engleski

The influence of adhesion parameters on material and organic recycling of thermochromic prints

Within this dissertation, material and organic recycling of thermochromic prints was examined. Adhesion parameters between thermochromic printing inks and printing substrates were examined as well, and their impact on studied methods of disposal was elaborated on. The obtained results indicate that thermochromic offset prints are poorly deinkable due to very high adhesion of inks to paper. Since thermochromic printing inks contain some toxic substances, their presence in the recycled pulps was also considered. Results showed that BPA was present in recycled pulps and it was above maximum permitted limits. The concentration of heavy metals cations Zn and Fe in all samples originate from printing substrate, while Mn and Co originate from drying catalysts present in inks. The growth of Bacillus subtilis and Aspergillus niger was not inhibited in all tested samples indicating that there was no release of toxic substances, despite the presence of BPA and heavy metals. Thermochromic inks also affect the process waters increasing the COD and TOC values. Obtained results of UV curable and offset thermochromic prints biodegradation showed that biodegradation depends upon the adhesion, i.e. lower adhesion will result in reduction of biodegradation rate, while the strong adhesion will result in better prints and papers degradation. Reactions between paper and thermochromic ink will form different prints properties due to different affinity of paper for ink while interactions between them will affect the prints and papers biodegradation. Results indicated that better absorption of binder into the absorbent paper structure results in thinner layer of ink binder on the paper surface. In the case of absorbent paper, the higher rate of biodegradation was detected, resulting in a higher number of bacteria, higher weight loss, higher changes in colour (destruction and deformation of microcapsules) and reduction in thermochromic effect of the prints. The thickest layer of ink binder and classic pigment on non-absorbent paper surface causes the slowest rate of biodegradation of print. Results show that microcapsules are promoting the rate of paper biodegradation. Results also indicated that ink vehicle used in thermochromic offset ink is more stable than the polymer resin present in UV curable screen printing thermochromic ink. Thus, organic recycling can be better option for thermochromic prints waste management.

Thermochromic inks, deinking flotation, biodegradation, FTIR, SEM, colorimetric properties

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