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

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

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2008

Author dc:creator

• Carter, Humphrey Alexander Copsey

Advisors dc:contributor.advisor

• Shenoi, R.A.
• Jones, D.
• Carter, Y. Didier