Preparation And Properties Of Multiwalled Carbon Nanotubes And Nylon6(66) Composites By Solution Mixing Process

Nylon6(66), as an engineering plastics, is widely used with excellent properties. However, it also has some defects in its performance, such as high water absorption, easy ageing in air and low impact strength at low temperature. So the application of nylon6(66) is limited, and using reinforcing fillers for polymers to modify nylon6(66) has received considerable attention. On the other hand, carbon nanotubes (CNTs) have been recognized as extremely promising reinforcing fillers for polymers owing to their excellent mechanical, thermal and electronic properties. Our study is intended to improve the mechanical and thermal properties of nylon6(66) through adding CNTs.In this paper, multiwalled carbon nanotubes (MWCNTs) were treated by the mixture of H2SO4and HNO3(3:1, v/v), and then modified by1,6-hexamethylene diamine (HDA) with N,N’-dicyclohexylcarbodiimide (DCC) for introducing reactive amine groups on the surface of MWCNTs. With formic acid as solvent, the modified MWCNTs were used to fabricate MWCNTs/nylon6(66) composites by solution mixing process. The crystallization behaviors of composites were investigated. The morphology, structure and properties of products were characterized by Fourier transformation infrared spectrometry, field emission scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetry, and tensile and impact measurement. The results are as follows: 1. The result of Boehm’s titration shows that the amounts of total oxygen-containing groups and carboxyl groups of the parent MWCNTs were7.713x10-4mol/g and2.054xlO-4mol/g, respectively, and the amounts of total oxygen-containing groups and carboxyl groups grafted on the surface of acidified-MWCNTs were14.156xlO-4mol/g and5.150xlO-4mol/g, respectively. The amide groups and carboxyl groups were grafted on the surface of MWCNTs by acidification-amination treatment. The morphology of MWCNTs also changed significantly during the treatment process. Acidification made the MWCNTs dense, and amination made the MWCNTs loose again.2. The dispersion of MWCNTs in nylon6(66) matrix and interfacial adhesion with PA66matrix were improved by chemical modification, especially for d-MWCNTs.3. The thermal stability of the MWCNTs/nylon6(66) composites was improved through adding MWCNTs, especially for d-MWCNTs. The thermal stability of composites gradually increased with the increase of d-MWCNTs content.4. The crystallization degree of the MWCNTs/nylon6(66) composites increased with respect to that of pure nylon6(66) through adding d-MWCNTs. When the content of d-MWCNTs reached7.5wt%, the crystallization degree of the MWCNTs/nylon6composite was the biggest (56.62%), the grain sizes of a1and a2-form of MWCNTs/nylon6composite were the smallest. When the content of d-MWCNTs reached2.5wt%, the crystallization degree of d-MWCNTs/nylon66composite was35.82%, and only0.57%smaller than that for5wt%d-MWCNTs addition, the grain sizes of y-, a1and a2-form of MWCNTs/nylon66composite were the smallest.5. The tensile Young’s modulus and tensile strength of the d-MWCNTs/nylon6(66) composites increased significantly with respect to that of pure nylon6(66) through adding d-MWCNTs. The tensile Young’s modulus of the d-MWCNTs/nylon6(7.5wt%) composite was24.11%bigger than that of pure nylon6, and the tensile strength of the d-MWCNTs/nylon6composite was41.80%bigger than that of pure nylon6. The tensile Young’s modulus and tensile strength of the d-MWCNTs/nylon66(2.5wt%) composite were65.00%and17.67%bigger than those of pure nylon66, respectively.6. The impact strength of the d-MWCNTs/nylon6(66) composites increased significantly with respect to that of pure nylon6(66) through adding d-MWCNTs. The impact strength of the d-MWCNTs/nylon6(7.5wt%) composite was27.16%bigger than that of pure nylon6. The impact strength of the d-MWCNTs/nylon66(2.5wt%) composite was10.89%than that of pure nylon66.