Gluing plastic: choosing the adhesive must start from the type of material

How to glue plastic correctly? There is no doubt about it: plastics are among the most widely used and most appreciated products in the industrial context, but they are also among the most critical materials when it comes to fastening. It should be noted that the surface energy of plastics is much lower than that of other materials such as metals (it is not by chance that gluing metals is easier. on average). However, using special adhesives for plastics has many advantages over traditional mechanical methods: it is, therefore, essential to identify the exact type of plastic you are dealing with to understand which adhesive to use. Let’s have a look at how and why.

Gluing plastic: an introduction to the material

Before outlining why to choose the best professional adhesive products for gluing plastic you need, first, to recognize the material, let’s briefly have a look at why plastics have become so essential for the current industrial world. This is a very light, cheap, highly workable material, as well as resistant to corrosion and recyclable. There are many possible options, with the most varied polymers available for companies to use. Consider the fact that, in recent years, polymers have been developed that, due to their great mechanical performance, as well as their great resistance to high temperatures, can actually be used as alternative materials to metals. Which, until a few years ago, was absolutely unthinkable.

The variety of plastics available is certainly an advantage, because every need can find “its own” ideal plastic material: the polymers used for different applications in construction, packaging, automotive, electronics, medical industry, and so on change depending on the use case. Even more so because new types of plastics continue to be developed; just think of the fact that half of the plastics currently used in the industrial sector have been invented in the last twenty years.

When needing to glue plastics, however, this leads to some small drawback: different polymers have different characteristics, how to choose specific double-sided adhesive tapes differs from case to case.

The types of plastics

The world of plastics can be divided into categories according to different criteria. For example, we can sort these materials into two large groups: on the one hand, are amorphous polymers, which are easier to fasten, and on the other are semi-crystalline polymers, less prone to adhesion. What makes the difference is the absence, in the former, of chemical crosslinking which reduces the polarity of the molecules; generally, as the polarity of the molecules increases, the ease of fastening, as double-sided tape creates an electrostatic phenomenon, increases as well. Semi-crystalline polymers – among which polypropylene is also found – therefore have lower affinity to gluing. That said, with the right products and the best techniques these obstacles can be overcome.

Or, plastics can be divided in an even more useful manner by considering the need to glue the plastic, considering their surface energy alone. While surface energy is always lower among plastics than metals, it is also true that there are plastics with medium surface energy and others with low surface energy, with different surface tension values.

Here are the main types of plastics with a low surface energy value:

·         Polypropylene

·         Polystyrene

·         Polyethylene

·         Ethylene vinyl acetate

The main types of plastic with an average surface energy value are:

·         Composite materials

·         Polyester

·         Rigid PVC

·         Polyamide

·         Polycarbonate

·         ABS

·         Acrylic

Gluing plastic: further issues

There are other factors besides low surface energy making gluing plastics more difficult on average: for example, the presence of plasticisers, which when migrating to the surface of the polymer can lead to a lower grip of the adhesive. Furthermore, consideration should be given to any release agents embedded on the surface of the polymer, as well as possible thermal expansion. We’d like to reiterate that none of these factors prevents the use of adhesives to glue plastic at a professional and industrial level. It’s all about choosing the best adhesive and possibly preparing the surface properly. Each professional industrial double-sided adhesive tape product for fastening plastic shows in its description the materials on which it can be applied, as well as any usage conditions (requiring, for example, the use of a primer for fastening plastics).