates in a continuous manner however, it is usually employed with vinyls and ABS polymer sheets. 

When designing a compound, the chemist considers several factors in line with design imperatives  

Note Parts by weight of typical rubber. a Ethylene-propylene diene monomer. b Nitrile rubber. 

The external barrel is heated, which, together with frictional shear heating, softens the feed material. The material has a reduced viscosity due to the process and is quite deformable by the end of the screw where the die imparts the frnal shape to the profile. The screw has three sections - the feed section (which conveys feed material and helps expel voidage gases), the transition section (which heats and mixes the materials) and the compression section (which homogenizes the material and builds up the pressure necessary to convey the material consistently through the die). 

Quality-control tests and important process variables 

Important processing and material variables for rubber moulding processes are 

Typical elastomer systems have been mentioned in the previous section, Section 6.7.1. 

Internal mixers are made in two types tangential and intermeshing. Banbury mixers are the most popular and they are tangential mixers.  

In any of the above systems plasticizers are added manually or automatically directly into a mbber mass according to the adapted technological process. Some rubber products are manufactined from emulsion. These products also need the incorporation of the plasticizer as shown in Figiue 14.31. Plasticizer may be premixed with other additives and added in any mixing order required. 

Addition of fragile componertts of the mixture (e.g., fibers or mictobaloons) or components which are likely to be affected by moisture (e.g., desiccarrt) requites ptedisper-sion of the additive in the plasticizer. The plasticizer frequently helps to wet powdery taw materials.  

Plasticizers affect matty properties in rubber. They improve low temperature properties, help to increase rate of surface plasticization acting partially as surfactants, increase modulus of side wall of tire insert by compatibilizing starch with rubber, or increase heat resistance of the rabber compound.  

Action of the plasticizer depends also on the stracture of the rabber. For example, a low amount of chlorine in chlorinated rubber decreases compatibility of chlorinated rubber with the plasticizer and the other resins.  

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Table 1. U.S. Sales of Organic Rubber-Processing Chemicals, 10 kg...

Rubber processed in latex form accounts for about 10% of new mbber consumption. Rubber latex is a Hquid, oil-in-water emulsion which is used to make foam or thin-walled mbber articles. The same accelerators and antidegradants used in dry mbber are used in latex, with longer-chain versions preferred for greater oil solubiHty. To prepare these and other additives for addition to latex, they must be predispersed in water and the surface of the powder or oil droplet coated with a surface-active agent to prevent destabilization (coagulation) of the latex. 

Polynorbomene is also of interest to the plastics processor since by using a dry blending process for mixing and a modified injection moulding process for fabricating, the use of conventional rubber-processing equipment may be avoided. 

Some typical properties of a Vulkollan-type polyurethane cast rubber and a black-reinforced polyurethane rubber processed by conventional techniques are compared with black-reinforced natural and nitrile rubbers in Table 27.2 ... 

Rubber manufacturing and processing giving rise to rubber process dust and rubber fume Used engine oils... 

Rubber fume Rubber process dust Rubber solvent (naphtha)... 

Determination of rubber process dust and mbber fume (measured as cyclohexane-soluble material) in air... 

An antiozonant should have no adverse effects on the rubber processing. 

Thermoplastic polyurethane (TPU) is a type of synthetic polymer that has properties between the characteristics of plastics and rubber. It belongs to the thermoplastic elastomer group. The typical procedure of vulcanization in rubber processing generally is not needed for TPU instead, the processing procedure for normal plastics is used. With a similar hardness to other elastomers, TPU has better elasticity, resistance to oil, and resistance to impact at low temperatures. TPU is a rapidly developing polymeric material. 

J. S. Dick, and H. A. Pawlowski, Applications for the Rubber Process Analyzer. Rubber Division of the American Chemical Society, Nashville, Tennessee, November 3-6 (1992). 

Advantages of Thermoplastic Elastomer over Thermoset Rubber Processing... 

Roy Choudhury N. and Bhowmick A.K., Hysteresis of thermoplastic mbber vulcanizates, Plast. Rubber Process. Appl., 11, 1989, 185. 

P-plastomers provide a unique combination of ease of processing, such that conventional thermoplastic-processing routines and arid equipment can be adapted to this polymer as weU as for a final fabricated product that is elastic. This combination of properties leads to the easy fabrication of elastic materials such as fibers and films, which traditionally have only been made inelastic by the use of thermoplastics. This advance opens the pathway to the introduction of desirable elastic properties to a host of fabrication processes very different from either the conventional rubber-processing equipment or the conventional rubber products, such as tires. P-plastomers and their fabricated products are not only soft, but also elastic. 

Mooney Viscometer studies at 100°C and 120°C show lower viscosity of the Al-hlled gums. Lower viscosity compounds require less energy input for extrusion. Comparative results on the dynamic mechanical properties, measured using a rubber process analyzer (RPA), show that at the... 

FIGURE 17.6 Plot of tan S versus temperature for Al- and A2-cured compounds measured using a rubber process analyzer (RPA). 

Measurement of Dynamic Mechanical Characteristics Using Rubber Process Analyser... 

The curing properties were determined with the aid of a rubber process analyzer (RPA 2000, Alpha Technologies) at a temperature of 160°C. The compounds were cured in a laboratory press at 160°C and 100 bar at a time corresponding to the fgo of the specific compound. 

Nonlinear Viscoelasticity along Rubber Processing Lines.830... 

Stream Effects and Nonlinear Viscoelasticity in Rubber Processing Operations... 

Effect of the various processing steps FIGURE 30.3 Stream or cascade effects in rubber processing. 

With respect to stream rheological effects in rubber processing, and despite all the restrictions discussed above, it seems nevertheless that the key information is how the nonlinear viscoelasticity is related to the processing behavior of mbber compounds. Such information can be deduced from the appropriate test procedure with the RPA, providing one considers the capabilities of the instmment to provide nonlinear viscoelastic data. 

NONLINEAR VISCOELASTICITY ALONG RUBBER PROCESSING LINES... 

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