Effect of polyfunctional monomers on properties of radiation crosslinked EPDM/waste tire dust blend

Abstract

In this study, waste tire dust is recycled as filler and blended with ethylene-propylene diene monomer (EPDM) rubber. Three different polyfuntional monomers (PFMs) are incorporated into the standard formulation and irradiated under electron beam at different doses up to maximum of 100 kGy. The combined effects of PFMs and absorbed dose on the physical properties of EPDM/WTD blend are measured and compared with sulfur crosslinked formulation. Thermogravimetric analysis showed that radiation developed better crosslinked network with higher thermal stability than sulfur crosslinked structure. The physical properties of radiation crosslinked blend are similar to the sulfur crosslinked blend. The absence of toxic chemicals/additives in radiation crosslinked blends made them an ideal candidate for many applications such as roof sealing sheets, water retention pond, playground mat, sealing profile for windows etc.

Introduction

Elastomeric materials have numerous applications in all major sectors, including industries, automotive, aerospace, defense and biomedical due to their elasticity, stretchability and durability (Allcock et al., 2003; Yasin et al., 2003). However, their large amount is used as tires for aeroplanes, trucks, cars, two-wheelers etc. During serviceable period, only 1% of the rubber part is consumed and the remaining amount of the worn out tires are discarded as such. Statistics showed that about one worn out tire is produced/year/person in the developed countries (Roy et al., 1990). The biostable nature of worn out tires needs very long time for its natural degradation which is further enhanced due to its crosslinked structure and presence of stabilizers and additives. Huge piles of tires can be seen everywhere which occupy large space and cause a major threat to environment. Therefore, it is imperative to address this issue, so different solutions have been proposed for its waste. One approach is to recycle this waste and use it as filler in different polymers (Kim and Burford, 1999, Zhang et al., 2010). The other possible solution is to use it as a source of energy, but this has many environmental concerns (Adhikari et al., 2000, Roy et al., 1990).

Now-a-days, tire recycling has become a necessity and the used tire rubber is being converted into powder. This waste tire dust (WTD) could be utilized as filler and blended with other polymeric materials to obtain a range of properties. Blends of WTD with different polymers have been prepared and in some cases the effect of ionizing radiation has also been studied (Magioli et al., 2010, Sonnier et al., 2006, Grigoryeva et al., 2005, Radhesh Kumar et al., 2002, Naskar et al., 2001, Anissakinah et al., 2011).

The use of ionizing radiation for the modification of polymers is well established and is used in many industrial processes to improve the thermal stability and mechanical properties (Chmielewski and Haji-Saeid, 2004). This process is very clean, requires less energy, permits greater processing speed and operates at ambient temperature (Tabata et al., 1991, Machi, 1995, Cleland et al., 2003b). These consequences are not possible in other process induced by thermochemical means. Electron beam (EB) crosslinking of elastomers has been commercialized since long. Generally, high radiation doses are required to get the desired properties which can be lowered by using polyfuntional monomers (PFMs). Now, PFMs are successfully used in many polymer blends and composite materials (Vijayabaskar and Bhowmick, 2005, Hung et al., 2004, Yasin et al., 2002, Lee et al., 2003, Yasin et al., 2005, Majumder and Bhowmick, 2000, Yunshu et al., 1998, Abdel-Aziz et al., 1995).

This study has been carried out on the radiation crosslinking of EPDM/WTD in the presence of PFMs. EPDM has been selected for this study due to its excellent resistance to heat, oxidation, ozone and aging properties. It has good electrical resistivity and no swelling in polar solvents such as water, acids, alkalies and alcohols (De and White, 2001). It also responds well to high filler and plasticizer loading (Karpeles and Grossi, 2001, Ver Strate, 1986). As these blends are crosslinked by radiation and do not contain toxic chemicals/additives, so these can be used safely in many applications such as roof sealing sheets, water retention pond, playground mat, sealing profile for windows etc.