sulphur crosslinks in the rubber crumb the process effectively unzips the crumb and opens up the three dimensional polymer network for further reaction until the devulcanization process has been completed to the desired level an alternative reaction pathway which is thermally initiated is represented by reactions 3 and 4 r u2032 u2014 s u2032 n r u2033 u2014 s u2032 z n z 1 h 2 gt r u2032 u2014 s n u2014 h r u2033 u2014 s z n u2014 h z h 2 s reaction 4 reaction 3 represents breakage of the sulphur linkages the weakest chemical bond in the vulcanized rubber by the application of heat alone to produce sulphide radicals these radical are highly reactive and can follow a number of possible reaction pathways one possible reaction pathway involves reaction with dissolved hydrogen to form sulphides as shown in reaction 4 reaction 4 represents the ideal situation for thermal reaction whereby devulcanization occurs without any degradation of the polymer other reaction pathways involving u25a1 elimination or condensation reactions are possible which could lead to degraded or higher molecular mass products respectively several embodiments of the catalytic devulcanization process are described in the following examples a 1 l batch autoclave equipped with a mechanical stirrer and temperature controller was used to ensure a consistent particle size for the rubber crumb used in these tests the crumb was dry sieved and narrow size.