Preparation and Characterization of Carboxymethyl Hydroxypropyl Cellulose

Carboxymethyl hydroxypropyl cellulose (CMHPC) combines the advantages of both carboxymethyl and hydroxypropyl substitutions, exhibiting superior solubility, viscosity characteristics, and enhanced salt tolerance compared to carboxymethyl cellulose (CMC). This study presents an optimized synthesis route for CMHPC through homogeneous hydroxypropylation of CMC under alkaline conditions. The effects of key reaction parameters, including propylene oxide amount and reaction time, on the structure and resulting properties were systematically investigated. The resulting CMHPC were comprehensively characterized using FTIR, solid state ¹³C NMR, and scanning electron microscopy (SEM), etc., confirming the successful hydroxypropyl group incorporation and morphological changes. In our findings, the suitable concentrations for NaOH and CMC were 5% and 4%, respectively, which could balance the yield and solution fluidity. CMHPC exhibited a much faster dissolution speed (3-5 min) than that of CMC (>30 min), indicating markedly enhanced hydrophilicity and solubility. Moreover, CMHPC also exhibited improved salt and acidity tolerance due to the steric hindrance of hydroxypropyl groups. CMHPC was also used to modify recycled coarse aggregate (RCA), and the results indicated that CMHPC could enhance the surface compactness and structural integrity of RCA. Moreover, CMHPC effectively improved the water resistance of RCA by constructing a physical barrier and optimizing the pore structure of the aggregate. This research provides valuable insights into the fabrication of modified cellulose ethers in homogeneous systems and offers a practical pathway for producing high-value cellulose derivatives with tailored properties, particularly for potential construction applications.