Hydroxyalkylation of condensed tannins: Comparison of proanthocyanidin extraction process and epoxide chain length on physicochemical properties

Abstract

Bio-based chemical feedstocks are increasingly being sought for the polymer industry, including polyols for polyurethane synthesis. Proanthocyanidins, isolated from Pinus radiata bark using different extraction methodologies, were investigated as starting materials for the synthesis of polyols. A mild-base, solvent-free and anhydrous hydroxyalkylation using varying chain length epoxides was employed with the aim of producing bio-based polyols with viscosities suitable for polyurethanes. The method of proanthocyanidin extraction influenced the reactivity towards epoxide, with water and ethanol-water extracts providing product yields greater than 80%. Epoxide chain length was increased from propylene to hexylene oxide without detrimental effect on the yield or molar substitution. A key attribute of the method employed was the minimisation of side reactions, with homopolymer contents typically less than 10%. At the highest molar substitution levels, melt and flow behaviour was obtained with sub ambient glass transition temperatures and viscosities suitable for direct application in polyurethane synthesis.