Hydroxypropylation of Polyphenol-Rich Alkaline Extracts from Pinus radiata Bark and Their Physicochemical Properties

• Published in: Molecules (Basel, Switzerland) Switzerland), 2022-12, Vol.27 (24), p.9002
• Main Author: Mun, Sung Phil
• Format: Article
• Language: English
• Subjects: alkaline extract; Bark; Glass transition temperature; Hydroxyl groups; hydroxypropylation; Lignin; molar substitution (MS); Neutralization; NMR; Nuclear magnetic resonance; PEG#400; Physicochemical properties; Pinus - chemistry; Pinus radiata; Pinus radiata bark; Plant Bark - chemistry; Plant Extracts - chemistry; Polyols; Polyphenols; Polyphenols - analysis; propylene oxide (PO); Salts - analysis; Solubility; Spectroscopy, Fourier Transform Infrared; Spectrum analysis; Transition temperatures
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules27249002

bark is a rich source of polyphenols, which are mainly composed of proanthocyanidins. This study aimed to utilize bark as a polyol source for bio-foam production in the future. Polyphenol-rich alkaline extracts (AEs) from bark were prepared by mild alkaline treatment and then derivatized with propylene oxide (PO). Hydroxypropylated alkaline extracts (HAEs) with varying molar substitutions (MS 0.4-8.0) were characterized by FT-IR, NMR, GPC, TGA, and DSC. The hydroxyl value and solubility in commercial polyols were also determined. The molecular weights of the acetylated HAEs (Ac-HAEs) were found to be 4000 to 4900 Da. Analyses of FT-IR of HAEs and H NMR of Ac-HAEs indicated that the aromatic hydroxyl groups were hydroxypropylated and showed an increase in aliphatic hydroxyl group content. The glass transition temperature (T ) of AE and HAEs were 58 to 60 °C, showing little difference. The hydroxyl value increased as the hydroxypropylation proceeded. Although salts were produced upon neutralization after hydroxypropylation, HAEs still showed suitable solubility in polyether and polyester polyols; HAEs dissolved well in polyether polyol, PEG#400, and solubility reached about 50% ( / ). This indicated that neutralized HAEs could be directly applied to bio-foam production even without removing salts.