Question

I am a quality engineer looking for some chemistry expertise that can hopefully assist in solving a problem we are having at our company. We are a water filtration company and our location produce the filters used for our machines which are in restaurants and stores around the world. For simplicity, the filter is comprised of an aluminum can that we extrude, wash, add a polyethelyene coating (liner), then add the filter material and a cap with an O-ring. We often get reports from the field of filters that are leaking during use. Upon return, we open the filter up and see that the polyethelyene liner is not adhering to the inside of the aluminum can and has started to tear, creating a leak path past the O-ring. Our current focus is on the cleanliness of the inside of the aluminum can. Much like anything else, the more dirt on the surface, the less likely anything will adhere to it. We are trying to improve cleanliness to increase adhesion. Another thought I had was when we heat the cans to around 500F during the polyethelyene coating process, the contraction of the can after the thermal expansion when we quench is causing the liner to detach. What I am asking from a chemist is, what can improve the adhesion of the polyethelyene to the inside of the aluminum can? Are we chasing the wrong thing with cleanliness? Is my thermal expansion theory completely off?

Answer 1

To improve adhesion of polyethylene to the inside of the aluminum can, surface cleaning, promoting surface roughness, and priming or pre-treatment can be considered. Thermal expansion and contraction could potentially affect adhesion, so minimizing these effects during the manufacturing process is important.

Step-by-step explanation:

In order to improve the adhesion of polyethylene to the inside of the aluminum can, there are a few potential approaches you can consider:

1. Surface cleaning: Ensuring that the inside of the aluminum can is properly cleaned before applying the polyethylene liner can help improve adhesion. Dirt or contaminants on the surface can interfere with the bonding process. Using appropriate cleaning agents and techniques can help remove any impurities.
2. Promoting surface roughness: Roughening the surface of the aluminum can, either through abrasive treatments or chemical etching, can create more surface area for the polyethylene to adhere to. This can enhance the bonding strength between the two materials.
3. Priming or pre-treatment: Applying a primer or pre-treatment agent to the aluminum can before coating it with polyethylene can enhance adhesion. These agents can improve the compatibility between the can and the polyethylene, promoting better bonding.

As for the thermal expansion theory, it is possible that the rapid cooling after the heating process could cause the polyethylene liner to detach. Thermal contraction can create stress and strain within the materials, which can impact adhesion.

It might be worth exploring how you can minimize the effects of thermal expansion and contraction during the manufacturing process to improve the adhesion of the polyethylene liner to the aluminum can.