Interfacial compatibility and physical adhesion of bamboo fibre composites C. A. Fuentes a, *, L.Q.N Tran a , M. Van Hellemont b , V. Janssens a , C. Dupont-Gillain c , A.W. Van Vuure a , I. Verpoest a a Department of Metallurgy and Materials Engineering (MTM), Katholieke Universiteit Leuven; Leuven, Belgium b Unit Matter, GROUP T - Leuven Engineering College; Leuven, Belgium c Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain; Louvain-la- Neuve, Belgium *Corresponding author: Carlos A. Fuentes Rojas E-mail: Carlos.Fuentes@mtm.kuleuven.be Tel. +32-16-321448; Fax +32-16-321990 ABSTRACT The use of bamboo fibres as reinforcement fibre in (polymer) composite materials has attracted interest due to specific mechanical properties which are comparable to glass fibres. In this study, the molecular-kinetic theory of wetting is used to interpret the contact angle experimental data of bamboo fibres. Results suggest that the bamboo fibre surface represents a well-defined system for wetting analysis. The surface free energy components were calculated according to the acid-base theory. These values were then used to calculate the theoretical work of adhesion and interfacial energy. In order to improve the compatibility for bamboo fibre, chitosan coating was applied. The effect of this treatment was evaluated by using contact angle measurements following the Wilhelmy technique. The wetting behaviour of various thermoplastic matrices (polypropylene, maleic anhydride-grafted polypropylene, polyvinylidene-fluoride, and polyethylene-terephthalate) was characterized. Surface chemical components were identified using XPS. Additionally, transverse 3-point bending tests and single fibre pull-out tests were performed. This integrated physical-chemical-mechanical approach was used to study the effect of adhesion on the mechanical strength of thermoplastic composites reinforced with bamboo, showing that increase in physical adhesion can explain the improved interfacial and longitudinal strength in bamboo polyvinylidene-fluoride (PVDF) composites compared to the other thermoplastic matrices used in this study. Surface energy components of bamboo fibres and PVDF were matched, resulting in an improvement of the physical adhesion. For MAPP, no increase in physical adhesion is predicted, but for chitosan coated bamboo an increase in longitudinal strength was observed, which may be attributed to a chemical adhesion mechanism. INTRODUCTION The use of bamboo fibres as reinforcement fibre in (polymer) composite materials has attracted interest due to their physical and mechanical properties. The latter are comparable to glass fibres, while thermal conductivity is low, which could make them suitable for thermal barrier purposes [1]. Furthermore, natural fibre composites may exhibit a non-brittle fracture on impact, which is a key requirement for automotive applications. Low cost, environmental friendliness and natural abundance make such fibres possible substitutes to synthetic reinforcing fibre materials, especially for polymer matrix composites. To achieve good wetting and adhesion of the bamboo fibre with different polymers, the fibre surface needs to be characterized. However, natural fibres have several complex characteristics such as liquid sorption, different cross sections along the fibre length, chemical heterogeneity, which make obtaining meaningful data from wetting measurements particularly challenging. Therefore, the interpretation of their wetting behaviour as quasi-equilibrium phenomena can be invalid [2]. The use of thermoplastics as matrices for natural fibre composites represents an approach with low environmental effects. However, the hydrophilic nature of natural fibres reduces their potential as reinforcing agents due to low interfacial interactions with hydrophobic thermoplastic matrices, such as