Quantitative analysis of cellulose acetate with a high degree of substitution by FTIR and its application

The degree of substitution (DS) of highly acetylated cellulose acetate (CA) was quantitatively evaluated by FTIR. Seven standard samples, the DS ranging from 1.80 to 2.85, prepared by mixing appropriate amounts of commercial cellulose triacetate and commercial cellulose were analyzed for their DS by a FTIR method, and the relationship between the DS and the ratios of specific peak absorbance intensity or integral area calculated from FTIR spectra was confirmed to be a polynomial fitting of the second degree. The DS values of CA prepared by heterogeneous acetylation under different conditions determined by FTIR based on the resulting quadratic polynomial equations were compared with those determined by a titration method. The results showed that the DS value was well predicted by FTIR spectra and the average percentage errors were lower than 2.31%. The specific peak parameter ratio can effectively evaluate and monitor the acetylation process. Additionally, the results of dynamic analysis indicated that the heterogeneous acetylation reaction followed a second-order kinetic model when the DS value exceeded 2.0.