PHYSICAL AND MECHANICAL PROPERTIES OF GLUED-LAMINATED LUMBER FROM FAST-GROWING TREE SPECIES USING MAHOGANY TANNIN ADHESIVE

Abstract

Tannin from mahogany bark extract contains polyphenols that could be used in adhesives. In this study, tannin (T) was reacted with resorcinol (R) and formaldehyde (F) at a ratio of 100:3:5 (w/w/w) under alkaline conditions to make an adhesive. The physical–chemical properties of tannin and TRF adhesive were assessed. Three-layer glued–laminated lumber (glulam) made with wood from jabon (Anthocephalus cadamba), pine (Pinus merkusii), and sengon (Falcataria moluccana) was bonded using TRF with a glue spread of 280 g/m2, cold pressed at 1.47 MPa for 4 h, and then clamped for 24 h. Glulam physical–mechanical properties were tested based on Japanese Agricultural Standard (JAS) 234-2007. Comparison of the physical properties of mahogany tannin and TRF showed that the solids content of mahogany tannin increased after becoming TRF. Compared with phenol resorcinol formaldehyde (PRF) resins, TRF had a similar appearance and specific gravity, but differed in solids content, viscosity, and gel time. Matrix-assisted laser desorption/ionization (MALDI)-time of flight mass (TOF) spectra revealed that mahogany tannin could be classified as hydrolyzable, and pyrolysis Gas Chromatograph-Mass Spectroscopy (GC-MS) showed that the phenolic content was 8.87%. Copolymerization in TRF was indicated by a shift in wave number in Fourier transform IR, reduced percentage of the phenolic component, and increased pH and melting temperature. Mahogany tannin could be prepared for cold-set TRF glulam adhesive, and all glulams fulfilled JAS 234-2007 with regard to MC and MOR. Although TRF adhesive contained a small amount of resorcinol, it was suitable for low density wood, and in dry condition performed equal to PRF.