ABSTRACT:The rheological properties, morphology, and oil resistance in natural rubber and nitrile-butadiene rubber (NR/NBR) blends are investigated as functions of the blending conditions. It is found that the Mooney viscosity of the blends depends more strongly on the blending time than the rotor speed. The size of the NR dispersed phase is approximately independent of the rotor speed, but it decreases with increasing blending time up to 25 min. With a further increase in the blending time the NR dispersed phase size decreases. The results for the relative tensile strength, which is an indicator of oil resistance, are in agreement with those of the blend morphology, indicating that the oil resistance in a 20/80 NR/NBR blend strongly depends on the phase morphology of the blend. The smaller the size of NR dispersed phase, the higher the blend resistance to oil.

Rheological properties, morphology, and oil resistance in natural rubber (NR)/nitrile rubber (NBR) blends were investigated as functions of blending conditions and viscosity ratios of the blends. As for the blending condition effects, Mooney viscosity of the blends depended more strongly on blending time than rotor speed. Size of the NR dispersed phase was approximately independent of rotor speed but decreased with increasing blending time up to 25 min. As blending time further increased, NR dispersed phase size increased. The results of relative tensile strength, which is an indicator for oil resistance, in this study were in agreement with those of the blend morphology, indicating that the oil resistance in 20/80 NR/NBR blend depended strongly on the phase morphology of the blend. The smaller the size of NR dispersed phase was, the higher was the resistance to oil of the blend. However, a decrease in the size of the dispersed phase by the modification of the viscosity ratio via the use of low-molecular-weight rubber (i.e., liquid natural rubber and epoxidized liquid natural rubber) did not result in an improvement in the oil resistance.

Changes in rheological properties, morphology, and oil resistance in NR-NBR blends by viscosity ratio have been investigated. In this study, the viscosity ratio was modified by mechanical mastication and addition of liquid natural rubber (LNR) and epoxidised liquid natural rubber (ELNR). The results reveal that as viscosity ratio increased from 0•5 to 1•0, Mooney viscosity of the blends increased, and then decreased sharply as the viscosity ratio further increased from 1•0 to 2•0. The addition of LNR and ELNR for plasticising NR and NBR, respectively, does not significantly affect cure properties of the blends. The phase size of the NR dispersed phase depends strongly on the viscosity ratio. The high viscosity of the matrix and/or the low viscosity of the dispersed phase promote breaking up of the dispersed phase. Unexpectedly, a decrease in size of the dispersed phase by the modification of viscosity ratio via the use of low molecular weight rubber (i.e. LNR and ELNR) did not result in an improvement in oil resistance.

ABSTRACT:The phase morphology and oil resistance of 20/80 NR/NBR blends filled with different types of fillers and copolymers were investigated. In the case of filler effect, N220, N330, and N660 carbon blacks with different particle sizes were used. Additionally, the blends filled with nonblack-reinforcing fillers, that is, precipitated and silanetreated silica, were investigated. To study the compatibilization effect, maleated ethylene propylene diene rubber (EPDM-g-MA) and maleated ethylene octene copolymer (EOR-g-MA) were added to the blends. The results revealed that the addition of filler, either carbon black or silica, to the blend caused a drastic decrease in NR dispersed phase size. Carbon blacks with different particle sizes did not produce any significant difference in NR dispersed phase size under the optical microscope. Silica-filled blends showed lower resistance to oil than did the carbon black-filled blends. In addition, it was determined that neither EOR-g-MA nor EPDM-g-MA could act as a compatibilizer for the blend system studied. The oil resistance of the blends with EPDMg-MA is strongly affected by the overall polarity of the blend. In the case of EOR-g-MA, the oil resistance of the blends is significantly governed by both overall polarity of the blend and phase morphology.