Bonding of THM modified Moso bamboo (Phyllostachys pubescens Mazel) using modified soybean protein isolate (SPI) based adhesives

The bondability/gluability of THM modified Moso bamboo specimens was tested and compared with unmodified Moso specimens as a reference. Five different SPI based adhesives were used for bonding. The SPI powder was thermally modified in a vacuum chamber at 50 or 100 °C and dispersions prepared at 24, 50, or 90 °C. Bond shear strengths of the adhesives were determined by lap-shear tests. Surface characteristics (roughness indices, Ra and Rz; and sessile droplet contact angle, CA) of compressed and uncompressed bamboo were measured. Bond shear strengths were mostly lower for THM-compressed bamboo tissue than uncompressed tissue. In the uncompressed controls there were no significant differences between adhesives. However in THM-compressed specimens, one formulation (50 °C modification temperature and 24 °C dispersion preparation temperature) had significantly higher bond shear strength. THM surfaces were characterised by high surface smoothness, likely little or no adhesive penetration into the surface due to observed void closure, and loss of adhesive from the bondline during pressing, all of which were believed to contribute to the significantly lower bond shear strength compared with control veneers.