Nondestructive Testing Of Wood-Plastic Composites Adhesive Joint

Wood-plastic composite (WPC) has been developed into a new and important wood-based composites due to its benefits on environment, economy and recyclability. It will greatly broaden its application on the construction field when bonding them with structural adhesive. Herein, epoxy resin and acrylic ester were combined with different pretreatment methods, such as coupling agent and plasma processing, to bond WPC adhesive joints. Shear strength and failure mode of adhesive joints were determined and investigated. Resonant frequency and dynamic Modulus of Elasticity (MOE) of WPC adhesive joints were measured with the longitudinal vibration method. Meanwhile, this study also investigated the correlation between vibration parameter and shear strength of WPC adhesive joints.Different adhesives were used to bond WPC, and a correlation between the dynamic parameters and bonding strength was established. The results indicated that epoxy led to a better bonding quality than acrylic ester for WPC glued joints. There was a close correlation between dynamic MOE and shear strength for epoxy bonded WPC joints, while the ratio between dynamic parameters (resonance frequency and dynamic MOE) before and after bonding had a significant correlation with shear strength for acrylic ester bonded WPC joints. WPC specimens were then treated with different surface pretreatment methods before epoxy bonding. After conducting non-destructive testing and mechanical testing, the correlations between the dynamic parameters and bonding strength of WPC specimens were also established. Results showed that there was no correlation between resonant frequency and the shear strength of WPC specimens regardless of surface pretreatment methods. Both dynamic MOE and dynamic MOE ratio had significant correlations with the shear strength for the WPC specimens treated with silane coupling agent, which was better than these correlations for the WPC specimens only treated with sanding process. The ratio of resonance frequency before and after bonding had a certain correlation with the bonding strength for the WPC specimens only treated with sanding process. The resonance frequency had no obvious correlation with the shear strength for the WPC specimens treated with co-processing. In all the exploration, the WPC treated with plasma processing exhibited weaker correlations between dynamic properties and bonding properties than those of the others. The effect of curing time on the correlation between dynamic parameters and bonding properties was also investigated in this study. It was found that there was a significant correlation between the dynamic MOE and bonding strength for the WPC specimens cured at room temperature for 24h and those cured under the normal condition. The resonance response of WPC specimens cured under the normal condition was better than that of specimens cured with short time, which also led to a much better correlation between the dynamic MOE ratio and shear strength of WPC specimens.