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  • 1.
    Adamopoulos, Stergios
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Lankveld, Chiel
    Accsys Group, Netherlands.
    Acoustic properties of acetylated wood under different humid conditions and its relevance for musical instruments2018In: Proceedings of the 9th European Conference on Wood Modification 2018, Arnhem, The Netherlands / [ed] Jos Creemers, Thomas Houben, Bôke Tjeerdsma, Holger Militz and Brigitte Junge, The Netherlands: Practicum , 2018, p. 236-243Conference paper (Refereed)
    Abstract [en]

    In musical instrument making, less expensive wood species and materials with good characteristics and acoustical properties can provide potentials to find alternatives to the traditional exotic wood species used today. Modified wood could be such a choice if shows similar sound characteristics to wood coming from endangered and expensive tropical species with problematic commercial availability. In musical instruments, the overall functionality depends on the contribution of wood to different material performance indexes like sound radiation coefficient (R), characteristic impedance (z) and acoustic conversion efficiency (ACE). In this study, the performance indexes were measured for acetylated beech, maple and radiata pine and compared with these obtained for the reference wood materials maple, mahogany, alder and ash. A non-destructive free-free flexural vibration test method was used at constant temperature (20oC) but in different humid conditions- dry (35% RH), standard (65% RH) and wet (85% RH). Dimensional changes in the different humid conditions were also taken in account. Acetylated wood showed lower EMC with higher dimensional stability at each humidity level as compared with the reference wood materials. These properties are considered important factors for making quality musical instruments. Based on the acoustical properties, acetylated wood materials, especially radiata pine, showed good potential for use for musical instruments where specific characteristics of sound are required. However, the other types of acetylated wood can also be used for specific musical instruments.

  • 2.
    Hemmilä, Venla
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Towards low-emitting and sustainable particle and fibreboards: Formaldehyde emission test methods and adhesives from biorefinery lignins2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High volumes, fast production speed, and low material costs have been historically the driving factors of the particle- and fibreboard industries. However, in recent years the fossil-fuel dependency and health issues of the formaldehyde-containing adhesives used in the production have gained attention from both legislators and consumers. The latest example of legislation development is the change that the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety of Germany  (Bundesministerium für Umwelt, Naturschutz und Nukleare Sicherheit) made to their testing method, effectively lowering the formaldehyde emission levels of wood-based panels in Germany from the European emission level of 0.1 ppm (E1, EN 717-1) to 0.05 ppm. As the emission levels of requirements decrease, market opportunities arise for formaldehyde-free bio-based adhesive systems. The aim of this thesis was thus to evaluate the different formaldehyde test methods at low emission levels (<0.05 ppm), and to explore new adhesive alternatives to the formaldehyde and petroleum-based systems used today.

    As formaldehyde emissions decrease, choosing the right measurement method becomes increasingly important. Repeatability and correlation between the main European and American formaldehyde measurement chambers, described in EN 717-1 and ASTM D 6007 standards respectively, were determined. In addition, an alternative fast factory method based on emissions was evaluated, and the effect of reducing the conditioning time before emission measurements was investigated. A literature research was conducted on different bio-based raw materials in order to review their potential, from both scientific and industrial viewpoints, as alternatives to the current petroleum-derived and formaldehyde-based adhesives. Lignin residues from biorefinery processes were chosen for further testing due to their increasing volumes and potential to suit various pathways for adhesive making. Three different biorefinery lignins were compared, and ammonium lignosulfonate was chosen for making adhesives for particleboards by using one petroleum-based and one bio-based crosslinker.

    The main conclusion of the formaldehyde emission part of the thesis was that formaldehyde emissions can be measured both accurately and quickly at low levels using chamber methods, even at factory environment. There was a good correlation between the American D 6007 and European EN 717-1 chamber methods at emission levels <0.05 ppm for both particleboards (r2 = 0.9167) and fibreboards (r2 = 0.9443). Further understanding on the effect of edge-sealing of boards and analytical methods described in the standards was obtained. It was confirmed that a fast chamber method with 1 day conditioning and 15 minutes measuring time could be used for factory formaldehyde control for most board types.

    The bio-based adhesives’ literature review revealed a large amount of studies on different sustainable adhesive systems, some of which seem promising. Both soy protein and tannin were found to be partially commercialized, with certain pre-requisites. Kraft-lignin was especially well researched, but was found to be difficult to use for other applications than partial replacement of phenol in phenol-formaldehyde (PF) adhesives due to poor water solubility and purity. Lignin residues from biorefinery processes were found to be a less studied, growing raw-material source with a lot of potential. Thus, supercritical water hydrolysis lignin (SCWH) and two biorefinery lignosulfonates were chemically and thermally characterized, and evaluated as raw materials for value-added applications, including adhesives. SCWH lignin was found to have more β-R linkages and lower amount of impurities than the lignosulfonates. High amount of phenolic hydroxyl groups indicated that SCWH would be well suited for phenol replacement in PF adhesives. The two lignosulfonates had more aliphatic hydroxyl groups, which can be interesting for other crosslinking reactions than PF. Ammonium lignosulfonate (ALS) was chosen for further evaluation as having slightly better properties than sodium lignosulfonate (SLS). ALS was combined with one bio-based crosslinker, furfuryl alcohol (FOH), and one synthetic crosslinker, 4,4’-diphenylmethane diisocyanate (pMDI), and tested as particleboard adhesive. Although in veneer tensile shear strength testing the crosslinkers worked equally well, pMDI provided significantly better results in particleboards. In addition, higher emissions than what can be expected from wood particles alone were detected from the particleboard samples crosslinked with FOH, even though FOH can be classified as non-formaldehyde added adhesive system. Further research is needed to elucidate how much the lignin contributes to the final adhesion strength when it is used together with pMDI.

    This thesis has provided new insights on formaldehyde emissions and bio-based adhesives towards healthier and more sustainable particle- and fibreboards. It has been proven that formaldehyde emissions can be measured accurately at emission levels of wood, enabling comparisons of formaldehyde-free systems. Formaldehyde-free adhesives based on a biorefinery lignin type and pMDI showed promising results for particleboards. However, these results need to be improved by different modifications of the lignin in order to bring the adhesive system to the economical and performance level required by the particleboard industry.

  • 3.
    Hemmilä, Venla
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Linnaeus University.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ahmed, Sheikh Ali
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Ammonium Lignosulfonate Adhesives for Particleboards with pMDI and Furfuryl Alcohol as Crosslinkers2019In: Polymers, ISSN 2073-4360, E-ISSN 2073-4360, Vol. 11, no 10, p. 1-17, article id 1633Article in journal (Refereed)
    Abstract [en]

    Tightening formaldehyde emission limits and the need for more sustainable materials have boosted research towards alternatives to urea-formaldehyde adhesives for wood-based panels. Lignin residues from biorefineries consist of a growing raw material source but lack reactivity. Two crosslinkers were tested for ammonium lignosulfonate (ALS)—bio-based furfuryl alcohol (FOH) and synthetic polymeric 4,4′-diphenylmethane diisocyanate (pMDI). The addition of mimosa tannin to ALS before crosslinking was also evaluated. The derived ALS adhesives were used for gluing 2-layered veneer samples and particleboards. Differential Scanning Calorimetry showed a reduction of curing temperature and heat for the samples with crosslinkers. Light microscopy showed that the FOH crosslinked samples had thicker bondlines and higher penetration, which occurred mainly through vessels. Tensile shear strength values of 2-layered veneer samples glued with crosslinked ALS adhesives were at the same level as the melamine reinforced urea-formaldehyde (UmF) reference. For particleboards, the FOH crosslinked samples showed a significant decrease in mechanical properties (internal bond (IB), modulus of elasticity (MOE), modulus of rupture (MOR)) and thickness swelling. For pMDI crosslinked samples, these properties increased compared to the UmF. Although the FOH crosslinked ALS samples can be classified as non-added-formaldehyde adhesives, their emissions were higher than what can be expected to be sourced from the particles. 

  • 4.
    Hosseinpourpia, Reza
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Mai, Carsten
    Georg-August-University Göttingen, Germany.
    Taghiyari, Hamid Reza
    Shahid Rajaee Teacher Training University, Iran.
    Properties of medium-density fibreboards bonded with dextrin-based wood adhesive2019In: Wood research, ISSN 1336-4561, Vol. 64, no 2, p. 185-194Article in journal (Refereed)
    Abstract [en]

    This study focuses on manufacturing of medium density fibreboard (MDF) panels bonded with dextrin-based wood adhesive and crosslinked in situ with various weight ratios of synthetic (e.g., polymeric-methane diphenyl-diisocyanate, pMDI) or bio-based (e.g., glyoxal) crosslinkers. The physical and mechanical properties of the panels were evaluated and compared with those from panels without crosslinker (control). Modulus of rupture (MOR) and internal bond (IB) strength of the MDF panels were considerably increased by increasing the crosslinkers’ content. While, slight improvements were observed in modulus of elasticity (MOE) of the panels as a function of crosslinker type and content. Addition of crosslinkers clearly reduced the thickness swelling (TS) and water absorption (WA) of the panels, whereas, the panels with pMDI showed superior performances than the control and glyoxal added ones within 4 h and 24 h immersion in water. The results indicate the potential of dextrin as wood panel adhesive along with the use of appropriate crosslinkers.

  • 5.
    Jiang, Wen
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Kumar, Anuj
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. Natural Resources Institute Finland (Luke), Finland.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Liquefaction of lignocellulosic materials and its applications in wood adhesives — A review2018In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 124, p. 325-342Article in journal (Refereed)
    Abstract [en]

    Liquefaction, a useful method of turning whole biomass into liquids, provides advantages for energy andpolymers and finds applications in many sectors. This paper reviews the different liquefaction technologies andrecent advances in the development of sustainable wood adhesives. Current liquefaction technologies includehydrothermal liquefaction (HTL) and moderate acid-catalyzed liquefaction (MACL). HTL produces bio-oils asprimary products, and solid residues and gases as by-products. MACL depends on the solvent types used, whichare grouped to polyhydric alcohols and phenols. Bio-polyols from alcohol liquefaction, phenolated biomass fromphenol liquefaction and phenolic compounds rich-HTL bio-oils have been used in the production of liquefiedbiomass-based adhesives, which have shown competitive properties but face challenges for industrial uses. Yet, abetter understanding of reaction pathways and optimization of the liquefaction processes is needed.

  • 6.
    Kroon, Martin
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Crack Growth in Low-density Polyethylene2018In: Presented at EMMC16, European Mechanics of Materials Conference in Nantes, France, 26-28 March, 2018, 2018Conference paper (Refereed)
  • 7.
    Kroon, Martin
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Andreasson, Eskil
    Tetra Pak.
    Olsson, Pär
    Malmo University.
    Modelling of Damage and Crack Growth in Semi-crystalline Polymers2018In: Presented at International Conference on Plasticity, Damage and Fracture 2018, Puerto Rico, Neat press , 2018Conference paper (Refereed)
    Abstract [en]

    Crack growth in semi-crystalline polymers, represented by polyethylene, is considered. The material considered comes in plates that had been created through an injection-molding process. Hence, the material was taken to be orthotropic. Material direction were identified as MD: molding direction, CD: transverse direction, TD: thickness direction. Uniaxial tensile testing was performed in order to establish the direction-specific elastic-plastic behaviour of the polymer. In addition, the fracture mechanics properties of the material was determined by performing fracture mechanics testing on plates with side cracks of different lengths. The fracture mechanics tests were filmed using a video camera. Based on this information, the force vs. load-line displacement could be established for the fracture mechanics tests, in which also the current length of the crack was indicated, since crack growth took place. In parallel to the experimental testing, an anisotropic plasticity model for finite strains was developed, which accounts for orthotropic elasticity and orthotropic plastic yielding and hardening. That plasticity model was implemented as a user subrouting in Abaqus. The crack growth experiments were then simulated using Abaqus, using the implemented plasticity model in combination with a damage model. Different types of crack initiation and growth criteria were explored, and the force-displacement-crack length data from the experiments could be well reproduced. Furthermore, the direction-specific work of fracture had been established from the experiments and these energies could be compared to the values of the J-integral from the simulations for the different crack lengths.

  • 8.
    Kroon, Martin
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Andreasson, Eskil
    Tetra pak;Blekinge Technical University.
    Petersson, Viktor
    Tetra pak.
    Olsson, Pär
    Malmö University;Lund University.
    Experimental and numerical assessment of the work of fracture in injection-moulded low-density polyethylene2018In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 192, p. 1-11Article in journal (Refereed)
    Abstract [en]

    The fracture mechanics properties of injection-moulded low-density polyethylene (LDPE) sheets were investigated both experimentally and numerically. The total work of fracture was determined experimentally, by means of fracture mechanics testing of sheets of injection-moulded LDPE with side cracks of different lengths. A multi-specimen method, proposed by Kim and Joe (1987), was employed. The total work of fracture was estimated to 13 kJ/m(2). The experiments were simulated numerically using the finite element method. Crack growth was enabled by inclusion of a cohesive zone, and the constitutive response of this zone was governed by a traction-separation law. The local (or essential) work of fracture was estimated through numerical analyses, where the initiation of crack growth was simulated and the outcome was compared to the experimental results. The local (i.e. essential) work of fracture was estimated to 1.7 kJ/m(2), which is consistent with previous experimental measurements for the material in question. The total work of fracture, retrieved from the present experiments, agreed well with the far field values of the J-integral in the numerical analyses.

  • 9.
    Kumar, Anuj
    et al.
    Czech Technical University in Prague, Czech Republic.
    Petrič, Marko
    University of Ljubljana, Slovenia.
    Kričej, Borut
    University of Ljubljana, Slovenia.
    Žigon, Jure
    University of Ljubljana, Slovenia.
    Tywoniak, Jan
    Czech Technical University in Prague, Czech Republic.
    Petr, Hajek
    Czech Technical University in Prague, Czech Republic.
    Škapin, Andrijana Sever
    Slovenian National Building and Civil Engineering Institute, Slovenia.
    Pavlič, Matjaž
    University of Ljubljana, Slovenia.
    Liquefied-Wood-Based Polyurethane–Nanosilica Hybrid Coatings and Hydrophobization by Self-Assembled Monolayers of Orthotrichlorosilane (OTS)2015In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 3, no 10, p. 2533-2541Article in journal (Refereed)
    Abstract [en]

    We have produced hybrid liquefied-wood-based polyurethane (LW-PU) and LW-PU/nanosilica hybrid coatings for wood substrates. The prepared hybrid polyurethane coatings were hydrophobized by self-assembled monolayers of orthotrichlorosilane (OTS) via a sol–gel dipping process. The nanosilica addition into the LW-PU system enhanced the physical properties of coatings like surface hardness and stability toward cold liquids. The OTS hydrophobized coatings were characterized by Fourier transforms infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA). The surface became hydrophobic as the contact angle (CA) for the water droplet on a modified hybrid coating was ∼115° and very stable. The FTIR, SEM, and EDS analysis confirmed the formation of OTS monolayers on hybrid coatings.

  • 10.
    Kumar, Anuj
    et al.
    Natural Resources Institute Finland (Luke), Finland.
    Ryparová, Pavla
    Czech Technical University in Prague, Czech Republic.
    Hosseinpourpia, Reza
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Prošek, Zdeněk
    Czech Technical University in Prague, Czech Republic.
    Žigone, Jure
    Czech Technical University in Prague, Czech Republic.
    Petrič, Marko
    University of Ljubljana, Slovenia.
    Hydrophobicity and resistance against microorganisms of heat and chemically crosslinked poly(vinyl alcohol) nanofibrous membranes2019In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 360, p. 788-796Article in journal (Refereed)
    Abstract [en]

    Poly(vinyl alcohol) (PVA) is a water-soluble, semi-ionic and biocompatible polymer with excellent chemical and thermal stability. The chemical crosslinking of PVA membrane improve its stability towards humidity and water. In the present work, PVA nanofibrous membranes were fabricated using roller electrospinning techniques. The prepared membranes were crosslinked by heat treatment, glutaraldehyde dipping, and glutaraldehyde vapour. Furthermore, octadecyltrichlorosilane (OTS) treatment was used for hydrophobization of the crosslinked membranes. The prepared crosslinked membranes were analysed by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The hydrophobization of PVA nanofibrous membranes were analysed by employing optical goniometer and auto-dynamic vapour sorption (AVS) techniques. Further, the PVA membranes were tested against algae and mould growth at in-vitro laboratory conditions. The SEM and FTIR results revealed significant differences in the morphology of the PVA nanofibrous membranes and in chemical bond formation due to crosslinking treatments. Water contact angle and AVS data confirmed a hydrophobization of PVA membranes by the treatments.

  • 11.
    Kumar, Anuj
    et al.
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Vlach, Tomáš
    Czech Technical University in Prague, Czech Republic.
    Ryparovà, Pavla
    Czech Technical University in Prague, Czech Republic.
    Sever Škapin, Andrijana
    Slovenian National Building and Civil Engineering Institute, Slovenia.
    Kovač, Janez
    Jožef Stefan Institute, Slovenia.
    Adamopoulos, Stergios
    Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.
    Hajek, Petr
    Czech Technical University in Prague, Czech Republic.
    Petrič, Marko
    University of Ljubljana, Slovenia.
    Influence of liquefied wood polyol on the physical-mechanical and thermal properties of epoxy based polymer2017In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 64, p. 207-216Article in journal (Refereed)
    Abstract [en]

    Epoxy resins are mostly produced from petroleum-based bisphenol A and epicholorhydrin. Bisphenol A is synthesized from non-renewable petroleum-based phenol and acetone. Biomass derived epoxy-based polymers (EBPs) are becoming the most promising alternative for petroleum-based counterparts, but still these biomass-based EBPs have inferior properties. In the present work, two types of epoxy resins were prepared with different weight percentages of resin (bisphenol A) and hardener. They were then modified with different weight percentages of liquefied wood from spruce sawdust. The derived EBPs were analysed in terms of tensile strength and tensile modulus, fractured surface morphology, thermal stability, long-term water adsorption and resistance to brown-rot fungus decay. The results revealed that the percentages of hardener and liquefied wood significantly influenced the overall properties of the EBPs.

  • 12.
    Nicholls, Ian A.
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences. Uppsala Univ.
    Chavan, Swapnil
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Golker, Kerstin
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Karlsson, Björn C. G.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences. Bioorganic & Biophysical Chemistry Laboratory.
    Olsson, Gustaf D.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Rosengren, Annika M.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Suriyanarayanan, Subramanian
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Wiklander, Jesper G.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
    Theoretical and Computational Strategies for the Study of the Molecular Imprinting Process and Polymer Performance2015In: Molecularly Imprinted Polymers in Biotechnology / [ed] Mattiasson, B. & Ye, L., Berlin: Springer, 2015, p. 25-50Chapter in book (Refereed)
    Abstract [en]

    The development of in silico strategies for the study of the molecular imprinting process and the properties of molecularly imprinted materials has been driven by a growing awareness of the inherent complexity of these systems and even by an increased awareness of the potential of these materials for use in a range of application areas. Here we highlight the development of theoretical and computational strategies that are contributing to an improved understanding of the mechanisms underlying molecularly imprinted material synthesis and performance, and even their rational design.

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