Differences In Polyurethane Binders And The Causes Of Yellowing

Aromatic polyurethane binders are sold through the globe and is the most common binder

for the installation of rubber wetpour and safety rubber surfacing. Aromatics offer flexibility and longevity however, be aware that all aromatic binders are prone to yellowing due to the UV light intensity in the Australian climate.

Aliphatic polyurethane binders are also sold around the globe, however, this product is unaffected by UV light. Therefore, using TPV by Rosehill Polymers and the aliphatic binder will not result in yellowing of the surface. This is a fantastic product however, not widely used in the Australian market for softfall and safety rubber due to major cost implications.

Yellowing Of MDI-Based Prepolymers

All MDI-based prepolymers yellow when exposed to light, particularly UV radiation. It is a chemical reaction involving the MDI part of the prepolymer.

Assuming that the prepolymer is protected from light before use the yellowing takes place during and after the curing process but is probably faster during the actual curing process. The higher the UV levels the more marked the discolouration.

We have to stress that this doesnt always happen either. Over a period of months if this reaction has occurred then intense summer UV in the sunlight can burn off this yellow tinge.

UV stabilisers, which are expensive, can be and are, on request, added to binders. These only retard the yellowing of the softall or rubber surfacing but do not prevent it from taking place. It also has to be noted that in areas of extremely high UV they are not really all that effective either.

When MDI-binders are used with coloured EPDM granules problems can arise. The thin film of binder is yellowing over a background of coloured material. With green and red EPDMs the effect is not dramatic. In the case of blue, orange, yellow and buff EPDMs the observed colour change can be very noticeable.

For reference, aliphatic isocyanate base prepolymers are unaffected by light. However there are major cost implications associated with this type of binder and generally although, deemed to be effective, they are once again only as good as the coloured granules that they are bonding together. The yellowing may be rectified but they certainly will not mask the fading issues related to inferior quality EPDMs.

by: limi

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