Sulfur-Free Prevulcanization of Natural Rubber Latex by Ultraviolet Irradiation in the Presence of Diacrylates

Natural rubber (NR) latex was prevulcanized by ultraviolet (UV) irradiation in the presence of different diacrylate coagents. Prevulcanization was affected by the aliphatic hydrocarbon chain length of the coagents. The following diacrylate coagents with increasing aliphatic hydrophobic chain lengths were used: 1,4-butanediol diacrylate (BTDA), 1,6-hexanediol diacrylate (HDDA), and 1,9-nonanediol diacrylate (NDDA). Oxygen inhibition of the free-radical reactions of prevulcanization and the effects of the inert CaCO3 filler (concentration range = 040 parts per hundred rubber) on properties of the prevulcanized NR films were investigated. The hydrocarbon chain length of the coagent influenced its hydrophobicity and therefore its affinity toward NR, and this affected the prevulcanization outcomes. HDDA showed the greatest affinity for NR and thus was the most suitable coagent for prevulcanization of NR. Prevulcanization via UV irradiation was insensitive to oxygen and the filler tested. The CaCO3 filler proved to be satisfactory and could be added either before or after UV irradiation.