Sealant Manufacturers produce a wide variety of highly engineered polymer-based products that serve a multitude of functions. These are generally used for joints, seams and cracks in structures such as walls, roofs, floors and doors. The majority of modern sealants are formulated from synthetic elastomeric polymers. These include polysulfides, urethanes, acrylics and chloroprenes among others. In addition to base polymers sealants also typically contain fillers, plasticizers, thixotropic agents, adhesion promoters and curing agents. Various external accessory materials like primers, bond breakers, back-up materials and caulking tools are often required during the application of a sealant.
A wide range of sealants are available in the market that vary by performance, application and environment. For example, a sealant may be designed to adhere to glass, ceramics, metals, concrete, wood, plastics, rubbers and many other substrates. In addition, a sealant may be designed to resist specific chemicals or temperatures. Other important features of a sealant are its weatherability, flexibility and flexibility, paint-over ability, movement considerations, low surface tension, ease of use and cost.
There are several types of sealants that fall between the high-strength adhesive-derived sealants and coatings at one end of the spectrum to the low-strength putties, waxes and caulks at the other. The higher-strength sealants are usually supplied as two component systems consisting of a resin and hardener that must be mixed together prior to application at a rate set for each product. Examples of this category are epoxy sealants.
These systems are often characterized by their quick cure times and ability to withstand some level of vibration. They are also very flexible, which allows them to move with the substrates they are bonded to and can help prevent movement between adjacent surfaces within a structure.
Some sealants are able to expand before curing to allow them to fill gaps that might otherwise be too small to be bridged with the normal amount of material. This is common in automotive sealants, which are usually formulated with gas-releasing additives to achieve this effect. Hot-melt and RTV sealants are also available that can expand when heated to the point of bubble formation.
Other mechanical properties that can be significant for some applications are a sealant’s compressibility, tensile strength and stress relaxation. Compressibility is the measure of how much a sealant will stretch or compress with a given force and is affected by temperature, loading conditions and surface preparation. Tensile strength is the maximum tensile stress that a sealant will endure under load and is influenced by its chemical composition and the design of the joint to which it is being applied. Stress relaxation is a property that describes how fast the stress in a sealant will decrease as it is progressively applied and compressed. It is sometimes referred to as creep, and it is an important factor in determining the integrity of a sealant’s long-term performance. Detailed information about these properties can be obtained by examining the results of accelerated testing performed under a variety of environmental and loading conditions, which are usually published by sealant manufacturers.