Elastomer blends reactive elastomers

Unlike incompatible heterogeneous blends of elastomer-elastomer, elastomer-plastic, and plastic-plastic, the reactively processed heterogeneous blends are expected to develop a variable extent of chemical interaction. For this reason the material properties, interfacial properties, and phase morphology of reactively processed blends would differ significantly from heterogeneous mixtures. 

Elastomer blends in which the components react (reactive blending) with each other provide the best route to obtain a homogeneous product with improved physicals. The negative free energy... 

Figure 14.7 Schematic highlighting the microstructure of rubber-toughened PET and performance improvements when non-reactive elastomers are blended with reactive elastomers (adapted from Atofina literature entitled Lotader and Lotryl )...

E-EA-GMA (see Table 14.3) and EEA are often used in combination as a toughening system. The optimum blend ratio of reactive elastomers non-reactive elastomers (e.g. Lotader Lotryl) is 30/70. Since the E-EA-GMA terpolymer and EEA copolymer are mutually miscible, when blended together with PET the mixture acts as a single elastomeric phase, which is interfacially grafted to the PET continuous phase. 

The sales of plastics continue to increase in a large part due to technical and economic advancements of polymer blends. Reactive blending is a useful technique for elastomers but, it appears that chemistry could also play an important role in the correct microstructure adjustment of thermoplastic alloys. Interfacial reactivity should be the focal point in maintaining the expected structure during subsequent stages of manufacture. Besides industrial examples, various kinds of polymeric co-reacting systems are also presented in order to emphasise the key factors of reactive blending. 

Extrusion of Polymer-1 containing monomer of Polymer-2, followed by post reaction to Polymer 2 (polyimides, electrically conductive polymer blends, reactive blends, e.g., with crosslinked elastomers), etc. 

Hence a low molecular weight, reactive elastomer is normally used for impact modification of thermosets. The low molecular weight of the mbbery prepolymer aids its easy dissolution or dispersability in the thermosetting resin. The reactive functionality couples the rubber covalentiy to the growing polymer network during the curing reaction. Hence the rubber toughened thermosets may also be considered as co-reacted thermosets and not true blends. 

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. 

Staining with volatile reactive metal oxides, OSO4 and RUO4, is the preferred method for achieving interphase contrast for TEM analyses. It is applicable to blends of elastomers with different degrees of unsaturation such as NR-EPDM blends. 

Y.-Y. Cui, B.-J. Dong, B.-L. Li, S.-C. Li, Properties of polypropylene/poly(ethylene terephthalate) thermostimulative shape memory blends reactively compatibilized by maleic anhydride grafted polyethylene-octene elastomer. Int. J. Polym. Mater. Polym. Biomater. 62, 671-677 (2013)... 

In bromobutyl/chlorobutyl rubber blends, both elastomers have the polyisobutylene backbone and halogen reactive functionality. These polymers, being molecularly miscible, constitute an ideal system for co-vulcanization. Bromobutyl and chloro-butyl can be used interchangeably without significant effect on state of cure as measured by extension modulus, tensile strength, and cure rheometer torque development. Bromobutyl will increase the cure rate of a blend with chlorobutyl. However, where bromobutyl is the major part of the blends, chlorobutyl does not reduce scorch tendencies because the more reactive halogen unit can dominate. 

In another study by Cherian et UPA was modified by blending with functionalized rubbers such as ENR, hydroxyl-terminated natural rubber, and maleated nitrile rubber. The elastomers bearing reactive functional groups showed better compatibility with the resin and improved the toughness and impact resistance of the cured resin substantially, compared to unmodified elastomers. Maleated nitrile rubber (NBR) was far superior to all other... 

In IIR -I- CIIR or IIR -I- BIIR blends, the elastomer structures are essentially similar, but the different reactive functionalities provide completely different vulcanization behavior. In this situation it is... 

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