Chlorinated elastomer, blends

Chlorobutyl rubber is prepared by chlorination of butyl rubber (chlorine content is about 1 wt%). This is a substitution reaction produced at the allylic position, so little carbon-carbon double unsaturation is lost. Therefore, chlorobutyl rubber has enhanced reactivity of the carbon-carbon double bonds and supplies additional reactive sites for cross-linking. Furthermore, enhanced adhesion is obtained to polar substrates and it can be blended with other, more unsaturated elastomers. 

Although two dissimilar elastomers—e.g., chlorinated butyl rubber and polybutadiene—may crosslink when in contact with one another, does bonding exist between the two interfaces Based upon thermodynamic theory as well as microscopic observations, we know that two such elastomers are not molecularly dispersed in a blend, so the diagnostic problem is one of considering two dispersed phases. 

Fig. 7a-c. Phase contrast microscope pictures of a blend of ethylene-vinyl acetate copolymer (40% vinyl acetate) with chlorinated polyethylene (43 % chlorine) before and after phase separation. Since both polymers are elastomers the mobility is quite high. The original pictures are coloured red and green. These black and white pictures have enhanced contrast to make the phase separation clear... 

Halobutyl rubber (HIIR) is used primarily in tire innerliner and white sidewalls. These elastomers are best for tire air retention owing to lower air permeability as well as aging and fatigue resistance. The chlorinated (CIIR) and brominated (BUR) versions of isobutylene isoprene rubber (HR) can be blended with other elastomers to improve adhesion between HIIR compounds and those based on general purpose elastomers, and improve vulcanization kinetics [16]. 

As a consequence, before 1953, the only possible blends were those of LDPE with other polymers than PO or with elastomers (e.g., chlorosulfonated polyethylene rubber, CSR chlorinated butyl mbber, CBR ethylene/propylene/diene copolymers, EPR, EPDM thermoplastic olefinic elastomer TPE, TPO). However, in addition to the original autoclave polymerization, already in 1938, a tubular reactor was introduced and its product had different properties than that from the autoclave. Also varying the reaction condition affected the degree of short- and long-chain branching in LDPE thus, blending different LDPEs offered a way for optimizing the resin to specific applications. 

The recent proliferation of metallocene-based polyolefins and polyolefin elastomers have gained their popularity owing to their density, cost, and ease of processabUity. PVC/POE blends have therefore been investigated as flexible PVC compounds. However, these blends are thermodynamically immiscible and needed suitable compatibiUzers such as the chlorinated polyethylenes (Eastman and Dadmun 2002). Since they are not miscible, POEs do not lower the PVC modulus sufficiently unless some plasticizer or a compatible elastomer such as EPE is also added. Commercially, some PVC/POE alloys are offered by TeknorApex under Flexalloy trade name with a shore A hardness 40-60 and brittle points down to —50 °C. They are claimed to have excellent low-temperature toughness, flexibility, compression set-resistance, and oil resistance. Suitable applications include automotive hoses, seals, gaskets, wire jacketing, etc. 

Alcryn Chlorinated olefin/EVAl/acrylate ester blends PVC/ethylene-carbon monoxide-vinyl chloride copolymer TP elastomers E. I. du Pont de Nemours... 

Details are given of the preparation of blends of bitumen with BR, butyl rubber, polyisobutylene, chlorinated PF, polychloroprene latex, and a PU elastomer. Characterisation was undertaken using fluorescence optical microscopy, DSC, and dynamic mechanical thermal analysis. 18 refs. 

In practice, the existence of both UCST and LCST has been established for polymer-solvent systems. About 10 years ago, Schmitt discussed UCST, LCST and combined UCST and LCST behavior in blends of poly(methyl methacrylate) with poly(styrene-co-acrylonitrile) (PMMA-PSAN), Ueda and Karasz reported the existence of UCST in chlorinated polyethylene (CPE) blends using DSC, Inoue found that elastomer blends of cis-l,4-polybutadiene and poly(styrene-co-butadiene) exhibit both UCST and LCST behavior and Cong et al. (72) observed that blends of polystyrene and carboxylated poly(2,6-dimethyl-l,4-phenylene oxide) copolymers with a degree of carboxylation between molar fraction 8% and 10% exhibit both UCST and LCST behavior. They used DSC to establish the phase diagram. 

Asymmetric double cantilever beam and peel test experiments were completed by Eastwood et al. (Eastwood and Dadmun, 2002) to evaluate the ability of multiblock or blocky distributed chlorinated polyethylenes (bCPEs) to strengthen the PVC/POE interface compared to that of randomly distributed chlorinated polyethylene (rCPE). Additionally, the dependence of molecular weight and chlorine content of the bCPE (composition) will be evaluated to ascertain the influence of these parameters on the compatibilization process. Chlorinated polyethylenes to compatibil-ize poly(vinyl chloride) (PVC) and polyolefin elastomer (POE) blends. A series of chlorinated polyethylenes that are blocky in nature (bCPEs) with varying composition (% chlorine), and molecular weight (melt index) were used for this experiment. 

To achieve good toughness, required for many applications, impact modifiers are added to PVC. Chlorinated polyethylenes, ethylene-vinyl acetate copolymers, styrene-methyl methacrylate grafted elastomers, vinyl rubbers, and polyacrylates are the most frequently used (316). These polymers are blended together with other additives. Blending conditions are extraordinary important for morphology control and consequently for final properties of the blends. 

Chlorinated polyethylene elastomer (CPE) has been produced by the introduction of chlorine atoms onto the polyethylene backbone in order to reduce the crystallization ability of polyethylene. In addition, the enhancement in resistance to hydrocarbon oil, heat and weathering is also achieved. To gain desired properties of the final products, CPE has been blended with many polymers, including polyvinyl chloride, styrene-acrylonitrile and polyurethane. Compared to NR, CPE is relatively expensive and therefore the blending of CPE/NR is one of methods to reduce the production cost of the final products requiring CPE properties. Some researchers from Thailand are working with this kind of blend. ... 

It is necessary for the dispersed rubbery substance to have a Tg value lower than the temperature at which the high-impact material is to be used. Many elastomers will satisfy this condition they are butyl rubber, polybutadiene, SBR, BAN, ethylene-propene elastomer, polychloroprene, EVA, polyisoprene, polyacrylates, PIB, and chlorinated polyethylene (CPE) elastomers. However, they are not all useful for specific blends such as PVC-based blends because they do not fulfill the other necessary properties. 

Chlorinated polyolefins are used as adhesion promoters for coatings and inks on polyolefin plastics. They can be used as primers on polyethylene, polypropylene, and thermoplastic polyolefins (polypro-pylene/elastomer blends). They are used for adhesion of paint to plastic surfaces in the automotive industry. 

Chlorobutyl can be readily blended and cured with other, more highly unsaturated elastomers. In the adhesives and sealants area, it has been blended with both regular butyl and natural rubber and then preferentially cured through the chlorine to improve strength. The reactive chlorine will also tend to increase adhesion to many polar substrates. 

Solvent cements are generally produced by removing the milled elastomer from the mill and dissolving it in solvent. This cutting of the rubber into a solvent is accomplished in low-speed mixing equipment known as chums or in a variety of high-speed, heavy-duty mixers. For natural rubber and SBR, solvents such as toluene, hexane, or naphtha are commonly used. For nitrile, neoprene, and other polar polymers, polar solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), or chlorinated solvents may be used, alone or in blends with the nonpolar solvents. The blend of solvents finally used by the adhesive producer will depend not only on solvent power, but on the relative rates of evaporation which control drying time. The dissolved rubber can then be blended with whatever additives are needed to obtain the desired adhesive performance. 

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