Hydrogenated skim natural rubber prepared by diimide reduction and its vulcanizates

Abstract

Hydrogenation is an important method of chemical modification, which improves the physical, chemical and thermal properties of diene based polymers. Skim natural rubber latex (SNRL) produced as a by-product from the production of concentrated natural rubber latex, could be hydrogenated to a strictly alternating ethylene-propylene copolymer (EPDM) by diimide reduction, using hydrazine and hydrogen peroxide with copper sulfate as catalyst. The hydrogenated products were characterized by FTIR and NMR spectroscopy. The effect of various reaction parameters on the hydrogenation level, were investigated. Low temperature, long reaction time, high amount of hydrazine and lesser amount of hydrogen peroxide and copper sulfate were required to optimize the hydrogenation reaction of SNRL. Copper acetate was a highly active catalyst for the reaction. The kinetic result indicated that the diimide hydrogenation of SNRL exhibited a first order behavior with respect to the C=C concentration. The activation energy of catalytic and non-catalytic diimide hydrogenation of SNRL was 9.5 and 21.1 kJ/mol, respectively. The thermogravimetric analysis indicated that the thermal stability of hydrogenated skim natural rubber (HSNR) was higher than their parent polymer. From TEM micrograph of hydrogenated SNRL particles, non-hydrogenated rubber core and hydrogenated rubber layer were observed according to the layer model. The particle size and particle size distribution of hydrogenated SNRL were not changed during hydrogenation. In addition, the mechanical properties and ozone resistance of vulcanized HSNR blends were also investigated. The increase in HSNR content in the blends could retard the ozonolysis resulting in the surface cracking.