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Kiln drying is the most energy-consuming operation in the industrial production of sawn timber and optimising the process is necessary to improve its efficiency. A key to achieving this is to speed up the drying, but this must not come at the cost of deteriorating the quality of the sawn timber. X-ray computed tomography (CT) can help in increasing the efficiency of the process, as it is a research tool that can be applied to study moisture transport in wood during drying. The moisture content (MC) can indeed be estimated at a sufficiently small spatial scale but many stages of image processing operations are required. This complexity has until now restricted the computation of MC distributions to only one cross-sectional plane of the sawn timber volume, consequently limiting the potential of the method. A milestone of this PhD study work, now at its halfway point and hereby presented as a licentiate thesis, has been to develop a method based on four-dimensional CT (4DCT) for estimating the MC in each volume-element (voxel) from a repetitively CT-scanned volume of sawn timber during a drying process. The development of this method is supposed to result in a strong tool for experimental studies into the further optimisation of the industrial drying process. An image-processing algorithm capable of efficiently estimating MC distributions from 4DCT data was successfully implemented and validated against experimental data. Further processing allows the determination of the moisture gradient (MG) as a time-dependent vector field. Initial studies carried in this doctoral project suggest that it is a relevant parameter for investigating the optimisation of the industrial drying process. The image-processing algorithm, coded in Python software, requires limited preprocessing or parameter tuning, resulting in significantly reduced computational time compared to previous algorithms. The method has been validated, and errors were quantified by performing linear regressions between the CT-estimated MC spatially averaged at a volume of 1 cm3 and gravimetric measurements performed at the same scale. The sources of error were identified as the image processing and the density measurement uncertainty of the CT scanner. The root mean square error of the CT method for a 1 cm3 volume is 3.8 percentage points in average. The method was used to investigate the impact of different drying schedules on the degree of checking of sawn timber. As the MG is one of the driving forces of moisture transport, thus controlling the drying rate, and it triggers cracking, it was the parameter chosen to be studied. The MG was calculated and its evolution was correlated with different drying schedules and regimes. The evolution of MG and checking in the experimental studies suggested that the models for creating kiln schedules in the industry are too conservative, i.e. the drying process can be accelerated without significantly lowering the sawn-timber quality due to cracking. The outcome of this research will lead to a better understanding of moisture transport and drying stresses in sawn timber which will improve drying simulations, providing a strong tool for the optimisation of the industrial drying processes, and ultimately benefitting the sawmilling industry.

Wooden pallets are essential part of the supply chain carrying approximately 80% of all products shipped domestically. The production of pallets is also strongly correlated with the U.S. G.D.P and manufacturing G.D.P. This research was conducted to obtain important information on the market and raw material usage trends in the wooden pallet and container industry from 2019 through 2021. These trends have been compared to historical data that has been collected by Virginia tech and U.S. Forest Service pallet surveys from 1991-2016. This study was conducted by sending out physical and online surveys to 2319 companies who produce and broker wooden pallets and crates. The wooden pallet and container industry produced and estimated 919 million new pallets in 2021 which is an estimated 75% increase since 2016. The 48"x40" pallet size continues to be the dominant new pallet size with a 29% market share. The share of softwood lumber used in the industry steadily increased since 2016 and accounted for 81% of the lumber used in pallet production. The industry used 38.6% percent of the total sawn softwood lumber produced and 37.6% of the total sawn hardwood lumber produced in the U.S. The industry also produced 280 million repaired and remanufactured pallets. This is an estimated 16.4% decrease from previous research conducted in 2016. In 2021 approximately 89% of all recovered wooden pallets are converted to repaired or remanufactured pallets. Approximately 22% of respondents stated that they were not affected by the pandemic. A majority of 51% of respondents stated that they exceeded their 2019 sales, with 12% seeing no change in sales in 2020 compared to 2019. / Master of Science / Wooden pallets are the backbone of the supply chain especially because 80 percent of the products produced in the US are transported on wooden pallets. The number of new wooden pallets produced annually also has a strong correlation to the U.S. manufacturing GDP that further highlights the importance of pallets. This study was conducted to obtain key information about the market trends in the wooden pallet industry from 2019-2021. This data was compared to historical trends researched by Virginia Tech and the U. S. Forest service from 1991-2016. This study was conducted by sending out physical and online surveys to 2319 companies who produce and broker wooden pallets and crates. This data is important so that companies can use it to make better descension by looking at the important modern trends in the industry. The wooden pallet industry continued to trend upward from previous surveys conducted. In 2021, total pallet production increased 40% from 2016 increasing to 1.18 billion. As pallet production increased so did material usage. In 2021 the wooden pallet industry used an estimated 17.9 billion board feet of lumber which is a 95% increase from 2016. As for repaired and recycled pallets there were an estimated 280 million produced in 2021. This is a 16.4% decrease from the previous survey conducted. Though with this decrease approximately 89% of all received pallet cores were either repaired or used during the remanufacturing process. This study also delved into the impacts of the Covid-19 pandemic on the wooden pallet and container industry. The results of the covid section implied that the industry was stable throughout the pandemic. Approximately 22% of respondents stated that they were not affected by the pandemic. A majority of 51% of respondents stated that they exceeded their 2019 sales, with 12% seeing no change in sales in 2020 compared to 2019.

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This dissertation includes two parts: Part I “natural fiber/thermoplastic composites” and Part II “studies of organo-clay synthesis and clay intercalation by epoxy resins”. The use of light weight renewable natural materials instead of heavy mineral-based materials is important to generate lighter materials for sustainable human development. Renewable natural fibers have already been used to reinforce thermosetting and thermoplastic polymer composites. The abundance of hydroxyl groups in natural fibers causes two problems: (1) high water moisture uptake and (2) incompatibility with hydrophobic polymer matrices. Surface modifications have been used to solve these problems. In part I of this dissertation, the modifications of wood fiber/flour by acid chlorides and maleated polypropylene were studied. High density polyethylene (HDPE)/wood flour (WF) composites were investigated in Chapter 1 of Part I. Polypropylene (PP)/WF composites were studied in Chapter 2 of Part I. In Chapter 3 of Part I, kenaf/PP composites were explored. Finally, the effect of carbon nanofibers (CNF) and composite blending processes were studied in Chapter 4 of Part I. Composite flexural properties and water absorption properties were evaluated. Flexural strengths and flexural moduli were obtained by four-point bending tests. Micromorphologies were investigated by scanning electron microscope (SEM). Part II presents studies of organo-clay syntheses and the mechanism of clay intercalation by epoxy resins. Ammonium and imidazolium pillaring agents were synthesized and then used to modify clay. A pillaring agent with epoxy functional groups was also synthesized. Clay intercalation by epoxy resins was affected by the epoxy resin polymerization rate, viscosity and temperature. The diffusion rate of monomers and polymers into and out of clay galleries is a function of temperature and a major factor in intercalation. The clay’s degree of nano dispersion in epoxy composites were investigated by TEM. The clay thermostabilites were studied by TGA.

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No description available.

No description available.

Syftet med den här avhandlingen var att undersöka mekaniska egenskaper hos olika arter av lövträd, och koppla egenskaperna till cell- och cellväggsstrukturen i materialet. Arterna som omfattades av undersökningen var Europeisk asp (Populus tremula), hybridasp (Populus tremula x Populus tremuloides) och ek (Quercus robur). Arterna inom familjen Populus, inklusive den snabbväxande hybridaspen, har på senare tid kommit att användas inom ett stort antal projekt inom genforskningen. Det har i sin tur ökat behovet av noggrannare bestämning av mekaniska egenskaper hos dessa arter. Ek har sedan tusentals år tillbaka varit ett populärt konstruktionsmaterial; något som har resulterat i ett stort antal arkeologiska ekfynd. Konservering av dessa inkluderar ofta dimensionsstabilisering med hjälp av polyetylen-glykol (PEG); en kemikalie som man vet påverkar de mekaniska egenskaperna. I vilken utstäckning detta sker är däremot inte helt klarlagt. Studien på euoropeisk asp och hybridasp inkluderade utveckling av en ny metod för provning av små juvenila prov i grönt tillstånd. Töjningsmätningar gjordes med hjälp av digital speckelfotografering (DSP). Axiell dragstyvhet och draghållfasthet var av speciellt intresse. Sämre mekaniska egenskaper hos hybridaspen korrelerade med medelvärden på densitet, som var lägre för hybriden än för den Europeiska aspen. Ek undersöktes i svällt tillstånd, där svällningen inducerades med hjälp av PEG (molekylvikt 600). Axiell dragstyvhet och draghållfasthet samt radiell tryckstyvhet och ytspänning undersöktes. Töjningsmätningar i axiell riktning gjordes med hjälp av videoextensiometer, medan töjning i radiell riktning gjordes med hjälp av DSP. Övrig karakterisering av materialet inkluderade scanning electron microscopy (SEM), röntgenmikrotomografi och wide angle X-ray scattering (WAXS) för bestämning av mikrofibrillvinkel. Axiell dragstyvhet och draghållfasthet påverkades bara marginellt av PEG-behandlingen. WAXS-mätningarna visade att mikrofibrillvinkeln i materialet var mycket liten. Därigenom blir de mekaniska egenskaperna i axiell riktning till stor del beroende av mikrofibrillerna, vilket samtidigt minimerar den mjukningseffekt som PEG-impregneringen har på cellväggsmatrisen. De mekaniska egenskaperna i radiell kompression påverkades däremot starkt negativt av impregneringen. Detta antogs bero på den försvagande och uppmjukande effekt som PEG:en har på de radiellt orienterade märgstrålarna i veden. / The aim of this work was to investigate the mechanical properties of different hardwood species and relate the properties to the structure at the cellular and cell wall level. The species examined were European aspen (Populus tremula), hybrid aspen (Populus tremula x Populus tremuloides) and European oak (Quercus robur). The Populus species, including the fast-growing hybrid aspen, are used in a large number of projects using transgene technology, which also has raised the demand for a more extensive determination of mechanical properties of the species. Oak have been a popular construction material for thousands of years, esulting in a vast number of archaeological findings. Preservation of these often includes dimensional stabilization by polyethylene glycol (PEG), an impregnation agent which affects the mechanical properties. To which extent is not properly investigated, however. The study on European and hybrid aspen included development of a method for tensile testing of small, juvenile specimens in the green condition, where strain was measured using the digital speckle photography (DSP) technique. Mechanical performance of the species in terms of longitudinal tensile stiffness and strength were of special interest. Inferior mechanical properties of hybrid aspen corresponded well to mean values of density, which were lower for the hybrid aspen compared to European aspen. Oak was examined in the swollen state, where swelling was induced by PEG with molecular weight 600. Longitudinal tensile stiffness and strength as well as radial stiffness and yield strength in compression were compared. Longitudinal and radial strain was measured using video extensiometry and DSP, respectively. Additional characterization of the material included imaging from scanning electron microscopy (SEM), X-ray microtomography and determination of microfibril angle using wide angle X-ray scattering (WAXS). Tensile stiffness and strength in the axial direction were only slightly affected by PEG-impregnation. WAXS measurements showed that microfibril angles were close to zero which implicates that cell wall properties are strongly dependent on the microfibrils, and only marginally influenced by the plasticization effects from PEG on the lignin/hemicellulose matrix. In the radial direction, on the other hand, mechanical performance was strongly decreased by PEG-impregnation. This was believed to originate from softening of rays. / QC 20101105