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This yellow, billowing, cinder toffee-like material is polyurethane foam. Polyurethane is produced by reacting two ingredients together; an isocyanate and a polyol, in the presence of a catalyst or by activation with ultraviolet light. To make it into a foam, water is added to the mixture during the reaction, which forms carbon dioxide gas when water reacts with isocyanate. This gas forms bubbles which become trapped when the liquid ingredients solidify, creating a foam.
The different types of isocyanates and polyols used can influence the materials properties of the resulting polyurethane; polyols with long and flexible molecules produce soft, elastic polyurethane, whereas more crosslinking makes a tougher, more rigid material. Unlike thermosoftening plastics like polyethylene which can be heated and remoulded, polyurethane is a thermoset, so can’t be reshaped by heating.
Polyurethane foams can be either ‘closed-cell’, where the bubbles remain separate from each other in the polyurethane matrix, or ‘open-cell’, where the bubbles are interconnected. Open-cell forms tend to be used for seat cushions, mattresses, and soundproofing whereas closed cell foams tend to be used in shock absorption and thermal insulation applications. Closed cell foams with very tiny bubbles (less than 50 microns in size) are called microcellular foams, and are used in the soles of shoes for cushioning. Some polyurethanes will discolour from white to yellow on exposure to ultraviolet light.
The mushroom-shaped sample in a cup (1364) was made for the 2015 Octagon Gallery exhibition Dangerous Diaries, which explored the risks and rewards of hands-on experiences with materials. Polyurethane has been favoured by a number of key 20th Century artists such as John Chamberlain and César Baldaccini because of its unpredictable, almost life-like qualities during the foaming process. Once reacted, polyurethane is chemically inert, but during reaction the presence of a range of volatile chemicals pose a risk to human health. In particular exposure to amines during the production of polyurethane has been attributed to lesions in the eyes and throat.
The omelet-like flat sample (1028) and the polyurethane foam chair (1020 - no longer in the collection) were made as part of our 2013 Foam Public Open Day.
Sample ID: 52, 1020, 1028 & 1364
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