Amine-cured epoxy networks

In addition to the fracture topography observations in the slower crack propagation regions of epoxies a number of additional observations also indicate permanent molecular flow can occur in amine-cured epoxy networks in the glassy state. 

Incorporation of monofunctional epoxy POSS into an amine-cured epoxy network increased and broadened the Tg without changing the crosslink density and enhanced the thermal properties. Additionally, it was found that the thermal and thermal-mechanical properties of resultant styrene-POSS vinylester resin nanocomposites were dependent on the percentage of POSS incorporated into the resin [171]. Over a range of POSS incorporations, the Tg of the copolymers changed very little, but the flexural modulus increased with increasing POSS content. 

Creep Behavior of Amine-Cured Epoxy Networks Effect of Stoichiometry... 

Amine light stabilizer, melamlne-acryllo copolymer degradation, 281-83 Amine-cured epoxy networks cross-link density, 166-67,177-81 structure characterization, 172-73... 

Chemical Structure. Amine-cured epoxy networks generally form exclusively from epoxide-amine addition reactions i.e.. 

The formation of networks by addition polymerization of multifunctional monomers as minor components included with the monofunctional vinyl or acrylic monomer is industrially important in applications as diverse as dental composites and UV-cured metal coatings. The chemorheology of these systems is therefore of industrial importance and the differences between these and the step-growth networks such as amine-cured epoxy resins (Section 1.2.2) need to be understood. One of the major differences recognized has been that addition polymerization results in the formation of microgel at very low extents of conversion (<10%) compared with stepwise polymerization of epoxy resins, for which the gel point occurs at a high extent of conversion (e.g. 60%) that is consistent with the... 

Macosko and Miller (1976) and Scranton and Peppas (1990) also developed a recursive statistical theory of network formation whereby polymer structures evolve through the probability of bond formation between monomer units this theory includes substitution effects of adjacent monomer groups. These statistical models have been used successfully in step-growth polymerizations of amine-cured epoxies (Dusek, 1986a) and urethanes (Dusek et al, 1990). This method enables calculation of the molar mass and mechanical properties, but appears to predict heterogeneous and chain-growth polymerization poorly. 

There are a number of models which can be used to predict the effect that absorbed diluents, in particular water, have on a cured polymeric resin. One of the most powerful of these is Group Interaction Modelling (GIM), a continuum-type model with a set of versatile input parameters based on the number and type of chemical functional groups present in the network. This allows the complex chemistty of amine-cured epoxy resins to be catered for whilst retaining the speed afforded by using a set of linked constitutive equations of state for property prediction. 

Epoxy structural adhesives which employ carboxylic polybutadiene/acrylonitrile solid and liquid (CTBN) elastomers as modifiers have increased in number and proliferated in use since their introduction in the mid- 60 s. Such adhesive systems are now used in aircraft, electronics, automotive and industrial bonding operations. In the mid- 70 s, amine-reactive versions of the liquid polymers (ATBN) were issued, thereby offering another way to introduce rubber modification into a cured epoxy network. References are cited which provide detailed discussions of nitrile rubber, carboxylic nitrile rubber and both carboxyl- and amine-terminated nitrile liquid polymers (1-4). ... 

The reactive groups attached to the molecules of an epoxy resin can react with several curing agents, such as amines, anhydrides, acids, mercaptans, imidazoles, phenols and isocyanates, to create covalent intermolecular bonds and thus to form a three-dimensional network. Among these compounds, due to the enhanced environmental stability of amine-cured epoxy resin (Dyakonov et al., 1996), primary and secondary amines are the curing agents most commonly used in particular aliphatic or cycloaliphatic amines for low-temperature epoxy systems as adhesives or coatings and aromatic amines to produce matrices for liber-reinforced composites (Pascault and Williams, 2010). In Fig. 5.14 the structures of both an aliphatic and an aromatic amine are shown. 

Dyakonov and co-workers [25] used programmed TGA and IR spectroscopy in their stndies of the thermal and oxidative stability of some amine-cured epoxy resin systems based on the glycidyl ether of bisphenol-A and aromatic primary amines. They stndied changes in network epoxy resin model systems brought about by exposure to elevated temperatures in the presence and absence of oxygen. 

A comparative study between silica- and CNT-fiUed amine-cured epoxy nanocomposites [249] revealed the opposite behavior of nanocomposites upon UV irradiation. Thus, silica-filled samples underwent a high rate photochemical degradation followed by a significant accumulation of nanoparticles at the surface, which yielded in nanoparticles release. CNT-filled specimens displayed a high density CNT network at the nanocomposite surface, which limited the in-depth photochemical degradation of the material and prevented the nanoparticles release. The conceptual models for the silica nanoparticles release and CNT preservation upon UV exposure may be used for other multicomponent systems based on epoxy resins in order to assess their potential risks. 

Accelerated UV weathering of CNT-epoxy nanocomposites was investigated and most reports did concur in their assessment that it is unlikely for CNTs to be readily released into the environment given their aggregation in high density networks [249, 252, 254—257]. Moreover, an addition of 0.72 or 0.75 wt% [249, 252] of MWCNTs to an amine-cured epoxy-based nanocomposite yielded in an UV radiation resistant material with a surface containing a dense network of nanoparticles that remained unaffected for long terms, without MWCNTs release. 

For example, the strain-to-failure of the network formed by curing DGEBA with nadic methyl anhydride (NMA) and the catalyst benzyldimethylamine (BDMA) decreases from 12 % to 6 % after 56 days at 23 °C [5]. Physical aging has also been observed in amine cured epoxy resin systems and in an uncross-linked 28,000 g/mol linear epoxy resin tested under wet conditions [6]. In contrast, DGEBA homo-polymerized with piperidine (subsequently... 

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