"Is there a temporary adhesive to bond glass and withstand 1400°F?"

Before this question can be answered, we need to ask for the definition of temporary. Only some materials will withstand up to 1400°F. Companies like Cotronics Corp and Aremco (to name a few) offer high-temperature adhesives. These adhesives are often modified with fillers like Alumina, Zircon, mica, ceramics, etc. that allow the adhesive to withstand higher-temperature environments. Some materials, including liquid materials or tape-type products, have a continuous service temperature of 1500°F, and a melting point of 2800°F. So in one sense, it is permanent at 1500°F, but temporary as you raise the temperature. Some epoxy systems can withstand up to 400°F and 500°F, so the question becomes - how long does it need to survive at 1400°F? If the answer is minutes, then finding a material that can survive short bursts of high temperature for only a little while may be sufficient. There are a number of different chemistries available such as silicone or epoxy. Typically, unfilled organic adhesives like acrylics and urethanes will break down long before 1400°F.

Other questions to ask are about which properties are required, such as: Does it (the adhesive) need to be clear or is opaque okay, or how do you want to remove the material? Unfortunately there isn’t a simple answer to this question. Some of the technical support groups at these companies may be able to help further, or recommend other options for you to consider.

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"I am using some UV curing adhesives and was told that there is a risk of leaving uncured monomers in the adhesive that could cause adhesive failure long term (like 6+ months) where the monomers dissolve or soften the cured resin. Assuming my cured adhesive is very hard and tests good for tensile strength is there any truth that uncured monomers (in very small amount) can cause the adhesive bond to weaken over time?"

If a material is fully cured, there is no risk of re-solvating the adhesive due to uncured monomers left behind since everything that could react has been reacted. However, it is our experience that many people who use a light-curable adhesive do not actually reach a fully cured state. Instead of reaching a fully cured state of 96-100% conversion of reactable materials, sometimes a particular process or part configuration will only reach 75-80% conversion. If a material only reaches semi-cured status, it could appear to be cured, and give good tensile strength and a cured surface, but have unreacted monomers at some level within the adhesive - which can then resolvate or attack the surrounding adhesive, thereby weakening the adhesive and the bond joint. This would be noticed with accelerated aging or within 1-6 months. A good qualification process will eliminate this risk.

• Evaluate various safety factors (cure time or intensity at 1.3x, 1.5x, 2.0x, 3.0x) to verify that the adhesive strength and properties have reached a plateau
• Run accelerated aging at a moderate temperature to verify long-term stability
• Evaluate the adhesive in a process by FTIR to identify the presence of uncured monomer (a skilled analytical chemist can identify a double bond peak, indicating the presence of uncured adhesive, and the lack of a double bond peak indicating that all reactable materials have been reacted), or use photo-differential-scanning calorimetry to measure the change in crosslink density.

Building a process to ensure that you reach a fully cured state, and have a good safety margin is the key to successfully using a light-curable adhesive.

See-Cure Technology available from DYMAX has a color indicator that changes from a blue color to clear when full cure has been reached. This helps to identify when you have reached a fully cured state.

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"Our research lab is looking for a medical-grade adhesive to bond:
1.) Dacron cloth to silver plate and
2.) Glass and PMMA optical cylinder in a silver tube.
It needs to be moisture resistant and should last for a long time (20 years).
Please suggest a product."

Dacron is a commercial name for PET, or polyethylene terephthalate. Bonding cloth to a rigid substrate like a silver plate can be done in a few different ways. Bonding to cloth is mostly a mechanical lock that forms by encapsulating strands of the cloth and then locking them to the rigid substrate. The viscosity of the adhesive will play a role, as the thinner the viscosity, the more it will wick into the cloth. A very high viscosity will not wick very far into a cloth. A 2-part epoxy, such as found from Loctite or 3M, or a 2-part urethane, such as found from Lord Corporation, are just two products that you might want to explore. A silicone adhesive may also do the trick, and would suggest contacting representatives of Dow Corning, Momentive Performance Materials, NuSil Technology, or any of the other silicone manufacturers.

To bond glass and PMMA you may be able to use the same adhesive, but the application might require a lower-viscosity material, depending on the gap between the parts and method of assembly. The epoxy and silicone systems will be moisture resistant and have good usage life, but most manufacturers will not warrantee a 20-year usage lifetime. A 1-part, light-curable urethane acrylate, like 203A-CTH or 209-CTH from DYMAX, are options if you can get light to the adhesive.

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"I need to bond ABS to ABS in a pure-water environment (50° to 180° F). Concern for leaching chemicals into the pure water is high. What FDA-approved solvent choices do I have?"

One website that I found listed various solvents like Cyclohexanone, Cyclohexanone/THF, Cyclohexanone with various medical-grade acrylic polymers dissolved in the solvent for added strength, and various other combinations. www.ineos-nova.com. The grade of solvents are typically not listed as Medical Grade or FDA approved, but based on the level of purity of the solvent. Obtaining the solvent of choice with the highest purity (99.9% or higher) would limit the potential leachables into the water. Sigma Aldrich or Alpha Aesar both carry small quantities of these solvents in various grades for evaluation. Methyl ethyl ketone (MEK) is an alternative solvent system. Using a solvent requires special handling due to the smell, flammability, and explosive storage requirements, and is carefully monitored by the EPA. Dispensing systems like those from Technoideal are options to limit operator exposure . If you want to consider a solvent-free adhesive, you might look at a 1-part, light-curable adhesive like DYMAX 1161-M if you can get visible light to the bond line (non-opaque parts), or a 2-part urethane or epoxy from companies like Epoxy Technology or 3M (to name a few) may be considered. These alternatives to solvent can provide a bond almost as strong as solvent, fill gaps in the molded ABS bond lines, and are much more environmentally friendly.

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