Nanocomposites stress transfer

Gong L, Kinloch IA, Young RJ, Riaz I, Jalil R, Novoselov KS. Interfacial stress transfer in a graphene monolayer nanocomposite. Adv Mater. 2010 Jun 25 22(24) 2694-7. 

The various functional groups on the CNT surface permit coupling with the polymer matrix. A strong interface between the coupled CNT/polymer creates an efficient stress transfer. As mentioned previously, stress transfer is a critical parameter for controlling the mechanical properties of a composite. However, the covalent treatment of CNT reduces the electrical and thermal properties of CNT and these reductions affect the properties of nanocomposites [42-57]. 

Choi et al. [139] fabricated BC/silk fibroin nanocomposite plates with strength (12.8-187.7 GPa) similar to that of human cortical bone, via an impregnation process. The BC nanofibers acted as excellent reinforcement for the stress-transfer produced by the interactions between the BC nanofibers and the silk fibroin matrix, as confirmed by Raman spectroscopy. 

In a more fundamental vein, Zhang et al. [157] studied the confined crystallization behavior of PLA/acetylated BC nanocomposites prepared by compression molding. The results indicated that acetylated BC favored the crystallization of PLA at higher temperatures. In a similar mode, Quero et al. [158] investigated the micromechanical properties of laminated BC/PLA nanocomposites by Raman spectroscopy as a mean to understand the fundamental stress-transfer processes in these nanocomposites and as a tool to select appropriate processing and volume fraction of the fibers. Results showed that Young s modulus and stress at failure of PLA films were foimd to increase by 100 and 315%, respectively, for 18% volume fraction of BC and BC membranes cultured for 3 days exhibited enhanced interaction with PLA because of their higher total surface area. 

In addition to interfacial interactions between the CNT and the polymer matrix, the dispersion of CNTs in the polymer has signifieant influence on the performance of a CNT-polymer nanocomposite. Many different approaches have been used by researchers in an attempt to disperse CNT in polymer matrix such as physical sonication and chemical modification of CNT surface [124-126]. Functionalization of CNT surface can lead to the construction of chemical bonds between the nanotube and polymer matrix and offers the most efficient solution for the formation of strong interface. A strong interface between the coupled CNT-polymer creates an efficient stress transfer [31]. It should be noted that covalent functionalization of CNT may disrupt the grapheme sheet bonding, and thereby reduce the mechanical properties of the final product. However, noncovalent treatment of CNT can improve the CNT-polymer (Fig. 23.10) composite properties through various specific interactions [127]. 

FIGURE 2.8 Tensile moduli (relative to bulk value) for various nanocomposites (a) polyamide-6/MMT nanocomposites, with low-, medium-, and high- molecular weight polyamide-6 matrix, as an example of high improvement in mechanical properties due to effective stress transfer from polymer to filler (b) polyurethane and polyurethane copol3mers/MMT nanocomposites, as an example of high improvement in mechanical... 

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