Comparison of salicin and fibre contents in the barks and woody cores of willow (Salix spp.) clones as potential feedstocks for an integrated biorefinery

Valorisation of willow could be achieved by bioactive extraction (salicin) from the bark and using the remaining woody core to produce biobased materials and chemicals. It is therefore important to understand whether optimal concentrations of both the salicin in the bark and cellulose content in the woody core can be obtained within the same clone. This study evaluated the salicin levels in the bark of five clones grown for one-year in Northern Ireland by extraction in aqueous ethanol (80 %), where the contents were found to range from 0.33 % to 1.02 % DM (dry matter). The composition (hemicellulose, cellulose, lignin) was determined by sequential detergent and acid extraction of fibre (0.5 g), which indicated that there were significant differences only in the cellulose content across the samples. Cellulose in the woody cores ranged from 48.1 % to 54.5 % DM and in the bark from 15 % to 27 % DM. Subsequent statistical analysis indicated a correlation coefficient between salicin and cellulose contents of 0.77 (P = 0.01) in the woody core and between salicin and non-fibre contents of 0.73 (P < 0.05) in the bark. Significant correlation coefficients were determined within the woody cores between hemicellulose and cellulose of 0.69 (P < 0.05), and within bark between hemicellulose and both cellulose of 0.67 (P < 0.05) and lignin of 0.86 (P < 0.01) contents. Potentially, willow clones could be selected as biorefinery feedstocks which have high salicin concentrations in the bark for medical applications and high cellulose content in the woody core for use as biomaterials.