Milan Šernek

Bio: Milan Šernek is an academic researcher from University of Ljubljana. The author has contributed to research in topics: Adhesive & Curing (chemistry). The author has an hindex of 17, co-authored 68 publications receiving 1268 citations.

Effect of wood content in FDM filament on properties of 3D printed parts

Abstract: The effect of wood content in 3D printing materials on the properties of 3D printed parts was investigated. Six filaments using polylactic acid (PLA) with varying loading levels of wood particles from 0% to 50% by weight were produced and used for 3D printing. The density of the filaments and 3D printed parts used in this study slightly decreased with increasing wood content. The tensile strength of the filaments increased from 55 MPa to 57 MPa with an addition of 10% wood, but decreased with higher levels of wood content to 30 MPa for filaments with 50% wood content. The surface of the parts printed from the filament without the addition of wood was smoother and the printed part had no voids within the structure. With increasing wood content the surface becomes rougher, more voids were present, and had visible clusters of wood particles (due to wood particle clustering and clogging in the printer nozzle). Higher wood content in 3D printed parts decreased the storage modulus. measured with torsional loading on a rheometer, but did not change the glass transition temperature.

Comparative Analysis of Inactivated Wood Surfaces

Abstract: The surface inactivation of two wood species, yellow poplar (Liriodendron tulipifera) and southern pine (Pinus taeda), was studied following high temperature drying. Surface analysis involved X-ray photoelectron spectroscopy, sessile drop wettability and fracture mechanics of the adhesively-jointed surfaces. The results showed that wood drying at high temperature (i.e., >160 to 180°C) caused modifications in surface composition. The oxygen to carbon ratio (O/C) decreased and the ratio of carbon atoms bonded to other carbon or to hydrogen atoms vis-a-vis carbons bonded to oxygen atoms (i.e., the C1/C2 ratio) increased with drying temperature. In addition, the contact angle increased with the temperature of exposure, but decreased with time. A dependence on wood species was evident: southern pine surfaces always exhibited higher contact angles than yellow poplar. Also, the rate of contact angle decline with time, dθ/dt, was found to vary with surface composition: this rate corresponded to O/C ratio-changes, especially in the case of southern pine. Southern pine was most susceptible to inactivation particularly when bonded with PF adhesive. Yellow poplar surfaces did not show significant inactivation when exposed to drying temperatures below ca. 180°C. The results are explained by a relative enrichment of wood surfaces with non-polar substances, hydrophobic extractives and volatile organic compounds that become visually evident during the drying process at temperatures above ca. 160°C. Little change was observed if drying temperatures remained below 150°C.

Density profile and morphology of viscoelastic thermal compressed wood

Abstract: The viscoelastic thermal compression (VTC) of low-density hybrid poplar (Populus deltoides × Populus trichocarpa) from fast growing trees was performed in order to produce specimens with three different degrees of densification (63, 98, and 132%). The morphology and density profile of the VTC specimens were studied. Three different methods for the preparation of specimens for microscopy were used in order to find a technique that makes it possible to examine the VTC wood microscopically in the completely deformed state. It was found that the abrasive surface preparation of oil-embedded blocks was the most promising technique. Microscopic observation revealed that the deformations in the VTC wood were mostly the result of the viscous buckling of cell walls without fracture. The volume of the void areas in the specimens decreased with the degree of densification. The results showed that the density profile of the VTC wood varied with the degree of densification as a consequence of different temperature and moisture gradients formed before and during wood compression. The density profile is also visible on the cross-section of the VTC specimens.

Penetration of Liquid Urea-Formaldehyde Adhesive into Beech Wood

Abstract: The main objective of this research was to evaluate the penetration of a liquid urea-formaldehyde adhesive (UF) into beech (Fagus sylvatica L.) wood as influenced by moisture content (MC) and the method of curing. The maximum penetration of the UF adhesive was detected at 9% MC within the MC range of 4 to 13%. Adhesive penetration was greater with samples that were cured in a conventional press when compared with high-frequency pressing. Penetration in the tangential direction was greater than in the radial direction. The application of mechanical pressure to the bondline greatly increased penetration, whereas extended open assembly times did little to increase penetration.

The mechanical properties of densified VTC wood relevant for structural composites

Abstract: The mechanical properties of densified wood relevant for structural composites were studied Low density hybrid poplar (Populus deltoides × Populus trichocarpa) was densified using the viscoelastic thermal compression (VTC) process to three different degrees of densification (63, 98, and 132%) The modulus of rupture (MOR) and the modulus of elasticity (MOE) of the control (undensified) wood and of the VTC wood were determined The bonding performance of the control and VTC wood, using two phenol-formaldehyde (PF) adhesives, was studied Four different 3-layer composites were also prepared from undensified and VTC wood, and tested in four-point bending The results showed that the bending properties of the VTC wood (MOR and MOE) were significantly improved due to the increased density The bonding performance of VTC wood with PF adhesives was comparable with or better than in the case of the control wood Increased density of the face layers in the 3-layer VTC composites was advantageous for their mechanical performance

Wood modification by heat treatment: a review.

Abstract: Wood heat treatment has increased significantly in the last few years and is still growing as an industrial process to improve some wood properties. The first studies on heat treatment investigated mainly equilibrium moisture, dimensional stability, durability and mechanical properties. Mass loss, wettability, wood color, and chemical transformations have been subsequently extensively studied, while recent works focus on quality control, modeling, and study the reasons for the improvements. This review explains the recent interest on the heat treatment of wood and synthesizes the major publications on this subject on wood properties, chemical changes, wood uses, and quality control.

An overview of the oil palm industry in Malaysia and its waste utilization through thermochemical conversion, specifically via liquefaction

Abstract: Malaysia is among the top most important palm oil producers in the world. The country is experiencing a robust development in new oil palm plantations and palm oil mills. This commodity plays a significant role in the Malaysia economic growth. As this industry becomes bigger and wider, a substantial amount of oil palm wastes is generated and create the problem of biomass waste overload. This problem tends to burden the operators with disposal difficulties and escalates the operating cost. Oil palm waste has significant potential in many applications. Traditionally, through mechanical conversion, some of the wastes are converted into organic fertilizers, animal feedstock or soil conditioner in oil palm plantations. Apart from mechanical conversion, thermochemical processes such as direct combustion, gasification, pyrolysis and liquefaction are the methods that are useful to transform the waste into value-added products. Recently, liquefaction has gained good attention in order to utilize the waste because of its simplicity and ability to yield a product that combine both of the useful functional groups present in liquefying solvents and the biomass. Within the scope, the objective of this paper is to review the current situation related to the oil palm industry in Malaysia, availability of the oil palm waste and its utilization through thermochemical conversion, with specific regards to the liquefaction process.

Cure kinetics characterization and monitoring of an epoxy resin using DSC, Raman spectroscopy, and DEA

Abstract: R. Hardis, J. Jessop, F. E. Peters, M. R. Kessler. Cure Kinetics Characterization and Monitoring of an Epoxy Resin for Thick Composite Structures, Composites Part A: Applied Science and Manufacturing, 2013, 49, 100-108. doi:10.1016/j.compositesa.2013.01.021.

FDM 3D Printing of Polymers Containing Natural Fillers: A Review of their Mechanical Properties

Abstract: As biodegradable thermoplastics are more and more penetrating the market of filaments for fused deposition modeling (FDM) 3D printing, fillers in the form of natural fibers are convenient: They have the clear advantage of reducing cost, yet retaining the filament biodegradability characteristics. In plastics that are processed through standard techniques (e.g., extrusion or injection molding), natural fibers have a mild reinforcing function, improving stiffness and strength, it is thus interesting to evaluate whether the same holds true also in the case of FDM produced components. The results analyzed in this review show that the mechanical properties of the most common materials, i.e., acrylonitrile-butadiene-styrene (ABS) and PLA, do not benefit from biofillers, while other less widely used polymers, such as the polyolefins, are found to become more performant. Much research has been devoted to studying the effect of additive formulation and processing parameters on the mechanical properties of biofilled 3D printed specimens. The results look promising due to the relevant number of articles published in this field in the last few years. This notwithstanding, not all aspects have been explored and more could potentially be obtained through modifications of the usual FDM techniques and the devices that have been used so far.

Adhesive penetration in wood—a review

Abstract: Adhesive bond performance between wood elements is presumed to be significantly influenced by the degree of penetration of the adhesive into the porous network of interconnected cells. Research on the bondline performance has been conducted through microscopic examination and associated techniques in an effort to establish relationships with the bond performance. The purpose of this communication is to provide a technical review of research on adhesive penetration, and to promote the efficient use of adhesives in regard to cost and performance, particularly in reference to the manufacture of wood-based composites. Assessment techniques, influence on bond performance, and distinctive characteristics of common adhesives used for the wood-based composites industry were the main focus of this review. Variability between wood species, the wide variety of adhesive application and curing processes, and the many types of adhesive chemistries and formulations make sweeping generalities difficult. However, troubleshooting bonding problems and designing new adhesive systems and processes may be facilitated by understanding the fundamentals of adhesive penetration.