Mechanical response of longleaf pine to variation in microfibril angle, chemistry associated wavelengths, density, and radial position

The composite structure of the S2 layer in the wood cell wall is defined by the angle of the cellulose microfibrils and concentration of polymers and this structure impacts strength and stiffness. The objective of this study was to use near infrared spectroscopy and X-ray diffraction to determine the effect of lignin and cellulose associated wavelengths, microfibril angle, density, and radial position within the tree on strength and stiffness. The aromatic portion of lignin provided a good predictive role on strength and stiffness at high microfibril angles. However, in mature wood where microfibril angle and lignin content was low, cellulose associated wavelengths became increasingly important. The increased importance of the aromatic portion of lignin (1665 nm) on the strength as microfibril angle increased was attributable to the plastic deformation of lignin that occurred beyond the yield point. Finally, a fourfold increase in stiffness was observed when the microfibril angle dropped from 40 to 5°.