What is polyurethane?
Otto Bayer discovered polyurethane in 1937 by chance. It was only ten years later that polyurethane was manufactured into customized materials. Polyurethane (PUR) is formed by the reaction of a diol (alcohol with two reactive hydroxyl groups) or a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polyfunctional isocyanate (with more than two reactive sides) in the presence of suitable catalysts and additives. Polyurethane is well known as one of the most difficult polymers to conserve as the hydrogen bonding makes it very unstable and sensitive to natural aging processes, as well as its soft domain (composed by the polyol component) which is more prone to the interaction of deterioration agents. However, this material has been very popular in the fashion industry since the 1960s – 1970s, because of its customizability and broad functional, and aesthetic characteristics. Polyurethanes are very diverse, versatile, and have different applications. They can be rigid, soft, foam, elastic, matte, or glossy. They are known as the first polymeric materials that have rubber elasticity and thermoplastic properties, which is, of course, very much appreciated in a fashion industry looking to offer choice to customers. Thermoplastic polyurethane (TPU) coatings can be custom-made with desired properties, for example, they can make clothing waterproof yet breathable, abrasion and stain resistant, as well as washable. PUR is a group of plastics with different compositions and a very large variety of applications. Because of all these possibilities, it is very difficult to conserve objects with PUR, which makes conducting research for a standard conservation solution very challenging.
In museums they occur in different forms:
- Cellular materials including flexible and rigid foams;
- Films;
- Surface coatings and adhesives;
- Elastomers: fibers, soft and hard rubbers.
The most commonly used techniques for producing coated fabrics for fashion are calendaring, solution applications, and reactive coatings. These different types of applications make the material even more complex, because of the unlimited possibilities in composition, shine, thickness, type of substrate, … The unlimited chemical and physical diversity of the material makes understanding polyurethane’s morphology crucial for understanding its properties and long term behavior. For preventive conservation, this is very important, as without proper knowledge of a material’s composition, it is impossible to work out guidelines for preventive conservation.
An example of a commercial trade name is Corfam, developed by DuPont as an example of a popular polyurethane-based leather. It was a three-ply laminate synthetic leather composed of a polyurethane reinforced with a polyester fiber base and a top coat of urethane copolymer . According to an article written by Debra Hughes at the Hagley Museum(1.https://www.hagley.org/librarynews/museum-collectionthe-short-life-dupont%E2%80%99s-corfam), Corfam is an excellent example of a synthetic product that did not live up to its expectations over time for DuPont. Corfam was created in the late 1950s. It was a material created to look like leather with a high shiny gloss surface which resembled patent leather. Corfam was mainly used for the production of dress shoes as well as other kinds of articles such as purses. From 1964 to 1969, 7.5 million pairs of Corfam shoes were sold, but after that the market declined for several reasons including the popularity of vinyl shoes. The fact that Corfam did not breathe and did not stretch, resulted in numerous consumer complaints, so in 1971 the production stopped.
Fashion designers of the 1960s and 1970s known to work in modern materials include André Courrèges, Paco Rabanne, Emilio Pucci and Pierre Cardin. André Courrèges in particular made use of polyurethane artificial leathers. The use of coatings to provide a glossy finish was also common in the 1970s, as has been confirmed by Susana França de Sá (PHD:What does the future hold for polyurethane fashion and design? Conservation studies regarding the 1960s and 1970s objects from the MUDE collection). When leather goods required glossy finishes, polyurethane was also an option.
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