Khoshkava Vahid, Kamal Musa R
Department of Chemical Engineering, McGill University , 3610 University Street, Montreal, Quebec H3A 2B2, Canada.
ACS Appl Mater Interfaces. 2014 Jun 11;6(11):8146-57. doi: 10.1021/am500577e. Epub 2014 Jun 2.
Polypropylene (PP) nanocomposites containing spray-dried cellulose nanocrystals (CNC), freeze-dried CNC, and spray-freeze-dried CNC (CNCSFD) were prepared via melt mixing in an internal batch mixer. Polarized light, scanning electron, and atomic force microscopy showed significantly better dispersion of CNCSFD in PP/CNC nanocomposites compared with the spray-dried and freeze-dried CNCs. Rheological measurements, including linear and nonlinear viscoelastic tests, were performed on PP/CNC samples. The microscopy results were supported by small-amplitude oscillatory shear tests, which showed substantial rises in the magnitudes of key rheological parameters of PP samples containing CNCSFD. Steady-shear results revealed a strong shear thinning behavior of PP samples containing CNCSFD. Moreover, PP melts containing CNCSFD exhibited a yield stress. The magnitude of the yield stress and the degree of shear thinning behavior increased with CNCSFD concentration. It was found that CNCSFD agglomerates with a weblike structure were more effective in modifying the rheological properties. This effect was attributed to better dispersion of the agglomerates with the weblike structure. Dynamic mechanical analysis showed considerable improvement in the modulus of samples containing CNCSFD agglomerates. The percolation mechanical model with modified volume percolation threshold and filler network strength values and the Halpin-Kardos model were used to fit the experimental results.
通过在内部间歇式混合器中进行熔融共混，制备了含有喷雾干燥纤维素纳米晶体（CNC）、冷冻干燥CNC和喷雾冷冻干燥CNC（CNCSFD）的聚丙烯（PP）纳米复合材料。偏光显微镜、扫描电子显微镜和原子力显微镜显示，与喷雾干燥和冷冻干燥的CNC相比，CNCSFD在PP/CNC纳米复合材料中的分散性明显更好。对PP/CNC样品进行了流变学测量，包括线性和非线性粘弹性测试。小振幅振荡剪切测试支持了显微镜结果，该测试表明含有CNCSFD的PP样品的关键流变学参数值大幅上升。稳态剪切结果显示，含有CNCSFD的PP样品具有很强的剪切变稀行为。此外，含有CNCSFD的PP熔体表现出屈服应力。屈服应力的大小和剪切变稀行为的程度随CNCSFD浓度的增加而增加。研究发现，具有网状结构的CNCSFD团聚体在改变流变性能方面更有效。这种效果归因于具有网状结构的团聚体更好的分散性。动态力学分析表明，含有CNCSFD团聚体的样品的模量有显著提高。使用具有修正体积渗流阈值和填料网络强度值的渗流力学模型以及Halpin-Kardos模型来拟合实验结果。
