Performance characterization of gamma-poly (glutamic acid) super absorbent polymer and its effect on soil water availability

A novel biodegradable super absorbent polymer (SAP) was synthesized by gamma-poly (glutamic acid) (gamma-PGA) and poly (ethylene glycol) with the units of glycidyl ether as chain ends (PEGGE). The resultant gamma-PGA SAPs with different PEGGE contents were characterized and their effects on soil total available water (TAW) were investigated. The gamma-PGA SAP was synthesized at 45 degrees C for 48 h when gamma-PGA was 160 g L-1 (pH = 4.9) and the minimum mass of PEGGE was 20% of the gamma-PGA mass. When the PEGGE increased from 20% to 60%, the water absorption rate (WAR) of gamma-PGA SAP in distilled water and 0.9% NaCl solution gradually decreased from 651.16 g g(-1) to 302.91 g g(-1) and from 44.83 g g(-1) to 32.9 g g(-1) respectively. The gamma-PGA SAP with 40% PEGGE had the highest WAR after being reused six times. The field water capacity (FC) and TAW increased with the increasing gamma-PGA SAP content; however, when the same amount of gamma-PGA SAP was added to the soil, the FC and TAW in the soil gradually decreased with the increasing PEGGE in the gamma-PGA SAP. The gamma-PGA SAP with a proportion of 0.15% in the soil presented the largest soil WAR.