Since it was first synthesised in 1864 by C.A. Wurtz, Polyurethane (PUR) has been widely used for industrial purposes thanks to its great versatility. For this same reason, PUR has also become a popular material for designers and artists in the creation of artworks and every-day objects. However, as a synthetic material that deteriorates more quickly than traditional art materials, PUR has also become the subject of many in-depth scientific studies, and a particular focus in the research of Thea van Oosten and coworkers.
In this research project we focused on several case studies from the Triennale Design Museum in Milan – all of which belong to the Multipli series by the Italian brand Gufram® – including three examples of a sofa called the Pratone (which reproduces a patch of grass on a giant scale), three “stone” shaped seats entitled Sedilsasso e sassi, a coat rack in the shape of a red Cactus and the Capitello recliner. All of these design objects were produced at different times during a period which stretches from the middle of the 1970’s up until today’s “polyurethane foam and washable latex” (as reported in the catalogue), and are already showing the results of different degradation processes.
In addition to identifying the differing material composition and degradation phenomena which affect these artefacts, so as to develop preventive conservation plans for their future maintenance, our research sought to identify whether there were differences in the materials and manufacturing techniques used to produce the same series over the years and if these differences can be correlated to their state of conservation.
To obtain information relative to the compositional materials involved (PUR foams, painted layers, varnishes and protective layers) and the relative degradation processes, micro-samples taken from the objects were analysed using different analytical techniques (vis-UV optical microscopy, XRF, SEM-EDS, FTIR-ATR, Py-GC-MS and TG-DSC).
The results indicated that the objects’ PUR inners have different compositions at different production times: the first examples were analysed as TDI (toluene diisocyanate) urethane ethers with polypropylene glycol as the flexible part, while latter objects are composed of TDI- polypropylene glycol urethane ether with the addition of styrene acrylonitrile (SAN). Several additives -being introduced to the polymeric compositions- were identified, such as: butylated hydroxytoluene (BHT) and dioctyldiphenylamine as antioxidants; tris(3-chloropropyl) phosphate, dibutylphthalate (DBP) and dioctylphthalate (DOP) used as plasticizers. In all cases, the painted layers appeared to be a polyisoprene-based latex containing both inorganic and organic pigments, fillers (silica) and extenders (calcium carbonate, gypsum); benzimidazole and benzothiazole- used in the vulcanization process of the isoprene, were detected as well. For the protective layers we found the use of varnishes based on polymetacrilate in the early objects and on polyetheretherketon for the more recent ones.
With the help of the owners of Gufram®, we were able to analyse and compare our results in order to align the object’s historical evolution, the reasons behind variations in the production processes and of course, changes in the material composition of the PUR used in these objects, with the aim of acquiring a 360° working knowledge and evaluate the contingent factors which can affect PUR during the ageing process.