Cardolite FormuLITE products are user friendly and high performance. The guidelines below provide additional information on how to best use these products. Please contact your Cardolite sales representative if more information is required.
Epoxy resins are characterized by very good mechanical and thermal properties, low cure shrinkage, very good chemical and water resistance, high thermal resistance and excellent adhesion to reinforcing fibers and substrates. Thanks to these excellent properties, epoxy resins are used in many applications.
Two components (2K) epoxy systems, resulting from a blend of an epoxy resin (part A) and an amine hardener (part B), offer the possibility to obtain different properties by combining different parts A and B.
FormuLITE 2K epoxy systems have been designed for use in fiber-reinforced composites, however, they can be a valuable choice in other applications such as adhesives.
HOW 2K EPOXY SYSTEMS REACT
The blend of an epoxy resin and an amine hardener (epoxy system) is a reactive liquid that undergoes an exothermic cross-linking reaction during which heat is released. After mixing the two components, the blend viscosity slowly increases as a result of the cross-linking.
The pot-life (also known as open time, or pour time, or processing time) is a measure of reactivity and defines the period during which the epoxy system is workable, i.e. its viscosity is appropriate for many composite applications. The pot-life values indicated in the Technical Data Sheets have been measured on a 100 g amount of system at 25°C. As a guideline, pot-life decreases when temperature increases or large amounts of mixture are prepared due to the exothermic reaction. As a result, it is recommended to split large amounts of mixture into smaller containers. The user should choose the epoxy system with a pot-life compatible with the expected working time, at the temperature of the workshop.
The tack-free time is the interval before the surface of the cured epoxy system can resist damage by touch or from settling dirt.
Before starting the manufacturing of a composite part or any other use of FormuLITE epoxy systems, we advise user to carry out preliminary trials to verify that the pot-life in the actual working conditions fits the requirements of the manufacturing process.
HOW TO PREPARE AN EPOXY FORMULATION
Always follow the health, safety and environmental guidelines recommended on the material safety data sheet (MSDS). Copies of the MSDS can be requested on the Cardolite website or via your local sales representative.
The mix ratio in 2K epoxy systems (i.e. the amount of the part B to be added to the part A) is calculated on the basis of the reactive groups of the epoxy and the hardener. In order to obtain the properties described in the Product Technical Data Sheet, the mix ratio (by weight or by volume) has to be carefully followed and the two components have to be mixed thoroughly in a clean container until a homogeneous blend is obtained. If a balance is available, it is advised to carefully weight part A and part B in two separate containers, then pour part B into part A and mix thoroughly with a wooden or metallic thin spatula, limiting the entrapping of air. In case of excessive air entrapment, appropriate quantities of air release additives can be used.
EVALUATION OF THE CURING STAGE
The maximum performance of an epoxy system is reached only when the composite piece has been completely cured. In some industrial processes, like RTM (Resin Transfer Molding), the formulated system is usually warmed up before the injection into the heated mold, where the temperature is high enough to enable the rapid curing of the composite piece and its demolding in a few minutes. In many other applications, from vacuum infusion to DIY works, the composite parts is left at room temperature.
The evaluation of the curing stage of an epoxy resin or composite can be carried out with several methods, depending upon the available equipment. If a well-equipped quality control laboratory is available, the best way to evaluate the degree of curing is to use a DSC technique (Differential Scanning Calorimeter) to measure the Tg (glass transition temperature), which is a good proxy of the softening point of the cured epoxy. In many composites production facilities the degree of curing is inferred from the surface hardness of the piece, which can be measured by Barcol or Shore D testers. For DIY applications, when the mentioned equipment is not available, a simple method is the tactile assessment of the surface: when it is tack-free, the epoxy resin has reached an acceptable curing stage (although not optimum).
To evaluate if the mechanical, thermal and chemical properties of the composite piece are adequate for the specific application after room temperature curing only, the user can expose it to the real working conditions (mechanical loads, aggressive fluids, etc.) and verify its performances. In case of negative results, it is necessary to allow a longer curing time at room temperature or to consider a post-curing procedure.
A tack-free surface after ambient curing does not mean that the piece has reached its optimum properties. To develop the best mechanical and thermal properties, a post-curing is needed, i.e. adequate and uniform heating has to be provided to the composite part.
Industrial equipment for post-curing includes ventilated ovens and IR lamps. In case of small pieces in DIY applications, a common IR lamp is enough for the part to achieve the required curing level. In case hot ventilation is available, 6 to 16 hours at 50-60°C (depending upon the size and shape of the composite part) are usually enough to provide the needed energy for post-curing.
FormuLITE 2500A/2501A/2501A + FormuLITE 2401B systems are brittle after RT curing only. Before demolding the piece, it is strongly recommended to post-cure at 50-60°C for 2-4 hours.
Technical assistance can be provided upon request.