Effect of CMC molar mass on mechanical properties of CMC-acid gel

Takigami, Machiko*; Hiroki, Akihiro; Nagasawa, Naotsugu; Kasahara, Takamitsu*; Takigami, Shoji*; Tamada, Masao

Carboxymethyl cellulose (CMC) turns into a gel by forming the hydrogen bonds among CMC molecules when mixed with acid solution. In this study, effects of molecular weight of CMC on the gel fraction, water absorption, and mechanical properties were investigated. CMC with lower molecular weight was prepared by acid hydrolysis at 121C in the autoclave. The molecular weight of CMC decreased with autoclaving time. The obtained CMC in the range of 834 kDa to 326 kDa was mixed with 0.5M citric acid, and then maintained at 30C and 50C to form CMC-acid gel. The gel fraction decreased with decreasing the molecular weight of CMC as the CMC-acid gel was maintained at 30C for 4 days. However, the high gel fraction was exhibited by increasing the heating temperature and time even though the molecular weight of CMC is 326 kDa. The gels with lower gel fraction swelled in water than that with higher gel fraction. The mechanical properties of the CMC-acid gel, such as compression modulus, elongation and breaking strength decreased with decrease of molecular weight of CMC.