The effect of the natural degradation process on the cellulose structure of Moroccan hardwood fiber: a survey on spectroscopy and structural properties

Abstract

The aim of this work is to study the effect of natural degradation on the cellulose structure conformation changes of 2 ageing Moroccan hardwoods (400 and 500 years) compared to recent one considered as a reference; and to provide information on the polymorphs content variability from two-phases material (crystalline and amorphous) influenced by a long time of ageing and environmental degradation effects. In order to investigate the effects of both natural degradation conditions and a long time of exposure on cellulose structure conformation (examined samples) with estimating their content (crystalline and amorphous cellulose), three combined techniques XRD, ATR-FTIR and FT-Raman spectroscopy were used. XRD results associated with the crystallographic planes and Miller indices provide information on the presence of a mixture of celluloses polymorphs (crystalline cellulose I, II, Ib and amorphous phase). The decrease in crystallinity-index values from recent to aged ones (38 to 19.5%) confirms well the occurred alteration of crystalline cellulose fibres and their evolution towards a high content of the amorphous form. The prominent regression in the intensities of three FTIR fingerprint cellulose regions evolving towards an overall increase in the intensities of C=O area (1733-1630 cm-1) is a sign on the introduced changes on cellulose conformation and cellulose fibres degradation more accentuated in the case of the very aged sample (500 years). Similar results were confirmed by combining FT-Raman spectroscopy as a vibrational technique. No work has been done on this genus of degraded Moroccan hardwood and the relevance of this study is to investigate the compositional content and structural conformation, to determine the variability in the forms of both crystalline and amorphous cellulose phases with estimating the evolution of their polymorphism, and to monitor the degree of crystalline cellulose fibres deterioration.