Epoxy Toughening with Low Graphene Loading

Abstract

The toughening effects of graphene and graphene‐derived materials on thermosetting epoxies are investigated. Graphene materials with various structures and surface functional groups are incorporated into an epoxy resin by in situ polymerization. Graphene oxide (GO) and GO modified with amine‐terminated poly(butadiene‐acrylonitrile) (ATBN) are chosen to improve the dispersion of graphene nanosheets in epoxy and increase their interfacial adhesion. An impressive toughening effect is observed with less than 0.1 wt% graphene. A maximum in toughness at loadings as small as 0.02 wt% or 0.04 wt% is observed for all four types of graphene studied. An epoxy nanocomposite with ATBN‐modified GO shows a 1.5‐fold improvement in fracture toughness and a corresponding 2.4‐fold improvement in fracture energy at 0.04 wt% of graphene loading. At such low loadings, these graphene‐type materials become economically feasible components of nanocomposites. A microcrack mechanism is proposed based on microscopy of the fracture surfaces. Due to the stress concentration by graphene nanosheets, microcracks may be formed to absorb the fracture energy. However, above a certain graphene concentration, the coalescence of microcracks appears to facilitate crack propagation, lowering the fracture toughness. Crack deflection and pinning likely contribute to the slow increase in fracture toughness at higher loadings.

Improving the fracture toughness properties of epoxy using graphene nanoplatelets at low filler content

“…The aspect ratio of the f-GNPs used here was found to be 432, which is comparable to material used in previous studies, which ranged from 90 to 933. 9,[59][60][61] However it has been suggested that aspect ratios as high as 35 000 are needed for full stress transfer into the filler particles, [62][63][64] implying that the current system will not achieve optimized reinforcement. It was also noted that the presence of functional groups on the f-GNPs may improve the interfacial stress transfer.…”

A novel route for tethering graphene with iron oxide and its magnetic field alignment in polymer nanocomposites

“…This model has now, therefore, been used to estimate G Ic for the randomly-orientated nanocomposites studied in the present work. For the present functionalised GO SENB 75% (0.1 wt%) [44] Graphite nanoplatelets SENB 50% (1.0 wt%) [45] Thermally reduced GO 40% (0.5 wt%) [46] GO SENB 111% (1 wt%) [47] 4,4'-methylene diphenyl diisocyanate modified graphene CT 200% (4 wt%) [48] 4,4'-diaminophenylsulfone modified graphene CT 196% (1 wt%) [49] Poly(butadiene acrylonitrile) modified graphene oxide (GO) CT 140% (0.04 wt%) [50] Thermally expanded GO CT 115% (0.125 wt%) [51] The fracture surfaces were examined to identify the toughening mechanisms. Distinct "thumbnail lines" were observed on the fracture surface as shown in Fig.…”

Epoxy nanocomposites containing magnetite-carbon nanofibers aligned using a weak magnetic field

“…The introduction of carbon nanofillers into polymers can greatly improve their electrical and mechanical properties [4e6]. The enhancements in these properties can be achieved at relatively low loadings, which arises from their high aspect ratio, leading to them frequently being superior fillers compared to the conventional micrometer-sized fillers [7]. However, the property improvements achieved to date using carbon nanofillers are still well below the theoretical predictions due to the difficulty in achieving (i) a uniform dispersion of the nanofillers in the polymer matrices, (ii) appropriate interfacial bonding with the polymer matrices [3,5,8], and more importantly, (iii) alignment of the nanofillers.…”