Journal of Thermal Analysis and Calorimetry, Vol. 66 (2001) 343–348 CALORIMETRIC ANALYSIS OF THE POLYMERISATION PROCESS OF LINSEED OIL B. Turri, S. Vicini, S. Margutti and E. Pedemonte Department of Chemistry and Industrial Chemistry, University of Genova, Via Dodecaneso 31, 16146 Genova, Italy Abstract In this paper the polymerisation of linseed oil is studied in order to prove the catalytic action of some inorganic pigments. The results show that the calorimetric technique is able to monitor the polymeri- sation process in the temperature range between 130 and 220°C; reproducible values for isothermal analysis are obtained between 130 and 150°C; finally the results are quantitative and can be justified by kinetic equations. Keywords: catalytic action, linseed oil, pigments Introduction The painting layer of an art work is a mixture of pigments and ligands [1]. Until the middle of the 15 th century, the most common technique was tempera painting and protein ligands such as egg, casein, etc. were employed. Afterwards, under the influ- ence of Flemish painters, the use of siccative oils as binding agents was introduced and rapidly spread. The main siccative oils used in painting are linseed oil, poppy oil and nut oil. Chemically speaking, they are complex mixtures of triglycerides, i.e. esters formed by the combination of one molecule of glycerine with three of higher fatty acids. The acids are generally different from one another and each oil has a different percentage of unsaturated fatty acids. The principal fatty acids in siccative oils are: oleic acid C 18 H 34 O 2 , with one car- bon–carbon double bond; linoleic acid C 18 H 32 O 2 , with two carbon–carbon double bonds; linolenic acid, C 18 H 30 O 2 with three carbon–carbon double bonds. The latter is the main component of linseed oil. Furthermore, linseed oil contains over 80% of un- saturated fatty acids and is, therefore, classified as a ‘harden dry’ siccative oil [2]. The percentage of unsaturated fatty acids is the base of the chemistry of these materials because it is directly linked to the tendency of the double bond to polymer- ise. The polymerisation reaction of siccative oils is a three-step radical chain reaction: induction, propagation and termination [3–5]. The oxygen of the air is the initiating agent in the first step of the desiccation process. This step is often preceded by an induction period that is due to the presence 1418–2874/2001/ $ 5.00 © 2001 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht