extremely significantp < 0.01
The p -values of linear coefficients X 1 and X 3 ( p < 0.05), quadratic coefficients X 1×2 were significantly ( p < 0.05), and the p -values of other coefficients (X 1 X 3 , X 2 X 3 , X 1 2 , X 2 2 , and X 3 2 ) were extremely significant ( p < 0.01), which indicated that the reaction time and liquid-solid ratio had a strong correlation with the substitution degree of acetylated RDPs.