MasterSil 981-LO

Master Bond MasterSil 981-LO is a two-component silicone designed for high performance bonding, sealing, and encapsulating applications. It does not require air for curing. The system features a flowable viscosity and a forgiving 1:1 mix ratio by weight for ease of handling. It is a minimal exotherm material with an extended open time of approximately 3–4 hours. MasterSil 981-LO is also noteworthy for its soft Shore A hardness, offering a low modulus and good flexibility. MasterSil 981-LO cures at ambient temperature in 48–72 hours, or more rapidly in 2–4 hours at 135–165°F. For optimal performance, an initial overnight cure at room temperature followed by 2–4 hours at 135–165°F is recommended. The system is 100% reactive, containing no solvents or diluents, and exhibits minimal shrinkage upon cure.

MasterSil 981-LO bonds well to a wide range of substrates, including metals, glass, plastics, ceramics, and many types of silicone rubbers. It is capable of withstanding rigorous thermal shock and cycling without cracking or imparting stress on bonded components. The material has a Shore A hardness of 20–30 and a service temperature range of -65°F to +400°F. While tensile lap shear strength is relatively low, it still forms tenacious bonds and should be considered a reliable adhesive.

The color of both Parts A and B is clear. Additional key features include optical clarity, particularly in thinner sections, and a strong electrical insulation profile. MasterSil 981-LO is well suited for use in aerospace, satellite, optical, and optoelectronic applications where a low viscosity silicone with a long open time is required.