Please use this identifier to cite or link to this item:
Title: The thermal and electrical properties of carbon black/liquid crystalline polymer composites
Authors: Lo, Kwan-leong
Keywords: Polymeric composites -- Thermal properties.
Polymeric composites -- Electric properties.
Crystalline polymers -- Thermal properties.
Crystalline polymers -- Electric properties.
Hong Kong Polytechnic University -- Dissertations
Issue Date: 2000
Publisher: The Hong Kong Polytechnic University
Abstract: Carbon black/liquid crystalline polymer (CB/LCP) composites were mixed by blending the carbon black powder with Vectra A950 by extrusion. Film samples of 1% to 7% and 10% CB were obtained from hot pressing the mixture in a mould with thin gaps. Wide-Angle X-ray diffraction was employed to determine the molecular orientation of the LCP matrix. The results reveal that at lower CB volume fraction, the LCP in the composite has a higher orientation whereas the LCP become randomly aligned at high CB volume fraction composite. The surface morphology of the film samples were studied by optical microscope and scanning electron microscope. From the optical photomicrographs, an increase in the CB volume fraction would increase the probability of forming large clusters. There is an obvious change from 3% to 4% CB of which the clusters grow and make contact. The CB aggregates are discernible from SEM of which the average size is about a few microns. The J-E characteristics of the CB samples reveal a linear relationship between the current and the applied voltage. It may be a result of highly conductive of the composites. Resistivities of the samples were also measured in the flow, transverse and thickness directions. The percolation threshold is found at between 3% and 4%. It is also found that the volume fraction dependence of resistivity satisfies the scaling law. The resistivity as a function of temperature was measured in the range from room temperature to 200 C. The resistivities of samples below percolation threshold exhibit negative temperature coefficient and the drop in resistivity is about three orders of magnitude. The resistivities against temperature of samples above the percolation threshold exhibit a negative slope at low temperature range. They reach a minimum at around 150 C then change to a positive slope up to 200 C. Thermal conductivity and thermal expansivity of the composites were determined by the laser flash radiometry method and the thermal mechanical analyzer respectively. The results can be correlated to the molecular orientation of the LCP matrix. Low CB volume fraction composites correspond to high molecular order, thus heat diffuse more easy relative to the high CB volume fraction composites which have lower molecular order. The results of sheet moduli of the composites determined by the laser induced ultrasonic method revealed the elasticity of the composites is also dominated by the molecular orientation of the LCP matrix.
Description: xi, 134 leaves : ill. (some col.) ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577M AP 2000 Lo
Rights: All rights reserved.
Appears in Collections:Thesis

Files in This Item:
File Description SizeFormat 
E-thesis_Link.htmFor PolyU Users 161 BHTMLView/Open
b15116001.pdfFor All Users (Non-printable)4.18 MBAdobe PDFView/Open
Show full item record
PIRA download icon_1.1View/Download Contents

Page view(s)

Last Week
Last month
Citations as of Sep 17, 2018


Citations as of Sep 17, 2018

Google ScholarTM


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.