Mechanical behaviour and practical adhesion at a bamboo composite interface: Physical adhesion and mechanical interlocking

Physical adhesion was experimentally determined by measuring contact angles with different liquids on bamboo and glass fibres, using the Wilhelmy technique, and by applying the acid–base theory for calculating the surface energy components and the theoretical work of adhesion. The mechanical strength of the interfaces was assessed by single fibre pull-out tests. In order to consider the real mechanisms of interfacial failure of natural fibre composites, the fibre matrix interfacial bond strength was characterised by the critical local value of interfacial shear stress, τd, and the radial normal stress at the interface, σult, at the moment of crack initiation. Both interfacial parameters are used for correlating thermodynamic work of adhesion and practical adhesion. Pull-out tests (taking into account friction), XPS, and profilometry techniques were used to study the influence of rough natural fibre surfaces on the interface between the fibre and a thermoplastic matrix, by comparing the mechanical behaviour at the interface of a smooth optical glass fibre with that of rough natural fibres. The results suggest that the physical and chemical compatibility between the bamboo fibre and the matrix does not improve substantially the composite performance if compared with glass composites. The relatively low off-axis strength of the bamboo fibres is suggested as the main reason for the low stress transfer capability at the fibre–matrix interphase. Furthermore, the pull-out process may be friction-dominated in bamboo fibre systems.