PU/CNT composites

Figure 6.1. Chemical route for the modification of CNTs and the fabrication of PU/ CNT composites. Reprinted from Xiong et al. (19) with permission from the Elsevier.

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].

Figure 6.8 DSC curves of polyurethane and its nanocomposites in the presence of different types of nanoparticles, (a) PU-Au nanocomposites, 1 for pure PU, 2, 3, and 4 indicate 1.74,4.35, and 6.5xl0 wt% of Au nanoparticles [104], (b) PU-CNT composites [80], and (c) PU-nanoclay...

Price et al. [23] PU/CNT - nano-composites Osteoblasts, chondrocytes, fibroblasts, plain muscular cells - contact with PU/CNT Adhesion increased only for osteoblasts absence of cytotoxicity... 

Hu et al. [26] PU/CNT - nano-composites Astrocytes, axons of rats -contact with PU/CNT nanocomposites Reduction of astrocyte adhesion, increased inhibition of axons. Cytotoxicity is absent... 

PU) composite Poly(lactic acid) (PLA)/CNT composite Increasing osteoblast proliferation. 

Figure 7.14 SEM micrographs of the fracture surface of the ultralightweight CNT/PU foam composite with a density of O.OSgcm. ...

Figure 7.15 Schematic diagram of the microstructural changes in the CNT/PU foam composites with the decrease of density. The thin black lines represent the CNTs and the wide lines represent the boundaries of the...

For example, Li et al. [153] used a simple solution-precipitation technique to improve the dispersion of CNTs in a polycarbonate solution by sonication at a frequency of 20 kHz for 10 min. They showed that the CNTs were uniformly dispersed in polycarbonate matrix on its consolidation. Safadi et al. [154] dispersed MWNTs in PS using ultrasonication and dismembrator at 300 W for 30 min. Uniform dispersions of CNTs in PS were achieved by using sonication. Recently, Cho and coworkers successfully prepared polyurethane (PU)/MWNT composites with better dispersion of CNTs up to 20 wt% in PU [155]. 

In situ polymerization has been widely used for the preparation of PMMA-CNT composites [180-183]. Conducting polymers are attached to CNT surfaces by in situ polymerization to improve the processability and electrical, magnetic, and optical properties of CNTs [184-187]. PU/MWNT [188,189] and PA/MWNT [190] composites were also synthesized by this method. 

The dispersion of carbon nanotubes in PU matrix can also be affected by the synthetic methods as well as the tensile stress etc. Xiong et al. found that the CNTs in the composites after tensile testing could easily take an ordered orientation along with the tensile direction on the cross-section perpendicular to the pressure direction, whereas the arrangement of the CNTs has not almost changed on the cross-section parallel to the pressure direction (62). The phenomenon that the SWNTs near the film substrate interface are driven to self-organize to a more ordered structure was discovered by Chen et al. (16). 

The gap between the predictions and experimental results arises from imperfect dispersion of carbon nanotubes and poor load transfer from the matrix to the nanotubes. Even modest nanotube agglomeration impacts the diameter and length distributions of the nanofillers and overall is likely to decrease the aspect ratio. In addition, nanotube agglomeration reduces the modulus of the nanofillers relative to that of isolated nanotubes because there are only weak dispersive forces between the nanotubes. Schadler et al. (71) and Ajayan et al. (72) concluded from Raman spectra that slippage occurs between the shells of MWNTs and within SWNT ropes and may limit stress transfer in nanotube/polymer composites. Thus, good dispersion of CNTs and strong interfacial interactions between CNTs and PU chains contribute to the dramatic improvement of the mechanical properties of the... 

The viscoelastic properties of carbon nanotube/polymer composites have both practical importance related to composite processing and scientific importance as a probe of the composite dynamics and microstructure. The viscosity for CNT/PU dispersion at mixing is also very important for in-situ formation of polyurethane nanocomposite. Lower viscosity means a better flow ability and more homogenous mixing with isocyanate. Furthermore, low viscosity is very helpful to remove the bubbles before curing, which is a key step for polyurethane preparation. 

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