PU nanocomposites

Maji et al. [136] have examined the effect of 30B loading on the mechanical properties of hyperbranched polyurethane (PU) nanocomposites. The extent of clay loading was varied from 2 to 16 phr. The nanocomposite containing 8 wt% 30B clay shows a 100% increase in the tensile strength as compared to unmodi-fied-clay-filled samples. Above 8 wt% clay loading, the mechanical properties decrease. The efficiency and good dispersion of 30B in the hyperbranched PU40... 

FIGURE 8.8 Rate of heat release curves of PU-nanocomposite coatings on PET knitted fabrics at 35kW/m2. (From Devaux, E. et al., Fire Mater., 26, 149, 2002. With permission.)... 

Better dispersion of MWNTs in the polymer matrix caused by the formation of the chemical bonds leads to uniform stress distribution and enhanced shape memory (23). Jana et al. prepared nanocomposites of PU and MWNTs via in-situ polymerization and conventional method (105). PU nanocomposites obtained via an in-situ method with PCL-g-MWNTs showed better shape recovery, compared to conventional nanocomposites. 

Wang and Pinnavaia [31] were able to prove for the organo-MMT-PU nanocomposite systems that the expansion of the organo-clay increased with increasing curing time (Fig. 14) at 95 °C. Gallery expansion beyond the initial value for... 

Figure 10.23 Scratching profiles of the GO/PU nanocomposites at the scratching rate of 3 pm/s (a) and 5 pm/s (b), respectively. Reprinted from [164] Copyright 2012, with permission from Elsevier.

Figure 1.6 TEM micrograph of a PU nanocomposite indicating complete misalignment of the filler platelets. Reproduced from reference [8] with permission from American Chemical Society.

Figure 7.4 FESEM images of the MWCNT(3wt%)/PU nanocomposite. Reproduced from Ref [17] with permission.

Figure 7.7 Two possible configurations for MWCNT-PU nanocomposite molecules (a) MWCNT-reinforced mixtures dissolved in DMF and (b) insoluble nanotube-crosslinked PU film. Reproduced from Ref. [19] with permission.

Figure 7.10 DSC curves of pure PU and MWCNT-PU nanocomposites. Reproduced from Ref...

Figure 7.17 Thermal conductivity of the MWCNT/PCL-based PU nanocomposites as a function of MWCNT content. The samples ( ) were consistently loaded with 1 wt% SDS. The...

Figure 7.18 Wide angle X-ray diffraction patterns of the PU/MMT nanocomposites (1) PU, (2) MMT, and (2) PU nanocomposite with 21.5% MMT. Reproduced from Ref [32] with permission.

Figure 7.32 Typical indentation load-displacement curves for pristine PU and its two types of PU nanocomposite thin films with different clay concentrations. Reproduced from Ref. [43] with permission.

Composites prepared using different types of nanoparticles can show superior properties compared to pure PU and have a wide range of applications in structural and biomedical fields. The surface morphology of nanocomposites is affected by the nature and amount of the nanoparticles embedded in polymer matrix. Different shapes and sizes of the nanoparticles play a significant role in enhancement of the mechanical, rheological, thermal, and fire retardant properties of the PU nanocomposites. Considerable improvements in antibacterial properties have been reported using nanocomposites compared to pure PU. Incorporation of the different kinds of nanoparticles in PU matrix alters the biocompatible nature of the composites, suggesting that PU composites may have use in biomaterial applications. 

FIGURE 10.10 Heat release rate curves of PU nanocomposites on PET knitted fabrics at 35 kW/m incorporation of nanoadditives in the second stage of sample preparation. (From Ref. 30, copyright 2002, John Wiley Sons Ltd., with permission.)... 

Many of the characteristic parameters, in obtained nanocomposites, were increased in their values by the addition of nanofiller. The viscosity and the storage modulus of PU/MWCNT and PU/Nanoclay systems increased in comparison to the unmodified polymer. In turn, for PU/POSS nanocomposites a strong influence of this type of nanofiller was observed, on glass transition temperature and PU toughness. Only for PU nanocomposites containing MWCNT and nanoclay, nonlinear viscoelastic behavior was observed. Generally, small filler particles maximize the interfacial area and provide great reinforcement. However, for the POSS nanofiller, the authors didn t observe such improvement, because this nanoparticles, in a polyurea matrix, doesn t behave like a conventional nanofiller, but rather like a chemically reactive additive [49],... 

For all of the previonsly mentioned reasons, PU nanocomposite foams conld comprise the advantages of PU foams (wide range of densities, versatile mechanical response, rednced thermal condnctivity, etc.) with those of incorporating nanosized particles into a polymeric matrix (improved thermal stability and mechanical... 

This section considers the most relevant works published in the last years about rigid and flexible PU nanocomposite foams, focusing on the influence of the incorporation of different types of nanoparticles on the structural and mechanical, transport, and other relevant properties of the resulting foams. 

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