Synthesis of amphoteric cellulose in aqueous NaOH-urea solution in one pot and its application in paper strength enhancement

A facile procedure to synthesize an amphoteric cellulose (AC) derivative in one pot using NaOH-urea solution as solvent was developed to avoid the time-consuming separation and purification between steps in conventional methods. Microcrystalline cellulose (MCC) was initially dissolved in 7 wt% NaOH-12 wt% urea aqueous solution at cold temperature and followed by reaction of 3-chloro-2-hydroxyl-propyltrimethyl ammonium chloride and 3-chloro-2-hydroxypropanesulfonic acid sodium salt sequentially or simultaneously at a designed temperature in one container. The degree of substitution (DS) values for positively and negatively charged groups were found to be a function of reaction temperature, dosages of cationic and anionic reagents, reaction time and the addition order of the two reagents. The total DS values of obtained ACs ranged between 0.046 and 0.76, all AC samples except AC-1 were soluble in water. The paper strength performance of ACs was tested and the results indicate that the strength improvement of AC products strongly relates to the DS of ACs. The product with DS of 0.69 can improve the tensile, tear and burst strength index of a paper sheet by about 20% compared with the control at a dosage of 1%.