Combinations of wood and metal are interesting hybrid composite materials, joining together the low density of wood with the stiffness and strength of metals. Different types of adhesives are used to ...connect wood and metal elements, but the compatibility between adhesives used and load-bearing materials must be sufficient, which often is challenging. In adhesive bonding technology, surface treatments are a crucial step in the process. In this study, an atmospheric plasma discharge was employed to enhance the adhesion strength of joints between common beech (
Fagus sylvatica
L.) wood, metals (steel and aluminum alloy), and four different types of adhesives. The optical properties of plasma discharges and its influence on treated substrates’ surface morphology depended on the inherent properties of the treated materials. X-ray photoelectron spectroscopy revealed the surface oxidation of all the materials after plasma treatment. Consequently, the surface free energy of all materials increased as well. The positive effect of the plasma treatment on the tensile shear strength of single-lap joints shows a high potential of atmospheric plasma treatment technology for enhancement of adhesives strength of joints combining wooden elements, wood and steel, or wood and aluminum alloys. In addition to that, expensive epoxy and polyurethane adhesives could be replaced by more affordable polyvinyl acetate and melamine-urea-formaldehyde adhesives, and still perform at equal levels if the plasma was applied prior to bonding.
The development of a simple surface barrier discharge plasma device is presented to enable more widespread access to and utilization of plasma technology. The application of the plasma device was ...demonstrated for pretreatment of wood prior to application of protective coatings for outdoor usage. The coatings' overall performance was increased, showing a reduction or absence of cracking due to weathering on plasma-pretreated specimens. Moreover, after ten months of outdoor weathering, the plasma-pretreated specimens showed fewer infections with biotic factors and improved adhesion performance in cross-cut tests, while the surface gloss performed independently from plasma pretreatment. In contrast to that, plasma-pretreated specimens were slightly more prone to discoloration due to outdoor weathering, whereas the plasma pretreatment did not impact the initial color after coating application.
Graphic abstract
In the process of wood bonding, the usage of aged and inactivated wooden elements can cause a reduction in mechanical properties of products containing wood-adhesive joints. Treating wood with an ...atmospheric air plasma represents a sophisticated technique for surface activation. With this regard, to enhance the bondability of normal beech wood (
Fagus sylvatica
L.) with urea-formaldehyde (UF) adhesive, a dielectric barrier discharge plasma in floating electrode configuration was implemented. In this study, fresh and aged wood specimen both, untreated and plasma treated, were investigated. X-ray photoelectron spectroscopy revealed promotion of carbon-rich species with ageing, but generation of a new functional oxygen-containing functional groups after plasma treatment. Microscopic observations with scanning electron microscope showed no obvious changes in the wood structure after plasma treatment. Surface oxidation consequently improved the wettability of the wood surface with water and UF adhesive. However, this enhanced wettability slightly diminished over time. As shown with dynamic mechanical analysis, the rheological properties of the UF adhesive in wood-adhesive joints were not affected by aging nor by plasma treatment. The positive influence of plasma treatment and negative impact of substrate ageing to the shear strengths of wood lap-joints were determined using an automated bonding evaluation system. Similarly, the negative effect of wood ageing and the positive effect of plasma pre-treatment were reflected in the bending strengths of the produced laminated veneer lumbers. Results showed that plasma treatment of beech wood improves the bonding performance of both fresh and aged wood.
Graphic abstract
Trdota predstavlja merilo odpornosti lesa proti prodiranju tršega telesa v njegovo notranjost in pogosto pogojuje uporabnost izbrane vrste lesa za določen namen uporabe. Poleg gostote, trdoto ...posamezne lesne vrste zelo pogojuje vlažnost lesa. V raziskavi smo ugotavljali trdoto lesa navadne smreke, uravnovešenega pri različnih relativnih zračnih vlažnostih. Meritve trdote smo izvedli z vtiskanjem kroglice v radialno površino lesa na inštrumentu za ugotavljanje mikromehanskih lastnosti materialov. Rezultati so pokazali, da se s poviševanjem vlažnosti lesa trdota lesa znižuje; vtisna trdota (HIT) in vtisni modul elastičnosti (EIT) sta tako pri absolutno suhem lesu znašala 110,8±11,7 MPa in 0,62±0,01 GPa, pri lesu z vlažnostjo točke nasičenja celičnih sten (29,4 %) pa 36,3±7,9 MPa in 0,40±0,05 GPa. Zniževanje trdote lesa s poviševanjem njegove vlažnosti se je pokazalo v povečevanju globine povzročenih vtisov in povečani hrapavosti površin vzorcev. Analiza lesnega tkiva z vrstičnim elektronskim mikroskopom je na območjih z vtisi razkrila usločenje celičnih sten lesa, njihovo gnetenje v lumne traheid, ter nastanek razpok znotraj celičnih sten.
Bacterial contamination of the membranes used during guided bone regeneration directly influences the outcome of this procedure. In this study, we analyzed the early stages of bacterial adhesion on ...two commercial dense polytetrafluoroethylene (d-PTFE) membranes in order to identify microstructural features that led to different adhesion strengths. The microstructure was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR). The surface properties were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM), and surface free energy (SFE) measurements. Bacterial properties were determined using the microbial adhesion to solvents (MATS) assay, and bacterial surface free energy (SFE) was measured spectrophotometrically. The adhesion of four species of oral bacteria (
,
,
, and
) was studied on surfaces with or without the artificial saliva coating. The results indicated that the degree of crystallinity (78.6% vs. 34.2%, with average crystallite size 50.54 nm vs. 32.86 nm) is the principal feature promoting the adhesion strength, through lower nanoscale roughness and possibly higher surface stiffness. The spherical crystallites ("warts"), observed on the surface of the highly crystalline sample, were also identified as a contributor. All bacterial species adhered better to a highly crystalline membrane (around 1 log
CFU/mL difference), both with and without artificial saliva coating. Our results show that the changes in polymer microstructure result in different antimicrobial properties even for chemically identical PTFE membranes.
Olja se uporabljajo za obdelavo površin lesa v notranji in zunanji uporabi. Če jim dodamo pigmente, lahko z njimi dosegamo dodatne vizualne učinke, kot so rustikalen izgled, poudarjanje lesnih por, ...obenem pa povečamo zaščitno sposobnost premaza proti fotodegradaciji lesne podlage. V naši raziskavi smo namesto klasičnih pigmentov uporabili naraven in obnovljiv vir, utekočinjen les (UL), ki smo ga v dve olji vmešali v dveh razmerjih. Tako pripravljene mešanice smo nanesli na vzorce bukovega in jesenovega lesa. Po nanosu smo najprej spremljali hitrost sušenja, po osušitvi pa smo določili še odpornost površin proti hladnim tekočinam ter suhi toploti. Površine smo tudi izpostavili pogojem umetnega staranja pod ultravijolično (UV) svetlobo in s tem preverili, kakšno vlogo pri tem igra dodatek UL. Barvne razlike smo določili z meritvami barve pred premazovanjem in po njem ter po izpostavitvi UV svetlobi. Naša raziskava je potrdila, da je UL kompatibilen s tungovim in Bio impregnol WM oljem, ter se posledično lahko uspešno uporablja za njuno za njuno obarvanje. Potrdili smo tudi, da dodajanje UL v tungovo olje ne vpliva na odpornost tako premazanih površin proti hladnim tekočinam in niti ne na odpornost površin obeh olj proti suhi toploti. Žal pa dodajanje UL v olja upočasnjuje hitrost sušenja. Dodatno smo tudi ugotovili, da z UL obarvani premazi niso najbolj fotostabilni.
V raziskavo smo vključili hrastovo hlodovino (Quercus robur, Quercus petraea) s 15. dražbe vrednejših sortimentov okroglega lesa v Slovenj Gradcu v letu 2021. Naključno smo izbrali 78 od 1318 ...licitiranih hlodov in jih skladno z veljavnim Pravilnikom o merjenju (2017) vizualno razvrstili po kakovosti (A, B, C). Vzporedno smo dendrokronološko analizirali priraščanje lesa ter z metodo frekvenčnega odziva pri vzdolžnem vzbujanju še akustične lastnosti hlodovine. Najkvalitetnejša hlodovina je bila večjih premerov, z več in povprečno širšimi branikami. Potrdili smo povezavo med vizualno določeno kakovostjo in doseženo ceno hlodovine. Hitrost vzdolžnega nihanja (v) in relativna učinkovitost akustične pretvorbe (RACE) sta bili s kakovostjo in ceno hlodovine pozitivno povezani. Frekvenčni spektri pri hlodovini nižje kakovosti odstopajo od teoretičnih. Raziskava je potrdila možnost uporabe nedestruktivnih akustičnih metod za oceno kakovosti hrastove hlodovine.
Phase change materials (PCMs) are ideal for thermal management solutions in buildings. This is because they store and release thermal energy during melting and freezing. Spruce (Picea orientalis (L.) ...Peterm.) sapwood was impregnated with n-heptadecane (100%) as a PCM. The decay-resistance properties and thermal energy storage (TES) characteristics of the n-heptadecane-impregnated wood were studied. The phase change properties of n-heptadecane (nHD)-impregnated wood were characterized by Fourier-transform infrared (FTIR), thermogravimetry (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses. As confirmed by DSC analysis, nHD-impregnated wood demonstrated moderate performance in storing and releasing heat during the phase change process. Significant increases were observed in the 2800–3000 cm−1 and 1471 cm−1 peaks in FTIR spectra of wood samples impregnated with nHD, which showed C–H stretching in methyl and methylene groups and asymmetric deformation vibration of the paraffin methyl group (CH3–) and C–O stretch in lignin, respectively. It was observed that there was a change in the crystal structure of spruce wood samples after nHD impregnation. This study revealed that PCMs are resistant to wood-destroying fungi. The performance of nHD-impregnated spruce wood proves that it can be used as a thermal regulating building material to reduce energy consumption. In addition, it has been proven on a laboratory scale that the PCM used is highly resistant to biological attacks. However, large-scale pilot studies are still needed.
The treatment of wood surfaces with gas discharges is one of the methods to achieve better surface adhesion properties. Good penetration, spreading and wettability of the applied liquid adhesives and ...coatings is a crucial factor for their adequate mechanical properties. Plasmas are the result of electrical discharge and can be created in different ways. The plasma treatment (PT) is frequently executed prior to material bonding or coating via the so-called dielectric barrier discharges (DBD) at atmospheric pressure. This literature review summarizes the essential aspects of DBD PTs aiming at a better wettability and surface adhesion. After introduction of the principle of DBD, the individual effects of internal and external parameters of the process will be discussed, which influence the final properties of treated materials.
Abstract
The coatings on wood must sometimes give aesthetic and basic protection to wooden elements and prevent the development and transmission of microorganisms. Several polymers containing ...different nanoparticles have already been offered to day for this purpose. The research presents a novel poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/polyvinylpyrrolidone (PVP) polymer composite with MoO
3
nanowires with the ability to form coating films on wood. The films of the developed coating exhibit elastic behaviour, which depends on the coating film thickness tested wet film thicknesses (90, 180 and 360) µm. The coating showed the ability to interact well with the surface of common beech (
Fagus sylvatica
L.) wood, in terms of wetting (contact angles of 15.6°), fast spilling on the surface, good penetration of the coating in wood structure and formation of up to 40 µm-thick films with excellent pull-off adhesion strength (6 MPa). An increased roughness of wood coated with C + MoO
3
was a consequence of wood etching by the dimethylformamide solvent present in the coating. Moreover, the presence of C + MoO
3
on wood made it considerably more hydrophobic, with contact angle of water raising to 123° from initially 46° measured on uncoated wood. The irradiation of wood surfaces with ultra-violet light resulted in visible colour changes on both uncoated and coated wood. The wood coated with C + MoO
3
has a good resistance to water, alcohol and dry heat (grade 3 to 4). The antimicrobial testing showed that the presence of MoO
3
in the coating plays an important role in the resistance of the coated wood to blue-stain fungi and mould development. The developed PVDF-HFP/PVP/MoO
3
coating has an excellent ability to interact with the wood surface and has the potential to be used as a protection for wood in sensitive environments.
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