Onset degradation temperature

For example, the 1% Cloisite filled system experiences a 40X increase in onset degradation temperature after 504 hours aging under moist air compared with the same system under dry N2 conditions, which exhibits an 1 PC increase after the same period. Such changes cannot wholly be accounted for by passive degradant loss and these data suggest that a chemical aging process is responsible. 

Figure 6. Onset degradation temperature as a function of age time for systems aged under dry N2. Squares, circles, up-triangles, down triangles and diamonds correspond to 0, 1, 2, 4 and 8% Cloisite filled systems respectively.

Detailed analysis of TGA graphs (Figure 3) allows claiming that thermal stability increase is achieved even by addition of 1 wt% of MWCNT to PP, while further addition does not lead to such fundamental growth. In addition, Figure 4 shows the comparative results for onset degradation temperatures (T ) and the maximum mass loss temperatures (T ) of PP/MWCNT nanocomposites with the different types and concentrations of MWCNT. One can see nonlinear relation of (T ) and versus MWCNT concentration in the PP compositions (Figure 4). 

FIGURE 4 Comparative diagrams showing the onset degradation temperatures (a) and the maximum mass loss temperatures (b) for PP and PP/MWCNT nanocomposites with the different types and concentrations of MWCNT. 

Onset degradation temperature Temperature of maximum rate of mass loss T inal degradation temperature... 

Thermogravimetric analysis (TGA) is the most widely used thermal analysis technique, although other techniques such as differential scanning calorimetry (DSC) and differential thermal analysis (DTA) have also been used for polymer blends (see Table 8.1). In this section, we will limit our discussion to TGA, as its results (such as onset degradation temperature, degradation rate, and kinetic parameters) are most indicative of the fire performance of materials in fires. 

Table 8.2 shows TGA data for PS-OMT-ArP nanocomposites prepared by the in situ polymerization method, including the onset degradation temperature at which 10% of the sample was lost the midpoint of the degradation... 

The analysis of the thermal decomposition curves estimates a mass loss that is associated with the degradation processes. Thermal decomposition of pure polymers, before degradation process, usually occurred in a single mass loss step. The copolymers or blends generally show more than one distinct mass loss step. The magnitude of each mass loss correlates with the content of the corresponding block in the copolymer or the blend materials [104]. The onset degradation temperature, defined by TGA, determines the thermal stability of the material. 

Zhu et al. studied polyurethane foams from soy reinforced with cellulose microfibers. They found an increase on the onset degradation temperature of the thermal degradation of polyurethane with the addition of 2 wt % cellulose fibers. They attributed this fact to the insulator effect of cellulose fibers [52]. Navarro-Baena et al. studied shape memory PU based on PLA-PCL-PLA block copolymer and reinforced with both CNCs and PLA grafted CNCs [72]. Aside the increment on the shape memory behavior of the polyurethane-based nanocomposites, they reported an increase on the thermal stability of the PU matrix in particular, they reported that, although CNCs improved the thermal stability of both PCL and PLEA blocks, in particular the thermal stability of the PCL block was improved in the nanocomposites increasing the maximum degradation temperature of about 40 with respect to the PCL block of the neat PU-matrix [72]. 

From the simple example in Figure 13.9 it can be shown that the degradation behavior of a silicone can be directly related to its structure. In the RTV condensation-cured system, the onset degradation temperature could be related to the levels of free silanol chain ends present in a complex silicone network. 

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