Evaluation of Suitability of Disulfide based Natural Product as a Reclaiming Agent for Ground Rubber Tyre

Abstract

Reclaimed ground rubber tyre is a solution for the shortage of raw rubber and the rise in the cost of virgin rubbers. Also, it reduces the rubber waste and hence the pollution caused by that waste. Therefore, there is a continual development of reclaiming technologies over the last few years. Ground rubber tyre (GRT) is already a vulcanized material. In the vulcanization process of rubber compounds crosslinks occur between polymer chains. Many researchers have shown that bonds between GRT and the rubber matrix are very weak because of the crosslink structure of GRT and lack of reactive sites on the GRT surface, resulting in a decrease of the mechanical properties of GRT and virgin rubber blend vulcanizates. A possible way to overcome this problem is to break the sulfur crosslinks in GRT before blending with other polymers. Therefore, work has been carried out in the past to modify GRT to enhance interfacial adhesion between the two phases. This process is called reclaiming or devulcanization. Zhang, et al., (2009) compared rubber blends containing raw GRT and rubber blends containing devulcanized GRT and have concluded that the rubber blends containing devulcanized GRT were easier to mix and exhibited much better mechanical properties than natural rubber/GRT vulcanizates. There are several physical and chemical devulcanization techniques. Physical and chemical processes normally are energy demanding or require hazardous chemicals. Tetramethylthiuram disulfide (TMTD) has been used as one of the disulphide reclaiming agents for GRT. TMTD is a synthetic and hazardous chemical. Therefore finding a natural reclaiming agent is a potentially attractive recycling and utilizing way of GRT. In this study disulfide based natural product (NP) was used as the reclaiming agent for ground rubber tyre (GRT) with the aim of replacing the hazardous reclaiming agent TMTD to formulate the tyre tread compounds.

Methodology

The current study was carried out at the Rubber Research Institute of Sri Lanka (RRISL), Ratmalana. Laboratory analysis was done at RRISL. In this study as step one, a series of samples of reclaimed GRT was produced by adding different amounts of the selected natural product and one sample was produced by adding TMTD. In the second step, rubber compounds were produced by blending the reclaimed rubber prepared using different amounts of NP and TMTD with virgin natural rubber (NR).In the third step, rubber vulcanizates were produced using the compounds prepared in step 2. Cure characteristics, physico-mechanical properties and anti-oxidant property of both rubber compounds and vulcanizates were evaluated and compared with those of the control; blend compound containing virgin NR and reclaimed rubber prepared with TMTD. Treatments adopted were 5phr (parts per hundred parts rubber) of TMTD [Control (1)], 1 phr of NP(2),3 phr of NP(3),5 phr of NP(4),7 phr of NP(5),9 phr of NP(6). The data were analyzed adopting the analysis of variance (ANOVA) using Minitab 16 software programme. Significant means of treatments were separated using the Least Significant Difference p<0.05.