Evaluation of Lignin Syringyl/Guaiacyl Ratio in Eucalyptus Camaldulensis across Three Diverse Sites Based on near Infrared Spectroscopic Calibration Modelling with Five Eucalyptus Species and its Impact on Kraft Pulp Yield

Lignin composition [syringyl/guaiacyl (S/G) ratio] and cellulose content in wood have an important bearing on pulp yield. This paper deals with the development of a calibration model for S/G ratio using five Eucalyptus species from different sites by diffuse reflectance near infrared spectroscopy. The model was constructed with 120 samples covering an S/G ratio range from 1.8 to 3.6, determined by pyrolysis-gas chromatography-mass spectrometry. The calibration plot has an R2 value of 0.825 which was validated in E. camaldulensis, E. urophylla and E. pellita. Variation in S/G ratio was studied in more than 3000 E. camaldulensis trees across three diverse sites in southern India. The S/G ratio was lower in a low rainfall site (Mahabubnagar) compared to a higher rainfall site (Ongole). A positive correlation (R2 = 0.72) was observed between S/G ratio and Kraft pulp yield in E. camaldulensis. Alkali consumption in Kraft pulping experiments was inversely proportional to the S/G ratio (R2 = 0.914).