Johannes Welling

Comparison of foam core materials in innovative lightweight wood-based panels

In the present paper, lightweight wood-based foam core panels were produced in a novel continuous process. Expandable microspheres (MS) and expandable polystyrene (EPS) were used as core materials. The influence of surface thickness and core materials on bending strength, internal bond and specific strength of the produced panel were investigated.With increasing the surface thickness, bending strength was increased in both core types of panels. The internal bond value of the panels with expandable microspheres was steadily raised while the surface thickness was increased. The internal bond for the expandable polystyrene with increasing face thickness was reduced. In comparison with conventional particleboards, the specific bending strength and internal bond were increased. In addition, FE-SEM-microscopy and gamma-ray densitometry were used to characterize the panels.ZusammenfassungLeichte Schaumkernplatten wurden in einem neuartigen einstufigen Verfahren hergestellt. In zwei Plattenvarianten wurden als Mittellagenmaterialien expandierbare Mikrosphären (MS) und expandierbares Polystyrol (EPS) eingesetzt. Der Einfluss der Decklagendicke und des Kernmaterials auf Biegefestigkeit, Querzugfestigkeit und die korrespondierenden spezifischen Festigkeiten wurde untersucht.Es konnte ein deutlicher Einfluss der Decklagendicke auf die Biegefestigkeiten beider Plattenvarianten und eine steigende Querzugfestigkeit der Platten mit MS-Mittellagen nachgewiesen werden. Die Querzugeigenschaften der Platten mit MS-Mittellagen reduzierten sich mit steigender Decklagendicke. Im Vergleich zu konventionellen Spanplatten konnte eine Erhöhung der spezifischen Biege- und Querzugfestigkeiten festgestellt werden. Die Analyse der Ergebnisse erfolgte mit Hilfe von FE-SEM-Mikroskopie und Gammastrahlen-Densitometrie.

Physiomechanical properties of ultra-lightweight foam core particleboard: different core densities

Abstract Ultra-lightweight foam core particleboards have been produced in a novel one-step process with resinated wood particles for the faces and expandable polystyrene (EPS) as core layer material. The mechanical and physical properties of panels were investigated in terms of the different foam core densities and press parameters (temperature, pressing and foaming time). The bending strength properties of the panels were not significantly changed with increasing foam core density from 80 to 120 kg m-3. Panels produced at a press temperature of 130°C (1-EPS) have an improved core-face interface and also a denser surface layer, which positively influences the internal bond and thickness swelling. The panels produced at a press temperature of 160°C (2-EPS) have smaller and more foam cells and an improved fusion of foam beads and properties, which have a positive influence on the edge screw withdrawal resistance and water absorption.

Effect of aluminosilicate powders on the applicability of innovative geopolymer binders for wood-based composites

In this research, a new binder class for wood based composites, named geopolymer binder, was developed based on pozzolanic by-products (e.g. fly ash). Additionally, effects of different amounts of silica fume, as a replacement agent with other aluminosilicate components (e.g. fly ash and metakaolin), have been evaluated in the innovative binder. The Automated Bonding Evaluation System technique was used to characterize the bonding shear strength of the developed geopolymer binder. It was shown that the best shear strength for fly ash based binders was obtained by the lowest press temperature and longest pressing time. The addition of silica fume (from 20% up to 100%) significantly influenced the bonding shear strength in all binder types. Due to the chemical and mineralogical compositions, silica fume displays higher pozzolanic activity than metakaolin whereas fly ash shows lower strength in comparison to metakaolin. The silica fume (100%) based binder has also superior shear strength compared to those of conventional UF resin and other geopolymer binders. Bonding shear strength like that for UF resin was achieved by substituting only 20% silica fume in geopolymer binder compositions.

Geopolymers as potential new binder class for the wood based composite industry

Abstract Geopolymer binders are an emerging class of mineral polymer that can be manufactured from natural raw materials and industrial byproducts containing high amounts of silica (Si) and alumina (Al) in mineral compositions. Various ratios of materials used for manufacturing geopolymer binder have been tested to evaluate the bonding performance of geopolymers with wood by means of tests performed on an automated bonding evaluation system (ABES). Tests with a binder based on sodium silicate water glass (Na 50T) are partly promising, which resulted only 10% lower shear strength than that based on urea formaldehyde. The binder characteristics were significantly influenced by changing the ratio of SiO2:M2O (M=Na or K) and the ratio solid content to chemical base in the water glass. Expectedly, increasing press temperatures and pressing times showed a positive correlation with the curing performance of geopolymer binder. It was also demonstrated that the binder properties can be changed in wide ranges to obtain binders which fulfill the minimum requirements set by industrial users.