Determination of degree of crosslinking in natural rubber vulcanizates. Part VII. Crosslinking efficiencies of di‐tert‐butyl and dicumyl peroxides in the vulcanization of natural rubber and their dependence on the type of natural rubber

Abstract

AbstractThe efficiency with which di‐tert‐butyl peroxide and dicumyl peroxide vulcanize (crosslink) natural rubber depends on the type of natural rubber. Crosslinking efficiencies of the peroxides are increased by acetone extraction of the rubber and by increasing the concentration of peroxide but in no case studied was either peroxide 100% efficient. These findings indicate that the natural rubber samples contain non rubber compounds which compete with the rubber hydrocarbon for reaction with the peroxide. The implications of these findings are: (1) that the values of chemical crosslinks determined by Moore and Watson from the yields of tert‐butyl alcohol and methane formed when an unextracted deproteinized pale crêpe is crosslinked with di‐tert‐butyl peroxide may be overestimated; and, thus, (2) the calibration of Mullins which relates the number of chemical crosslinks in a natural rubber–peroxide vulcanizate to the number of physically manifested crosslinks may require revision.