Polymer nanocomposites thermal decomposition

The incorporation of nanotubes into thermotropic liquid crystalline polymer (TLCP) was reported to enhance the thermal decomposition temperatures and the residual yields of the nanocomposites (35). It was reported that the nanotubes act as protective barriers in the nanocomposites against thermal decomposition and are likely to retard the thermal decomposition of the TLCP nanocomposites owing to building of barrier to hinder the transport of volatile decomposed products out of the nanocomposites. 

Tseng et al. (51) reported the epoxy nanocomposites in which the nanotubes were functionalized by maleic anhydride by using plasma treatment. The thermal decomposition temperature was reported to increase with increasing the extent of the nanotubes in the composites as shown in Figure 2.16a. Untreated nanotubes were also used to reinforce the polymer and the increase in the decomposition temperature was also observed in this system as a function of filler content, but the enhancement was more significant using the functionalized nanotubes. This was attributed to... 

The mechanism of the improvement of thermal stability in polymer nanocomposites is not fully understood. It is often stated [126-129] that enhanced thermal stabihty is due to improved barrier properties and the torturous path for volatile decomposition products, which hinders their diffusion to the surface material where they are combusted. Other mechanisms have been proposed, for example, Zhu et al. [130] recently proposed that for polypropylene-clay nanocomposites, it was the structural iron in the dispersed clay that improved thermal stability by acting as a trap for radicals at high temperatures. 

Zabihi O. Characterization and thermal decomposition kinetics of poIy(ethyIene 2,6-naphthalate) nanocomposites reinforced withtio2 nanoparticles. Polym-Plast TechnolEng 2012 51(1) 43-9. 

In general, when compared with the conventional polymer composites, polymer nanocomposites exhibit significant improvements in different properties at relatively much lower concentration of filler. The efficiency of various additives in polymer composites can be increased manyfold when dispersed in the nanoscale. This becomes more noteworthy when the additive is used to address any specific property of the final composite such as mechanical properties, conductivity, fire retardancy, thermal stability, etc. In case of polyolefin/LDH nanocomposites, similar improvements are also observed in many occasions. For example, the thermal properties of PE/LDH showed that even a small amount of LDH improves the thermal stability and onset decomposition temperature in comparison with the unfilled PE [22] its mechanical properties revealed increasing LDH concentration brought about steady increase in modulus and also a sharp decrease in the elongation at break [25]. While in this section, fire-retardant properties and electric properties of polyolefin/LDH nanocomposite were described in detail. 

The main conclusion from all the above is that except of MMT, where contradictory results were reported, in all other nanocomposites the addition of nanoparticles can lead to thermal stabilization effect of polymers during their decomposition. However, in this direction the effect of nanoparticles content is very crucial. In most of the cases the thermal stability enhancement takes place at low loading (4-5 wt%) of nanoparticles while at higher contents thermal stabilization becomes progressively lower. This is because at higher concentrations nanoparticles can form aggregates and thus effective area of nanoparticles in contact with polymer macromolecular is lower. In this case microcomposites may are formed instead of nanocomposites and thus the protective effect of nanoparticles becomes lower [22]. 

M.-T. Nistor, C. Vasile, TG/FTIR/MS smdy on the influence of nanoparticles content upon the thermal decomposition of starch/poly(vinyl alcohol) montmorillonite nanocomposites, Iranian Polymer Journal (English Edition) 22 (7) (2013) 519-536. 

Various researchers have reported on the thermal properties of PAI derived from / /s(4-trimellitimidephenyl) urea [93] and PAI-polydimethylsiloxane nanocomposites [94]. The former polymer had a decomposition temperature of 515 "C under nitrogen for a 10% weight loss. 

Currently, numerous procedures for the preparation of nanocomposite materials are available. Recently, the major synthetic approaches (e.g., evaporation of elemental metal with its deposition on polymeric matrices, plasma-induced polymerisation, vacuum evaporation of metals, thermal decompositions of precursors in the presence of polymers, and reduction of metal ions using different procedures including electrochemical) have been surveyed in books and reviews. However, the uniform distribution of ingredients is generally difficult to achieve when hybrid nanocomposites are prepared with the use of the above-mentioned procedures resulting in the nonuniformity of the properties of the material. The following three principal procedures are most commonly employed ... 

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