The Development of a lightweight three-layered Sandwich panel based on the raw material maize

The development of wood composites such as fibreboards or particle boards rely on the intention to improve the efficiency of the wood use and to expand the application of the material wood. The conventional wood composites do have a significant role in the timber industry. In the past decades, these products have been developed to versatile products which combine different resources, especially wood, efficiently. To achieve the best properties of these products and in addition to guarantee a sustainable and eco-friendly production, raw and waste wood are combined to produce wood composites such as particle boards. However, in the last years some factors have led to a competitive situation on the wood market, for instance political support of the bio energy sector, increased use of biomass and forest restructuring. These aspects have led to a competitive situation on the wood market and to a shortage of wood for the timber industry. Because of the shortage of wood resource and thus increasing prices the industry has started to search for alternative strategies. One promising opportunity to reduce the use of the resources might be the application of strategies based on lightweight construction. Therefore, the main topic of this research was to develop a new and innovative sandwich composite with a reduced density but without compromising the mechanical and physical properties. To achieve this objective it was planned to create a nature based composite consisting of almost 100 % popcorn granular. This popcorn composite was combined with thin and stiff face materials to achieve a light sandwich panel, with promising properties for the furniture sector. For the development of popcorn composites, an expanded popcorn granular of the agricultural raw material maize was used. This granular material was expanded in a special process of pressure and heat. Firstly, it was valid to evaluate the popcorn material and its properties for the suitability of manufacturing a three layered sandwich construction. After the determination of the chemical and physical properties of the popcorn material, the manufacturing of popcorn composites in laboratory scale with sufficient mechanical properties such as internal bonding, followed. Therefore, in a first step popcorn granulate was treated with resin, compressed to a board and afterwards hot pressed. The second step was to cover the popcorn core on both sides with selected face materials such as plywood or aluminium alloy, to achieve a stiff sandwich panel with a high strength. Afterwards, to evaluate the quality of the sandwich panel, properties such as bonding strength (three and four point bending), withdraw screw strength, were tested and compared to conventional light wood based composite. In the beginning of the examination it was necessary to investigate the properties of the popcorn granular. The results show that the bulk density and the particle size are suitable to produce low density boards. Besides this, the popcorn material does have a low pH value of 4,5 and a high protein content of 8% to 10%. Besides the chemical analysis the evaluation of the sandwich panels regarding mechanical properties were very crucial. Therefore in different test series the panels were produced under defined parameters and tested. The main topics of interest were the relation between density and internal bond of the popcorn composite, use of different binder systems and press parameters, influence of different manufacturing processes (one-step or two-step process) and also the evaluation of the effect of face materials on the sandwich panel properties. The results of the test series show that the production of a lightweight sandwich panel is possible and furthermore that the composites do have sufficient mechanical properties. The testing of the internal bond strength shows that the strength rises by threefold from 0.10 N/mm² to 0.30 N/mm² with an approximate panel density of 100 kg/m³ to 350 kg/m³ respectively. If a particle board achieves a similar internal bonding strength, the board needs a twofold higher density, and in addition to this, a higher amount of resources. The testing of bending strength of the sandwich boards shows that the strength of the core is sufficient. This results indicate that the popcorn based core layer is able to resist shear stress, caused by a bending force. Moreover the results point out that the bending strength is closely related to the properties of the selected face materials. The results indicate that popcorn based panels do have properties which are comparable and competitive with conventional light products such as paper honeycomb boards