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Wood: Moisture Content, Hygroscopicity, and Sorption


Wood is a hygroscopic material that has the ability to adsorb or desorb water in response to temperature and relative humidity of the atmosphere surrounding it. This affinity of wood for water is caused by hydroxyl groups accessible in the cell walls of wood. As a consequence, the moisture content of wood is one of the most important variables affecting its physical and mechanical properties. The present paper focuses on moisture content in wood and presents an account of various theories of moisture sorption such as unimolecular sorption, multilayer theories, solution theory, and cluster theory.
Citation: Hartley I., and Hamza M.F., Wood: Moisture Content, Hygroscopicity, and Sorption. In:
Saleem Hashmi (editor-inchief), Reference Module in Materials Science and Materials Engineering.
Oxford: Elsevier; 2016. pp. 1-7.
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... • The moisture buffering capacity of timber structures [158,159] and the relatively low thermal FIGURE 5.14. Wind blowing beneath the palafitic timber building. ...
... Timber structures are very hygroscopic, and thus they have the ability to exchange water vapour with the surrounding air continually, i.e. gaining and losing moisture until reaching an equilibrium point (equilibrium moisture content -EMC) [158,159]. The EMC is influenced by relative humidity and temperature, and any change in these parameters forces the material to adjust to a new equilibrium point [159]. ...
... Timber structures are very hygroscopic, and thus they have the ability to exchange water vapour with the surrounding air continually, i.e. gaining and losing moisture until reaching an equilibrium point (equilibrium moisture content -EMC) [158,159]. The EMC is influenced by relative humidity and temperature, and any change in these parameters forces the material to adjust to a new equilibrium point [159]. In the study of Silva et al. [158], from the three softwood species analysed, Maritime Pine (Pinus Pinaster) had the highest EMC (12.8%) and also the lowest ability to shrink and swell. ...
Vernacular architecture is characterised by embodying and expressing a plurality of factors - geographic, climatic, economic and cultural - of the places in which it is located. In its long evolution, and inserted in a context of scarcity, a range of pragmatic strategies and building techniques of adaptation to the surrounding environment were developed. These strategies/materials are usually simple, low-tech and have a low potential environmental impact. From a sustainability point of view, several studies highlight them as having the potential to reduce the environmental impacts of buildings. In Portugal, there are many expressions of vernacular architecture, whose specificities are an identity factor of several regions. However, there is a lack of quantitative studies on the thermal and environmental performance of vernacular buildings and materials in the Portuguese context. In this sense, this research work presents a qualitative and quantitative study of i) climate-responsive strategies; ii) the thermal performance and comfort conditions of different Portuguese vernacular buildings throughout the different seasons; and iii) the environmental performance of vernacular materials. The research focused on the study of three case studies, with specific features and located in three different zones of mainland Portugal. The thermal performance and comfort conditions of the case studies were evaluated through in situ monitoring of hygrothermal parameters, surveys on occupants’ thermal sensation, and the data analysed according to an adaptive model of comfort. To compare the influence of some strategies on the annual energy demand for heating and cooling, simulations under dynamic conditions for different scenarios were carried out. In the case of vernacular materials, although these are seen as ecological, the quantitative studies available are scarce and that allow establishing an equative comparison with conventional materials. Thus, the life cycle assessment of two earthen materials, rammed earth and compressed earth blocks (CEBs), was carried out and based on specific life cycle inventory values obtained from a producer company, following the guidance provided by the standard EN15804. From the results, in general, it was found that the case studies have shown a good thermal performance by passive means alone and that the occupants feel comfortable, except during winter when there was a need to use heating systems. In the case of materials, in a cradle-to-gate analysis of different walls, the use of earthen building elements can result in reducing the potential environmental impacts by about 50%, when compared to the use of conventional ones. Additionally, earthen materials have the advantage that they can be recycled/reused in a closed-loop approach.
... Perubahan kelembapan udara dan temperatur yang ekstrim di negara tujuan, yang umumnya memiliki empat musim dengan kadar air seimbang mencapai 10%, menyebabkan terjadinya penyesuaian kadar air kayu, sehingga mengakibatkan barang kerajinan tersebut mengalami penyusutan dan pengembangan, sehingga menjadi retak. Kandungan air pada kayu dipengaruhi oleh persentase kayu gubal dan teras, Kandungan air kayu gubal biasanya jauh lebih tinggi daripada kayu teras (Hartley & Hamza, 2016). Alat pengering yang saat ini banyak digunakan pelaku usaha kerajinan kayu furnitur kebanyakan pada skala besar yaitu pengeringan konvensional yang membutuhkan investasi besar dan volume pengeringan kayu >25 m 3 . ...
Indonesia merupakan salah satu negara pengekspor kerajinan kayu ke 193 negara, namun dalam prosesnya sering mengalami kerugian akibat pengembalian produk oleh pihak pemesan karena mengalami cacat retak pada saat barang tiba di negara pemesan. Salah satu upaya meningkatkan kualitas kerajinan kayu adalah dengan mengeringkan kayu sesuai negara tujuan agar dimensi dan kelembabannya relatif stabil. Proses pengeringan kayu skala industri membutuhkan investasi yang tinggi, sehingga perlu dikembangkan pengering skala kecil untuk pengrajin. Penelitian ini bertujuan membuat desain dan pengujian kinerja pengering kayu sederhana dengan kapasitas 1,5 m³, dengan biaya terjangkau, mudah dioperasikan dan digunakan oleh masyarakat. Contoh uji yang digunakan berupa batang dan cabang kayu jati (Tectona grandis L.f.). Pemanas yang digunakan adalah kombinasi panas matahari dan listrik, yaitu panas cahaya matahari dipertahankan dan dialirkan ke dalam ruang pengering kayu melalui kipas yang menghisap udara panas dari ruang bakar ke dalam ruang pengering. Udara panas disirkulasikan ke saluran hisap lagi secara terus menerus untuk didistribusikan kembali ke ruang pengering. Hasil uji coba menunjukkan suhu rerata harian dari panas surya yang diterima ruang pengering berkisar antara 40−50°C, sementara suhu untuk pengeringan kayu jati berkisar antara 45−70°C. Dari evaluasi yang telah dilakukan, plat pemanas kurang efektif dalam pemanasan ruang sehingga perlu dilakukan penggantian dengan modifikasi pemasangan elemen pemanas di dinding oven bersumber baterai.
... According to Equation (2), MC may range from 0% for oven-dry wood to over 100% when the water in the wood weighs more than the wood substance. The maximum MC depends of tree species and may achieve 140-150% [28]. The only direct method to determine MC in wood material is to measure the water content in a wood sample and the weight of oven-dry sample. ...
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Typical tree health assessment methods are destructive. Non-destructive Ground Penetrating Radar (GPR) technique can provide a diagnostic tool for assessing the health status of live tree trunks based on internal dielectric permittivity distribution. Typical GPR acquisition technique—common-offset—is not helpful in providing robust and high-resolution quantitative results. In the current work we evaluate the capabilities of GPR tomography on locating tree-decays in a number of different tree species, imaging the interval structure of a healthy tree and quantitative estimation of moisture content (MC) based on distribution of dielectric permittivity, directly related to MC. The measurements described in this work were made on the trunks of live trees of different species in different conditions: a “healthy” English oak (Quercus robur), a “dry” Siberian fir (Picea obovata), a Horse chestnut (Castanea dentata) and a European aspen (Populus tremula) with rot inside. The results of the suggested approach were confirmed by resistography. Different parts of the trunk (bark, core, sapwood), as well as healthy and affected areas differ in moisture content, so the method of GPR tomography allowed us to see both the structure of the trunk of a healthy tree, and the presence and dimensions of defects.
... At a certain point, equilibrium is attained between moisture in the leaf and that in the surrounding atmospheric environment, and this situation is the best for the tea transport conditions. This is where the tea leaves will not gain or lose any moisture with time and it is known as the equilibrium moisture content of the tea [Hartley and Hamza, 2016]. Simulation models for dryer design, dryer optimization and control for several agricultural products use the difference between the actual moisture content and the equilibrium moisture as a measure for the driving force for drying. ...
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In sea transport, a very important thing is an assignment of cargo to a particular class of storage climate conditions and it is carried out on the basis of the requirements that cargo places upon its storage atmosphere. The water content of black tea must not fall below 2%, as the product otherwise becomes hay-like and its essential oils readily volatilize, while on the other hand, it must not exceed 9% as it then has a tendency to grow mould and become musty. Therefore, tea requires particular temperature, humidity/moisture and possibly ventilation conditions. In this context, tea is a hygroscopic material that has the ability to absorb or desorb water in response to temperature and relative humidity of the atmosphere surrounding it. The moisture content of tea is one of the most important variables affecting its chemical and sensory properties. Therefore, to explore and predict the behaviour during transport of tea, its equilibrium moisture content must be determined for a range of transport temperatures and relative humidities. The present paper focuses on the evaluate the hygroscopic properties of tea from Rwanda with different degree of fragmentation based on isotherms of water vapour sorption and characteristics selected parameters of the surface microstructure determining transport conditions and therefor microbiological stability of teas.
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The palafitic timber constructions of the central Portuguese coastline are an example of the adaptation to site-specific conditions (climate and sand landscape morphodynamics) using the available endogenous resources. Thus, in a context of environmental awareness and climate change, it is relevant to understand their features/strategies and how they perform. This work analyses the energy performance and thermal condition evaluation of a vernacular timber building-palheiro-from Praia de Mira, through in situ measurements, subjective analysis and energy simulation provided by DesignBuilder/EnergyPlus. The results show a good or satisfactory thermal performance during most of the seasons by passive means only. Despite, it was not possible to guarantee thermal comfort conditions for the occupants during winter. In the energy performance analysis, five scenarios, with different external walls, were compared. In the two scenarios that satisfy the maximum U-value for the climate zone, the current conventional building had a slightly better performance on heating and cooling (less 1.1 and 1.4 kWh/m2 , respectively) than the timber building. However, the difference between the two construction solutions is not substantial in the annual energy demand (2.5 kWh/m2 , 7.3%), indicating that timber structures are suitable in this mild climate area.
Acoustic properties of wood are best recognized when listening to the tone and clarity of wood instruments such as the violin, piano, xylophone, or guitar. Less recognized, however, are the major roles acoustic properties play in helping to minimize sound transmission from one room to the next and in providing sound barriers to highway noise. Acoustic waves are also used to evaluate strength properties in wood, evaluate processing variables during manufacturing, and elucidate anatomical characteristics of wood. The acoustical properties of wood are discussed in details within this article.
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