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Wednesday, 18 September 2019
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Raw materials & technologies, Technologies, Functional coatings

Moisture-absorbing and abrasion-resistant coating on polystyrene

Wednesday, 22 July 2015

A common phenomenon concerning cold surfaces which are subjected to a warmer, more humid atmosphere is condensation in the form of water droplets (fogging) or even ice crystals (icing).

The coating overcomes the problem of fogging and icing by being able to absorb the condensing water and preventing it from crystallising. Source: artusfoto/Fotolia
The coating overcomes the problem of fogging and icing by being able to absorb the condensing water and preventing it from crystallising. Source: a...

Thus, a previously transparent object becomes opaque because light is scattered by the droplets or crystals. This may impair the usability of that object.

Overcoming the problem of fogging

Reserchers from Switzerland developed an anti-fogging/icing coating which overcomes the problem of fogging and icing by being able to absorb the condensing water and preventing it from crystallising. The coating consists of poly(1-vinyl-2-pyrrolidone) (PVP) crosslinked by UV light using hydrogen peroxide (H2O2). Benzophenone (BP) is used to attach PVP to the surface of the polystyrene (PS) substrate. At temperatures as low as -60°C, the PVP coating can absorb up to 70 wt% of water and still inhibit its crystallisation. However, at surface temperatures of around -18°C, opacity is only observable at 150 wt% of absorbed water and higher. An increasing coating thickness as well as a decreasing crosslink density improves the anti-fogging/icing effect because the coating can absorb more water. The abrasion resistance of the coating is impaired by a decreasing crosslink density.

The study is published in: Journal of Coatings Technology and Research, July 2015, Volume 12, Issue 4, pp 669-680.

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