SPECTROSCOPIC EVALUATION OF THERMOCHROMIC PRINTED CARDBOARD BIODEGRADATION

Abstract

Municipal solid waste, containing mostly organic fraction, paper and board, wood and textiles, continues to be a major environmental problem. In addition, paper and cardboard are the most important sources of packaging materials. Packaging waste comprising about one-third of all municipal solid waste, mainly plastic and paper based. Anaerobic degradation is one of the most environmentally friendly methods for solid organic waste treatment and widely applied for bio-energy production. In this study, the biodegradation potential of three different cardboard materials (Umca Color UC, Propack PP, Lux Pack LP) and UV curable screen printing thermochromic ink applied on them (UV), were studied using the soil burial test under anaerobic conditions. Unprinted and printed cardboard samples were evaluated for changes over 4 months by FT-IR spectroscopy. FTIR spectra revealed the existence of CaCO3 and kaolin in cardboard coating. No significant changes occurred in the FTIR spectra of unprinted cardboard samples during biodegradation. In addition, FTIR spectra showed the presence of polyurethane acrylate in the UV thermochromic printing ink since all typical vibrational bands of polyurethane acrylate (3385 cm−1 (NH stretching), 2955–2855 cm−1 (symmetric and asymmetric CH2 stretching), 1726 cm−1 (C=O stretching), 1365 cm−1 (C–N stretching ) and 1111 cm−1 (C–O–C stretching ), 810, 987 and 1408 cm−1 (CH2=CH–), 1636 cm−1, (C=C stretching), 1064, 1195 and 1296 cm−1 (C–O stretching)) were obtained. After biodegradation of all three prints a decrease of band intensities located in the 2955–2855 cm−1 range (symmetric and asymmetric CH2 stretching), carbonyl peak around 1726 cm−1, ester linkages at 1260 – 1200 cm-1 and 1100-1000 cm–1 range (C-O stretching vibration) were observed. The changes in those bands may indicate the breaking down of the ester linkages, which lead to changes in polymeric structure of polymerized thermochromic ink. The highest changes in the whole spectral range were observed for the printed PP and LP cardboard, mainly in the 2955–2855 cm−1 spectral range and carbonyl peak around 1720 cm−1. In addition, the changes to the dynamic colour properties of the samples were described. The highest changes in colour after biodegradation were observed for PP-UV sample, followed by UC-UV sample. This can be explained by the best absorption of ink into the cardboard structure. The studied spectroscopic methods individually are not effective methods for the evaluation of thermochromic prints changes during degradation studies, but in a combination, they can give a brief insight into the state of material.