Effect of microfiber reinforcement on the morphology, electrical, and mechanical properties of the polyethylene/poly(ethylene terephthalate)/carbon nanotube composites

Abstract

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...

On the phase affinity of multi-walled carbon nanotubes in PMMA:LDPE immiscible polymer blends

“…Cardinaud and McNally [2] theoretically predicted and experimentally proved the preferential localization of MWCNTs in the PET phase of several PET/LDPE blends. The same result was achieved by Yesil et al [3] for PET/HDPE and Goldel et al [4] found that even minor differences in the wetting behavior were enough for MWCNTs with large aspect ratios to migrate to the more favorable PC phase in PC/SAN blends. Moreover, the wetting coefficient also proved to be successful at predicting the locations of three different silica nanoparticles in LDPE/PEO blends [5].…”

“…The polymers used in this study were: a) poly(methyl methacrylate) (PMMA) Plexiglas 6N, from Evonik Industries (an amorphous thermoplastic moulding compound, with T g =99ºC, MVR at 230 ºC/3.8 kg = 12 cm 3 /10min, and melt density= 1.10 g/cm 3 ); b) low density polyethylene (LDPE) LD605BA, from ExxonMobil (a general purpose LDPE grade, with T m =108 ºC, MFI at 190 ºC/2.16 kg = 6.5 g/10min, and melt density= 0.76 g/cm 3 ). Non-functionalized multi-walled carbon nanotubes (MWCNTs) NC7000, from Nanocyl S.A, Belgium were used.…”

Influence of Blend Composition and Compatibilizer on Mechanical and Morphological Properties of Recycled HDPE/PET Blends

“…This is typical behaviour for fibre reinforced composites [15]. The decrease of SB with rPET concentration in uncompatibilized blends were due to the low strain at break and brittle nature of PET fibres, which restrict the mobility of polymer molecules [13] [16]. This is an indicator of the material flexibility, which shows that the incorporation of rPET makes the rHDPE-rich blend stronger but more brittle.…”

“…The compatibilized blends containing 45 wt% and 50 wt% rPET fibres could not be compression molded for tensile testing. The presence of a compatibilizer in the blend hinders the nucleation effect of rPET fibres, leading to a little thermal contraction; however, rHDPE undergoes crystallization and contracts strongly during cooling from the melt [16]. Meanwhile, the introduction of relatively low stiffness compatibilizer may firstly produce plastic deformation at the interface [17].…”

Characterization of Physical Properties for Multi-Scale Polymer Composites Under Various Processing Conditions

“…They found that after an initial increase in tensile strength, the addition of microfibers and MWCNTs decreased the performance since there was a lack of compatibility with the polymer phase beyond 30 wt% loading of PET [29].…”