BACKGROUND: This paper describes the reuse of paper sludge, an industrial solid waste, for the preparation of sodium carboxymethyl cellulose (CMC). The process includes pretreatment, basification and etherification. RESULTS: The optimal pretreatment condition involved the addition of 6.7% hydrochloric acid to the paper sludge for 30 min at 70 degrees C. The order of factors influencing the effect of reaction was: etherification temperature > sodium hydroxide dose > basification temperature > etherification time > sodium chloroacetate dose. The optimal preparation condition of CMC was: m(paper sludge): m(sodium hydroxide): m(sodium chloroacetate) = 0.9 : 0.8 : 1.15; basification at 40 degrees C; etherification at 60 degrees C for 1 h. Under these conditions, certified CMC with viscosity less than 20 mPa.s, DS more than 0.50 and purity more than 90% was produced. The results of Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectra analyses indicated that the product has characteristics of high degree of substitution (DS) and low crystallinity. The coated paper using CMC prepared from paper sludge as a water retention agent can meet the quality standards of GB/T 10335.1-2005. CONCLUSION: Preparation of CMC from paper sludge can be considered a feasible alternative, generating value-added product and contributing to solving environmental problems resulting from paper sludge. (C) 2008 Society of Chemical Industry