CW nanocomposite

Fig. 3.26 Casting-evaporating procedures for preparation of polymer/CW nanocomposites...

Most of the recent reported polymer/CW nanocomposites were prepared by this method. The reported polymer matrixes contain poly(styrene-co-butyl acrylate) [36], poly(caprolactone) [37], natural rubber [39,140,141], soy protein isolate [38], poly(vinyl alcohol) [42, 44], chitosan [41, 141], silk fibroin, [142], alginate [44], starch [143], hyaluronan-gelatin [55], and waterborne polyurethane [144, 145]. 

This section discusses the results of reactive molding of CW nanocomposites using FA as a polymerizable solvent medium to produce CW-PFA nanocomposites. Cellulose whiskers are not commercially available, and therefore, they were prepared by hydrolysis of MCC with sulfuric acid. The preparation of the CW was followed by their thorough morphology characterization, and finally, by the polymerization of FA to PFA in their presence. To characterize the polymerization behavior and to investigate how the presence of CW influences the polymerization of FA, FTIR spectra were collected before and during the resinification process. Finally, characterization of the thermal stability of the CW-PNC, as measured by TCA, is discussed and compared to the pure polymer. The results provide a useful qualitative measure of the CW dispersion in the cured PNC. 

While the linear absorption and nonlinear optical properties of certain dendrimer nanocomposites have evolved substantially and show strong potential for future applications, the physical processes governing the emission properties in these systems is a subject of recent high interest. It is still not completely understood how emission in metal nanocomposites originates and how this relates to their (CW) optical spectra. As stated above, the emission properties in bulk metals are very weak. However, there are some processes associated with a small particle size (such as local field enhancement [108], surface effects [29], quantum confinement [109]) which could lead in general to the enhancement of the fluorescence efficiency as compared to bulk metal and make the fluorescence signal well detectable [110, 111]. 

Jeschke et al. studied the impact of surfactants on the nanocomposites in particular and in a combined CW EPR and pulse (ESEEM-based) approach demonstrated that there are two types of surfactants present in the composites. They could distinguish surfactants that adhere strongly to the surface of the nanoplatelets from those that are intercalated and interact most strongly with the added polymer (in this case poly(styrene)) [87]. 

Thereafter, CWs have been increasingly used in many other polymer matrices. Following processing steps are involved in the manufacturing of polymer/chitin whisker bio nanocomposites. 

Tensile testing of single crystalline metallic microwhiskers can also be studied following the experimental tensile testing constructed by Brenner and (b) results of whisker fracture strength as a function of whisker size, showed the clear size dependence (Fig. 3.34). The chitin whiskers are usually incorporated into polymer matrix to prepare CWs reinforced polymer nanocomposite. Thus, the mechanical... 

In general, infrared spectroscopy can be used to investigate the chemical bonds of the NR matrix and the chemical links of the inorganic filled added to the matrix. For infrared spectrum of composites and nanocomposites based on NR, it is possible to identify all of the vibration band characteristics of the poly(cw-l,4-isoprene) structure being principally two main sets of bonds. The first set around 3000 cm and the second set around 1500 cm For the inorganic filler, it is expected to identify bands mainly between 800 and 200 cm that it can be attributed mainly to the metal-oxygen bonds. 

Chang HY, Lin CW (2003) Proton conducting membranes based on PEG/Si02 nanocomposites for direct methanol fuel cells. J Membr Sci 218(l-2) 295-306... 

Polymer nanocomposites can be synthesized using cellulose in the form of cellulose nanocrystals or CWs. Pure cellulose is a biopolymer, specifically the polysaccharide of D-anhydroglucose units connected through the (1-1,4-glycosidic ether bond [31], as shown in Figure 6.2. 

The overall objectives of the reactive molding of ceUulose whisker nanocomposites were to (i) disperse CWs in a FA monomer, and (ii) to achieve in-situ polymerization of the CW-FA dispersion using FA as a polymerizable solvent medium. 

In CW-PFA, the onset of degradation (temperature at 5% weight loss) is at 323 °C, which is 77 °C higher compared to y-Al-PFA, and remarkably, also 20-30 C higher compared to the MMT-PFA nanocomposites. The residual weight of CW-PFA is 6wt% (units) higher at 500°C and 4wt% (units) higher at 800 C compared to pure PFA. Table 6.2 summarizes the main TGA results. 

To characterize the polymerization behavior of FA and to investigate how the presence of MMT influences this polymerization, FTIR spectra were collected before and during the resiniflcation process. The dispersion of the MMT in the PFA matrix is shown both directly and indirectly. The direct evidence consists of the XRD patterns of the FA-MMT suspension, which was used to monitor the process of intercalation and exfoliation of the MMT at various stages of resinifica-tion. The dispersion is indirectly evidenced in increased thermal stability of the MMT-PFA nanocomposite, as measured by TGA. The thermal stability is discussed and compared to the pure polymer and to the CW-PFA nanocomposites. In addition, the important differences between oxidative and nonoxidative degradation of the NaMMT-PFA nanocomposite is discussed, and a mechanism is proposed to explain the difference in terms of acid-catalyzed degradation. 

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