Effect of chemical modification of wood on the mechanical and adhesion properties of wood fiber/polypropylene fiber and polypropylene/veneer composites

The effect of acetic, maleic or succinic anhydride modifications of wood fiber on the mechanical properties and dimensional stability of differently bonded fiber boards was studied. The binders for the fiber boards used in this work were: powdered phenol formaldehyde resin of the novolak type (PF), polypropylene (PP) and a combination of the two. In the second part of the research, birch veneers modified with succinic or phthalic anhydride were laminated with PP films and the effect of the modifications on the interfacial bond between the two materials was studied. Significant improvement in the mechanical properties of the PP-bonded boards was generally observed as a result of the anhydride modifications. Modification of wood fibers with maleic anhydride resulted in a reduction in the modulus of rupture of the PF- and PF/PP-bonded boards, whereas acetylation and modification with succinic anhydride did not cause any significant changes in the modulus of rupture of the boards. The anhydride modifications improved the internal bond strength of the fiber boards regardless of the binder type used. Dimensional stability of the fiber boards was observed to increase significantly as result of the modifications. Adhesion between the PP films and wood veneer showed an increasing trend as function of the degree of modification. In addition, SEM micrographs of the fiber boards and PP-coated veneer revealed improved interaction between the two components due to the anhydride modifications.