Thermal degradation, polymers

In the present study, PU s containing lignin were investigated with reference to thermal stability, which is one of the basic thermal properties of polymers. Thermal degradation of PU s which were obtained from solvolysis lignin was studied using thermogravimetry (TG). The inflammability of... 

Liu, N. A. and Fan, W. C. Critical consideration on the Freeman and Carroll method for evaluating global mass loss kinetics of polymer thermal degradation. Thermochemica Acta 1999 338 85. 

For many polymers thermal degradation is characterised by the breaking of the weakest bond and is consequently determined by a bond dissociation energy. Since the change in entropy is of the same order of magnitude in almost all dissociation reactions, it may be... 

A complete picture of polymer thermal degradation is clouded because multiple reaction mechanisms can be operable for a single polymer at a single temperature, leading to a host of volatile products and residues. Therefore, one has to consider the relative rates of these competing reactions to establish an optimized and controlled binder burnout. 

Pyrolysis of the formed polysilazane at 750° C generates several alkylsilanes such as dimethylsilane, trimethylsilane, ethyldimethylsilane, tetramethyidisiloxane, pentamethyidisiloxane, methylenebisdimethylsilane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, etc. The presence of the cyclic compounds similar to those from poly(dimethylsiloxane) was an indication that some polysiloxane sequences may be present in the polymer. Thermal degradation studied between 350° C and 650° C showed the formation of some hydrogen, methane, ethane, and propene. 

The interest here is focused mainly on heavy hydrocarbons feedstocks, as in the case of certain refinery processes, and on polymer thermal degradation. A radical chain mechanism is also involved in the liquid- or condensed-phase pyrolysis. This is once again characterized by initiation, radical recombination... 

According to the pathways described above, the thermal decomposition of polymers often involves the formation of volatile species within a highly viscous polymeric matrix. Transport of these species through the molten polymer mass towards the vapour phase is not a straightforward process, and so the occurrence of mass transfer limitations can be expected. Various authors have observed that the rate of polymer thermal degradation depends on factors such as the surface area and thickness of the polymer sample, showing that the polymer decomposition is controlled by the diffusion and/or the vaporization of the volatile species.13,14... 

Trityl-2,3-di-0-methylcellulose, 6 Polymer 6 gave satisfactory elemental analysis (Table 1), however, the conversion of polymer 4 to 5 resulted in a drop in the average DPw from 353 to 251 anhydroglucose units. While many mechanisms can be postulated to explain DP loss upon reactions with base, acids, organometals, and the like, none are satisfactory. Therefore, in this article we report DP loss upon reaction, but do not attempt to explain it. The polymer thermally degraded above 224 C, and we were imable to generate films for DMA analysis. 

Polymer Thermal degradation Photo-oxidation Ozone... 

Except montmorillonite, other clays like layered double hydroxide (LDH) can enhance thermal degradation of polymers. In such nanocomposites there are no reported for accelerating effect of LDH on polymer thermal degradation. This is because LDH can be more easily dispersed in intercalated or exfoliated structures, compared with MMT, into a polymer matrix and thus the stabilization effect is higher [22]. 

Mechanistic reaction kinetics of polymer thermal degradation processes show that the overall mass loss (fuel generation) rate should be first order with respect to the instantaneous mass if the reactive intermediates (free radicals) maintain a steady-state concentration, regardless of whether thermal degradation occurs by random or end-chain scission. A first-order thermal degradation scheme that accoimts for the main pyrolysis products is (4,7,10)... 

By measuring the fraction of crystallized material, with time t, a value of the constant n equal to 4 was evaluated by Miyata and Masuko [37] who observed, in nonisothermal crystallization experiments from the melt, a remarkable increase in the polymer crystallization at decreasing cooling rates and a maximum value of the isothermal crystallization rate at 105°C. A similar trend was observed by lannace and Nicolais [36]. However, these results could be affected by the polymer thermal degradation induced at a low cooling rates, as previously described by Migliaresi et al. [27]. 

When temperatures near the surface become high, thermal degradation reactions occur and evolve small gaseous degradation products. The majority of the evolved products are combustible. Depending on the nature of the polymer, thermal degradation reactions may proceed by various... 

Electrospinning (melt) Nanofibres are uniform, long and continuous Solvent-free Polymers thermal degradation Electric discharge problematic Low fibres diameters difficult to obtain... 

Meltblowing Long, continuous fibres High productivity No solvent recovery required Limited types of polymers Thermal degradation of polymers Low fibre diameters require special equipment High fibre diameter distribution... 

Recently, various studies have recognised MALDI and ESI as valuable techniques for analysing chemical modifications in the structure of synthetic polymers induced by degradation processes [154-158]. Even tough, MALDI and ESI MS appear considerably less extensively used in the thermal degradation of polymers than in other degradation processes [160], In fact, the study of polymer thermal degradation by MALDI has been limited to a few classes of polymers likely since it is a useful method to analyse pyrolysis products from soluble polar macromolecules. 

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