Mirko Kariz

Use of wood powder and adhesive as a mixture for 3D printing

In recent years there has been much development in the field of additive manufacturing technologies, but only a few attempts have been made to use natural materials like wood for 3D printing. In this research different ratios of wood powder were used as a component in adhesive mixtures for 3D printing. Polyvinyl acetate and urea–formaldehyde adhesives were used as binders, and the optimum mixture was determined by measuring the corresponding extrusion forces. Simple blocks were 3D printed and the bending properties of these blocks were investigated. The bending strength depended on the amount of wood powder in the mixture and on the type of adhesive.

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde and polyurethane adhesives

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde (MUF) and polyurethane (PUR) adhesives was monitored by measuring their rheological properties by means of a rheometer. Instead of the standard aluminium discs, wooden discs, made from heat-treated wood with different degrees of thermal modification and conditioned in different climates, were used. The wooden discs provided more realistic curing of the adhesives compared to the real-life bonding of wood, because of solvent absorption. The results of the rheological measurements suggested that the modified wood inhibited the curing of MUF and PUR adhesives. The curing of the MUF adhesive was slower because of the reduced absorption of water from the adhesive. The curing of the one-component PUR adhesive was affected by the lower moisture content (MC) of the modified wood.

Bonding of Heat-Treated Spruce with Phenol-Formaldehyde Adhesive

The modified chemical, physical and structural properties of wood after heat treatment can affect the bonding process with adhesives. The objective of this research was to determine to what extent the degree of heat treatment influenced the bonding of treated wood with phenol-formaldehyde (PF) adhesive. Spruce (Picea abies Karst) lamellas were heat treated at 180°C and 220°C and then bonded. The shear strength and wood failure of the differently pretreated specimens were determined. Wettability and penetration of the adhesive were also investigated. The results showed that the shear strength of the PF adhesive bond was influenced by the heat treatment of the spruce wood, and depended on the type of pretreatment of the wood specimen prior to testing. The observed reduction in the shear strength of the PF adhesive bond was ascribed to a decrease in the wood strength itself, caused by the heat treatment, and also to other effects induced by exposure of the wood to elevated temperatures. The changes in wettability and adhesive penetration did not significantly influence the bonding process of the heat-treated wood with the PF adhesive.

Adhesive bonding of 3D-printed ABS parts and wood

Abstract Additive manufacturing, also known as 3D printing technology, has experienced massive growth in the last decade. Instead of printing the entire product, 3D printing can be used to produce only the most complex parts, which are then combined with simple, non-printed parts from other materials to make the final product. In addition to mechanical connections, adhesive bonding is most commonly used to combine printed parts with other elements. In this study, the influence of 3D-printing parameters on the bond shear strength of 3D-printed Acrylonitrile-butadiene-styrene copolymer parts bonded to beech wood was investigated. Three printing settings with different layer thicknesses (0.39, 0.19, 0.09 mm) and a posttreatment method that utilized acetone vapour were used. The three different adhesives applied were commercial one-component polyurethane adhesive, hot melt adhesive for edge bonding, and a two-component polyurethane adhesive. The results show that the type of adhesive had the biggest influence on the strength of the bond. The highest bond strength was achieved using a two-component polyurethane adhesive. The type of failure (failure in wood, plastic, adhesive, or cohesive failure) depended greatly on the type of adhesive and thickness of the printed layer.

Determination of the percentage of wood failure by 3D scanning of the adhesive bondline

The quality of the wood-adhesive bond is usually determined by its shear strength and the percentage of wood failure, the latter usually being determined by visual evaluation and prone to the examiner’s subjective evaluation. A new technique of 3D scanning was used to evaluate the percentage of wood failure, and the results obtained were compared to those obtained by means of existing methods, i.e. the visual evaluation and image analysis techniques. Evaluation by 3D scanning showed comparable values for samples with a high percentage of wood failure, but large differences in the case of samples showing mainly adhesive failure.