The mechanisms and mechanics of the toughening of epoxy polymers modified with silica nanoparticles

Abstract

The present paper considers the mechanical and fracture properties of four different epoxy polymers containing 0, 10 and 20 wt% of well-dispersed silica nanoparticles. Firstly, it was found that, for any given epoxy polymer, their Young's modulus steadily increased as the volume fraction, v f, of the silica nanoparticles was increased. Modelling studies showed that the measured moduli of the different silica-nanoparticle filled epoxy-polymers lay between upper-bound values set by the Halpin-Tsai and the Nielsen 'no-slip' models, and lower-bound values set by the Nielsen 'slip' model; with the last model being the more accurate at relatively high values of v f . Secondly, the presence of silica nanoparticles always led to an increase in the toughness of the epoxy polymer. However, to what extent a given epoxy polymer could be so toughened was related to structure/property relationships which were governed by (a) the values of glass transition temperature, T g , and molecular weight, M c , between cross-links of the epoxy polymer, and (b) the adhesion acting at the silicananoparticle/epoxy-polymer interface. Thirdly, the two toughening mechanisms which were operative in all the epoxy polymers containing silica nanoparticles were identified to be (a) localised shear-bands initiated by the stress concentrations around the periphery of the silica nanoparticles, and (b) debonding of the silica nanoparticles followed by subsequent plastic void-growth of the epoxy polymer. Finally, the toughening mechanisms have been quantitatively modelled and there was good agreement between the experimentally measured values and the predicted values of the fracture energy, G c , for all the epoxy polymers modified by the presence of silica nanoparticles. The modelling studies have emphasised the important roles of the stress versus strain behaviour of the epoxy polymer and the silica-nanoparticle/epoxy-polymer interfacial adhesion in influencing the extent of the two toughening mechanisms, and hence the overall fracture energy, G c , of the nanoparticle-filled polymers.

Epoxy resin composites with surface‐modified silicon dioxide nanoparticles: A review

“…Mechanisms for the toughening effect of nanosilica were discussed as well, and the model from Kinloch et al 22 was confirmed; see the next two sections in this article. Matrix shear banding was the dominant mechanism, matrix void growth was secondary, and the debonding of silica nanoparticles had only a minor effect.…”

“…16 They found exactly the same 17% improvement in the modulus at 20 wt % nanosilica like Kinloch et al 22 and a 40% improvement at a 40 wt % loading level. The strength was slightly improved at the 40 wt % level.…”

“…By extensive microscopic work, the initiation and development of a thin dilatation zone and nanovoid formation were identified as the dominant toughening mechanisms. Kinloch et al 22 investigated DGEBA and a DGEBA/DGEBF blend cured with a difunctional short-chain poly(ether amine). They reported only very small increases in the modulus (17 and 10%, respectively) with 20 wt % nanosilica.…”

“…Kinloch et al 22 also investigated a high-performance, high-T g epoxy resin system similar to the industrial benchmark RTM6. 22 Nanosilica-filled TGMDA was cured with a blend of 4,4 0 -methylenebis(2,6-diethylaniline) and 4,4 0 -methylenebis(2,6-diisopropylaniline). At a 10 wt % nanosilica loading level, the modulus was increased by 26%, and G 1c was increased by 146%, although it was still at a very low level of 172 J/m 2 .…”

A Sinusoidally Architected Helicoidal Biocomposite

“…[43][44][45] The extent of plastic deformation of the epoxy is enhanced so as to dissipate more energy in regions surrounding the crack tip. [43,44] . The particulated region is delimited by the dashed line.…”