Tannin extracts from spruce and pine barks

Barks of indigenous spruce (Picea abies) and pine (Pinus sylvestris) were extracted with different solvents and various extraction conditions. Solvent and extraction procedures had great influence on yield and reactivity of extracts toward formaldehyde (Stiasny reaction). Under favorable conditions, hot water treatment yielded about 14 to 16% extracts for spruce bark and about 6% extracts for pine bark. But the tannin content of the water extracts for spruce bark and about 6% extracts for pine bark. But the tannin content of the water extracts was low (Stiasny number about 50). Using different chemicals such as sulfite or alkali, polyphenolics with higher yields and satisfactory reactivities toward formaldehyde could be extracted. Especially extraction with alkali considerably increased the yield of extracts. To reduce the viscosity of alkali extracts, a treatment with sulfite or phenol at pH 5 was necessary. Furthermore, polyphenolics were extracted by pulping barks with mixtures of water and organic solvents. Satisfactory yields with high tannin content were extracted at a temperature of 140°C even from pine bark. Some adhesive properties of spruce and pine bark extracts are pointed out in detail.