Curing Characteristics And Properties Of Epoxidized Natural Rubber ( Enr )
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Date
1997-07
Authors
MD. SADEQUL AMIN
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Abstract
The cure characteristics of accelerated sulphur vulcanization of epoxidized
natural rubber containing 25 mol % of epoxidation ( ENR 25 ) was studied
while one grade of unmodified natural rubber - standard Malaysian rubber
light ( SMR L ) was used as a control. The influences of different accelerator
types - zinc dimethyldithiocarbamate ( ZDMC ), tetramethylthiuram disulphide
(TMTD), diphenylguanidine ( DPG ), N-t-butylbenzothiazole-2-sulphenamide
(TBBS ), and 2-mercaptobenzothiazole ( MBT ) at various temperatures
were investigated. Three vUlcanization systems - conventional high-sulphur
vulcanization ( CV ), semi-efficient vulcanization ( semi-EV ) and efficient
vUlcanization ( EV ) were also investigated. Mooney Shearing Disk
Viscometer ( MV 2000 ) and Moving Die Rheometer ( MDR 2000 ) were used
to determine the Mooney scorch time and cure time respectively in the
temperature range of 100 to 180 DC. The results obtained indicate that
Mooney scorch time and cure time decreases exponentially with increasing
temperature for the two type of rubbers studied. At fixed curing temperature,
ENR 25 shows shorter scorch time and cure time compared to that of SMR L.
These differences in scorch behaviour and cure time is attributed to the
activation of the double bond by the adjacent epoxide group in ENR 25. The
investigation involving different accelerators show that mooney scorch time
decreases in the order, TBBS > TMTD > DPG > MBT > ZDMC. Studies of
the effect of varying amounts of MBT at a fixed sulphur concentration show
that scorch and cure time decrease as the accelerator concentration
increases.
From this study it has been fOLJnd that the cure index of SMR L is higher than
that of ENR 25, especially at lower temperatures of study, i.e., 120 DC and
below. This is attributed to the activation of double bonds by the adjacent
epoxide group in the ENR compound. ENR 25 shows higher torque
maximum than SMR L. This observation can be related to the oxirane group
which is bulky and this accounts for increased glass transition temperature
with increase in the level of epoxidation.
ENR 25 contains epoxide groups that activate the adjacent double bonds,
thus a faster cure is observed. In all the vulcanization systems, CV shows the
highest torque maximum followed by semi-EV and than EV. This differences
are attributed to the amount of active sulphurating agent which increases with
increasing accelerator concentration.
ENR 25 shows lower activation energy than SMR L for all the three different
vulcanization systems and the accelerators studied. This is obviously due to
the presence of epoxide groups that activate the adjacent double bonds, thus
lowering the activation energy of vulcanization. However, some differences in
the magnitude of cure time, cure index, torque maximum and activation
energy in the temperature and accelerator studies are observed between
ENR 25 and SMR L.
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Keywords
Curing Characteristics And Properties , Of Epoxidized Natural Rubber ( Enr )