Effect of alkaline delignification process on the anatomical characteristics and some mechanical properties of tropical woods of different densities

Abstract

Abstract Wood delignification is a straightforward process of great interest in the development of advanced materials and products for sustainable applications. This process can reduce the stiffness of the wood cell wall by using selective chemical reagents that remove lignin/hemicellulose and thus facilitate its modification in combination with other treatments. This study aimed to compare the efficiency and uniformity of the partial delignification process using the sodium hydroxide and sodium sulfite (NaOH/Na2SO3) mixed aqueous solution in the three hardwood species Brosimum utile (Sande), Carapa guianensis (Andiroba), and Dipteryx oleifera (Choiba). These are important tropical tree species, providing essential material for the wood industry. The effects and distribution of the solution were studied based on the variations exhibited by the center and ends of the delignified woods, using chemical composition analysis techniques, FT-IR spectra, optical microscopy, and scanning electron microscopy (SEM). The process allows the partial chemical removal of lignin/hemicellulose in different non-uniform proportions between the center and the ends of the woods under study. The lignin/hemicellulose removal ratios varied widely between the different wood species. The density of delignified wood did not vary significantly after treatment. The modulus of rupture (MOR) and modulus of elasticity (MOE) of delignified wood decreased. The results suggested that denser tropical wood requires the adjustment of the process variables while the proposed method can treat less dense tropical woods. Partially delignified tropical hardwood can be used to develop advanced materials and products for diverse applications.