Utilization of carbon nanotube towards the improved properties of polyamide 6 nanocomposites
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Date
2015-06-01
Authors
Ali Hassani Joshaghani
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Abstract
Polymer/CNT nanocomposites are promising materials with unique properties for wide range of applications. Interfacial interaction between CNTs and polymer matrix play a key role in final properties of nanocomposite. The major objective of this study was to increase this interaction to achieve more impact on polymer matrix.
Multi-walled carbon nanotubes (MWCNTs) based on bimetallic Co-Mo/MgO catalyst were produced by chemical catalytic vapour deposition method (CCVD). The source gas was methane. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy proved carbon nanotube formation with the diameter of 10-20 nm. Effect of unmodified and modified as-produced carbon nanotubes (PCNTs) and commercial ones (CCNTs) with same diameter on mechanical, morphological, thermal and rheological behaviour PA6 was investigated.
Purification and oxidation of CNTs carried out with several routes to standardize the best reaction conditions i.e. time, temperature and acid concentration. Treatment of CNTs in 12 M hydrochloric acid (HCl) at 70 °C and 6 hr removed about 95% of impurities of CNTs. Nitric acid, mixture of sulphuric acid and nitric acid, and piranha solution used to purify and oxidize CNTs and to introduce carboxyl, hydroxyl and keton groups on the CNTs. Presence of functional groups on the surface of CNTs approved by Fourier transform infrared spectroscopy (FTIR), TGA and Raman spectroscopy. Ethylenediamine (EDA), hexamethylenediamine (HDA) and octadecylamine (ODA) were successfully grafted on the surface of CNTs. PA6 composites containing unmodified and modified CNTs prepared at different CNT’s loading by simple melt mixing. XRD patterns of all nanocomposites showed CNTs changed the crystalline structure of neat PA6 from α/γ form to more thermodynamic stable α-phase structure. Differential scanning calorimetry (DSC) thermograms depicts unmodified and modified CNTs shifted crystallization temperature about 10-15 C to higher temperatures due to the nucleating effect of nanotubes. Furthermore, degree of crystallinity increased by more than 50% in some composites. TGA thermograms revealed onset of thermal degradation of nanocomposites increased for samples containing functionalized CNTs. Non-isothermal degradation mechanism of nanocomposites studied using Coats-Redfern and Horowitz-Metzger methods. Activation energy and pre-exponential Arrhenius factor for thermal degradation of nanocomposites under air and nitrogen estimated by these methods.
The results indicate that the tensile strength and modulus of nanocomposites increased (about 43 and 55%) with increasing modified CNTs content up to a certain level, depending on the type of CNTs. Stiffness and ductility increased by CNT contents.
Nanocomposites melt viscosity increased at high CNTs loading due to the filler-matrix entanglements.