Characterization of acetylated eucalyptus wood fibers and its effect on the interface of eucalyptus wood/polypropylene composites

The acetylation of eucalyptus wood fibers (WFs) was conducted in 50%/50% (v/v) of acetic acid and acetic anhydride catalyzed by sulfuric acid at 60 °C for 2 h. Twenty one percent weight percent gain (WPG) level was achieved. Then the contact angles of three probe liquids on the surface of unacetylated and acetylated eucalyptus WFs were tested by the capillary rise method, and the surface free energies of unacetylated and acetylated eucalyptus WFs and their dispersion and polar components were calculated according to the method suggested by Owens–Wendt–Kaelble. The results show that the surface free energy of unacetylated eucalyptus WFs is 24.7 mJ/m2, and its corresponding dispersion and polar components are 14.8 mJ/m2 and 9.9 mJ/m2, respectively. However, the surface free energy of acetylated eucalyptus WFs is 38.3 mJ/m2 which is higher than the surface free energy of PP (29.4 mJ/m2), and its corresponding dispersion and polar components are 35.6 mJ/m2 and 2.7 mJ/m2, respectively. So it is possible for the spreading of PP on the surface of acetylated eucalyptus WFs and forming a good interfacial adhesion between acetylated eucalyptus WFs and PP. The better interfacial compatibility between acetylated eucalyptus WFs and PP was corroborated by the scanning electron microscopy (SEM) micrographs.