A study of melt-compounded nanocomposites of polycarbonate and carbon nanotubes in the melt and solid states

Choong, Gabriel Y. H. (2014) A study of melt-compounded nanocomposites of polycarbonate and carbon nanotubes in the melt and solid states. PhD thesis, University of Nottingham.

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Abstract

Polycarbonate-carbon nanotube nanocomposites are promising materials for electrostatic shielding and conductive packaging applications. The nanotubes impart electrical conductivity and increases thermal conductivity and stiffness of the matrix. However, the nanofiller also affects the rheology, and hence the evolution of a filler network during processing. This thesis examines the effects of matrix molar mass and of compounding temperature on the thermal, rheological, electrical and mechanical properties of these materials.

Thermal analysis demonstrated that the glass transition decreased as a consequence of the nanotubes. Degradation of the matrix was ruled out as a possible cause, and the decrease was attributed to a poor interface between matrix and filler. Thermal conductivity of the matrix increased with the addition of nanotubes, in line with model predictions. Furthermore, the nanofillers also marginally increased thermal stability of the matrix in atmospheric conditions.

Oscillatory shear rheology showed that the nanocomposites deviate from linearity earlier than the matrix polymers. A technique was developed to assemble mastercurves over an extended frequency range. The nanocomposites exhibit a low frequency plateau at ∼10^5 Pa, identified as the stiffness of the nanotube network. Relaxation times estimated from the peak in loss tangent scale with matrix molar mass in the same way as terminal relaxation times in pure matrix materials, providing evidence that relaxation of the polymer network is the dominant relaxation mechanism in filled and unfilled polymers.

The effects of melt processing on electrical and mechanical properties were investigated using nanocomposites melt-compounded at a range of extrusion temperatures, but subsequently produced by either injection moulding or compression moulding. Electrical resistivity measurements obtained using a two-terminal method revealed that the resistivity of compression moulded specimens was an order of magnitude lower than that of injection moulded specimens. The compounding temperature had only a mild effect on resistivity. Compression moulded specimens also exhibited greater surface hardness and lower modulus than injection moulded specimens. The elastic modulus recorded is in line with expectation due to nanotube orientation, demonstrated using a modified Halpin-Tsai model. The model can explain much of the observed effects, but suggests that nanotubes may be considerably shortened by melt processing.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: De Focatiis, D.
Warrior, N.A.
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 14236
Depositing User: EP, Services
Date Deposited: 08 Oct 2014 10:45
Last Modified: 14 Sep 2016 19:47
URI: http://eprints.nottingham.ac.uk/id/eprint/14236

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