Thermal and mechanical properties of polymers filled with copper powder
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Date
2005-02
Authors
Molefi, Jonathan Andrew
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
The aim of this study was to prepare LOPE-Cu and LLOPE-Cu composites containing different amount of copper, and to determine the morphology, surface free energy, thermal and mechanical properties, as well as thermal and electrical conductivities of the samples. The copper powder particle distributions were found to be relatively uniform at both low and high copper contents. There was cluster formation of copper particles at higher Cu contents, as well as the formation of percolation paths of copper in the PE matrices. The surface free energy results show an increase in the total surface free energy and its disperse part, but a decrease in the polar part of the surface free energy for the Cu-PE composites in comparison with pure PE. There was an initial increase, followed by a decrease in melting temperature of LOPE with increasing copper content. When the observed enthalpy was compared with the expected enthalpy, a higher enthalpy was observed in the presence of low copper contents. For LLOPE the melting temperatures did not change appreciably. Comparison of the observed and expected enthalpies also showed that there was very little increase in total crystallinity. The TGA results show that there was a general decrease in thermal stability with increasing copper content in both LOPE and LLOPE. For LOPE the elongation and stress at break slightly decreased with increasing copper content, while the decrease in the case of LLOPE was much more significant. Young's moduli of LLOPE and its composites had slightly higher values than those of LOPE and its composites, because LLOPE is more crystalline and therefore more stiff than LOPE. These values strongly decreased from the values for both pure LOPE and LLDPE to those of their composites containing 2 vol.% copper, after which the moduli slightly increased with increasing copper content. The thermal conductivities of the composites were higher than that of the pure polyethylene matrix for both LOPE and LLOPE. A linear increase in thermal conductivity was observed with an increase in filler content. The electrical conductivity of polyethylene-copper composites increased with increasing copper content in the composite for both LOPE and LLDPE. From these results the percolation concentration was determined as 18.7 vol.% copper for both polymers.
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Keywords
Dissertation (M.Sc. (Chemistry))--University of the Free State (Qwaqwa Campus), 2005, Polymeric composites, Conductive polymers, Fillers (Materials), Polyethylene additives