Sealants are formulated materials used to bridge gaps and resist relative movement between substrates. They can include both an elastomeric compound for flexibility together with filler products. Sealants convey a variety of properties including water resistance, acoustical and thermal insulation as well as fire barriers. They may also function as coatings, smoothing or filling agents, and electrical conductors. They often have to be durable, easy to apply and compatible with a range of substrates.
The vast majority of modern sealants are based on synthetic elastomeric polymers. These have a number of advantages over older materials such as sulfides, acrylics and chloroprenes. Various accessory materials, such as primers, bond breakers and back up material are commonly required to support the performance of the sealant.
Sealant Manufacturers produce a wide range of formulations to meet most application requirements. These range from low strength putties and caulks to high-performance silicones and RTVs that provide long-life, a wide temperature range and are unaffected by UV or extreme weather conditions. These materials are used in a wide range of applications including joint sealing, waterproofing and structural glazing.
Adhesive and sealant manufacturers use a wide range of raw materials to manufacture their products, from petrochemicals to resins and polymers. Many of these chemicals are in short supply due to the pandemic, and the resulting disruption to supply chains has driven up prices.
However, demand is increasing, especially in the construction sector, where a number of major projects are being restarted. As a result, these companies are expanding their capacity.
Most sealants are applied by spray, brush, spatula or gun. A gun system includes PVC made cartridges and nozzles to deliver the sealant to the joint area. The base and accelerator for the formulation are separately filled into the cartridges. When mixed they react and form a thick paste. A syringe with a pump can also be used to dispense the sealant.
Once the sealant has been applied to a joint, it needs time to cure. The curing process is governed by the chemical composition and the environment. Polyurethanes, for example, require ambient temperatures of 50-70°F to cure properly. Some elastomeric sealants can be cured in the sun, but they generally need to be confined to small areas and are best suited for outdoor applications.
Important mechanical properties of a sealant are its elongation, compressibility and modulus of elasticity. These are particularly important for sealing joints that will experience significant movement. Other critical mechanical properties are tensile strength, shear strength, fatigue resistance and tear resistance.
Most sealants have very little strength and are primarily designed to bridge gaps and resist movement between two surfaces. They can be formulated with various additives to improve their mechanical properties. These may include fillers, plasticizers, thixotropic agents and adhesion promoters. They can be cured with heat or cold, in liquid or solid form and can be modified to have different viscosities. Other characteristics that are considered when selecting a sealant include the ease of application and the time taken to dry.