Thermal-Mechanical Degradation

Rideal, G. R. and Padget, J. C, The thermal-mechanical degradation of high density polyethylene, J. Ptdym. Sri, Pofym. Sympos. Ed., 57,1-15 (1976). 

High-temperature thermoplastics, such as polysulfone, polyether sulfone, polyphenylene sulfide, polyether imide, polyaryl ether ketone, and polyphenylene ether are processed at high temperatures (some above 300 °C). Here, the limit of pyrolysis is almost reached. Degradation and cross-linking as well as discoloration can occur thermal-oxidative and thermal-mechanical degradation under processing conditions have not been sufficiently investigated [38]. 

During the unavoidable thermal-mechanical degradation during manufacture and processing, thermal and mechanical effects act in combination. 

The challenge in these designs is to lower the NO without degradation in unit stability. In the combustion of fuels that do not contain nitrogen compounds, NOx compounds (primarily NO) are formed by two main mechanisms, thermal mechanism and the prompt mechanism. In the thermal mechanism, NO is formed by the oxidation of molecular nitrogen through the following reactions ... 

What is mechanical degradation Why is it less commonly encountered relative to thermal and photo-oxidative degradation ... 

Eggert and Courtney-Pratt and Rogers state that the decomposition of silver azide under the influence of irradiation has a thermal character, i.e. that light absorbed by a thin surface layer of the crystal is degraded into heat in a very short time interval (less than 1/50 fisec), whereupon explosion occurs by the normal thermal mechanism. 

Free radicals are also produced by chain scission during deformation of polyethylene and FT-IR has been used to follow this process 237). The polyethylene samples were unaxially drawn and the resultant spectra corrected for orientation. An increase in the vinyl and methyl end groups created by decay of the free radicals occured in going from draw ratios of 5 to 20 44). A similar study involving deformation was made of polystyrene 246) and a comparison demonstrated between the results of thermal and mechanical degradation 24S. ... 

Polysulfone Plastics. These plastics which were commercialized by Union Carbide are actually aromatic polyethers containing periodic sulfone groups which provide additional resonance stabilization. They have good mechanical properties, creep resistance, and dimensional stability but their outstanding quality is their high heat distortion temperature (345°F.) and resistance to thermal oxidative degradation. Limitations are difficult thermoplastic processability, amber color, and sensitivity to organic solvents. 

Large-scale applications are limited because of the sensitivity of polymers to chemical, thermal, and/or mechanical degradation (Martischius). Thus, the use of polymers should either be limited to open-ended systems with short distances to be covered (such as in the use of water hoses in fire fighting) or an additional injection device must be used in pipeline transportations, to automatically adjust the content of (fresh) flow improvers in case of decreased effectiveness. 

Destructuring the native organization of the raw agricultural products is possible with a combination of thermal, mechanical and chemical effects in an extruder (Figure 5.21). In the first constraint zone, the matter is roughly crushed. In the second, a compression (up to 20 bars) in the reverse screw induces a non-degradative break... 

The material and information on molecular weight data were kindly supplied by R. H. Burr, Phillips Petroleum Co. Mw = 129,000, Mn = 107,000, Mw/Mn = 1.21, styrene content 40% by weight. (Our own GPC measurements showed styrene content 39% and Mw/Mn = 1.38 without correction for band spreading.) SBS and SB materials caused problems because of thermal (and possibly mechanical) degradation. 

This chapter first presents a brief discussion on the synthesis of PLA, then, it gives an overview of various processing techniques used to fabricate PLA nanocomposites, with a special focus on the microcellular technology. Lastly, the chapter discusses various viscoelastic, thermal, mechanical, thermal degradation, electrical... 

Thermal-Mechanical Criteria. The thermal and mechanical properties must not be degraded. The toughness properties (crack and impact resistance) must be improved, and the system should be rather insensitive to the rate of loading (or temperature) of a given test. 

The macromolecular structure of (vulcanized) rubber can be degraded using thermal, mechanical, and chemical means [14]. The resulting reclaim was once incorporated in limited amounts in new tyres. Safety and quality considerations dried up this outlet. 

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