PU/clay nanocomposites

Fig. 31. Stress-strain curves for (A) a pristine PU elastomer and (B) a PU-clay nanocomposite...

Figure 7.29 Cone calorimeter profiles of PU and PU/clay nanocomposite. Reprinted with permission from M. Berta, C. Lindsay, G. Pans and G. Camino, Polymer Degradation and Stability, 2006, 91, 1179. 2006 Elsevier Publishers...

Figure 6.2 XRD patterns of PU and its nanocomposites with different types of nanoparticles (a-i) pure PU, (a-ii) pure nano-Ti02, and (a-iii) PU-nano-Ti02 composite [79], (b) PU-CNT composites [80], (c) PU-clay nanocomposites [9], and (d) PU-AIPO4-5 zeolite composites [81].

In this paper, we present results on shape memory behavior of polyurethane (PU)/clay nanocomposites. These nanocomposites were prepared via bulk polymerization method and contained exfoliated clay particles as revealed by transmission electron microscopy and wide angle X-ray diffraction method. The PU matrix contained a crystalline soft segment, which was responsible for shape fixity. The presence of clay decreased the crystallinity of soft segments and consequently shape fixity, but the magnitude of shape recovery stress increased, e.g., by 20% with only 1 wt% clay. The mechanism of reinforcement was studied by monitoring stress relaxation and phase separation. 

Figure 1 shows the WAXD patterns of Cloisite 30B clay and PU/clay nanocomposites. A peak at 20=4.9° in clay curve manifests that it had an interlayer spacing of 1.8nm. No peak is observed in the nanocomposite with lwt% clay, indicating fully exfoliated state. To confirm this result, TEM image was taken and single layers can be... 

The study showed that shape recovery stress of shape memory polyurethane can be increased significantly with the inclusion of reactive nano-clay and subsequent exfoliation. Fully exfoliated 1 wt% PU/clay nanocomposite showed highest recovery stress, excellent shape recovery ratio and large enhancement in mechanical properties. A faster stress relaxation in the case of composite with 5 wt% limited the maximum shape recovery stress, although largest improvement in tensile properties was seen in this case. 

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