Blends of rubber

Two-roll mills are used rnainlv for preparing color pastes for the ink, paint, and coating industries. There are a few applications in heaw-diitv blending of rubber stocks, for which corrugated and masticating rolls are often used. 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

Generally, systems developed in the USA favour a combination of polyethylene with either butyl-rubber or hot-applied mastic adhesives, the latter consisting of a blend of rubber, asphalt and high molecular weight resins. In European and Far East coating plants, epoxy type primers and hard ethylene copolymer adhesives have been successfully employed. 

Some of the most difficult heterophase systems to characterize are those based on hydrocarbon polymers such as mbber-toughened polypropylene or other blends of rubbers and polyolefins. Because of its selectivity, Ru04 staining has been found to be useful in these cases (221,222,230). Also, 0s04 staining of the amorphous blend components has been reported after sorption of double-bond-containing molecules such as 1,7-octadiene (231) or styrene (232). In these cases, the solvent is preferentially sorbed into the amorphous phase, and the reaction with 0s04 renders contrast between the phases. 

Figures 6 and 7 show DSC cooling scans of the pure rubbers, LDPE, and blends of rubber with 50 phr LDPE. The crystallization temperature (Tcr) of LDPE (largest exothermic peak) is decreased six kelvins in the presence of the amorphous EPDM and is decreased 12 kelvins in the presence of the crystalline EPDM. This Tcr decrease could be attributable to partial solubility of EPDM rubber and LDPE. The soluble EPDM chains would have to be expelled from the LDPE crystal-...

Blends of rubber modified SMA and PBT could be used to produce ductile blow-molded containers suitable for low-temperature environments (Harrats and Makhilef 2006c). 

Blending of rubber has been tried out for toughening phenolic resin. Phenolic-nitrile rubber (NBR) was developed in the early 1950s, which has found wide applications [242] such as structural adhesives, O-rings, and gaskets. However, it was reported that when NBR is mixed with resole and cnred, they phase separate into undesirably large domains with low adhesion between the phases [243]. A discussed earlier, for an effective toughening effect the domain size and interfacial adhesion are important. 

Adhesives. Contact adhesives are blends of rubber, phenolic resin, and additives supplied in solvent or aqueous dispersion form they are typically applied to both surfaces to be joined (98). Evaporation of the solvent leaves an adhesive film that forms a strong, peel-resistant bond. Contact adhesives are used widely in the furniture and construction industries and also in the automotive and footwear industries. The phenolic resins promote adhesion and act as tackifiers, usually at a concentration of 20-40%. In solvent-based contact adhesives, neoprene is preferred, whereas nitrile is used in specialty applications. The type and grade of phenolic resin selected control tack time, bond strength, and durability. 

The introduction of thermoplastic elastomers (TPEs) during the late 1950s is one of the most important developments in the field of polymer science and technology. TPEs are a relatively new class of material, a blend of rubber and thermoplastic that combine a wide range of the physical properties of elastomers, such as elasticity, at room and service temperatures, and the excellent... 

Walters and Keyte [102] first observed dispersed particles in blends of rubber pol)m[iers by phase contrast optical microscopy. Marsh et al [103] studied elastomer blends by both optical phase contrast and TEM. Electron microscopy was applied to study blends of natural rubber, st)n-ene-butadiene rubber (SBR), a s-polybuta-diene (PB) and chlorobutyl rubber [104]. It became obvious that both hardening of the... 

Guided by the above studies, we have developed a number of experimental rubbers, and blends of rubbers, for application in tire treads. The experimental rubbers consist of vinyl BR s, SBR s, and high trans SBR s prepared by the anionic polymerization techniques, previously described in this paper. Tan 6 and Tg results for some of these rubber compositions are plotted in Figure 19. Also shown are the corresponding results for rubber compositions based on conventional rubbers used in the past. These data show that the experimental compositions have significantly lower lYO tan 6, and have simultaneously higher glass transition temperatures, when compared to compositions based on conventional rubbers. 

Blends of rubbers with crystalline thermoplastics of similar chemical structure. This approach, involving blends of olefin polymers and copolymers, has recently become of major importance in rubber technology. 

A masterbatch of polymer and filler can be prepared on a mill or in a Banbuiy and this masterbatch is then solvated in another mixer. For very high viscosity mixtures (essentially like conventional rubber compounds), such as blends of rubber with filler (and/or plasticizers), mills and Banbuiys are the best choice. 

Pressure Sensitive Adhesives.Solution pressure sensitive adhesives (PSA s) for tapes and labels are primarily blends of rubber and tackifying materials such as resins. The low... 

Figure 4 shows an example of a nylon-alloy. In order to improve the impact-strength of nylon, we used to blend rubber with nylon, but the blend of rubber resulted in the reduction of tensile-modulus and heat-stability. We then, improve tensile-modulus and heat-stability by meansof blending the nylon-alloy with polyphenylene oxide, which possesses a higher glass transition temperature. When rubber and polyphenylene oxide are blended separately or independently in nylon, we could not obtain the desired properties. But when the micro-structure of the blend is controlled, as polyphenylene oxide is first blended in nylon and the rubber is finely dispersed in the polyphenylene oxide phase, a heat-stable, high impact-strength nylon is obtained. 

Reactive blends of rubber and plastics are well known thermoplastic elastomers [132]. However, only a few blends with PBT are described. Cai and Isayev [113,114] reported the obtaining of new thermoplastic elastomers from blends of a copoly(ether-ester) (PBT- PTMO) and poly(acrylonitrile-butadiene) rubber (NBR) by the dynamic vulcanization process. These types of TPE show... 

Reports on blending of rubbers with TPEs are scarce. This is likely due to the very conservative attitude of the rubber industry and the high price of the TPE grades. 

It is important to stipulate therefore that this section covers a different type of recycled product than Chapter 7, which reviews the work that has been carried out to produce and characterise products from blends of rubber crumb with virgin rubber, thermoplastics and other materials (e.g., asphalt). In Chapter 7, the rubber crumb that is used is either unmodified, or has been through a surface activation process, but it has not been devulcanised. 

Blends of rubbers and plastics, which give rubber-like materials, can be roughly divided into two categories. These are, those in which the plastics material has a low level of crystallinity and which derive their rigidity from the base plastics material this has a relatively high glass transition temperatures (Tg), for example, PVC. The second class is based on thermoplastics materials which have a high level of crystallinity, for example, polypropylene (PP) or its copolymers. 

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