Handbook of Polymer Nanocomposites. Processing, Performance and Application by Kamal K. Kar Jitendra K. Pandey & Sravendra Rana

Author:Kamal K. Kar, Jitendra K. Pandey & Sravendra Rana
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

5 Crystallization of PEO in the Presence of Carbon Nanotubes

One of the most significant influences of nanoparticle incorporation in polymer matrices results from the convergence of relevant length scales that control the underlying physics of the structure and dynamics of such systems [2, 3]. In semicrystalline polymers, the average inter-nanoparticle distance is comparable or significantly smaller than the crystalline lamellae length scale, even at modest loadings of nanoparticles. As a consequence, the nanoparticles act as impenetrable objects and result in substantial changes in the polymer crystallization behavior. In this context, investigation of polymer crystallization in the presence of well-dispersed nanoparticles is an interesting and fundamental problem.

Carbon nanotubes are found to act as nucleating system for many families of semicrystalline polymers (such as poly(ε-caprolactone), poly(vinyl alcohol), poly(ethylene), poly(propylene), etc.) [17, 18, 117–120]. However, especially for poly(ethylene oxide), SWNTs are known to disturb the crystal formation and decrease the overall crystallinity of the system [33, 87, 121, 122]. Zhou and coworkers [87] first reported a decrease in PEO peak melting temperature from 72.0 °C to 65.0 °C in the presence of 10 wt% functionalized SWNTs for non-isothermal crystallization process. Below 6 wt% F-SWNTs loading, the nanocomposites behave homogeneously (a single PEO melting peak in non-isothermal DSC thermogram), but at higher loading phase, separation takes place which results in a low peak melting temperature (65 °C) for PEO chains in vicinity to the CNTs and a high peak melting temperature (72.3 °C) for the bulk PEO. Krishnamoorti and coworkers [33] reported DSC-based thermograms for non-isothermal heating and cooling with a decrease in area (i.e., decrease in fractional crystallinity) and a depression in the peak melting (T m,p ) and peak crystallization (T c,p ) temperature at low (0.05–0.5 vol%) SWNT loading (Fig. 13.8). Interestingly, wide-angle X-ray measurements (Fig. 13.9a) revealed that the PEO unit cell structures in these nanocomposites are preserved with little broadening of major reflection peaks indicating more disorder.

Fig. 13.8Melting (left) and crystallization (right) behavior for PEO and different nanocomposites for a constant heating (cooling) rate of 10 °C/min (Reprinted with permission from Ref. [33])

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