Heliyon (Sep 2019)
Structural characterization of Argania spinosa Moroccan wooden artifacts during natural degradation progress using infrared spectroscopy (ATR-FTIR) and X-Ray diffraction (XRD)
Abstract
The present work is focused on spectroscopic study of four samples of Argan wooden artifact pertaining to the 17th, 18th, 20th and 21st centuries. The objective is to characterize their unknown structures by the study of their non degraded parts and to investigate changes occurred in their degraded parts due to the natural degradation process. Attenuated total reflectance Fourier transform infrared spectroscopy gauges the presence of many functional groups related to cellulose I and/or II (OH, C–O–C and –CH2), hemicelluloses (particularly C=O acetoxy ester band at 1732 cm−1), and lignin (OH phenolic, Car-O and C=Car) and provides qualitative information on the state of wood alteration by informing on the evolution of new former C=O bands. The degree of conversion to carbonyl group, especially quinone or p-quinone at 1650 cm−1, is correlated to lignin degradation, while the absence of the C=O acetoxy absorption is ascribable to occurred deterioration in hemicelluloses, and partial degradation of cellulose with enhancement of the C=O region between 1730-1630 cm−1. X-ray diffraction determines the presence of two forms of cellulose; amorphous cellulose at 18.5° 2θ and predominant crystalline cellulose Iβ at 2θ = 22.6° which characterized by an intense peak. The decrease of crystallinity index values confirms the deterioration level and obvious changes in crystallinity level. However, the microcrystalline structure appears unaltered because no significant changes were observed for calculated cristallite seize. The obtained results depend on the prolonged time of ageing, natural deterioration phenomena, and wood part (internal or external) that is exposed to degradation. The combination of these two methods is useful for an accurate estimation of the degradation level of argan wood.
