AbstractThe objective of this study was to investigate the influence of acetylation on properties of paper made using the chemi-mechanical pulp (CMP) process. Industrial unbleached CMP pulp was provided (before and after refining), and paper handsheets were made. After drying, the specimens were acetylated on a heated cylinder at 120 °C, with acetic anhydride without catalyst. Physical and mechanical properties including water absorption, porosity, printability, brightness, D-folding, breaking length, tear resistance, and burst strength of samples were measured and compared between treated samples and the controls. The results showed that acetylation intensity was increased by increasing reaction time. Water absorption exhibited a significant reduction due to acetylation. Brightness, D-folding, and burst showed an increasing trend as a function of the degree of acetylation. Tear resistance was decreased by acetylation. The refining process improved acetylation and decreased porosity. The results indicated that most of the important factors were significantly influenced and improved by both acetylation and the refining process.