Rubber thermal degradation

Hall, Patel [30] Polysiloxane rubber thermal degradation Cyclic oligomers PDMS... 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

For abrasion this is, however, a much more dominating process than for cut growth. The main reason is that the energy consumption in the abrasion process raises the temperature in the interface between rubber and track and thereby modifies this process. The temperature in the contact patch is a function of the power consumption and depends, therefore, also on the sliding speed. The temperature not only influences the oxidation and cut growth process, but also causes thermal degradation. 

Thermal degradation studies of EB-cured terpolymeric fluorocarbon rubber [430] by nonisothermal thermogravimetry in the absence and presence of cross-link promoter TMPTA reveal that thermal stability is improved on radiation and more so in the presence of TMPTA. Initial decomposition temperature, maximum decomposition temperature and the decomposition... 

Jha, A. and Bhowmick, A.K., Thermal degradation and ageing behaviour of novel thermoplastic elastomeric nylon-6/acrylate rubber reactive blends, Polym. Degrad. Stab., 62, 575, 1998. 

Polymers can exist as liquids, as elastomers or as solids but can be transferred into the gaseous state only under very special conditions as are realized in, for example, MALDI mass spectrometry. This is because their molecular weight is so high that thermal degradation sets in before they start to evaporate. Only a few polymers are technically applied in the liquid state (silicon oils, specidty rubbers) but most polymers are applied either as elastomers, or as rigid amorphous or semicrystalline solids. 

Thermal Degradation Behavior of Rubber-Based Nanocomposites... 

The dithiocarbamates have the pentacoordinate binuclear structure (44). The diamyl- and diethyl-dithiocarbamate complexes have been found to inhibit the hardening of asphalt, but the effect appears too weak to be useful.127 The latter complex is an effective antioxidant for polyethylene,128 polypropylene,129 polystyrene,130 poly(methyl methacrylate)130 and an isoprene-styrene copolymer.131 The di-n-butyldithiocarbamate complex is important in the vulcanization and injection moulding of rubber,132 as a stabilizer against photolytic and thermal degradation. 

As in purely thermal degradation, thermal oxidation of rubber is accompanied by formation of low-molecular-weight products in yields too high to be accounted for by random attack on the... 

Hydrogenation is an important method of chemical modification of elastomers. Because of the absence of carbon-carbon unsaturation, hydrogenated elastomers have good resistance to oxidative and thermal degradation, improved weatherability and good resistance towards chemicals and fluids [5-7]. Nitrile rubber (NBR) is a specialty rubber, and because of its oil resistance properties, it has been used in oil-wells and the automotive industry. Hydrogenation of NBR has been studied extensively because of its technological importance [16-19]. 

Thermal and Chemical Stability. In addition to load-bearing properties, tire reinforcement must be able to resist degradation by chemicals in cured rubber and heat generation. The most critical degradant depends on the material in use. Most thermoplastic reinforcements are either modified direedy or stabilized with additives to offset some, mosdy thermal, degradation (32,33). 

Much of the behavior of thermosetting materials can be clarified in terms of the TTT cure diagram through the influence of gelation, vitrification and devitrification on properties. For example, gelation retards macroscopic flow, and limits the growth of a dispersed phase (as in rubber-modified systems) vitrification retards chemical conversion and devitrification, due to thermal degradation marks, the limit in time for the material to support a substantial load. 

In this Section, an experimental approach for constructing isothermal TTT cure diagrams has been described, TTT diagrams of representative epoxy systems including high Tg and rubber-modified epoxy resins have been discussed, and perturbations to the TTT cure diagram due to thermal degradation and rubber modification have been illustrated. 

For high temperature and rubber-modified epoxy resins, thermal degradation events and the cloud point curve are included on the diagrams, respectively. Two degradation events have been assigned devitrification, or a glass-to-rubber event and revitrification, which is associated with char formation. The cloud points and depressions of Tg for different rubber-modified epoxies can be compared and related to volume fractions of the second phase and to the mechanical properties of the cured materials. 

M. Lopez-Manchado, L. Torre and L. M. Kenny, Kinetic analysis of the thermal degradation of PP-EPDM blends. Rubber Chemistry and Technology, 23, 73-84 (2002). 

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