Role of interface in optimisation of polyamide-6/Fe[formula omitted]O[formula omitted] nanocomposite properties suitable for induction heating

Abstract

Induction heating of magnetic nanoparticles (MNPs) and localised melting of the surrounding high temperature engineering polymer matrix by generating microscopic or macroscopic eddy currents during magnetisation of a polymer nanocomposite (PMC) is crucial for realising induction heating aided structural bonding. However, the polymer heating should be homogeneous and efficient to avoid local pyrolysis of the polymer matrix, which results in degraded mechanical properties, or requiring a large coil for generating a high frequency magnetic field. Increasing the interfacial area by homogeneously dispersing the MNPs in the polymer matrix provides many microscopic eddy currents to dissipate the power through magnetisation and polarisation, leading to micro eddy current induced uniform heating of the PMC. However, the application of a hydrophobic coating on MNPs to aid dispersion can perturb the generation of eddy currents and affect the crystallinity and size of the crystallites responsible for the mechanical properties. In this work, the dielectric and magnetic properties, as well as the degree/size of crystallinity of a PMC containing oleic acid (OA) (22 and 55 w/w%) and silica coated (Stöber and reverse emulsion method) Fe3O4 MNPs were measured to evaluate the effect of the interfacial coating and its chemistry. The correlation between the measured properties and dispersion state of the MNPs was established to demonstrate the comprehensive effects of interfacial coating on the PMC and this is a unique method to select a suitable PMC for induction aided structural bonding applications. The results showed that the lower amount of OA (22 w/w%) helped achieve the best dispersion to reduce the crystallinity size and increase degree of crystallinity, and to give the best candidate for achieving mechanical properties of the bonded carbon fibre reinforced polymer (CFRP). Moreover, the low concentration of OA helped achieve high polarisation for dielectric heating as well as eddy current formation due to the relatively high magnetic saturation. The silica coating proportionally reduced the magnetic response and electric polarisation of the PMC, which could affect its eddy current generation that is responsible for induction heating.