Magnetocuring and Magnetorheology of Composites

Abstract

Magnetocuring of carbon and glass fibers was performed using Curie temperature tuned magnetic nanoparticles (CNP) embedded in adhesives, aka magnetoadhesive. Interestingly, these fibers were cured under alternating magnetic field (AMF) within a few minutes. In-situ heating of the magnetoadhesive were controlled by CNP loading and AMF strength. The heating of the CNP switches off above its Curie temperature, which prevents overheating. For the first time, custom made AC-magnetorheometry was employed to understand the kinetics of curing of the magnetoadhesive under AMF. The storage modulus of the magnetocured adhesive exceeded 10 MPa at shear strain of < 10%.Introduction:Magnetic field activated adhesive curing, aka magnetocuring have recently been reported[1]. Magnetocuring overcomes the limitations of available curing techniques e.g. photocuring[2], snap-curing[3], and electrocuring[4], etc, it allows the adhesive to be activated on-demand when an alternating magnetic field is applied. Carbon fiber is increasingly being used to make lighter and stronger parts in many industries including aviation, automobile, marine, sports, defence, IT, etc.[5] However, in most of the applications, these fibers need to bond with suitable thermosets/thermoplastics in order to achieve high stiffness, for which thermal curing is required. Magnetocuring of carbon and glass fibers can be applied in a range of commercial applications. The present work addresses the design and application of one-pot epoxy adhesives by the ‘modifier’ methodology for on-demand contactless curing under alternating magnetic field (AMF).Material and Methods:Curie nanoparticles (CNP) were synthesized by the hydrothermal method and functionalized using oleic acid and epoxy [1]. Functionalized CNP were mixed into commercial 1C epoxy adhesive and cured under an alternating magnetic field (AMF, 400 kHz, 140 Oe). The kinetic parameters, real-time properties of the adhesive and composite were evaluated using a custom made AC magneto-rheometry setup.Results and Conclusions:Magnetoadhesive applied carbon and glass fibers were passed through the magnetic field generated solenoid coil and cured within 5 min (Fig. 1A). This fast curing is important for in-line manufacturing of fiber based components. The magnetoadhesive property under AMF and at room temperature were studied using AC-magnetorheometry. The gelation point of the magnetoadhesive with 30wt.% CNP was achieved within 70 s of AMF exposure (Fig. 1B and 1C). On applying the magnetic field, a decrease in the loss modulus (G’) and increase in the storage modulus (G’’) was observed due to the initiation of crosslinking and composite hardening. The storage modulus of the magnetocured adhesive was observed to be >10 MPa at shear strain of < 10% (Fig. 1C). These results suggest that magnetocuring is an attractive technology for in the sports goods, automotive, aerospace and medical industries. It offers an energy efficient, remote, and wireless method of on-demand adhesion by exploiting self-regulating Curie nanoparticles (CNP). Real time magnetorheology measurements were used to determine the properties, fast gelation within 70 s was observed..Acknowledgement:Authors acknowledge the financial support from the Agency for Science, Technology and Research (A*Star) for the grant IRG17283008 “Microprocessor- based methods of composite curing. **