Analysis of Viscoelastic Behavior of Polypropylene/Carbon Nanotube Nanocomposites by Instrumented Indentation
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Manufacturing
2.2. SEM Analysis
2.3. Indentation Experiments
- (a)
- 2-step indentation test (Figure 1a) that consists of linear loading to 1000 mN and unloading back to zero with the same rate of 2000 mN/min.
- (b)
- 3-step indentation test (Figure 1b) that consists of loading, holding, and unloading. Both loading and unloading steps were carried out with the same rate of 2000 mN/min. A holding step of 40 s at constant force of 1000 mN was added at the end of the loading step. The 3-step indentation test is carried out in order to evaluate the mechanical properties based on the O and P method [32].
- (c)
- 2-cycle indentation test (Figure 1c), which combines a 2-step indentation test with loading and unloading at the same rate (2000 m N/min) with a 3-step indentation test (loading/unloading with 2000 N/min, and a 300 s holding at 1000 mN). The interval time between the two cycles was set to 0 s and the tests were carried out on the same surface position.
3. Results and Discussion
3.1. Morphology of PP/MWCNT Nanocomposites
3.2. Load Displacement Curves
3.3. Indentation Modulus and Hardness
3.4. Creep of PP/MWCNT Nanocomposites
3.4.1. Indentation Creep Displacement
3.4.2. Creep Compliance Function
4. Conclusions
- At micro-scale level, the addition of nanotubes into the polypropylene has a positive effect on the mechanical properties of the PP/MWCNT nanocomposites. The indentation hardness and elastic modulus increased significantly with increasing MWCNT loading, without statistically significant differences among different regions.
- The creep resistance of the PP/MWCNT nanocomposites improved with the addition of MWCNTs, with creep displacement reduced by up to 20% with increasing MWCNT loading from 1 to 5 wt %. It is suggested that the creep deformation of the PP/MWCNT nanocomposites would proceed by deformation of the matrix and the role of the nanotubes would be to increase the creep resistance by restricting the polymer chain movement.
- The Maxwell–Voigt–Kelvin model accurately predicted the shear creep indentation behavior of PP/MWCNT nanocomposites and its change with increasing MWCNT loading, providing an indirect method to estimate the equivalent indentation modulus. However, the equivalent indentation modulus was found to be sensitive to the number of Voigt–Kelvin units: the more Voigt–Kelvin units used, the better the model predicts the equivalent indentation modulus.
Author Contributions
Funding
Conflicts of Interest
References
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MWCNTs (wt %) | HIT (MPa) | EIT (GPa) |
---|---|---|
1 | 85.33 (± 3.58) | 1.71 (± 0.05) |
3 | 99.52 (± 8.22) | 1.99 (± 0.09) |
5 | 122.09 (± 5.28) | 2.21 (± 0.05) |
Number of VK Units | 1 wt % | 3 wt % | 5 wt % | ||||
---|---|---|---|---|---|---|---|
i | Ji (MPa) | τi (s) | Ji (MPa) | τi (s) | Ji (MPa) | τi (s) | |
3 | 0 | 1.757 | - | 1.439 | - | 1.234 | - |
1 | 0.505 | 5.70 | 0.360 | 6.77 | 0.405 | 4.92 | |
2 | 0.685 | 30.89 | 0.251 | 36.18 | 0.266 | 28.30 | |
3 | 0.374 | 235.54 | 0.450 | 252.97 | 0.474 | 223.29 | |
SSq | 1.61 × 10−1 | 1.07 × 10−1 | 1.39 × 10−1 | ||||
RMSE | 0.004 | 0.003 | 0.003 | ||||
MPE (%) | 1.03 × 10−2 | 9.2 × 10−3 | 1.12 × 10−2 | ||||
5 | 0 | 1.198 | - | 1.003 | - | 0.878 | - |
1 | 0.950 | 2.09 | 0.589 | 1.28 | 0.584 | 1.42 | |
2 | 0.444 | 22.69 | 0.273 | 11.96 | 0.275 | 10.89 | |
3 | 0.693 | 201.20 | 0.219 | 48.68 | 0.210 | 43.26 | |
4 | 1.04 × 10−4 | 200.05 | 6.53 × 10−7 | 199.63 | 0.111 | 194.59 | |
5 | 6.28 × 10−5 | 300.04 | 0.443 | 301.26 | 0.366 | 321.70 | |
SSq | 6.58 × 10−1 | 1.31 × 10−1 | 1.07 × 10−1 | ||||
RMSE | 0.007 | 0.003 | 0.003 | ||||
MPE (%) | 2.02 × 10−2 | 9.96 × 10−3 | 9.24 × 10−3 |
Number of VK Units | Modulus (GPa) | MWCNTs | ||
---|---|---|---|---|
1 wt % | 3 wt % | 5 wt % | ||
3 | G0 | 0.285 | 0.348 | 0.405 |
G∞ | 0.602 | 0.800 | 0.841 | |
5 | G0 | 0.417 | 0.499 | 0.570 |
G∞ | 0.609 | 0.792 | 0.825 |
MWCNTs wt % | Methodology | |||
---|---|---|---|---|
S + nVK Model | Oliver and Pharr [32] | |||
4G0 (GPa) | EIT (GPa) | M (GPa) | ||
S + 3VK | S + 5VK | |||
1 | 1.14 | 1.67 | 1.71 (±0.05) | 1.91 |
3 | 1.39 | 1.99 | 1.99 (±0.09) | 2.19 |
5 | 1.62 | 2.28 | 2.21 (±0.05) | 2.43 |
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Stan, F.; Turcanu, A.-M.; Fetecau, C. Analysis of Viscoelastic Behavior of Polypropylene/Carbon Nanotube Nanocomposites by Instrumented Indentation. Polymers 2020, 12, 2535. https://doi.org/10.3390/polym12112535
Stan F, Turcanu A-M, Fetecau C. Analysis of Viscoelastic Behavior of Polypropylene/Carbon Nanotube Nanocomposites by Instrumented Indentation. Polymers. 2020; 12(11):2535. https://doi.org/10.3390/polym12112535
Chicago/Turabian StyleStan, Felicia, Adriana-Madalina Turcanu (Constantinescu), and Catalin Fetecau. 2020. "Analysis of Viscoelastic Behavior of Polypropylene/Carbon Nanotube Nanocomposites by Instrumented Indentation" Polymers 12, no. 11: 2535. https://doi.org/10.3390/polym12112535
APA StyleStan, F., Turcanu, A. -M., & Fetecau, C. (2020). Analysis of Viscoelastic Behavior of Polypropylene/Carbon Nanotube Nanocomposites by Instrumented Indentation. Polymers, 12(11), 2535. https://doi.org/10.3390/polym12112535