Structural Sealant and Adhesive
Structural sealants are used to prevent the loss of pressure or liquids, and to provide excellent adhesion on a variety of substrates. They are also known for their high strength and durability.
To assess the performance and durability of building joint sealants, a performance-based durability test method was developed based on simultaneously exposing system test specimens to artificial weathering and complex, multiaxial mechanical loadings.
Adhesives
Adhesives are a type of sealant used to bond and secure substrates together. They can provide strength and durability that may be better than mechanical fasteners, such as screws, rivets, and studs. They also help to eliminate the need for welding or threaded fasteners, which can be expensive, difficult to work with, and often break.
Structural adhesives offer high-strength, permanent bonding to a wide range of substrates, including metals, plastics, glass, rubbers, ceramics and composites. They are commonly formulated from thermosetting polymers that are cured chemically using heat, catalysts and/or chemicals.
Choosing an adhesive for your application involves first determining the type of substrate it will be attached to and the thermal and environmental conditions it must withstand. Then, engineers can select chemistries that best meet the application’s requirements. For example, if the product will be exposed to a lot of sunlight or moisture, then an adhesive that has UV-curable properties is recommended.
There are many different chemistries for structural adhesives. Some are more suited to certain substrates than others, depending on the substrate’s surface energy and thermal conductivity. For example, epoxies are best for adhesion to metals, while acrylics are more suited to plastics.
In addition to the chemistry, structural adhesives must also meet the application’s surface preparation and surface hardening requirements. The surfaces must be clean and free from any contamination that could inhibit their performance.
Once the substrates are properly prepared, the application can begin. It is critical that the surfaces are well bonded to each other so that they will hold up under stress. This requires the application of a surface treatment Structural Sealant to prepare the surfaces for adhesion, removing rust, grease, and other types of contaminants.
The surface treatment must increase the active bonding area and activation of surface free energy, which helps the adhesive to bind to the substrate. This can be accomplished through the use of a variety of methods, such as degreasing.
In addition to shear strength, structural adhesives are able to fill large gaps, which is another benefit that improves the assembly’s strength and dampens movement. These features make them ideal for a wide range of applications, including magnetic bonding, multiple-surface bonding, NVH – noise, vibration and harshness reduction, potting and encapsulating, and many more.
Sealants
Structural Sealant is a sealant which is used to attach various types of components like glass, window frames and stone. They are moisture curing polymers which take in the surrounding moisture to polymerize and form a tough, flexible and temperature resistant rubber compound. They also have high bonding strength, minimal shrinkage and long term durability when exposed to different environmental and operating conditions.
They are primarily used for sealing between structural elements such as windows and doors, curtain walls, airfield runways, highways, bridges and other engineering joints. They can be applied by spray, brush or squeegee and are easy to use. They are also inexpensive and can be applied in a clean environment.
The longevity of a sealant depends on many factors such as proper joint design for anticipated movement, correct surface preparation, and adequate adhesion to the substrates. Durability also depends on the amount of exposure the sealant will receive to heat, moisture, UV light and other external environmental factors.
A sealant will fail to perform if it is not designed and installed correctly. This includes the right amount of primer applied to the substrates and proper application of the sealant. The application of the sealant should be based on information provided by the manufacturer.
There are numerous industry test methods that will determine the compatibility of a sealant with the various materials of construction to which it will be applied. These tests can be performed by the manufacturer or by an independent testing company. The results of these tests will tell if the sealant will work properly with the other material or if it will degrade, harden, stain, swell, liquefy or cause other issues.
These tests can be done with either liquid or pre-formed joints. Liquid sealants are generally more sag resistant than pre-formed joints but can still degrade.
It is essential to choose a sealant that has the required mechanical properties for your building. This will ensure that the joint will perform properly when it is subjected to tensile forces.
The initial mechanical strength of a sealant is measured by the ability of a bond to resist the tensile force of a test specimen at various temperatures. This is a critical aspect of the safety in use (SiU) requirements of ETAG 002.
The stability of cohesive and adhesive properties are critical to determining whether a structural sealant will meet the SiU requirements of ETAG 002. They can be tested by subjecting the sealant to multiple durability cycles which simulate one year of natural aging and enforced movement. The results of the durability tests are then compared to the performance requirements set forth in ETAG 002.
Adhesive Tapes
Adhesive tapes are an effective and simple way to seal joints and seams. They offer a high degree of flexibility and resistance to environmental conditions. They are also easy to apply and require less maintenance than fasteners or welding.
Tapes are composed of a carrier or backing material, an adhesive and a release liner. The backing or carrier can be paper, plastic film, cloth, foam or foil. Some are self-adhering, while others require water or heat to activate the adhesive.
Pressure sensitive adhesives are tacky in dry form and adhere to a wide range of surfaces, including glass, metal, wood, plastic, cement and more. They also offer superior weather-stripping capabilities, and do not need solvent or heat activation.
Structural sealant tapes provide a reliable and durable bond between glass elements and framing systems for structural glazing applications. They can be used in a variety of fenestration types, including curtain wall, window wall, ribbon windows, storefronts and entrance door systems.
The tapes provide a uniform distance between the glazing panel and the structure, which helps to ensure proper curing of the silicone. Spacer tapes, such as Thermalbond V2200, are a key component in a structural silicone glazing system. They maintain a uniform gap between the glass and the framing system and allow for a smooth surface to apply the silicone sealant.
These tapes are a cost-effective and durable solution for structural glazing systems. They are used with a 90-mil, monolithic, foamed acrylic adhesive system for sealing curtain wall, window wall, ribbon windows and storefronts.
A variety of adhesives can be used in these applications, including epoxy resins, polyurethanes and isocyanates. Epoxy adhesives are known for their high strength and low shrinkage during curing. They are resistant to harsh environments and have excellent UV stability.
SikaReinforcer(r)-600 is a highly abrasion-resistant, heat-expandable Structural Sealant structural sealant that offers excellent adhesion and sealing properties on many types of metals. It provides a high level of mechanical performance (Youngs-modulus 1600 MPa, 18 MPa in tensile strength), with or without oily treatment.
3M(tm) Structural Adhesive Tape SAT1010 is a single layer, expandable, structural epoxy tape for automotive industry (BIW) applications that is formulated to provide bonding strength and isolation of dissimilar materials. It has a cleaner application than liquid adhesives and is compatible with existing OEM processes. It can reduce manufacturing costs associated with material prep and cleaning, and is available in customer-specific die cuts to fit specific application needs.
Sealant Accessories
Sealant accessories are used in a wide range of structural sealant applications. These accessories may include pre-cured strips of sealant, adhesive tapes and other materials that can help keep moisture, air and other contaminants from entering the joint and creating leaks or corrosion.
Sealants are formulated from polymers that have many different possible extenders and additives. Some of these additives may offer special performance properties, such as resistance to freezing, thawing or exposure to the elements.
Typical sealant systems are designed to perform several important functions, including adhesion, sealing and bonding. These functions depend on the base polymer, the additives in the formulation and the application conditions.
Adhesion requires that the sealant bond with substrates during service and provide a barrier to prevent the release of fluids or other substances. The sealant must also be resistant to moisture, temperature extremes and movement. These factors are correlated to the sealant’s mechanical properties, such as elongation, compressibility, tensile strength and modulus of elasticity.
Elasticity of a sealant is the ability of the sealant to expand and contract under load without losing adhesion. In some sealant joints, elasticity is more important than strength. In other cases, a low-modulus, low-strength sealant may be needed to prevent substrate failure under stress.
The amount of movement that a sealant is able to handle depends on the temperature, rate of change and the joint configuration. In addition, a sealant’s long-term weatherability is an important consideration in the selection of an appropriate sealant.
There are also some concerns regarding safety and toxicity effects when using certain types of sealants. Chemical reactions and solvent evaporation can cause toxic fumes or heat, which could harm the environment or people in the workplace.
Some sealant manufacturers offer accelerated testing of their sealants on different surfaces under specific loading and environmental conditions to provide data that can be useful in the selection of an appropriate sealant. The test results are usually available for a particular product family.
For example, the ASTM C719 standard test method for adhesion and cohesion of elastomeric joint sealants under cyclic movement is an essential short-term performance test for sealants. However, if the sealant is not able to pass this test, it will likely be unable to perform well in a field application under similar load conditions and environmental conditions.
