A technical evaluation of veneer cutting and boring of coconut (Cocos nucifera L.) stem wood

Abstract

Increased usage of wood products and a decline in supply of wood creates a major gap in the demand and supply chain. Severe restrictions in the felling of trees from natural forests create pressure on the plantations. But the limited supply from plantations alone will not be sufficient for meeting the current demand. Here, the role of trees outside forest especially from the home gardens is significant. Coconut, widely cultivated in home gardens of Kerala is considered as “Kalpavriksha” since, the entire part of the coconut palm is used. However, the coconut palm stem is underutilized and even considered as waste and farmers have to pay high prices to remove the old, diseased and senile palms from their field. Coconut palm stem has huge potential to substitute the hardwoods and softwood, their use is limited to fewer applications like conventional furniture mainly. Conversion of the coconut palm wood is very difficult due to the hard fibrovascular bundle distribution and low recovery rate leads to avoiding this cheap wood material despite its tremendous potential to replace more conventional species. The wood industry, especially the small and medium enterprises are reluctant to saw the coconut palm stem due to the damage caused to their machineries due to the hard fibro vascular bundles. Veneers are thin sheets produced by sawing, slicing or the rotary peeling process. Veneer production is another method for better utilization of logs for enhancing the recovery percentage. Peeling of coconut palm is also not practically feasible using the conventional spindle peeler because of its soft core which does not have enough strength to hold the chunk of the conventional peeler machines. Spindle less peeler is the only option for peeling coconut logs in an efficient way. Veneers produced by peeling of coconut logs using spindle less peeler can be used for the production of veneer-based products like plywood, laminated wood etc. Veneer-based products has lots of advantages as compared to solid wood. They have better strength, dimensional stability, durability and low shrinkage as compared to solid wood and also have lower costs. 99 Our study shows that pre-treatment of coconut log using steam or boiling makes the fibers soft and reduces the cutting force and also enhances the quality of veneers produced. We also found that peeling temperature is an important factor for peeling of coconut logs to reduce the cutting force and enhance the veneer quality. Above 50-600C is considered necessary for peeling the coconut logs of high density and temperature will vary according to the density of coconut logs. Appropriate lathe setting is necessary for peeling operations and will be different from species to species. Peeling and sawing at 2.5 mm thickness is considered ideal for veneer production coconut stem wood. Peeling at 4 mm nose bar gap reduce the thickness variations within the sheets. The setting of saw blade is important for the sawing and for the coconut log it is about 20 degree for left and right and zero degree for straight which is considered ideal for reducing the saw marking and also to remove the saw dust from the log without jamming the blade inside. The green veneer recovery of coconut log on peeling was higher for the middle part (66 %) of the coconut palm stem and lower for the upper portion (49 %) and the lower part of coconut palm stem has about 49 % of recovery. The average green veneer recovery of the peeling and sawing as about 51 % and 35 % respectively. It is lower as compared to other timber species. But peeling of coconut log showed enhanced recovery as compared to sawing due to the low residue left after the process. The veneer defects classification is important for the determination of the end uses of the veneer sheets. The coconut veneer sheets show significant defects like roughness, collapse and handling splits. All of these defects can be reduced by appropriate lathe settings and pretreatment of the coconut logs prior to peeling. Veneer can be used for manufacture different veneer-based products and composites. Coconut plywood with 3-ply and 5-ply and coconut rubber wood plywood with 3-ply and 5-ply were manufactured using resorcinol formaldehyde adhesive. In this study we developed 8 types of plywood from coconut and coconut composites. The static bending test of coconut plywood with (IS 1734: 1983) shows the maximum MOR of 114.81 N/mm² for the 5-ply coconut rubber plywood of 100 density more than 700 kg/m³ in the perpendicular direction of the face veneer. The MOE of 8834.6 N/mm² is the highest MOE for the 5-ply coconut plywood of density more than 700 kg/m³ with parallel direction of the face veneer. On the other hand, the 3-ply coconut plywood with density 400-700 kg/m³ had lowest MOR and MOE of 12.93 N/mm² and 2964.95 N/mm². 5-ply plywood using both coconut and coconut rubber plywood showed good results and can be used for construction purposes like load bearing. All the plywood samples made of 5-plies meet the minimum requirement as per the Indian standard and also showed significant results compared to other plywood species. The boring of coconut log for the construction of hollow cylindrical prototype was not successful due to the failure in the holding of the log with larger dimension on the single chunk of the lathe. The coconut log was able to bore only up to 1meter length with 4 inches of bored diameter. The coconut log can be bored to longer dimension by appropriate modifications on the lathe by providing support for the log for holding during the rotation of the logs.