INVESTIGATING THE EFFECT OF VULCANIZATION IN TREAD RUBBER APPLICATIONS Jatinder Kumar 1,a and Rupinder Singh 2,b 1. Dept. of Mechanical Engineering, ARNI University, Kathgarh-Indora, Distt- Kangra, H.P., India 2. Dept. of Production Engineering, Guru Nanak Dev Engineering College, Ludhiana, Punjab, India a Er_jatinderkumar@yahoo.com, b rupindersingh78@yahoo.com Keywords: Tread, vulcanization, retreading, strength, elongation, hardness, curing temperature. Abstract. Retreading has many potential applications in tyre manufacturing industry. There is a critical need for optimization of ‘vulcanization processes used in tread manufacturing. Not much work hitherto has been reported for optimization of efficient sulphur vulcanization process of the tread manufacturing. The present experimentation work highlights approach to macro-model strength, elongation and hardness during vulcanization of rubber. Relationship between strength, elongation, hardness and other parameter has been deduced by using Taguchi L9 orthogonal array (OA). Results indicate that the hardness, elongation and strength of tread rubber while vulcanization depends significantly on the ‘natural: synthetic rubber ratio’ (NR: SR), ‘curing time’ and ‘curing temperature’ of the rubber. Intorduction Vulcanization is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulphur or other equivalent chemical known as “curatives" [1]. These additives modify the polymer by forming cross-links between individual polymer chains. The vulcanized material is less sticky and has superior mechanical properties [5]. The un-vulcanized natural rubber is sticky, easily deforms when warm, and is brittle when cold. In this state it cannot be used to make articles with a good level of elasticity [2]. The reason for inelastic deformation of un-vulcanized rubber is due to its chemical structure: rubber is composed of long polymer chains. These chains can move independently relative to each other, which enables the material to change shape [4]. The cross linking introduced by vulcanization prevents the polymer chains from moving independently. As a result, when stress is applied the vulcanized rubber will deform, but upon release of the stress, the material will revert to its original shape. Kok [2] examined the effect of compounding ingredients on the reversion of accelerated sulphur vulcanization of NR. Accelerators which normally provide fast cures are found to cause more severe reversion than slower accelerators. MgCO3, CaCO3, silica and china clay all increase reversion but the severity depends on the accelerated system employed. Mukhopadhyay et al. [9] investigated the effect of vulcanization temperature (150°–180°C) on the structure and technical properties of NR vulcanizates with four different accelerator {2-(morpholinodithio)-benzothiazole} : sulphur ratios (A - 0.6:2.4, B-1.5:1.5; C - 2.4:0.6; D-3.0:0.0) at the respective optimum cure times. The influence of cure temperature on the chemical crosslink density was determined. Results show that elevated cure temperatures produce a network with lower crosslink density. Kuriakose and Rajendran [1] proposed the use of raw rice bran oil in the vulcanization of carbon black and silica filled systems in NR compounding in place of process oil, antioxidant and fatty acid and concluded that results are not much affecting the cure characteristics of the mixes and physical properties of the vulcanizates. Apart from the low cost of the product, it will be helpful in also saving energy during mixing. The high free fatty acid content and non-toxic nature of this non-edible natural oil could therefore be an added advantage in the rubber product manufacturing industry[11]. Ismail and Chia [3] investigated the concentration effects of multifunctional additive (MFA) and vulcanization systems on silica filled epoxidized natural rubber (ENR 25) in the concentration range 0–7.5 phr. Three vulcanization systems were used; conventional vulcanization (CV), semi-efficient vulcanization (semi-EV) and efficient vulcanization (EV). The cure time and scorch time of all vulcanization systems decrease Materials Science Forum Vol. 751 (2013) pp 1-7 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.751.1 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 1.38.17.216-14/02/13,09:14:06)