|Titel:||Green developers for heat-sensitive layers of thermal paper||Sprache:||Englisch||Autor*in:||Fagbemigun, Taiwo Kayode||Schlagwörter:||Green Developers; Thermal Paper; tannin; lignin; Bio-based; Heat-sensitive||Erscheinungsdatum:||2021-07-08||Tag der mündlichen Prüfung:||2021-06-08||Zusammenfassung:||
Bisphenol A (BPA) in the manufacturing of several consumer products has implications on human health and the environment. In particular, the exposure to BPA used as a developer in thermal paper is a known cause of endocrine disruption in humans and non-humans. For this reason, local, national,and global regulations have been put in place toreduceor eliminate BPA in thermal paper. However, several known and commercially available alternatives to BPA havesimilarhealth and environmental-threatening effect occasioned by their structural similarity to BPA.
This work aimed to assess the potential of bio-based substances to function as an alternative developer in the heat-sensitive layer of thermal paper. These substances are called 'green developers.'The interactions between fluoran dye, ODB-2, and green developers selected from the class of organic carboxylic acids, tannin, and lignin-derived monomers in colour-developing compositions were evaluated in this study. Spectroscopic techniques such as UV-Vis, NMR, and FTIR were employed to monitor these interactions. The thermal and colourimetric behaviour of these compounds in a ternary mixture containing solvent was also studied. Furthermore, phenol resins and phenol-amine complex of high thermal stability were synthesised using methanol extracts of vegetabletannin and pure tannin model compounds. Finally, the performance of these green developers in thermalpaperwas evaluated as a function of their print density.
The NMR, FTIR,and UV spectroscopy investigation confirmed the lactone ring-opening interaction between fluoran dye and green developers. Most of the studied compounds produced black colour on interacting with fluoran dye under the influence of heat. These compounds also showed potential for utilisation in thermochromic systems like thermal paper.
Of the organic carboxylic acids studied, ascorbic acid, ascorbyl palmitate,and citric acid produced clear colour-forming dispersion and optical print density of 1.1, 0.79, and 0.25,respectively,in thermal paper. The print from the ascorbic acid-coated thermal paper was,however,unstable. Within sevendays of printing, 90% of the density was lost. In addition, exposure to oil, water,and solvent led to an 80% reduction in colour density. Also, the unprinted citric acid-coated paper appeared greenish-grey with a whiteness value of 79% -about 11% less than the target value viii(≥90%). This relatively low whiteness caused a poor contrast between the printed and unprinted paper. On the other hand, ascorbyl palmitate-coated paper produced a fine, solid, legible,and more stableprint.The thermal paper produced with vanillin gave a characteristic sweet smell on printing, suggesting a partial sublimation of the phenol compound on heating. However, under a higher humid condition of 90%RH, the printout faded and was unrecognizable. Also, the printed image with vanillin displayed an irregularand heterogeneous pattern different from thesmooth surface of a BPA-coated paper. Other vanillin derivatives such as vanillic acid,isovanillic acid,and isovanillin showed a weak interaction in colour forming composition and could not be usedin thermal paper.
The optical densities of print obtained with thermal paper coated with commercially available tannin compounds such Tanal 02, Tanex 20, Tanal 40,and tannin were 0.66, 0.07, 0.55,and 0.64 respectively. Methanol extract of mimosa tanningave a low print densityof 0.40,while other extracts from mimosa-sulphite and grape seedshowed a weak thermal reaction on printing. Application of external heat through flame markedly improvedthe optical print density ofpapers coated withthe tannin compounds. However, this showed that the applied temperature mightnot be sufficient to achieve an optimum print density with the tannin compounds. A higher applied printing temperature, unsuitable for energy-efficient technical applications, would be required to achieve a deeper colouration and higher print density. The amine complex produced from resorcinol and Hexamethylenediamine (HMDA)meltedlike BPA.
The thermal paper made from this coat gave an optical print density of 0.50. Thus, the resorcinol-amine complex might help ease premature colour formation associated with phenol-based thermal paper. Other phenol-amine complexes did not produce colour, possibly due to high thermal stability, requiring printing temperature greater than achievable with the thermal printer.Some phenol-glyoxal polymers showed promising potential as a developer in a thermal paper. For example, the thermal paper produced from the polymer of grape seed extract gave a print density of 0.24.
ix Alternatively, the use of a mixture of developers in thermal paper was considered and simulated. The colour density of mixtures containing vanillin and vanillic acidvaried from 1.2 to 1.9. The highest colour density was obtained when vanillin and vanillic acid were combined in mole ratio 3:1. The black colour showed average moisture resistance of 80% after 24 hours in 50% relative humidity. The values of colour densityalso revealed that higher colour density and potentially higher stability could be achievedwhen organic carboxylic acids, lignin monomers,or tannin model monomers were mixed with phenol-glyoxal polymers in varying ratios.This study showed that several bio-based compounds offer a route to a safer and environmentally friendly alternative to BPA as a developer in thermal paper. Thesesubstances can be used either in pure form, modified form, orbuilding blocks for higher valued chemicals. The use of various commercially available tannins and phenol polymers as a developer in thermal paper comes with many advantages. Tannin is a high molecular weight polymer with little or no known toxicity. In addition, high molecular weight compounds such as tannin and phenol polymers are associated with low dermal migration potential. Thus, they may help overcome the skin-penetration and bioaccumulation problem associated withBPA, Bisphenol S (BPS), and similar compounds. The use of phenolic polymers in thermal paper is recommended because these polymers are easy to synthesise with commercially available compounds. Their high thermal stability could be an advantage. In addition, it ensures that prints are only produced at end-use temperature. However, more work is still needed to improve the properties of these polymers to ensuretheir suitability as a developer in thermal paper. The synthesis of more bio-based high molecular weight and high thermally stablephenol resins from bio-based phenols and simple aldehydes, which could function as a developer in thermal paper,is worth further investigation.
|Enthalten in den Sammlungen:||Elektronische Dissertationen und Habilitationen|
geprüft am 01.08.2021
geprüft am 01.08.2021