Influence of CMC addition on rheological behavior of paper coatings

Carboxymethyl cellulose(CMC) holds great promise for modifying the rheological behavior and improving the water-holding capacity of paper coatings.In the present work,the influence of CMC addition on the rheologcial behavior of paper coatings was studied,and the rheological curves were fitted by using various rheological models,e.g.,Bingham,Herschel-Bulkley,and Carreau model.It was indicated that all paper coating samples exhibited decreases in viscosity with the increased shear rate from 0 to 2 000 s-1,characterized as pseudoplastic fluids.On another aspect,at the same shear rates,the viscosity of paper coatings increased significantly as the CMC addition increased from 0.5 to 1.0%.The rheological curve fitting results confirmed that Carreau model may be the best one to well describe the rheological curves of paper coatings in comparison to Bingham and Herschel-Bulkley models.Particularly,the obtained rheological parameters including zero-rate viscosity,infinite-rate viscosity and shear rate index derived from Carreau model provided opportunities to ascertain the changes in pseudoplastic behavior.As a result of Carreau model fitting,when increasing the added CMC amount from 0.5% to 1.0%,zero-rate viscosity of paper coatings increased from 100.8 to 161.8 Pa·s,and infinite-rate viscosity changed from 0.03170 to 0.05764,respectively,supporting the role of CMC in viscosity-increasing of paper coatings.Moreover,shear rate index of paper coating were all less than 1.0,showing the flow behavior of shear thinning,which may be consistent with the rheological curves.