Conditions for the extraction of polyphenols from radiata pine (Pinus radiata) bark for bio-foam preparation

The use of polyphenol extracts from radiata pine (Pinus radiata) bark as raw materials for bio-foams was investigated along with the optimal NaOH extraction conditions. The targeted yield of alkaline extracts was 60%, and the targeted pH was 11 to 12. The radiata pine bark was composed of 70% of a 1% NaOH extract, which contained mainly polyphenols, such as proanthocyanidin (PA). As the particle size of the bark decreased, the yield of the 1% NaOH extracts increased from 57 to 87%. A range of NaOH concentrations, liquor ratios, and extraction times were explored to establish an economic polyphenol extraction method. More than 60% of the alkaline extract was extracted, and the pH of the extract was approximately 12 when the optimum extraction conditions were employed, i.e., a liquor to bark ratio of 5:1, a NaOH dosage of 17 to 18% based on the bark weight, and a 1 h extraction time. Following neutralization of the alkaline extract, structural analysis indicated severe structural changes in the PA during the alkaline extraction. Because the alkaline extract was barely soluble in the solvent used for the structural analyses, it is assumed that chemical modification is required to increase the solubility of the alkaline extract for the production of bio-foams. © 2020, Korean Society of Wood Science Technology. All rights reserved.