NMR Estimation of Extractables from Bark: Analysis Method for Quantifying Tannin Extraction from Bark

Abstract Extraction and recovery of radiata pine bark tannin for use in adhesives should endeavour to be optimal to ensure process viability. A NMR method has been developed to directly gauge the extent of tannin extraction from bark by analyzing processed residues. 13C Solid-state NMR spectra were obtained for a series of bark and residue samples. The respective peak areas and heights of extractable polyphenolic tannins were compared with residual lignocellulosic materials. From the ratio of NMR peak intensities, diminishing polyphenolic content was apparent with increasing degree of extraction. The percentage polyphenolic tannins removed by extraction could be estimated by a simple equation comparing integrated areas of a sample with those of pure bark. A comparison of percentage extraction values determined gravimetrically with NMR peak ratios gave a good relationship from which the extractables removed from a bark residue could be estimated, potentially providing a measurement of extraction efficiency of a bark processing operation.

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