Elastomers mixing process

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... 

Mixing. Ethylene—acrylic elastomers are processed in the same manner as other elastomers. An internal mixer is used for large-scale production and a mbber mill for smaller scales. In either case, it is important to keep the compound as cool as possible and to avoid overmixing. Ethylene—acryflc elastomers require no breakdown period prior to addition of ingredients. Mixing cycles for a one-pass mix are short, typically 2.5—3.5 min. When compounds are mixed on a mbber mill, care should be taken to add the processing aids as soon as possible, after the polymer has been banded on the mill. Normal mill mixing procedures are followed otherwise. 

An obsolescent term for compound room - the area where the elastomers and compounding ingredients are weighed out in the proportions called for by the compound formula, prior to the mixing process. 

V. Collin and E. Peuvrel-Disdier, Disperion Mechanisms of Carbon Black in an Elastomer Matrix, Elastomery, Vol. 9 (2005) Special Edition JSSN PL 1427-3519 see also V. Collin and E. Peuvrel-Disdier, presentation at the Conference of European Rubber Research Practical Improvements of Mixing Processer, Paterbom, Germany, January 25-26 (2005), pp. 219-241. 

Mixing and extrusion techniques are usually applied to elastomers for processing and improvement of physical properties. These mechanical processes normally lead to the occurrence of radical reactions such as chain scission, chain coupling, and crosslinking. The 13C-NMR analysis of EP showed that the shearing of polymer resulted in hydrogen abstraction. This was followed by disproportionation reaction to form olefins [75]. 

Two important types of elastomeric polyolefin blends are reactor-made iPP/ EPR blends and postreactor blend iPP/EPDM. The latter is called thermoplastic vulcanizates (TPVs), produced by dynamic vulcanization of blends containing a thermoplastic and an elastomer. To make iPP/EPDM TPV, the two polymers PP and EPDM are mixed with curatives, such as peroxides, phenolic resins, or sulfur with accelerators, and dynamically cured in an extmder resulting in a blend consisting of micrometer-sized elastomer particles dispersed in the PP matrix (20-24). Paraffinic oils are added in the melt mixing process for viscosity control and cost. In iPP/ EPDM TPV, the crystalline iPP resin is normally the minor phase. Recently, polyolefin plastomers have been added to the class of elastomeric polyolefin blends. Polyolefin plastomers are ultralow molecular weight linear low density polyethylenes (ULMW-LLDPE). Nonelastomeric polyolefin blends are blends of polyolefins with mostly nonpolyolefin (other thermoplastic) matrices as mentioned earlier. 

A new method known as reactive mixing has developed recently to increase the cure rate of EPDM by modifying the EPDM phase to make it more reactive toward curatives, using commercially available sulfur donors such as bis-alkylphe-noldisulphide (BAPD), in combination with dithiocaprolactam (DTDC) and/or dithiomorpholine (DTDM). The refinement of reactive mixing process with cost effective sulfur donors is one of the challenges in the maximum utilization of these elastomer blends. 

The behaviour of elastomers in internal mixers reflects consequently a combination of shear and extensional responses. Any model of the mixing process has to take account of both shear flow and transitory extensional flow, since for the latter the steady state cannot be achieved. Therefore the response of the elastomers in the earlier times of an elongational process gives information about the mixing behaviour. Using a high rate extensometer,... 

The reinforcement of rubber composites by CB and/or silica is greatly affected by the rubber filler interactions, the agglomeration of the filler particles within the rubber matrices, and the occlusion of the rubber into the internal voids of the dispersed aggregates. Furthermore, filler-elastomer interactions play a major role in the filler dispersion achievable during mixing process. 

Mixing Processes. Technical elastomers are blends of up to about 30 different compoimds like natural rubber, styrene-butadiene rubber, silicate and carbon-black fillers, and mobile components like oils and waxes. Improper mixing leads to inhomogeneities with corresponding variation in mechanical and thermal properties. An important source of heterogeneities of this type is represented by filler... 

Usually, elastomers are processed through extrusion, forming in matrices, mixing. The first observations on the cold degradation of rubber by two roll-mixing, in the last century, refers to the fact that, under prolonged processing, natural rubber becomes sticky [703-705],... 

The influence of the two roll-mixing process parameters on the mechanical properties of the product resulting by the simultaneous processing of PVC with an elastomer, was thoroughly studied with a PU containing dibenzyl diisocyanate-ethylene glycol and adipic acid as an elastic component [712],... 

TPU elastomers are processed on rubber equipment, injection molded, extruded, compression molded, transfer molded, and calendered. To be fabricated into products, such as athletic shoe outer soles, the elastomer and ingredients are mixed in conventional rubber equipment (two-roU mills, internal mixers) and compounded. Subsequently, the compound is processed for example, injection molded. ... 

There are two types of these materials—simple blends of the hard polymer and the elastomer and the dynamically vulcanized products in which the elastomer is cross-linked during the mixing process. Both the hard polymers and the elastomers used to make these products can be obtained off the shelf. Thus an almost unlimited range of combinations can be investigated quickly and easily. Similarly, commercial products can be made without the very high capital investment required to produce novel polymers. 

Criteria that influence the mixing process of elastomers are discussed, together with their relationship to achieving quality and turiformity in a cost-effective manner and to putting a system in place to achieve optimum results. It is shown, with particular reference to suppliers of seals for aerospace applications, that these mixing concepts need to be incorporated into the strategic plans because cooperation is required between all departments of a company. 8 refs. 

The two TPO blends, A and B, were manufactured using an internal batch mixing process under standard conditions. Both blends were typical 12% talc-filled TPOs with comparable MFRs (21 dg/min 230°C). However, the estimated viscosity ratio of TPO A was 2.5 times higher than the estimated viscosity ratio of TPO B. The viscosity ratio was calculated based on the average MFR of the PP phase measured at 230°C and the MFR of the elastomer phase estimated at 230°C. 

Considerable work has also been conducted to try to find thermoplastic elastomers that can be used to simplify processing by enabling dry blending and melt casting instead of the conventional mixing and curing process (see Elastomers, synthetic). 

The elastomer process is very similar to the Dennis process. It involves a number of steps in which a gas, formerly carbon dioxide and now fluorocarbon, is mixed with a plastisol under pressure. When released to atmospheric pressure, the gas expands the vinyl compounds into a low density, open-ceUed foam which is then fused with heat. 

Oxidation Catalysis. The multiple oxidation states available in molybdenum oxide species make these exceUent catalysts in oxidation reactions. The oxidation of methanol (qv) to formaldehyde (qv) is generally carried out commercially on mixed ferric molybdate—molybdenum trioxide catalysts. The oxidation of propylene (qv) to acrolein (77) and the ammoxidation of propylene to acrylonitrile (qv) (78) are each carried out over bismuth—molybdenum oxide catalyst systems. The latter (Sohio) process produces in excess of 3.6 x 10 t/yr of acrylonitrile, which finds use in the production of fibers (qv), elastomers (qv), and water-soluble polymers. 

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