The toughness of epoxy polymers and fibre composites modified with rubber microparticles and silica nanoparticles

Abstract

The present paper investigates the effect of adding silica nanoparticles to an anhydride-cured epoxy polymer in bulk and when used as the matrix of carbon-and glass-fibre reinforced composites. The formation of 'hybrid' epoxy polymers, containing both silica nanoparticles and carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber microparticles, is also discussed. The structure/property relationships are considered, with an emphasis on the toughness and the toughening mechanisms. The fracture energy of the bulk epoxy polymer was increased from 77 to 212 J/m 2 by the presence of 20 wt.% of silica nanoparticles. The observed toughening mechanisms that were operative were (a) plastic shear-yield bands, and (b) debonding of the matrix from the silica nanoparticles, followed by plastic void-growth of the epoxy. The largest increases in toughness observed were for the 'hybrid' materials. Here a maximum fracture energy of 965 J/m 2 was measured for a 'hybrid' epoxy polymer containing 9 wt.% and 15 wt.% of the rubber microparticles and silica nanoparticles, respectively. Most noteworthy was the observation that these increases in the toughness of the bulk polymers were found to be transferred to the fibre composites. Indeed, the interlaminar fracture energies for the fibre-composites materials were increased even further by a fibre-bridging toughening mechanism. The present work also extends an existing model to predict the toughening effect of the nanoparticles in a thermoset polymer. There was excellent agreement between the predictions and the experimental data for the epoxy containing the silica nanoparticles, and for epoxy polymers containing micrometre-sized glass particles. The latter, relatively large, glass particles were investigated to establish whether a 'nanoeffect', with respect to increasing the toughness of the epoxy bulk polymers, did indeed exist.

Graphene nanoplatelet-modified epoxy: effect of aspect ratio and surface functionality on mechanical properties and toughening mechanisms

“…The GNP-COOH and GNP-O 2 functionalised GNPs were well bonded to the epoxy, as shown in Figure 21 observed from these modified epoxies as shear band yielding is generally accepted to be a major toughening mechanism [40].…”

“…However, this is still low compared to the rubber modified epoxies which can have G c values above 1000 J/m 2 [40]. Clearly, the GNP modified epoxies are still relatively brittle, even at the highest concentrations possible.…”

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

“…Kinloch and coworkers 22,34 observed for a 20 wt % silica nanoparticle modification an increase in the modulus of 30% and an increase in K 1c of 73%. A slight decrease in T g was noted.…”

Improvement of adhesive toughness measurement

“…15-20 wt% rubber is sufficient to achieve effective toughening effect, and causes 10-30% loss of the Young's modulus and tensile strength of the matrix. Studies have been conducted on the adhesive toughness of several types of adhesive joints bonded by rubber-modified adhesives [15][16][17][18].…”