Effect of Storage Conditions on Viscoelastic Properties of Crepe Rubber
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Date
2013
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
Latex crepe rubber is one of main raw natural rubber types produced in Sri Lanka. Rubber is a
viscoelastic material, which consists of both viscous and elastic properties. Viscoelastic
properties of raw rubber influence the processability of a rubber compound. Even though Sri
Lanka is the leading manufacturer of latex crepe rubber, converting crepe rubber into products
is carried out in other countries and as a result, manufactured crepe rubber should be kept under
storage conditions prior to processing. The objectives of this study were to study the effect of
storage conditions on the viscoelastic properties of raw crepe rubber, viscoelastic properties of
compounded crepe rubber and the effect of the non-rubber content on viscoeastic properties of
crepe rubber.
Methodology
Two factor factorial design was employed as the statistical design of the study. Three different
grades of crepe rubber such as Fractionated Bleached (FB), Un-Fractionated Un-Bleached
(UFUB), Yellow Fraction (YF) crepe rubber samples were obtained, same batch from crepe
rubber factory at Dartonfield, Agalawatta. These crepe rubber were stored at different
temperatures such as 2 C, 22 C, 30 C and 40 C. Samples were drawn in every two weeks
interval up to six weeks. Crepe rubber samples were analyzed for viscoelastic behaviour by
analyzing Mooney viscosity and stress relaxation. Plasticity Retention Index (PRI) and un-aged
plasticity (P0) of crepe rubber were also measured to study the thermo-oxidative respect to
different storage temperature and time. Three different grades of crepe rubbers were
compounded by adding Calcium Carbonate as the filler and Mooney viscosity and stress
relaxation were measured at the initial stage and at the end of the sixth week, under different
storage temperatures. SAS statistical software was used for the analysis of the data and
Duncan’s Multiple Range Test was used for mean comparison.
Results and Discussion
Mooney Viscosity is a measurement of flow behavior of raw rubber. Higher Mooney viscosity
implies a higher resistance to flow and also provides indirect measurement of molecular weight
of raw rubber as un-aged plasticity. By considering the three grades of crepe rubber, an
increment of Mooney viscosity and un- aged plasticity was observed with the increase of the
storage temperature and storage time (Figure 1 and 2). This phenomenon is named as the
storage hardening. The phenomenon of storage hardening in solid natural rubber (NR) is
presumed to occur by means of reactions between some non-rubber components and abnormal
groups in rubber molecule. The main non-rubber constituents in natural rubber composed of
proteins and lipids (Yunyongwattanakorn et al., 2003). Carbonyl groups present in the rubber
molecule are responsible for cross linking on storage of dry rubber. The highest increase of the
Mooney viscosity was exhibited by Yellow Fraction crepe rubber. That might be the highest
non- rubber content in that crepe. High amount of non-rubbers cause to create large number of
C storage
temperature in each storage time. This could be due to low humidity storage condition in the
oven of which crepe rubber samples were stored. Significant increase can be seen in the storage
and
phospholipids at the chain-ends of rubber molecules may interact with water under ambient
condition, thus the water may disturb the formation of branching points by hydrogen bonding
(Jitladda et al.,2012).
Description
Keywords
Agriculture, Export Agriculture, Rubber Production, Rubber Technology, Rubber