Acrylic Adhesive Cure Temperatures

The common adhesives used in the equine market fall into two basic groups:

• Acrylics and
• Urethanes

These materials are not only differentiated by their chemistry but also by their unique performance properties. This document is concerned only with the acrylic adhesives used by Sound Horse and by many farriers – epoxy-methylmethacrylate.

The acrylic adhesive used by Sound Horse to apply the Series I, Series II and Series III fabric cuff, urethane rim pad, “glue-on” horseshoes is the “slow set” variety. Sound Horse uses this because it is very predictable in its “open” or “working time” and generates a relatively low peak temperature during the exothermic cure process. The low peak temperature is a characteristic that, when used with the fabric cuff, assures that the horse will not be uncomfortable when the shoe is applied to the hoof.

It can be shown that the measured temperature is directly related to the weight of the material and the volume and/or surface area of the patch or repair. In short a large, thick patch will generate a higher temperature than a thin patch. The same weight of acrylic adhesive applied over a large surface area (as with the Sound Horse fabric cuff) will generate a lower temperature during cure. The lower temperature is a function of the low density polymer cuff fabrics spreading the total weight of adhesive and the large surface area of the cuff acting as a radiator to diffuse the heat. None of the common acrylic adhesive temperatures, however, come close to the 700-900ºF seen when the horse is hot-fitted with a steel shoe.

Results: (see chart & graph – Test conducted at room temp of 70ºF)

The common acrylic adhesive used by Sound Horse to affix the fabric-cuffed “glue-on” horseshoe to the hoof will generate a temperature of approximately 115º F. This is well below the threshold that would generate any discomfort for the animal and will not cause any temperature related injury to the hoof.

Discussion of Results:

Based on these tests (conducted at a room temperature of 70ºF), data and observations (as well as 10+ years of commercial experience), we can state that the “slow set” acrylic equine adhesive used by Sound Horse (branded as EquAcrylic) generates a peak temperature of ~ 115º Fahrenheit when used to saturate the 2-ply Polyester/Vectran fabric cuff on the Series I, II and Series III products for application to the horse’s hoof. This is a much lower exothermic peak temperature than that generated by a ¼ inch thick repair (160 ºF) or the peak temperature of a large sample (say 2 ounce) contained in a mixing cup (164ºF+). The reason for the difference – a lower peak cure temperature in the 2-ply fabric adhesive saturated sample – is that the polymeric fabric used has a very low density, a low specific heat capacity and, finally, will not absorb liquids into the individual fibers (unlike many natural fibers). This means that the saturated fiber matrix acts in two ways to reduce the cure temperature: 1) the fabric volume reduces the effective density of the adhesive (adhesive weight per unit volume) and 2) the large surface area of the fabric cuff may be acting as a radiator to effectively dissipate the heat during the cure process.

How can you demonstrate this yourself?

Materials required: stop watch, infra-red thermometer, repair fabric, fixed dimension ring (to simulate a thick repair), standard acrylic adhesive, mixing materials, and rubber gloves.

Now what?

• Start the stop watch
   
• Mix Adhesive …. thoroughly.
   
• Fill the repair sample – we used a 1/4 –inch thick section of ABS thin wall pipe. The wall is 1/16 inch thick so the net internal diameter is 1.375 inch. Surface area is 1.485 square inch. Volume is 0.371 cubic inch. Net weight of adhesive is 6.5 grams.
   
• Saturate the fabric with adhesive – we used Polyester/Vectran braided tape 4 inch wide by 7.75 inch long and folded it in half to simulate our 2-ply cuff. Fabric weight was 8.9 grams. The saturated sample had a gross weight of 26.2 grams for a net adhesive weight of 17.3 grams. The final cured thickness of this sample was 0.125 inch for a volume of 1.9375 cubic inches.
   
• The gross weight of the adhesive, cup & stick is 59.7 grams with cup & stick at 5.6 grams. The net weight of adhesive is 54.1 grams (about 2 ounces). The surface area of the adhesive in the cup is 3.976 square inch. The cup is filled to a depth of 1 inch (this would be a monster repair). The adhesive sample volume is 3.34 cubic inch.
   
• Measure & record the temperatures at one (1) minute intervals while the adhesive cures.
   
• Chart the graph the results.

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