Adhesive & Sealants: Safe De-Bonding and Removal
We often fall into thinking – if a little adhesion is good, more is better. This isn’t the case with many applications. Adhesives and sealants are available in a variety of formulations to provide the desired amount of strength when needed, and means for de-bonding when needed. Examples include removable threadlockers and very flexible form in place gaskets which are easily removed without damaging softer metals. In other applications the bond area can be increased or reduced to dial in the strength needed.
Most structural adhesives have been developed to form the highest strength bonds possible and to be as resistant to chemicals and heat as possible. Removing the adhesive is quite an arduous task and parts can become damaged in the process.
When considering bonding with an adhesive, also consider if the assembly will ever need to be disassembled for repair. Some basic tips on adhesive de-bonding can be found here https://www.permabond.com/blog/2009/07/09/adhesive-removal/
For those cases when the need to dismantle a bonded joint was unexpected, the head scratching begins… how do you break the adhesive joint without destroying the parts? This is a tough question which is dependent on a number of factors:
- The type of adhesive chemistry that has been used to bond the components (e.g., anaerobic cyanoacrylate, epoxy etc.)
- The size of the area that has been bonded and the configuration of the joint
- The nature of the substrate materials and how strong these are – whether the parts will withstand the adhesive de-bonding process
- Sensitivity of other parts in the vicinity of the bond (e.g., sensitive electronics or weak plastics which could be damaged by heat or chemicals).
Removing Adhesives by Adhesive Type
Anaerobic Threadlockers: These are available in a range of strengths. The low strength products can easily be undone with tools such as spanners or wrenches. For high strength permanent threadlocking adhesives, using heavy duty tools can result in shearing the bolt that you are trying to undo. If you have used a threadlocker on a large diameter bolt and/or it has a long engagement, even if you have used a low strength “dismantleable” product, it may be very difficult to undo due to the large bond area.
Anaerobic Gasketmakers: Placing a flat-bladed screwdriver or similar implement and hitting it with a hammer in an effort to prize the components apart should be enough to pop the gasket. Anaerobic adhesives are very good in tensile shear or compression but weak under peel or cleavage stress.
Anaerobic Thread Sealants aka Pipe sealants: Normally these are low strength products which can be undone with a suitably sized wrench. Like the threadlockers, if used on large diameter or long engagement pipes these could prove more difficult to undo.
Anaerobic Retaining Compounds: Retaining compounds are actually for permanent bonding of bearings, housings, shafts, keyways and other concentric joints. They are typically very high strength and impossible to remove without using heat or chemicals.
Removing a stubborn Anaerobic Adhesive: By heating the bond area with a blow-torch, or placing the item in an oven to heat up will help weaken the adhesive. Attempt adhesive de-bonding while the parts are as hot as possible (once they cool back down the original strength will come back!). You will require oven or foundry gloves to hold the parts. Once components have been successfully dissembled, clean up before re-bonding. A wire brush, wire wool, wet and dry paper are all good for removing cured anaerobic (which often appears as a white-colored powdery solid). Wipe down with acetone. Stubborn cured lumps will come off after soaking in an aggressive solvent such as acetone or methylene chloride. Parts which refuse to come apart can be soaked in such solvents overnight and the disassembly process attempted the next morning. Do remember to ensure no solvent residue is present on parts and the solvent bucket has been taken away when using the blowtorch…
Always store the solvent in tins with the lid on in a flame proof cabinet.
These recommendations assume all component parts are metal.
Cyanoacrylate Instant Adhesives: Removing the adhesive is more difficult, as often they are used to bond plastics and rubber which will not withstand high temperatures or aggressive solvents. These adhesives are generally fairly brittle so pulling parts apart with a peeling motion will make the bond easier to break. If possible heat the parts to above 80°C (the point at which most cyanoacrylates lose a lot of strength) and then attempt to pull apart. If parts are metal and not delicate, they can be subjected to more extreme heat or solvent soaking in acetone or methylene chloride. Skin bonded with cyanoacrylate will need to be soaked in hot soapy water; stuck fingers can be prised apart by rolling a pencil gently between the fingers. It is not recommended to use solvent on hands as it will de-fat the skin. Soapy water is not only good for de-bonding adhesive from skin, if your components can take a nice long bath, they will de-bond over time. To shorten the time use hot water.
Epoxy, Polyurethane, Structural Acrylic Adhesives: These types of high strength adhesives can be tricky to de-bond. Certain products have both high shear and peel strengths so trying to peel parts apart may not work. Check the maximum operating temperature of the adhesive and assess if you can heat the component parts above this temperature to attempt disassembly. Most 2-part epoxies, acrylics, and PUs will start to degrade permanently at 200°C. Single part epoxies will need to be taken even higher. Methylene chloride can be used to remove cured adhesive, but if you have a large or complex joint, it will only “eat” into the edges very slowly.
UV Cure Adhesives: Extra care needs to be taken as substrates are typically glass and cannot be peeled, whacked or levered of course! The heating method of adhesive de-bonding could be a problem if the substrate materials are glass to metal as differential thermal expansion and contraction could cause glass cracking. However, glass to glass you could heat to the point the adhesive degrades permanently (>200°C). Glass to metal can be soaked in solvent as per other adhesive types. Plastics which have been bonded with UV adhesive such as polycarbonate or acrylic will be attacked by solvent. Even if you manage to get the components apart, removing cured adhesive will be a problem. Check the water absorption rates with the manufacturer; some products will absorb water. Boiling the parts in water may allow the adhesive to absorb enough water to soften it. Complete the removal while the adhesive is still wet as upon drying the strength will return.
Industry Developments in Adhesive De-Bonding
Professionals have realized there is a specialist market for adhesives that will need to be de-bonded at some stage and there are a number of innovative methods:
Magnetic particles: researchers at the Fraunhofer Institute in Germany are working on a project involving nanoscale magnetic particles which will cause the adhesive to fail if exposed to electromagnetic radiation (e.g., placed in a microwave).
Temperature: French researchers are working on adhesives that lose their tacky nature above 35°C. US scientists are investigating an epoxy which breaks apart when heated but re-bonds again at lower temperatures.
Explosives: Japanese scientists are looking at microcapsules filled with foaming agents or some kind of explosive ingredient to blast the components apart!
Other options could be radio-frequency sensitive products which will break apart at a specified wavelength.
As long as we don’t end up in cars which fall apart when someone sticks a magnetic sign on the bodywork….!
Until these ideas become working solutions, consider the possibility of removing adhesives prior to selecting a product. Then review the three methods of adhesive de-bonding; Dissolving, Thermal, Physical stress. Generally, a combination of all three of these with the right amount of time can free the bond.
For further help and advice, please contact Permabond.