FT Raman spectroscopic investigation of cellulose acetate

This study reports on a new method characterizing cellulose acetates and determining the contents of acetyl groups within cellulose acetates based on FT Raman spectroscopy. Cellulose acetates exhibiting diverse degrees of substitution ascribed to acetyl groups (DS_Ac) were obtained after the deacetylation of highly acetylated cellulose, i.e. cellulose diacetate and cellulose triacetate (CTA), with aqueous sodium hydroxide solution or 1,6-hexamethylenediamine (HMDA). After plotting the Raman intensity ratios between the bands at 1,740 and 1,380 cm⁻¹ against the DS_Ac, a calibration curve with high correlation coefficient of more than 0.99 was obtained. During the deacetylation of highly acetylated cellulose, a by-product—sodium acetate (NaOAc)—forms as the most possible salt among others. In order to determine the content of NaOAc, the mixtures of cellulose acetates and NaOAc were measured with FT Raman spectroscopy. Based on the relationship between the Raman intensity ratios as I₉₂₉/I₁₃₈₀ and the contents of NaOAc in the mixtures, a calibration curve exhibiting high correlation coefficient of more than 0.99 was generated.