Adhesive Systems for the Aerospace Industry

Engineers often want to know whether an adhesive is low outgassing or generic. And while there are cases when nothing but a low outgassing product will do, the truth is that many so-called generic adhesives inherently have low outgassing levels. What's more, most bonding, potting, encapsulation and sealing applications don't need to meet a defined outgassing specification. Here's a guide to understanding when low outgassing adhesives are the right choice.

Master Bond is offering a new, easy to read, 28 page catalog with performance and processing data on its extensive line of epoxies, silicones, UV curing compounds and specialty systems for the aerospace industry. These products ensure reliability in the assembly of aircraft structures, components, interiors and MRO applications. They are widely used for structural bonding, sealing and gap filling. Additionally, conformal coatings and potting/encapsulation compounds are frequently employed to protect sensitive electronic parts against extreme conditions. These advanced adhesive, sealant and coating systems feature many outstanding performance properties including toughness, high temperature resistance, cryogenic serviceability, thermal/electrical conductivity and excellent bond strength to both similar and dissimilar substrates. Specific grades are halogen free, meet NASA low outgassing specifications and are UL 94V-0 rated for flame retardancy. This catalog is available for immediate download in PDF format or in print. It can be requested at https://www.masterbond.com/catalog/adhesives-sealants-and-coatings-aerospace-industry.

In several published research articles, patents, and manufacturers’ specifications, scientists and engineers have identified EP21TDC-2LO for use in their applications due to its unparalleled performance in one or more areas. The table below highlights two research applications that use Master Bond EP21TDC-2LO.

Selecting the right adhesive for space applications is extremely important, mainly due to the high vacuum (around 10-8 Torr) and the variation in temperatures. A key concern is the outgassing property of these adhesives. Any outgassing might lead to contamination of electronic or optical components, which can have a drastic impact on the optical properties of the system.Since outgassing is an important consideration in selecting the right adhesive for a space application, NASA and many other government agencies require these adhesives to pass the ASTM E-595 outgassing test. This test requires the total mass loss (TML) and collected volatile condensable materials (CVCM) to be less than 1% and 0.1%, respectively. TML is the weight of the product lost after an exposure to vacuum (less than 5 x 10-5) for 24 hours at 125°C. CVCM is the amount of volatiles which condense in a plate maintained at 25°C. Curing schedule also plays a vital role in achieving the best low outgassing properties.Apart from low outgassing, excellent resistance to temperatures over a wide range is a desired property for adhesives in space applications. Good performance at very low temperatures (around -110°F) is particularly important. Also of major significance for adhesives not sandwiched between two adherends is their capability of withstanding exposure to proton, electron and heavy ion types of radiation.Master Bond offers an extensive range of products which meet NASA low outgassing specifications combined with resistance to very low and high temperatures. Many of the low outgassing products offer optical clarity, thermal conductivity/electrical insulation, electrical conductivity and cryogenic serviceability.

Master Bond EP3HT-LO is a single component, non-premixed & frozen, heat cured epoxy, with an unlimited working life at room temperature. This system passes ASTM E595 tests for NASA low outgassing, making it well suited for use in the aerospace, electronic, microelectronic and optical industries. EP3HT-LO features a good strength profile, with a lap shear strength of 1,600-1,800 psi, a tensile strength of 5,000-6,000 psi and a tensile modulus of 250,000-300,000 psi. It withstands 1000 hours of 85°C/85% RH exposure. This formulation offers reliable electrical insulation properties with a dielectric constant of 3.9 at 60 Hz and a volume resistivity of greater than 1014 ohm-cm, at room temperature. EP3HT-LO withstands a variety of chemicals such as water, oils, fuels, acids and bases. This high temperature resistant system is serviceable from -60°F to +400°F (-51°C to 204°C). As a one-part compound, EP3HT-LO offers convenient handling and processing. It cures with heat, quickly polymerizing in as little as 5-10 minutes at 300°F (~ 150°C). This epoxy bonds well to metals, glass, composites, ceramics and many plastics. EP3HT-LO is available for use in ½ pints, pints, quarts, gallons and syringes. It has a shelf life of 6 months at ambient temperatures in original, unopened containers.