EFFECT OF SHELLAC AS A RETARDER IN THE NATURAL RUBBER VULCANIZATION PROCESS
DOI:
https://doi.org/10.55766/sujst-2024-03-e06005Keywords:
Cure time, Natural rubber, Retarder, Scorch time, Shellac, VulcanizationAbstract
This research aims to improve the natural rubber compound (NR) for the complex rubber molding process using shellac flake from Lac as a retarder in the vulcanization process. To reduce some chemicals, steric acid which is a retarder in the vulcanization process was replaced by shellac to reduce the risk of health problems and to make the environmentally friendly. The effect of shellac on the mechanical and physical properties of rubber compounds was studied. Steric acid and shellac were mixed into five ratios as follows; 100:0, 75:25, 50:50, 25:75, and 0:100. (NR/shellac0, NR/shellac25, NR/shellac50, NR/shellac75 and NR/shellac100). Tensile strength, elongation at break, and modulus of elasticity were investigated using the Ultimate tensile test. It emerged that NR/shellac0 showed a higher modulus of elastic and maximum tensile strength than NR/shellac100 but NR/shellac0 exhibited lower viscosity, scorch time, and optimum time (tc90) than NR/shellac100. When considering NR/Shellac25, NR/Shellac50, and NR/Shellac75, it was found that scorch time (ts2), cure time (tc90), molecular weight between crosslink, maximum tensile strength, and elongation at break increased with increasing shellac ratio. On the other hand, crosslink density and modulus of elasticity decreased with increasing shellac ratio. Shellac has a large structure with hydrogen bonding between the carbonyl group and hydroxyl group in their structure so it can interrupt the mixing of shellac and zinc oxide. Consequently, the combination of stearic acid/shellac with zinc oxide (ZnO) slows down the action of the sulfur in the curing process. Compatibility of other inorganic and organic substances including the rubber molecules in the crosslinking system slowly occurred so shellac could act as an inhibitor in the curing process. However, despite this delay, the compatibility of organic and inorganic substances together with rubber molecules in the cross-linking system remained, although at a slower rate.
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