Comparative rheological characteristics of industrial polyflavonoid tannin extracts

Abstract

Commercial, industrially produced mimosa, quebracho, pine, and pecan polyflavonoid tannin extracts water solutions of different concentrations were examined by rheometry by measuring dynamic moduli both as a function of strain amplitude and at varying frequency. The water solutions of these materials have been found to behave in general mainly as viscous liquids at the concentrations that are generally used for their main industrial applications. Clear indications of viscoelastic response are also noticeable, among these the crossover of the elastic and viscous moduli curves at the lower concentrations of the range investigated, with some differences being noticeable between each tannin and the others—pine and quebracho tannin extracts showing the more marked viscoelastic behavior. Other than pH dependence (and related structural considerations), the parameters found to be of interest as regards the noticeable viscoelastic behavior of the tannin extracts were the existence in the solutions of labile microstructures that can be broken by applied shear. This is supported by the well‐known thixotropic behavior of concentrated, commercial polyflavonoid tannin extracts water solutions. Such microstructures appear to be due (1) to the known colloidal interactions of these materials already reported, or (b) to other types of secondary interactions between tannin oligomers and particularly between tannin and carbohydrate oligomers. The latter is supported by the dependence of this effect from both the average molecular masses of the tannin and of the carbohydrate oligomers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1634–1642, 2001

Influence of solvent additives on the aqueous extraction of tannins from pine bark: potential extracts for leather tanning

“…However, viscosities of the 50% solutions were 325.0 and 820.2 mPa.s for the 0.5 and 1.0% NaOH extracts, respectively, which were considerably higher than the acidic and organic ones. The alkaline solutions' high viscosities are characteristic of the presence of polymeric carbohydrates derived from degraded hemicelluloses, which heavily contribute to the extract's viscosity due to secondary force associations between tannins and carbohydrates , . The possible presence of carbohydrates in these extracts was mentioned before.…”

“…This situation may explain the great differences encountered in the quantification of tannins in the alkaline extracts: 35.1–55.3% for the hide powder assay, decreasing with the NaOH dose, and 0.896–1.20% for the vanillin assay. Polysaccharides and lignin, most probably present in these alkaline extracts as previously noted, eventually became directly linked with collagen via hydrophobic or hydrogen bonds,, or indirectly linked through the existence of secondary force associations (hydrophobic and electrostatic) with linked tannins , …”

“…Aqueous solutions of pine bark extracts and of commercial tannin‐rich products were prepared at two different concentrations, namely 20 and 50% (w/v), to cover the concentrations applied in their most common industrial applications . Mixtures were moderately stirred at room temperature using a magnetic stirrer.…”

Tannins and Tannin Agents

“…Furthermore mimosa bark (Acacia mearnsii), quebracho wood (Schinopsis balansae), pine bark (Pinus radiata), oak bark (Quercus sp. ), grape (Vitis vinifera) and wattle (Acacia mearnsii), are used for industrially produced tannin extracts and preparations (Cadahía et al, 1998, Garnier et al, 2000Vivas et al, 2003). At present the most intensive use of tannins is in the manufacture of wood adhesives and leather (Taiwo and Ogunbodede, 1995;Garnier et al, 2000;López-Suevos and Riedel, 2003;Li et al, 2004).…”

Effect of poly(ethylene glycol) on the hydrophobic interactions and rheology of proanthocyanidin biopolymers from Pinus radiata

“…Pizzi and Stephaou6 studied many of the condensation mechanisms, including those of Pinus radiata , which frequently lead to processing difficulties at the higher concentrations required for adhesive formulations. Interactions due to colloidal self‐associations7–9 and secondary interactions10 have been shown to dictate their detailed rheological response. Strong nucleophiles such as phloroglucinol, m ‐phenylene diamine, and urea have been shown to block the mechanisms of self‐condensation8, 11 and colloidal or molecular association12, 13 in solution.…”