Characterization of southern yellow pine bark layers by Attenuated Total Reflectance (ATR) and Fourier Transform Infrared (FT-IR) Spectroscopy
The outer bark (rhytidome) of the southern yellow pines is a complex structure comprised of alternating layers of obliterated phloem and periderm tissues, with the latter comprised of three layers, those being phellem, phellogen, and phelloderm. An attenuated total reflectance (ATR) sampling accessory, coupled with a Fourier transform infrared (FTIR) spectrometer, provided a facile means to probe the chemical nature of these layers to near nano-scale levels. Comparison of the spectra for both surfaces of the obliterated phloem specimens showed no significant differences whereas comparison of the spectra for the inner (phelloderm) and outer (phellem) surfaces of the periderm specimens were quite different. Relative to the spectrum for the outer periderm surface, the inner periderm surface had significantly greater signals for aliphatic and carbonyl functionalities. Spectral subtractions after solvent extractions were consistent with the removal of resinous and phenolic extractives. Results provide not only the first demonstration of the chemical functionalities of individual layer/surfaces in pine bark by FT-IR spectroscopy, but also new evidence suggesting moisture barrier properties for the phelloderm.