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Abstract:
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Nanoscale 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 particle size
of silica was calculated to be 13 nm from the XRD results and the surface area was
found to be 295 m2/g by BET method. 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. Nanosilica was found to be
effective reinforcing filler in natural rubber compound. Filler-matrix interaction was
better for nanosilica than the commercial silica. The synthesized nanosilica was used in
place of conventional silica in HRH (hexamethylene tetramine, resorcinol and silica)
bonding system for natural rubber and styrene butadiene rubber / Nylon 6 short fiber
composites. The efficiency of HRH bonding system based on nanosilica was better.
Nanosilica was also used as reinforcing filler in rubber / Nylon 6 short fiber hybrid
composite. The cure, mechanical, ageing, thermal and dynamic mechanical properties
of nanosilica / Nylon 6 short fiber / elastomeric hybrid composites were studied in
detail. The matrices used were natural rubber (NR), nitrile rubber (NBR), styrene
butadiene rubber (SBR) and chloroprene rubber (CR). Fiber loading was varied from 0
to 30 parts per hundred rubber (phr) and silica loading was varied from 0 to 9 phr.
Hexa:Resorcinol:Silica (HRH) ratio was maintained as 2:2:1. HRH loading was
adjusted to 16% of the fiber loading. 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. Tensile strength showed a dip at 10 phr fiber loading in the case of
NR and CR while it continuously increased with fiber loading in the case of NBR and
SBR. The nanosilica improved the tensile strength, modulus and tear strength better than
the conventional silica. Abrasion resistance and hardness were also better for the nanosilica
composites. Resilience and compression set were adversely affected. Hybrid composites
showed anisotropy in mechanical properties. Retention in ageing improved with fiber
loading and was better for nanosilica-filled hybrid composites. 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 all the elastomeric composites followed a first-order reaction. Dynamic
mechanical analysis revealed that storage modulus (E’) and loss modulus (E”) increased
with nanosiica content, fiber loading and frequency for all the composites, independent of
the matrix. The highest rate of increase was registered for NBR rubber. |