Cast elastomers Mechanical properties

With the development of technical grade HER (HER TG), the processing temperature of the HER was further lowered without sacrificing the physical and mechanical properties of the final cured cast elastomers. The major difference between HER HP and HER TG chain extenders is the presence of some higher molecular weight (MW) reactive aromatic diol monomer in the technical grade material. With this unique... 

The experimental details on the cast elastomers prepared using Baytec MS-242 and Baytec ME-050 prepolymers and their physical, mechanical and dynamic mechanical properties are given in Tables 8.10 and 8.11. 

In order to demonstrate that HER compared to butanediol-based elastomer has better physical and mechanical properties at elevated temperatures, cast elastomers with 95% stoichiometry have been made from an MDI terminated polyester prepolymer (Baytec MS-242) extended with butanediol and HER-HP (from INDSPEC Chemical Corporation). Test specimens were cut from a sheet post cured at 110 °C for 16 hours, for the tensile, tear, DSC and DMA determinations. In the preparation of material for the dry heat aging evaluation, tensile, DSC and DMA samples were placed in an air oven with the temperature controlled within 2 °C of the set point and aged for 28 days at 100 °C, 21 days at 120 °C and 14 days at 135 °C. Then, all the samples were stored for at least seven days at room temperature and 50% relative humidity before testing. 

Table 8.16 Heat ageing and mechanical properties of cast elastomers from Baytec MS-242 ... 

The mechanical properties of highly filled elastomers have led to their use as solid propellants in rocketry. Composite propellants consist of elastomers highly filled with inorganic oxidiser. Mixing is effected in an uncrosslinked state in which the polymer still has a low MW and the consistency of a viscous fluid. The compounded mixture is cast or extruded into the desired shape and hardened by polymerisation... 

At a non-stoichiometric ratio of the reagents, one can prepare a crosslinked polymer by two-step synthesis. A different result is obtained in the reaction of the polyurethane prepolymer (PP, dissolved in DMF) with ADMH [19,20]. At a 2-, 5-, and even 10-fold increase of the PP molar fraction, DMF-soluble macromolecular compounds are formed. The respective solution-cast films have mechanical properties similar to those of classical polyurethane elastomers (Table 3). 

Silicone polymers may be filled or unfilled, depending on the properties desired and the application. They can be cured by several mechanisms, either at room temperature by room-temperature vulcanization (RTV) or at elevated temperatures. Their final form may be fluid, gel, elastomer, or rigid plastic. There are three primary types of silicone resins (1) flexible two-part, (2) flexible one-part, and (3) rigid silicones. Silicone rubber resins for casting, potting, and other liquid processes are available from Dow Coming (Silastic) and GE Silicones. 

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