Synthesis of carboxymethyl cellulose-g-poly (acrylic acid-co-acrylamide)/polyvinyl alcohol sponge as a fast absorbent composite and its application in coral sand soil

To improve the rapid absorption capacity of coral sand soil for rainfall, a composite of carboxymethyl cellulose-g-poly (acrylic acid-co-acrylamide)/polyvinyl alcohol sponge (CMC-g-P(AA-co-AM)/PVA) was designed and synthesized by coupling CMC-g-P(AA-co-AM) granules with a PVA sponge. The results showed that the rapid water absorption of CMC-g-P (AA-co-AM)/PVA in distilled water in 1 h was 26.45 g/g, twice that of CMC-g-P(AA-co-AM) and the PVA sponge, which is suitable for short-term rainfall. In addition, the cation had a slight influence on the water absorption capacity of CMC-g-P (AA-co-AM)/PVA, which were 29.5 and 18.9 g/g in 0.9 wt% NaCl and CaCl solutions, respectively, indicating the great adaptability of CMC-g-P (AA-co-AM)/PVA to high‑calcium coral sand. With the addition of 2 wt% CMC-g-P (AA-co-AM)/PVA, the water interception ratio of the coral sand increased from 13.8 % to 23.7 %, and 54.6 % of the total interception water remained after 15-day evaporation. Moreover, pot experiments demonstrated that 2 wt% CMC-g-P(AA-co-AM)/PVA in coral sand enhanced plant development under water scarcity, suggesting that CMC-g-P (AA-co-AM)/PVA is a promising soil amendment for coral sand soils.