Bending properties and joint efficiency of some tropical hardwoods finger-jointed in green and dry states

Abstract

This study investigated the bending properties and joint efficiencies of some tropical hardwoods finger jointed in green and dry states. Two groups of finger-jointed pieces were produced from mill off-cuts of four different tropical timber species using PVA (protovil D3). One group was produced from pieces initially kiln dried to approximately 12 % MC while the other group was produced from green pieces (approx. 25 % MC). Solid wood test samples, treated to similar MCs as the finger jointed samples, served as a reference group. The results showed that the joint efficiencies in MOE of test group finger jointed in dry state ranged between 58 and 89 % for medium and low density species, respectively. A much lower joint efficiencies in MOE were recorded for test groups finger-jointed in green state: 49.4 and 54.7 % for medium and low density species, respectively. For MOR, the minimum and maximum joint efficiencies for test group finger jointed in dry state were 14.5 and 50.7 %, respectively compared to 12.9 and 40.1 %, respectively for test group finger jointed in green state. The results show that the joint efficiency in stiffness appears to be much higher than that in strength. Low density tropical timber species appear to exhibit higher joint efficiency than medium density ones. The synergy between density and moisture condition of wood prior to finger jointing affects the joint efficiency in MOE while only the density of species affects the joint efficiency in MOR. Finger jointing lumber with PVA may be used for non-structural applications. Further research is required to obtain enough data to confirm the possibility of using low density tropical timber species finger jointed in dry state with PVA for structural applications.