From Natural Woods to High Density Materials: An Ecofriendly Approach

Abstract

Recently, different methods have been proposed to develop wood materials, termed “densified woods”, with density increment and improvement in mechanical proprieties. Almost all the proposed methods involve the use of reducing agents and strong bases. In this work, a new method has been developed involving the use of less polluting agents. The formation of densified woods is divided into two steps: delignification involves the removal of lignin, hemicelluloses, and shorter chains of cellulose, whereas densification involves the plastering of the delignified woods. The obtained materials showed a density increase of two to four times. The obtained densified woods were characterized by spectroscopic, microscopic, and thermogravimetric techniques and mechanical tests. The characterizations aimed at determining the variations of chemical and structural compositions of the samples after delignification and densification processes, showing, respectively, a decrease in lignin and a significant increase in the density and force necessary to bring the materials to yield. The final density of wood was two to three times higher and the force necessary to reach the yield point reached more than three times the initial one for some of the studied samples. These characterizations showed how different woods, with different properties, reach comparable densities and final mechanical properties after delignification and densification process. The increased mechanical properties of the materials allow their application in place of other composite woody materials.

Surface changes in wood submitted to thermomechanical densification

“…Investigations of wettability and surface roughness have been performedinvolving different densification processes (Bekhta and Krystofiak 2016, Bekhta et al 2018, Chu et al 2019, Zao et al 2020, Gao and Huang 2022, Gullo et al 2023, with different results.Temperature, time and pressure act in the process, along with the compaction rate, which should be especially considered since it dictates the behavior as a function of the chemical and anatomical structure of wood of different species. Densification is considered an effective to wayimprove the mechanical properties of wood (Luan et al 2022, Cabral et al 2022, butto achieve good results, information is required about the optimal combinations of treatment parameters to improve the properties of specific woods (Schwarzkopf 2020, Cabral et al 2022.…”

Two-step hot isostatic pressing densification achieved non-porous fully-densified wood with enhanced physical and mechanical properties

“…As a rst step, they softened the anatomical structure of the wood by chemical lignin removal (deligni cation), a process that has been extensively researched in combination with other wood modi cation treatments [28][29][30][31] . The aim of the lignin removal was to facilitate access to the cellulose chains in order to subsequently modify the material 29,32 . However, the disadvantage of the densi cation process used in the aforementioned study is that it was not possible to fully densify the wood vanishing porosity (density of 1.3 g/cm 3 ), with a signi cant volume loss of about 79% CR in the radial direction due to uniaxial densi cation being found 33 , and it requires a timeconsuming process.…”