Healing Efficiency of CNTs-Modified-UF Microcapsules That Provide Higher Electrical Conductivity and EMI Shielding Properties

Abstract

In this study, the effect of the addition of multi-walled carbon nanotubes (MWCNTs), at three percentages, into the urea-formaldehyde (UF) shell-wall of microcapsules on the healing efficiency is reported. The modified shell-wall created a conductive network in semi-conductive epoxies, which led to an improvement of the electromagnetic interference shielding effectiveness (EMI SE); utilizing the excellent electrical properties of the CNTs. The microcapsule’s mean diameter and shell wall were examined via scanning electron microscopy (SEM). Thermal stability was evaluated via thermogravimetric analysis (TGA). The healing efficiency was assessed in terms of fracture toughness, while the electrical properties were measured using impedance spectroscopy. The measurements of the EMI SE were carried out in the frequency range of 7–9 GHz. The derived results indicated that the incorporation of the CNTs resulted in a decrease in the mean size of the microcapsules, while the thermal stability remained unchanged. In particular, the introduction of 0.5% w/v CNTs did not affect the healing efficiency, while it increased the initial mechanical properties of the epoxy after the incorporation of the self-healing system by 27%. At the same time, it led to the formation of a conductive network, providing electrical conductivity to the epoxies. The experimental results showed that the SE increased on average 5 dB or more after introducing conductive microcapsules.

Capsule-Based Self-Healing and Self-Sensing Composites with Enhanced Mechanical and Electrical Restoration

“…The microcapsules were manufactured according to our previous studies via the in situ emulsification polymerization method [ 12 , 13 , 37 ]. Two types of microcapsules were produced for the tests, neat (with a neat healing agent) and nanomodified (with a nanomodified healing agent).…”

“…However, the use of external sensors either on top or inside the composite can degrade the structural performance since the sensors may act as damage initiation sites or internal defects [ 9 , 10 ]. In this case, many researchers have focused on the development of smart materials, and led to the production of structures with various functionalities, such as self-sensing [ 11 ], self-healing [ 12 , 13 ], electromagnetic shielding [ 13 ], energy harvesting [ 14 , 15 ], etc. Self-sensing is a valuable capability since the composite can identify internal deformations [ 16 , 17 ] and in-service damages [ 11 , 18 ], as well as additional functionalities such as curing monitoring [ 19 ] without the usage of external or embedded sensors.…”

3R Composites: Knockdown Effect Assessment and Repair Efficiency via Mechanical and NDE Testing

“…The repair efficiency is defined as the ability of a 3R composite to regain its initial mechanical properties [13][14][15][16][17][18][19] and is calculated according to Equation (4).…”

“…The prerequisites for advanced composites, apart from high specific properties, are typically high fracture toughness and good fatigue performance. On the other hand, advanced functionalities include structural health monitoring (SHM) capability [5][6][7], electromagnetic shielding [8], energy harvesting [9][10][11][12], and self-healing capability [13][14][15][16][17][18][19].…”

Optimization of CNTs and SiO₂ for thermostability and mechanical properties of PF microcapsules: used for self-healing of closed wall cracks in goaf

“…Carbon nanotubes improved the heat resistance and storage modulus of PPF-CNTs nanocomposites. Kosarli et al (2021) added multi-walled carbon nanotubes to urea-formaldehyde resin microcapsules, and studied the effect of multi-walled carbon nanotubes on the healing rate of microcapsules. The study found that the introduction of 0.5% w/v CNTs did not change the healing rate of microcapsules, but it increased the mechanical properties of epoxy resin.…”