We know how frustrating it is to try and choose a proper glue that will work on your project that involves polypropylene plastic – while using glue sounds obvious at first, it is actually harder to achieve ‘gluing’ of these surfaces.
You might initially assume that all glue types are the same – after all, aren’t they all glue, and won’t they all achieve the goal of sticking two surfaces together? However, using these glues reveals a shocking result – not every glue you see is multipurpose, and you need to consider your options carefully.
We learnt that lesson the hard way, when we attempted to glue two polypropylene plastic pieces together. There are many lessons to learn, and we aim to teach you that so that you do not make the same mistakes we did.
Keep in mind that polypropylene is a unique plastic that we term as having ‘very low surface energy’, which makes it hard for most glues to make solid bonds with it. Therefore, if you are using a super glue, it is worth noting that you can only do the repair once – any more than that, and you compromise the integrity of the plastic. A recommendation we would definitely go for is the Loctite super glue, which is versatile enough to work on all plastics.
How does glue for polypropylene work?
Because polypropylene is a unique plastic that we term as having ‘very low surface energy’, which makes it hard for most glues to make solid bonds, it is very important to choose a different glue than from what you would usually use in other plastics. The reason of ineffectiveness of the usual glues on polypropylene surfaces is the ‘low surface energy’ making it challenging for the glue to wet the surface and make a strong bond.
Due to its ‘low surface energy’, polypropylene and polyethylene are used in vessels such as food containers, because they allow liquids and other substance to roll off easily. Therefore, when choosing an adhesive for this surface, it is always best to choose a glue that can ‘wet’ low energy surfaces.
In order to understand why this is an issue, it is helpful to know how glue generally works, and you will understand this by looking at cohesive force (this makes the glue molecules stick together) and adhesive force (this allows the glue molecules to ‘wet’ the surface). If the adhesive force is weaker than the cohesive force, then that means the glue cannot wet and penetrate, making the glue remain in form of blobs that dry up.
The work of glue depends on the adhesive and cohesive forces being equal – when you apply it on the surface, the glue has to spread out and ‘wet’ the surface, then the glue needs to dry up and make different surfaces stick together.
On the other hand, super glue (which is also known by its industrial name cyanoacrylate adhesive) is a fast-bonding, instant, and high-strength adhesive that is specially engineered to bond almost all materials. They are highly valuable, because of their resistance to moisture and temperature, and work well on most surfaces including ceramic, glass, stone, metal, and so on.
Super glue works in the same way as the usual glue in the bonding process, but it instead uses anionic polymerization. It will actually bond into a mesh structure that is durable enough to form a rigid, strong bond. Since it uses a ‘lock and key’ mechanism when bonding two surfaces, it will not work very well on a non-porous surface like some plastics and glass.
Why should you choose super glue for polypropylene?
Part of the challenge is getting the best glue that will help in your task, as you cannot take a ‘one size fits all’ approach. The problem with that approach is that it is not guaranteed to work, or you might notice parts falling off because the glue cannot hold them together.
The best way to know whether super glue will work (or damage) your polypropylene surface or tool is to find out whether it will risk damaging the surface or repair it effectively.
How can you repair polypropylene using super glue?
Before using a super glue on your polypropylene plastic, know that it is not always going to deliver perfect results, and some cases mean that it is prohibitive to use in bulk because of the costs involved.
Therefore, in order to increase the effectiveness of super glue on polypropylene, you can purchase a primer as well as liquid plastic adhesive that can help the plastic be more receptive to the glue. However, keep in mind that you cannot continuously glue polypropylene, or else you will damage it – therefore, if you will repair it, do it only once.
There are some tools you will need during repair:
- Primer and liquid plastic adhesive
In order to apply glue in the repair process, you can follow the following steps:
- Flatten the surfaces that you are planning to glue, and scrape away any protrusions or bumps. Wipe this area with a damp washrag to clean it up and make the adhesive more effective.
- On each surface, apply a layer of the primer, and allow it to sit for 1 minute. This primer will become stickier as it dries.
- On each surface, apply the plastic adhesive, and tightly press the two surfaces together immediately. Hold them in place for at least half a minute, and you can use vices or clamps to hold them together as tightly as possible if you have them around.
- If you notice any excess glue that is seeping out of the joint you have created, scrape it away. If the glue is dry, you can use a scraper or knife, and use a towel or rag if it is wet.
- Before using the polypropylene plastic, leave it overnight to dry and set in place.
Polypropylene is a chemically resistant plastic, and you are not meant to glue it at all – unless you use an adhesive that is specially formulated for it. Even then, the adhesive will only have a limited-time effect, so if the plastic breaks again, it is best to dispose it.