The Use of Oil Palm Trunks for Wood Products

Worldwide, oil palms cover an area of nearly 25 million ha with over 75 % located in Asia. After 25 years of age, the palms are felled and replaced due to declining oil production. The average annual total volume of trunks from plantation clearings amounts to more than 100 million m3. Like all other biomass, the trunks remain on the plantation site for nutrient recycling. But this leads to increased insect and fungi populations causing problems for the new palm generation. Many regions where oil palms grow currently suffer from a decline in timber harvested from their tropical forests. An extensive project, involving partners from both R+D and industry, is studying the possibility of improving the use of oil palm trunks to manufacture marketable timber products. The consortium consists of some 20 partners mainly from Germany, Malaysia, and Thailand. Areas of development are: harvesting and storage of trunks, sawmilling, drying, processing into various products like solid wood-based panels (block-board), flash doors, furniture elements as well as CLT and gluelam for the building sector. All sectors have shown remarkable success. Introduction The availability of timber from tropical forests is steadily declining due to over logging and measures taken towards sustainable forest management and conservation of tropical forests. In Asia the demand for wooden products is rising due to a growing population and greater economic development. The declining wood supply from tropical forests in Southeast Asia is partly being compensated for by imported timber (i.e. from North and Latin Americas, Australia, New Zealand, Europe), and new fiber sources are also being developed. Rubberwood from Indonesia, Malaysia, and Thailand has found its way into the markets and the use of bamboo is rapidly increasing. Rubberwood, however, is limited in quantity, because rubber plantations are being converted into oil palm plantations due to improved economy. Fast growing forest trees like albizzia (Albizia falcataria (L.) Fosberg) are being promoted but can hardly fill the increasing supply shortage. Palms have long been a source of fiber for manufacturing products, but mainly fibers from husks (i.e. coconut fibers) or, to a lesser extent, from palm fronds or fruit bunches. Also nut shells are often used as fillers of (activated) coal. The trunks of coconut palms are widely used as building material, for furniture and crafts. A good example is in the Philippines were coco-wood has an important market share. But utilization is performed more locally in small workshops with partly inferior processing techniques and tools, resulting in low quality and more simple products. Processing is difficult as density of coconut trunks is high and hard vascular bundles, ash and silica causes high tool wear. The trunks from date palms generally have lower and evenly distributed density making processing easier. Nevertheless, date palms are less available, By-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 69-80 doi: https://doi.org/10.21741/9781644900178-3 70 because as their growing area is much smaller (Table 1 and Table 2) and the average age of a palm is high, resulting in less felled palms. Oil palms (Elais guineensis JACQ.) were introduced in Asia around 100 years ago. With initially limited distribution, the plantation areas have grown steadily since around the 1970s, first in Malaysia, later in Thailand and Indonesia. Table 1 shows the estimates for the plantation area, which is worldwide above 25 million ha with a growing tendency, especially in Indonesia and some Latin-American countries. Experts estimate global coverage will range between 30 to 40 million ha in the year 2030. Table 1: Palms with potential for industrial conversion of trunks into products. palms world area [million ha] number of palms [million] rotation period [years] number of available palms [million] available million m3 [palm trunks per year] oil palm 25 3,000 25 120 180 coconut palm 12 1,200 50 24 40 date palm 0.8 110 55 2 3 Table 2: Main growing countries for palms and areas in million ha (various sources). oil palm coconut palm date palm Indonesia 13.0 Indonesia 4.0 Iran 0.22 Malaysia 5.0 Philippines 3.5 Iraq 0.21 Nigeria 3.5 India 2.0 UAE 0.16 Thailand 1.0 Brasil 0.5 S. Arabia 0.04 World >25.0 world ∼12.0 world ∼1.0 Past attempts to use oil palm trunks (OPT) as a supplement or substitute for tropical timber in product manufacturing failed due to the palms’ different material properties and processing behavior compared to traditional wood species. Intensive R+D, especially in Malaysia [i.e. 1, 2, 3, 4], has provided a clearer understanding of the material (structure, mechanical, and chemical properties) and worked to test manufacture of products. With the exception of plywood manufactured in Malaysia (some 50.000 m3/y), all efforts towards semi industrial or industrial use proved unsuccessful. Product quality, processing of the material (i.e. sawing, planing, drying) and logistics / supply did not meet high enough standards to make to a manufacturing break through. Yet, given the tremendous supply of OPT (180 million m3/y, see Table 1) and the rapid decline in common timber stocks, the need to launch a “new start in OPT utilization” is obvious. After several years of scientific oriented material research in various German and Asian universities and research centers, a consortium was founded consisting of five industrial core partners and some 20 associated partners from academia and industry in Germany resp. Europe, Malaysia and Thailand. Information about the consortium can be found on the project website, www.palmwoodnet.com. By-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 69-80 doi: https://doi.org/10.21741/9781644900178-3 71 OPT Harvesting: Potentials and Logistics After 25 years of age, oil palms are felled and replaced due to declining oil production (remarkably less than 5 t/ha palm oil). Plantations are cleared on plots ranging from only a few hectares to up to 100 ha (or more) depending on ownership, age distribution, and site conditions. Generally, clearing starts at the beginning of the dry season, the sites are prepared for replanting at the beginning of the following wet season. Traditionally, most of the biomass from the clearing was piled up in rows and burned (with the help of sprayed diesel) at the end of the dry season. The main aim was to avoid pests caused by fungi (Ganoderma) and beetles. Today, most countries have introduced a zero-burning-policy so now the trunks are chipped and evenly distributed (together with fronds and leaves) on the site ore piled up in rows of 10 or 20 m distance (in-between the rows for re-planting) to let the material rot. For the OPT volume to be harvested for use, PalmwoodNet developed a concept for removing some 70 m3 of OPT per ha (from 150 – 180 m3/ha in total) for reasons of nutrient management (among others K, P, Ca, N, Mg) and soil quality. Normally, the palms are felled by “pushfelling” where an excavator pushes the palms to the ground and chips it into pieces between 20 – 40 cm in length. The felling technique will be modified to secure less or no damage to the trunks. The discrepancy between felling within two dry periods per year of 2 – 3 months only and a continuous supply of processing mills must be bridged by either extension of the plantation clearing periods and / or appropriate storage techniques for the trunks. Intensive laboratory research followed by field tests has led to storage techniques and conservation of the trunk cross cut sections with “green chemicals” in order to avoid rapid and intensive manifestation of mold followed by stain of the wood. The results have shown little damage to the wood even after storage of 2 – 3 months; the techniques are also very cost effective. Properties of Oil Palm Wood A large number of publications describe the basic properties of oil palm wood, but quite often as secondary literature. Experimental research is not always systematic in terms of material selection and methods applied. In the following, a general overview of the properties is given, some references are made. The partners of PalmwoodNet have dealt with material properties relevant for processing and use of the palm wood. Density variation: As a monocot, the density varies remarkably along the trunk diameter and along the trunk length. The outer peripheral zones (at the trunk base) show dry densities of 0.5 – 0.7 g/cm3 caused by high density fibers / fiber cups of the vascular bundles (VB) and high share of the VB of the wood volume. The more inner / central part of the trunk show densities between 0.2 – 0.3 g/cm3 (less VB). Fig. 1 and 2 show typical density distribution. Along the trunk axis, the density decreases to 0.4 – 0.5 g/cm3 at the periphery and 0.15 – 0.25 g/cm3 in the inner zone due to younger age of the cells. The cell walls show “secondary growth” of their thickness by additional cell wall layers with the age. This might be one of the reasons for the higher density of coconut wood compared to oil palm wood as coconut palms are only harvested at the age of 50+. By-Products of Palm Trees and Their Applications Materials Research Forum LLC Materials Research Proceedings 11 (2019) 69-80 doi: https://doi.org/10.21741/9781644900178-3 72 Figure 1: Density distribution in an oil palm trunk. Figure 2: Cross section of an oil palm trunk. Moisture content: For reasons of physiology (to bridge water shortage during dry seasons) the tissue of OPT contains a high percentage of water – generally the parenchyma cells show almost maximum moisture content (which depends on the density). Fig. 3 shows moisture contents (based on dry density) of between > 100 % (peripheral zone, base of trunk) and 600 % (inner zone, top of the trunk). The high moisture content results in t