2D-Boron Nitride for Enhanced Epoxy Nanocomposites

UoM administered thesis: Phd

  • Authors:
  • Jason Hui

Abstract

Hexagonal boron nitride nanosheets (BNNSs) are thin-layer lattices of alternating boron and nitrogen atoms. They are structurally analogous to graphene, a single layer of graphite, which has exhibited remarkable mechanical and electronic properties. However, unlike graphene which is black and a well-known electrical conductor, boron nitride is white and is an electrical insulator. To fully realise the potential of BNNSs, they are integrated into epoxy matrices to form epoxy nanocomposites. Efforts were made to improve, explore and characterise exfoliated BN from different commercial suppliers, with Alfa Aesar revealed to be most useful commercial source for the purposes of improving polymer properties. The yields of liquid phase exfoliation of bulk boron nitride were slightly improved by applying increased concentrations and by adopting a recycling methodology. Organic solvents tetrahydrofuran, dichloromethane and ethyl acetate were investigated as potential solvents, with ethyl acetate exhibiting good quality flakes. Atomic force microscopy (AFM) was used to analyse the exfoliation efficiency and lateral dimensions, while Raman spectroscopy proved an insight about the quality of the boron nitride flakes. Dynamic light scattering was used as a method to estimating the lateral sizes of boron nitride flakes. To fully facilitate dispersion and better interfacial interactions with the epoxy polymers, attempts to functionalise the BN flakes were made. A direct covalent method utilising the Suzuki Palladium catalyzed cross coupling reaction was attempted on hydroxylated BN flakes. The reaction was unsuccessful due to the formation of palladium salts. Inspired by layer-by-layer processes, polymer-adsorption techniques were adopted by adsorbing PEI onto BN flakes. The functionalisation strategy was successful and the subsequent PEI@OH-BN was characterised using several unique methods to investigate the surface properties such as zeta potential, wettability, AFM pull-off test, solvent dispersion, Raman, AFM, XRD, TGA, DSC. Fluorescence methods were also applied during the project as a potential method to monitor flake dispersion. Thermomechanical tests of BNNS/epoxy composites reveal that the BNNS, as well other boron containing compounds interferes with epoxy curing. This was validated by tests with other boron-containing molecules. The Tg of the resulting badly cured composites were found to decrease. Various surface coatings tests (adhesion pull-off tests, solvent uptake) were performed to analyse and compare BNNS/Macropoxy M922 composites with formulations with the PEI@OH-BN flakes. Electrical Impedance Spectroscopy measurements were also conducted on samples of graphene and BNNS within commercial Araldite 2954 Araldur LY564 and Macropoxy M922 epoxies. BNNS was found to be substantially improved compared to the graphene equivalents. These were also tested with the formulations of the PEI@OH-BN flakes but was found that PEI was detrimental within the Macropoxy formulations.

Details

Original languageEnglish
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Award date1 Aug 2020