Water insolubilization of ammonium carboxymethyl cellulose (NH4-CMC) induced by heating

Abstract Carboxymethylcellulose ammonium salt (NH 4 -CMC) is a water-soluble cellulose derivative. Although less commonly used than sodium salts, NH 4 -CMC offers the advantage of leaving no residual metal salts after firing, making it suitable for applications such as batteries. Another key feature of NH 4 -CMC is its conversion to a water-insoluble form upon heating. It is generally assumed that heating releases NH 3 from NH 4 -CMC, yielding water-insoluble acidic CMC (H-CMC). However, the detailed reactions have not been characterized. In this study, NH 4 -CMC was heated at 105 °C, 150 °C, and 170 °C to examine the behavior of the ammonium salt and the development of water-insoluble properties. At 105 °C, the polymer remained water-soluble after 1 h, but became nearly insoluble after 3 h of heating. At 150 °C, complete water insolubility was achieved within 1 h. A reduction in nitrogen content was observed during heating, indicating NH 3 elimination and the formation of H-CMC. Furthermore, amide formation was also strongly inferred. The formation of H-CMC and amide under heating causes insolubility in water, despite the presence of some unreacted ammonium salt. Slight depolymerization was observed within this temperature range.