ABSTRACT:The effect of mercapto-modified ethylene vinyl acetate copolymer (EVALSH) on the rheological and dynamic mechanical properties of acrylonitrile butadiene rubber (NBR) and ethylene vinyl acetate copolymer (EVA) blends was evaluated at different blend compositions. The addition of 5 phr of EVALSH in the blends resulted in an increase of the melt viscosity and a substantial decrease of the extrudate swell ratio. These results can be attributed to the interactions occurring between the double bond of the NBR phase and the mercapto groups along the EVALSH backbone. The power-law index also presents a slight increase in the presence of EVALSH, indicating a decrease in the pseudoplastic nature of the compatibilized blends. The reactive compatibilization of NBR/EVA blends with EVALSH was also confirmed by the decrease of damping values and an increase of glass transition temperature, in dynamic mechanical analysis.

SYNOPSISThe effect of ethylene-vinyl acetate (EVA) modified with mercaptoacetic acid on mechanical, thermal, and morphological properties of blends of natural rubber (NR) and EVA copolymers has been investigated. The introduction of EVASH promotes a crosslinking of natural rubber phase as indicated by extraction experiments and microscopy analysis. This crosslinking may be attributed to bonding between sulfhydryl groups along the EVASH backbone and double bonds in rubber phase and may be responsible for the hardness improvement of most of the studied blends. Better results on hardness and ultimate tensile strength with EVASH addition were achieved for NR-EVA (60 : 40) ratio, probably due to cocontinuous morphology of this composition. The influence of EVASH on crystallinity degree of NR-EVA blends was also studied by differential scanning calorimetry. The morphology of the blends was studied through scanning electronic microscopy. 0 1995 John Wiley & Sons, Inc. I NTRO DU CTI 0 NThe development of new polymeric materials with new commercial applications and lower costs has stimulated several studies on polymer blends. In this field, the thermoplastic elastomers are receiving special attention to obtain products with elastomeric properties while maintaining excellent thermoplastic processing. Several studies and books deal with this Blending rubber with plastic to achieve good mechanical properties is not an easy process because of the incompatibility of most of these blends. Several strategies have been employed to minimize the phase separation and increase interfacial adhesion that include the addition of physical or chemical c~mpatibilizers.~~~ Considering rubber-based blends, other parameters such as cure system and aging stability must be taken into account.Ethylene-vinyl acetate (EVA) copolymers are being considered as a good partner for several poly-

SYNOPSISNatural rubber (NR)-poly(ethy1ene-co-vinyl acetate) (EVA) blends have been studied by incorporation of mercapto-modified EVA (EVASH) combined with dicumyl peroxide (DCP) as a curing agent. The mechanical, thermal, and morphological properties of NR-EVA blends as functions of blend composition and compatibilizer and/or curative additions were investigated. An EVASH-DCP combined system leads to the greatest improvement in tensile strength when EVA is dispersed within the NR matrix. Higher performance on Shore A hardness was also achieved with this combined system. For blends characterized by NR domains dispersed in the EVA matrix, the efficiency of pure DCP in improving the tensile strength is higher. Morphological observations and selective extraction experiments indicate the cross-linking of NR phase in both systems. A cross-linking of the EVA phase is also suggested by DCP or an EVASH-DCP combined system, based on the decreasing degree of crystallinity of this phase.

ABSTRACT:The compatibilizing effect of mercapto-modified ethylene-vinyl acetate (EVALSH) was investigated in vulcanized nitrile rubber (NBR)/ethylene-vinyl acetate (EVA) copolymer blends. EVALSH increased the ultimate tensile strength, mainly in blends containing larger amounts of NBR. In addition, an accelerating effect of this functionalized copolymer was observed in blends vulcanized with the sulfur system. This behavior was confirmed with oscillating disk rheometry and differential scanning calorimetry analyses. The improvement of the mechanical performance was attributed to the interfacial action associated with the increase in the crosslink density of the NBR phase promoted by the mercapto groups in EVALSH. The effects of EVALSH on the morphology and dynamic mechanical properties were also studied.