All epoxy resins molecules contain at least one reactive epoxy group although most have two or more.
Figure 1 shows a molecule of a common epoxy resin made with bisphenol A.
Figure 2 shows a polyamidoamine hardener molecule used for the manufacture of ‘hardeners’. An epoxy group can react with an amine group (NH2 or NH) by displacing its hydrogen atom. The polyamidoamine molecule in figure 2 has 5 amino nitrogen atoms and can therefore react with 5 epoxy groups.
Until the introduction of low cost digital scales it was difficult to accurately proportion the components on site and various methods were devised such as measuring pots, graduated sticks, syringes and proportioning pumps. Unfortunately, all these methods are inaccurate and are the source of many failures. Why people still insist on using these unreliable methods is a mystery.
The only way to be certain that you are getting the best properties out of your expensive resin is to weigh it and the hardener accurately. If you use any other method your resin may still set hard but how do you know whether it’s heat distortion temperature is 25oC or 55oC or if it is only 50% at strong as it should be, or is tough or brittle?
WEIGHING RESIN & HARDENER Digital kitchen scales are sufficiently accurate to obtain excellent results. The scales shown are accurate to 1 gramme, cost less than £10.00 and are guaranteed for 10 years. Simply tare off the scale, pour out an approximate amount of resin, calculate the amount of hardener required, tare off the scales again and accurately weigh out the hardener.
MIXING Thorough mixing is also critical to the correct curing of the product and although small amounts can easily be mixed by hand, a spiral mixer used in a pneumatic or cordless drill is essential for mixing larger amounts. The pot life that is stated in the products literature will depend on the amount mixed and the ambient temperature. Large volumes and higher temperatures will shorten pot life. Pot life can be extended by pouring the mixed material into trays which will allow the exothermic heat generated by the curing reaction of the resin and hardener to dissipate.
CURING SYNAMIN ambient cure hardeners will cure down to 8oC but the physical properties of the cured resin will be less than when cured at higher temperatures, SYNAMIN heat cure hardeners must be cured according to the specified schedule.
FILLERS & ADDITIVES
There are numerous fillers and additives that can be mixed with epoxy resin to make it suitable for a wide range of applications. A few examples are given below.
Cellulose fibres are excellent for giving body to the resin to enable it to be used more easily as an adhesive and improve its gap filling properties as shown in the picture.
Hard fillers such as powdered calcium carbonate, dolomite or solid glass micro-spheres can be incorporated with epoxy resin to make a moulding or casting compound. The viscosity of the mixed product varies according the the amount of filler added.
An excellent filleting compound can be made with a mixture of hard filler and cellulose fibres.
Low density fillers such as hollow glass micro-spheres and phenolic micro-spheres can be mixed with epoxy resin to make an easy to sand low density filler. However, a pre-mixed filler such as Easy Fair is easier to use and is dust free when mixing.
Fumed or colloidal silica is used as a thixotropic (thickening) agent but it must be mixed in with a high sheer mixer to avoid making the resin brittle. Garamite is a better thixotropic agent because it can be stirred in by hand.
Reactive Resins stocks numerous other fillers and additives. Please ask if you do not see what you require.
HEALTH AND SAFETY
Reactive Resins provide safety data sheets for all products. We send then automatically with commercial orders and they are available from our web site or by post upon request.
Our epoxy resins are non toxic but they are irritants and being viscous and sticky are difficult to remove from skin. Our hardeners are also non toxic but some are corrosive and will cause nasty burns if allowed to stay in contact with skin for any length of time.
Always use rubber gloves when using epoxy materials. Long nitrile gloves are best because they resist solvent better than most other types. If rubber gloves are to be worn for long periods also use barrier cream and wear cotton under-gloves to prevent dermatitis. Always clean gloves with a solvent soaked rag before removing them. Do not clean hands with solvent, it will penetrate through the skin and also remove the natural oils from the skin and cause cracking and dermatitis.
Some of our coatings contain solvents. Some solvents are potentially more hazardous than epoxy resins and hardeners. In addition to being flammable they have low occupational exposure limits, therefore coatings that contain solvents should be used outdoors or in areas with adequate ventilation. If ventilation is inadequate or if the product is being sprayed, it is essential that all personnel in the area wear air fed masks or masks fitted with filters that are approved for use with organic solvents. Dust masks will not offer protection from solvents.
When sanding epoxy coatings, fillers etc always wear a dust mask. Partly cured resins contain free amines and other chemicals that may be potentially dangerous if inhaled.
Safe and successful use of Syntac Epoxy Resins
and Synamin Hardeners