Renewable Photopolymer Films Derived from Low-Grade Lampante and Pomace Olive Oils

Abstract

Thiol-ene photoinduced copolymerization between a polythiol cross-linker and low-grade unsaturated olive oil provides an eco-efficient route to dry, flexible and rubbery films in the matter of minutes. The synthetic methodology uses low cost olive oils resulting from non-edible grades (lampante olive oil) and waste production (pomace olive oil) without prior chemical modification. The resultant photopolymer thioether cross-linked films contain up to 80-85% of renewable resources, and UV-driven drying proceeds despite the limited unsaturations' concentration. Photopolymerization is triggered with a conventional medium-pressure mercury lamp in presence of three different thiol cross-linkers: 2,2′-(ethylenedioxy)diethanethiol, hexanedithiol or trimethylolpropanetris(3-mercaptopropionate) and a radical photoinitiator (2-hydroxy 2-methylpropiophenone). Using real-time Fourier transform infrared spectroscopy (RT-FTIR), we show that cross-linking proceeds essentially via a step-growth thiol-ene polymerization, and to a minor extent, by a conventional photo-oxidation mechanism.

Practical applications: Olive oil is the second largest produced vegetable oil, and in 2016 world production amounted to 3.5 million tons. An excess of low-grade pomace and lampante olive oils is generated annually from the conventional extraction process; however, declared unfit for human consumption, they have a limited number of uses, and it is difficult to find new outlets. Despite this excess, the development of synthetic and processing methods to convert these non-edible olive oils in useful materials has not been investigated widely. Here we report a method based on thiol-ene photopolymerization to prepare a new range of UV-curable films. Using time-resolved infrared spectroscopy, this study sheds light into reaction kinetics and polymerization mechanism.

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