The grafting of an olefinic monomer like acrylonitrile (AN), methyl methacrylate (MMA), and styrene (ST) onto natural rubber (NR) was carried out to enhance the polarity of the new chemical groups on the NR backbone and, in turn, to improve the filler-rubber interaction. The grafted natural rubber (GNR) produced was compounded and then vulcanization was carried out in the presence of silica as a reinforcing filler. The physical properties and aging resistance provided by the presence of the polar functional groups of the GNR composites were investigated and compared with other rubbers such as SBR, NBR, and NR. The GNRs provided significant improvements in resistance of the composites to thermal, oil, and ozone while maintaining the mechanical properties of the rubber. Therefore, these properties can be controlled as a function of the polarity of functional groups on the NR backbone. Morphological studies confirmed a shift from ductility failure to brittle with the presence of the polar group on the rubber chains. 1. Introduction Natural rubber (NR) obtained from Hevea brasiliensis is a natural biosynthesis polymer possessing excellent characteristics such as high tensile strength due to its ability to crystallize upon stretching. However, NR is highly susceptible to attack by atmospheric oxygen and ozone, and hence, its heat and ozone resistance are very poor, mainly due to the presence of the double bonds in the main chain [1]. In addition, it does not perform well when exposed to oils and hydrocarbon solvents, as a result of its nonpolar character [2]. In general, the improved products from natural rubber (NR) have potentially wide applications as a result of reinforcing by fillers such as carbon black or silica [3, 4], as well as physical blends with other polymer particles [5, 6] or chemical modification [7], thus enabling these materials to compete with synthetic rubbers. In order to increase polarity and widen the application of natural rubber, natural rubber was modified by graft copolymerization with a polar functional monomer to produce grafted natural rubber (GNR) having good thermal, oil, and ozone resistance and high tensile strength. Several studies have been carried out on the grafting of NR with various olefinic monomers like acrylonitrile (AN), methyl methacrylate (MMA), and styrene (ST) which are capable of being polymerized to produce hard plastic materials [8–14]. The combination of high strength and oil resistance properties of GNR with a polar functional monomer is being evaluated in such applications as oil-resistant oil handling
References
[1]
C. Mei, W. Yong-Zhou, L. Guang, and W. Xiao-Ping, “Effects of different drying methods on the microstructure and thermal oxidative aging resistance of natural rubber,” Journal of Applied Polymer Science, vol. 126, no. 6, pp. 1808–1813, 2012.
[2]
V. Tanrattanakul, B. Wattanathai, A. Tiangjunya, and P. Muhamud, “In situ epoxidized natural rubber: improved oil resistance of natural rubber,” Journal of Applied Polymer Science, vol. 90, no. 1, pp. 261–269, 2003.
[3]
J. W. ten Brinke, S. C. Debnath, L. A. E. M. Reuvekamp, and J. W. M. Noordermeer, “Mechanistic aspects of the role of coupling agents in silica-rubber composites,” Composites Science and Technology, vol. 63, no. 8, pp. 1165–1174, 2003.
[4]
S.-S. Choi, K.-J. Hwang, and B.-T. Kim, “Influence of bound polymer on cure characteristics of natural rubber compounds reinforced with different types of carbon blacks,” Journal of Applied Polymer Science, vol. 98, no. 5, pp. 2282–2289, 2005.
[5]
U. N. Okwu and F. E. Okieimen, “Preparation and properties of thioglycollic acid modified epoxidised natural rubber and its blends with natural rubber,” European Polymer Journal, vol. 37, no. 11, pp. 2253–2258, 2001.
[6]
Z. Oommen, M. R. G. Nair, and S. Thomas, “Compatibilizing effect of natural rubber-g-poly(methyl methacrylate) in heterogeneous natural rubber/poly(methyl methacrylate) blends,” Polymer Engineering and Science, vol. 36, no. 1, pp. 151–160, 1996.
[7]
S. Roy, S. Bhattacharjee, and B. R. Gupta, “Hydrogenation of epoxidized natural rubber,” Journal of Applied Polymer Science, vol. 49, no. 3, pp. 375–380, 1993.
[8]
Y. Fukushima, S. Kawahara, and Y. Tanaka, “Synthesis of graft copolymers from highly deproteinised natural rubber,” Journal of Rubber Research, vol. 1, no. 1, pp. 154–165, 1998.
[9]
F. E. Okieimen and I. N. Urhoghide, “Graft copolymerization of acrylonitrile and methyl methacrylate monomer mixtures on crumb natural rubber,” Journal of Applied Polymer Science, vol. 84, no. 10, pp. 1872–1877, 2002.
[10]
G. Lu, Z.-F. Li, S.-D. Li, and J. Xie, “Blends of natural rubber latex and methyl methacrylate-grafted rubber latex,” Journal of Applied Polymer Science, vol. 85, no. 8, pp. 1736–1741, 2002.
[11]
V. George, I. J. Britto, and M. S. Sebastian, “Studies on radiation grafting of methyl methacrylate onto natural rubber for improving modulus of latex film,” Radiation Physics and Chemistry, vol. 66, no. 5, pp. 367–372, 2003.
[12]
S. H. C. Man, A. S. Hashim, and H. M. Akil, “Studies on the curing behaviour and mechanical properties of styrene/methyl methacrylate grafted deproteinized natural rubber latex,” Journal of Polymer Research, vol. 15, no. 5, pp. 357–364, 2008.
[13]
S. Kawahara, T. Kawazura, T. Sawada, and Y. Isono, “Preparation and characterization of natural rubber dispersed in nano-matrix,” Polymer, vol. 44, no. 16, pp. 4527–4531, 2003.
[14]
W. Arayapranee and G. L. Rempel, “Preparation of a natural rubber core/polymer shell in a nanomatrix by graft copolymerization,” Journal of Applied Polymer Science, vol. 110, no. 4, pp. 2475–2482, 2008.
[15]
“Historical Standard: ASTM D5289-07a Standard Test Method for Rubber Property-Vulcanization Using Rotorless Cure Meters,” ASTM D5289-07A, 2007.
[16]
“Rubber, unvulcanized—Determinations using a shearing-disc viscometer—part 1: Determination of Mooney viscosity,” ISO 289-1, 2005.
[17]
“Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers—Tension,” ASTM D412, 1998.
[18]
“Standard Test Method for Rubber—Deterioration in an Air Oven,” ASTM D573, 1994.
[19]
“Historical Standard: ASTM D471-06 Standard Test Method for Rubber Property-Effect of Liquids,” ASTM D471-06.
[20]
N. Z. Noriman and H. Ismail, “Effect of epoxidized natural rubber on thermal properties, fatigue life, and natural weathering test of styrene butadiene rubber/recycled acrylonitrile-butadiene rubber (SBR/NBRr) blends,” Journal of Applied Polymer Science, vol. 123, no. 2, pp. 779–787, 2012.
[21]
“Methods of testing vulcanized rubber—Determination of resistance to ozone cracking (static strain test),” ISO 1431/1, 1980.
[22]
S.-S. Choi, C. Nah, S. G. Lee, and C. W. Joo, “Effect of filler-filler interaction on rheological behaviour of natural rubber compounds filled with both carbon black and silica,” Polymer International, vol. 52, no. 1, pp. 23–28, 2003.
[23]
M. Arroyo, M. A. López-Manchado, J. L. Valentín, and J. Carretero, “Morphology/behaviour relationship of nanocomposites based on natural rubber/epoxidized natural rubber blends,” Composites Science and Technology, vol. 67, no. 7-8, pp. 1330–1339, 2007.
[24]
N. Sombatsompop, S. Thongsang, T. Markpin, and E. Wimolmala, “Fly ash particles and precipitated silica as fillers in rubbers—I. Untreated fillers in natural rubber and styrene-butadiene rubber compounds,” Journal of Applied Polymer Science, vol. 93, no. 5, pp. 2119–2130, 2004.
[25]
H. Ismail, S. M. Shaari, and N. Othman, “The effect of chitosan loading on the curing characteristics, mechanical and morphological properties of chitosan-filled natural rubber (NR), epoxidised natural rubber (ENR) and styrene-butadiene rubber (SBR) compounds,” Polymer Testing, vol. 30, no. 7, pp. 784–790, 2011.
[26]
R. M. B. Fernandes, L. L. Y. Visconte, and R. C. R. Nunes, “Curing characteristics and aging properties of natural rubber/epoxidized natural rubber and cellulose II,” International Journal of Polymeric Materials, vol. 60, no. 5, pp. 351–364, 2011.
[27]
S. H. El-Sabbagh and A. A. Yehia, “Detection of crosslink density by different methods for natural rubber blended with SBR and NBR,” Egyptian Journal of Solids, vol. 30, no. 2, pp. 157–173, 2007.
[28]
B. T. Poh, H. Ismail, E. H. Quah, and P. L. Chin, “Cure and mechanical properties of filled SMR L/ENR 25 and SMR L/SBR blends,” Journal of Applied Polymer Science, vol. 81, no. 1, pp. 47–52, 2001.
[29]
N. A. Darwish, A. B. Shehata, A. A. Abd El-Megeed, S. F. Halim, and A. Mounir, “Compatibilization of SBR/NBR blends using poly acrylonitrile as compatibilizer,” Polymer-Plastics Technology and Engineering, vol. 44, no. 7, pp. 1297–1306, 2005.
[30]
M. S. Sobhy, D. E. El-Nashar, and N. A. Maziad, “Cure characteristics and physicomechanical properties of calcium carbonate reinforcement rubber composites,” Egyptian Journal of Solids, vol. 26, no. 2, pp. 241–257, 2003.
[31]
S.-Y. Fu, X.-Q. Feng, B. Lauke, and Y.-W. Mai, “Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate-polymer composites,” Composites Part B, vol. 39, no. 6, pp. 933–961, 2008.
[32]
C. Sareena, M. T. Ramesan, and E. Purushothaman, “Utilization of peanut shell powder as a novel filler in natural rubber,” Journal of Applied Polymer Science, vol. 125, no. 3, pp. 2322–2334, 2012.
