Ask Dr. Dave: Why are some waterborne adhesives called latex, others called dispersions and yet others emulsions?
Dave Dunn's August 2014 column.
Question: What can I add to a reactive acrylic adhesive to increase the heat resistance?
Answer: A lot depends on the cost implications from modifying your formulation. If cost is no object and you have a very high-value application, consider adding substantial amounts of difunctional or trifunctional monomers to get additional crosslinking. There are some very heat-resistant monomers, such as monomers based on aromatic backbones like ethoxylated bisphenol-A dimethacrylate or acrylate.
Other possible materials that can often give improvement are additives (0-10%) such as bismaleimides or cyanate esters. These materials often do not cure when your adhesives are cured at ambient temperature, but do cure and crosslink at very high temperatures. In some cases, your adhesive will actually exhibit higher strengths when aged at high temperatures. Note that these additions will tend to make your adhesive harder and perhaps more brittle.
Question: Why are some waterborne adhesives called latex, others called dispersions and yet others emulsions?
Answer: You may recall news headlines in the 1990s about the residual proteins in natural rubber causing severe latex allergies. Many companies have been using the terms “dispersion” or “emulsion” in place of latex to disassociate their water-based adhesives from adhesives based on natural rubber latex. Although synthetic latex does not have this problem—and it can also be eliminated in natural rubber by processing—the association of latex with allergies still lingers.
Any views or opinions expressed in this column are those of the author and do not represent those of ASI, its staff, Editorial Advisory Board or BNP Media.
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