Optically Clear, High Flexibility Silicone Meets NASA Low Outgassing Specifications

Master Bond MasterSil 981-LO is a two component, addition cured silicone system designed for bonding, sealing, coating, and encapsulating applications. It meets NASA low outgassing specifications and features optical clarity, particularly in thin sections, making it well suited for aerospace, satellite, optical, and optoelectronic applications. The compound is 100% reactive, contains no solvents or diluents, and exhibits minimal shrinkage upon cure.

MasterSil 981-LO features a Shore A hardness of 20–30, a low modulus, and good flexibility, with an elongation of 200–300% at 75°F. It withstands thermal shock and cycling without cracking or imparting stress on bonded components. The system is serviceable over a temperature range of -65°F to +400°F (-54°C to +204°C) and provides electrical insulation properties, including a dielectric strength of 450 volts/mil (1/8 inch thick specimen) and a volume resistivity greater than 10¹⁴ ohm-cm at 75°F. The refractive index measures 1.437.

This system features a forgiving 1:1 mix ratio by weight and a flowable, mixed viscosity of 12,500–17,500 cps at room temperature. Its 3–4 hour working life for a 100-gram batch allows sufficient time for application and processing. The recommended optimal cure schedule is overnight at room temperature, followed by 2–4 hours at 135°F to 165°F. MasterSil 981-LO bonds to a variety of substrates, including metals, glass, plastics, ceramics, and many silicone rubbers. It is available in standard packaging ranging from 30 cc syringe kits to gallon kits, and is compatible with gun dispensers for automated applications.