Deciding on the best adhesive to use is never an easy process. Methyl methacrylate adhesives (MMAs for short) are a very common type of structural adhesive. But how can you tell whether they would be a good fit for you?
Here at Forgeway, we created our own range of methyl methacrylate adhesive products. We know they are fantastic products, but they may not be a good fit for everyone.
We have created this article to go over the benefits and drawbacks of using methyl methacrylate adhesives. By the end of the article, you will have a better idea if they are a good fit for you.
What are the advantages of using methyl methacrylate adhesives?
Methyl methacrylates have a very fast cure time
When using a structural adhesive in a manufacturing process, you want the adhesive to either fully cure or reach ‘handling strength’ before you move on to the next stage of the manufacturing process.
Some companies prefer this curing process to take longer, but others like this to happen very quickly. Typically, MMA’s will achieve 90% of their overall strength within the first four hours after the curing process has occurred.
Methyl methacrylates will offer a very fast cure time. They have what we would call a ‘snap cure’. This means they will turn from a liquid to a solid very quickly. You can get different formulations that have different open times, but all MMAs will quickly turn from liquid to solid. This process takes minutes (between 10-30) with MMAs.
Most other structural adhesives have a much more gradual solidification process. For example, epoxy and polyurethane-based adhesives can take 14-21 days to achieve their final end strength under ambient conditions.
The other advantage of methyl methacrylate’s cure is that the environment is less likely to have an effect. Other structural adhesives’ cure time can be very susceptible to environmental changes (like temperature and moisture levels).
The temperature will still affect MMA’s cure time, but not to the extent as some other structural adhesives.
Methyl methacrylates have a high shear strength
They are so strong that we would class them as structural adhesives. This means they become part of the structure they are bonding and will be able to withstand significant force to hold the structure together.
In more technical terms, they have a lap shear strength of up to 20 MPa. This literally means they can withstand 20 Kg of force per square millimetre of adhesive. Epoxy-based adhesives are the only other adhesive that can achieve higher lap shear strengths of up to 30 Mpa. Polyurethanes can achieve strengths of up to 15 Mpa and MS polymers can achieve strengths of up to 5 Mpa.
To put that into perspective we will provide a very literal example. If you applied 50 millimetres squared of methyl methacrylate adhesive to a substrate, it would be able to withstand a tonne of force.
So if you wanted to pick up a car that weighed a tonne, all you would need to bond the cable to the car is 50 millimetres squared of MMA.
Surface contamination isn’t a problem for MMAs
With most other structural adhesives, you will need to prepare the surface for the bond to be effective. Some adhesives just require you to clean the surface. Others will need you to fully abrade the surface.
Methyl methacrylates will not need either of these. Whilst we always recommend you clean the surface before applying an adhesive, MMAs can cut through surface contamination. Obviously, if the surface is completely covered in dirt or grease, the MMA will not be able to bond. But as long as it is free from significant contamination, you won’t need to extensively clean or abrade the surface.
So if you don’t have the time or capability to prepare the surface before applying the adhesive, use a methyl methacrylate adhesive. This will enable you to skip the surface preparation part of the application process.
Methyl methacrylates can stick to a variety of materials
This is quite a significant factor for some companies when choosing which adhesive would be best for them. Some will refer to this as having a good adhesion profile.
One such example of this is low surface energy (LSE) plastics (like polypropylene). Adhesive manufacturers have been able to develop methyl methacrylate adhesives that bond LSE plastics.
The adhesion profile is so good that we would say there isn’t a commonly-used substrate that you are able to bond with methyl methacrylates.
Methyl methacrylates are very versatile
The reason methyl methacrylates are versatile is mostly due to the fact that they are a two-component adhesive. By versatile, we mean that adhesive manufacturers are able to adjust these components and make the MMA product better suited to whatever your application needs.
This versatility is very useful. It even allows for most of MMA’s drawbacks to be eliminated by adjusting the formulation. For example, if you want a methyl methacrylate with a longer open time and more flexibility, you can get it. The formulation can be adjusted to meet those requirements.
What are the disadvantages of using methyl methacrylate adhesives?
As we have mentioned already, most of the drawbacks we are about to discuss can be eliminated by adjusting the formulation. However, these drawbacks are what you will typically find with standard MMAs.
Methyl methacrylates are flammable
This flammability can be a problem for three reasons:
- It can present a health and safety risk
- It will not be competent where you require a fire-retardant adhesive.
- Depending on what region you are in, shipping restrictions may apply. This can increase transportation costs.
There are recent developments that have adjusted the formulation to create a flame-retardent product. However, all uncured MMAs are flammable and this could present a problem.
There is a strong odour associated with MMAs
This odour isn’t harmful, but it isn’t very pleasant. Once again, you can get formulations of MMAs that eliminate this smell. But these variations will affect the performance of the glue.
If you are using an MMA that has this high odour, we recommend you take a few precautions. Always ensure there is enough ventilation in the room in which you are applying the adhesive. Providing PPE for the operatives applying the glue will also help deal with the smell.
Methyl methacrylates have poor heat resistance
This is also known as glass transition temperature (Tg for short). It is basically where the adhesive turns from a solid state into a rubbery state.
Methyl methacrylates Tg will usually be around 120℃. This means whenever it is exposed to temperatures above 120℃, the MMA will start to become rubbery. Performance severely depreciates when it reaches this temperature.
MMAs can cure with a high exothermic reaction temperature
Once again, you can get formulations that have a low exothermic reaction temperature. However, in general, you will find that MMAs have a high exothermic reaction temperature during their curing process compared to other adhesive chemistries.
If you intend to use a large mass of MMA (a bond line thickness greater than 15mm) to bond your assembly then the adhesive could ‘boil’.
The other problem with the heat of the exothermic reaction is the effect on the substrate you are applying it to. When applying MMA to a substrate that has low heat resistance (like some plastics), the heat could cause ‘read through’ or ‘witnessing’ on the substrate. This will ultimately damage the aesthetics.
How do you know if methyl methacrylates are a good fit for you?
This question is very difficult to answer. Not only do we not know your specific application, but we also don’t know the characteristics you want from your adhesive.
Only you know what you want from an adhesive. Here at Forgeway, we create tonnes of methyl methacrylate products every year. We know they are a great adhesive option if you want a strong, versatile adhesive that has a very quick cure time. If you want to research a few of the methyl methacrylate adhesives we sell, you can view our Purok range. Or you may want the help of a team member to guide you through the best match for you.
However, if you think the strong smell or high exothermic reaction temperature is going to be a problem, you will want to look at an alternative option. Our article on structural adhesives will give you a good idea of the other adhesives that will work for you. Or, you can download our comparison chart of structural adhesives.