Polyester Resin

Polyester resin is normally polymerized by using a catalyst.  The most common catalysts are liquids which contain an organic peroxide and other materials.  The rate of polymerization or also known as the gel time, pot life, etc... is a function of various parameters including:

• Age of resin polymers
• Chemistry of resin
• Chemistry of hardener (catalyst)
• Amount of catalyst used
• Initial temperature of the resin
• Amount of mixing

I am running some tests to start characterizing the polymerization of polyester resins to help provide some tools for mixing and working with this resin.  

The test is performed by mixing a known mass of resin with a controlled amount of catalyst at a specific temperature.  The relative amount of polymerization is observed versus time and then plotted.  The intent will be that this will create a family of curves with which one can use to estimate the gel time or pot life of a particular resin mix at a known temperature.

The hardness of the curing resin is qualitatively scaled from 0 to 10 based on these observable features

• 0 - Virgin resin
• 1 - First noticeable increase in thickness
• 2 - Increasing thickness
• 3 - Thick
• 4 - Very thick, but still fluid
• 5 - Start of gelling
• 6 - Gelling
• 7 - Semi-solid jello-like
• 8 - Rubber-like
• 9 - Semi-hard
• 10 - Fully hard

Using this scale, one would be able to work with the material while it was less than 4, preferably 0 to 2.  When the material reached 4, you would sense that it is about to gel.  It is "going off".  

Resin System A

• Resin - Evercoat Premium Marine Resin [100554].  This contains Polyester Resin (proprietary), Styrene, and amorphous silica
• Catalyst - Rocket Plastics Liquid Hardener - This contains Propanoic acid, ester; Methyl Ethyl Ketone Peroxide, Hydrogen Peroxide, Methyl Ethyl Ketone, Water
• Mass of Resin - 1 ounce
• Mass of Catalyst - 12 drops
• Amount of stirring - 20 seconds

The manufacturer of this resin claims a working time of 10-12 minutes before gelling at a temperature of 71 to 90 degrees F.  Below 60 degrees F, the resin may not cure.  

The results of two tests are shown in the graph below.  

One sees that with this resin/catalyst system at 62 degrees F, the useful working time is about 23 minutes and at 56 degrees F the useful working time is extended approximately 5 minutes to 28 minutes. The gelling event which is seen as an inflection point is also delayed by about 14 minutes due to the change in temperature.   A graph of all of the current data for 12 drops of hardener is shown in the graph below:

A variation of this system is to change the amount of hardener at a constant temperature.  Three tests at the same initial temperature of 57 degrees F were run with 12, 18, and 24 drops of hardener.  The results from this test are shown below:

One sees that the amount of catalyst noticeably changes the rate of polymerization and it appears to be non-linear.  Another way to look at this data is to graph the various "times" versus the amount of hardener.  This information is in the graph below: