Abstract
This paper presents influence of the type of carbon nanotube functionalization on properties of poly(L-lactide) (PLLA) based nanocomposite materials. For this purpose surface modifications of multi-walled carbon nanotubes (MWCNTs) were performed by chemical and irradiation techniques, while thermo gravimetric analysis, UV-Visible and Fourier-transform infrared (FT-IR) spectroscopies confirmed successful covalent functionalization. Series of PLLA bionanocom-posites with different contents of functionalized MWCNTs (0.7; 1.6; 2.1 wt%), were synthesized via ring-opening solution polymerisation of L-lactide. FT-IR analysis confirmed that grafting of L-lactide, under controlled condition, is possible to perform starting from the surface of functionalized MWCNTs. From differential scanning calorimetry results it was concluded that even low contents of chemically and irradiation functionalized MWCNTs had a significant effect on thermal properties of the prepared nanocomposites, raising the values of melting and glass transition temperatures. Thermogravimetric analysis (TGA) has shown that the degradation onset temperature for composites with chemically functionalized MWCNTs, was much higher than that for the neat poly(L-lactide) sample and composites with irradiation functionalized MWCNTs. Morphology studies by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that poly(L-lactide) covered surfaces and separated functionalized MWCNTs. Good dispersion of carbon nanotubes in polymer matrix enabled conductivity of synthesized materials, as determined by conductivity tests.
Highlights
Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima [1], they have received a lot of attention due to many potential applications that they might have
The characteristic peak assigned to this electron transition blue shifted for both applied functionalization methods [33,34,35]. This peak is more intense for chemically functionalized multi-walled carbon nanotubes (MWCNTs) in comparison to irradiated ones, due to oxidation of chf-MWCNTs in acids, which leads to a higher number of carboxyl groups on the nanotube surface
This finding is attributed to the higher degree of functionalization of chf-MWCNTs, which led to formation of more chemical bonds with PLA chains
Summary
Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima [1], they have received a lot of attention due to many potential applications that they might have. By exhibiting unique properties (electric, thermal, mechanical, etc.), CNTs hold promise for development of fundamentally new materials, especially polymer nanocomposites [2,3]. The extent of functionality induced by – COOH and –OH groups depends on the oxidation procedures and oxidizing agents [9] The presence of these groups on the nanotube surface supports attachment of organic [10,11] or inorganic materials, which is important for solubilisation of nanotubes. Functionalization of CNTs by polymer grafting is significant for processing of advanced composites [12,13] and can be formed by covalent attachment of highly soluble linear polymers onto the surface of nanotubes [14,15]. Poly(lactide) (PLA) based nanocomposites represent a new class of nanosized biobased, biodegradable and biocompatible materials, exhibiting unique properties and functionalities. Synthesized biocomposites with the addition of differently functionalized MWCNTs were analysed regarding conductivity
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