Abstract: Wheat straw was split into layers,and the chemical composition of each layer was analyzed by chemical and modern instrumental analysis for the purpose to find the differences among layers.Following to the specific characteristics of the outer layer,7 different coupling agents were used to explore the variation of adhesion properties.Results showed that outer layer accounts for 20% thickness of the whole stalk and containes somewhat different contents of components,in which ash content is 21.95% higher than that of the whole stalk,while SiO₂ content in its ash is more than 100% higher than the whole stalk;and phenol-EtOH extractive is 21.95% higher than the whole stalk.ESR (analysis) indicated that free radicals in the whole stalk is higher than outer layer.SEM results demonstrated the smooth cuticle surface of the outer layer,as well as the absence of cuticle on inner layer,and the later is beneficial to wetting,diffusion and permeation of UF resin.The coupling agent KH-550 exhibited good adhesion property toward each layer of the stalk,especially the significant increase of bonding strength toward outer surface,while other coupling agents showed no significant effect.

Key words: wheat stalk, adhesion properties, coupling agent