Abstract
One of the major challenges currently in the field of material science is finding natural alternatives to the high-performing plastics developed in the last century. Consumers trust synthetic products for their excellent properties, but they are becoming aware of their impact on the planet. One of the most attractive precursors for natural polymers is tannin extracts and in particular condensed tannins. Quebracho (Schinopsis balansae) extract is one of the few industrially available flavonoids and can be exploited as a building block for thermoset resins due to its phenol-like reactivity. The aim of this study was to systematically investigate different hardeners and evaluate the water resistance, thermal behavior, and chemical structure of the quebracho tannin-based polymers in order to understand their suitability as adhesives. It was observed that around 80% of the extract is resistant to leaching when 5% of formaldehyde or hexamine or 10% of glyoxal or furfural are added. Additionally, furfuryl alcohol guarantees high leaching resistance, but only at higher proportions (20%). The quebracho-based formulations showed specific thermal behavior during hardening and higher degradation resistance than the extract. Finally, these polymers undergo similar chemistry to those of mimosa, with exclusive reactivity of the A-ring of the flavonoid.
Highlights
IntroductionIn a context of growing interest in sustainable products and a circular economy, the need for high-performing bio-based solutions is rising exponentially [1,2]
The aim of this study was to systematically investigate different hardeners and evaluate the water resistance, thermal behavior, and chemical structure of the quebracho tannin-based polymers in order to understand their suitability as adhesives
Bioplastics are an attractive alternative, because they have the potential to combine the high performance we are used to having with a lower environmental impact compared to oil-based synthetic resins [3,4]
Summary
In a context of growing interest in sustainable products and a circular economy, the need for high-performing bio-based solutions is rising exponentially [1,2]. Among the main natural resources of particular interest as building blocks for thermosetting resins, condensed tannins are one of the most attractive alternatives due to their availability and their phenol-like chemistry [5,6] These polyphenols are industrially extracted from mimosa (Acacia mearnsii) and quebracho (Schinopsis balansae) for several applications, especially in the leather tannery row [7,8], in oenology [9,10], as antitumor and anti-oncogenic activities in pharmaceutical and medical applications [11,12], for thermal valorization [13,14], and water remediation [15,16]. In the study of Pizzi et al, as well as in that of Yurtsever and Sengil, stable polymers were formed by the reaction between quebracho and formaldehyde [17,18] This flavonoid substrate was used for the preparation of wood preservatives and adhesives for bio-based composites in combination with hexamine [19–21]. Despite the number of studies performed, a systematic assessment of the polymerization parameters has not yet been presented [28]
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