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Islamabad, Pakistan

Khan M.B.,Center for Energy Systems | Bassyouni M.I.,King College | Bassyouni M.I.,Higher Technological Institute | Khan Z.M.,Center for Energy Systems
Journal of Applied Polymer Science

Variant concentrations of ceramic fibers (CerFs) were incorporated into acrylonitrile butadiene rubber (NBR) to fabricate elastomeric ablative composites for ultrahigh temperature applications. The CerFs introduction into the polymer matrix has enhanced the ablation resistance up to 59% and successfully reduced the backface temperature of the polymer composite up to 110oC during the ultrahigh temperature ablation investigation. Thermal decomposition of the polymer composites was diminished up to 10% with increasing fiber concentration in the rubber matrix. Thermal conductivity was reduced equal to 63% while thermal impedance was enhanced up to 84% with the utmost fiber incorporation into the NBR matrix. The CerFs have adversely affected the mechanical properties of NBR matrix due to their brittle/inert nature and weak interface bonding with the host matrix. Scanning electron microscopy along with the energy dispersive x-ray spectroscopy was used to examine the ablated specimens and the fiber dispersion within the host matrix. Copyright © 2013 Wiley Periodicals, Inc. Source

Bassyouni M.,King Abdulaziz University | Bassyouni M.,Higher Technological Institute | Iqbal N.,University of Punjab | Abdel-Hamid S.M.-S.,Higher Technological Institute | And 4 more authors.
Polymer Degradation and Stability

Elastomeric ablative composites for ultrahigh temperature applications were processed and characterized to elucidate the potential of short carbon fibers (SCF) to tailor the thermo-mechanical and ablation characteristics of acrylonitrile butadiene rubber (NBR) composites. SCF was dispersed within NBR using dispersion kneader and two roller mixing mill. Ablation and thermal properties versus back-face temperature elevation during oxy-acetylene flame test, linear/radial ablation rates, percent char yields, insulation index, and thermal conductivity of the fabricated ablatives were measured. Experimental results revealed that the thermo-mechanical and ablation characteristics were significantly improved with increasing SCF concentration in the presence of coupling agent. Improvement in tensile strength, hardness and reduction in elongation at break were obtained with increasing SCF to matrix ratio. The microscopic analysis of the tensile fracture and ablation specimen showed the porosity generation during ablation and uniform dispersion of the impregnated SCF in NBR. ©2014 Elsevier B.V. All rights reserved. Source

Khan M.B.,Center for Energy Systems | Rafique H.M.,University of Punjab
Polymer Engineering and Science

Pristine multiwalled carbon nanotubes (MWCNTs) along with the silane coupling agent were incorporated into ethylene propylene diene monomer (EPDM) rubber using dispersion kneader and two roller mixing mill to fabricate ablative nanocomposites used in hyperthermal environment encountered by space vehicle or rocket motor. The 1 wt% addition of MWCNTS in the rubber matrix has remarkably reduced the backface temperature elevation up to 40°C during the ablation testing of the ablatives. The linear and mass ablation resistances have been diminished up to 125% and 74%, respectively, while insulation indexes at 110°C backface temperature of the composite specimens have been elevated up to 51% with increasing the MWCNTS incorporation into the EPDM matrix. Thermal stability and heat absorbance capability of the polymer composites were progressed with increasing the filler to matrix ratio. Thermal conductivity/impedance of the ablatives have been conducted according to the ASTM E1225-99 and D5470-03, respectively to execute the effect of MWCNTs concentration on the thermal transport characteristics of the tested specimens. Tensile strength of the composite specimen was augmented up to 42% with increasing nanotubes to polymer ratio. Evenly dispersed MWCNTs in the polymer matrix, polymer pyrolysis, and voids formation in the ablated samples can be scrutinized in the scanning electron microscopy images. © 2013 Society of Plastics Engineers. Source

Khan M.B.,Center for Energy Systems
Journal of Applied Polymer Science

To enhance the ablation performance and mechanical strength of silicone rubber (SR), pristine multiwalled carbon nanotubes (MWNTs) were dispersed in the polymer matrix using dispersion kneader and two roller mixing mill. Electrical resistivity (100-300°C) was reduced with increasing filler concentration in the host matrix due to the presence and even dispersion of the nanofiller in the rubber matrix. The SR nanocomposite (1 wt % filler contents) has 28% better thermal stability and 100% improvement in the ultimate tensile strength is achieved as compared with the pristine polymer matrix counterpart. Oxy-acetylene torch was used to evaluate the ablation rates, % char yield, and backface temperature evolution at the back facet of nanoablators during the flame exposure for a specific duration. Ablation performance of the fabricated ablative nanocomposites was enhanced with increasing nanotubes concentration in the polymer matrix. Thermal stability and heat quenching ability of the SR nanocomposites were gradually augmented with increasing filler loadings in the host matrix. Porous silica char, polymer pyrolysis, char composition, and uniform dispersion of MWNTs in the rubber matrix were also analyzed using scanning electron microscopy and energy dispersive spectroscopy. Copyright © 2012 Wiley Periodicals, Inc. Source

Javaid U.,King Abdulaziz University | Javaid U.,National University of Sciences and Technology | Khan Z.M.,Institute of Space Technology | Khan M.B.,Center for Energy Systems | And 6 more authors.
Composites Part B: Engineering

In this study, the fabrication and thermo-mechanical characteristics of glass fiber/vinyl ester composite materials for 2.4 m wind turbine rotor blade with tower height of 6 m are investigated. Hand lay-up technique with matching molds was used to produce the wind rotor blades according to National Advisory Committee for Aeronautics (NACA) 4527 aerofoil profile. Bending stiffness was found to be 14.80 kN/m. Results demonstrate the manufactured composite rotors process to manufacture wind turbine blades with structural integrity. Dynamic testing was performed to verify the structural integrity of wind turbine at 400 r.p.m. In dynamic mechanical testing, the storage modulus decreases with increase in temperature. The glass transition temperature of glass fiber/vinyl ester composite was obtained at 73.4 °C based on loss modulus behavior. FT-IR analysis of cured vinyl ester (Hetron 922) showed presence of acrylol double bound confirming proper curing of vinyl ester. FT-IR analysis at temperature 25, 50 and 100 °C does not show significant change in resin chemical structure. Glass fiber/vinyl ester composites exhibit approximately 23 °C higher decomposition temperature than neat vinyl ester using thermogravimetric analyzer. Eco audit study showed that the energy and carbon emission are mainly due to use phase. It is found that materials phase has 6.1% CO2. © 2016 Elsevier Ltd. Source

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