Possibilities for use of thermally modified poplar veneer were evaluated for the production of plywood boards in industrial conditions. Formats of poplar veneer were treated at temperatures of 190 ...°C, 200 °C, 210 °C, and 215 °C for 1 h. By combining the treated and non-treated formats of veneer, thirteen different types of board were made. Analyses showed that the examined physical and mechanical properties were influenced by both the type of construction and the applied thermal treatment. Boards composed only of thermally modified veneer achieved the best results regarding moisture absorption and dimensional stability, and boards composed of the combined veneers had better mechanical properties. Treatments at 200 °C and 210 °C proved to be optimal, while the treatment at 215 °C was too harsh and should not be used for the thermal modification of poplar veneer.
The choice of optimal pressing regime for certain types of substrate is of great importance in production of veneered panels. In this paper, the impact of pressing regime on the bonding strength of ...beech and oak veneers, glued with urea-formaldehyde (UF) adhesive, on medium-density fiberboard (MDF), and moisture-resistant MDF (MR MDF) substrates was examined. The analyses showed a generally higher bond strength with oak veneer compared to beech veneer, which was also the case with regular MDF compared to moisture-resistant MDF. Multivariate analysis of variance (ANOVA) showed that with beech veneer, all of the used regimes produced better results on regular MDF compared to moisture-resistant MDF. In contrast, with oak veneer, the influence of pressing regime had a more noteworthy impact than the type of substrate used. These results indicated that the use of MR MDF as substrate in combination with UF adhesive was inadequate.
This paper presents the results of experimental testing of the bending strength and modulus of elasticity in edgewise bending of unreinforced and reinforced seven-layer LVL (laminated veneer lumber) ...poplar veneer panels. The aim of the research is to determine the influence of woven carbon fibers on the improvement of the bending properties and modulus of elasticity of LVL bending in the plane of the plate, as well as the influence of adhesives on the bending properties of the composite product, in order to test the potential of using this newly obtained material as a structural element. Bending was performed on small-scale samples. The main research task is the examination of three types of reinforcement, which differ from each other in position, orientation, and number of layers of reinforcement, using two different types of adhesives: epoxy adhesive and Melamine Urea Formaldehyde Resins (MUF). The composite material was produced in four different combinations in relation to the orientation and position of the reinforcement in the layup. The applied reinforcement is defined through three different configurations (EK1, EK2, and EK3) and a fourth control sample (EK4). Each configuration was produced by applying the two previously mentioned types of adhesives. The research findings showed that in the case of samples produced by applying CFRP (carbon fiber reinforced polymer) using epoxy adhesive, it significantly affected the increase in bending strength and flexural modulus of elasticity. The average improvement in bending strength is 32.9%, 33.2%, and 38.7%, i.e., the flexural modulus of elasticity is 54.1%, 50.7%, and 54.7%, respectively, for configurations EK1, EK2, and EK3, compared to control sample EK4. During the testing, the test samples from reinforced panels EK1 and EK2 showed partly plastic behavior up to the fracture point, while the diagram for the test samples from reinforced panels EK3 shows elastic behavior to a considerable extent, with a significantly smaller plastic behavior zone. This research proved the impossibility of using melamine-urea formaldehyde adhesive to form a composite product based on veneer and carbon fabric. The greatest contribution of this work is the experimentally verified and confirmed result of the possibility of applying poplar veneer to design structural elements in LVL using epoxy adhesive.
The subject of this paper was a research of physical and mechanical
properties of LVL composed of peeled poplar veneers in core layers and only
outer layers of beech peeled veneers, so as the ...examination of window frame
glue joint strength produced of this material. LVL boards have been hot
pressed in industrial conditions, using appropriate phenol formaldehyde (PP)
adhesive. Samples for corner window frame glue joint strength testing were
glued with PVAc D4 class adhesive. Statistical analysis showed that there
were significant differences both in moisture content and density of LVL
boards regarding their thickness, while in the case of hardness this
difference did not exist. Examinations of LVL glue line shear strength
showed that both phenol formaldehyde (PP) and PVAc D4 class adhesives
fulfilled standard requirements. The results of corner window frame double
tenon glue joint strength produced from combined poplar-beech veneer LVL
indicated that such material could be used to produce window frame corner
joint, strong enough to withstand the additional load, without an increase
of the cross section.
nema
Some properties of plywood panels made from untreated and thermally modified (90 min. at 200 ºC) poplar veneers and their combinations have been analyzed. The change in equilibrium moisture content ...and the change in dimensions of the samples conditioned above water in closed containers were examined. The analysis using F-test (ANOVA) at the significance level of 95% confirmed that, regarding moisture content, all combinations of plywood panels differed significantly from the control panels. However, the analysis of thickness swelling showed that there was no significant difference among the plywood panels of similar construction. The highest values of anti-swelling efficiency were shown by plywood panels made from thermally modified veneers.
Some properties of plywood panels made from untreated and thermally modified (90 min. at 200°C) poplar veneers and their combinations have been analyzed. The change in equilibrium moisture content ...and the change in dimensions of the samples conditioned above water in closed containers were examined. The analysis using F-test (ANOVA) at the significance level of 95% confirmed that, regarding moisture content, all combinations ofplywood panels differed significantly from the control panels. However, the analysis of thickness swelling showed that there was no significant difference among the plywood panels of similar construction. The highest values of anti-swelling efficiency were shown by plywood panels made from thermally modified veneers. Key words: thermal modification, poplar veneer, plywood panels, dimensional stability, ASE U radu su istrazena neka svojstva ploca izradenih od nemodificiranih i od termicki modificiranih (90 min pri 200°C) topolovih furnira te njihovih kombinacija. Istrazivana je promjena ravnoteznog sadrzaja vode i promjene dimenzija uzoraka u uvjetima iznad vode u zatvorenim posudama. Analiza uz pomoc F-testa (ANOVA) na razini znacajnosti od 95 % potvrdila je da se, s obzirom na sadrzaj vode, sve ispitne ploce znatno razlikuju od kontrolnih ploca. Medutim, analiza podataka o debljinskom bubrenju pokazala je da ne postoji znacajna razlika izmedu ploca slicne konstrukcije. Najvecu ucinkovitost u sprjecavanju debljinskog bubrenja pokazale su ploce izradene od toplinski modificiranih furnira. Kljucne rijeci: toplinska modifikacija, topolov furnir, ploce od uslojenog drva, dimenzijska stabilnost, ASE
U radu su istražena neka svojstva ploča izrađenih od nemodificiranih i od termički modificiranih (90 min pri 200 ºC) topolovih furnira te njihovih kombinacija. Istraživana je promjena ravnotežnog ...sadržaja vode i promjene dimenzija uzoraka u uvjetima iznad vode u zatvorenim posudama. Analiza uz pomoć F-testa (ANOVA) na razini značajnosti od 95 % potvrdila je da se, s obzirom na sadržaj vode, sve ispitne ploče znatno razlikuju od kontrolnih ploča. Međutim, analiza podataka o debljinskom bubrenju pokazala je da ne postoji značajna razlika između ploča slične konstrukcije. Najveću učinkovitost u sprječavanju debljinskog bubrenja pokazale su ploče izrađene od toplinski modificiranih furnira.
Mesenchymal stem cells (MSCs) are adult stem cells that reside in almost all postnatal tissues where, due to the potent regenerative, pro-angiogenic and immunomodulatory properties, regulate tissue ...homeostasis. Obstructive sleep apnea (OSA) induces oxidative stress, inflammation and ischemia which recruit MSCs from their niches in inflamed and injured tissues. Through the activity of MSC-sourced anti-inflammatory and pro-angiogenic factors, MSCs reduce hypoxia, suppress inflammation, prevent fibrosis and enhance regeneration of damaged cells in OSA-injured tissues. The results obtained in large number of animal studies demonstrated therapeutic efficacy of MSCs in the attenuation of OSA-induced tissue injury and inflammation. Herewith, in this review article, we emphasized molecular mechanisms which are involved in MSC-based neo-vascularization and immunoregulation and we summarized current knowledge about MSC-dependent modulation of OSA-related pathologies.
The accuracy of guiding a spindle is greatly influenced by the thermal load of the bearing. Increased thermal load implies deformation of the bearing parts which is directly reflected in the work ...quality of the machine system. For this reason, the aim of this paper is to analyse the influence of the material and the geometry of the housing on the temperature field of the threaded spindle bearing assembly, which was realised by "radially mounting" of axial angular contact ball bearing ZKLN. This paper represents a new approach for thermal analysis of the special bearings, type ZKLN which are not involved in the relevant standards for the determination of the reference speed. At the same time the value of this paper finds itself in finding of the guideline at engineering practice which is very important at early design phase of the systems with threaded spindle. The analysis was carried out using experimental and numerical methods. Combination of the mentioned methods gave result which was used to define appropriate guideline regarding influence of housing material and geometry on thermal stability of the ZKLN bearing.
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