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So what’s the real problem with Zinc?

Lately you may have heard about some new non-zinc or non-metal floor finishes. These were supposedly developed to eliminate the adverse effect that zinc has on the environment. This is true, but as Paul Harvey says… now the rest of the story.
Zinc cross-linking was originally developed to make floor finishes easily stripable while at the same time have good detergent resistance. Before this, non zinc cross-linking floor finishes had either good detergent resistance and poor removal characteristics, or they had poor detergent resistance and good removal characteristics. The addition of zinc to floor finish polymers provided the cross-linking density necessary for good abrasion and detergent resistance while allowing the finish to be removed by "uncross-linking" with ammonia. Ammonia forms a stable complex with zinc, pulling the zinc out of the polymer allowing the polymer to dissolve in the stripping solution. In simple terms, by removing the zinc the finish is allowed to "float" again.
Since zinc cross-linking allows for such a major improvement in floor finish performance, there must be some major environmental problem that zinc is responsible for in order to cause major floor finish polymers manufacturers to develop non-zinc polymers. New polymer development is very costly and time consuming, especially when it involves completely new polymer chemistry and testing.
The real problem with zinc going down the drain is its effect on certain bacteria in waste treatment plants. Too much zinc kills these bacteria which are necessary for the bio-degradation of the waste. But the actual amount going down the drain due to stripping old floor finishes is so small that everyone in a large town would have to strip their floor at the same time to cause a measurable effect on waste treatment plants will all the thousands of gallons of waste being treated.
There are however, some source of zinc that are large enough to cause problems. Among these large zinc emitters are the chemical plants where the zinc cross-linked polymers are manufactured. These plants must spend many thousands of dollars to have their effluent treated to remove their zinc waste. In fact, it’s getting so expensive to get rid of the zinc that several of these manufacturers have developed non-zinc polymers.
Betco Corporation’s evaluation of these non-zinc polymers currently available shows that these new polymers are not nearly as good as zinc-crossed linked polymers. All of the non-zinc finishes were found to be deficient in either detergent resistance, re-wetting, removability, abrasion resistance, gloss, or a combination of the above.
Through zinc from finishes is not a major problem compared to other pollutants, misinformation, media hype and the public perception that heavy metals are bad will drive the creation of non-zinc finishes. At this time Betco does not feel that the environmental pluses of non-zinc finishes justify the performance negatives.
Betco will continue to evaluate non-zinc polymers. Betco will not sell a non-zinc floor finish that does not meet their rigid quality and performance standards.

Written by Tom Wright, Technical Director of Betco Corporation, text copyrighted by Betco 1991, Web layout copyright 2010 by Michco Inc.

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