Abstract

Natural rubber (NR)-barium ferrite (BaF) composites (RFCs) have been prepared. Structural features of the composites were characterized by Infrared spectroscopy and scanning electron microscope (SEM). Differential scanning calorimetry (DSC) analysis showed that there is small variation of glass transition temperature (≈ –1℃). The activation energy of glass transition was calculated by Kissinger method and has values between (53-110 kJ/mol). Thermodynamic parameters such as activated entropy, enthalpy and Gibbs free energy were calculated for glass transition also. Thermogravimetric analysis TG and its derivative DTG showed one stage thermal decomposition between 300℃-400℃ with weight loss between (19.47%-52.13%). Increasing barium ferrite loading will increase the thermal stability of natural rubber. The kinetic parameters such as activation energy, entropy, enthalpy and Gibbs free energy for composites in the decomposition region were calculated and analyzed using Coats-Redfern technique.

Keywords

Natural Rubber; Barium Ferrite; TG; Thermal Stability

Share and Cite:

1. Introduction

Natural Rubber (NR) has long been considered as an excellent general purpose polymer with wide-ranging industrial applications. Also, its unique combination of properties has made it an elastomer of choice for many of the sophisticated engineering applications [1]. However, one of the limitations of NR is its low value of hightemperature stability. Quite often, the additives, such as plasticizers, fillers, curatives, flame-retardants, etc., used for compounding, affect the thermal and thermo-oxidative stability of the base polymer, good information about which may be obtained from thermal analysis methods such as TGA, DSC. Hard ferrite or ceramic permanent magnets are considered to be an important and sophisticated class of engineering materials, which are used extensively in various applications. Hexaferrite magnets have found acceptance in many electronic products, as a result of their superior cost efficiency, large corecivity, and specific magnetic saturation associated with their high magnetic and chemical stability [2,3]. The advantages of polymer bonded magnets over their metallic and ceramic counterparts include low weight and cost, resistance to corrosion, ease of machining and forming, and capability of high production [4]. The impregnation of magnetic fillers in the matrix imparts magnetic properties and modifies the physical properties of the matrix considerably [5]. A few researches have reported the processing and dynamical properties of polymer composites containing hexaferrite prepared by ordinary methods up to 120 phr (part per hundred part of rubber). The result indicates poor adhesion between ferrite particles and polymer, in spite of the fact that the percolation was not achieved yet for these types of composites. The maximum loading was about 120 phr [6-9].

This work forms part of a comprehensive study focusing on the fabrication of hard magnetic ferrite and rubber-ferrite composites (RFCs), and study their physical properties (curing, mechanical, magnetic, and electrical properties) as a function of ferrite content. The present manuscript is an attempt to understand the IR, thermal stability and decompositions characteristic in the case of high coercivity materials-polymer composites as a function of ferrite loading up to 200 phr.

2. Experimental Procedure

Barium ferrite powders having a coercive force of 5.2 kOe, magnetization 67 emu/gm and 45 - 200 µm particle size were prepared by a coprecipitation method according to Makled et al. [10]. After characterization they were mixed with a natural rubber ADS (air dried sheet) by various loading up to 200 phr to form rubber-ferrite composites (RFCs). The recipe used for this study is given in Table 1. The composites were prepared in a two-roll mixing mill and after homogenization they were cured and molded into thin sheets of 1 - 2.5 mm in thickness at 150˚C using a hydraulic press according to ASTM D-15. The SEM samples were prepared by fracturing the samples and polishing the surfaces under liquid nitrogen, followed by carbon coating. The IR analysis was performed using a PYE spectrophotometer over the range 200 - 1000 cm^–1. Thermal analysis was carried out using a computerized DSC and TGA, TA-50 Schimadzu Corporation, Kyoto, Japan. Measurements were carried under nitrogen atmosphere (30 ml/min).

3. Results and Discussion

3.1. SEM Characterization

Figure 1 shows the distribution of ferrite particles in rubber matrix at 200 phr. The variation of particle sizes, the broad particle distribution, and the homogeneous

Conflicts of Interest

The authors declare no conflicts of interest.

References