Ike Setyorini, Ihda Novia Indrajati, and Indiah Ratna Dewi. Center for Leather, Rubber and Plastics, Ministry of Industry Republic of Indonesia

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1 INFLUENCE OF STORAGE TEMPERATURE AND TIME ON MOONEY VISCOSITY AND BOUND RUBBER FORMATION IN NATURAL RUBBER COMPOUNDS FILLED WITH CARBON BLACK AND LOCAL SILICA Ike Setyorini, Ihda Novia Indrajati, and Indiah Ratna Dewi Center for Leather, Rubber and Plastics, Ministry of Industry Republic of Indonesia Abstract Aging experiments were carried out on natural rubber compound filled with both carbon black and silica. The type of silica employed in this research was local silica. Silica loading was, 5,, 15 and phr, and carbon black was set to be fixed. The samples were subjected to thermooxidative aging at temperatures mainly at o C, 45 o C, o C, 55 o C, and o C. The samples were taken out everyday up to four days storage time to investigate Mooney viscosity and bound rubber. In this study, Mooney viscosity increases with increased storage temperature and storage time. The storage temperature at C gives an extreme effect on Mooney viscosity of uncured rubber compounds so the measurement cannot be performed. Bound rubber decreases with increased silica content, and the storage temperature and time do not significantly affect the bound rubber content. Keywords: natural rubber compound, carbon black, silica, mooney viscosity, bound rubber INTRODUCTION Rubber is a material which is used in many different industrial applications. For each application, rubber is prepared using different ingredients such as reinforcing fillers to obtain the required final. Silica and carbon black have been used as important reinforcing fillers in natural rubber compounds(ulfah et al., 15), (Rattanasom, Saowapark, & Deeprasertkul, 7). After the compounding process, rubber compounds are stored for the next process. The storage conditions of rubber compounds directly influence the characteristics of rubber compounds and their process ability. Environmental influences such as heat, low temperature, humidity and light during storage may have an essential effect on the processing and quality. Choi (2) investigated the influence of storage time and temperature on bound rubber formation in silica filled styrene-butadiene rubber compounds. Increase of the bound rubber content by storage is explained by the formation of chemical bonds between the filler and rubber through the silane (S.-S. Choi, 2). Schwatzh et.al (3) 8

2 Influence of storage temperature and time on mooney viscosity and bound rubber investigated the changes in the electrical properties of carbon black filled rubber compounds under several different aging conditions (Schwartz, Cerveny, Marzocca, Gerspacher, & Nikiel, 3). Mooney viscosity (ML 1+4) C is one of the parameters usually used as the main indication of the quality of raw rubber materials and uncured rubber compounds which depend on molecular weight, distribution, structure, non-rubber constituent, and polymer crosslink (J I Ř Í MaláČ, 11). Mooney viscosity is often correlated with bound rubber formation of raw rubber compounds. Bound rubber is the remaining fraction of elastomer that cannot be extracted by good solvents. It happens because of interaction between elastomer and renforcing fillers. In fact, there is a relationship between storage time effect on the Mooney viscosity and bound rubber(leblanc & Staelraeve, 1994). Indonesia is one of the countries that has a potential source of minerals containing silica. It is important to observe the use of local materials as filler in rubber compounds. This paper is the second publication about natural rubber compounds filled with carbon black and local silica. The first paper investigated the processability characteristics of the rubber compounds (Setyorini, Dewi, & Indrajati, 16). In the second publication, evaluation has been made of their performance after storage of the uncured compounds. The uncured compounds was observed to thermooxidize in moderate temperatures (below C). Influence of storage temperature and storage time on Mooney viscosity and bound rubber formation was investigated. Materials MATERIALS AND METHODS Rubber Sheet Smoked (RSS) was supplied by local industry in Indonesia (PTPN). Local silica was prepared by Balai Besar Keramik, Indonesia. The particle size ranged from.1 to.2 μm, density 2.65 g/cm 3 and ph Carbon blacks were grade N-3 and N-6 (Ex.OCI). Other compounding additives included polyethylene glycol (PEG ) Ex. Korea, ZnO were purchased from Bratachem, Indonesia. Antioxidant 2,2,4-Trimethyl-1,2-Dihydroquinoline (TMQ) Ex.Kemai, activator Aflux 42M, paraffinic oil was purchased from CV. Indrasari, Semarang, Indonesia, N-Cyclohexylbenzothiazole-2-Sulfenamide (CBS) Ex. Northeast and Sulfur SP-325 Ex.Miwon. 851

3 Proceedings of International Rubber Conference 17 Apparatus Two roll mill laboratory scale equipped with cooling water and Mooney Viscometer MonTech MV-. Compound Preparation and Test Materials Compound preparation was made with the composition and technique described in the first publication(setyorini et al., 16). NR and the additives were compounded using the two roll mill as described at Table 1. After compounding, the rubber compounds were soaked in water for 5 min to terminate the vulcanization. The compounds were then stored in a conditioned room for 24 h before subsequent processes. Uncured compounds were stored in the oven at temperatures of C, 45 C, C, 55 C, and C for 4 days. Samples for Mooney viscosity and bound rubber formation were taken every day. Table 1. Compounds formulation (phr) Ingredients TK TKL1 TKL2 TKL3 TKL4 RSS..... ZnO Aflux 42 M N N Local Silica Paraffinic oil TMQ PPD CBS Sulfur PEG Mooney Viscosity Testing Mooney viscosity, ML(1+4), were measured using MonTech Mooney Viscometer MV at ºC. The large rotor was applied with a speed of 2 rpm (.21 rad/sec). The temperature at upper and lower die were maintained at ±.3 ºC. Samples were prepared using a sample cutter, then placed in the lower die. The term ML (1+4) means 1-minute preheating and 4-minutes viscosity testing. 852

4 Influence of storage temperature and time on mooney viscosity and bound rubber Bound Rubber Testing Bound rubber (BR) was measured according to a technique described, using toluene solvent(leblanc & Staelraeve, 1994). Essentially the sample was cut into small pieces and immersed in the basket filled in toluene for 72 hours at room temperature. Then the basket was slowly removed from the solvent and dried until of constant weight. Weights of the samples before and after the extraction were measured and the bound rubber contents were calculated using equation 1. ( ) ( ) ( ) ( ( ) Where m a is the weight of sample before immersion (in grams), m b is the weight of sample after immersion and dry (in grams), CPD is the total of filler (in phr). Mooney Viscosity RESULTS AND DISCUSSION Figure 1 illustrates the effect of storage temperature and time of rubber compounds containing carbon black and various levels of silica filler. The figure shows that the Mooney viscosity of the compounds increases along with an increase in silica filler. The first publication showed that local silica have a narrow distribution but agglomerate (Setyorini et al., 16). Increasing silica levels cause increasing aglomeration spot that make increasing shear stress on Mooney tester. Figure 1 also shows that there is a substantial increase in the Mooney viscosity along with an increase in storage temperature and time of rubber compounds. The increase in Mooney viscosity with increasing storage temperature and time is an indication of premature cross-linking of rubber compounds (Kaewsakul, Sahakaro, Dierkes, & Noordermeer, 13). Storage temperature of rubber compounds should range between +15 and +25 o C. With higher temperatures the material may start to vulcanize prematurely. 853

5 Proceedings of International Rubber Conference 17 Figure 1. Effect of storage at different temperatures on Mooney viscosity 854

6 Influence of storage temperature and time on mooney viscosity and bound rubber In Figure 1 (a), (b), (c), (d) the measurement cannot be performed at aged C at day 2 and Figure 1(e) at aged C even at one day. It means storage temperature at C gives an extreme effect on Mooney viscosity of uncured rubber compounds. This is confirmed in Table. 2 that shows the rate of increasing Mooney viscosity increase with increase in storage temperature of rubber compounds. Table 2. Rate constant for aging of NR compounds filled with carbon black and local silica, in terms of effect on Mooney viscosity CB/silica content (phr) Aging Temperature (C) k R 2 / / / / / Bound Rubber Bound rubber measurements were carried out to estimate the interfacial layer between filler and polymers. Figure 2 shows variations of bound rubber of the rubber compounds with different local silica filler content at various storage temperatures. It show that different storage temperatures have the same effect on bound rubber content. Bound rubber content decreases along with an increase in silica filler that contradictive with increasing Mooney viscosity. 855

7 Proceedings of International Rubber Conference (a)aged at C (b) Aged at 45 C (c)aged at C (d) Aged at 55 C (e)aged at C Figure 2. Effect of storage time and temperature of rubber compounds on bound rubber 856

8 Influence of storage temperature and time on mooney viscosity and bound rubber This is due to the physical interaction of silica filler and polymer and the formation of chemical bonds between rubber and silica filler being unstable. Flocculation (aglomeration) of local silica filler in the rubber compounds cause decreasing interfacial interaction layer between silica and polymer. Silica has hydroxyl groups on the surface that cause strong filler-filler interactions. Silica filled natural rubber needs a coupling agent like a silanol group. The sulfide group of the silane reacts with the elastomer to form a crosslink between the filler and rubber (S. S. Choi, Nah, Lee, & Joo, 3). The silica flocculation can be decreased with coupling agent (Mihara, S, Datta, RN, Noordermeer, JWM, 9). Figure 2 shows that storage temperature and time do not significantly affect the bound rubber of the rubber compounds. This phenomenon is happens because there is no coupling agent like silane. Silica filled rubber compounds with coupling agent, increasing mixing dump temperature causes increasing chemically bound polymer due to a higher degree of silanization(mihara, S, Datta, RN, Noordermeer, JWM, 9). CONCLUSION Local silica and carbon black were used as filler in natural rubber compounds. Mooney viscosity increases with increasing storage temperature and storage time. Bound rubber decreases with increased silica content, and the storage temperature and time do not significantly affect the bound rubber content. Silica-filled natural rubber compounds need a coupling agent to give chemically bound filler and polymer. ACKNOWLEDGEMENT The authors gratefully acknowledge the support from Balai Besar Keramik for the local silica supply. REFERENCES Choi, S.-S. (2). Influence of Silane Coupling Agent on Properties of Filled Styrene-Butadiene Rubber Compounds. Polymer Testing, 21, Choi, S. S., Nah, C., Lee, S. G., & Joo, C. W. (3). Effect of filler-filler interaction on rheological behaviour of natural rubber compounds filled with both carbon black and silica. Polymer International, 52(1),

9 Proceedings of International Rubber Conference 17 J I Ř Í MaláČ. (11). Mooney Viscosity, Mooney Elasticity and Procesability of Raw Natural Rubber. Journal of Materials Science and Engineering with Advanced Technology, 3(1), Kaewsakul, W., Sahakaro, K., Dierkes, W. K., & Noordermeer, J. W. M. (13). Optimization of Rubber Formulation for Silica-Reinforced Natural Rubber Compounds. Rubber Chemistry and Technology, 86(2), Leblanc, J. L., & Staelraeve, A. (1994). Studying the storage maturation of freshly mixed rubber compounds and its effects on processing properties. Journal of Applied Polymer Science, 53(8), Mihara, S, Datta, RN, Noordermeer, JWM. (9). Flocculation in Silica Reinforced Rubber Compounds. Rubber Chemistry and Technology, 82(5), Rattanasom, N., Saowapark, T., & Deeprasertkul, C. (7). Reinforcement of natural rubber with silica/carbon black hybrid filler. Polymer Testing, 26(3), Schwartz, G. A., Cerveny, S., Marzocca,??ngel J., Gerspacher, M., & Nikiel, L. (3). Thermal aging of carbon black filled rubber compounds. I. Experimental evidence for bridging flocculation. Polymer, 44(23), Setyorini, I., Dewi, I. R., & Indrajati, I. N. (16). Processability Characteristic of Natural Rubber Hybrid Composites : Carbon Black-Silica Filler System, (Ml), Ulfah, I. M., Fidyaningsih, R., Rahayu, S., Fitriani, D. A., Saputra, D. A., Winarto, D. A., & Wisojodharmo, L. A. (15). Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound. Procedia Chemistry, 16,