Improving Thermo-mechanical Properties of Styrene Butadiene Rubber Nanocomposites Using Eggshell Bio-filler

Mohammad Reza Saeb Polymer Engineering Department

Islamic Azad University of Mahshahr Khoozestan, Iran

E-mail: mrsaeb2008@gmail.com

Raha Sarami Polymer Group, Technical Faculty

Tarbiat Modares University Tehran, Iran

E-mail: r_sarami1980@yahoo.com

Hadi Ramezani-Dakhel Polymer Engineering Department

Amirkabir University of Technology Tehran, Iran

E-mail: hadi.ramezani@gmail.com

Abstract— In this work, styrene butadiene rubber (SBR) nanocomposites were produced at three (5, 10, 15 phr) different levels of loading by using after hatching eggshells (AHES) as bio-fillers and their thermo-mechanical properties were well compared with those prepared by calcium carbonate (CA) nanofillers. AHES fillers were first surface modified by stearic acid and consequently were used while CA nanofillers were coated by provider. Tensile strength and elongation at break data showed considerable improvement through employing AHES nanofillers. In addition, thermogravimetric analysis onto produced samples showed higher thermal stability of samples which were fed with AHES at 5 phr loading than that of CA nanofillers and similar thermal stability of nanocomposites were obtained when 10 and 15 phr of both kinds of nanofillers were used separately.

Keywords-eggshell biofiller; calcium carbonate; SBR nanocomposites; thermo-mechanical properties;

I. INTRODUCTION

Styrene butadiene rubber (SBR) is extensively used in elastomeric compounds toward industrial applications. Regardless of the organic nature of an elastomer (polar or nonpolar), using this materials without reinforcing agents cannot be justifiable. Among different types of inorganic fillers, calcium carbonate (CA) is customary applied in almost polymeric compounds due to its abounding and also process ability at high level of loading in incorporation stage of mixing [1-6]. There are some approaches on polymer composites by employing the CA nanofillers in SBR nanocomposites [1, 6]. Some studies have shown that, employing the surface modified fillers reduces the surface energy at filler-polymer interface and consequently lowers the probability of agglomerates formation [7]. The modification procedure which is conducted by using stearic acid caused enhancing the adhesion properties toward

polymer-filler interaction [6, 7]. Nevertheless, nano size CA has been partially employed as reinforcing agent in SBR compounds, the resulting materials showed superior thermal and mechanical properties [6]. It must be considered that, the shape, particle size, aggregate size, surface energy and the matrix properties have showed effective aspects [7]. Mishra et al. [6] studied the effect of nano-sized CA on the SBR matrix. They found both thermal and mechanical properties can be improved when the filler size reduced from 21 to 15 and then 9 nm, respectively. The results of our previous studies [1, 8 and 9] showed that using eggshell biofiller can improve some mechanical properties compared to micron-sized CA. Among three types of these bio-fillers (after hatching, before hatching and boiled eggshells), the after hatching eggshell (AHES) showed better properties than that of another two types. Also, we found that increasing ultimate properties, while using eggshell bio-fillers, can be attributed to porous nature of these materials, which caused enhancing surface area contribution toward interface adhesion.

II. STATE OF THE ART

To reduce environmental contaminations, it is absolutely logical to use waste materials in industrial processes. Although there are some applied attempts based on polymeric materials, to our knowledge, employing the eggshell bio-fillers in elastomeric compounds firstly advised through our present attempts [1, 8, and 9]. As the micron size fillers showed improving compared to CA fillers, we were interested to compare nano size CA and AHES fillers in this research. Ultimate mechanical and thermal properties of vulcanized SBR showed peculiar results which are challenged in the present paper. The surface modification of nano size eggshell fillers was conducted by using stearic acid for the first time as well.

2010 Fourth International Conference on Quantum, Nano and Micro Technologies

978-0-7695-3952-2/10 $26.00 © 2010 IEEE

DOI 10.1109/ICQNM.2010.9

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Figure 1. SEM micrographs of modified (a) CA and (b) AHES fillers.

III. EXPERIMENTAL

A. Materials

SBR 1502 with mooney viscosity of 53 was purchased from Bandar Imam local company. Sulfur, paraffin, stearic acid, zinc oxide (ZnO) and TMTD were obtained from Iranian suppliers and MBTS was purchased from MeyorsChemical Co., Ltd. The nano size precipitated calcium carbonate (NPCCA-201) was obtained from SHANDONG HAIZE NANOMATERIALS Co., Ltd. The provider declared that it was coated with stearic acid to increase dispersion and compatibility toward polymeric matrices. The calcium carbonate had cubic shape with an average primary size of about 50 nm.

After hatching eggshell (AHES) was obtained from local companies. In order to prepare homogeneous fine sized particles for incorporating stage, the following procedure was conducted: 1) Eggshell was washed and dried. 2) Triturated using a planetary mill for 6 h. 3) Dried over night at 80°C. The particle size and geometrical shape of CA and AHES are compared in Figure 1. The mean particle size and specific surface area of both nano size fillers are also compared in Table 1 as well.

Table 1. Comparison between mean particle size and specific surface areas of the used fillers.

Filler type Mean particle size(nm) BET area(m2/g)

CA 50 24.51 AHES 349 8.50

B. Sample Preparation

The eggshell particles were surface modified by stearic acid, so that 8 wt% of powdered stearic acid was dissolved in toluene and then AHES powder was added to the solution and stirred at room temperature over night. The resulting product were washed, filtered and dried at 80 C over night.

Based on 100 phr of SBR elastomer, 6 formulations prepared with different kinds of fillers (CA and AHES) at three different (5, 10 and 15 phr) loading level. It must be noted that, A/B/C formulation is consisted of "A" type of elastomer, "B" type of filler and "C" phr content of the used filler. TMTD, stearic acid and paraffin were added to each formulation at constant levels of 1 phr. Also, zinc oxide, MBTS and Sulfur were exerted at constant content of 5, 0.75 and 1.75 phr onto every compound, respectively. A laboratory two roll mill was used for incorporating elastomers. Two millimeter sheets were formed by using a hydraulic press at 160° and 70 bar according to results obtained from rheometric test.

Elongation at break and tensile strength tests were carried out onto produced samples using 20 KN Zwick apparatus in accordance with ASTM D1412.

In order to study the filler-matrix interaction in SBR nanocomposites, dispersion homogeneity was studied by scanning electron microscopy (SEM) technique. Therefore, the fracture surfaces of specimens were detected by using a Philips XL30 scanning electron microscope after gold sputtering. The thermal stability of the samples was measured by means of thermogravimetrical analysis (TGA) with a TGA-50 Shimadzu TG by recording the weight loss as a function of temperature. Each sample was heated from 30 to 600°C at a scanning rate of 10°C/min in the presence of nitrogen atmosphere.

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Figure 3. SEM micrographs of cross-sectional area of SBR-based compounds: (a) SBR/CA/5 (b) SBR/AHES/5 (c) SBR/CA/10 (d) SBR/AHES/10.

IV. RESULTS AND DISSCUSSION

As it's known, the ultimate properties of a nanocomposite are influenced by the nature of the matrix and the filler type and content [1, 2, 8 and 9]. Fig 2 shows the tensile strength and elongation at break of produced samples versus filler content simultaneously.

Figure 2. Tensile strength (CA: , AHES: ) and elongation at break

(CA: , AHES: ) of SBR based compounds at three different filler content .

As it can be seen, enhancing the mechanical properties is remarkable, while using AHES nanofillers, whereat the degree of improvement is more appreciable at 5 phr content. In order to study the interfacial adhesion, the scanning electron micrographs at 5 and 10 phr content are compared for both kinds of fillers, as illustrated in Fig 3. It must be

noted that considering relative similar trend (see Fig 2), the comparison at 15 phr content have not been detected. By comparing these micrographs at 5 phr content, it can be realized that higher porosity of AHES caused enhancing mechanical properties. However, by increasing the filler content, the higher surface area of CA nanofillers overcame the porosity contribution of AHES biofillers at the same filler content and a similar trend was observed. In the other words, by increasing the filler content from 5 to 10 and 15 phr, the role of filler size distribution would be more pronounceable while at lower contents (5 phr), the effect of surface roughness (porosity) was predominant.

Table 2. Thermal stability factors of SBR based nanocomposites obtained from TGA.

Sample (IDT) (Tmax) Char content at 590°C (%)

SBR/CA/5 423.38 439.48 17.54

SBR/CA/10 424.39 441.98 19.38

SBR/CA/15 423.27 442.94 21.68

SBR/AHES/5 425.34 442.74 16.95

SBR/AHES/10 422.51 439.76 19.97

SBR/AHES/15 424.88 440.48 23.47

The thermal stability behavior of the cured samples was additionally compared in table 2. The stability parameters, including the initial decomposing temperature (IDT), the temperature at the maximum rate of weight loss (Tmax), and the char content at 590 °C (%), were calculated from the

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obtained TGA thermograms. Mishra et al. [6] illustrated that reduction in nano size and increase in amount of inorganic nano filler can improve the thermal stability of SBR based compounds.

As can be seen, even at the 5 phr content, decomposition temperatures has been increased slightly. The decomposition temperature at 10 and 15 phr content was approximately the same for both CA and AHES filled compounds which can be attributed to the nature of the used fillers.

V. CONCLUSION

The surface modified nano size calcium carbonate (CA) and eggshell bio-filler (AHES) were compounded with SBR elastomer at different level of loading (5, 10, 15 phr). The evaluation of the tensile properties revealed improvement of tensile strength and elongation at break of almost all vulcanizates containing AHES compared to CA filled compounds. The remarkable trend through improving the tensile properties have been realized at 5 phr content which can be expected due to porous structure of AHES biofillers. Thermogravimetric analysis results showed an improvement at 5 phr content of AHES and approximately the same thermal stability at 10 and 15 phr compared to CA filled compounds whereat higher surface area of CA nanofillers proceeds the ultimate properties. As a state of art, eggshell nanofillers can be employed as excellent fillers in SBR compounds instead of CA traditional fillers. Finally, it is convinced by reasoning that some waste materials can be used as suitable fillers to improve ultimate properties of elastomeric compounds, herein for eggshell biofillers we tried it out.

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