PEER-REVIEWED ARTICLE bioresources.com Özmen et al. (2013). “Effect of Acetylation on WPCs,” BioResources 8(1), 753-767. 753 Effect of Wood Acetylation with Vinyl Acetate and Acetic Anhydride on the Properties of Wood-Plastic Composites Nilgül Özmen, a Nihat Sami Çetin, a* Fatih Mengeloğlu, a Emre Birinci, b and Kadir Karakuş a Chemical modifications of Scots pine (Pinus sylvestris) wood flour were performed with vinyl acetate (VA) and acetic anhydride (AA) in the presence of potassium carbonate as a catalyst. Scots pine wood flour samples were successfully acetylated with VA (19 wt% gain) and AA (24 wt% gain). The effect of chemical modification of the Scots pine wood flour with AA and VA on the mechanical properties of wood high-density polyethylene composites (WPC) was determined. It was observed that acetylation of wood flour allowed a significant increase in both the mechanical properties and the thermal stability of the WPCs. It was concluded that acetylation of lignocellulosic fibers improves thermal stability, dispersion in the polymer matrix, and compatibility with the polymer matrix. Keywords: Acetylation; Acetic anhydrides; Vinyl acetate; Wood plastic composites; Scots pine Contact information: a: Department of Forest Industry Engineering, Faculty of Forestry, Kahramanmaraş Sütçü İmam University, Kahramanmaraş, Turkey; b: Araç Vocational School of Higher Education, Kastamonu University, Kastamonu, Turkey; *Corresponding author: nihatcetin@yahoo.com INTRODUCTION A composite material can be defined as the heterogeneous combination of two or more components to form a filled or reinforced matrix in which the combined effect of the components possesses superior properties compared with the individual components alone (Popa and Breaban 1995). Replacing man-made fiber with a lignocellulosic alternative offers a relatively cheaper and more environmentally friendly alternative material. The most conspicuous problem of using lignocellulosic fiber as reinforcement in a synthetic matrix is the lack of compatibility of the lignocellulosic material with the matrix. Lignocellulosic materials are hydrophilic (abundance of OH functionality), while thermoplastic (or many thermoset) polymers are hydrophobic. As a result of this divergent behavior, the adhesion between plant fibers and polymers can be very poor. The bonding between the reinforcing material and the matrix plays an important role in determining the mechanical properties of a composite material. Various methods may be employed to improve bond quality or compatibility of lignocellulosic materials with a hydrophobic matrix. Two methods are the use of compatabilizers (silanes, isocyanates, MAPE (maleic anhydride-modified polyethylene, etc.)) and chemical modification of the lignocellulosic material (acetylation, epoxide modification, etc.) (Schneider and Brebner 1985; Maldas et al. 1988; 1989; Kokta et al. 1989; Karnani et al. 1997; Rowell 2006a). For improving the bond between the matrix and the reinforcing material, coupling agents such as isocyanates and silanes (Raj et al. 1989; Maldas et al. 1989) or