Synthesis, Characterization and Cure Kinetics of Polyaniline Modified Clay / Epoxy Nanocomposites
This research work focuses on the synthesis characterization and processing of conducting polymer coated both carbon fiber and montmorillonite clay based nano-particles to improve the mechanical, thermal, and adhesive properties of epoxy based micro and nano composites. The entire research work mainly consists of two parts.
In the first part, homogeneous and uniform coatings of polyaniline were successfully deposited onto carbon fibers by aqueous electrodeposition technique using p-toluene sulfonic acid as the electrolyte. Electrochemical deposition of aniline was carried out by cyclic voltammetry in the potential range of -0.2 V to 1.0 V vs. SCE. The electrochemical deposition parameters such as the number of cycles, scan rate (SR), initial monomer ([M]) and electrolyte concentration ([E]) were systematically varied. The amount of composite coatings on carbon fibers was dependant on the electrochemical deposition parameters. From the weight gain analysis, rate of the reactions (Rp) were calculated. As the aniline concentration was increased up to 0.35 M and electrolyte concentration up to 0.5 M, the deposition rate also increased, whereas an increase in scan rate decreased the deposition rate. The kinetic analysis showed that the rate equation for the p-toluene sulfonic acid system is Rp ? SR-1.25 [M]0.73 [E]0.95. IR spectra also show an increase in the deposition of polyaniline coatings on carbon fibers with a decrease in the scan rate and an increase in both monomer and electrolyte concentration. The ratio of two oxidation states of polyaniline namely emeraldine and pernigraniline obtained during electrodeposition can be varied by changing the electrochemical deposition parameters. SEM results show that carbon fiber surface was uniformly coated with polyaniline resulting a dense, rough and reactive surface that increases the compatibility and wettability of carbon fibers. The effect of PANi coated carbon fibers on the curing behavior of diglycidyl ether of bisphenol-A (DGEBA) epoxy prepolymer crosslinked with tri ethylene tetra amine (TETA) was analyzed by DSC. The tensile, flexural and impact tests of carbon fiber epoxy micro composites showed that PANi coated carbon fiber epoxy systems have higher modulus, toughness and mechanical strengths compared to unmodified carbon fiber epoxy composites.
In the second part of the research work, conducting polyaniline (PANi) montmorillonite (MMT) clay nanocomposites were synthesized by using in-situ polymerization. The X-Ray diffraction patterns showed that polyaniline was intercalated between clay galleries in the order of nanoscale. From the SEM micrographs, it was revealed that, in-situ polymerization of aniline took place both in and out of the clay galleries. Polyaniline surface modified clay nanoparticles were then dispersed in diglycidyl ether of bisphenol-A (DGEBA) epoxy prepolymer using high shear mixing and ultrasonication. The viscosity measurements of modified and unmodified clay dispersed in epoxy prepolymer systems showed that PANi modified clay has lower viscosity than the pristine clay that provides easiness during processing. Infrared spectroscopy data proves that reactive secondary and tertiary amine groups on the fully dispersed polyaniline modified clay platelets react with epoxy resin resulting a strong chemical and physical interaction between nanoparticles and polymeric matrix. The effect of PANi surface modified nano particles on the curing reaction and kinetics of epoxy with tri-ethylene tetra amine (TETA) was analyzed by using DSC and explained by modified Avrami equation. The X-Ray diffraction pattern of fully cured 5% (w/w) PANi-MMT clay epoxy nanocomposites showed exfoliation behavior. Thermal analysis showed that for 5% (w/w) PANi-MMT filled epoxy nanocomposites has higher thermal stability than both fully cured pristine epoxy and 5% (w/w) clay epoxy nanocomposite. With the addition and exfoliation of 5% (w/w) PANi modified clay an increase of 8 ?C in glass transition temperature was observed with respect to pristine epoxy. Thermal analysis also showed that polyaniline on the surface of nanoparticles improves crosslinking reaction by reducing the curing time and helping the reaction to occur at lower temperatures. Mechanical testing results for 5% (w/w) polyaniline clay epoxy nanocomposites showed 30 to 35% increase in the tensile strength compared to the pristine epoxy. This enhancement of the tensile strength is ascribed to the resistance exerted by the clay itself as well as the aspect ratio of the clay layers and the partial exfoliation and/or fully intercalation of clay galleries. The degree of intercalation of the clay platelets in the epoxy matrix is proportional to an increase in the flexural strengths. In-situ polymerization of aniline within the clay galleries causes a more homogeneous exfoliation of the clay in the epoxy matrix.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:polyaniline montmorillonite clay epoxy nanocomposite curing kinetics conducting polymer
Date of Publication:01/01/2008