Silicone rubbers, vulcanized

TP/Si-V TPV of a vulcanized silicone rubber dispersed in a thermoplastic phase... 

While unaffected by water, styrofoam is dissolved by many organic solvents and is unsuitable for high-temperature applications because its heat-distortion temperature is around 77°C. Molded styrofoam objects are produced commercially from expandable polystyrene beads, but this process does not appear attractive for laboratory applications because polyurethane foams are much easier to foam in place. However, extruded polystyrene foam is available in slabs and boards which may be sawed, carved, or sanded into desired shapes and may be cemented. It is generally undesirable to join expanded polystyrene parts with cements that contain solvents which will dissolve the plastic and thus cause collapse of the cellular structure. This excludes from use a large number of cements which contain volatile aromatic hydrocarbons, ketones, or esters. Some suitable cements are room-temperature-vulcanizing silicone rubber (see below) and solvent-free epoxy cements. When a strong bond is not necessary, polyvinyl-acetate emulsion (Elmer s Glue-All) will work. 

Room-temperature-vulcanizing silicone rubber (General Electric and Dow Corning) is available at hardware stores and is very useful as an adhesive and sealant. Atmospheric moisture is necessary to effect the cure, so broad areas of impermeable materials should not be cemented with these preparations. The uncured material evolves acetic acid, and the cured material appears to lose some weight in high vacuum but if used with moderation, it can be considered a satisfactory vacuum sealant for most chemical vacuum systems. 

Many porous ion exchange membranes with high cation or anion selectivity have been described (B3, P13, S18). Sparingly soluble crystalline materials have been used as anion sensors, the membrane consisting of single crystals or pressed pellets often embedded in a vulcanized silicone rubber matrix. Examples include electrodes for fiuoride (LaF), sulfide (silver-silver sulfide), iodide, and sulfate. These probably function as... 

Figure 8.60. Compression set of vulcanized silicone rubber vs. surface area of silica. [Data from Okel T A, Waddell W H, Rubb. Chem. Technol., 68, No. 1, 1995, 59-76.]...

Room-temperature vulcanizing silicone rubbers (RTV rubbers) are low-molecular-weight liquid silicones with reactive end groups and loaded with reinforcing fillers. Several types are available on the market. 

The latter describes vulcanized silicone rubbers exhibiting very good mechanical resistances and obtained starting from hybrid silicone copolymers prepared via hydrosilylation of dimethyl silyl vinyl ended siloxanes with poly dimethyl methyl hydrogeno siloxanes, in the presence of a Pt catalyst (cf. Scheme 31) ... 

Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of Cr Uses Catalyst, crosslinking agent used for curing heat-vulcanized silicone rubbers, food-contact rubber articles Manuf./Distrib. Gelest http //www.geiest.com Trade Name Synonyms Aztec DCLBP-50-PSI [Aztec Peroxides] Perkadox PD t[Flexsys http //www. fiexsys. com]... 

Definition Room-temp, vulcanizing silicone rubber Properties Sol. in org. soivs. dens. 1.12 (20C) low surf, tension... 

D. Wrobel, Structure and Properties of Hot-Vulcanized Silicone Rubbers", in Silicones — Chemistry and Technology, (Eds. G. Koemer, M. Schulze, J. Weis), Vulkan Verlag, Essen, 1991, p. 61. 

Wang, J. Chen, Y, Preparation of an Organomontmorillonite Master Batch and Its Application to High-Temperature-Vulcanized Silicone-Rubber Systems. J. Appl. Polym. Sci. 2008,107, 2059-2066. 

Catheters must withstand often substantial stresses, from the weight of urine when the collection bag is full, as well as from movement of the user, and these stresses induce fatigue. The catheter can break near the tip, in which case the end must be extracted surgically. Just this happened to a patient, Miss C, in 2007, and she experienced great discomfort and pain, not to mention distress without the device before a new catheter was implanted. The failed parts were returned, and she gave them to her pharmacist for examination, but they were discarded or lost, and so the cause of failure was never determined. However, the replacement catheter she was sent showed failure of almost exactly the same kind, and she sued the manufacturer as a result. The presence of a clean radial fracture (Fig. 9.33) without any applied stress implied a manufacturing defect in the material, vulcanized silicone rubber. 

Vulcanized silicone rubber is characterized by its wide temperature use range (-50 to >200°C), excellent electrical properties, and resistance to air oxidation and weathering conditions (484). Improvements in properties such as heat aging can be achieved by in situ treatment of the filler during rubber manufacture (480). Silicone rubber is also extremely permeable to gases and water vapor. The mechanical properties of silicone rubber are generally inferior to most organic (butyl)... 

Flexmould. Tradename. Flexible polyvinyl chloride or room temperature vulcanizing silicone rubber is used for... 

Room-temperature vulcanizing silicone rubbers (RTV) are also available commercially and are used as adhesives, caulks, and coatings [67]. The RTV systems usually improve the reaction of silanols with ethyl silicate catalyzed by tin compounds (dibutyltin dilaurate) to eliminate ethyl alcohol with the formation of the resin [Eq. (29)]. The time required for the final cure is about an hour at 150°C or 24 hr at room temperature. 

As epoxy and silicone rubber are completely immiscible, the addition of a compatibilizer is necessary to obtain a satisfactory dispersion of the rubber in the resin. The main objective of Kasemura and coworkers [216] was to find an appropriate surface-active agent to reduce the interfacial tension between the resin and the rubber, in order to compatibilize the two components. These authors achieved adequate compatibility in the epoxy resin with the use of a polyester-modified silicone oil to disperse an RTV (room temperature vulcanizing) silicone rubber or silicone diamine. The results showed that the impact fracture energy of the resin was increased by the addition of the RTV silicone rubber, up to two times that of the unmodified resin, whereas the addition of silicone diamine had almost no effect, possibly because the molecular weight was too low. Moreover, T-peel strengths of aluminum plates bonded by epoxy resin filled with RTV silicone rubber and with silicone diamine effectively increased with the silicone content, showing a maximum at 10-20 pph. By scanning electron microscopy, many particles of silicone rubber, 1-20 xm, were observed across the whole of the fracture surface. 

Room-temperature vulcanized silicone rubber Ureas (from carbamide to tetraphenylurea)... 

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