Modification of Polypropylene by overtreatment by plasma

[Paolo6691]

Hi

I am trying to understand what kind of physical change in polypropylene are caused by Plasma treatment.

I have to bond PP using adhesive (mostly CA) and using different settings I can get more than 48 or more than 60 Dyne/cm.

With the highest setting the material has a shiny shadow and when the adhesive bond is tested (for instance using a termal shock test) it fails.

I have some theories and I would like to know if I am on the right path: I think that an over treatment with plasma causes the material to be more brittle and probably some localized skrinkage that then comes into play when the assembly is tested, am I right?

Do you have any idea on the right test to check for this material characteristic changes and so define a treshold, be able to sample production, be able to controll the process better?

Thank you in advance

Paolo

 

[Compositepro]

Plasma treatment bombards the surface with high energy molecules that break existing chemical bonds in the surface molecules. This makes the surface more chemically reactive and more "wettable" (higher surface energy). Over-treatment degrades the material on the surface to the extent that it becomes weak.

 

[Paolo6691]

Yes I know, but how can I test it, and furthermore if it is more wettable why then my adhesive joints fail? what changed in the material?

Cheers Paolo

 

[Compositepro]

It sounds like you already have a test. How did you get your data?
Your joint fails because the material you are bonding to is degraded and weak. Plasma treatment is usually controlled to a certain dyne level. You can get dyne pens that are felt tip pens with different surface tension inks.

 

[Paolo6691]

Yes I do have Inks and pens, but I am more interested in a way to find what kind of micro-structural changes trigger the failure and at which point they happen.

So it is not a surface tension test that I need but a material one to understand what changed inside the material, and how other properties are affected.

Thanks

Paolo