Ask Dr. Dave

Ask Dr. Dave’s Greatest Hits

DrDave242@windstream.net (Dave Dunn Ph.D.) — Mon, 21 Feb 2022 00:00:00 -0500

After more than 20 years of sharing his expertise and wisdom in the monthly Ask Dr. Dave column, Dave Dunn has retired as a columnist. Here we share some of his most popular columns over the years.

Alternative Cure Systems for RTV Silicone Sealants

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 25 Jan 2022 00:00:00 -0500

Room-temperature vulcanizing (RTV) silicones are well-known for their extreme durability. They are convenient one-component sealants that cure by reaction with moisture from the atmosphere.

Bonding Polystyrene to Glass

DrDave242@windstream.net (Dave Dunn Ph.D.) — Fri, 17 Dec 2021 00:00:00 -0500

Many adhesives will probably do the job, such as tough acrylics and epoxies. The simplest to source and start with might be a clear 5-min epoxy, dispensed from a twin-syringe and fitted with a static mixer.

Bonding Polystyrene Foam

DrDave242@windstream.net (Dave Dunn Ph.D.) — Fri, 19 Nov 2021 00:00:00 -0500

Bonding polystyrene foam to steel and wood is an application that was traditionally done with contact cements or other solvent-based adhesives. Due to health and flammability concerns, however, the modern trend is to use 100% reactive systems.

Vibration- and Shock-Resistant Adhesives

DrDave242@windstream.net (Dave Dunn Ph.D.) — Wed, 20 Oct 2021 00:00:00 -0400

You have a wide range of possibilities here. Normally, you would require an adhesive that has been toughened with a rubber for this.

Bonding Fluoroplastic Parts to Metals

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 21 Sep 2021 00:00:00 -0400

Polytetrafluoroethylene (PTFE) is a high-performance plastic used in a variety of industries, particularly for its heat and chemical resistance and “non-stick” properties. However, PTFE has a low surface energy that does not allow adhesives to wet its surface and subsequently bond.

Bonding with Differing Coefficients of Thermal Expansion

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 17 Aug 2021 00:00:00 -0400

We are using epoxy adhesives to bond steel substrates that are exposed periodically to both 150˚C and as low as 0˚C. Our problem is in maintaining adhesion to the two steel surfaces at such divergent temperatures because of the response of materials to thermal conditions when going through heating and cooling cycles. Do you have any suggestions?

Adhesives for Fiberglass Bonding

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 20 Jul 2021 00:00:00 -0400

Called thermoset polyesters, these materials are glass fiber-reinforced unsaturated polyesters. They are also often referred to as “sheet molding compounds” (SMCs), “fiber-reinforced plastics” (FRPs), or simply “fiberglass.”

Moisture-Sensitive Urethane Adhesives and the Pros and Cons of Epoxies

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 15 Jun 2021 00:00:00 -0400

Question: My colleague and I are working on a unique challenge of trying to find a solution for manufacturing urethane-based adhesives that are quite sensitive to moisture exposure.

Packaging Moisture-Sensitive Sealants

DrDave242@windstream.net (Dave Dunn Ph.D.) — Mon, 17 May 2021 00:00:00 -0400

You can obviously package your moisture-sensitive sealant in glass or metal cans or tubes, which will totally prevent moisture ingress. Aluminum tubes are widely used for this type of product, as long as you have good crimps.

Superglues vs. Polyurethane Glues

DrDave242@windstream.net (Dave Dunn Ph.D.) — Mon, 19 Apr 2021 00:00:00 -0400

I have worked with companies that manufacture superglue and polyurethane glue, both of which are single-component, no-mix adhesives. Superglue, which is the common term for cyanoacrylate adhesive, has been around for about 60 years. In contrast, the polyurethanes are about 20 years old in the retail market and somewhat older in professional woodworking. I admit to using both types of adhesive regularly.

Understanding Two-Component Adhesives

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 16 Mar 2021 00:00:00 -0400

I realize that the meter/mix equipment can be a major inconvenience. Adhesives come in two forms, namely two component or one component. Two-component adhesives are mainly epoxies, reactive acrylics, or polyurethanes.

Vibration- and Shock-Resistant Structural Adhesives

DrDave242@windstream.net (Dave Dunn Ph.D.) — Fri, 19 Feb 2021 00:00:00 -0500

You have a wide range of structural adhesive possibilities here. Normally, you require an adhesive that has been toughened with a rubber for this. Very rigid, quite brittle adhesives have been successful, however.

Debondable Structural Adhesives

DrDave242@windstream.net (Dave Dunn Ph.D.) — Wed, 13 Jan 2021 00:00:00 -0500

Numerous technologies and patents cover debondable structural adhesives. For your small parts, however, I can suggest a few simple alternatives.

Adhesives for Solar Panel Manufacturing

DrDave242@windstream.net (Dave Dunn Ph.D.) — Wed, 25 Nov 2020 00:00:00 -0500

Adhesives have become prevalent in solar applications to replace mechanical fasteners and welding.

Surfactants and Sustainability

DrDave242@windstream.net (Dave Dunn Ph.D.) — Fri, 28 Aug 2020 00:00:00 -0400

Surfactants are widely used in a range of adhesives and sealants, primarily to promote the wetting of surfaces to promote adhesion. Unfortunately, some of them have been found to have suspect toxicity profiles or environmental issues.

Solvent-Based Adhesives

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 04 Aug 2020 00:00:00 -0400

Solvent-based adhesives were traditionally attractive systems for both industrial users and consumers. They are low-cost systems that dry quickly and frequently give high performance, particularly on plastics where the solvents soften or dissolve the surface layers.

Can we replace welding and screws with an adhesive to assemble steel panels?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Thu, 02 Jul 2020 00:00:00 -0400

We assemble steel panels with welding and screws. Can we replace these with an adhesive?

Could you please suggest an epoxy resin, along with a hardener and accelerator, to use as a raw material in the production of a high-temperature-resistant adhesive?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Fri, 29 May 2020 00:00:00 -0400

It may be a one- or two-part system. We need temperature resistance up to 500˚C, and the adhesive will be applied to fill small gaps in a hot mild steel structure. The required initial setting time is 5 min.

What type of adhesives would you recommend for bonding glass to steel that will be exposed from -20-100˚F in an outdoor environment?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Mon, 11 May 2020 00:00:00 -0400

You don’t indicate which substrate is on the outside, and this does make a difference in the possible choice of adhesive. Epoxy adhesives were traditionally used for this application, but they should be used with care as they may be too rigid.

How can we ensure full cure when using a UV-cured coating/adhesive on irregularly shaped parts?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Thu, 23 Apr 2020 00:00:00 -0400

You need to look at so-called “shadow curing” options. Most UV-cured systems are based on acrylates and methacrylates and cure free-radically by the decomposition of a photoinitiator.

Can you recommend a method for bonding aluminum to aluminum for use in an application for continuous immersion in water?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Thu, 20 Feb 2020 00:00:00 -0500

All adhesives tend to lose strength on immersion in water. Water acts in two ways on a bonded assembly: It can be absorbed into the adhesive and soften it, and it can degrade the interface between the adhesive and the bonded surfaces.

What is your recommendation for bonding small ceramic tiles vertically to a fireplace surround?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Thu, 23 Jan 2020 00:00:00 -0500

The most desirable type of adhesive is one that sets quickly and has some heat resistance.

What are some options and recent developments in bookbinding adhesives?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Sun, 29 Dec 2019 00:00:00 -0500

Bookbinding is an important application area for adhesives, and requirements are becoming more demanding.

What is the difference between thermoplastic and thermoset adhesives?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Mon, 18 Nov 2019 00:00:00 -0500

Adhesives can be classified in several ways, including their material origin (e.g., natural or synthetic) and their type of cure (e.g., physical curing such as drying or chemical curing).

What cure systems are available for UV adhesives?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Thu, 24 Oct 2019 00:00:00 -0400

Adhesive and coating systems that use ultraviolet (UV) or visible light to begin the curing are intrinsically very attractive systems to the manufacturing engineer, allowing assembly of components and then “curing on command” by exposing to the radiation.

How can acrylic adhesives be used at very high temperatures?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Tue, 03 Sep 2019 00:00:00 -0400

Acrylics such as tough acrylics and anaerobics are routinely used at 150˚C in situations like automotive under-the-hood applications.

What are the best adhesives and sealants to use for home repairs and craft projects?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Mon, 26 Aug 2019 00:00:00 -0400

Over a long career, I have worked with several adhesive and sealant technologies and have tried many of them at home.

What would you recommend for bonding PVC plastics?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Fri, 26 Jul 2019 00:00:00 -0400

In the plumbing industry, solvent-based PVC cements are used for bonding PVC plastics. However, if you need a solvent-free system, cyanoacrylates and reactive acrylics have been widely used on rigid PVC.

Why do monomers from different suppliers result in different cure speeds and stabilities for anaerobic adhesives?

DrDave242@windstream.net (Dave Dunn Ph.D.) — Mon, 24 Jun 2019 00:00:00 -0400

I started my career as a chemist with Loctite Corp., and we used to manufacture our own monomers.