Rubber thermal stability

The high thermal stability of the carbon-fluorine bond has led to considerable interest in fluorine-containing polymers as heat-resistant plastics and rubbers. The first patents, taken out by IG Farben in 1934, related to polychlorotri-fluoroethylene (PCTFE) (Figure 13.1 (a)), these materials being subsequently manufactured in Germany and the United States. PCTFE has been of limited application and it was the discovery of polytetrafluoroethylene (PTFE) (Figure... 

Block copolymers can contain crystalline or amorphous hard blocks. Examples of crystalline block copolymers are polyurethanes (e.g. B.F. Goodrich s Estane line), polyether esters (e.g. Dupont s Hytrel polymers), polyether amides (e.g. Atofina s Pebax grades). Polyurethanes have enjoyed limited utility due to their relatively low thermal stability use temperatures must be kept below 275°F, due to the reversibility of the urethane linkage. Recently, polyurethanes with stability at 350°F for nearly 100 h have been claimed [2]. Polyether esters and polyether amides have been explored for PSA applications where their heat and plasticizer resistance is a benefit [3]. However, the high price of these materials and their multiblock architecture have limited their use. All of these crystalline block copolymers consist of multiblocks with relatively short, amorphous, polyether or polyester mid-blocks. Consequently they can not be diluted as extensively with tackifiers and diluents as styrenic triblock copolymers. Thereby it is more difficult to obtain strong, yet soft adhesives — the primary goals of adding rubber to hot melts. 

Naqvi and Sen [155] studied the thermal stability and thermal characteristics of PVC and c/5-polybuta-diene rubber (PBR) blends. The conclusions of their study may be summarized as follows ... 

Silicones This term is given to a wide range of polymers including fluids, rubbers and thermosetting resins. Although rather expensive relative to most other plastic they are particularly noted for their thermal stability and their water repellency. 

Moorite Propellant. A series of rocket proplnts submitted to PicArsn for evaluation in 1949. They consisted of an oxidizer (such as K perchlorate) 70, and a cured rubber hydrocarbon plus accelerators, 30%. Although the examined samples proved to possess desirable props for rocket proplnt use, their thermal stability was poor and their press exponent undesirably high. It was concluded that further work was required on the method of prepn to eliminate these defects... 

The nitro polymer is compatible with both NC and rubber in wt % ratios of from 20—80%. The Qc is 3556cal/g at 25° (Ref liq H20), The Q is -278kg cal at 25°. Impact sensy using a BM machine with a 2kg wt is over 100cm at the 50% point (RDX, 28cm). Thermal stability at 65.5° for a 1.3g sample using KI-Starch paper colored the paper in 11 mins (Ref NC, 10 mins, no color), at 134.5° the Methyl violet paper colored in 10 mins and then the sample expld in 22 mins (Ref NC, 30 mins, no color)... 

Uses. n-Pentane has found use as an anesthetic an expl suppressant when mixed with a halogen-ated hydrocarbon and included in aircraft fuel (Ref 13) a jet engine fuel (Ref 16a) as a base for synthetic rubbers and plastics a parent compd for the formation of nitropentanes and azido nitro pentanes used as expls and propints (Refs 15a, 15b 21a) also, as a parent compd for fluorine-contg resin binders which impart both thermal stability and, in conjunction with metal hydrides, high impulse to solid propints (Ref 15b)... 

Literatures are available on POSS-polymer composites synthesized from different thermoplastics [71-74]. These composites are lightweight and show good fire retardancy, thermal stability, and mechanical reinforcement. Literatures on POSS-rubber composites are yet to come in a big way. 

Another vulcanizing agent for diene rubbers is m-phenylenebismaleimide. A catalytic free-radical source such as dicumyl peroxide or benzothiazyldisulfide (MBTS) is commonly used to initiate the reaction [61]. Phenolic curatives, benzoquinonedioxime, and m-phenylenebismaleimide are particularly useful where thermal stability is required. 

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... 

This is very useful for generating modulus versus temperature data on rubber compounds. The effects of temperature on this important material property can be obtained over a wide temperature range (typically -150 to +200 °C), along with the glass transition temperature and information on thermal stability. 

On the other hand, silicones are used in organic composites. The application of alloys composed of the fully cured silicone rubber particles in a continuous thermoplastic phase, called thermoplastic silicone vulcanizate, which offers high-performance materials, has been reported.506,507 Functionalized POSS was not only co-polymerized, but also blended with poly(methylmethacrylate) to study the effect of silsesquioxanes on the thermal stability of thermoplastics.508... 

For applications where only mechanical properties are relevant, it is often sufficient to use resins for the filling and we end up with carbon-reinforced polymer structures. Such materials [23] can be soft, like the family of poly-butadiene materials leading to rubber or tires. The transport properties of the carbon fibers lead to some limited improvement of the transport properties of the polymer. If carbon nanotubes with their extensive propensity of percolation are used [24], then a compromise between mechanical reinforcement and improvement of electrical and thermal stability is possible provided one solves the severe challenge of homogeneous mixing of binder and filler phases. For the macroscopic carbon fibers this is less of a problem, in particular when advanced techniques of vacuum infiltration of the fluid resin precursor and suitable chemical functionalization of the carbon fiber are applied. 

These products find use in specialty applications requiring better thermal stability than available in the sulfur vulcanized elastomers. Other processes are also used to crosslink polydiene rubbers (Secs. 9-2c and 9-2d). 

Polyolefins and PVC Improving thermal stability, uniformity, and fine structure for packaging and insulation, rubber sheeting Cross-linking with high-energy electrons... 

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