Please use this identifier to cite or link to this item: http://hdl.handle.net/1783.1/7226

Mechanical and thermal properties of benzoxazine nanocomposites containing multiwalled carbon nanotubes

Authors Kaleemullah, Muhammad
Issue Date 2011
Summary Due to the need for thermally resistant materials in microelectronic insulators, high-speed aircraft structures, and structural components of space vehicles require high temperature polymer composites. The general requirements for a high temperature composite consist of good retention of mechanical properties at high temperatures and in the environment to be encountered, long shelf life, an acceptable manufacturing process, and quality control procedures, along with inspectability and repairability. Polybenzoxazine, a new kind of thermoset resin, has been known for its unique characteristics as compared to conventional phenolics and epoxy resins, such as excellent mechanical properties, near zero volumetric shrinkage, low water absorption, excellent resistance to heat and chemicals, UV light and high glass transition temperature (Tg). Carbon nanotubes (CNTs) have attracted much interest in different fields, and they hold the promise of delivering exceptional mechanical properties and multi-functional characteristics with unique physical, mechanical and transport properties, However, if these materials are to be utilized as effective reinforcements in polymer composites, proper dispersion and good interfacial bonding between the CNTs and the polymer matrix have to be guaranteed. The objective of this project is to combine two materials having good mechanical and thermal properties to arrive at a product with further improved mechanical, and thermo mechanical properties and dimensional stability. To achieve this goal CNT-Benzoxazine nanocomposites were made successfully without any solvent. By using triton functionalization of MWCNT and dispersion technique a three roller mill machine (Calendaring) is used to promote CNT dispersion and interfacial adhesion with a new polymer matrix. The effects of CNT functionalization on the dispersion characteristics, mechanical and thermal properties of matrix nanocomposites containing different contents of CNTs are investigated. The mechanical and thermal properties of benzoxazine nanocomposites containing multiwalled carbon nanotubes (MWCNTs) are studied. The influence of carbon nanotubes on benzoxazine nanocomposites brings significant improvements in terms of flexural modulus and strength. However, the increased modulus is at the expense of a reduction in impact fracture toughness. SEM observations are performed on the fracture surface to characterize the failure behavior. The thermo-mechanical properties are characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermo-gravimetric analysis (TGA) and thermo-mechanical analysis (TMA). The results show that by using differential scanning calorimetry (DSC), the catalytic effect of CNTs accelerates the curing process at low temperatures. Enthalpy decreases due to a reduction in the degree of cure and increase in viscosity of the nanocomposites. Dynamic mechanical analysis (DMA) shows the storage modulus and glass transition temperature increase with increasing CNT content. The addition of CNTs has an ameliorating effect of lowering the coefficient of thermal expansion in both the regions below and above glass transition temperature. The char yield increases with increasing CNT content due to the physical barrier effect of CNTs. Carbon nanotubes impedes the propagation of decomposition reactions in the nanocomposites. These observations have a particular implication for using the benzoxazine nanocomposites requiring low shrinkage and accurate dimensional control. The mechanical and thermal properties of CNT-benzoxazine nanocomposites containing both treated and untreated CNTs are compared with those of typical epoxy nanocomposites containing similar CNTs. The effects of CNT addition to the polymers are discussed based on reinforcing mechanism and cure kinetics. The results confirm that samples with functionalized CNTs show much better dispersion in the matrix with associated improved mechanical and thermal properties than those without functionalization and epoxy nanocomposites. Rheological studies were also carried out to optimize suitable processing parameters for the potential manufacturing of CFRP composite prepregs based on benzoxazine nanocomposites containing CNTs.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2011
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Language English
Format Thesis
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