Effect of Emulsion Particle Size on the Natural Rubber Latex Film Properties in the Presence of Renewable Lipid Emulsions

Mineral oils are widely used as plasticizers in dry rubber processing. In view of mineral oils are primarily obtained from petrochemicals, renewable coconut oil (CKO) and soybean oil (SBO) present as an attractive options as plasticizer for rubber application. In this research, two CKO/SBO emulsions, E1 and E2 were successfully formulated with 1:9 oil-to-surfactant (O/S) ratio by different emulsification method. From particle size analysis, E1, formulated with low energy input emulsification method, has recorded a nano-size of 11.38 nm; whereas, E2, formulated with high shear rate emulsification method, has documented a macro-size of 547.00 mn. It Was found that, E1 has swollen up the rubber particle size extensively compared to E2, where NR/E1 blends have recorded a large particle size of 536 nm. Furthermore, NR/E1 has a greater swelling index, 544 % than that of NR/E2 due to smaller oil droplet of emulsion. However, NR/E1 exhibited tensile stress of 5.327 MPa, which is lower than that of NR/E2 (11.504 MPa). This demonstrates that emulsion particle size can affect the mechanical strength of latex film significantly, where small emulsion particles (nano-size) are proved to reduce the tensile stress extensively due to its effective swelling of rubber particles. From contact angle measurement, low contact angle (<90 degrees) was obtained for all NR latex films regardless of emulsion particle size, indicating no oil blooming and good compatibility between NR and lipid emulsions.