Analysis of wood surfaces and ground wood by diffuse reflectance (DRIFT) and photoacoustic (PAS) Fourier transform infrared spectroscopic techniques

Infrared diffuse reflectance and photoacoustic spectra were measured from wood powder and solid wood blocks and compared with the corresponding transmission spectra measured from thin wood sections. Studies indicated that high quality spectra could be obtained from either solid wood blocks or powder by diffuse reflectance (DRIFT) and photoacoustic (PAS) techniques. Positions of IR bands measured from different hardwood species by DRIFT and PAS technique are approximately same. However, the relative intensities of IR bands vary among species. For obtaining reproducible DRIFT spectra from the solid wood surfaces, roughness and structure of the cut (tangential, radial or transverse) must be identical. Whereas, for wood powder, smallest particle size results in best resolved spectrum. Specular reflection causes distortions in the intensities of the bands in the range 1150-950 cm(-1), which can be minimised either by diluting sample powder in KBr (concentration <2%) or by increasing the surface roughness of the solid block. FTIR-PAS spectra measured from wood powder are quite similar to spectra obtained by transmission and/or DRIFT techniques. Relative intensity and position of various IR bands measured by photoacoustic technique are independent of size of the particle and its concentration. These results indicate the usefulness of PAS technique over other solid sampling techniques.