Abstract
Surface modification of nanoparticles with functional molecules has become a routine method to compensate for diffusion-controlled crosslinking of thermoset polymer composites at late stages of crosslinking, while bulk modification has not carefully been discussed. In this work, a highly-crosslinked model polymer nanocomposite based on epoxy and surface-bulk functionalized magnetic nanoparticles (MNPs) was developed. MNPs were synthesized electrochemically, and then polyethylene glycol (PEG) surface-functionalized (PEG-MNPs) and PEG-functionalized cobalt-doped (Co-PEG-MNPs) particles were developed and used in nanocomposite preparation. Various analyses including field-emission scanning electron microscopy, Fourier-transform infrared spectrophotometry (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM) were employed in characterization of surface and bulk of PEG-MNPs and Co-PEG-MNPs. Epoxy nanocomposites including the aforementioned MNPs were prepared and analyzed by nonisothermal differential scanning calorimetry (DSC) to study their curing potential in epoxy/amine system. Analyses based on Cure Index revealed that incorporation of 0.1 wt.% of Co-PEG-MNPs into epoxy led to Excellent cure at all heating rates, which uncovered the assistance of bulk modification of nanoparticles to the crosslinking of model epoxy nanocomposites. Isoconversional methods revealed higher activation energy for the completely crosslinked epoxy/Co-PEG-MNPs nanocomposite compared to the neat epoxy. The kinetic model based on isoconversional methods was verified by the experimental rate of cure reaction.
Highlights
Enhancement of properties of thermoset resins via surface modification of nanoparticles has been practiced over the years [1,2,3]
Poor cure state is obtained in the case of epoxy containing polyvinyl chloride (PVC) functionalized Co-doped magnetic nanoparticles (MNPs) [30]
The long arms of Polyethylene glycol (PEG) on the surface of MNPs diffuse through the crosslinked networks of epoxy at later stages of cure and react with the remainder of epoxide rings, which results in accelerating the curing when gelation is dominant
Summary
Enhancement of properties of thermoset resins via surface modification of nanoparticles has been practiced over the years [1,2,3]. A larger curing widow is the result of nanoparticle incorporation into the thermoset resins, but modification of nanoparticle surface introduced as the solution has hindered or caused incomplete crosslinking [4,5,6]. Surface functionalization of Co-doped MNPs with different molecules posed different effects on the cure state of epoxy. Poor cure state is obtained in the case of epoxy containing polyvinyl chloride (PVC) functionalized Co-doped MNPs [30]. The effect of both bulk and surface modifications of nanoparticles to cure behavior and kinetics of a model nanocomposite based on epoxy and MNPs was studied.
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