how to measure if HDPE flakes are clean? 1

[Kakashi-01]

I am working on cleaning a small batch of HDPE flakes obtained from motor oil containers. My goal is to remove contaminants such as residual oil, and adhesives to evaluate the cleaning efficiency of the cleaning solution.The flakes I received from the processor were supposed to be pre-washed, but upon inspection, they still appear contaminated.

Since HDPE has very low surface energy, a surfactant that gives a very low surface tension and has a high wettability for HDPE is required. Based on this, I am reaching out to a supplier to find a suitable non-ionic surfactant for my application.

How to clean the flakes and how to measure whether they are clean given my limited equipment?

Since I do not have access to fancy lab equipment, only basic tools like containers, stirring rods, and heating sources and reagents which I will still purchase.My intial plan was to submerge the flakes in the cleaning solution to ensure contact and measure their weight before and after the experiment.However the weight difference might be too small to detect unless the flakes are heavily contaminated. Could I instead evaluate the cleaning efficiency based on the change in flakes color, stickiness (by touch) by counting the number of "cleaned flakes"without residual stickiness or visible contamination and compare this to the original number of flakes, and report the ratio as a measure of cleaning efficiency.

 

[pointsman]

Droplet contact angle measurement can be done without specialized lab equipment. Clean vs oily HDPE will have different contact angles. This method could be worth a try if your flakes are large enough to support a droplet of water.

 

[btrueblood]

I like pointsman's droplet contact idea, but it might be tough to replicate depending on the surface finish of the flakes.

Another possible test would be to take a cleaned, dry chip/flake, and dip/immerse it into a puddle of distilled water on a petri dish, and examine the surface of the water for oil sheen.

 

[Kakashi-01]

Droplet contact angle measurement can be done without specialized lab equipment. Clean vs oily HDPE will have different contact angles. This method could be worth a try if your flakes are large enough to support a droplet of water.

Thanks @pointsman I will give it a try. I have attached a picture of the flakes, they are large enough to support a droplet of water, but their surfaces vary. I was thinking of using a hammer to flatten them slightly before applying the water droplet and capturing the contact angle with my smartphone.

I like pointsman's droplet contact idea, but it might be tough to replicate depending on the surface finish of the flakes.

Another possible test would be to take a cleaned, dry chip/flake, and dip/immerse it into a puddle of distilled water on a petri dish, and examine the surface of the water for oil sheen.

@btrueblood Thanks. I didn’t observe any oil forming with the caustic wash but when I used ethyl acetate with water as my cleaning solution I noticed a floating oil layer indicating that some oil had been extracted. However oil isn’t just on the surface, some has likely migrated into the plastic itself. That means there might still be residual oil that hasn’t been removed. While I can qualitatively see that oil has been removed I have no way to quantitatively measure how effective my cleaning solution was since I don’t know how much oil was originally in the plastic before washing.

 

[IRstuff]

Doesn't sound particularly high density if oils can get inside.

As for removal, assuming you can 100% remove the solvent and there's a measureable amount of oil, there ought to be a weight change. Alternately, one could imagine heating the HDPE and doing a mass spectrometry on the outgassing, assuming there is any.