Abstract
Devulcanisation of filled rubber vulcanisates through mechanical/ mechano-chemical processes in a two-roll mill is a well-established technique. The general mechanism of mechano-chemical devulcanisation suggests blocking of possible reunion of free radicals produced via crosslink scission. Hence the efficiency of shear induced devulcanisation processes can be improved significantly by the effective utilization of a chemical /process that can instantaneously block the reunion of the radicals formed by bond scission. A new concept of blocking the reunion free radicals formed by shear breaking of crosslinks using a stable free radical and thereby increasing the efficiency of devulcanisation is presented. A cyclic nitroxide stable free radical viz. 4-hydroxy 2, 2, 6, 6-tetramethylpiperidine 1-oxyl free radical (4-Hydroxy TEMPO abbreviated as 4HT) assisted mechanical devulcanisation of carbon black filled NR vulcanisates (un-aged and aged) in which 4HT was used to block the recombination of the radicals formed by bond scission. Stable free radical increased the per cent devulcanisation and revulcanisate properties of devulcanised rubber in all cases under consideration. The recombining capacity of different type of cleaved crosslinks (mono-, di- and poly- sulphidic) were found to decisively influence the per cent devulcanisation of samples under shear induced devulcanisation. The influence of factors like cure system, crosslink density, the extent of ageing etc. of the original sample on the devulcanisation efficiency and the subsequent revulcanisate properties are discussed in detail.
NSTL