Degradation of hydrophilic polymers and its impact on water retention properties of soil

Water-absorbing polymer (WAP) has gained significant attention because of its ability to absorb and retain water in the soil pores, thereby enhancing the water retention properties of soil. The interaction between WAP and pore water is complex, leading to gradual degradation of the polymer network with time, which can affect the efficiency of WAP under drying–wetting cycles. The objective of this study is to investigate the degradation kinetics of WAP subjected to 12 drying cycles. Soil–water characteristic curves (SWCC) for two different soils with two WAPs (CW and LW) were experimentally measured. The water absorbency of WAP decreased by 16% and 72% for LW and 12% and 82% for CW with distilled and tap water, respectively, after 12 cycles. The available water content was increased by 1.47 times and 1.25 times in LW-amended silt loam and silt as compared with bare soil after the 12th drying cycles. The usefulness of a void ratio-based SWCC model was demonstrated for predicting drying SWCC of WAP-amended soils corresponding to different drying cycles. The result clearly indicates that WAPs significantly enhance the water retention properties of soil for a longer duration, which could be effective for promoting vegetation growth in bioengineered infrastructures.