chemistry noun chem•is•try | \ 'ke-me-stre 1 : a science that deals with the composition, structure, and properties of substances and with the transformations that they undergo 2 : the composition and chemical properties of a substance // the chemistry of iron 3 : a strong mutual attraction, attachment, or sympathy // they have a special chemistry
Come in both two-part adhesives (that cure upon mixing the two components) and one-part adhesives (that cure with heat or when allowed to thaw). They generally have the highest strength and overall performance. They also provide the best resistance to high temperatures, chemicals and solvents and outdoor weathering. They adhere well to metals, wood, composites, stone and concrete. Flexible epoxy adhesives also bond to some plastics and rubbers. Epoxy adhesives usually require clean, abraded surfaces to obtain their maximum bond strength.
Acrylic Adhesives are two-part adhesives that provide excellent bond strength and durability albeit sometimes slightly less than comparative epoxy adhesives. They do however have several features that make them easier to use in some applications. These include a faster setting speed and shorter time to achieve a full cure, a higher tolerance for oily or unprepared bonding surfaces and the ability to bond a wide variety of materials, including nearly all plastics. Newer acrylic adhesive formulations are room temperature stable with a long shelf life.
Urethane adhesives are two-part adhesives that are tough to highly flexible when cured. They tend to have excellent impact resistance and good adhesion to most plastics. They also bond well to paint or primed metals, composites, woods, concrete and rubbers. However, they have reduced resistance to solvents and high temperatures compared to epoxies and some acrylic adhesives. Uncured adhesives components may be sensitive to moisture.
Cyanoacrylate Adhesives: Cyanoacrylate adhesives (instant adhesives) are one component liquid or gel formulations that cure extremely quickly with just contact pressure and surface moisture. They adhere well, often in thin bond lines, to plastics, metals and rubbers. With the use of primers, they can also adhere to low surface energy plastics and elastomers. They tend to have low flexibility, peel strength and impact resistance compared to other structural adhesives. They are generally used for applications such as gasket bonding, wire tacking, and many small assembly operations.
Anaerobic Adhesives: Anaerobic adhesives are one-part adhesives that cure on active metal surfaces when oxygen gets excluded from the bond line. These products help manufacturing operations run efficiently by reducing maintenance and leakage. They do not bond well to glass, plastics or rubbers, and are primarily used for applications such as thread-locking and sealing pipe connections.
PUR ADHESIVES (Polyurethane Reactive)
Polyurethane-reactive adhesives are one part adhesives that apply like a hot melt, but cure with ambient moisture to achieve bond strength close to that of structural adhesives. They set quickly and rapidly build bond strength over the next 24-48 hours, reaching as much as 1,000 psi in overlap shear strength. They are flexible and resistant to temperature extremes and most solvents. Most commonly used in bonds where at least one substrate contains or transmits moisture (such as wood or plastic).