Enhancing the knowledge of wood properties and processing characteristics of PNG timbers - Gluing characteristics of PNG timber species for various wood product applications

Gluing is considered one of the most important technologies in the production of value-added wood product. In the majority of wood products, both appearance (e.g. furniture, flooring) and structural (e.g. glue-laminated beams, plywood, LVL) timber elements are joined together into larger components through edge and surface laminating, finger jointing and other types of joints. In order to meet requirements and criteria for strength and performance of glued components and products a sound knowledge of gluing characteristics of PNG timbers is required. The present document presents the gluability behaviour of 24 species sourced from the Morobe and West New Britain provinces, Papua New Guinea. Seven species have been harvested from plantations and 17 from secondary forests. The group included 3 softwoods and 21 hardwoods. Two species, Eucalyptus pellita and Wau Beech (Magnolia tsiampacca) could not be assessed because of lack of enough timber. The report is based on activity 1.5 results which consisted in laboratory testing of glue-bond strength and performance of various types of glues for PNG selected timber species in various climatic conditions to simulate service conditions in potential market destinations. Two criteria, namely shear strength and wood failure, have been used to determine if a species can meet the minimum requirements for either dry use or wet use applications. Five species showed to bond very well i.e. achieved satisfactory results for both dry use and wet use applications: PNG Basswood (Endospermum medullosum), White Cheesewood (Alstonia scholaris), Erima (Octomeles sumatrana), Labula (Anthocephalus chinensis), and Klinki Pine (Araucaria hunsteinii). A second group of seven species provided results satisfying or able of satisfying the requirements for dry use applications: Grey Canarium (Canarium oleosum), Pencil Cedar (Palaquium warbargianum), Pangium (Pangium edule), Caribbean Pine (Pinus caribaea), Hoop Pine (Araucaria cunninghamii), PNG Quandong (Elaeocarpus sphaericus), Taun (Pometia pinnata), and Brown Terminalia (Terminalia brassii). Where PNG Boxwood (Xanthopyllum papuanum), Kwila (Intsia bijuga), PNG Mersawa (Anisoptera thurifera), PNG Rosewood (Pterocarpus indicus), and PNG Vitex (Vitex cofassus) could not meet the requirements for dry use applications using a standard cross-linking PVA, preliminary trials using a non-structural polyurethane showed they could possibly satisfy the requirements for dry use applications and even wet use applications in some cases (e.g. PNG Vitex). Two species classified under bond with difficulty, namely White Albizia (Falcataria moluccana) and Water Gum (Syzygium spp.), would most probably achieve satisfactory results (i.e. upgrade to bond well) with optimisation of gluing parameters. Four species provided low shear strength results and very limited wood failure resulting in them being classified as very difficult to bond: Blackbean (Castanospermum australe), Heavy Hopea (Hopea iriana), Kamarere (Eucalyptus deglupta), and Malas (Homalium foetidum). Not surprisingly, most of them are high or very high-density species which are known to be very difficult to bond. One species (Heavy Hopea) failed to meet the requirements for both dry and wet uses when using EPI. Such species would probably need some mechanical or chemical surface treatment to improve adhesion. Additional tests with dense species from 2nd batch i.e. Blackbean, Water Gum, Kamarere, and Malas would also be recommended to fully assess their suitability for non-structural applications.