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Can Polypropylene Tanks Cause EN-P Adhesion Issues?

Q. Hello,

We plate Al6082 aluminum with high-phosphorus electroless nickel in a 40L polypropylene tank and have noticed a consistent issue:

In new EN-P baths, adhesion is excellent.

After 1-2 bath cycles, adhesion becomes unreliable, even though all process parameters are kept consistent.

Here's what's puzzling:

We often test the same substrates in a small glass beaker, using the same bath chemistry and prep. Results in the beaker are consistently good — no adhesion problems.

We’re now considering whether the polypropylene container itself could be the variable. The tank is cleaned between bath changes with nitric acid, followed by ammonia and DI rinses.

My questions:

Could the polypropylene tank leach or be etched by the EN-P bath, affecting bath chemistry or contaminating the solution?

Is passivating or leaching of PP tanks before reuse standard practice in EN plating?

Why might a glass beaker give consistently better adhesion if everything else is constant?

Any insights, similar experiences, or references would be greatly appreciated.

Thanks in advance!

Isibabale Sikade
Chemical Engineer - Johannesburg, Gauteng
July 9, 2025

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