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 f rom wood powder and solid wood blocks and compared with the correspond ing transmission spectra measured from thin wood sections. Studies ind icated that high quality spectra could be obtained from either solid w ood blocks or powder by diffuse reflectance (DRIFT) and photoacoustic (PAS) techniques. Positions of IR bands measured from different hardwo od species by DRIFT and PAS technique are approximately same. However, the relative intensities of IR bands vary among species. For obtainin g reproducible DRIFT spectra from the solid wood surfaces, roughness a nd structure of the cut (tangential, radial or transverse) must be ide ntical. Whereas, for wood powder, smallest particle size results in be st resolved spectrum. Specular reflection causes distortions in the in tensities of the bands in the range 1150-950 cm(-1), which can be mini mised either by diluting sample powder in KBr (concentration <2%) or b y increasing the surface roughness of the solid block. FTIR-PAS spectr a measured from wood powder are quite similar to spectra obtained by t ransmission and/or DRIFT techniques. Relative intensity and position o f 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.