In this interview AZoM talks to Rohit Ramnath, Senior Product Engineer from Master Bond, about surface preparation, and why optimal adhesion is recommended.
Why is it advisable to prepare your plastic substrates for bonding?
Surface preparation plays a vital role in ensuring that good bond strength is achieved. It is also important to recognize that each type of plastic poses a different challenge from a surface preparation standpoint. It is therefore critical to follow the surface preparation recommendations by the manufacturer of adhesives.
What are the methods typically used for good surface preparation?
Degreasing, abrasion, physical methods (such as corona discharge, flame treatment, or plasma treatment), and chemical treatments, are among the many methods most often recommended for surface preparation.
How do you degrease a plastic substrate?
All bonding surfaces should be carefully cleaned, degreased, and dried to obtain maximum bond strength. Degreasing is carried out in order to remove any loosely held dirt or other contaminants from the plastic surface.
Some of the solvents that can be used to degrease surfaces are toluene, acetone, methyl ethyl ketone, methyl alcohol, isopropyl alcohol, and trichloroethylene. Note that while using a solvent, it is important to ensure that appropriate environmental, health, and safety regulations are adhered to.
What are the necessary steps needed to degrease a plastic substrate?
There are typically 3 main steps in the degreasing process. To start, vapor degrease, clean, and rinse the materials with the appropriate solvents. Second, immerse the substrates in a fresh bath of solvent for the wash and follow by immersion in the second tank for a rinse. Finally, clean and dry the substrate after degreasing.
How is a surface abraded?
An abrasion is a form of roughening. Surfaces must be degreased and cleaned both before and after abrasion, to remove any pre-existing contaminants on the surface. The specific abrasion technique recommended will depend on the specific plastic being used.
For example, roughening the surface with sandpaper can be a successful approach for many plastics, such as PEEK, nylon, polycarbonate and others.
PEEK coupons before and after surface roughening with 60 grit sandpaper accompanied by a magnified image of the partially roughened surface. Image Credit: Master Bond
What are the physical methods for surface preparation?
Physical techniques use the surface reactivity of the plastics and modify the surface chemistry to achieve better adhesion. Some of the most common physical methods include corona discharge, flame treatment, and plasma treatment.
In corona discharge, the ionized air generated by this technique reacts with the surface of the substrate to form free radicals. The reaction with oxygen in the atmosphere increases the surface energy of the substrate to be bonded.
In flame treatment, the surface to be bonded is exposed to a gas flame for a few seconds. The flame oxidizes this surface and increases the surface energy by forming higher surface energy functional groups. Warping might be a potential hindrance during processing with this method.
Plasma treatment differs from corona discharge and flame treatments in that it is typically carried out under partial vacuum. In plasma treatment, gas plasma is activated by the appropriate techniques to produce excited species that react with the plastic substrate.
Some plastics which are plasma, corona or flame treated include but are not limited to polyimide and polyolefins such as polypropylene as well as polyethylene.
Can you tell us about chemical treatments for prepping the surfaces of plastics substrates prior to the adhesion process?
Chemical treatments alter both the physical and chemical properties of the surface, in order to improve adhesion. A wide range of acids and alkalis are used for this purpose.
Typically, the specific chemical, or a mixture of chemicals, is placed in a chemically resistant container. The chemical bath is then heated to the appropriate temperature and the plastic substrate is immersed in the chemical bath, for the required amount of time.
After chemically treating the surfaces, it is important to rinse the surface with DI water and thoroughly dry the surface before it is subjected to further use.
Extreme care, fume hoods where applicable, and good laboratory skills should be taken while handling chemicals. It is advisable to wear the appropriate personal protective equipment and personnel should be well trained in handling these chemicals.
Fluoropolymers and acetal require that they chemically etched prior to bonding since the efficacy of abrasion and plasma treatment is not high.
About Rohit Ramnath
Rohit Ramnath is a Senior Product Engineer for Master Bond Inc., a custom formulated adhesives manufacturer. He analyzes application-oriented issues and provides product solutions for companies in the aerospace, electronics, medical, optical, and oil/chemical industries. He graduated from Carnegie Mellon University with a Master's Degree in Chemical Engineering.
Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.