Two different types of surface modifiers, 3-aminopropyltriethoxysilane and formamide, were applied to carbon black (CB) particles to lower electrical resistivity of polymer composites prepared by treated CB. Two different matrices, low-density polyethylene and nylon 6, were chosen to compound with surface modified CB. Surface energy of CB was increased by adding amine or amide functional groups during surface treatment of CB. According to electron spectroscopy for chemical analysis (ESCA), chemical modification in surface chemistry of CB was obtained with the chemicals used for the treatment due to the nitrogen atoms in their structures, which may act as dopant atom. As a result of this, electrical resistivity of composites prepared by treated CB decreased. In addition, there was not any significant change in tensile strength and tensile modulus of the composites with the surface treatment.
Surfaces of multiwalled carbon nanotubes (CNT) were functionalized by treatment with strong acid mixture (purification) followed by modification with sodium dodecyl sulfate, poly(ethylene glycol) (PEG), and diglycidyl ether of Bisphenol A (DGEBA). Poly(ethylene terephthalate) (PET)-based conductive polymer composites were prepared by using these CNT by means of melt mixing with a twin screw extruder. Amount of carboxylic acid groups on the CNT surface increased after acid treatment but decreased with surface modification due to the consumption of these groups during the chemical reactions between the surface modifiers and CNT surface. Fourier transformed infrared spectroscopy (FTIR) and nuclear magnetic resonance analyses of the composites revealed the increase in the interactions between PET and CNT surface after treatment with PEG and DGEBA. Mechanical strength of the composites prepared with modified CNT were higher than that of the untreated CNT-filled composite owing to the enhanced interactions between PET and CNT.
In situ microfiber reinforced conductive polymer composites consisting of high-density polyethylene (HDPE), poly(ethylene terephthalate) (PET), and multiwalled carbon nanotube (CNT) were prepared in a twin screw extruder followed by hot stretching of PET/CNT phase in HDPE matrix. For comparison purposes, the HDPE/PET blends and HDPE/PET/CNT composites were also produced without hot stretching. Extrusion process parameters, hot-stretching speed, and CNT amount in the composites were kept constant during the experiments. Effects of PET content and molding temperature on the morphology, electrical, and mechanical properties of the composites were investigated. Morphological observations showed that PET/CNT microfibers were successfully formed in HDPE phase. Electrical conductivities of the microfibrillar composites were in semi-conductor range at 0.5 wt% CNT content. Microfiber reinforcement improved the tensile strength of the microfibrillar HDPE/PET/CNT composites in comparison to that of HDPE/PET blends and HDPE/ PET/CNT composites prepared without hot stretching POLYM. ENG. SCI., 50:2093-2105, 2010. ª 2010 Society of Plastics Engineers INTRODUCTIONRecently, there is a great interest in industry on electrically semiconductor materials with superior mechanical properties and thermal stability [1]. Especially, conductive polymer composites have received significant attention for use in various engineering applications such as sensors, antistatic coatings, electromagnetic interference shielding, and electrolytes in the fuel cells [2,3]. They are generally a synergetic combination of conductive filler and insulating polymer matrix. They exhibit a series of unique features, such as a percolation phenomenon, sensitivity to pressure, temperature and gas, improved mechanical and thermal properties.Conductive polymer composites are usually prepared by incorporating conductive fillers into polymer matrix through melt mixing either by using an extruder or an internal mixer. However, to obtain high electrical conductivity with this method, high loadings of the conductive fillers are usually required, which may result in poor mechanical properties and high cost [4][5][6][7][8]. In the literature, several processing techniques have been used to lower the percolation threshold, in which electrical conductivity of composite increases by several orders of magnitude with the formation of current conductive structures [2]. These techniques are in situ polymerization of the polymer in the presence of conductive particles [9] and selective localization of conductive filler in one of the phases or at the interface of a polymer blend composed of two polymer constituents, in which filler forms the conductive network in the dispersed phase. This phase also constitutes continuous conductive structure in the major phase, which is called as double percolation [10][11][12]. However, in situ polymerization technique is hard to apply in the industrial scale, and in the second technique the incompatible nature of the polymer constituents of th...
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