Effects of alkali pretreatment and drying methods on densification process of bamboo

• Ano de defesa: 2024
• Autor(a) principal: Godoy Júnior, André Luiz Pereira de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Bamboo; Bambu; Delignification; Densificação; Densification; Deslignificação; Drying; Secagem
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/74/74133/tde-29072024-092748/

Due to its fast growth, short rotation period, and very promising properties including a higher cost-efficient compared to conventional bricks and reinforced concrete, bamboo can be considered as one of the best options for replacing conventional materials, being one of the oldest building materials used in human history. Despite bamboos promising properties, some problems and unwanted effects like inhomogeneous mechanical properties, dimensional instability, and degradation must be overcome to have a proper role as a building material. As a solution, some kinds of pre-treatments can be used, followed by the densification process. There are numerous reviews of wood treatment in the scientific literature, but few reviews of how these treatments and the drying method affect the bamboo. In this study, a two-step process of delignification and densification was carried out on Dendrocalamus asper bamboo specimens. It is aimed to investigate the densification properties of the bamboo samples after partial removal of the lignin. To delignify the samples, two different approaches were applied. The first group was treated in a room-temperature NaOH + NaSO3 solution, while the second group was treated in the same solution at 100°C. Afterward, the samples were dried in either an oven with 100°C or at room temperature of 25°C. Hence, a total of four different groups of delignified and dried samples were produced with an average moisture content of 7 - 10%. The samples were then densified to 50% of their original thickness having the thickness reduction determined a priori using a thermo-mechanical press system at 160°C. The results indicated that all alkali treated samples required a lower load for the densification process compared to the reference. This implies that alkali treatment could enable a greater degree of densification with consistent energy consumption. This outcome has the potential to improve the material\'s mechanical properties and boost its density. Average compression stress of 17.0 MPa for the reference, 10.3 MPa for the samples treated with alkali solution at room temperature, and 7 MPa for the boiled alkali solution and dried at room temperature samples needed only 40% of the stress applied on non-treated bamboo. This finding implies a significant decrease in the energy and load needed to achieve a 50% densification degree. The drying process also affected the compression resistance of bamboo and oven-dried specimens showed an increase of 30% and 17% for room temperature and boiling temperature treatment respectively. The modulus of rupture, limit of proportionality, and elastic modulus of densified bamboo were all negatively impacted by the pre-treatment, according to the results of the bending test. Overall, untreated and treated bamboo displayed similar behavior for physical attributes in densified samples. After being treated with alkaline solution, bamboo showed reduced levels of lignin as well as hemicellulose and cellulose, according to chemical tests. To summarize, subjecting bamboo to this concentration of alkali solution in an open system with a densification degree of 50% is not enough to have a proper densification compromising the mechanical properties of the material.