Composition of non-woody plant lignins and cinnamic acids by Py-GC/MS, Py/TMAH and FT-IR

Lignins from different non-woody plants such as hemp (Cannabis sativa), flax (Linum usitatissimum), jute (Corchorus capsularis), sisal (Agave sisalana) and abaca (Musa textilis), commonly used for manufacturing specialty papers, were analyzed by pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) in the absence and in the presence of tetramethylammonium hydroxide (TMAH) and by Fourier-transform infrared (FTIR) spectroscopy, after alkaline isolation. Hemp and flax lignins showed a predominance of guaiacyl (1-hydroxy-2-methoxyphenyl) units, while jute, sisal and abaca lignins contained predominantly syringyl (1-hydroxy-2,6-dimethoxyphenyl) units. p-Hydroxycinnamic acids, namely p-coumaric and ferulic acids, were also found in the isolated lignins, linked by alkali-resistant ether bonds, especially in abaca and sisal lignins. The presence of the latter compounds in the isolated lignins, as well as in their respective whole fibers, was shown by pyrolysis in the presence of tetramethylammonium hydroxide (Py/TMAH), p-coumaric acid being especially abundant in abaca.