Study of the molecular weight of bark extracts and products of their reaction with formaldehyde

The molecular weights of sodium hydroxide extracts of various barks were determined by means of gel permeation chromatography (GPC). Products of these bark extracts were then obtained by allowing those extracts to react with formaldehyde or with formaldehyde and phenol. Following this, the molecular weight of the products were determined to investigate their reactivity.

The molecular weight and reactivities of bark extracts toward formaldehyde differed with respect to species and extraction conditions. Reactivity was improved by adjusting the pH of reaction mixture before the reaction. After reacting with formaldehyde, bark extracts of high temperature extraction decreased their molecular weight, whereas those of low temperature extraction decreased their molecular weight; however, the molecular weight of low temperature extracts increased by adjusting the pH of the extracts to the same level as the high temperature extracts before the reaction. The chromatogram of acetylated samples obtained from three reactants (southern pine bark extracts, formaldehyde and phenol) shifted toward the higher molecular weight side, as compared to that of extracts before reaction.