This work seeks to answer the question whether or not the presence of acid functional groups accelerate epoxy-amine curing reaction. Epoxy/Fe3O4 nanocomposite was considered as a case, where discussions are based on chemistry, mechanism behind curing reactions and fracture behavior influenced by acid assistance to crosslinking. Fe3O4 magnetic nanoparticles (MNPs) with nanosilica decorative layer (B-MNP) were synthesized and subsequently functionalized with 2-acrylamido-2-methylpropanesulfonic acid (AMPS-MNP), then characetrized for chemical bonding by FTIR spectroscopy. The grafting ratio of ca. 14% was calculated for AMPS-MNP by comparing TGA curves of B-MNP and AMPS-MNP. Epoxy nanocomposites containing B-MNP and AMPS-MNP were then prepared and their potential for epoxy ring opening was compared via nonisothermal DSC analyses at different heating rates. Calorimetric analyses demonstrated that addition of B-MNP to epoxy/amine system increases curing enthalpy from 499 to 532 J/g. By contrast, although curing level was not improved in the presence of AMPS-MNP, curing rate was enhanced remarkably at low heating rates, suggesting strong preference of epoxy to cure with sulfonic acid functional groups rather than amine curing agent, which was chemically and mechanistically explained on account of prematured gelation as well as possible competitive reactions caused by AMPS acid: (i) Chain-growth homopolymerization of epoxide, (ii) Intensified step-growth epoxide ring-opening with amine; and (iii) Reaction of AMPS with amine groups of curing agent that possibly deactivated hardener. Fracture behavior of the blank epoxy, epoxy/B-MNP and epoxy/AMPS-MNP were analyzed using SEM micrographs for interfacial interaction demostration.
Acid-aided epoxy-amine curing reaction as reflected in epoxy/Fe3O4 nanocomposites: Chemistry, mechanism, and fracture behavior
Puglia D.;
2018
Abstract
This work seeks to answer the question whether or not the presence of acid functional groups accelerate epoxy-amine curing reaction. Epoxy/Fe3O4 nanocomposite was considered as a case, where discussions are based on chemistry, mechanism behind curing reactions and fracture behavior influenced by acid assistance to crosslinking. Fe3O4 magnetic nanoparticles (MNPs) with nanosilica decorative layer (B-MNP) were synthesized and subsequently functionalized with 2-acrylamido-2-methylpropanesulfonic acid (AMPS-MNP), then characetrized for chemical bonding by FTIR spectroscopy. The grafting ratio of ca. 14% was calculated for AMPS-MNP by comparing TGA curves of B-MNP and AMPS-MNP. Epoxy nanocomposites containing B-MNP and AMPS-MNP were then prepared and their potential for epoxy ring opening was compared via nonisothermal DSC analyses at different heating rates. Calorimetric analyses demonstrated that addition of B-MNP to epoxy/amine system increases curing enthalpy from 499 to 532 J/g. By contrast, although curing level was not improved in the presence of AMPS-MNP, curing rate was enhanced remarkably at low heating rates, suggesting strong preference of epoxy to cure with sulfonic acid functional groups rather than amine curing agent, which was chemically and mechanistically explained on account of prematured gelation as well as possible competitive reactions caused by AMPS acid: (i) Chain-growth homopolymerization of epoxide, (ii) Intensified step-growth epoxide ring-opening with amine; and (iii) Reaction of AMPS with amine groups of curing agent that possibly deactivated hardener. Fracture behavior of the blank epoxy, epoxy/B-MNP and epoxy/AMPS-MNP were analyzed using SEM micrographs for interfacial interaction demostration.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
