The effects of surface modification by using phytic acid-based hybrid complexes on the interfacial properties of heat-treated wood

Heat-treated wood is widely used in outdoors due to its good dimensional stability and biological durability, while the reduced surface hydrophilicity negatively affects its bonding performance with water-soluble adhesives. In this work, a convenient surface modification strategy was prepared on heat-treated wood by surface modification with phytic acid or phytic acid combined with Fe3+ to improve its interfacial bonding properties. Results showed that the phytic acid and phytic acid-Fe3+ chelate are distributed both in the cell cavity and cell wall, and phytic acid surface coating is smooth while phytic acid-Fe3+ seemed layer-by-layer. These coatings bring a large number of hydroxyl groups to improve the surface wettability of heat-treated wood. Therefore, the water contact angle of both phytic acid treated wood and phytic acid-Fe3+ treated wood at 60 s is smaller than that on control wood. The water contact angle in the earlywood of phytic acid treated wood even reaches 0 degrees. The average penetration and effective penetration of phenol formaldehyde adhesive into heat-treated wood also increase after treatment. On average, the average penetration and effective penetration value of phytic acid treated wood increased from 870 to 997 & mu;m, and 35 to 62 & mu;m, respectively. The average penetration value of phytic acid-Fe3+ treated wood is decreased due to the accumulation of chelates. But its effective penetration value is more than twice that of heat-treated wood. The digital image correlation results that the tensile strength of phytic acid treated wood is much higher than that of heat-treated wood. The shear strain of phytic acid treated wood is distributed more homogeneously. However, the maximum tensile stress of phytic acid-Fe3+ treated wood is poor due to the glueline being too thick to closely connect with wood.