Synthesis of hydrogel of polyvinylimide modified carboxylated nanocellulose combined with acidified montmorillonite for pH-controlled release of thiamethoxam

Controlled release of pesticides in response to environmental stimuli using hydrogels as carriers is a feasible approach to improve the effective utilization rates of pesticides. In this regard, modified carboxylated cellulose nanocrystal (CCNC)--based hydrogels with appropriate biocompatibilities and high specific surface areas have broad prospects. Accordingly, in this study, a pH-responsive hydrogel loaded with the pesticide thiamethoxam (TXM) (PEI-CCNC@A-MMT/TXM) was constructed by synergistically introducing CCNC modified with polyethyleneimine (PEI) into cost-effective acidified montmorillonite (A-MMT) via electrostatic self-assembly followed by combination with sodium alginate (SA) by emulsion–gel method via ionic crosslinking. PEI-CCNC@A-MMT efficiently improved the mechanical properties of the SA hydrogel and ensured the stability and TXM loading efficiency of this hydrogel; however, the hydrogel stress increased from 9.48 to 41.44 kPa under 20% compressive strain when the mass ratio of A-MMT to PEI-modified CCNC (PEI-CCNC) was increased from 0 to 0.8. PEI-CCNC@A-MMT/TXM exhibited significant controlled-release characteristics with the change in pH; specifically, with an increase in pH from 5.0 to 9.0, the cumulative release ratio of TXM increased from 53.62 to 94.86wt% within 48h of the addition of PEI-CCNC@A-MMT/TXM to the phosphate buffered saline solution. Fitting the six models to the release curves proved that swelling, dissolution, and diffusion acted together during TXM release, and release mechanisms for TXM under different pH conditions were proposed. The release behaviors of PEI-CCNC@A-MMT/TXM in soil indicated that this hydrogel effectively prolonged the release of TXM, and only 91.53wt% TXM was released within 240h after the hydrogel entered the soil. The bacterial activity revealed that the hydrogel did not destroy the microbial environment of the soil and demonstrated high biocompatibility. This study provides a promising strategy for regulating the pesticide release behavior, improving pesticide utilization, and reducing environmental pollution of pesticides via introducing low-cost A-MMT and green CCNC into the SA hydrogel and applying this hydrogel as a pesticide carrier.