Characterization of maintenance industrial alkyd resins prepared with Plukenetia volubilis L. oil.

Abstract

In this doctoral thesis, alkyd resins synthesized with high unsaturation renewable plant sources and polyols with different functionalities were characterized. Alkyds are synthetic resins modified with vegetable oils, whose level of unsaturation provides the resin the ability to cure in air without using a catalyst. Oil sources with high content of fatty acids and elevated concentration of double bonds are preferred in the surface coating field as they increase the crosslinking density of alkyd resins, forming a continuous film that acts as a barrier against corrosive species. In the present work, Sacha inchi oil, a Peruvian low cost agricultural feedstock, was used due to its high content of unsaturated fatty acids and its similarity to linseed oil’s composition, a drying oil widely used in the coating industry. This commercial oil was used also for comparative purposes. Glycerol and pentaerythritol, polyols with dissimilar levels of crosslinking, were used for resin manufacturing. The use of a multifunctional polyol such as pentaerythritol sought to increase branching and promote the obtainment of high solid alkyds with better film properties and weathering resistance. This study focuses on comparing the effect of the polyol and oil/fatty acid type on alkyd’s physical properties such as colour, density, viscosity, and thermal stability, and film coating’s performance (drying, hardness, chemical resistance). FT-IR, One- (1D) and two-dimensional (2D) 1H- and 13C-NMR spectroscopy were performed for alkyd structural verification. Curing process was also evaluated by a standard proceeding and Raman spectroscopy. The oxidative crosslinking time tendency was corroborated by the quartz crystal microbalance (QCM) technique. This technique has been recently applied for resin characterization and proves to be a useful tool for monitoring more precisely curing stages. Gel permeation chromatography was also carried out to characterize the molecular weight distribution and dispersity of alkyds. The protective capacity of oil-based resin films on aluminium substrates was studied by Electrochemical Impedance Spectroscopy. Moreover, the anticorrosive behaviour of primers prepared with the most representative synthesized oil-based resins was verified by accelerated corrosion tests. In general, the performance of the Sacha inchi-based alkyd resins was found to be comparable to an alkyd resin prepared with linseed oil. Accelerated weathering tests showed that the mixture of pentaerythritol and Sacha inchi oil improves properties of alkyd resins and enhances the anticorrosive performance of alkyd primers. From this study, it can be concluded that Sacha inchi oil and fatty acids extracted from it have the necessary characteristics to be used as raw materials for the production of alkyd resins. The exploitation of a Peruvian non-traditional vegetable oil as a raw material in a new sector of the economy could generate direct or indirect income in the production chain collaborating with the development of the Amazon region and improving the competitiveness of the Peruvian market worldwide.