Biodegradation of thermochromic offset prints

In this study, biodegradability aspect of thermochromic leuco dye print on two different paper materials were studied using the soil burial test under anaerobic conditions. Printed paper samples were evaluated for changes by visual examination, weight loss measurements, FTIR spectroscopy, SEM, microscopic images, and colorimetric measurements. SEM micrographs indicated that microcapsules on non- absorbent synthetic paper are covered with thicker layer of ink binder, which was also confirmed by the IR spectra. Therefore, the microcapsules on SEM micrograph aren’t visible. SEM analysis shows significant penetration of the binder in the structure of absorbent recycled paper, making the microcapsules more visible even though they are covered with a thinner layer of a binder. Colour degradation of the print on the recycled paper is significant – the colour changes from green to yellow – green. The SEM micrograph shows certain deformation of the microcapsules for the print on recycled paper. Lower degradation was noticed for the print on synthetic paper for which the obtained SEM micrograph indicates destruction of the binder and possible interactions of bacteria with microcapsule at a place of resulting cracks. FTIR spectra show that vegetable oil in ink vehicle was oxidized on all prints during biodegradation test.