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Developing a Non-toxic, Soft Polyurethane Compound


Developing a non-toxic, soft Polyurethane compound suitable for applications involving long term skin contact.


The Project

Develop a Polyurethane compound with a maximum shore hardness of 5A, suitable for long term skin contact to replace a currently used silicone formulation.


The Basic Requirement

Since the final application involves lengthy and immediate skin contact, the formulation must pass cytotoxicity testing. This means the cured polyurethane product cannot impede human cell growth or cause cell death, it must be non-toxic.


The Formulating Problem

Normally, when formulating any product, initial development draws on precedence. For example, formulating food grade products would require food grade raw materials that suppliers list in product catalogues. However, no catalogue exists for cytotoxicity related raw materials.


The Solution

Working with the customer we developed a testing strategy where they would provide testing for candidate urethane formulations. Initial attempts focused on developing a < 5 shore A urethane containing raw materials not likely to leach out of the final compound over time. In theory, removing these materials removes toxicity since they will not interact with any cells. Unfortunately several versions of these urethanes did not pass cytotoxicity testing.


With all the leeching materials removed, theoretically the likely causes of toxicity would have to be the formulation itself or the casting method. The compound itself could possibility cause toxicity from incomplete cure. In response to this, modified formulations incorporated only food grade raw materials with optimized cure schedules to ensure complete reaction. Additionally, casting of all subsequent samples used a low surface energy mould without the application of mould release. These two changes in material selection and casting technique proved pivotal in the success of the final material. The compound passed cytotoxicity testing receiving the highest rating of non-toxic.


The final non-toxic Polyurethane compound cures to a 20-25 shore 00 hardness with excellent flexibility and, we believe, is the only silicone replacement suitable for extended skin contact applications on the market. This unique polyurethane compound exhibits excellent processing and cured properties for the intended and similar application requirements.


This is another example of a success resulting from working together with our customer to solve unique application problems.

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