Densification and Press-Drying of Wet Oil Palm Lumber

Sustainable use of renewable raw materials is an important issue of policy and industry. Wood prices are rising because of increasing market demand while simultaneously forests are challenged through conservation issues, deforestation and hazards. The main reasons for deforestation are agriculture, infrastructure and wood harvesting. Oil palm plantations stock on former tropical forest land and cover some 25 Mio ha worldwide. They are replanted every 25 years due to reduced productivity. Using the available wooden trunk material of the cleared plantation not only makes sense in ecological terms but is also a big chance for economy and trade. Research over the last 30 years has led to several ideas in the use for products. The biggest challenge is the anatomical structure of palm wood which is different to coniferous or broadleaf trees. Hard vascular bundles are embedded in low-density parenchyma storage tissue with high moisture content. The soft and sponge-like parenchyma tissue can be compressed easily and a significant share of the water (mc up to 600 % based on dry wood) can be squeezed out. Through press drying, the volume of the parenchyma can be reduced and the wood density increases. Wood strength and stiffness are related to its density and can be improved by densification. TH OWL developed a four-step densification process for oil palm boards. Oil palm lumber was produced from oil palm trunks in a sawmill and then densified under defined conditions. The densification process includes (1) compression to remove a certain percentage of the palm sap, (2) plastification under heat and moisture to soften the wood, (3) hot compression to achieve the densification and remove more water, and (4) press-drying to dry and harden the material. A future perspective on how the laboratory tests could be scaled up to an industrial application with a possible machinery set-up is presented.