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Sulfur group analysis in unaccelerated vulcanization of natural rubber
Author(s) -
Chakravarty Shomnath,
Chatterjee Pronoy K.,
Sircar Anil K.
Publication year - 1965
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1965.070090417
Subject(s) - vulcanization , polysulfide , sulfur , natural rubber , hydrogen sulfide , chemistry , sulfide , curing (chemistry) , polymer chemistry , inorganic chemistry , chemical engineering , materials science , organic chemistry , electrode , engineering , electrolyte
The reaction of lithium aluminum hydride forming mercaptan with disfulfides and mercaptan as well as hydrogen sulfide with polysulfides has been applied in order to characterize the structure of the crosslinks in the case of unaccelerated vulcanization of natural rubber with sulfur. The mercaptans formed were determined amperometrically, and the hydrogen sulfide was determined as cadmium sulfide. These measurements, coupled with the estimation of total crosslinks as measured by swelling, provide valuable information as to the distribution f different crosslinks (monosulfide, polysulfide, cyclic structures, etc.) in the vulcanizate. When extended to compounds of different sulfur concentrations (2.92‐33.9%) these studies show how the distribution of different linkages changes with sulfur concentration from compositions corresponding to soft rubber to those corresponding to hard rubber. The present study provides conclusive evidence that the long polysulfidic crosslinks first formed during vulcanization decrease in chain length as vulcanization progresses. Polysulfides also increase with the increasing sulfur content in the stock except in the range 6‐10%. Monosulfidic crosslinks increase with increasing sulfur in the stock. In contrast to accelerated vulcanization, a high proportion of combined sulfur was found to be present in cyclic structures, and this increases with temperature of curing. These findings tally with the results of the earlier workers and have been explained with the present day ideas of the vulcanization reaction. Inaccuracies in the measurements and inherent limitations of the method were discussed.