Browsing by Author "Ratnayake, U. N."

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    Effect of Storage Conditions on Viscoelastic Properties of Crepe Rubber
    (Uva Wellassa University of Sri Lanka, 2013) Jayasinghe, A.C.C.; Rathnayaka, R.M.S.D.; Ratnayake, U. N.
    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).