Abstract
The detailed study presented herein of gelatins modified with tannins as greener binder systems for stone wool and related materials has unveiled a versatile technology that offers a wide range of possibilities for tailor-making properties toward various application areas. Thus, high unaged and aged mechanical strengths in combination with low water solubilities may generally be obtained from the use of gelatins with higher gel strength (and hence, generally, higher molecular weights), low-to-mid range tannin addition levels (3–20%), alkali metal hydroxides for pH adjustment, and final pH in the range 8–9. Comparatively low water uptake properties may be obtained using higher gel strength type A gelatins, lower tannin addition levels, alkali metal hydroxides for pH adjustment, and lower final pH. Even lower water uptake properties may then be obtained using Ca(OH)2 in place of alkali metal hydroxides. If desired, higher water uptakes may be obtained using type B gelatins (or lower gel strength gelatins in general), higher tannin addition levels, and higher final pH. Mechanistic studies indicated that the optimal modification of gelatin with the tannin component occurs via several pathways.
Highlights
Stone wool is a remarkably versatile material, which is finding an increasing use in addressing critical global challenges
Article calcium), and the final pH (7−11). These studies have unveiled a greener binder technology that offers a wide range of possibilities for tailor-making properties toward various application areas
The combination of high unaged and aged mechanical strengths and low water solubilities is generally favored by the use of gelatins with higher gel strength, lowto-mid range tannin additions levels (3−20%), alkali metal hydroxides for pH adjustment, and final pH in the range 8−9
Summary
Stone wool is a remarkably versatile material, which is finding an increasing use in addressing critical global challenges. The conventional binder systems typically include components that are harmful in uncured form They generally require high temperatures to cure properly (i.e., well above 200 °C), leading to high energy consumption and possibly emissions that may require post-treatment. Striving to address these sustainability problems, the invention of greener binder systems based on nontoxic biopolymers, which were able to cure in the vicinity of ambient temperatures, was recently disclosed.[5−9] the first systematic studies and direct comparisons of various properties of binder systems based on type A gelatins modified with tannin from chestnut trees in the presence of NaOH at pH 9 or with transglutaminase at pH 5 were recently published.[10] As an essential element in advancing and understanding the greener binder technology based on gelatins modified with tannins, this paper presents the first systematic studies of the effects of varying the nature of the gelatin component, the tannin component, the metal cation of the hydroxide base, and the final pH. The second pathway occurs by the formation of covalent bonds between the tannins and gelatins under oxidative conditions.[16,22,26] The reaction sequence is promoted by basic conditions, where phenolate anions derived from the tannins may readily be oxidized to yield electrophilic quinone species, which react with nucleophiles such as the lysine side chains from gelatins
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