Rubber blending modification

Rubber blends with cure rate mismatch is a burning issue for elastomer sandwich products. For example, in a conveyor belt composite structure there is always a combination of two to three special purpose rubbers and, depending on the rubber composition, the curatives are different. Hence, those composite rubber formulations need special processing and formulation to avoid a gross dissimilarity in their cure rate. Recent research in this area indicated that the modification of one or more rubbers with the same cure sites would be a possible solution. Thus, chlorosulfonated polyethylene (CSP) rubber was modified in laboratory scale with 10 wt% of 93% active meta-phenylene bismaleimide (BMI) and 0.5 wt% of dimethyl-di-(/ r/-butyl-peroxy) hexane (catalyst). Mixing was carried out in an oil heated Banbury-type mixer at 150-160°C. The addition of a catalyst was very critical. After 2 min high-shear dispersive melt mix-... 

Blend of (1) and (2) type categories mostly include the modification of engineering thermoplastics with another thermoplastic or rubber. PS-EPDM blends using a low-molecular weight compound (catalyst) Lewis acid have been developed [126]. Plastic-plastic blends, alloys of industrial importance, thermoplastic elastomers made by dynamic vulcanization, and rubber-rubber blends are produced by this method. 

Surface Modification of Fillers and Curatives by Plasma Polymerization for Enhanced Performance of Single Rubbers and Dissimilar Rubber/Rubber Blends... 

Even in the phase separated blends, where some degree of partial miscibility or compatibility exists between the components, simple melt blending in an intensive shear mixer is adequate for making a well dispersed, reasonably stable blend product with useful combination of properties, such as polypropylene/ethylene-propyl-ene rubber blend, ABS/polycarbonate blend, etc. The self-compatibUizing nature of these blends stems from partial miscibility and the mutual interpenetration of polymer chains at the interface. Slight modifications of the polymer backbone are often employed, particularly in the case of styrenic and ABS resins to induce partial miscibility with other resins. 

The modification of a given bitumen with crumb rubber (wet process) depends on the particle size of the crumb rubber, the quantity of crumb rubber blended, the mixing temperature and the duration of mixing. 

PLA can be mixed with natural rubber [71]. PLA and natural rubber are melt mixed and vacuum dried. The dried blend is cooled to room temperature, and then chopped into small granules. The composites are obtained by injection molding [71]. Without any interfacial modification, the transition from brittle to ductile failure was observed in this blend. The composite made of PLA and natural rubber blend showed good impact strength when compared to corresponding neat PLA composites [71]. 

Furthermore, the C=C bonds in the natural rubber structure might induce poor thermal and oxidative resistance in the natural rubber blends. Thus, Thawornwisit and coworkersproposed the preparation of hydrogenated natural rubber, which is one of the chemical modifications available to improve the oxidation and thermal resistance of diene-based natural rubber before blending with poly(methyl methacrylate-co-styrene). The poly(methyl methacrylate-co-styrene) was resistant to the outdoor environment and had excellent optical properties with a high refractive index, but it was extremely brittle and had low impact strength. Hydrogenated natural rubber could, however, be used as an impact modifier, as well as to improve its thermal and oxidative resistance for these acrylic plastics. 

Natural rubber blends have not been substantially limited to only reactive blends, such as those produced by grafting, epoxidation and halogenation studies. IPNs are one choice for modification of the natural rubber to increase the compatibility between natural rubber and acrylate polymers. Full IPNs of natural rubber and acrylate polymers are defined as a polymer blend having a crosslinked polymerization of each polymer type in their networks. Semi-IPNs, in contrast, are those in which only one type of polymeric component, mostly acrylate polymer, is crosslinked. The polymerization of IPNs would be a potential method for the modification of natural rubber. ... 

In rubber-rubber blend nanocomposites, nanoparticles are incorporated into a blend which can significantly affect the properties of the matrix. The properties of these composites depend on the type of nanoparticles that are incorporated, their size and shape, their concentration and their interactions with the polymer matrix. It is difficult to produce monodispersed nanoparticles in a rubber blend because of the agglomeration of nanoparticles. This problem can be overcome by modification of the surface of the nanoparticles. Surface modification improves the interfacial interactions between the nanoparticles and the polymer matrix. Nanofillers when added to blend systems are known to cause a considerable change in dynamic properties. 

The properties of rubber-rubber blend composites depend on the size and shape and concentration of nano particles and their interactions with the individual mbber matrix. The interaction between the filler and the matrix are improved by surface modification. In the mbber industry the uniform distribution of nano particles is considered to be important as it affects the mechanical properties and performance of the composite. For mbber-mbber blend composites fillers like carbon black prefer to migrate to less polar, less viscous mbber phase whereas silica and clay particles migrate to more polar mbber phase. CNTs mainly reside in the highly polar and non-polar mbbers but not in weakly polar ones. The Tg remain unaltered for a completely incompatible blend. In the case of partially compatible blends, the Tgs of the blend components are expected to shift towards each other as compared with the pure components. Shifting of Tg of polymers to lower or higher values in a blend depends on the polarity difference and the difference in the thermal expansion coefficient of the respective polymers in the blend. 

Zhang Qixia, Fan Hong, Bu Zhiyang, Li Bogeng. Blending modifications of PP by EPDM. China Synth Rubber /ndnst2004 27(3) 1000-1255. 

As with other rigid amorphous thermoplastic polymers such as PVC and polystyrene (see the next chapter) poly(methyl methacrylate) is somewhat brittle and, as with PVC and polystrene, efforts have been made to improve the toughness by molecular modification. Two main approaches have been used, both of which have achieved a measure of success. They are copolymerisation of methyl methacrylate with a second monomer and the blending of poly(methyl methacrylate) with a rubber. The latter approach may also involve some graft copolymerisation. 

Initial materials of this super-tough type were blends of nylon 66 with an ionomer resin (see Chapter 11). More recent materials are understood to be blends of nylon 66 with a modified ethylene-propylene-diene terpolymer rubber (EPDM rubber—also see Chapter 11). One such modification involves treatment of the rubber with maleic anhydride, this reacting by a Diels—Alder or other... 

Tackifying resins enhance the adhesion of non-polar elastomers by improving wettability, increasing polarity and altering the viscoelastic properties. Dahlquist [31 ] established the first evidence of the modification of the viscoelastic properties of an elastomer by adding resins, and demonstrated that the performance of pressure-sensitive adhesives was related to the creep compliance. Later, Aubrey and Sherriff [32] demonstrated that a relationship between peel strength and viscoelasticity in natural rubber-low molecular resins blends existed. Class and Chu [33] used the dynamic mechanical measurements to demonstrate that compatible resins with an elastomer produced a decrease in the elastic modulus at room temperature and an increase in the tan <5 peak (which indicated the glass transition temperature of the resin-elastomer blend). Resins which are incompatible with an elastomer caused an increase in the elastic modulus at room temperature and showed two distinct maxima in the tan <5 curve. 

Id. Thus, it is expected that in the modified PRP-EVA blend, probably due to interface modification by reactive processing, a transesterification between the pendant MAH group in MAH-PP, and acetate groups in the EVA elastomer, as predicted in reaction Scheme 1, the dispersed rubber particles become more efficient in craze initiation. 

Although, the heat resistance of NBR is directly related to the increase in acrylonitrile content (ACN) of the elastomer, the presence of double bond in the polymer backbone makes it susceptible to heat, ozone, and light. Therefore, several strategies have been adopted to modify the nitrile rubber by physical and chemical methods in order to improve its properties and degradation behavior. The physical modification involves the mechanical blending of NBR with other polymers or chemical ingredients to achieve the desired set of properties. The chemical modifications, on the other hand, include chemical reactions, which impart structural changes in the polymer chain. 

Roy Choudhury N. and Bhowmick A.K., Compatibilization of natural rubber-polyolefin thermoplastic elastomeric blends by phase modification, J. Appl. Polym. Sci., 30, 1091, 1989. 

Improvement in the processing and vulcanized qualities of a range of systems have been reported over the past decades. Modification of natural rubber, due to work in the British Rubber Producers Research Association, yields some of the most striking applications of microgel. A detailed study at the MV Lomonosov Institute of Fine Chemical Technology, in Moscow, on the effect of microgels on mechanical properties of cis-polyisoprene and butadiene-styrene rubbers extensively illustrates the properties of blends from latex combination of microgel and conventional or linear systems.(31)... 

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