Elastomeric formulations

Compression set and durometer hardness are also important mechanical properties. Compression set is defined as the amount by which an elastomer fails to return to its original thickness after being subjected to a standard compressive load or deflection for a specified time at a specified temperature. A low percent compression set typifies a more compression resistant elastomeric formulation. Compression set of a closure on a sealed vial is a factor in maintaining the sterility and potency of the drug itself. 

Current good manufacturing practices (CGMPs) indicate that a parenteral manufacturer should confirm supplier certification on packaging components. The following characteristics are usually monitored for a specific elastomeric formulation ... 

A hydrocarbon prepolymer containing terminal carboxyl groups (28) is available to the propellant chemist. These polymers were synthesized to eliminate some of the variables found in the copolymers. The carboxyl groups can be made of the same types with like reactivity. These linear non-branched polymers impart greater extensibility to elastomeric formulations. The chemistry in propellants is similar to the random functionality polymer. As 20 years of the chemistry of crosslinked propellant binders is reviewed, one familiar with the art cannot fail to predict solid propellant formulations using these polymers tailored to the specific requirements of the solid rocket design with the confidence that any discipline of science can be practiced. 

Waxes Waxes are an additional class of materials used to improve rubber ozone protection primarily under static conditions. Waxes used in elastomeric formulations fall into two categories microcrystalline and paraffin. Microcrystalline wax has a melting point in the range of 55-100 C and is extracted from residual heavy lube stock of refined petroleum. Paraffin wax has melting points in the range of 35-75°C and is obtained from the light lube distillate of crude oil. 

In summary, a number of empirical guidelines can be used to develop an antidegradant system for an elastomeric formulation ... 

Vulcanization, named after Vulcan, the Roman God of Fire, describes the process by which physically soft, compounded rubber materials are converted into high-quality engineering products. The vulcanization system constitutes the fourth component in an elastomeric formulation and functions by inserting crosslinks between adjacent polymer chains in the compoimd. A typical vulcanization system in a compound consists of three components (1) activators (2) vulcanizing agents, typically sulfur and (3) accelerators. 

Two primary limitations of these modeling efforts involve the representation of tissue properties across the entire limb and the interface condition between the residual limb and prosthesis. The ability of current finite-element models to estimate prosthetic interface stresses, while performing reasonably well in some cases, has not been highly accurate. Nevertheless, the methodology has potential. Advances in finite-element software enabling nonlinear elastomeric formulations of bulk soft tissue, contact analysis, and dynamic analysis may help address some of the current model limitations. Corresponding advances in pressure-transducer technology will help validate the computer models and facilitate interpretation of the analyses. 

The optimal lyophilization formulation will have the correct hardness and reinforcement materials, which will balance the need for good seal integrity (softer, low compression set) and good machinability (harder, higher durometer). The compression set of an elastomeric formulation is... 

Magnesium hydroxide can impart flame retardancy and smoke suppression to a wide variety of thermoplastics and elastomeric formulations. It is temperature... 

Briganti, E., Lost, R, Raffl, A., Scoccianti, M., Munao, A., Soldani, G., 2006. Silicone based polyurethane materials a promising biocompatible elastomeric formulation for cardiovascular applications. Journal of Materials Science Materials in Medicine 17, 259-266. 

By contrast, the second conformal coating in Table 3.3 (9) can best be described as an elastoplastic resin a resin with highly elastic properties. Supplied in solvent, it can again be applied in several ways but forms a harder, more slippery surface after cure than the elastomeric formulation. Maximum elongation at 100% is less than for elastomeric product (4) but is adequate for most applications. Curing is... 

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