In this work a model system has been developed to quantitatively study esterification of cellulosic material during drying and heating in which solid-state conditions can be said to predominate. The formation of ester cross-links in cellulosic or lignocellulosic composite materials during drying and heating is of interest for production of paper and wood composite boards, for wood modification and in giving cotton materials improved characteristics. The results support the hypothesis that direct ester formation, without anhydride intermediate, occurs between carboxylic acids of suitable structure and cellulosic hydroxyls at elevated temperatures even after such short reaction times as 5 minutes. Ester formation has been observed at temperatures ranging from 90°C to 180°C. Another important conclusion is that a hydroxy or keto group in alpha position of the carboxylic acids seems to favour ester formation. A critical parameter for ester formation is pH, and the results indicate that pH 5-6. In the experiments, low moisture content, higher temperatures and longer reaction times also favour ester formation, with some exceptions. Another interesting finding is that three pyrrolidine structures are produced after esterification and aminolysis of 2- ketobutyric acid. One of the structures indicates that 2-ketobutyric acid is reactive in two positions and could therefore be a potential cross- linker. Esterifications of five structurally different carboxylic acids-2(R)- hydroxybutyric acid, 2-ketobutyric acid, 3-hydroxybutyric acid, hexanoic acid and veratric acid have been studied. The carboxylic acids and moisture were added to ordinary cellulosic filter paper. Samples were heated at temperatures ranging from 22°C to 180°C between 5 and 45 minutes. Quantitative analysis of ester formation, in this case between the monocarboxylic acids and the cellulose's hydroxyl groups, was performed using aminolysis/gas chromatography. / <p>Godkänd; 2006; 20070109 (haneit)</p>

Computed tomography (CT) can be used to study wood-water interactions in differentways, such as by determining wood moisture content (MC). The determination of MCrequires two CT images: one at the unknown moisture distribution and a second one ata known reference MC level, usually oven-dry MC. The two scans are then compared.If the goal is to determine the MC in local regions, when studying moisture gradients forinstance, wood shrinkage must be taken into account during the data processing of theimages. The anisotropy of wood shrinkage creates an obstacle, however, since theshrinkage is not uniform throughout the wood specimen. The objective of this thesis was to determine the shrinkage in wood in each pixel of aCT image. The work explores two different methods that estimate from CT images, thelocal shrinkage of a wood specimen between two different MC levels. The first methoddetermines shrinkage for each pixel using digital image correlation (DIC) and isembedded in a wider method to estimate the MC, which is the parameter verifiedagainst a reference. It involves several steps in different pieces of software, making ittime-consuming and creating many sources of possible experimental errors. The MCdetermined by this method showed a strong correlation with the gravimetricallymeasured MC, showing an R2 of 0.93 and the linear regression model predicted MCwith a RMSE of 1.4 MC percentage points. The second method uses the displacement information generated from the spatialalignment of the CT images in order to compute wood shrinkage in the radial andtangential directions. All the required steps are combined into a single computeralgorithm, which reduces the sources of error and facilitates the process. The RMSEbetween this method and the determination of shrinkage measured in the CT imagesusing CAD has shown acceptable small differences. Both methods have proved to be useful tools to deal with shrinkage in different ways byusing CT images. In one case MC was successfully estimated, being the shrinkagecalculation a necessary step in the process, and in the other case the radial and tangentialshrinkages were successfully estimated for each pixel. Nevertheless, the difficulty incomparing the shrinkage coefficient calculated for local regions with a reference valuesuggest that more research must be carried out in order to be able to draw reliableconclusions.

The interest in Wood-thermoplastic composites (WPCs) has increased during the last decades. WPCs are commonly used as building material for decking and railing because of its low need of maintenance. Wood is a renewable resource of good mechanical properties and this make wood fibers interesting to use as reinforcement in a thermoplastic composite. A drawback with this type of composite is the poor long-term mechanical properties which limit its field of applications. The objective of this work was to optimize the process and understand structure-property relations of silane-crosslinked WPCs produced in a one-step reactive extrusion. The specific goal of crosslinking the composite was to improve the interfacial strength and stabilize the polymer matrix in order to improve these composites long-term mechanical properties.Silane-crosslinked WPC was produced by adding wood flour, polyethylene and a silane-peroxide solution to a compounding extruder. The composites were thereafter conditioned in different environments to promote the formation of silane-crosslinks. Parameters like wood flour moisture content, amount/composition of silane-peroxide solution and different general types of polyethylene was studied and related to the efficiency of the process.It was found that silane-technology applied to WPCs can be optimized in terms of processability and achieved property improvements. All crosslinked composites in this study have improved in strength, toughness and creep resistance but it was shown that the tested parameters have affect on both processing and properties. A gentle use of peroxides in the process was concluded to be positive for both processability and resulting property improvements. The unintentional crosslinking in the extrusion process is a drawback but was limited by lower peroxide concentrations. The use of low density polyethylene as polymer matrix lead to twice as high crosslinking rate compared to a high density polyethylene matrix. However, too excessive moisture uptake in the composites appears to lower the efficiency of crosslinking. Future studies should evaluate long-term load behavior more thoroughly and also investigate the conditioning step more carefully. / Godkänd; 2009; 20090922 (grubb)

Wood as a raw material is useful for many purposes even though some properties are less than optimal, for example, dimensional stability and durability. These characteristics can however be improved by different treatment methods. Environmental awareness has led to an increased demand for environmentally friendly processes like thermal modification that does not add any chemicals to the wood in contrast to, for example, CCA-impregnated wood.This thesis mainly focuses on thermally modified wood from species such as pine, spruce and birch. The thesis present studies of physical attributes such as color, and chemical analysis of water-soluble compounds and degradation products. Treatment intensity is compared between two different industrial processes referred as Thermowood and WTT, which use respectively superheated steam and pressurized steam as heating media.Thermal modification processes darken the color of wood throughout its cross-section. The formation of darker color is related to a degradation processes that takes place during thermal modification. During thermal modification wood is exposed to temperatures between 160 - 220°C, and the temperature causes physical and chemical transformations that change some of the wood properties. Dimensional stability and durability are typically improved, but mechanical strength properties are usually negatively affected by the treatment.The studied wood species were Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and Birch (Betula pendula L.). Treatments using pressurized steam were carried out under temperatures of 160°C, 170°C and 180°C, and treatments using superheated steam at normal air pressure were carried out at temperatures of 190°C and 212°C. Results showed that similar L* (lightness) can be reached at lower temperatures using pressurized steam compared to superheated steam. The residual moisture content after completed thermal modification was approximately 10% higher in wood treated with the pressurized steam process. It was found that despite an approximately 25°C lower treatment temperature, birch modified in pressurized steam was more acidic compared to birch modified in superheated steam. This will likely have further consequences, requiring more research concerning surface treatment and fixation.The thesis also includes the development of an industrial-quality control procedure based on nondestructive color measurements verified in industrial environment. Treatment intensity in industry is today certified by inspection of documented process schedule and measuring the temperature and time of the process. Quality control in this context refers to the measurement of wood color as an indirect measure of treatment intensity. The color in our study was measured using L*C*H color space. The study shows that it is possible for quality control purposes to measure the color of thermally modified wood from the surfaces of planed boards instead of sawdust or board cross sections that have been used in other studies.The thesis has a final section about academia-industry collaboration that describes how trust building was established through a fruitful relationship involving academia and regional wood products industry in northern Sweden. The study presents an example of a successful research and development alliance between university and a group of small- and medium-sized enterprises (SMEs). This alliance has been a great example on international collaboration involving researchers originating from Finland, China, Bangladesh, Spain, Russia and Sweden. Through an in-depth multi-year study of how the research cooperation developed, the paper describes how the involved companies successfully entered into a new segment of the market. / För godkännande; 2016; 20160314 (olahof); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Ola Dagbro Ämne: Träfysik/Wood Physics Avhandling: Studies on Industrial-Scale Thermal Modification of Wood Opponent: Associate Professor Lidia Gurau, Faculty of Wood Engineering, Transilvania University, Brasov, Romania. Ordförande: Professor Diego Elustondo, Avd för träteknologi, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå. Tid: Torsdag 16 juni, 2016 kl 10.00 Plats: Luleå tekniska universitet, Campus Skellefteå

Godkänd; 1998; 20070404 (ysko)

Improved understanding of moisture and mechanical behaviour is an international objective for wood drying research. The main objective of this licentiate thesis work was to develop an experimental method suitable for collecting valuable response data related to the moisture and mechanical behaviour of drying wood. Another objective was to provide an example on how multivariate methods can be used to analyse response data. A method for simultaneous non contact measuring of two dimensional surface deformations and interior densities have been developed. This was done using Digital Speckle Photography, DSP, and X-ray Computerised Tomography (CT). Displacements and densities were used for calculation of strains and moisture contents using a custom software developed in Matlab. Experimental tests of the measuring method were made on cross sections of Scots pine. The following accuracy was stated for different properties: - Displacements measured with DSP could be measured with a random error down to 0.01 pixels. A more typical calculated displacement error of approximately 10 micrometres, was found in paper I. - Strains derived from the displacements had a maximal error of 1.11 mstrain in an experimental test in paper II. - Accuracy in density measurements was expected to be less than +-6 kg/m3 for wet wood with moisture contents ranging from 6-100% and less than +-2 kg/m3 in dry wood, at a significance level of 0.05. This was estimated for a 2x2x1.5 mm3 measuring volume. - Moisture content measuring accuracy was estimated by simulations in paper II, which resulted in a measuring accuracy of +-1.8% moisture content at a significance level of 0.05 in a measuring volume with the approximate size of 2x2x1.5 mm3. A multivariate analysing method has been used to present an example on multivariate modelling of shrinkage behaviour in Radiata pine. The method was found to be an easy-to-use tool and useful for valid prediction of radial, tangential, longitudinal and volume shrinkage in the moisture range between 0% and 22% moisture content of the studied wood. The method also proved to be effective for untangling relationships between variables and generating information out of data. Finally, it can be stated that the developed measuring technique and the tested multivariate analysing method will be of use to improve the understanding of the behaviour of drying wood, focusing on moisture and mechanical properties. / Godkänd; 2002; 20070222 (ysko)

Recently, the use of bio-based nanomaterials has attracted much interest in medical applications due to their cytocompatibility, good moisture stability, good mechanical properties, hydrophilic surfaces and their ability to form porous structures. The aim of this work is to develop porous nanocomposites based on nanochitin and nanocellulose with controlled pore size and porosity in order to facilitate cell growth and interconnectivity and to investigate their potential in wound dressing and cartilage regeneration. The first and second study focus on the electrospinning of chitosan-based nanocomposite mats reinforced with chitin nanocrystals (ChNC) and cellulose nanocrystals (CNC) with different surface characteristics for wound dressing. Electrospinning processing resulted in porous mats of fibers with diameters in the range of 223 to 1240 nm. The microscopy studies showed that diameter of the electrospun fibers decreased with the inclusion of both types of nanocrystals. The addition of nanocrystals as well as crosslinking had a positive impact on the mechanical performances of the mats. The tensile strength and tensile modulus of the mats were the highest with the addition of ChNC due to better compatibility with the matrix and increased further (tensile strength of 64.9 MPa and the modulus of 10.2 GPa) after crosslinking. Furthermore, surface charges of cellulose nanocrystals isolated with different hydrolysis process had a significant impact on the electrospinning solution properties as well as properties of the resulting fibers. The water vapor transmission rate and O2/CO2 permeability of the electrospun mats as well as cytocompatibility towards adipose derived stem cells were considered favorable for wound dressing.Investigated in the third study were nanofibrous porous scaffolds created via freeze-drying for use in cartilage repair. Cellulose nanofibers were used as reinforcement in a matrix of gelatin and chitosan and crosslinked using genipin. The scaffolds showed interconnected pores up to 250 µm and the pore walls had nanoscaled roughness. Compression modulus of the scaffolds was in the range of 1-3 MPa, which decreased significantly when tested in phosphate buffered saline (PBS) at 37°C. The moisture uptake was in the range of 1000 - 3000 wt %, due to moisture trapped in the pores. These scaffolds showed potential in cartilage repair because their high porosity (≈ 95%) and mechanical performance is favorable for cell attachment and extracellular matrix (ECM) production as well as its cytocompatibility towards chondrocytes.The work in all three studies showed that fully bio-based porous nanocomposites tailored using polysaccharide nanoparticles as reinforcements in biopolymer matrices have excellent potential in biomedical products and implants.

The interest in wood-polymer composites and their use in different applications has been growing over the last 10-15 years. Environmental issues and demands on lower material costs are the driving forces behind the increasing use of renewable materials such as wood and other natural fibres as reinforcement in polymer composites. Wood flour consisting of small wood particles is currently used as the main wood raw material in commercial wood-polymer composites. However, the reinforcing potential of wood flour is limited. A better reinforcement could be achieved by using wood fibres with a higher aspect ratio as raw material, but individual fibres are seldom used in composite manufacturing due to processing problems and high cost. Therefore, the objective of the work was to study the possibility to use wood chips as raw material and separate individual fibres with higher aspect ratios from the wood chips during the composite manufacturing process. First, the effect of the extrusion process only on wood raw material was studied without a matrix polymer, and then composites using polypropylene as matrix were made. The main goal was to produce wood particles/fibres with high aspect ratio during the manufacturing of wood polymer composites. The effects of extrusion parameters, different screw configurations, raw materials and raw material pre-treatments were evaluated. The size of the separated wood particles and fibres was measured using optical fibre analysis methods. Microstructure of wood particles as well as the fractured surfaces of prepared composites were examined using electron microscopy. The mechanical properties of the composites were measured using flexural and impact testing. The results showed that wood chips can be used as raw material in a one-step manufacturing process of wood-polymer composites. Also, individual fibres with a higher aspect ratio than wood flour were separated from the wood chips with suitable processing conditions

The use of natural components in nanocomposites has continuously increased, due to environmental problems that are growing day by day. The use of bio-residues from forest industries to develop new materials will not only alleviate ecological problems but also affect the economy of forest industries positively.The aim of this work was to characterize cellulose nanowhiskers isolated from two different industrial bio-residues, one from bioethanol production and another from specialty cellulose production. Furthermore, the structure and permeability of thin films made of these nanowhiskers were studied. In the first study, the characteristics of nanowhiskers isolated from bioethanol residue were compared with nanowhiskers from microcrystalline cellulose (MCC). The nanowhiskers from ethanol residue had lower surface charge compared with whiskers obtained from MCC when analyzed by conductometric titration. The AFM microscopy showed that both cellulose nanowhisker suspensions presented individualized whiskers with diameters less than 10 nm. Nanowhiskers from ethanol residue showed higher relative crystallinity than the nanowhiskers from MCC, and the films made from both whiskers showed transparency in visual light. In addition, the nanowhiskers extracted from bio-residue were more thermally stable than the whiskers extracted from MCC, having a higher degradation onset temperature and maximum degradation temperature.In the second study, nanowhiskers isolated from two different bioresidues were compared. It was seen that both nanowhiskers suspensions (reject cellulose and ethanol residue) exhibited flow birefringence. Transmission electron microscopy study showed that the nanowhiskers extracted from the reject cellulose were slightly longer (377 nm) than the ones extracted from the ethanol residue (301 nm). The casted films of nanowhiskers from reject cellulose showed a stronger interference in the UV and visible region, compared with the other films. The comparative crystallinity was higher for reject cellulose nanowhiskers than for ethanol residue whiskers. Moreover, the thermal stability was slightly higher for the ethanol residue whiskers than for the reject cellulose whiskers. In the last study, cellulose nanowhiskers were isolated from the reject cellulose using hydrochloric and sulphuric acid hydrolysis processes with a aim to obtain different surface characteristics. Sulfuric acid whiskers had higher surface charge than the hydrochloric acid whiskers. Thin spin-coated films with two different configurations were prepared; one with alternate layers of poly(allylamine hydrochloride) (PAHCl) and cellulose nanowhiskers, and the second one with a single layer of PAHCl coated with 25 layers of whiskers. In addition, the film roughness, and surface charge of the whiskers was shown to increase the hydrophilic behavior of the films, being highest for a single layer of PAHCl coated with cellulose nanowhiskers. The gas permeability was measured and the coefficient was highest for hydrogen (H2) followed by helium (He), oxygen, (O2) and carbon dioxide (CO2) and nitrogen (N2). It was observed that the surface charge did not affect the gas permeability of the films and did not display selective gas barrier. The results showed that CNW can be extracted from ethanol residue and reject cellulose, and that these whiskers had similar characteristics as nanowhiskers obtained from other non-residual sources. This work has demonstrated that bio-residues can potentially be used as a source of new nanosize materials, thereby increasing the value of the forest resources.

In recent years, composites made from natural fibers based on cellulose have received increasing attention since they have a low environmental impact and good mechanical properties. However, these fibers are short and discontinuous and the conventional spinning techniques used for these fibers results in continuous yarns with mechanical properties considerably lower than that of the single fibers. The aim of this work was to prepare continuous fibers where nano-sized cellulose crystals and cellulose nanofibers were used to improve the fiber properties. Two different strategies have been used to reach this aim. In the first study, bio-based fibers of cellulose acetate butyrate (CAB) and cellulose nanocrystals (CNC) using triethyl citrate (TEC) as plasticizer were prepared by melt spinning. Two different dispersion techniques were studied. In the first technique, the water content of the CNC suspension was reduced and exchanged to ethanol using centrifugation. In the second, the water in the CNC suspension was completely exchanged to ethanol by a sol-gel process. Results showed that tensile modulus and tensile strength of the nanocomposite fibers produced with the first technique were lower than CAB-TEC fibers, but the fibers produced by the sol-gel process showed an increase in the tensile modulus and had no decrease in the strength. Optical microscopy of the fibers indicated less aggregations in the sol-gel prepared materials. The results indicate that the sol-gel process is enhancing the dispersion of cellulose nanocrystals and can be a suitable way to prepare nanocomposite fibers. The second study is an extension of the first study. Here the effect of weight concentration of CNC and fiber drawing was studied. The microscopy studies showed that the addition of CNC in CAB resulted in defect-free and smooth fiber surfaces. An addition of 10 wt% CNC enhanced the storage modulus and increased the tensile strength and Young’s modulus. Fiber drawing improved the mechanical properties further. In addition, a micromechanical model of the composite material was used to estimate the stiffness and showed that theoretical values were exceeded for the lower concentration of CNC but not reached for the higher concentration. In conclusion, this dispersion technique combined with melt spinning can be used to produce all-cellulose nanocomposites fibers and that both the increase in CNC volume fraction and the fiber drawing increased the mechanical performance. In the third study a different strategy was used. Here low cost and environmentally friendly continuous fibers of native cellulose were prepared by dry spinning an aqueous suspension of cellulose nanofibers (CNF). The CNF were extracted from banana rachis, a bio-residue from banana cultivation in Columbia. The effect of spinning rate and CNF concentration on the mechanical properties of the fibers were investigated. The results showed that there was a relationship between the spinning rate and concentration. The modulus of the fibers was increased from 7.7 to 12.6 GPa and the strength increased from 131 to 222 MPa when the lowest concentration and highest speed was used. This improvement is believed to be due to an increased orientation of the CNF in the fiber. A minimum concentration of 6.5 wt% was required for continuous fiber spinning. However, this relatively high concentration is thought to limit the orientation of the CNF in the fiber. The process used in this last study has a good potential for up-scaling providing a continuous fiber production with well-controlled speed but further work is required to increase the orientation and subsequently the mechanical properties.The results from these three studies shows that it is possible to spin continuous fibers where nanocellulose is used as a reinforcing agent. It is also shown that the dispersion and alignment of the nanocellulose plays a key role in improving the mechanical properties.