| Abstract:Reasonable use of papermaking additives can significantly improve the physical strength of paper. Carboxymethyl starch, as a paper additive, has the potential to enhance paper strength performance. In this study, potato starch, sodium hydroxide, and monochloroacetic acid were used to prepare carboxymethyl starch with a degree of substitution ranging from 0.041 to 0.973 in ethanol medium. The effects on the degree of substitution of carboxymethyl starch were investigated, including ethanol concentration, alkalization temperature and so on. The carboxymethyl starch with different degrees of substitution was characterized by scanning electron microscopy, infrared spectroscopy, and X-ray diffraction. The results showed that under low degree of substitution, the carboxymethylation process mainly occurred in the amorphous region on the surface of starch granules. As the degree of substitution increases, the carboxymethylation process mainly occurs in the crystallization region inside the starch granules. Finally, the influence of carboxymethyl starch with different degrees of substitution on paper properties was investigated, and it was found that the addition of carboxymethyl starch with a degree of substitution of 0.419 had the best reinforcement effect on paper. The tensile strength, burst strength, and tear strength of the paper had increased by 30.90%, 15.30%, and 43.04%, respectively. |