A bandage with a removable adhesive.
Adhesives are natural or synthetic compounds, usually in liquid or paste form, used to join two objects. Depending on how they form a bond, adhesives can be classified as pressure-sensitive, reactive, drying, contact, light-curing, or thermoplastic. Their strength and how they react with other substances can vary widely, so it’s always wise to use the right glue for the job.
Permanent pressure sensitive adhesives may include adhesive tape.
Pressure sensitive adhesives come in permanent and removable forms. Examples of the permanent variety are masking tape used on heating, ventilation, and air conditioning (HVAC) systems, equipment safety and warning labels on machines and appliances, and to protect interior trim work from the vehicles. They can be removable when first applied, with bond strength increasing over hours or even days.
Glue is a common type of adhesive.
Removable adhesives create a temporary bond and typically cannot support a substantial amount of weight. Common examples of temporary pressure-sensitive adhesives are sticky tape, sticky notes, and price tags. They are also used in the manufacture of transdermal patches, such as those used for smoking cessation, birth control, and motion sickness prevention. This type of glue is also a component of common self-adhesive dressings, such as Band-Aids®.
PVC pipes require a special adhesive cement to seal the joints.
Reactive adhesives are applied in liquid form as a very thin layer. They are best used to secure items that must be completely level and do not require the adhesive to fill a gap between them. The reactive adhesive type is suitable for bonding wood, many plastics, metal and glass. This type of glue generally has a fast rate of strength increase along with a very fast cure time.
Drying adhesives are a combination of polymers and solvents. The adhesive hardens as the solvent evaporates. Common white glue is one of the most recognized adhesives of this type, along with rubber cement. By creating a relatively weak bond, drying glues are more suitable for home, school, and craft use.
Contact adhesives are unusual in that they must be applied to both surfaces to bond them together and then allowed to dry for a period of time before the objects can be pressed together. Neoprene and natural rubber are two common examples. Applications include bonding soles to shoes and bonding Formica® to countertops.
Light-cured adhesives cure quickly, some as fast as a single second. These extremely strong glues are capable of bonding dissimilar materials, such as plastics with glass, and are capable of maintaining integrity under extreme temperatures. Light-curing adhesives are used almost exclusively in industrial settings such as manufacturing, aerospace, electronics, medical equipment, and telecommunications.
Hot melt adhesives are also called hot melt glues. As the name implies, these glues are applied hot and then harden as they cool. Capable of adhering to a wide variety of different materials, hot glues are primarily used for home crafts using a hot glue gun for dispersion.