Performances of Larch (larix gmelini) Tannin Modified Urea-Formaldehyde (TUF) Resin and Plywood Bonded by TUF Resin

Tannin from larch (Larix gmelini) bark extracts, as a natural renewable resource, was used to prepare tannin-urea-formaldehyde (TUF) resin. The chemical structures of larch tannin and TUF resin were characterized by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and C-13 nuclear magnetic resonance. The thermal behaviors of TUF resin were evaluated by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The performances of TUF resin were investigated by measuring the bond strength and formaldehyde emission of its bonded plywood. It was clearly shown that larch tannin is mainly composed of prodelphinidin repeating units. Phenolic groups were introduced into TUF resin mainly linked by methylene bond. Larch tannin has an adverse effect on the resin curing. However, it promoted the rigidity and flexibility of the glued system and upgraded the properties of plywood. Therefore, larch tannin could be applied in the modification of urea-formaldehyde resin. (C) 2014 Wiley Periodicals, Inc.