Structure and Performance of Polyamide 6/Halloysite Nanotubes Nanocomposites

Abstract

Halloysite nanotubes (HNTs) are chemically modified via silylation with 3-(trimethoxysilyl)propyl methacrylate. The modified HNTs (m-HNTs) are characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, solid state 13 C NMR spectroscopy, thermogravimetric analysis (TGA) and extraction experiment. It is showed that the silane has been effectively grafted onto HNTs surface and renders the hydrophobicity to m-HNTs. The nanocomposites consisting of polyamide 6 (PA6) and m-HNTs show significantly improved mechanical properties and heat distortion temperature, which are attributed to the covalent interfacial bonding and the excellent dispersion state of m-HNTs. M-HNTs are found to disperse individually into PA6 matrix. The nucleation effect by m-HNTs is verified by the lowered fold-surface free energy of PA6/ HNTs nanocomposites and the observation of polarized optical microscopy (POM). Both high cooling rate and high m-HNTs loading are beneficial to the formation of gamma-crystals of PA6. The polymorphism could be correlated to the heterogeneous nucleation effects of m-HNTs and the interfacial interactions between m-HNTs and PA6 matrix.KEY WORDS: Polyamide / Halloysite / Nanocomposite / Mechanical Property / Crystallization / Polyamide 6 (PA6) with high fatigue strength, low friction coefficient and high resistance to a wide spectrum of fuels, oils, and chemicals, is an important semicrystalline engineering plastics and finds its applications in automobiles, electrical appliances, construction materials, transportation materials and so on. However, the drawbacks such as limited mechanical strength and dimensional stability restrict its applications. 1Since the first introduction of PA6/clay nanocomposites in 1993, 2,3 they have drawn much attention due to their unprecedented performance compared with their microcomposite counterparts. The PA6 nanocomposites with inclusions of organic montmorillonite (O-MMT), 4-6 carbon nanotubes (CNTs) 7-9 and attapulgite 10,11 have been intensively investigated.Halloysite nanotubes (HNTs) are a type of natural tubular nanoclay 12-16 and have been recognized as the effective nanosized reinforcement of polymers for better mechanical properties and thermal properties. [17][18][19][20] In the previous study, we have showed the reinforcing effects of the prinstine HNTs towords PA6. 21 In the present work, we attempt to further improve the dispersion of HNTs and the interaction between HNTs and PA6 chains through the surface treatment of HNTs by silane of 3-(trimethoxysilyl)propyl methacrylate. The mechanical properties and heat distortion temperatures of the resulted nanocomposites are presented. The kinetic parameters regarding the chain folding activation energy during the nonisothermal crystallization are calculated. The polymorphism of the nanocomposites, which is dependent of the cooling rate of the melt and HNTs loading, is revealed. The performances such as mechanical properties, heat distortion temperature and polymorphism are correlated to the heterogen...

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