Thermo-oxidative stability degradation mechanism

Phenolic networks are well known for their excellent thermal and thermo-oxidative stabilities. The mechanisms for high-temperature phenolic degradation include dehydration, thermal crosslinking, and oxidation, which eventually lead to char. 

Bikiaris, D., Vassiliou, A., Chrissafis, K., Paraskevopoulos, K. M., Jannakoudakis, J., and Docoslis, A. 2008. Effect of acid treated multi-walled carbon nanotubes on the mechanical, permeability, thermal properties and thermo-oxidative stability of isotactic polypropylene. Polymer Degradation and Stability 93 952-967. 

The coated particles possess greater thermo-oxidative stability than ICPs (300-3 50°C). so accommodating the majority of thermoplastics and thermosets currently used in industry without degradation or loss of conductivity. The filler has a greatly reduced surface area and pore volume compared with the original carbon black. In a number of plastics matrices, conductive blends can be produced with improved electrical, and mechanical properties. 

The comparison of the results obtained in this study for the LCP degradation imder processing temperatures with the peculiarities of some thermally stable polyheteroaiylenes degradation [14] brings to light some common features carbonization of the structure, H2 evolution, improvement in thermo-oxidative stability with transition metal compoimds. That is why we took into accoimt the stabilization of polysulfones, aiyl-aliphatic polyimides, polyamides etc. The approach to such stabilization is based on the following proposals on the mechanisms of the above said polymer degradation ... 

The objectives of the study carried out by Turk and co-workers [15] were to rank polymer thermo-oxidative stability via accelerated thermal techniques and to correlate these results with the long-term, high-temperature stabilities found via weight loss techniques. In particular, they used TGA, IGA, TGA-FTIR and IGA-FTIR to characterise the degradation pathways of four thermally stable PI and to determine their E. Three accepted mathematical methods were used to examine for correlations of accelerated ageing and real-life ageing of PI. Acceleration of the decomposition is obtained using elevated temperatures that can introduce additional decomposition mechanisms when compared with actual use temperatures. 

Forsstrom, D., Terselius, B. R Thermo oxidation stability of polyamide 6 films. I. Mechanical and chemical characterization. Polym. Degrad. Stab. 67, 69-78 (2000)... 

Besides organic polymers, inorganic polymers also are susceptible to thermo-oxidative degradation. Nielsen describes the stabilization of silicone fluids with redox systems of iron and cerium by a free radical mechanism. When stabilized, these fluids show oxidative stability up to 700°F. 

To clarify the mechanisms of the clay-reinforced carbonaceous char formation, which may be responsible for the reduced mass loss rates, and hence the lower flammability of the polymer matrices, a number of thermo-physical characteristics of the PE/MMT nanocomposites have been measured in comparison with those of the pristine PE (which, by itself is not a char former) in both inert and oxidizing atmospheres. The evolution of the thermal and thermal-oxidative degradation processes in these systems was followed dynamically with the aid of TGA and FTIR methods. Proper attention was paid also to the effect of oxygen on the thermal-oxidative stability of PE nanocomposites in their solid state, in both the absence as well as in the presence of an antioxidant. Several sets of experimentally acquired TGA data have provided a basis for accomplishing thorough model-based kinetic analyses of thermal and thermal-oxidative degradation of both pristine PE and PE/MMT nanocomposites prepared in this work. 

Since the discovery of HALS, a lot of research was done on their mechanism of action and many different mechanisms were proposed. At the moment, there is still no consensus, which might be related to the fact that the mechanism of action of HALS, as the UV degradation of polymers, is circumstances dependant. So are results of the mechanism of action in different polymers, UV degraded with different light sources and even thermo-oxidative compared. In the following an overview of the mechanistically work that was done on HALS as stabilizer as well as application data is given. 

Polyolefins are susceptible to several degradative mechanisms, out of which thermo-oxidative and thermomechanical are dominant. The PO stability depends on macromolecular configuration and it follows the order HOPE > LLDPE > LDPE > i-PP. Chemiluminescence, FT-IR, mechanical properties, and Ihermogravimetty have been used for detecting and quantifying degradations (Cran 2004). 

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo-oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one-dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behavior compared with neat PP. Evidently, the mechanism of nanocomposite flame retardancy is based on shielding role of high-performance carbonaceous-silicate char which insulates the underlying polymeric material and slows down the mass loss rate of decomposition products. 

HAS can protect polymers from thermo-oxidative degradation according to the two main mechanisms of stabilization already encountered, i.e., free radical scavenging, and hydroperoxide decomposition. The first type of stabilization reaction is based mainly on oxidation products of the amines, though for some time radical scavinging was considered to also be... 

Among the various methods used for studying thermal and thermo-oxidative degradation of PES, thermogravimetric analysis (TGA) and pyrolysis gas chromatography-mass spectroscopy (PGC-MS) have been used most frequently. These instruments enable comparisons of the relative thermal stability and thermal decomposition temperature, and give information about the degradation mechanism [9,24]. TGA also is an excellent technique for product characterization and quality control. 

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