Isothermal degradation

Figure 16.27. Arrhenius plot of first-order rate constants of isothermal degradation of polythiophene. Adapted from Bull. Mater. Sci. 18(3), 255 (1995), with pemiission of the Indian Academy of Sciences.

CBZ-PMDA), carbazole-1,4,5,8-naphthalene tetracar-boxylic dianhydride (CBZ-NTDA) and carbazole-benzophenone tetracarboxyl dianhydride (CBZ-BTDA) were synthesized by a similar method. Poly(N-vinyl-carbazole)-anhydride co-polycondensates such as PNVC-PhAn, PNVC-TMA, PNVC-PMDA, PNVC-NTDA and PNVC-BTDA were also prepared. Thermal stability characteristics of the various polycondensates have been compared in Table 16.18 and it was observed that (i) the initial decomposition temperature and the overall stability of a co-polycondensate of either CBZ or PNVC depends upon the anhydride moiety in the order of NDTA > BTDA > PMDA >TMA > PhAn (ii) initial decomposition temperature and the overall stability of a co-polycondensate with a fixed anhydride, vary in the order PNVC > CBZ and (iii) polycondensation of PNVC by anhydrides improves the thermal stability of the base polymer. It is suggested that the incorporation of thermally stable moieties, cross-links and rigidity is the main reason for enhanced initial decomposition temperature as well as overall thermal stability of these co-polycondensates. Table 16.19 gives the isothermal degradation stability of pairs of polycondensates and data confirm the high thermal stability... 

Samperi and co-workers [70] studied the isothermal degradation of PBT at a series of temperatures coinciding with the standard range of processing temperature for the polyester. Cyclic oligomers were present in the starting polymer and the level of these increased on... 

The thermal degradation of these polymers was studied by DTG, pyrolysis gas chromatography and isothermal degradation at temperatures near the temperature of maximum rate of degradation (Table 6). A temperature of 418°C. was found which was identical for H-H and H-T poly(methyl acrylate). Similar maximum degradation temperatures were observed for H-T poly(methyl crotonate) and H-T poly(methyl cinnamate) however, the corresponding H-H polymers of these B-substituted polyacrylates have maximum rate... 

The thermal degradation of PLA has been claimed to mainly occur via random scission based on a linear relationship between inverse of the number-average degree of polymerization P and time as shown in Equation 23.2 [28]. Recently, Aoyagi et al. [9] and Abe et al. [29] suggested that the isothermal degradation of PLLA at 220, 290, and 330°C proceeded not only via simple random scission, but also via an unzipping depolymerization of the polymer chain based on the nonlinear relationships of l/P and P with time. 

Seo, D., Ogawa, K., Tanno, M., Shoji, T., and Murata, S. (2007) Influence of heat exposure time on isothermal degradation of plasma sprayed CoNiCrAlY coatings. Surf. Coat. Technol, 201, 7952 7960. 

Lorenzo Abate, Antonino Pollicino, Antonino Recca, Ignazio Blanco, and Alice Orestano. "Kinetics of the isothermal degradation of model polymers containing ether, ketone and sulfone groups." Polymer Degradation and Stability, pp. 271-278,2005. 

Similar results for isothermal degradation of different alkylammonium-modified clays were obtained by Cui et al. [16], However, the authors noted that isothermal percentage mass loss data for samples with significantly different molecular weights do not precisely reflect the extent of degradation (conversion). Comparable stability was displayed when mass loss was related to moles of surfactant surfactants. 

Figure 3.24. Experimental oc-f data for isothermal degradation of PEN at 420 °C (circles) and a simulated a-t curve (solid line) obtained by assuming first-order kinetics [Eq. (3.14)]. Inset shows fitting oc-f data to the straight line, -hi(l - a) = k(r)f, to determine the rate constant.

The non-isothermal degradation kinetics of A, iV -di(diethoxythiopho-sphoryl)-l,4-phenylenediamine in N2 have been studied by TG-DTG techniques as mentioned earlier. The synthesis of dioxaphospholanes ligands... 

To improve the thermal stability of these polymers, Biswas and Mitra [349] prepared copolycondensates of carbazole (CBZ) with phthalic anhydride (PtiAn), trimellitic anhydride (TMA), pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalene tetracar-boxylic dianhydride (NTDA), and benzophenone tetracarboxy dianhydride (BTDA) along with similar copolycondensates of PNVC. The thermal stabihty of copolycondensates was observed to depend on anhydride moiety in the order NDTA > BTDA > PMDA > TMA > PhAn for both the types of materials as given in Table IX. Table X shows the isotherm degradation stability of pairs of polycondensates, and the data confirm the high thermal stability of NTDA over the other materials. 

From Equation 1.12, it can be seen that, from a single TGA trace and from a single isothermal degradation experiment, the value of E may be readily obtained irrespective of reaction order. Equation 1.12 has been plotted for Teflon degradation in a vacuum using an isothermal temperature of 494 °C. From the slope of the linear... 

The isothermal degradation and kinetics of PHB-based bionanocomposites were studied by Erceg et al. [245]. Their bionanocomposites consisted of OMMT Cloisite 30B (30B) and PHB prepared by solution casting and isothermally degraded at 230, 235, 240, and 245 °C. They found that the addition of 30B increased the thermal stability of PHB with the most pronounced effect being the addition of 1 wt% 30B. 

The aim of the present work was to describe the different methods, kinetic equations, and calculation procedures used for studying of the kinetic mechanism of solid-state reactions, and determining the kinetic parameters, obtained at non-isothermal degradation of solids. For illustration are showed the data for the kinetic mechanism of non-isothermal dehydration and decomposition of CaC O H O, thermal degradation of chitin, and rice husks (RH). 

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