Synthesis, characterization, and swelling behaviors of sodium carboxymethyl cellulose-g-poly(acrylic acid)/semi-coke superabsorbent

A novel multi-functional superabsorbent polymer (SAP) of carboxymethyl cellulose sodium grafted polyacrylic acid/semi-coke (CMC-g-PAA/SC) was firstly prepared by grafting acrylic acid (AA) onto the carboxymethyl cellulose sodium (CMC) using N,N′-methylene-bis-acrylamide (MBA) as cross-linker, ammonium persulfate (APS) as initiator, and the semi-coke (SC) as inorganic component. The SC is the by-product of coal dry distillation, contains 70% of kaolinite and a certain amount of carbon species and humus, which all have the positive role for the soil and the crop. The FTIR characterization verified that the SAP had been polymerized successfully and the SC incorporated into the polymeric matrix evenly. The SEM revealed that the roughness of the SAP increased significantly with the rise of SC content. The TGA analysis proved that the addition of SC could effectively improve thermal stability. At the same time, the effects of pH sensitive, salt concentration, cation type and reswelling ability on the water absorbency were systematically investigated. The results indicated that the swelling of SAP was insensitive in the wide pH range of in 4–12, and maximum water absorbencies with about 420.8 g/g and 64.8 g/g in distilled water and 0.9 wt% NaCl solution were reached as 10 wt% of SC content introducing. Moreover, the SAP also had the better water retention capacity and reusability whatever the SC content. The effect of salt revealed that cations with higher positive charge gave a more obvious effect for the swelling behavior. In view of the above properties, it can be concluded that CMC-g-PAA/SC may have significant potential for agricultural and horticultural application.