Silicone adhesive sealant MasterSil 981-LO

elastomerictwo-componentencapsulation

Product Overview
Master Bond MasterSil 981-LO is a two-component addition-cured silicone for bonding, sealing and encapsulation. It cures without air, has a flowable viscosity and a 1:1 mix ratio by weight. The system exhibits minimal exotherm, an open time of approximately 3–4 hours and cures at ambient temperature in 48–72 hours or 2–4 hours at 135–165°F with heat acceleration. An initial overnight ambient cure followed by 2–4 hours at 135–165°F is recommended for optimal performance.

Key Features

• Soft material (20–30 Shore A)
• Optically clear in thin sections
• Addition-cured, 100% reactive (no solvents or diluents)
• Easy processing: flowable viscosity, 1:1 mix ratio by weight

Typical Properties

• Viscosity: 12,500–17,500 cps
• Cure schedule: ambient 48–72 hours; 2–4 hours at 135–165°F for accelerated cure; recommended overnight ambient then 2–4 hours at 135–165°F
• Hardness: 20–30 Shore A
• Service temperature range: -65°F to +400°F
• Coefficient of thermal expansion: 450–500 x 10⁻⁶ in/in/°C
• Refractive index: 1.437

Applications

• Bonding
• Sealing

Certifications / Compliance

• Meets EU Directive 2015/863
• ASTM E595 compliant
• Meets NASA low outgassing specifications

Packaging

• Syringes
• Cans

Product Description (additional details)
MasterSil 981-LO bonds to metals, glass, plastics, ceramics and many silicone rubbers. It resists thermal shock and cycling without cracking or imparting stress on bonded components. Tensile lap shear strength is relatively low but provides tenacious bonds. Parts A and B are clear. The cured material offers good electrical insulation. It is suitable for aerospace, satellite, optical and optoelectronic applications that require a low viscosity silicone with extended open time.

Technical Specifications

• Brand: Master Bond
• Model: MasterSil 981-LO
• Product type: Two-component addition-cured silicone (100% reactive, no solvents or diluents)
• Mix ratio: 1:1 by weight
• Viscosity: 12,500–17,500 cps (flowable)
• Open time: approximately 3–4 hours
• Cure schedule: ambient 48–72 hours; 2–4 hours at 135–165°F for accelerated cure; recommended overnight ambient then 2–4 hours at 135–165°F
• Hardness: 20–30 Shore A
• Modulus: low (soft)
• Service temperature range: -65°F to +400°F
• Coefficient of thermal expansion: 450–500 x 10⁻⁶ in/in/°C
• Refractive index: 1.437
• Color (Parts A & B): Clear
• Exotherm: minimal
• Shrinkage upon cure: minimal
• Substrates: metals, glass, plastics, ceramics, many silicone rubbers
• Typical applications: aerospace, satellite, optical, optoelectronic, bonding and sealing where low viscosity and long open time are required
• Certifications: Meets EU Directive 2015/863; ASTM E595 compliant; NASA low outgassing