The synergistic activity of binary accelerator systems in rubber vulcanizat
ion is well known. Thiourea and its derivatives are important secondary acc
elerators in this context. It is suggested that thiourea containing binary
systems of rubber vulcanization proceed by a nucleophilic reaction mechanis
m. Amidinothioureas (ATUs), which are derivatives of thiourea, have been in
vestigated extensively as secondary accelerators. One of the aims of this s
tudy was to get further proof with regard to the theory of the nucleophilic
reaction mechanism in such binary systems. In the present study phenyl sub
stituted ATU was used as a secondary accelerator along with mercaptobenzoth
izyl disulfide, tetramethyl thiuram disulfide, or cyclohexyl benzthiazyl su
lfenamide in the sulfur vulcanization of natural rubber. The results showed
an appreciable reduction in the cure time for the mixes containing the ATU
compared to the reference mixes. These results are indicative of a nucleop
hilic reaction mechanism in the vulcanization reaction under review. These
vulcanizates also showed comparatively better tensile properties and good r
etention of these properties after aging. The optimum dosages of the second
ary accelerator required for these vulcanization reactions were also derive
d. (C) 2000 John Wiley & Sons, Inc.