# 1.1.13.2.5 Type of Reaction

> From: LOCTITE®X Digital Manual for Bonding (https://www.loctitex.com/en/manuals/bonding/1.1.13.2.5-type-of-reaction/)

###### 1.1.13.2.5 Type of Reaction

Adhesive cure mechanisms are many and varied and must be considered when designing a bonded joint. Some adhesives solidify simply by solvent evaporation, cooling from liquid to a solid, or a chemical reaction initiated by the mixing of components. An external energy source like heat, or an initiator such as moisture in the air, may be required for curing. Some systems have multiple cure mechanisms, such as activator-cured acrylic that may also be cured by heat. Others may require a dual cure, as in a light cure silicone that is fixtured by UV radiation but reaches its final form and properties via subsequent moisture curing.

The curing method will be a factor in adhesive choice. The cost or space requirements of specialised dispensing or curing equipment may also be a decision point, as will any health and safety concerns for the chemicals or energies required by a given adhesive system. Process speed will vary enormously by curing mechanism – a light cure acrylic may cure in seconds, while Room Temperature Vulcanizing (RTV) silicones may take hours to reach handling strength and days to fully cure. These factors must be balanced with the design requirements of the product, as cure mechanisms favour certain properties. For example, heat cured adhesive systems generally offer better thermal resistance from the additional crosslinking that occurs with a higher temperature cure. Light cure adhesives cure on demand but tend to display increased shrinkage compared to other technologies.

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