Hydroxylated multiwall carbon nanotubes (MWNTs)/epoxy resin nanocomposites were prepared with ultrasonic dispersion and casting molding. The effect of hydroxylated MWNTs content on reactive activity of composites is discussed. Then the flexural and electrical properties were studied. Transmission electron microscope was employed to characterize the microstructure of nanocomposites. As a result, the reactive activity of nanocomposites obtained increases with the increasing content of MWNTs. When MWNTs content of the composites is 1 wt%, as compared to neat resin, the flexural strength increases from 143 Mpa to 156 MPa, the modulus increases from 3563 Mpa to 3691 MPa, and the volume and surface resistance of nanocomposites decrease by two orders of magnitude, respectively.
Carbon nanotubes (CNTs), since their discovery in 1991 [
Epoxy resin is a thermosetting epoxy polymer, which is used in a variety of applications because of its properties, such as thermal stability, mechanical response, and electrical resistance. In general, epoxy resins are known for their excellent adhesion, chemical and heat resistance, excellent mechanical properties, and electrical insulating properties [
In the present work, the hydroxylated MWNTs (MWNTSOH) were added to the epoxy resin and sonicated to prepare MWNTSOH/epoxy resin nanocomposites. The gel time and curing dynamics of nanocomposites were studied, and their mechanical and electrical properties were also tested.
The hydroxylated MWNTs (MWNTSOH) used in this study were synthesized by chemical vapor deposition (CVD) and were provided by Chengdu organic chemicals CO., LTD. The average diameter of MWNTSOH (hydroxylated content: 3.06 wt%) was about 20–30 nm, the length was several micrometers, and the purity was >95 wt%. The MWNTSOH was used in our experiment without further purification. Epoxy resin 830 (epoxy number of 0.56–0.61 eq/100 g) was produced by Wuxi Di’aisheng epoxy resin CO., LTD. Aromatic hardener (JHB-590) with an acid value of 660–685 mgKOH/g was produced by Dalian-Jinshi Chemical Industry. The formula is 75 parts of hardener by 100 parts of epoxy resin.
The MWNTSOH was added to the epoxy resin at 80°C in order to lower the viscosity of the epoxy resin. Filler weight fractions ranging from 0 wt% to 5 wt% were dispersed in the epoxy resin and were sonicated (1200 W ultrasonic cell disruptor) for 1 hour. After cooling to room temperature, the hardener was added to the homogenous mixture and was compounded for another 30 min. The resulting mixture was then taken into a preheated steel mold coated with the mold release agent. The mold enclosed resulting mixture was degassed at 80°C under vacuum for 30 min to remove bubbles. The mixture was cured at 80°C for 1 hour, followed by 3 h at 120°C and another 3 hours at 140°C to complete the crosslink reaction.
MWNTSOH dispersion in the epoxy matrix was observed through transmission electron microscope (TEM Hitachi (Tokyo, Japan) H-800). The film samples with a thickness of 1
Differential scanning calorimetry (DSC) traces were collected using Q1000 TA instruments at a heating rate of 10°C/min.
The gel time was carried out by plate-spinning method. The mixtures were put into the plate at specified temperature to obtain the interval of time required for a colloidal solution to become a semisolid jelly or gel.
The flexural properties were measured using a universal testing machine under the three-point loading scheme (GB/T2571-1995) and the sample size is 80 mm × 15 mm × 4 mm. Ten specimens of each nanocomposite were tested and the mean values and standard deviations were computed.
The volume and surface resistance were measured by Ultrahigh resistance (1017) and microcurrent (
The gel time reflects effect of temperature-dependent activity of system. In this process, the influence of MWNTSOH contents on the gel time of the epoxy resin according to different temperatures was tested (shown in Figure
Gel time of MWNTSOH/epoxy resin nanocomposites versus temperature.
DSC was used to characterize the thermal properties of MWNTSOH/epoxy resin nanocomposites. The reaction enthalpy (
The influence of MWNTSOH on the thermal properties of nanocomposites.
MWNTSOH content/(%) |
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|
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0 | 118.70 | 190.63 | 151.78 | 268.6 |
0.5 | 117.37 | 188.94 | 150.68 | 297.1 |
1 | 116.46 | 187.07 | 149.98 | 301.0 |
2 | 114.01 | 186.13 | 149.55 | 311.0 |
5 | 110.52 | 183.13 | 148.09 | 331.2 |
The influence of MWNTSOH on the thermal properties of nanocomposites.
The flexural strength and flexural modulus of epoxy nanocomposites with various addition ratios of MWNTSOH were described in Figure
The influence of MWNTSOH on flexural properties of nanocomposites ((a) bending strength, (b) bending modulus).
When the content of MWNTSOH increased further, flexural properties of nanocomposites decreased. The less efficient improvement at higher contents is attributed to an increasing amount of observed agglomerates that cannot effectively transfer outside force. The locale agglomerate formed stress point leads to the generation of fracture source, which decrease the mechanical properties [
The application of conductive nanoparticles in the polymer matrix is supposed to decrease the electrical resistance. The experimental results of the nanocomposites are shown in Figure
The influence of MWNTSOH on the electrical properties of nanocomposites.
The TEM images of MWNTSOH/epoxy resin nanocomposites.
Figure
The MWNTSOH/epoxy resin nanocomposites were prepared by melt mixing. There is a homogeneous dispersion in polymer matrix of MWNTSOH through ultrasonic treatment. So MWNTSOH improves the reactive activity and increases the flexural and electrical properties of composites, whereas the shorter high aspect ratio damages the flexural and electrical properties of MWNTSOH which make the improved affectivity of composite’s properties reduced to a certain extent.
The authors greatly acknowledge a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institution, the Key Laboratory Funded by Jiangsu advanced welding technology, the Starting Research Fund (635061201) from the Jiangsu University of Science and Technology, and Jiangsu Provincial Natural Science Foundation of China (Grant no. BK2012279).