Jakimovska popovska, Violeta
Preferred name
Jakimovska popovska, Violeta
Official Name
Jakimovska popovska, Violeta
Main Affiliation
Email
jakimovska@fdtme.ukim.edu.mk
19 results
Now showing 1 - 10 of 19
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Item type:Publication, Impact of Veneer Layouts on Plywood Tensile Strength(Faculty of Forestry, University of Zagreb, 2017); ; The aim of the research presented in this paper is to study the plywood tensile strength through a change of the position of the layers in the structure of the panel around the central axis, without changing the number and the thickness of the veneers. So far it is known that the veneer layouts in plywood structure have significant impact on plywood bending properties. Besides these mechanical properties, the tensile strength of plywood is also a property that can defines the plywood use as structural or non-structural panel. For studying the impact of veneer layouts on plywpood tensile strength, experimental models of nine-layer plywood are made. The models are made from peeled beech veneers with thickness of 1.2, 1.5, 2.2 and 3.2 mm. The modelling is made on the basis of changing the position of veneers with thickness of 3.2 mm around the central axis. Pure water-soluble phenol-formaldehyde resin is used as plywood binder. The tensile strength of the plywood panels was tested in five directions: parallel and perpendicular to the face grain, as well as at the angle of 22.5°, 45° and 67.5° to the face grain of the plywood panel. On the basis of the obtained data for tensile strength in different directions of plywood panel the coefficient of the equality of the tensile strength of the plywood models was calculated (Ket). The coefficient of mass quality (Kmq) was calculated too. The research results showed that the different veneer layouts in plywood structure have significant impact on plywood tensile strength. All tested plywood models meet the defined values of tensile strength in accordance with the requirements of the national (МКС) standard for structural plywood for use in construction. The different layouts of veneer sheets in panel structure gives opportunities for production of panels with different strength characteristics. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Variations of the hardness of Balkan beech wood (Fagus moesiaca cz.)(Faculty of design and technologies of furniture and interior-Skopje, 2019); ; The aim of this research is to determine the significance of the impact of the origin of wood trees (generative or vegetative), height of the cross-section (1,3 and 5,3 m above ground) and relative age of annual rings (distance from pith in radial direction) in which the measurements are made, on the variation of wood hardness, at near same ecological factors. For determination of wood hardness Brinell method is used, and for statistical processing of the data from the measurements, software package SPSS Statistics 21 is used. On the basis of the obtained values form the tests for normal distribution of the hardness and analysis of the homogeneity of the variance, as well as on the basis of multiple comparison for determination of statistical significant differences between average values of wood hardness from different tree trunks, cross-section and age, it is found that the trees from vegetative origin produce wood with significantly higher hardness compare to the trees form generative origin. Among the two cases, the wood hardness of section 1,3 m is significantly higher than the wood hardness of section 5,3 mm. The increment of the relative age of annual rings in trees from vegetative origin in certain interval is followed by increment in wood hardness, whereupon the wood hardness decreases, while in trees from generative origin, first in certain interval the hardness is decreased, whereupon it is increased. The obtained results of these researches, supplemented with the comparative researches of processing of standard (from generative origin) and nonstandard (from vegetative origin) timber should be taken in consideration when choosing the technological process. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Water Resistance of Fiberglass Reinforced Plywood during Prolonged Water Exposure.(Faculty of Forestry and Wood Technolgy, University in Zagreb, 2023); Тhe aim of this research is to study the water absorption and thickness swelling of plywood reinforced with fiberglass fabrics pre-impregnated with alcohol-soluble phenol-formaldehyde resin during prolonged water exposure. Four experimental reinforced plywood models were made from peeled beech veneers with thickness of 1.5 mm and 1.85 mm bonded with the same resin used for fabric pre-impregnation. In each model, sheets of pre-impregnated fabric (prepreg) were incorporated in different adhesive layers of the plywood structure. One additional model was made without reinforcements as comparing plywood model. On the basis of the obtained data for the changes of water absorption and thickness swelling of reinforced plywood after immersion in water continuously for a period of 192 days, water resistance of experimental plywood was evaluated. The research results showed that the application of fiberglass prepreg as reinforcement in plywood structure significantly decreases the values of water absorption and thickness swelling. After full water treatment plywood models have good dimensional stability and do not show deformations. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Dimensional stability of multiplex plywood with mainly unidirectional grain orientation(SS. Cyril and Methodius University in Skopje, Faculty of design and technologies of furniture and interior-Skopje, 2021); ; Multilayer plywood made from wood veneers with mainly unidirectional grain orientation known as multiplex panels represent a significant group of modern wood-based panels. Application of these panels in modern construction and in other application areas necessitates achieving higher physical and mechanical characteristics of these materials, their consistency during prolonged water impact, humidity, heat, as well as their dimensional stability. The aim of the research presented in this paper is to study the dimensional stability of experimental multiplex plywood reinforced with cotton based prepreg. The cotton prepreg was made form cotton fabric pre-impregnated with alcohol-soluble phenol-formaldehyde resin. The experimental multiplex plywood was made of eleven layers of peeled beech veneers with thickness of 1,85 mm. Alcohol-soluble phenol-formaldehyde resin was used as plywood binder. The orientation of the veneers in the plywood structure is parallel to the longitudinal axis of the panel, with exception of the subsurface layers whose orientation is transverse to the longitudinal axis of the panel. The cotton prepreg reinforcements were inserted in each adhesive layer of plywood. To define the dimensional stability of the panels, laboratory tests on the most important physical properties were performed, as well as on bonding quality through the shear strength test. Tests of water absorption and thickness swelling were performed during prolonged water treatment. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Water absorption and thickness swelling of reinforced plywood during prolonged water exposure(Faculty of design and technologies of furniture and interior-Skopje, 2021); Тhe aim of this research is to study the physical properties during prolonged water exposure of experimental plywood reinforced with cotton fabrics pre-impregnated with alcohol-soluble phenol-formaldehyde resin. Plywood composition was consisted of eleven layers of peeled beech veneers with thickness of 1,5 mm and 1,85 mm. The veneers were bonded with alcohol-soluble phenol-formaldehyde resin. The pre-impregnated fabrics were incorporated in each adhesive layer of the plywood panel. On the basis of the obtained data for the changes of the physical properties of reinforced plywood after exposure to prolonged water treatment, water resistance of experimental plywood was evaluated. Tests for the thickness swelling, volume swelling and water absorption were made after immersion in water for prolonged period of 192 days in controlled laboratory conditions. The results from the research showed that the plywood model is characterized by uniform density; it is dimensionally stable during and after prolonged water exposure, without any deformations of the shape of the test specimens - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Janka hardness of plywood reinforced with pre-impregnated cotton fabrics(Faculty of design and technologies of furniture and interior-Skopje, 2021); Higher properties of plywood can be achieved trough applying different non-wood materials in their structure. Тhe aim of this research is to study the Janka hardness of experimental plywood reinforced with cotton fabrics pre-impregnated with alcohol-soluble phenol-formaldehyde resin. Plywood models were made of eleven layers of peeled beech veneers with thickness of 1,5 mm and 1,85 mm. Alcohol-soluble phenol-formaldehyde resin was used as plywood binder. The pre-impregnated fabrics were incorporated as layers in the structure of the plywood panel. Different models of reinforced plywood were made through a change of the position of the reinforcing layers in the structure of the panel. One additional model was made without reinforcements as comparing plywood model. Tests for plywood hardness according to Janka were done on each plywood model. The research results showed that the values of Janka hardness are affected by the use of pre-impregnated fabrics as reinforcements in plywood structure. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Impact of resin content on compressive strength and Janka hardness of composite wood-based panels(Faculty of design and technologies of furniture and interior-Skopje, 2022); The aim of the research presented in this paper is to study the impact of resin content on compressive strength and Janka hardness of composite wood-based panels. For this purpose three experimental models of composite wood-based panels were made that represent a combination of particleboards and constructive veneers. The core layer of composite panels was made of single-layer particleboard with thickness of 16 mm. Particleboards were overlaid on both sides with beech peeled veneer with thickness of 3,2 mm. Water-soluble phenol-formaldehyde resin with 10 %, 13 % and 16 % dry matters content on dry wood basis was used respectively for production of single-layer particleboard cores of the three composite models. The resin used in all three models was modified with epoxy resin. The veneers were bonded on the particleboard core with the same resin that was used for particle bonding, but without modifier. Tests for compressive strength were carried out according to МКС DA1.110. The results from the research showed that the resin content in particleboard core has significant impact on the values of compressive strength of composite wood-based panels. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Research on the properties of light boards from ligno-cellulose materials and cement(Faculty of design and technologies of furniture and interior-Skopje, 2019); The aim of this research is production in laboratory conditions of light weight boards from different types of ligno-cellulosic materials and Portland cement as inorganic binder. Wood particles from recycled coniferous wood (white pine) and recycled deciduous wood species are used as ligno-cellulosic materials, as well as particles from grape vine rods, flax and hemp. Gel made from aluminum sulphate and sodium silicate solution (water glass) is used for mineralization of the particles. Boards with thickness of 50 mm and dimensions of 400×400 mm are made in laboratory conditions. Test specimens for determination of the most important physical and mechanical properties re made from the boards. Some test specimens are used for determination of the coefficients of sound absorption and thermal conductivity. The results from the research show that light-weight boards from ligno-cellulosic materials and cement with density bellow 0,630 g/cm3 can be classified as structural-insulation materials. Insulation properties and strength properties of investigated boards indicate that the latter meet the requirements for application in construction as a material for components of wall panels, permanent formwork, roof panels, partition walls etc. The obtained light-weight boards made of ligno-cellulosic materials and cement are a good option for sustainable material management, with a view to protecting, preserving and improving the quality of the environment, protecting human health, ensuring prudent, efficient and rational utilization of natural resources. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Impact of resin content on water absorption and thickness swelling of composite wood-based panels(Faculty of design and technologies of furniture and interior-Skopje, 2021); ; Mihajlova, JulijaThe aim of the research presented in this paper is to study the impact of resin content on water absorption and thickness swelling of composite wood-based panels. For this purpose three experimental models of composite wood-based panels were made that represent a combination of particleboards and constructive veneers. The core layer of composite panels was made of single-layer particleboard with thickness of 16 mm. Particleboards were overlaid on both sides with beech peeled veneer with thickness of 3,2 mm. Water-soluble phenol-formaldehyde resin with 10 %, 13 % and 16 % dry matters content on dry wood basis was used respectively for production of single-layer particleboard cores of the three composite models. The resin used in all three models was modified with epoxy resin. The veneers were bonded on the particleboard core with the same resin that was used for particle bonding, but without modifier. Tests for the water absorption and thickness swelling after immersion in water for 2 hours and 24 hours, as well as after immersion in boiling water for 2 hours were carried out in controlled laboratory conditions. The results from the research showed that the resin content in particleboard core has significant impact on the values of the tested properties of composite wood-based panels. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Determination of the fiber saturation point of autochthonous and allochtonous wood species(Faculty of design and technologies of furniture and interior-Skopje, 2019); ; The aim of this research is to determine the fiber saturation point of wood from Fagus moesiaca, Quercus sessilis, Quercus conferta, Robinia pseudoacacia, Pinus nigra, Pinus silvestris, Abies alba, Picea excelsa, Pseudotsuga menziesii, Cupressus arizonica, Sequoiadendron giganteum, Pinus strobus and Larix decidua, as a contribution to the utilization of wood. The material used for investigation was collected from twenty-eight methodologically selected localities. The obtained average values of fiber saturation point are based on wood density and volume shrinkage, in accordance with the standard for wood investigation. The results from investigation of fiber saturation point of wood from autochthonous species are within the limits of the up to now empirical and scientific knowledge. The obtained values for the allochthonous species that are subject of our investigation, can significantly impact on further introduction.