Influences on nanocomposite structural performance: experimental study on materials processing and bonding

Nanocomposites have been widely reported to enhance performance in polymers, in bothmechanical and physical properties. An increasing amount of research has resulted in manynanocomposite polymers being applied to various consumer products from motorcars to golfballs. Yet, at this time, there are no structural applications despite a large number of reportsclaiming improved mechanical properties. Carbon nanotubes are renowned for their specificmechanical properties as well as their thermal and electrical properties. Researchers haveput a considerable amount of effort in adopting these nano-materials to structurally enhancean epoxy composite matrix. Though considered very promising many issues such as thedispersion and the bonding interface have been identified and there remains still noguaranteed structural improvement.The potential of epoxy/clay nanocomposite processing and application has been exploredincorporating a study of composite processing methods and characterisation techniques. Thekey goals were to reliably achieve full dispersion and exfoliation of nanoclay withoutinducing air into the composite system. Two mechanical processes were used forcomparison; a high shear rotary mixing and a laboratory bead mill. Microscopicobservations of the resin before curing shows agglomerated nanoclay visible in the sampleswhich decreases as the shearing time. Comparing the processing methods showed greaterdispersion in the bead mill processed samples. TEM and X-ray diffraction were used tomeasure the exfoliation of the nanoclay. The analysis showed that the nanoclays hadbecome intercalated, with the clay layer separation increasing from 2- 4 nm. Further testinglooked at the mechanical and thermal properties of the nanoclay composites, comparing thenanoclay processing in amine hardener or solvent. The effect of changing the amount ofnanoclay present in the epoxy was also recorded. Testing showed that a solvent processingIImethod gave best results, with a nanoclay loading of 2wt% processed with a solvent in abead mill.The performance of CNTs in epoxy composites was also assessed looking at differentbonding mechanisms (covalent and Vander Waals) of the carbon nanotube to the resin. Therheological, mechanical and fracture toughness properties were tested in epoxy resin withdifferent nanotube loadings. These properties were explored in a brittle and a flexible resin,achieved by using two amine curing agents. The covalently bonded tubes showedNewtonian rheological properties and the greatest enhancement in tensile compressive andflexural strength and modulus as well as K1c fracture toughness. MWNT resinsincorporating non-covalent bonds displayed shear thinning rheological behaviour andshowed greatest improvement in Charpy impact toughness. Fibre reinforced compositeslaminates have also been investigated by enhancing a formulated pre-preg material.Compressive properties and interlaminar shear stress were tested in a woven carbon fibrecomposite and some increased properties have been seen which shows potential for furtherresearch