Thermal ablation behavior

In the previous chapters experimental data on ablation of the designed polymers have been shown. Polyimide was applied as reference polymer to compare the ablation behavior of the designed polymers versus a commercial polymer which exhibits similar absorption properties. Polyimide is most probably also the most studied polymer in ablation, and numerous reference data about ablation, but also about the chemical properties, exist (e.g., thermal diffusivity, heat capacity, reflectivity, lifetime of exited states etc.). This is also the reason why many models are benchmarked against ablation data of polyimide. 

In order to ablate material with a laser, it is necessary to surpass a material-dependent energy volume density [19]. For fixed laser parameters, the ablation behavior of any sample is primarily influenced by its optical (reflectivity R, linear absorption coefficient a) and thermal (thermal diffusivity S) properties. Therefore, ablation thresholds Fth and rates per pulse d vary. 

The impact of the nanocomposite technology on polymers is huge, reflected in enhanced properties of the resulting PNs, such as enhanced mechanical, barrier, solvent-resistant, and ablation properties.12 The effect of nanocomposite technology on the thermal and fire performance of the polymers is primarily observed in two important parameters of the polymers (1) the onset temperature (7( ,nsct) in the thermogravimetric analysis (TGA) curve—representative of the thermal stability of the polymer, and (2) the peak heat release rate (peak HRR) in cone calorimetric analysis (CCA)—a reflection of the combustion behavior (the flammability) of the polymer. The Tonset will be increased and the peak HRR will be reduced for a variety of polymers when nanoscale dispersion of the nanoadditive is achieved in the polymer matrix. 

Similar values of thermal conductivity to those of the GFRP material were reported for the PB materials at room temperature (0.28W(mK) [26, 29] and 0.4W(mK) [25]) and similar behavior was also found for the temperature-dependent thermal conductivity of PB materials as presented in [25, 29]. As shown in Figure 9.9, the PB material exhibited a reduction in thermal conductivity at about 100 °C due to the voids introduced after water evaporation. This was followed by an obvious increase when the temperature exceeded 400 °C [29] or 600 °C [25, 26], due to the opening of cracks and ablation in the PB material at high temperatures. 

Carbon nanotubes have attracted huge attention ever since they were discovered because of their unique structures. The studies are mainly focused on the mechanical, electrical, and thermal properties of carbon nanotubes and the applications of their novel properties. Fluid behavior inside carbon nanotubes and fluid transport through carbon nanotubes have been investigated only recently and novel fluidic phenomena, such as abnormally low flow resistance, have been observed. Carbon nanotubes are usually synthesized by arc-discharge, laser ablation, and Chemical Vapor Deposition (CVD) [4]. The arc-discharge and laser ablation methods involve the condensation of carbon... 

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