Stan Felicia, Turcanu Constantinescu Adriana-Madalina, Fetecau Catalin
Center of Excellence Polymer Processing, Dunarea de Jos University of Galati, 47 Domneasca, 800 008 Galati, Romania.
Polymers (Basel). 2020 Oct 29;12(11):2535. doi: 10.3390/polym12112535.
In this work, the viscoelastic behavior of polypropylene (PP)/multi-walled carbon nanotube (MWCNT) nanocomposites was investigated by indentation testing and phenomenological modeling. Firstly, indentation tests including two-cycle indentation were carried out on PP/MWCNT nanocomposite with three MWCNT loadings (1, 3 and 5 wt %). Next, the Maxwell-Voigt-Kelvin model coupled with two-cycle indentation tests was used to predict the shear creep compliance function and the equivalent indentation modulus. The indentation hardness and elastic modulus of the PP/MWCNT nanocomposites extracted based on the Oliver and Pharr method were compared with the equivalent indentation modulus predicted based on the Maxwell-Voigt-Kelvin mode. The experimental results indicated that the addition of nanotubes into the polypropylene has a positive effect on the micro-mechanical properties of PP/MWCNT nanocomposites. Indentation hardness and elastic modulus increased significantly with increasing MWCNT loading. The creep resistance at the micro-scale of the PP/MWCNT nanocomposites improved with the addition of MWCNTs, with creep displacement reduced by up to 20% by increasing the carbon nanotube loading from 1 to 5 wt %. The Maxwell-Voigt-Kelvin model with three and five Voigt-Kelvin units accurately predicted the shear creep function and its change with increasing MWCNT loading. However, the equivalent indentation modulus was found to be sensitive to the number of Voigt-Kelvin units: the more Voigt-Kelvin units, the better the model predicts the equivalent indentation modulus.
在本研究中，通过压痕测试和唯象学建模对聚丙烯（PP）/多壁碳纳米管（MWCNT）纳米复合材料的粘弹性行为进行了研究。首先，对含有三种MWCNT负载量（1、3和5 wt%）的PP/MWCNT纳米复合材料进行了包括两循环压痕的压痕测试。接下来，将Maxwell-Voigt-Kelvin模型与两循环压痕测试相结合，用于预测剪切蠕变柔量函数和等效压痕模量。将基于Oliver和Pharr方法提取的PP/MWCNT纳米复合材料的压痕硬度和弹性模量与基于Maxwell-Voigt-Kelvin模型预测的等效压痕模量进行了比较。实验结果表明，向聚丙烯中添加纳米管对PP/MWCNT纳米复合材料的微观力学性能有积极影响。压痕硬度和弹性模量随MWCNT负载量的增加而显著提高。PP/MWCNT纳米复合材料微观尺度下的抗蠕变性随着MWCNT的添加而改善，通过将碳纳米管负载量从1 wt%增加到5 wt%，蠕变位移降低了高达20%。具有三个和五个Voigt-Kelvin单元的Maxwell-Voigt-Kelvin模型准确地预测了剪切蠕变函数及其随MWCNT负载量增加的变化。然而，发现等效压痕模量对Voigt-Kelvin单元的数量敏感：Voigt-Kelvin单元越多，模型对等效压痕模量的预测越好。
