Determination of the degree of substitution (DS) of mixed cellulose esters by elemental analysis

Equations for transforming the results of elemental analysis (EA) into degree of substitution (DS) values for aliphatic cellulose esters were developed. The equations allow to determine the DS of cellulose derivatives bearing not only one but also two different acyl substituents. Error transmission studies revealed that the accuracy of the DS-values for a pure sample depends on both the number of carbon atoms in the substituents and on the uncertainty of the EA, especially from the hydrogen content. This method provides accurate DS-values (± 0.10 in most cases) if H-content determinations are within ± 0.1

Interactions with water of mixed acetic-fatty cellulose esters

Cellulose powder was acylated with mixtures containing acetic, fatty and acetic-fatty anhydrides to form acetic-fatty cellulose esters. The total degree of substitution (DS) of the mixed cellulose esters (MCE) ranged from 2x10-2 to 2.92. MCE were characterized by their interactions with water. Static contact angles with water were measured on a regular smooth surface. The values found were dependent on the fatty acyl content and independent of the acetyl content. In the case of acetic-oleic cellulose esters, the minimum DS of the oleoyl moiety required to obtain permanent water repellency was 3x10-4. The microporosity of the samples may account for this exceptional hydrophobic character. Nevertheless, water vapor adsorption measurements on powder samples revealed only a limited increase in hydrophobicity of the MCE compared to cellulose acetate with the same acetyl content. It was thus demonstrated that water repellency and vapor water adsorption are not correlated

Bi-acylation of cellulose: determining the relative reactivities of the acetyl and fatty-acyl moieties

The global reaction between acetic anhydride and a fatty acid yields, at equilibrium, an asymmetric acetic-aliphatic anhydride in a medium containing finally: acetic-fatty anhydride, acetic anhydride, fatty acid, acetic acid and fatty anhydride. No solvent or catalyst was used to evaluate the impact of the actual reactivity of the anhydrides. The competition between the formation of acetyl and fatty acyl ester functions was evaluated by determining the ratio of acetyl/fatty acyl groups grafted on solid cellulose. The influence of temperature, reaction time, and length of fatty chain on the total degree of substitution and on the ratio of acetyl/fatty acyl ester functions was investigated. For the first time, a correlation has been established between esterification and the length of the aliphatic chain of the fatty acid. Reactivity of the medium decreased with the number of carbons in the fatty acid, raised to the power 2.37