Improving damping property of carbon-fiber reinforced epoxy composite through novel hybrid epoxy-polyurea interfacial reaction

Bulk Energy Transferability Linked to Critical N–H Modes of an Interfacial Nanoscale Surface Modification via Unique Isophorone Diisocyanate Amine Exchange Reaction

“…The role of aliphatic-based polyurea moieties is critical in the design of x-IEPM via epoxy surface treatment: in their reactive form, polyurea functional groups are introduced to a curing epoxy network, generating a three-part reaction of (epoxide) + (amine epoxy hardener) + (isocyanate) that produces new epoxy-urea chemical bonds. [17,30] This comprises the IEPM; see the boundary that separates epoxy from polyurea in Figure 1b. The role of epoxy is also critical, contributing to the IDA modification chemistry and serving as the structural (coupling) link between CF/E and IEPM that introduces the loss modulus property to C-IEPM.…”

“…The polyurea, produced by Versaflex, was a two-part aliphatic compound composed of (NCO)-based Part A and (NH 2 )-based Part B mixed at a 1:1 ratio (by volume), where the former is an isophorone diisocyanate derivative lacking the moisture-trapping polyol molecule common in aromatic polyurea that diminishes IEPM quality. [17] Attard [39] described the IEPM chemical structure and exchange reactions of the (-NCO) functional group with (-NH 2 ) group from epoxy, resulting in a 1,4 addition carbonyl-stable isocyanate-accepting epoxy modification, [39] shown in Figure 2. The results may be applied across multiple-scales to integrate various attributes into several largescale systems, including ballistic-resistant shields (military structures), [30] coastal bridges subject to large surge and lateral wave forces (hurricane resistance), [31] residential storm rooms (tornado resistance), [40] impact resistant and energy efficient tilt-up wall constructions (commercial warehouses), [41] moisture-resistant systems (flood control), [27] and carbon-fiber systems combine mechanical performance and reduced carbon fiber consumption to lower cost and the carbon-footprint.…”

“…Figure 12 shows that the loss modulus of pure polyurea is comparably small (17)(18)(19)(20) relative to that of pure epoxy although the storage modulus of the latter is one order of magnitude larger than that of pure polyurea. The results indicate that the elastic strain energy in an epoxy-polyurea purely physical mixture, i.e., 0-IEPM-24 (0 = no fiber), where nothing indicates the presence of chemical bonding, is largely a function of the storage modulus of epoxy.…”

“…IEPM chemical structures contain unique molecular vibrational modes, as illustrated in Figure 6, that, through the coupled IEPM and CF / E layers, provide essential damping and frac-ture toughness properties to C-IEPM and to their reinforced structures. [17,30] Using a nano-infrared instrument (Nano-IR2), Fourier-Transform Infrared Spectroscopy (FTIR) was used to identify changes in dipole moments (energy fluctuations per absorbed IR radiation) across each IEPM region of the six 0-IEPM-t c specimens, see Figure 7. Spectra were used to ascertain the various IEPM chemical structures following the reaction kinetics of (NCO) + epoxide + (NH 2 )-hardener-epoxy.…”

“…Secondarily, the IEPM region also helps to enhance epoxy matrix cross-linking and interfacial CF/E properties and increase moisture resistance. [27] Attard et al [17] and Zhou and Attard [28] altered the curing chemistry of epoxy functional agents via surface modification to improve material damping and fracture toughness in large-scale concrete girder applications. The consequent introduction of "internal damage barriers" [29] isolated microscopic damage to the concrete and CF/E structures, rendering individual cracks harmless.…”