From one of our suppliers website
http://www.gurit.com/exothermic-reactions.aspx
An exotherm is an uncontrollable reaction between a solvent-free resin and hardener, which happens when the heat generated by the resin-hardener reaction cannot escape readily.
The trapped heat accelerates the reaction, which in turn generates more heat and further accelerates the reaction until it becomes uncontrollable. This normally happens only in bulk mixes, as mixed resin applied to a job is usually in a thin film (e.g. coating, glue line, laminate layer, filler layer, etc) from which heat readily escapes.
Care should be taken to control excessive exotherms, which can result in overheating of the product and possible thermal decomposition.
There are several factors that can affect the degree of exotherm produced:
- The volume and configuration of the mixed mass as this can determine the degree of exotherm.
- The temperature of the mix, as this can increase the reaction rate.
- Not using the mixed materials quickly enough, particularly if it is a ‘fast’ resin / hardener system (gel time 5- 20 mins).
- The reactivity of the epoxy resin and the curing agent
The process should be carefully reviewed to determine the possibility of an exothermic reaction occurring before commencing operations. The potential for an excessive exothermic condition is related to batch size; and the larger the batch mix the greater the potential, even with relatively low reactivity curing agents.
As the heat of reaction builds up it causes a faster reaction rate, which can result in still greater heat generation and a runaway situation can quickly result.
For every 10ºC rise in temperature the reaction rate doubles. To reduce the risk of exothermic reactions reduce the batch size.