Within tree variation of lignin, extractives, and microfibril angle coupled with the theoretical and near infrared modeling of microfibril angle
A theoretical model was built predicting the relationship between microfibril angle and lignin content at the Angstrom (A) level. Both theoretical and statistical examination of experimental data supports a square root transformation of lignin to predict microfibril angle. The experimental material used came from 10 longleaf pine (Pinus palustris) trees. Klason lignin (n=70), microfibril angle (n=70), and extractives (n=100) were measured and reported at different ring numbers and heights. All three traits were strongly influenced by ring age from pith while microfibril angle and extractives exhibited more of a height effect than lignin. As such, the multivariate response of the three traits were different in the axial direction than the radial direction supporting that care needs to be taken when defining juvenile wood within the tree. The root mean square error of calibration (RMSEC) for microfibril angle of the theoretical model (RMSEC = 9.8) was almost as low as the least squares regression model (RMSEC = 9.35). Microfibril angle calibrations were also built from NIR absorbance and showed a strong likeness to theoretical and experimental models (RMSEC = 9.0). As a result, theoretical and experimental work provided evidence that lignin content played a significant role in how NIR absorbance relates to microfibril angle. Additionally, the large variation in extractives content coupled with sampling procedure proved important when developing NIR based calibration equations for lignin and microfibril angle.