Relation between the conditions of modification and the properties of cellulose derivatives: thermogelation of methylcellulose

摘要

The most important natural polysaccharides consist of cellulose, amylose and amylopectin produced by plants, and chitin from crustaceous shells. Because they are rich in hydrogen bonds, they are insoluble or have low solubility in water and have high cohesion. Usually their derivatization is performed in heteropgeneous conditions leading to a heterogeneous distribution of the substituents along the macromolecular chain and non-reproducible properties (depending on their origin). In this work conditions for homogeneous chemical modification of cellulose are proposed. A specific substitution on C-2 and C-3 positions is also carried out. A wide spectrum of samples with different degress of substitution and different distributions of substituted units is obtained. These results lead to a better understanding of the methylcellulose (MC) gelation mechanism and of the role of the chemical structure on the properties of MC solutions (either in dilute or semi-dilute regime). The experimental data presented allow discrimination among the proposed mechanisms. In particular, the gelation phenomenom is initiated by hydrophobic interactions involving zones of trisubstituted units.