Modification of stress-strain behaviour in aromatic polybenzoxazines using core shell rubbers

2,2-Bis(3,4-dihydro-3-phenyl-2H-1,3-benzoxazine)propane (BA-a) is blended with a commercial core shell rubber (CSR), Genioperl P52, based on a siloxane core and an acrylic shell, at a range of loadings (1–32 wt.%). Scanning electron microscopy and energy-dispersive X-ray analysis reveals an even distribution with good cohesion between the resin and CSR particles. Measurements carried out by dynamic mechanical analysis and thermogravimetric analysis show modest improvements in glass transition temperature (6 °C) and significant enhancement of thermal stability (20%) when CSR (32 wt.%) was incorporated. Such improvements are linearly related to CSR content. Moderate reductions in modulus (30%) were observed with the highest (32 wt.%) loadings of CSR and were also linearly proportional to CSR content. Thermal analysis demonstrated a small inhibitory effect, with activation energy raised by 4% with the blend containing 32 wt.% CSR and 3% in the blend containing 8 wt.% CSR. It was found that mechanical stirring of the CSR particles into the molten BA-a monomer was the most practical solution for dispersion and effectively broke down CSR agglomerates in the bulk and produced void free samples upon curing, although some minor defects were apparent with higher loadings of core shell rubber. Four batches of dog bone specimens (containing 0, 8, 16 and 32 wt.% CSR) were manufactured and underwent tensile testing. An average increase in extension was observed from 0.82 mm for the pristine poly(BA-a), to 1.14 mm (32 wt.% CSR) was achieved. The introduction of CSR has a deleterious impact on tensile strength (24.67 MPa, pristine poly(BA-a) compared with 20.48 MPa containing 32 wt.% CSR; Young's modulus of 5.4 GPa for pristine poly(BA-a) compared with 3.1 GPa containing 32 wt.% CSR). Following tensile tests, scanning electron microscopy reveals rubber cavitation as the principal toughening mechanism

A facile way to produce epoxy nanocomposites having excellent thermal conductivity with low contents of reduced graphene oxide

A well-dispersed phase of exfoliated graphene oxide (GO) nanosheets was initially prepared in water. This was concentrated by centrifugation and was mixed with a liquid epoxy resin. The remaining water was removed by evaporation, leaving a GO dispersion in epoxy resin. A stoichiometric amount of an anhydride curing agent was added to this epoxy-resin mixture containing the GO nanosheets, which was then cured at 90 C for 1 h followed by 160 C for 2 h. A second thermal treatment step of 200 C for 30 min was then undertaken to reduce further the GO in situ in the epoxy nanocomposite. An examination of the morphology of such nanocomposites containing reduced graphene oxide (rGO) revealed that a very good dispersion of rGO was achieved throughout the epoxy polymer. Various thermal and mechanical properties of the epoxy nanocomposites were measured, and the most noteworthy finding was a remarkable increase in the thermal conductivity when relatively very low contents of rGO were present. For example, a value of 0.25 W/mK was measured at 30 C for the nanocomposite with merely 0.06 weight percentage (wt%) of rGO present, which represents an increase of *40% compared with that of the unmodified epoxy polymer. This value represents one of the largest increases in the thermal conductivity per wt% of added rGO yet reported. These observations have been attributed to the excellent dispersion of rGO achieved in these nanocomposites made via this facile production method. The present results show that it is now possible to tune the properties of an epoxy polymer with a simple and viable method of GO addition. A

Lightning strike damage resistance of carbon‐fiber composites with nanocarbon‐modified epoxy matrices

Carbon‐fiber reinforced polymer (CFRP) composites are replacing metal alloys in aerospace structures, but they can be vulnerable to lightning strike damage if not adequately protected due to the poor electrical conductivity of the polymeric matrix. In the present work, to improve the conductivity of the CFRP, two electrically conductive epoxy formulations were developed via the addition of 0.5 wt% of graphene nanoplatelets (GNPs) and a hybrid of 0.5 wt% of GNPs/carbon nanotubes (CNTs) at an 8:2 mass ratio. Unidirectional CFRP laminates were manufactured using resin‐infusion under flexible tooling (RIFT) and wet lay‐up (WL) processes, and subjected to simulated lightning strike tests. The electrical performance of the RIFT plates was far superior to that of the WL plates, independent of matrix modification, due to their greater carbon‐fiber volume fraction. The GNP‐modified panel made using RIFT demonstrated an electrical conductivity value of 8 S/cm. After the lightning strike test, the CFRP panel remains largely unaffected as no perforation occurs. Damage is limited to matrix degradation within the top ply at the point of impact and localized charring of the surface. The GNP‐modified panel showed a comparable level of resistance against lightning damage with the existing copper mesh technology, offering at the same time a 20% reduction in the structural weight. This indicates a feasible route to improve the lightning strike damage resistance of carbon‐fiber composites without the addition of extra weight, hence reducing fuel consumption but not safety

Multifunctional epoxy composites modified with graphene nanoplatelets and carbon nanotubes

Epoxies are a class of thermoset polymers which find extensive use in high performance applications. However, epoxies are inherently brittle and are poor conductors of electricity and heat, which limits their ability to be employed in functional applications. Graphene, a one atom thin two-dimensional carbon material has attracted considerable attention as a potential filler for epoxies, due to its outstanding mechanical, electrical and thermal properties. The present work discusses the multifunctional properties of epoxy polymers modified with graphene nanoplatelets (GNPs) and carbon nanotubes (CNTs). Hybrids of GNPs and CNTs at 9:1 mass ratio were dispersed in the epoxy using three-roll milling. The distribution of the nanofiller in the matrix was fairly uniform and the dispersion quality did not change at higher concentrations. The addition of 1 wt% hybrid nanofiller resulted in an increase of more than 8 orders of magnitude in the electrical conductivity of the epoxy, while at the same time increased the fracture energy (GIC) from 85 ± 30 J/m2 to 240 ± 2 16 J/m . Analytical modelling showed an excellent agreement between the predicted and the experimental values of GIC. GNP-modified epoxies were coated onto steel substrates through a rod coating method to assess the corrosion behaviour of such coatings. Coated panels were immersed into an aqueous solution of 3.5 wt% NaCl and were exposed for a maximum of 5 days. Coating adhesion was evaluated using a tape test. Higher GNP loadings (≥ 0.5 wt%) resulted in a deterioration in the anti-corrosion performance of the coatings. Nanocarbon-modified epoxies were used as the matrices for carbon-fibre reinforced composites, which were subjected to simulated lightning current tests. Optical examination of the laminates following the tests revealed that modification with 0.5 wt% GNPs was sufficient to achieve a comparable level of lightning strike protection to the existing metal mesh technology.Open Acces