Question: We bond interlocking polystyrene and ABS tubes together with a solvent-based cement. Can you recommend a less hazardous and safer adhesive? The plastics are clear.

Answer: These plastics can be bonded with several adhesive types; I would suggest using a 100% solids acrylic adhesive. These adhesives are available as single-component heat-cured adhesives, as two-part adhesives, or single-component UV-cured systems. In your case, I would suggest a UV system, which would give you tremendous advantages over a two-part system in terms of productivity. With the correct choice of monomers, a UV-cured acrylic will give very strong bonds on these plastics and a crystal-clear bond line.

Question: We are making adhesives for bonding some optical components. These components are used in conditions where they go through heating and cooling cycles. What do you suggest?

Answer: Your major challenge is to overcome the differences in thermal expansion coefficients of the adhesives and glass. Adhesives generally have thermal expansion coefficients some four to 10 times higher than metals. This can create large stresses in the joints on temperature cycling; these stresses will often cause debonding from the surfaces or cause distortion of the glass and change its optical characteristics. In extreme cases, I have seen epoxies used to bond glass to stainless steel, where the glass has cracked on heat-curing the adhesives. The solution to the problem usually involves modifying the thermal expansion coefficient of the adhesive or making the adhesive more flexible so the stresses can be dissipated. High levels of fillers that have a very low thermal expansion coefficient will bring your adhesive much closer to the expansion coefficient of the substrate.

The other approach is to make your adhesive a little more flexible by incorporating elastomers. In critical applications, such as bonding lenses in astronomical telescopes, not only are specialty formulated adhesives used, but special glass and metals are used that have close to zero thermal expansion coefficients.