A novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites

摘要

In order to optimize the performance of the carbon nanotubes (CNTs) reinforced polymer composites, many efforts have been made to produce alignment of CNTs in the matrix, such as spinning CNT gel fibers [1,2], mechanical stretching of a polymeranotubes composite [3] and synthesis of aligned nanotubes by deposition of nanotubes onto chemically modified substrate [4], Dalton et al. [1] showed that their resulting composite fibers obtained by a type of coagulation-based CNT spinning method, which were about 50 mu m in diameter and contained around 60 percent SWNTs by weight, had a tensile strength of 1.8 gigapascals (GPa). Although using spinning technique to prepare alignment of CNTs in the matrix would greatly increase the mechanical (and other physical) properties of the CNT/polymer composites, CNT only oriented in x- or lambda-direction and hardly facilitated isotropic materials. Moreover, for most CNT filled polymer composite, the increases in strength and modulus are on sacrifice of toughness and ductility, due to embrittlement [5]. In this communication, we report a novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites by the following three steps: (1) preparation of CNT-polymer alpha compound by solution processing and/or melt mixing, (2) melt extrusion and hot stretching of CNT-polymer alpha compound and matrix polymer beta to generate in-situ CNT-polymer alpha microfibrils at a processing temperature of the higher melting component (usually polymer alpha, and (3) isotropization of the microfibrillar composite by melt mixing, extrusion, injection molding, and/or compressive molding at a processing temperature of the lower processing-temperature component (usually polymer P). A CNT-reinforced microfibrillar composite (CNT-MRC) based on polycarbonate (PC) and polyethylene (PE) was fabricated by this way in this study. In this material, well-defined CNT/PC microfibrils were generated in PE matrix, and almost all CNTs were preferably localized in the PC microfibrils. There was simultaneously an increase in the strength, modulus, and elongation at break of the CNT-MRC in two directions (horizontal and vertical), which defined this new CNT reinforced composite to be isotropic.