Preparation and characterization of formaldehyde-free wood adhesive from mangrove bark tannin

This study sheds light on the applicability of tannin as formaldehyde-free wood adhesives. In order to replace toxic formaldehyde that exists in most commercially available wood adhesives, condensed tannins extracted from Mangrove bark (Rhizophora apiculata) via acetone and methanol extracts were modified into tannin-acetone-phenol-glyoxal (TAPG) and tannin-methanol-phenol-glyoxal (TMPG) adhesives. The extracted tannins were characterized using different complementary techniques such as Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), thermal analysis techniques such as; thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), total phenolic content (TPC), total flavonoid content (TFC) and total condensed tannin (TCT). As for TAPG and TMPG wood adhesives, physico-chemical and mechanical properties were determined. It was found that tannin-acetone-extract (TAE) had higher TPC content compared to tannin-methanol-extract (TME). Various substitutions of adhesives were applied on plywood and mechanically tested. The 50 wt % TAPG and TMPG adhesives showed the highest tensile strength (TS) values at 70.1 ± 4.1 MPa and 66.5 ± 5.5 MPa respectively, as well as higher total solids content, viscosity, and shorter gel time compared to the control phenol-glyoxal (PG) adhesive.