Bonding to Plastics - Part 1

Tuesday, November 10, 2020
Bonding to Plastics: Part 1
Visit a hardware store, and you will discover dozens of different types of adhesives lining the shelves, yet none of them can successfully bond to all types of materials. Cyanoacrylates (super glues), the juggernauts in the industry, bond to several plastic types, but it struggles with polypropylene and polyethylene plastics. The “low surface energy” of these materials makes it difficult for the adhesive to bond to the plastic's surface. In some cases, Cyanoacrylates will form a bond; however, it will not achieve its maximum strength making a repair unsuitable for situations under high stress or pressure.
In today’s consumer market, manufacturers use a multitude of plastics. Often the consumer has no idea what type of plastic makes up their item, resulting in trial and error when choosing a proper adhesive.
This 2-part blog series will provide methods to increase cyanoacrylates' effectiveness on plastics, identify common types of plastics used in products today, and offer advice on the types of adhesives that can repair them.

Part 1: FAQ – Bonding to Plastics

When do I use a cyanoacrylate primer?
You should use a primer whenever the two surfaces being bonded are not adhesion friendly or when the two surfaces are difficult to bond.  In the case of some plastics, their surfaces are classified as low energy.  Low energy surfaces are slippery and non-porous making it difficult for a liquid adhesive to adhere.  A primer changes the surface of the plastic giving the adhesive a surface to grab. Keep in mind the strength of these bonds will be relatively weak and may not remain bonded when force is applied.

When do I use a cyanoacrylate accelerator/activator?
Accelerators are particularly useful when you need to speed up the drying time for a cyanoacrylate glue.  It should also help increase the strength of the bond.

How does sanding plastic help cyanoacrylates adhere to it?
Using sandpaper roughs up the surface making it less slippery.  This should allow most cyanoacrylates to affix to surfaces more easily.  This will not be an option for every scenario & it might not help every glue, but it does have its benefits.  We recommend using medium (80-120) or fine (150 to 180) for best results on plastic.

Does super glue work with 3D printing?
Depending on the material used, most cyanoacrylates will bond with 3D prints.  The most common materials used in 3D prints, ABS & PLA, are both viable options for cyanoacrylate.  Although many people side with using a solvent such as acetone to chemically bond materials together, this can sometimes take up to 24 hours to fully cure and it may not bond the way you want it to.  We have successfully tested RapidFix Dual Adhesive System on ABS and PLA 3D print materials.

How can I tell what kind of plastic an object is?
Sometimes it is difficult to identify the type of plastic an object is manufactured with.  Many plastics look the same.  Occasionally items may have a small label somewhere on it with an abbreviation, for example, PE or PP.  If they don’t have a label, you may be able to look up that specific product on the internet or possibly reach out the manufacturer of the plastic and see if they can tell which type of plastic it is.