Table of Contents
An Introduction To Polypropylene
If you work in the plastics industry then chances are you have come across polypropylene (PP) or polyprop as many call it. Whether its in sheet form, moulded components, blown films or extruded profiles, pipes or cables.

You might also have come across the various versions such as polypropylene homopolymer (PPHP), copolymer (PPCP), randomly copolymer (PPRCP) and then there’s also biaxially oriented polypropylene (BOPP). We found this processing guide and quick overview from Plastribution to be quite interesting.
Couple this with the fact that each specific supplier can add their own additives, colour master batch and mix of materials such as recycled content and you can see that even a simple polymer like PP can actually be very complex.
Whichever version you go for, there are often similarities. They might have their own specific processing and final properties, or cost points that influence you to go with one over the other, but the common theme with all versions of polyprop is that they will have a low surface energy and be difficult to print on, glue to or coat.
Many people choose this material due to its cost and ease of processing and if it’s being used as a case, a cap or something that doesn’t need adhesion then the low surface energy gives it chemical resistance and stain resistance through product life and means it’s a perfect material for so many applications.
Other users might want the same cost benefits but require an area printed, labelled or bonded and that’s where surface treatment comes in!
Our look at polypropylene and the advantages and disadvantages of surface treatments aims to give you some ideas on the different applications available to help with your adhesion and processing problems.
How Will Plasma and Corona Treatment Help With Polypropylene Processing?
Plasma or corona treating polyprop will increase surface energy by adding new chemistry to the material which is good for bonding. Treatment takes an inert material and tinkers with the very top layer of molecules to influence the interface between the glue or print and the material itself.
Plasma or corona treatment do not change the entire material so properties remain the same, there will be no difference in melting point, chemical resistance, stiffness or any other characteristic other than the wetting and bonding potential.
If you haven’t used treatment like this before it can be easy to think of it wrongly and assume that the part now feels sticky, or tacky. What treatment does is at a molecular level and while improving the adhesion strength of glues and coatings, it doesn’t actually make it tacky. Holding a plasma treated part will be no different to holding a standard part.

Photo of a lap shear pull test with untreated polypropylene bonded together with adhesive. Clean removal of the adhesive occurred.
After treating polypropylene, the change was dramatic and now the adhesive bond is stronger than the plastic itself.

With increased surface energy and improved wetting, which is the ability for a liquid to flow of a surface readily, we now attract adhesives and inks to the surface, pulling them intimately toward the polypropylene. This alone is often enough and that intimate flow of liquid over the surface leads to improved bonding, but we also have the improved chemistry on the surface that plays its part too to create new stable and strong chemical bonds between solid and liquid which all together means improved adhesion.
The treatment we’ve done on the surface is now permanent and will be there for good, once you have the bond, the bond is there for life. IF you haven’t made the bond and the part is being stored then there is a treatment life. This can be a complex topic so if you want to go more in depth you should read our article How Long Does Plasma Treatment Last?
Complexities aside, because polyprop is a relatively clean and stable material it will last weeks, months and maybe even years if stored and handled correctly.
Surface Treatment and Polypropylene
Polypropylene has been a material used by many industries for decades and over that time many surface treatments have been used to prepare the surface for additional processing. Lets take a look at some of the methods available to treat and prepare polypropylene.
Classic treatments include chemical etching, chemical primers and flame treatment. While these systems are still used frequently it’s often either historical or because of the volume of manufacturing. Primers for example are trickier to apply for high volume manufacturing, costly to buy and dispose of but at lower volumes a single primer bottle can be used which is much more cost effective than installing machinery.
Flame treatment is very forgiving and has a large area treatment which has kept it useful for applications like automotive bumper treatment to improve paint adhesion. However the cost of gas, safety implications of having a naked flame in the factory and the temperature associated causing issues on small or thin components means that flame isn’t right for everyone.

Plasma and Corona treatments have been used for decades on this material in applications where users want to avoid hazardous chemicals, which was especially important as REACH regulations were introduced in 2007. It has also been a big replacement for flame treatment due to safety and more recently cost and environment implications. Using flame treatment requires a gas source which fluctuates in cost, gives off CO2 and poses significant risks with open flames on factory shop floors.
These treatments, along with any others will typically work in one of three ways.
Material Change – Surface Treatments That Make a Molecular Change
Plasma, corona, ozone and flame treatment will all alter the surface chemistry by adding new molecules which are good for bonding. For most treatments the new chemistry that works the best is oxygen! Some times this might be from using pure oxygen, but in most cases the oxygen we use is free from the air around us.
Interface/ Tie Layer Coatings – Treatments That Add a Reactive Or Active Interface Layer
Applying a primer or coating in some way that’s aggressive enough to bond to the material and add a coating to the material adds an interface layer that is then good for other processes to bond to. This method can be very powerful because you can tailor the primer with specific chemicals, but the chemicals can also have some severe health and safety warning labels associated.
Abrasion and Surface Removal – Taking Away Loose Or A Bad To Bond To Bond To Surface

It’s worth mentioning the idea of abrasion, surface removal and increasing surface area because for many materials this is a fantastic method of improving performance. However with polypropylene if you remove the top surface, the surface underneath is just as bad to bond to so adhesion is still poor. The increased surface area might help but an inert surface is an inert surface so it’s certainly not a fix for many applications.
Plasma and Corona Treatment For Polypropylene
We don’t want to sound too biased, because honestly there are a number of preparation methods for PP and whichever suits your production process is the right one for the job. Primers are good for low volume or extra tricky projects where a physical interface layer is needed, or where exotic processes are being used that need specific chemistry. Flame is great for treating large areas quickly using a robot (although we would recommend our latest SpinTEC systems for this) and abrasion might just be good enough if your process is already quite harsh such as solvent based adhesives or hot melt adhesive bonding.
From our point of view here at Tantec and the Ebble Group we know that polypropylene treatment is the single biggest treatment type we do. Whether it’s automotive mouldings for interior trim material adhesion, medical device treatment for safety critical print or electrical case treatment to guarantee adhesion and sealing performance for ingress protection ratings (IP Ratings).

There are a few things that we have in mind when speaking with customers about polypropylene and whether treatment will be right for them…
Specific Material Information Such As Additive Content Is Useful
While we can’t usually tell a lot from supplier product codes, we can ask whether the material is homopolymer or copolymer, and we can get some understanding on additional additives, fillers and recycled content. The usual rule of thumb is that newer, low additive content polyprop is better and BOPP for example is one of the tricker PP versions to treat. But in general, all polypropylene versions can be treated and can be tested with surface energy dyne pens or contact angle to determine the change. Recycled content is becoming more popular and this can pose challenges but this can normally be overcome.
Other properties such as talc, glass fibres and other additives that aren’t oily usually don’t make much difference to treatment.
Age and Handling Conditions Can Make The Biggest Difference To Treatment Performance
Many manufactured components are made and intended for use straight away, or within a few hours and because the parts are polypropylene there is rarely any release agent or surface contamination to worry about. A fresh injection moulded part being treated and printed, coated or processed within hours of being made is usually positive.
Parts that are transferred from factory to factory, or bought as standard and then further processed can be much older and have handling contamination such as finger print oils on the surface. The age of the material can mean that additional crosslinking has taken place, or that additives have bloomed to the surface even if there aren’t many additives in the part.
Older components can be trickier to guarantee performance, especially if the incoming quality level is variable. It’s important to understand the variations and problems to know whether cleaning or more intense treatment is needed.
When Is The Next Process and How Soon It Will Take Place?
More traditional processes such as solvent based printing will only require a small amount of treatment and if the print process happens moments after treatment then we know that treatment amount isn’t critical and treatment life isn’t a consideration.
On the other hand, if the following process is UV cure ink printing and it will take place 6 weeks later at a separate site, treatment life will need to be long and treatment amount will need to be high enough that if it drops, it doesn’t go too low. For more information on treatment life you can also read What Is The Treatment Life of Plasma and Corona Treatment?
Plasma vs Corona Treatment
Many applications for treating polypropylene won’t matter at all which treatment method is used. There could be slight differences that means one is better than the other but more likely is that you would choose the right tool for the job.
Vacuum plasma is perfect for large injection moulded parts because it treats any exposed surface without the need for automation or tooling, but it is a batch process. Atmospheric plasma is perfect for extrusions and point and shoot treatment using robots or automation but treats a maximum 150mm per head and can be tricky to get in to difficult to reach areas.


Corona treatment is perfect for sheets and boards and can treat multiple meters wide and be installed inline with a printing process.
Looking at the different treatment types, the point is that while there’s hearsay and rumours that one works better than the other, or treatment life is better for one, the reality is that for the vast majority of applications the performance of treatment will be the same.
It more likely will come down to the best way to process the material, which is the most cost sensible machine and which best integrates into manufacturing and production lines.
You can read more on What Is Atmospheric Plasma? What is Corona? and What is Vacuum Plasma? in their own articles.
Alternatives To Surface Treatment
If bonding is critical to the part in question then there are other methods that might be useful, cost effective or more sensible for your production. The three key processes that we see are using low surface energy inks, adhesives and coatings, using physically joining techniques such as bolts and rivets, or perform some form of welding, either heat or ultra sonic.
It’s also worth taking a moment to consider cleaning and abrasion as alternatives as they are often cheap, quick and easy go to methods to try.
Low Surface Energy Adhesives and Inks
Low surface energy adhesives in particular have come a long way over the last few years and can be a fantastic for many applications. There are two main ways for a manufacturer to make these adhesives, either add specific adhesion promotors in the adhesive mixture or add harmful solvents which can attack the materials.
This can mean that they have specific considerations or be a bit more expensive than their standard counterparts, but without a need for surface treatment the overall manufacturing process can be simple and cheaper. Other times they can be costly and because the formula for these adhesives is more specific it might be that the adhesive or ink doesn’t have the same properties as others and if some of those properties missing are important it might rule this technology out.
Fasteners, Bolts and Rivets
Perhaps an obvious one as it’s about the oldest method of keeping two materials together, physical fasteners can be incredibly useful but can also introduce structural weaknesses, add weight and add bulk to the design.
Still a firm favourite for many industries including marine and aerospace where new joining methods are slower to be implemented.
Ultra Sonic Welding and Other Joining Methods
Heating or vibrating the material at high frequencies allows the material to melt and fuse to itself. Because polypropylene is a thermoplastic rather than a thermoset material it means that it can melt and reform over and over again which makes it perfect for these joining methods and for recycling.
This might not be so useful for dissimilar material bonding and joining areas that are tricky to reach or over a complex geometry but it certainly has its uses and is a very strong form of bonding that requires no adhesives or consumable materials.
Cleaning, Wiping and Abrading
Wiping a material can make a big difference, but there are usually two questions – what are you wiping with? What are you wiping away?
A strong solvent may make a difference to the material, but it’s likely to have hazardous implications. Wiping with a mild solvent like IPA will remove surface contamination but it won’t make any change to the material.
Wiping away a surface or grease, oils or debris is surely going to improve performance. However, cleaning alone is only likely to expose polypropylene which is still nonstick.
This is similar with abrading a material like this, it seems sensible to remove the top layer of the material but if the material is the same underneath then it’s unlikely performance will improve. Perhaps the larger surface area will help, but in this case it’s unlikely to give a big improvement.
Final Thoughts And Considerations
It’s been said within our walls many times “If it wasn’t for polypropylene, we wouldn’t have a business!” and its very true because this material has been centre stage on so many of our projects and importantly it’s a material that regardless of variation we feel confident that almost any blend or variation would be treatable.
It’s a brilliant material to work with for a number of reasons and many industries have embraced it’s qualities over the years. The future of the material is likely to move more toward recycled content and perhaps mixing with other materials such as hemp or other natural fibres for reinforcement and rigidity.
While it’s easy for us to say this information, we would always welcome a challenge and whether you want to buy equipment, test materials in our labs or run production with us through our subcontract treatment side of the business (Ebble Manufacturing); we would recommend you give the treatment a go and see whether its right for you.