Synthesis and characterization of fully biobased aromatic polyols – oxybutylation of condensed tannins towards new macromolecular architectures

Abstract

For the first time, different tannins were oxybutylated to obtain aromatic and fully biobased polyols. The main interest in using 1,2-butylene oxide (BO) instead of e.g., propylene oxide is because BO can be easily biobased and biosynthesized from biomass. BO can be obtained by epoxidation of butane, produced from biobased butanol, synthesized by biotechnological means. The oxybutylation was carried out using potassium hydroxide as a catalyst, in a high-pressure batch reactor, without solvent, in agreement with the main principles of green chemistry. Firstly, different biobased aromatic polyols were synthesized from gambier tannin (Uncaria gambir) and fully characterized. To better understand the conditions and mechanisms of the synthesis, the influence of the tannin/BO ratio was assessed through the evolution of the hydroxyl content, homopolymer content, molar mass distributions and the corresponding viscosities. In addition, the thermal properties were evaluated to better understand the final molecular architectures. Secondly, selected conditions of synthesis were applied to other types of tannins from pine (Pinus pinaster), mimosa (Acacia mearnsii) and quebracho (Schinopsis balansae and Schinopsis lorentzii). The corresponding results were compared to extend this study. For all tannins, the number and length of the grafted chains were carefully characterized. Great variations in reactivity have been found between the different botanical sources. Tailor-made, fully biobased and controlled aromatic macropolyols can be obtained by modulating the main parameters of the oxybutylation reaction and the type of botanical tannin source.

Solvent‐ and Halogen‐Free Modification of Biobased Polyphenols to Introduce Vinyl Groups: Versatile Aromatic Building Blocks for Polymer Synthesis

“…The worldwide annual production of lignins and tannins is around1 00 kt (Kraft, soda, ando rganosolv processes) [1] and 200 kt, [2] respectively.H owever,l arge increasesa re possible especially for lignin, because only approximately 2% of the lignins fractionated from biomass in paper pulp mills are actuallyi solated. [4][5][6][7] Lignins and tannins can be used as aliphatic poly-ols after,f or example, oxyalkylation, [8][9][10][11][12] fori nstance in polyurethanes. [4][5][6][7] Lignins and tannins can be used as aliphatic poly-ols after,f or example, oxyalkylation, [8][9][10][11][12] fori nstance in polyurethanes.…”

Synthesis and characterization of bio-polyols through the oxypropylation of bark and alkaline extracts of bark

“…The reported procedures for alkoxylation are quite varied, such as room temperature reactions in solvent (García et al, 2013), pressure controlled reactions through gradual addition of PO monomer into the reactor (Yoshioka et al, 2013), and higher pressure/higher exothermic reaction conditions that utilized PO as a solvent. Alkoxylation has already been performed on a variety of biomass resources such as chitin/chitosan, (Fernandes et al, 2008) cork (Evtiouguina et al, 2001), date seeds (Briones et al, 2011), lignin (Cateto et al, 2010;Nadji et al, 2005;Wu and Glasser, 1984), inulin, (Rogge et al, 2005) starch, (Yoshioka et al, 2013) sugar beet (Pavier and Gandini, 2000a,b), tannin (Arbenz and Avérous, 2014;García et al, 2013) and terpenes (De Meireles et al, 2014). Although lignin and tannins are both components in bark, bark has a wide variety of other extractive compounds and therefore its alkoxylation behavior could vary significantly from what has been reported previously by the literature.…”

“…Furthermore, the previous work done on tannins was performed at room temperature, (García et al, 2013) as opposed to 180 • C in this work. The work done by Arbenz and Avérous (2014) contrasted the oxybutylation behavior of different tannins and showed that a 100% bio-based polyol could be synthesized by using biosourced butylene oxide, instead of propylene oxide.…”

“…Compared to the viscosity of other oxypropylated biomass, oxypropylated bark was within the lower range of the viscosity values. For example the work done on chitosan produced polyols with an extremely high viscosity of 50,000,000 cP, (Fernandes et al, 2008) cork: 3000-13,000 cP, (Evtiouguina et al, 2002), lignin: 2300-2800,000 cP (Nadji et al, 2005), and tannin: 1000-250,000 cP (Arbenz and Avérous, 2014). This range in values.…”

“…Finally, few papers have performed GPC analysis on their polyols for comparison however, a study done on oxypropylated lignin shows M w and M n values are within a similar range, and that by changing the biomass/PO ratio and catalyst amount these values can be tuned (Cateto et al, 2010). This is supported by the GPC analysis of oxybutylated gambier tannins where the tannin/butylene oxide ratio varied the molecular weight from 3000 to 7000 g/mol and the homopolymer from 200 to 900 g/mol (Arbenz and Avérous, 2014). These literature results stress the fact that reaction conditions can be varied to tailor-make polyols and provide an opportunity for future optimization and customization.…”