SEM analyses
SEM was used to observe the fracture surface characteristics of the cured samples. The SEM images (Fig. 5) show a pore struc-ture for the cured defatted soy flour, control, and defatted soy flour based bio-adhesive. During the curing process, the increased gasification pressure and volume of water in the sample adhesives result in pore formation. However, the cured defatted soy flour based bio-adhesive had better compact structure and less pores than the cured defatted soy flour and control, implying that the defatted soy flour based bio-adhesive had better mechanical properties to resist the damage of water gasification in the curing process, because the crosslinked soy protein contributed to the higher mechanical properties of cured defatted soy flour based bio-adhesive (Chen et al., 2013a; Dastidar and Netravali, 2013; Lin et al., 2012). This is also in agreement with the results of bonding strength and the sol–gel test