We want to make polyurethane-type sealants for some construction applications but do not want to handle isocyanates. What are the alternatives?

The probable reason for your problem is the ultraviolet (UV) transparency of the plastic and the fact that epoxy bonds are not very UV resistant. Even epoxy coatings are not recommended for outdoor applications because they discolor under UV.

Both of these types of adhesives have the advantage of not containing solvents and being single component, so no measuring or mixing is involved. In addition, they both use moisture to initiate the curing.

Packages are chosen based on performance and cost. Specialty materials like anaerobic adhesives need oxygen to maintain their stability and shelf life. These materials were traditionally packaged in low-density polyethylene tubes or bottles to allow air diffusion into the package.

This is a very interesting question. Many adhesives are used in what is called a “zero gap” situation, where the adhesive is applied between two closely fitting surfaces, which are then clamped together.

The primary forces are shrinkage of the adhesive on curing and large differences in thermal expansion coefficients between the substrates and the adhesive. High stresses can cause delamination of bonds or damage to the substrates, such as glass cracking.

Dave Dunn's December 2017 column.

Dave Dunn's November 2017 column.