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

Nanocomposites have been widely reported to enhance performance in polymers, in both mechanical and physical properties. An increasing amount of research has resulted in many nanocomposite polymers being applied to various consumer products from motorcars to golf balls. Yet, at this time, there are no structural applications despite a large number of reports claiming improved mechanical properties. Carbon nanotubes are renowned for their specific mechanical properties as well as their thermal and electrical properties. Researchers have put a considerable amount of effort in adopting these nano-materials to structurally enhance an epoxy composite matrix. Though considered very promising many issues such as the dispersion and the bonding interface have been identified and there remains still no guaranteed structural improvement. The potential of epoxy/clay nanocomposite processing and application has been explored incorporating a study of composite processing methods and characterisation techniques. The key goals were to reliably achieve full dispersion and exfoliation of nanoclay without inducing air into the composite system. Two mechanical processes were used for comparison; a high shear rotary mixing and a laboratory bead mill. Microscopic observations of the resin before curing shows agglomerated nanoclay visible in the samples which decreases as the shearing time. Comparing the processing methods showed greater dispersion in the bead mill processed samples. TEM and X-ray diffraction were used to measure the exfoliation of the nanoclay. The analysis showed that the nanoclays had become intercalated, with the clay layer separation increasing from 2- 4 nm. Further testing looked at the mechanical and thermal properties of the nanoclay composites, comparing the nanoclay processing in amine hardener or solvent. The effect of changing the amount of nanoclay present in the epoxy was also recorded. Testing showed that a solvent processing II method gave best results, with a nanoclay loading of 2wt% processed with a solvent in a bead mill. The performance of CNTs in epoxy composites was also assessed looking at different bonding mechanisms (covalent and Vander Waals) of the carbon nanotube to the resin. The rheological, mechanical and fracture toughness properties were tested in epoxy resin with different nanotube loadings. These properties were explored in a brittle and a flexible resin, achieved by using two amine curing agents. The covalently bonded tubes showed Newtonian rheological properties and the greatest enhancement in tensile compressive and flexural strength and modulus as well as K1c fracture toughness. MWNT resins incorporating non-covalent bonds displayed shear thinning rheological behaviour and showed greatest improvement in Charpy impact toughness. Fibre reinforced composites laminates have also been investigated by enhancing a formulated pre-preg material. Compressive properties and interlaminar shear stress were tested in a woven carbon fibre composite and some increased properties have been seen which shows potential for further research.EThOS - Electronic Theses Online ServiceGBUnited Kingdo