Ask Dr. Dave: How can we ensure that our acrylic emulsion adhesive testing results will be predictive of the stability of all package sizes?
There is no reason that a 20-g sample should behave differently from a large sample.
Question: We are doing final testing on a glycol-free, acrylic emulsion adhesive for the art materials market. To permit shipping in freezing temperatures, the product has been formulated to be freeze/thaw stable. However, we are having trouble testing for freeze/thaw stability.
Original testing was done on 20-g samples, but we have found that testing 20 g is not predictive of the freeze/thaw stability of larger package sizes. We are currently testing quarts and gallons; however, 5-gal pails and 55-gal drums become too problematic to actually test due to their size. Is there some volume that, when tested, will be predictive of the stability of all package sizes?
Answer: There is no reason that a 20-g sample should behave differently from a large sample. Your 20-g sample has probably been placed in a refrigerator and cools down quickly because of the large surface-to-volume ratio, compared to your larger package sizes. There is evidence that the rate of cooling and thawing has an effect on the freeze-thaw stability. I suggest that you take your 20-g sample and cool and thaw it very slowly to simulate real-world circumstances.
Question: We want to vacuum impregnate electrical connectors to seal voids between plastic and metal (copper). What do you recommend?
Answer: Most impregnation sealants these days are based on methacrylate resins. The major issue with your components is that the thermal expansion coefficients of the metal and plastic are widely different (i.e., the expansion coefficient of the plastic is much higher than that of the metal). This creates stress in the sealed joint during temperature cycling of the component. There are two ways to compensate for this stress: either increase the adhesion of the impregnant or make it more flexible. In most cases, using a more flexible sealant will solve your problem.
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