Tensile modulus polypropylene nanocomposites

Polypropylene nanocomposites are remarkable for their better mechanical properties, such as high tensile strength and modulus, and for their dimensional stability. They have a wide range of applications in the automotive sector [7-11]. The PP composites are used in automotive industry as battery supports, instmment panel carriers, body panel reinforcements, front-end modulus, underbody aerodynamic covers, electronic boxes, pedals and their supports, door panels and door modules, bumper beams, fender extensions, wheel covers, hub caps, and trim rings for wheels (Fig. 11.4). 

Relative (a) tensile modulus and (b) yield stress of polypropylene nanocomposites plotted as a function of inorganic volume fraction of filler. The dotted lines serve as guides. (Reproduced from Mittal, V., Eur. Polym. 43, 3727, 2007. With permission from Elsevier.)... 

Relative tensile modulus of OMMT-polypropylene nanocomposites ( , Experimental) compared with the values considering different number of platelets in the stack [27]. (Reproduced from Mittal, V., /. Thermoplast. Compos. Mater., 22, 453, 2009. With permission from Sage Publishers.)... 

Tjong et al. produced polypropylene nanocomposites with 2 wt.% exfoliated vermiculite after pre-treating the vermiculite with maleic anhydride for in-situ compatibilizer generation the vermiculite aspect ratio was at least twice that of the montmorillonite. The tensile modulus improved from 0.84 GPa for their neat PP to 1.3 GPa for the 2 wt.% nanocomposite. The tensile strength improvement was also more striking going up from 28 MPa to 37 MPa. 

Table 1. Tensile modulus of pure polypropylene and its nanocomposites synthesized by various melt intercalation...

Tensile testing was performed on samples of PP and NC-2 exposed to distilled water for 42 days and 64 days at 85°C. The former corresponds to 635 s "7mm in Fig. 1, and the second to 784 s "7mm. The results obtained are given in Table 2. The role of the 5 wt % nanoclay as a reinforcer of the dry polypropylene matrix is clearly demonstrated it increases the modulus by 28% and the maximum stress by 12%, although the clay also limits plastic deformation of the polymer matrix and reduces the ductility. The water absorbed upon exposure plasticizes the matrix and improves the ductility, but at the same time it reduces the modulus and maximum stress. However, it is noteworthy that after 42 days exposure to water, the nanocomposite NC-2 matches the dry neat PP in terms of modulus and maximum stress, although not quite in terms of ductility. 

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