Heat Treatment Effect on Lignin and Carbohydrates in Corsican Pine Earlywood and Latewood Studied by PY–GC–MS Technique

Abstract

Lignin-derived degradation products from non-treated (NT) and heat-treated (T) Corsican pine (Pinus nigra subsp. laricio) obtained by pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) were investigated, whereby the earlywood (EW) and latewood (LW) parts of the annual ring were considered separately. The data evaluation was done by principal component analysis (PCA) and the Kruskal–Wallis test. There are no differences in the pyrolysis products composition between EW and LW, but NT and T samples were discernible by PCA applied to Py–GC–MS data. Less phenols with longer chains (4-vinylguaiacol, and trans-isoeugenol) than those with shorter chains (guaiacol, 4-methylguaiacol) and an increase of anhydrosugar (AHS) were found among the pyrolysis products after heat treatment. These signs for autocondensation and side chain cleavages in the lignin during heat treatment were more evident in the EW than in the LW and for the crystallization of cellulose. A slight decrease of the carbohydrate/lignin ratio (C/L) after heat treatment indicates a greater degradation of carbohydrates compared to lignin. The relation of pyrolysis products of lignin and mechanical properties of wood was evaluated by regression analysis. An inverse correlation between short-chain phenols and MOE and a direct correlation between long-chain phenols and compression strength was found in case of NT wood, while a weak positive correlation could be observed between short-chain phenols and the density in T wood.