Nanocomposites of polyethylene oxide (PEO) and polyvinylidene fluoride (PVDF) without and with low content of single and multiwalled carbon nanotubes (SWCNTs-MWCNTs) were prepared and studied by thermogravimetric analysis (TGA) using different heating rate. TGA results indicate that the thermal stability of neat PEO/PVDF blend was improved with both heating rate and incorporation of carbon nanotubes (CNTs). The degradation temperature for neat blend was lower than those of the nanocomposites after adding both SWCNTs and MWCNTs. As increase of heating rate, the onset of decomposition is irregularly moved to higher temperatures. This indicates that the thermal stability of the polymeric matrices has been improved after addition of CNTs. The residual weight of the samples left increased steadily with adding of both SWCNTs and MWCNTs. Kinetic thermodynamic parameters such as activation energy, enthalpy, entropy, and Gibbs free energy are evaluated from TGA data using Coats-Redfern model. The values of all parameters irregularly decrease with increasing of heating rate due to increasing of heating rate temperature, the random scission of macromolecule chain in the polymeric matrices predominates and the activation energy has a lower value.
Since the discovery of carbon nanotubes (CNTs) in 1991 by Iijima [
The CNTs have attracted much attention to apply for hydrogen storage, chemical sensors, and nanoelectronic devices. They are used as extremely strong nanoreinforcements for composites, which possess extraordinarily high strength with low weight and moderate electrostatic discharge properties [
Thermogravimetric analysis (TGA) is a process in which substance is decomposed in the presence of increase of temperature which causes breakage in the bonds within the molecules. The sample weight decreases slowly as the reaction begins, then decreases rapidly over a comparatively narrow temperature range, and finally levels off as the reactants become spent. The shape of TGA curve depends primarily upon the kinetics parameters. The estimated values of the kinetic parameters are very important in study of the thermal stability of the substances [
CNTs as filler incorporated polymer or polymer blend nanocomposites are excellent candidates for traditional thermal material owing to their good thermal stability, flexible processability, low weight, and excellent physical performance, which are in focus in the electronic and industry applications. CNT incorporation has previously been reported to improve the thermal and electrical properties of a range of polymers. Some researchers proposed thermal and electrical property improvements as a function of CNT type, degree of dispersion, and loading ratio [
This work reports the synthesis and investigation of PEO/PVDF nanocomposite films doped with low content of single and multiwalled carbon nanotubes using a simple method and studies the effect of different heating rate and kinetic parameters to achieve a dramatic enhancement in thermal properties.
Polyethylene oxide (PEO) has the following specifications: molecular weight ≈ 900,000, linear formula is (-CH2CH2O-)
Polyethylene oxide (PEO) and polyvinylidene fluoride (PVDF) were dried in a vacuum oven at 50°C before being used to remove moisture content. 2 gm of PEO and 8 gm of PVDF were dissolved in dimethyl sulfoxide (DMSO) as a solvent with stirring at 60°C about 6 h to obtain a good solution of the polymer blend. The polymer solution was cooled at room temperature about 3 h to remove any air bubbles during stirring. 0.1 gm of both SWCNTs and MWCNTs was added separately to 10 mL of DMSO on a beaker. Then, the beaker was immersed in ultrasonic(Eltrosonic Type 07) to give a good suspension about 40 min with 2 min as time interval. The PEO/PVDF nanocomposites containing CNTs were prepared using casting method by the following procedure: suspension solutions of SWCNTs and MWCNTs were added dropwise to blend solution with continuous stirring and under ultrasonic. After careful mixing blend solution containing CNTs was prepared by casting method. PEO/PVDF/CNTs films were obtained by peeling off from glass Petri dishes and putting them in oven at 60°C to evaporate the solvent. The obtained films were, namely, pure PEO, PVDF, PEO/PVF, PEO/PVDF/SWCNTs, and PEO/PVDF/MWCNTs.
The thermogravimetric analysis (TGA) was used to characterize the decomposition and thermal stability of prepared samples by Perkin-Elmer TGA-7. The mass of the samples amount (5.4–8.8 mg) was recorded while temperature is increased at a heating rate of 5, 10, 15, and 25°C·min−1 and the samples were heated from room temperature to 800°C in nitrogen atmosphere.
Generally in the reactions kinetic, the thermal degradation of a solid polymer can be shown as follows: Solid
The kinetics parameters of such reactions are described by various models taking into account the special features of their mechanisms. Usually the degree of decomposition (
In general, the kinetic equation has been proposed to characterize and analyze thermogravimetric measurements and curves [
On integration and approximation of (
Figures
TGA thermograms of neat PEO, PVDF, and PEO/PVDF blend and the blend with SWCNTs and MWCNTs nanocomposites at heating rates ranging between 5, 10, 15, and 25°C·min−1.
TGA thermograms of neat PEO, PVDF, and PEO/PVDF blend and the blend with SWCNTs and MWCNTs nanocomposites at heating rates ranging between 5, 10, 15, and 25°C·min−1.
TGA thermograms of neat PEO/PVDF blend and the blend with SWCNTs and MWCNTs nanocomposites at heating rates ranging between 5, 10, 15, and 25°C·min−1.
Generally, it is seen that all curves are smooth weight-loss curves. The decomposition behaviors at all values are similar. In Figure
The derivative thermogravimetric curves show two temperature broad peaks (
The values of degradation temperature (
Sample | Degradation temperature ( |
|||
---|---|---|---|---|
5°C·m−1 | 10°C·m−1 | 15°C·m−1 | 25°C·m−1 | |
PEO/PVDF | 360.14 | 364.10 | 366.20 | 474.23 |
PEO/PVDF/SWCNTs | 363.97 | 374.51 | 378.56 | 380.46 |
PEO/PVDF/MWCNTs | 366.72 | 383.42 | 385.04 | 392.32 |
The values of degradation temperature (
Sample | Degradation temperature ( |
|||
---|---|---|---|---|
5°C·m−1 | 10°C·m−1 | 15°C·m−1 | 25°C·m−1 | |
PEO/PVDF | 462.46 | 472.55 | 478.89 | 492.37 |
PEO/PVDF/SWCNTs | 457.74 | 461.35 | 466.46 | 477.02 |
PEO/PVDF/MWCNTs | 459.52 | 473.21 | 480.49 | 474.45 |
Moreover, the thermodynamics activation parameters of the main decomposition process in the second degradation region were evaluated by the Coats-Redfern equation [
A plot of
The value of apparent activation energy (
The entropy of activation
According the Coats-Redfern method, the calculated thermodynamic parameters values (
Kinetic parameters and activation energy for PEO/PVDF blend and the blend doped with SWCNTs and MWCNTs at 5, 10, 15, and 25 heating rates.
Sample | Heating rate |
|
|
|
|
---|---|---|---|---|---|
Blend | 5 |
|
|
145543.7 | 465.61 |
10 |
|
|
143748.1 | 432.35 | |
15 |
|
|
142713.5 | 415.72 | |
25 |
|
|
142370.1 | 399.09 | |
|
|||||
Blend/SWCNTs | 5 |
|
|
143260.8 | 407.41 |
10 |
|
|
142723.5 | 349.20 | |
15 |
|
|
141694.7 | 324.26 | |
25 |
|
|
141090.6 | 299.32 | |
|
|||||
Blend/MWCNTs | 5 |
|
|
144646.5 | 490.55 |
10 |
|
|
144107.1 | 415.72 | |
15 |
|
|
143029.7 | 415.72 | |
25 |
|
|
138886.8 | 374.15 |
Solid polymer blend films based on PEO/PVDF unfilled and filled with low concentration of single and multiwalled carbon nanotubes were prepared using casting method. Thermal studies at different heating rates and kinetic parameters were performed using thermogravimetric analysis (TGA) and its first derivative (DTG). The kinetic thermodynamic parameters such as activation energy, enthalpy, entropy, and Gibbs free energy were evaluated from TGA data using Coats-Redfern relation. The lower values of percentage weight loss are nearly from 3.2 to 20% due to splitting or volatilization of small molecule and evaporation of moisture. The main decomposition region in TGA curves has a percentage of weight loss from 33 to 70%. The degradation temperature for neat blend was lower than those of the nanocomposites after adding both CNTs and an increase of heating rate. The decomposition temperature is moved to higher temperatures indicating that the thermal stability of the polymeric has been improved.
The author declares that there is no conflict of interests regarding the publication of this paper.