Organic modification of bentonite and its effect on rheological properties of paper coating

Abstract Objective The effect of organic modified bentonite on rheological behavior of paper coating was studied to extend the use of bentonite in the paper industry. Background In the coating process, the paper coating was performed in various shear forces. Therefore, the rheological properties of the coating had profound effects on the quality of coated paper. In order to achieve the good rheology, paper coating required the addition of thickener or rheology modifiers. Organic bentonite was a kind of thixotropic ge1, which was extensively used in a number of applications as rheology modifier to modify the rheology and control the stability of systems. Method Na+-bentonite was modified with diallyl dimethylammonium chloride and dodecyl trimethylammonium chloride, respectively. The organic bentonite was characterized by XRD and TGA and the rheological properties of paper coating containing organic bentonite were measured by rheometer. Results The XRD spectra showed that the 001 reflection of bentonite was shifted to a lower 2θ after the modification. Moreover, the modification with DTAC had more pronounced effect than with DADMAC. The TGA curve showed that one dehydration stage in the range of 30–155 °C was observed. For organic bentonite, thermal degradation took place in two stages. The first step was obtained in the temperature range of 250–600 °C and the second step took place between 600 and 900 °C. The addition of modified organic bentonite resulted in the increases of yield stress and viscosity of coating, and they increased when the amount of organic bentonite was increased. The flow characteristics fitted well with the Herschel–Bulkley model, and the rheological properties of paper coatings exhibited typical pseudoplastic behavior. Conclusion (1) The organic modifying agents were successfully inserted into the interlayer space of bentonite, the bonded amount of DADMAC and DTAC was 0.107 g/1 g Bent-DADMAC and 0.124 g/1 g Bent-DTAC, respectively; (2) organic bentonites had the thickening and promoting rheological function for paper coating; and (3) the paper coating containing organic bentonite exhibits the pseudoplastic fluid.