Model compound studies on the de-vulcanisation of natural rubber at different temperatures

The mechanism of de-vulcanisation of sulphur-vulcanised natural rubber with aromatic disulphides and aliphatic amines is studied using model compounds (MC): Low-molecular-weight polymer compounds are used as replacement of the reactive unit of the polymeric rubber. The devulcanisation efficiency depends on the distribution of the sulphur ranks: Higher ranks of the sulphide crosslinks are de-vulcanised quite easily whereas the lower trisulphidic and disulphidic ranks react slowly. The monosulphidic addition product is not de-vulcanised at all in the temperature range used in this study. Aromatic disulphides are more effective than amines in breaking the polysulphidic products resulting in a high percentage of monosulphidic crosslinks. The efficiency of breaking up the polysulphides is lower for aliphatic amines but with the advantage that less monosulphidic crosslinks are formed.