Surface Modification of Waste Tire by Grafting with Styrene and Maleic Anhydride

Yassin A. Aggour, Ayed S. Al-Shihri, Mohamed R. Bazzt

Chemistry Department, College of Science, King Khalid University, Abha Kingdom of Saudi Arabia.

DOI: 10.4236/ojpchem.2012.22009                

Abstract

Waste tire powder, as waste rubber WR was subjected to grafting with styrene (St) and maleic anhydride (MA). Hydrogen peroxide H2O2 was used to initiate the free radical copolymerization of St onto WR. A thermal initiation was used in case of grafting of MA onto WR. Effect of initiator and monomer concentrations together with the influence of reaction temperature and reaction time were investigated. The grafting was estimated by weight, and the grafted copolymers were characterized by FT/IR, DSC and SEM to prove the grafting. It has found that the grafting increases with increase monomer and initiator concentrations. The increase in the reaction temperature and time also causes increasing levels of the grafted St and MA.

Keywords

Waste Rubber; Grafted Copolymerization; Styrene; Maleic Anhydride

1. Introduction

Vulcanized waste rubber especially the scrap tires, cause several environmental problems. Recycling of waste rubber by grafting or blending with polymeric material has become an important in last decades. Surface modification of ground waste tire powder by chlorination and amination reactions, and by photo grafting using UV energy, have been studied [1-3]. Recently authors are modified the surface of rubber crumb with ozone [4], the enhancement of mechanical properties by blending of polypropylene with ground waste rubber powder were done [5]. Also the scrap tires are used as adsorbents for adsorption of organic and inorganic solutes [6]. Grafting copolymerization methods are increasing employed, because of permanent modification effects [7,8]. Styrene is widely used monomer for grafting reaction, due to high reactivity of benzene ring. Therefore, many efforts have been devoted to investigate the grafting of styrene onto various substrates [9,10]. Surface graft polymerization is important because it can provide materials with tailored properties for practical application. The ground tire rubber particles can be modified by grafting with styrene and acrylate [11]. Zhang et al., show that the grafted styrene onto waste rubber powder form core-shell structure [12]. The main advantages of polystyrene are its transparency, high stiffness, excellent process ability and good dielectric properties. Pukkata et al. [13], found that graft polymerization depend not only on the number of active site generated on rubber particles but also on feed of styrene.

Modification of different kinds of rubber using maleic anhydride (MA) is useful to enhance compatibility of immiscible blends as well as improving interfacial adhesion in polymeric composites [14]. Maleic anhydride was successfully photo grafted onto low density polyethylene film, and the surface hydrophilic properties of the grafted films were improved [15,16]. The grafting of maleic anhydride onto natural rubber, was generally carried out in the molten state [17-19]. The initiation system used in the grafting was peroxide initiator [20], or the shearing action [16-18] of the materials in an internal mixer at high temperature. Very limited data on preparation of MA grafted natural rubber in the solution state [21]. Different techniques have been reported to know the MA content grafted onto rubber, such as titration of acid group, gravimetry, infrared spectroscopy and so on [22].

In this work, powdered waste tires (as waste rubber), were used as a polymer backbone for the grafting reaction with styrene and maleic anhydride.

The effect of monomers (St or MA), initiator concentration (H₂O₂) (in case of St) as well as the reaction time and reaction temperature was studied. The surface chemistry of untreated and treated waste rubber (WR) was characterized by FT/IR spectroscopy, DSC thermal analysis and by scanning electron microscope (SEM).

2. Experimental

2.1. Materials

The ground scrap tires with an average particle size 0.2 - 0.4 mm was prepared from waste tires SBR (styrenebutadiene rubber), USA, which contain about 60% SBR and 40% various additives. Styrene and maleic anhydride (Aldrich) are used without further purification. H₂O₂, fuming H₂SO₄ (Fluke). The other chemical solvents and reagents used are of analytical pure grade.

2.2. Surface Grafting Process

The appropriate quantities of WR and St were added in a special designed steel reactor. The requisite amount of H₂O₂ (initiator) were added and the reactor closed tightly at the required temperature for certain demand time. After the reaction completed, reactor is cooled and opened carefully, then the polymerization mixture was poured into acetone and leaved for 24 h. Washing of grafted polymer carried using chlorobenzene, followed by drying at 40˚C for two days to constant weight.

The above procedure was used for grafting of MA onto WR without using chemical initiator, only by thermal initiation. Sulfonation of WR and WR-g-St was carried using fuming conc. H₂SO₄ at 80˚C for 8 h. All treated waste rubber material was dried in an oven at 40˚C for 24 h prior to further use.

2.3. Determination of Grafting Yields

Grafting yields were characterized by the following parameters:

Grafting percentage: Gp% = (A – B/B) × 100 Weight conversion: Wc% = (A ÷ B) × 100 where A and B are the weights of the grafted product and WR respectively.

2.4. Characterization Methods

FT/IR spectra were recorded using JASCO FT/IR 460 plus spectrophotometer. Scanning electron microscope (SEM) 6360 (LA) were used to investigate the microstructure of the polymers. Thermal date was obtained by using Shimadzu DSC-50 instrument.

3. Results and Discussion

The grafting of St or MA onto WR was performed at various conditions to get the most suitable conditions for grafting. The variables studied were temperature, time, and the amounts of monomers and initiator.

3.1. Effect of the Reaction Temperature

The graft copolymerization of St onto WR was carried out at four different temperatures ranging from 75˚C to 150˚C. The initiator and WR concentration were 0.5 and 0.25 g/ml respectively, for three days. In Table 1, we see that at higher temperature up to 125˚C, higher level of grafted St and Gp% and Wc% increases. These are attributed to high temperature lead to dissociation of H₂O₂, and the free radicals increased on the WR chains leading to improve the grafting. Also at such temperature the mobility of WR chains will improved, which enhance the reaction process. Higher temperature than 125˚C cause the grafting decreased, which could be due to degradation of the grafted polymer [23,24].

Table 2 shows the effect of temperature on the grafting of MA onto WR, at temperature ranged from 130 to 250˚C without initiator, at time 5 h and concentrations of MA and WR were 0.3 and 0.25 g. Again as temperature increase the mobility of WR chains increase, leading to reach of MA onto active sites of WR and grafting increase. However, at elevated temperature cause decompose of grafted polymer, resulting Gp% and Wc% declined.

Conflicts of Interest

The authors declare no conflicts of interest.

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