Mechanical degradation of elastomers in the presence of silica and inhibitors using a new design of mechano reactor

From free radical chemistry analysis supported by DFT calculations it is inferred that H abstraction and 1-3 double bond addition by chain scission allyl radicals can be major paths for crosslinking initiation, the addition mechanism acquiring importance with increasing reaction time. The oxygen uptake is approximately linear with process time and consequently does not fit the formation and decay kinetics of scavengeable mechano-radicals; it is suggested that the contribution by other mechanisms involving mechanical excitation coupled with thermal activation may be important. The addition of SiO2 filler causes an increase of total absorbed mechanical energy and a decrease of the equilibrium molecular weight limit (enhanced chain scissions). In contrast, the scavengeable mechano-radicals yield is found to be less than 50% of that determined in the absence of SiO2. These observations are related to the mechanical degradation of bound rubber in conditions of enhanced cage effect and build up of frictional energy by silica-rubber Van der Waals interaction.