hi,

Usually when we are mixing two or more components together to make some new composite, whether it is hard or soft, the energy for its components to bind with each other comes from the ambient thermal energy. If either the unmixed components or the mixed components are kept at lower temperature the binding processess within them can be significantly affected. For this, one has to go through empirical approach as most of the time such data is not available easily. I was able to do this with PDMS, a silicone based elastomer. Its binding time was controlled from few seconds to 2 days by either exposing it to high pulsed temperatures or down below the freezing point of water.

Regards

Hi . In my opinion , firstly, you should determine the EEW (Epoxy Equialent Weight) of utilized epoxy . based on EEW, add hardener.

Some tips:

1. Using other hardeners, such as aromatic or cycloaliphatic amines

2. Decreasing the temperature to postpone the curing process

3. Adding hardener step by step

4. Instead of hardener, trying to epoxy homopolymerization by cationic or anionic initiators

Dear Khaled,

Question you have asked is typically interesting me. If you are interested in gel time please follow first part. It says about recommended gel time and temperature required for a theromset system.

Gel time enquiry

This is used for thermoset system. It is customary for a thermoset system with a gel time of say 60 minutes, to advise the customer that the material must not be disturbed, moved, handled after it has cured for 50 minutes. Gel time can be measured by following the viscosity until there is a point when the viscosity is so high it is no longer liquid. Gel timers measure this time by having a spindle rotate in the liquid until the time when rotation stops because the viscosity is too high, i.e. the material has gelled. The polymer will continue its cure from a gel to a solid, which is the final state of the thermoset system. Gel time is the time it takes for a mixed resin system to gel or become so highly viscous that it can no longer be considered workable or able to be handled. A thermoset resin system converts from a liquid mixture of chemicals to a solid material that has a highly cross-linked polymer as the major structural material. The gel time is the time when the polymer formation is in its early stages of cross-linking to the point that if the polymer gel state is disturbed then the final polymer will have properties that are not well established.

It is also important to mention that the pot life, working life, and gel time are only useful to the researcher if the temperature is defined. Room temperature systems would have these properties defined at 25°C. If the system is a heat-cured system then the temperature could be 65°C or 100°C or another temperature that the supplier considers applicable. Viscosity increase could be monitored at 100°C, the gel time could be measured at 100°C and the working life would be specified after the gel time at 100°C is measured.

Process consideration:

The resin component and the hardener component are mixed together. The mixed resin and hardener are thawed out after having been stored in a frozen state. These frozen systems have all the components necessary for curing except the temperature in the frozen state is so low that the reaction cannot start. When the system is removed and allowed to thaw to room temperature, the curing reaction can start. The resin and hardener are heated to start the curing reaction.

Now one can wish to know how long they have to work with the curing resin system and they also need to know when the system has gelled, which is the first state in the transformation from a liquid to a solid. You no need not disturb a material after it has gelled because the final polymer will have a poorly cross-linked structure and inadequate physical properties.

Pot life is a defined timed during which the viscosity of the mixed system doubles. Example: if a mixed resin system has an initial viscosity of 10,000 cps and the viscosity increases to 20,000 cps after 30 minutes, then the pot life is 30 minutes. In some instances, if the starting viscosity is very low, e.g. 500 cps, then the pot life can be defined as the time it takes for the viscosity to increase by a factor of 4, or 5, or some other defined number.

The time factor for pot life does give an indication of how fast the system is curing (progressing from a liquid state to a solid state), however it does not necessarily define the amount of time the customer has to work with the resin, in terms of being able to use it in their process to make acceptable parts. In the example, even if the viscosity is 20,000 cps the customer may still be able to cast the material or use it as an adhesive, sealant, or encapsulant. What the pot life is best used for is to compare systems. If one system has a 30 minute pot life and one has a 100 minute pot life, the customer has an indication of how fast or how slow the two systems are curing.

Hope it is a useful for you.

Ashish