There are four big medium density fibreboard (MDF) plants in New Zealand with a total production capacity of close to one million cubic meters per year. A significant quantity of boards (nearly 3% or about 30,000 cubic meters per year) is rejected due to defects such as weak core, low modulus of rupture and elasticity, low internal bonding and delamination. The main cause of these defects, is lack of complete understanding of the inter relationship during the hot-pressing stage between the initial inputs such as temperature, moisture content, platen pressure and its impact on the properties of boards. The best solution is to develop a mathematical model to assist in understanding these relationships and to solve the equations in the model by using advanced software. This will reduce the number of expensive experiments and will enable us to see some of the parameters, which are otherwise difficult to visualise. Several earlier researchers have tried to model hot pressing of wood composites, mostly either for particle board or oriented strand board (OSB), and only a few are for MDF. The type of numerical methods used to solve the model equations and various assumptions, changes from one investigator to the other. The non-availability of source code to convert the mathematical equations into programme, is one of the reasons for this model development. To improve the productivity of MDF plants in New Zealand, there was a need to develop a computer programme which can include all the latest findings and can remove the defects which are present in earlier models. This model attempts a more complete integration than in the previous models of all the components such as heat transfer, moisture movement and vertical density profile formation in a one-dimensional model of hot pressing of MDF. One of the important features added in the heat and mass transfer part of the model is that the equilibrium moisture content (EMC) equation given for solid wood was modified to be applicable for the MDF fibres. In addition, this EMC equation can cover the complete range of hot pressing temperature from 160ºC to 200ºC. The changes in fibre moisture content due to bound water diffusion, which was were earlier neglected, was considered. The resin curing reactions for phenol formaldehyde and urea formaldehyde resins are also incorporated into the model, with the energy and water released during the curing reaction being included in the energy and mass balances. The validation of the heat and mass transfer model was done by comparing the values of core temperature and core pressure from the model and the experiments. The experimental value of core pressure and core temperature is obtained by putting a thermocouple and pressure transducer in the middle of the mat. The experimental core temperature results show qualitative agreement with the predicted results. In the beginning, the core temperatures from both experiment and model overlap each other. In the middle of the press cycle, the experimental core temperature is higher by 10ºC and by the end the difference decreases to 5ºC. The vertical density profile (VDP) is a critical determining factor for the strength and quality of MDF panels. The earlier concept of ratio of modulus of elasticity of the layer to the sum of modulus of elasticity of all the layers in the previous time step, given by Suo and Bowyer (1994), is refined with the latest published findings. The equation given by Carvalho et al. (2001) is used to calculate the MOE of different layers of the mat. The differential equation of a Maxwell element given by Zombori (2001) is used to measure stress, nonlinear strain function and relaxation of fibres. The model gives good agreement of peak and core density at lower platen temperature at 160ºC but with the increase of platen temperature to 198ºC, the rise in peak density is comparatively higher. There is a distinct increase in predicted peak density by 150 kg/m³ in comparison to the experimental result, where the increase is only by 10 kg/m³. There is a large decline (50 kg/m³) in core density in the experimental results in comparison to only a slight decline (13 kg/m³) in the predicted results. The use of Matlab provides a very convenient platform for producing graphical results. The time of computation at present is nearly 20 hrs in a personal computer with Pentium four processor and one GB RAM. The model can predict properties of a pressed board for the standard manufacturing conditions and also the new hot pressing technologies such as the use of steam injection or a cooling zone in the continuous press. A comparative study has been done to show the advantages of using new hot pressing technology. The present model will become an important tool in the hands of wood technologist, process engineers and MDF manufacturing personnel, to better understand the internal processes and to improve production and quality of MDF boards. This theoretical model helped in developing better understanding of internal processes. By using it, we can analyse the impact of platen temperature, moisture content on the core temperature, core pressure and density profile. It gives better insight into the relationship between core pressure and delamination of the board. The model is also able to predict the internal changes in the new hot pressing technologies such as the steam injection pressing and the use of a cooling zone in a continuous press. Using the simulation results, the exact time needed for the complete curing of resin can be calculated and then these results can be applied in the commercial plants. If the pressing time is reduced, then the over all production of both batch press and continuous press will increase. The second part of the project is the development of an empirical model to correlate the physical properties from the MDF board to the mean density. The empirical model is simple and straightforward, and thus can be applied in commercial operation for control and optimization. The empirical model can predict peak density, core density, and modulus of rupture, elasticity and internal bonding within the limits in which those relationships are derived. The model gives good results for thickness ranging from 10 to 13.5 mm and density ranging from 485 kg/m³ to 718 kg/m³.

Currently, the demand for wood-based panels has been growing solidly in European countries. Medium density fibreboard (MDF) manifests the potentialities for outstanding physical and mechanical properties. However, MDF from different fiber sources is normally designed for internal applications due to the poor moisture resistant capability. This study was conducted on acetylated MDF (Medite® MDF Exterior) to evaluate how physical (i.e. density, moisture content, dimensional stability, thickness swelling) and mechanical (i.e. modulus of elasticity, internal bonding strength before and after accelerated aging, bending stiffness and bending strength) properties behave at different relative humidity (i.e. 35 %, 65 % and 85 % RH at constant temperature of 20 ℃) levels. Bending stiffness was measured non-destructively by means of resonance method. The material used for control samples was commercial MDF. The size, quantity, conditioning and test method were followed in accordance with respective standards. The results showed that physical and mechanical properties were less influenced by Medite® MDF Exterior compared to commercial MDF. Medite® MDF Exterior were superior to commercial MDF in moisture resistance. Medite® MDF Exterior had more stable mechanical properties than commercial MDF with the changes of relative humidity.

The New Zealand kiwifruit and apple industries export the two largest horticultural crops by value and tonnage on long sea routes to distant markets. The long storage and shipping times, low temperature (~0°C) and high humidity (>70 %RH) conditions require boxes manufactured from high performance corrugated fibreboard. As the corrugated fibreboard boxes are a significant expense, improvements to reduce the weight and therefore the cost of the corrugated fibreboard, while maintaining their vertical compression strength, would increase the apple and kiwifruit industries profitability Through analysis of the literature it was established that the greatest contributor to box compression strength was the corrugated fibreboard edgewise compression strength, which is significantly affected by moisture. The strength of corrugated fibreboard decreases with increasing moisture content, which tends to be high in low-temperature high-humidity cool-stores. The literature also indicated that temperature and moisture content of the fluting medium could be optimised to reduce the damage caused during the fluting process. The objectives of this study included improving box compression strength predictions by measuring the effect of moisture and temperature on the strength of the corrugated fibreboard and measuring the relationship between temperature, humidity and corrugated fibreboard moisture content. The objectives also included developing a mathematical model to optimise the operations preceding the fluting process by predicting the fluting medium moisture content and temperature just prior to the fluting process. The measurements of corrugated fibreboard properties enabled the widely known McKee’s equation to be modified to enable the prediction of box compression strength over a range of moisture contents (7 to 30 %db), the valves of which could be estimated using the moisture sorption isotherms developed in this study over the temperature and relative humidity range of 0 to 20°C and 40 to 90 %RH. A mathematical model was developed to predict how the operation of the corrugator would affect the temperature and moisture content of the fluting medium just prior to the fluting process. The model was tested by running the corrugator at normal and extreme settings based on the model’s predictions, and measuring the strength properties of the corrugated fibreboard produced. The measured strength properties indicated that the machine speed and steam shower could have an effect but the too were inconsistent to established firm conclusions.

L'objectif de ce travail est de développer l'utilisation de la biomasse ligno-cellulosique dans le domaine des matériaux. Ce travail explore trois voies différentes d'utilisation de la ligno-cellulose afin de balayer un large spectre de constituants et de matériaux finaux. La première voie concerne l'incorporation de fibres naturelles dans la fabrication de panneaux utilisant la lignine comme adhésif. Des améliorations dans la fabrication de ces panneaux de fibres ont été apportées, par traitement chimique ou ajout de nouveaux compatibilisants, permettant un renforcement des propriétés mécaniques. La seconde voie a consisté à développer un procédé original de mise en forme sous haute pression testé et mis en place sur du coton dans le but d'obtenir des objets tridimensionnels sans étape de dissolution/régénération de la cellulose. Une fois le protocole défini, les effets des paramètres de mise en forme et de la variété de coton sur la microstructure et les propriétés mécaniques des objets en coton compressé ont été étudiés. Enfin, une troisième voie à consisté à élaborer des matériaux nanocomposites à partir d'hydroxydes double lamellaire modifiés par la lignine (HDL/LS). L'utilisation de cette nanocharge dans l'amidon a montré une capacité de renforcement pour un faible taux de charge. Ce composite amidon-(HDL/LS) a ainsi été utilisé avec une matrice polyéthylène afin d'augmenter la part renouvelable de la matrice sans diminuer significativement ses propriétés mécanique. Ce travail permet d'envisager des développements futurs pour ces différents matériaux développés et offre ainsi de nouvelles possibilités d'utilisation de la biomasse ligno-cellulosique dans l'élaboration de matériaux techniques. / This work aims at developing new ligno-cellulosic biomass based materials as a way for giving added value to this raw material. This study aimed at developing three different new ways of using ligno-cellulosic components to get a large overview of the possible technical materials. The first way deals with the preparation of natural fibres filled lignin fibreboard panels. Improvements in panels forming have been achieved by using either chemical treatment or novel compatibilisation to improve the strength of the prepared fibreboards. In a second way, an original forming process by high pressure has been tested and carried out on cotton fibres in order to produce 3D objects without dissolution/coagulation processes of cellulose. After setting up the forming procedure, effects of process parameters and cotton variety on microstructures and mechanical properties of highly compressed cotton have been studied. Finally, a third way was the study of new nanocomposites made of layered double hydroxide modified by lignin (LDH/LS). Using such nanofillers into thermoplastic starch turned out to be an efficient solution to reinforce mechanical properties with low nanofillers loading. This starch-(LDH/LS) nanocomposite was also blended with polyethylene to increase the bio-content without a degradation of the mechanical properties. This study is an advanced basis for a further development of these three different materials and offers a broad range of applications suitable for the preparation of new technical materials.

Avec la performance thermique croissante des bâtiments, les codes de simulation utilisés en conception requièrent des données de plus en plus précises sur les matériaux de construction. De plus, l’utilisation de matériaux biosourcés qui sont hygroscopiques (leur teneur en eau s’équilibre avec l’air humide ambiant) est en pleine expansion. Leur conductivité thermique et leur diffusivité massique doivent ainsi être caractérisées précisément. Un facteur essentiel affectant ces propriétés est la microstructure des matériaux. Ce travail de thèse propose de prédire les propriétés macroscopiques d’épicéa et de panneaux de fibres de bois (matériaux hétérogènes et anisotropes) à partir de leur morphologie réelle 3D. Celle-ci est obtenue par micro-tomographie synchrotron aux rayons X, outil très performant pour caractériser la structure interne d’un matériau de façon non destructive. Un traitement d’images permet de segmenter les phases solide et gazeuse. La méthode numérique choisie pour modéliser la diffusion de chaleur et de masse est la méthode Lattice Boltzmann car elle est simple à implémenter et à paralléliser et qu’elle peut facilement traiter des morphologies complexes. Les conductivités thermiques et diffusivités massiques équivalentes sont calculées dans trois directions orthogonales pour chaque matériau. Les résultats mettent en évidence l’influence de la structure interne et la forte anisotropie des matériaux étudiés (rapport 2 entre les directions tangentielle et longitudinale du bois en thermique et 30 en massique). La conductivité thermique transversale du panneau léger est de 0,04 W m−1 K−1. / As thermal performance of buildings is increasing, the simulation codes used during design require more accurate construction material data. Moreover, the use of bio-based materials which are hygroscopic (their moisture content balances with the ambient moist air) is booming. Their thermal conductivity and mass diffusivity must therefore be accurately characterized. A key factor affecting these properties is the microstructure of the materials. This work is dedicated to the prediction of macroscopic properties of spruce and fibreboards (heterogeneous and anisotropic materials) from their real 3D morphology. This is obtained by synchrotron X-ray microtomography, a powerful and nondestructive technique to characterize the internal structure of materials. Image processing allows the segmentation of the solid and gaseous phases. To model heat and mass diffusion, we choose the Lattice Boltzmann method because of its simple numerical development, suitability for parallel computing and easy processing of complex morphologies. The equivalent thermal conductivity and mass diffusivity are calculated in three orthogonal directions for each material. The results highlight the influence of the internal structure and the strong anisotropy of the materials studied (ratio of 2 between tangential and longitudinal directions of wood for heat diffusion and of 30 for mass diffusion). The transverse thermal conductivity of the lightweight board is about 0,04 W m−1 K−1.

The objective of this thesis is to create the documentation for building construction. Designed building is a mountain guesthouse. Building plat is located in the cadastral Poteč. Project documentation has been prepared in accordance with applicable laws, regulations and standards. The object is designed as one floor building with basement and residential loft and is fitted in sloping terrain. The building is shaped in layout L with the longest plane dimensions 40,11 x 39,05 m. Foundations are designed as strips of plain concrete. The building is designed as a wall support system. Wall system is combined of shuttering blocks filled with concrete, ceramic brick blocks and wood timbering. Roofed building is realized through the roof with a vertical stool. The ceiling above the ground floor is designed as a reinforced concrete slab ceiling and above the first floor as the timber.

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