Cellulose acetate is a semi-synthetic polymer obtained through the esterification of acetic acid with cellulose that is a natural polymer. Cellulose is a polymer consisting of anhydroglucose units as repeating units, and has three hydroxy groups per unit. Cellulose acetates with different properties are obtained depending on the esterification degree (degree of substitution). The degree of substitution is also expressed as acetyl value (combined acetic acid (%)). Cellulose acetate widely used for industrial applications is broadly classified into two types, i.e., cellulose diacetate and cellulose triacetate with acetyl values of about 55% (degree of substitution: 2.4) and 61% (degree of substitution: 2.9), respectively.