EFFECT OF ZINC OXIDE LEVEL AND BLEND RATIO ON VULCANIZATE PROPERTIES OF BLEND OF NATURAL RUBBER AND ACRYLONITRILE-BUTADIENE RUBBER IN THE PRESENCE OF EPOXIDIZED NATURAL RUBBER

Effect of Zinc Oxide level and blend ratio on vulcanizate properties of natural rubber (NR)/acrylonitrile-butadiene rubber (NBR)/epoxidized natural rubber (ENR) blend was studied. NR/NBR/ENR vulcanizates with compositions of 100/100/0 ; 100/90/10 ; 100/70/300 ; 100/50/50 ; 100/30/70 ; and 100/10/90 wt. %, respectively were each prepared with Zinc Oxide level of 0, 2.0, 4.0, 5.0, 6.0, 7.0, and 8.0 phr. The effect of Zinc Oxide level and blend ratio on tensile strength, modulus, elongation at break, hardness, abrasion resistance, compression set, and swelling behaviour of the vulcanizates were investigated. Results obtained show that the use of lower or higher than recommended level of Zinc Oxide in rubber vulcanization can lead to inferior or poor quality vulcanizate. Zinc Oxide level of 5.0 phr gave vulcanizates with optimum tensile strength, modulus and abrasion resistance. Further addition of Zinc Oxide was accompanied by a steady decrease in these properties. Of all blend systems studied, blend sample with composition NR/NBR/ENR: 100/70/30 produced the highest value of these properties. Hardness and compression set showed an increasing trend with increase in Zinc Oxide level due to increase in crosslink density; whereas elongation at break decreased with increase in Zinc Oxide level for the same reason. All vulcanizates exhibited a decreasing trend in swelling ratio as Zinc Oxide level increased up to 5.0 phr, and then increased with further increase in Zinc Oxide. The values of Gibbs free energy (ΔG) and volume fraction of NR in all vulcanizates studied increased with increase in Zinc Oxide level, reaching a maximum at 5.0 phr Zinc Oxide. This signifies progressive improvement in the interfacial interaction between blend components. These interactions lead to an increase in the effective degree of crosslinking, which improves the mechanical properties of the vulcanizates.