Isolation and comparative characterization of a Björkman lignin from the saponified cork of Douglas-fir bark

Cork from Douglas-fir bark (Pseudotsuga menziesii) was separated, extracted and submitted to suberin depolymerization by transesterification with sodium methoxide in methanol. As a result a saponified cork fraction (corksap) with a yield of 19% was obtained. From corksap a milled cork lignin (MCLsap) was isolated using the Björkman procedure with a yield of 0.75% (based on corksap, corresponding to 0.14% based on original cork). The isolated Douglas-fir MCLsap was characterized by elemental analysis and OMe determination, FT-IR spectroscopy and analytical pyrolysis (Py-GC/FID). Data are presented in comparison with those of MCLsap isolated from cork-oak (Quercus suber) and milled wood lignins (MWL) of spruce. All data revealed that the Douglas-fir cork lignin has a guaiacyl-type structure (G-lignin). Results of Py-GC/FID demonstrate that this polymer consists of approximately 97% guaiacyl, 2% p-hydroxyphenyl and 1% syringyl units.