Tear strength silicone rubber

Silicone rubber has both excellent low temperature and high temperature properties. It can withstand temperatures up to 315°C and workable at -65°C. Poor performance with low tear strength and abrasion resistance limit their use in most applications. Liquid silicone compounds LTV which are room temperature vulcanizable are useful for small repairs and sealing application and have been used for poured-in-place gaskets. 

As with silicone oil, the properties of silicone rubber change slowly with temperature the elasticity persists down to —55° C. Although the mechanical properties require improvement before the material can be recommended for usage under severe stress or abrasion, it is well suited to other applications where thermal stability and resistance to chemical reagents are more important than tensile strength or tear resistance. 

Figure 8.23. Silicone rubber tear strength vs. surface area of silica. [Data from Okel T A, Waddell W H, Rubb. Chem. Teck ol.,6 , iioA, 1995, 59-76.]...

Silicone polymers, crosslinked by radiation in the absence of fillers, form rubbers with poor tensile and tear strength. Much better properties can, however, be obtained for small doses by the inclusion of a filler such as silica or carbon black [425]. 

The Lambda series of Medicaflex is a polyurethane-based TPE polymer that exhibits low modulus characteristics with high tear strength and abrasion resistance. Those listed in the tables have passed USP Class VI compatibility tests and have been used as replacements in some natural rubber latex and silicone rubber applications. The polymer has been applied to uses such as catheters, tubing and films where softness, low durometer hardness, low modulus or high elongation are needed (Tables 4.3, 4.12, and 4.13). 

Various micronized polytetrafluoroethylene powders were compounded with silicone rubber (MQ) and the mechanical properties of the composites were evaluated. At a PTFE level of only 5 wt%, the fractured surface of the composites showed layered structure morphology. This stracture effectively improved the tear strength of the MQ but it also lowered the tensile properties of the composites. The addition of fluorosUicone rubber (FMQ) as a compatibilizer, improved considerably the tensile and tear strength of the composites. Extrusion of the MQ/PTFE/FMQ composites on an electric wire indicated that the spherical PTFE powder was suitable for the extrusion process [55]. 

Among the patents, some describe procedures for the preparation of silicon rubber with excellent improvement in chemical and temperature resistance (331), mechanical properties such as tensile strength and high tear strength gas, permeability (332), and other desirable properties of gels. Especially... 

Cured silicone LIM rubber can be fabricated with physical properties equivalent to heat-cured rubber (500). Shore A hardness can range from 30 to 70, depending on formulations. Typical physical properties include tensile strengths as high as 9.7 MPa (1400 psi), elongations at break of 500-775%, and tear strengths... 

To minimise risks of mechanical rupture a range of silicone rubbers, both LR and HTV grades are available in different levels of mechanical strength and Shore hardness. Table 11.11 gives a brief survey and comparison with standard properties. This table is simplified as it refers to tear resistance only. 

Sealant, ablative, silicone base, room temperature curing and primer Sealant, silicone rubber, room temperature vulcanizing Sealing compound, high tear strength Sealant, electrically conductive... 

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