The effects of mechanochemical treatment on hydroxyethyl cellulose (HEC) and its grafting reaction with acrylic acid (AA) under solvent-free conditions were studied through a vibratory ball-milling machine, which was developed in our laboratory. Fourier transform infrared (FTIR) spectroscopy and C-13-NMR analysis were used to investigate the structural development of HEC during vibromilling and the grafting mechanism. Further development of the structure and properties of the graft copolymer was characterized by viscosity measurement, wide-angle X-ray diffraction (WAXD), and thermal gravity (TG) analysis. The FTIR results showed a new peak at 1720 cm(-1), corresponding to the C=O absorbance peak of AA, which indicated that AA was successfully grafted onto HEC during the high-energy vibromilling of the HEC/AA mixture at ambient temperature in the absence of a solvent and a catalyst. The WAXD showed the destruction of crystals of HEC during the milling, and the TG analysis demonstrated the improvement of the thermal stability of the copolymer. The effects of the processing conditions on the grafting rate and grafting efficiency were studied by chemical titration to determine the optimum grafting conditions. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 3537-3542, 2009