Structure, thermal and fracture mechanical properties of benzoxazine-modified amine-cured DGEBA epoxy resins

Abstract

Abstract. First, traditional diamine hardeners of epoxy resins (EP) were checked as potential accelerators for the benzoxazine (BOX) homopolymerization. It was established that the acceleration effect depends on both the type and amount of the diamine compounds. In the follow-up work amine-curable diglycidyl ether bisphenol A (DGEBA) type EP was modified with BOX keeping the EP/BOX ratio constant (75/25 wt.%). The amine hardeners, added in the EP in stoichiometric amounts, were of aliphatic and aromatic nature, viz. diethylenetriamine (DETA), 4,4!-diaminodiphenyl methane (DDM), and their 1/1 mixture. The thermal, viscoelastic, flexural and fracture mechanical properties of the EP/BOX hybrids were determined and compared to those of the reference EPs. Based on dynamic-mechanical thermal analysis and atomic force microscopy the formation of co-network between EP and BOX was concluded. Homopolymerized BOX was built in the network in nanoscaled inclusions and it was associated with internal antiplasticization. Incorporation of BOX improved the charring, enhanced the flexural modulus and strength, and reduced the glass transition of the parent EP. The fracture toughness and energy were not improved by hybridization with BOX.

Characterizations of polybenzoxazine modified with isomeric biphenyltetracarboxylic dianhydrides

“…Moreover, polybenzoxazine provides some characteristics such as excellent dimension stability, high heat resistance, flame retardance and low moisture absorption as well as good dielectric properties in which cannot be found in traditional phenolic resins [6,7]. Alloying of polybenzoxazine with various other resins or polymers has been reported to economically provide a novel class of resin systems with superior performance [1,4,[8][9][10][11][12][13][14][15]. However, the major shortcoming of polybenzoxazine is its relatively high rigidity.…”

Novel epoxy-benzoxazine water-based emulsions with reactive benzoxazine surfactants for coatings

“…However, as a consequence of lowered curing onset temperature, even broader exothermic peaks were observed. This indicates that during the curing process different reactions take place [8,14,15,17,19]. Figure 7 also shows that benzoxazine surfactants were completely cured already after first DSC runs, since no exothermic peak was observed in DSC thermograms of second runs.…”

“…line™ FP, Binder, Tuttlingen, Germany). The long residence time at 210°C, recommended also by group of Grishchuk [14,15,18], was selected based on FT-IR analysis to achieve complete curing of both epoxy and benzoxazine resins. Transparent brownish epoxy-polybenzoxazine thin films were obtained after curing.…”

“…The steric hindrance induced by long polyether tails prolonged the curing process to higher temperatures. The catalytic effect of amine moieties on curing processes of benzoxazines was demonstrated and published by several authors [2,10,[13][14][15]. O-dianisidine (10 wt%), with diamine structure, was used as curing agent to reduce the temperature of curing.…”

“…A promising way to achieve a higher cross-linking density is the incorporation of epoxy resins into the benzoxazine matrix [8,10,11], because the ringopening polymerization of a benzoxazine produces phenolic groups, which can react with epoxy compounds. Unfortunately, also copolymerization of benzoxazines with epoxy resins takes place at elevated temperatures [8,[10][11][12][13][14][15][16][17][18]. However, combining epoxy and benzoxazine resins seems a very perspective approach to design thermosets of enhanced properties, since also epoxy resins possess some excellent properties, such as good chemical resistance to solvents and good adhesion to many substrates [8,11,18,19].…”