Search

Introduction: Short fibers can be incorporated directly into the rubber compound along with other additives, the resulting composites are amenable to the standard rubber processing steps of extrusion, calendering and the various type of molding operations such as compression, injection and transfer molding (1). Properties of short fiber elastomer composite critically depend upon the interfacial bonding between fiber and the matrix (2-6) The role of silica is to improve wetting of the fiber surface (7-10). As small particles have higher surface area, nanosilica can be more effective in improving wettability of the fibers. Sreeja et al. studied the cure characteristics and mechanical properties of natural rubber / short Nylon 6 fiber composites (11). The reinforcement of rubbers using particulate fillers such as carbon black or precipitated silica has also been studied at length (12-15). Murtyet al. (16) also reported the effect of particulate fillers on the processing characteristics and physical properties of jute fiber reinforced natural rubber composites. In all these studies they have used conventional precipitated silica with particle size in microns (17-21). As small particles have higher surface area, nanosilica can be more effective in improving the properties of the hybrid composites. Methods: Nano silica was synthesized by precipitation method using sodium silicate and dilute hydrochloric acid under controlled conditions. The synthesized silica was characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), BET adsorption and X-Ray Diffraction (XRD). The performance of this synthesized nanosilica as a reinforcing filler in natural rubber (NR) compound was investigated. The commercial silica was used as the reference material. A new hybrid rubber composite prepared by the utilizing short Nylon fibers which is a waste product from fiber industries. These composites combine the rigidity of the fiber and the elasticity of the rubbers. The fiber can be incorporated as one of the compounding ingredients during the mixing process. The cure, mechanical, ageing, thermal and dynamic mechanical properties of n.anosilica / Nylon 6 short fiber / Natural Rubber hybrid composites were studied. Short nylon fiber content varies from 0,10, 20 & 30 phr and nanosilica content varies 3,6, &9 phr for the compounds A,B,C,D respectively and E for commercial silica.Natural rubber-100 phr, Zinc oxide-5 phr, Stearic acid-2 phr, N-(1,3- dimethylbutyl)N’-phenyl-p-phenylenediamine) -1 phr, CBS-0.6 phr, TMTD- 0.2 phr and sulphur-2.5 phr were common to all mixes. Results & Discussions: The minimum torque increases with fiber loading and nanosilica content for all the mixes, indicating that the processability becomes more energy intensive by the introduction of fiber and silica. Scorch time increases with silica content and decreases with fiber loading for all the mixes. The delayed start of cure reaction in the presence of silica may be attributed to the possible interaction of the silica with the accelerators, making it unavailable for cure reaction. Cure time increases with fiber content and silica loading for all the mixes This may be due to the interaction of silica with the accelerators. Cure rate increases with fiber loading and decreases with silica content. Increase in cure rate with fiber content is due to the accelerating effect of nylon fiber on the cure reaction. Decrease in cure rate with silica content may be due to the interaction of silica with the accelerators. The differential torque is a measure of the extent of the cross link formation and the filler–matrix interaction. The higher values for the nanosilica compounds indicate that the matrix is more restrained. The tensile strength increases with fiber content with an initial minor drop at 10 phr fiber loading. This drop may be due to the dilution effect of the fibers at lower loadings (22, 23). At higher fiber loadings, however, the reinforcing effect takes over, resulting in an improved ultimate strength. At any fiber content the tensile strength is higher for the nanosilica filled samples. This may be attributed to better chances of interaction between the fiber and the matrix through silica surface. Silica is also known to improve the wetting of short fibers in natural rubber matrix (22). There is a drastic fall in the abrasion loss with increasing fiber loading. A stiffer matrix has lower abrasion loss. In this case the presence of strong interfacial adhesion between the fiber and the matrix renders the matrix stiffer and lowers the abrasion loss. The nanosilica also improved the thermal stability of the hybrid composite better than the commercial silica. All the composites underwent two-step thermal degradation. Kinetic studies showed that the degradation of composites followed a first-order reaction. Conclusions: Nanosilica was found to be effective reinforcing filler in natural rubber compound. Filler-matrix interaction was better for nanosilica than the commercial silica. Minimum torque, maximum torque and cure time increased with silica loading. Cure rate increased with fiber loading and decreased with silica content. The hybrid composites showed improved mechanical properties in the presence of nanosilica. Hybrid composites showed anisotropy in mechanical properties. The nanosilica also improved the thermal stability of the hybrid composite better than the commercial silica. All the composites underwent two-step thermal degradation. Kinetic studies showed that the degradation of composites followed a first-order reaction. Key words: NanoSilica, Short fiber, hybrid Composite, Natural rubber References De S.K., White J.R. 1996, Short fiber- polymer composite, Woodhead Publishing Ltd. Rajeev R. S., Bhowmick A. K., De S. K., Bandyopadhyay S., J. Appl. Polym. Sci., 2003, 90, 544. Suhara F., Kutty S. K. N. , Nando G. B., Polym. Plast. Technol. Eng., 1998, 37, 241. Yu. Yang Chunxiang., Lu.Xiaolei, SuXinkui Wang, J. Mater. Sci., 2007, 42, 6347. Sreeja T. D., Kutty S. K. N., Polym. Plast. Technol. Eng., 2002, 41, 77. Seema A., Kutty, S. K. N., Polym. Plast. Technol. Eng., 2005, 44, 1139. DunnomD.D., Hi-Sil Bulletin (PPG Ind. Inc.), 1967, No.35. Derringer G. C., J. Elastoplast, 1999, 3, 230. Murty V. M., De S. K., Polym. Eng., 1984, Rev. 4, 313. Ismail M. N., Ghoneim A. M., Polym. Plast. Technol. Eng.1999, 38, 78. Sreeja T.D., Kutty S.K.N., J.Elast.Plast., 2001, 33, 225. Guth E., Gold O., Phy., Review, 1938, 53, 322. Wanger M. P., Rubber Chem. Technol.,1976, 49, 703. Waddel W. H., Evans L. R., Rubber Chem. Technol., 1996, 69, 377. Neogi C., Basu S. P., Bhowmick A. K., J. Mater. Sci., 1990, 25, 3524. Murty V.M., De S.K., J.Appl. Polym. Sci. 1982, 27, 4611. Rajeev R. S., Bhowmick A. K., De S. K., Bandyopadhyay S., J. Appl. Polym. Sci., 2003, 90, 544. Derringer G. C., J. Elastoplast 1999, 3, 230. Rajeev R. S.; De S. K., Bhowmick A. K., J. Mater. Sci. 2001, 36, 2621. Ismail M. N., Ghoneim A. M., Polym. Plast. Technol. Eng. 1999, 38, 78. GeethammaV. G., Mathew K. T., Lakshminarayanan R., Sabu Thomas, Polymer 1998, 39, 1483. Murty V.M., De S.K. RubberChem.Technol. 1982, 55, 287. Sreeja T. D., Kutty S. K. N., Polym. Plast. Technol. Eng., 2003, 42, 239. &nbsp