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A unique Polyurethane potting compound for filter membranes

 

The project

A customer requested us to develop a Polyurethane compound, which could be cured in the presence of moisture without foaming. For those who are familiar with Polyurethane formulations, this is like trying to fit a square peg into a round hole.

 

The basic need

The customer required a Polyurethane potting material, which could be cured in the presence of moisture without foaming, and would remain moisture resistant after cure in service. The requirement included a 30 minute working time (gel time) and a cured hardness of 90 shore A.

 

The formulating problem

Because polyurethane casting resins will foam in the presence of moisture, the essence of the problem was; “how to make foam that does not foam?” To meet this requirement we had to develop a polyurethane system that could cure in the presence of moisture and be able to operate continuously in the presence of moisture after cure.

Our initial idea was to develop a formulation utilizing ingredients to trap and isolate moisture thereby preventing it from impeding the reaction. This was initially successful but the customer noticed that for some reason foaming began to occur over a certain period of time. It appeared that the water eventually saturated the moisture-trapping ingredients, rendering them ineffective.

Based on these results, we decided to change our formulating approach and re-formulate using ingredients that would repel instead of trapping the moisture. These ingredients discourage the moisture "outside" from entering the system while, at the same time, would also help to remove moisture already inside the formulation.

 

The solution

Working with the customer, we devised a test protocol that utilized our formulations and their end use materials to test if our latest hydrophobic formulation could withstand water during and after cure. Test results showed little to no bubbling inside the potted filter. This confirmed that our urethane could cure even in the presence of water. Subsequent test results were as expected and confirmed that the formulation has excellent water resistance after cure. In addition, this system also had a 70 min room temperature gel time and a Shore A hardness of 93 as requested by the customer.

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