This study focuses on the hygrothermal performance of Moso bamboo. The knowledge in this aspect is remarkable important for the research of building energy saving and the low carbon building design. However, the detailed hygrothermal properties of Moso bamboo are fairly rare. To obtain these data, a series of experimental works have been done for measurement of density, porosity, thermal conductivity, specific heat capacity, water vapour permeability, hygrothermal expansion and sorption isotherm of Moso bamboo. To obtain further understanding on the hygrothermal performance of Moso bamboo, a number of dynamic heat and moisture transfer experiments were conducted. These experiments simulated two extreme outdoor environments and one indoor environment. The temperature and RH responses of Moso bamboo panels were monitored. Then a coupled transient heat and moisture transfer numerical simulation at the material level was conducted to predict and validate the hygrothermal performance of Moso bamboo. A sensitivity study of the hygrothermal properties of bamboo was also presented to indentify the influence of each hygrothermal property of Moso bamboo. Major findings include the following aspects. Both experiment and simulation results appear to be consistent with the results of measurements of the basic hygrothermal parameters. The parametric study found that density can be regarded as the most sensible parameter to influence the temperature simulation results at the transient state, while the thermal conductivity dominated the temperature variation at the steady state. The water vapour diffusion resistance factor can be regarded as the most critical parameter to influence the RH simulation results. The influence of liquid water diffusivity is negligible in this study. The parametric study results indicated that the simulation with moisture is more accurate than the simulation without moisture in both equilibrium and transient state. The results also imply that the existence of moisture could increase the heat capacity and reduce the thermal conductivity. The results of this study recommend that the external part of the bamboo culm wall can be utilised to minimise the RH variation of the panel while the internal part of the bamboo culm wall is suitable to increase the thermal insulation performance of the panel. To avoid hygroexpansion, the implementation of external part of bamboo culm wall needs to be minimised.

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23950号 / 農博第2499号 / 新制||農||1091(附属図書館) / 学位論文||R4||N5385(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)准教授 岡田 直紀, 教授 井鷺 裕司, 教授 柴田 昌三 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

[pt] O bambu é um recurso natural, típico de regiões tropicais e subtropicais, cujas fibras vêm atraindo interesse para reforço de materiais compósitos, pelas suas excelentes propriedades mecânicas. Entretanto, como toda fibra vegetal, as fibras de bambu apresentam alto grau de higroscopicidade, inchando quando da presença de água, limitando seu uso devido à perda de durabilidade. Dessa forma, este trabalho visa estudar melhorias nas propriedades de flexão do bambu através do processo de hornificação por ciclos de molhagem e secagem, tratamento muito utilizado em polpas de madeira ou papel, que leva a reduções na capacidade de absorção e retenção de água das fibras, reduzindo seus poros e tornando sua estrutura mais enrijecida. Para isso foram investigados os efeitos de 3, 5 e 10 ciclos de molhagem e secagem sobre as propriedades físicas e comportamento mecânico (flexão e módulo de elasticidade) do bambu da espécie Moso (Phyllostachys pubescens). Com relação às propriedades físicas foram avaliadas as variações na capacidade de absorção e retenção de água do bambu ao longo dos ciclos, incluindo avaliação das variações dimensionais dos feixes vasculares ao final dos ciclos, realizada por meio de análise e processamento de imagens obtidas por microscópio estereoscópico. Ademais, o comportamento à flexão foi estudado por meio de ensaios de flexão a quatro pontos, avaliando possíveis melhorias na resistência à flexão, deflexão e módulo de elasticidade do bambu após os ciclos de molhagem e secagem, incluindo análise da influência do cisalhamento na flexão. As análises físicas demonstraram que com os ciclos ocorreu redução na capacidade de retenção de água do bambu, além de reduções na área superficial de seus feixes de fibras. Na flexão houve ganho de rigidez após os ciclos, chegando a aumentar em 70 por cento o módulo de elasticidade. / [en] Bamboo is a natural resource, typical of tropical and subtropical regions, whose fibers are attracting interest to reinforce composite materials, due to its excellent mechanical properties. However, like all plant fibers, bamboo fibers present a high degree of hygroscopicity, swelling when water is present, limiting its use due to loss of durability. Thus, this work aims to study improvements in the flexural properties of bamboo through the process of hornification by wetting and drying cycles, a treatment that is widely used in pulps of wood or paper, leading to reductions in the water absorption and retention capacity of the fibers, reducing its pores and making its structure stiffer. The effects of 3, 5 and 10 wetting and drying cycles on the physical properties and mechanical behavior (flexure and modulus of elasticity) of the Moso bamboo species (Phyllostachys pubescens) were investigated. Regarding the physical properties, the variations in the bamboo water absorption and retention capacity were evaluated along the cycles, including evaluation of the dimensional variations of the vascular bundles at the end of the cycles, performed by means of analysis and processing of images obtained by a stereoscopic microscope. In addition, the flexural behavior was studied by means of four-point flexural tests, evaluating possible improvements in flexural strength, deflection and modulus of elasticity of the bamboo after the wetting and drying cycles, including analysis of the influence of shear on flexion. The physical analyzes showed that with the cycles there was a reduction in the water retention capacity of bamboo, as well as reductions in the surface area of its fiber bundles. In flexion, there was a gain of stiffness after the cycles, increasing the modulus of elasticity by 70 per cent.