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.
A new two-step densification method for wooden materials is proposed. This method achieved wood that was virtually non-porous and fully densified exceeding any value ever reported for a hardwood species. In the first step, the compressive strength of the anatomical wood structure is reduced by delignification, and, in the second, a full densification is achieved by hot isostatic pressing under argon atmosphere. Three tropical hardwood species with distinct anatomical characteristics and properties were used to test the method. The HIP-densified wood's microstructural, chemical, physical, and mechanical properties were assessed. The results indicate that proposed method was effective for all the tested species, obtaining a material that it is mostly non porous, shows homogenous density patterns, preserves the original volume, features great stability and it has enhanced mechanical properties. Therefore, the HIP wood densification may be a promising densification technique since it overcomes several limitations faced by previous wood densification methods.
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