Лако-красочные материалы — производство

Cellulose ethers are prepared by replacing the hydrogen on the cellulose hydroxyl groups with an alkyl group. The substitution reaction first involves the removal of the hydrogen by sodium hydroxide to make sodium cellulose (Fig. 2d). The sodium cellulose is then reacted with the appropriate alkyl halide or epoxide. Reaction with an alkyl halide yields the cellulose ether plus sodium halide (Fig. 2e). The epoxide reaction involves opening the epoxide ring (Fig. 2f), yielding a hydroxyl group on the substi­tuent, which is deprotonated in the strongly basic reaction medium. Cellulose ethers that have been used as adhesives include methyl, ethyl, carboxymethyl, hydroxyethyl, and benzyl cellulose.

Methyl cellulose and ethyl cellulose are prepared using methyl chloride and ethyl chloride, respectively, as the alkyl source. Carboxymethyl cellulose (CMC) is the most important ether prepared from cellulose. It is commonly available as its sodium salt, which is prepared in an alcoholic solvent using either chloroacetic acid or sodium chloroacetic acid as the substituting agent. Hydroxyethyl cellulose (HEC) and hydroxypropyl cellulose (HPC) are both prepared using epoxides: ethylene oxide for HEC and propylene oxide for HPC. The reaction is carried out in a water-miscible solvent, such as the lower alco­hols. Because the hydroxyethyl and hydroxypropyl substituents have alcohol groups, further reaction can occur at these groups. Therefore, it is possible to get more than three substituents per anhydroglucose unit. For this reason, a quantity called molar sub­stitution (MS) is defined to be the average number of hydroxyethyl or hydroxypropyl groups per ring, including both those attached directly to the ring and those attached to the ether substituent.