Improvement of the Bondability of Wheat Straw Treated by Water Vapor Plasma for Bio-composites Manufacture

Yicheng Xu, Minzhi Chen, Xiaoyan Zhou

Abstract


Wheat straw (WS) was first modified with water vapor plasma to enhance its interfacial bonding performance. The treatment effects during the entire exposing process were investigated in terms of surface wettability, physicochemical characteristics, and mechanical properties of glued test-pieces (three different forms) using contact angle analysis, free energy analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and shear strength analysis. The results showed that 180 s of plasma treatment time resulted in a low instantaneous and equilibrium contact angle of urea-formaldehyde (UF) – 40.8% and 46.5% lower, respectively, in comparison with that of the untreated WS exterior surface. Obvious etching morphology was observed on the WS surfaces and positive activation was detected, demonstrating a remarkable increase in the surface free energy and O/C ratio. With the water vapor plasma treatment, the use of electrochemical reaction to introduce polar groups and etching to produce glue nails, were effective methods for improving the bonding performance of the WS.

Keywords


Wheat straw; Water vapor plasma; Wettability; Bonding performance; Morphology; Surface chemistry

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