Co-written with Elizabeth Kidd, BTG Labs' Custom Applications Scientist.
There's a logical fallacy akin to a "what's good for one is good for all" mindset that is devastating when applied to surface treatment in adhesion processes. Polymers are rapidly being developed and synthesized for niche applications to push the limits of current physical properties of materials. Polymers that are available today did not even exist a few years, or even months, ago. These different materials possess very particular molecular qualities that require distinct treatment approaches in order to compensate for their differences.
In order to utilize these cutting-edge plastic technologies, manufacturers need to be aware of the effect on the full material system – the baseline material, the adhesion, and outcome of bond performance.
The chemical make-up of the baseline material surface is where it all begins and controlling this aspect of the process can stop adhesion failure at the source. This is, however, often the most overlooked and least understood component of successful adhesion.
To illustrate how seemingly minor differences in material molecular structure can make or break a treatment process, let’s look at two of the most commonly used polymers in manufacturing; high density polyethylene (HDPE) and Teflon (PTFE).
If you take a look at the monomer (one link in the chain that makes up the entire polymer) for each of these materials it’s easy to notice that there is only one meaningful molecular difference. The hydrogen molecule connected to the carbon molecule in HDPE is replaced with a fluorine molecule in PTFE. This small differentiation has a massive impact on what kind of surface treatment is necessary in an adhesion process.
Plasmatreat, a manufacturer of plasma treatment systems, recently did a study on various substrates to demonstrate how materials respond to the same preparation approach. These charts below show contact angle measurements gauging the effectiveness of Openair™ atmospheric plasma treatment on HDPE and PTFE. The measurement of the contact angle decreases as the surface energy (how amenable a material is to bonding) increases. Creating a surface with high surface energy can ensure a successful bond.
As you can see, the treatment had little effect on the PTFE but brought the contact angle on the polyethylene down to the range where strong and stable adhesion is possible.
These two materials are just the tip of the iceberg when it comes to polymer differentiation. It’s crucial to match treatment to what the materials require. This treatment needs to be monitored, measured and verified. This is not easy since the chemical structure of surfaces gets more complex.
The situation sounds dire, and it is, but it’s also possible to fully understand your materials, modify your preparation methods and ensure perfect adhesion. Contact BTG Labs using the form below to inquire about getting a free process walk that will reveal steps you can take to eliminate bond failure.