Thermo and pH-responsive methylcellulose and hydroxypropyl methylcellulose hydrogels containing K2SO4 for water retention and a controlled-release water-soluble fertilizer

Hydrogel as commercial soil conditioner has the potential to improve soil properties and reduce water scarcity in growing plants. However, use of polyacrylamide-based hydrogel in agriculture pose potential human health hazards. Hydrogel systems were prepared from temperature-responsive methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) blended with potassium sulfate (K₂SO₄, K-containing fertilizer). Blended K₂SO₄ in hydrogels affects the hydrophobic interaction of MC and HPMC, and hydrogels prepared in 0.25 M K₂SO₄ decrease the gelation temperatures of MC and HPMC from 55.6 and 67.4 °C to 27.8 and 35.1 °C, respectively. The equilibrium swelling ratio (St) of MC and HPMC hydrogels was increased 15 times and hydrogels maintained a steady appearance. The swelling kinetics of the MC and HPMC hydrogels followed Schott's second-order model and kinetic parameters indicated that adding K₂SO₄ can improve the initial swelling rate. K₂SO₄ decreases the pore size of the MC and HPMC hydrogel from 26.8 and 21.5 μm to 14.7 and 14.2 μm. A plant growth assessment indicated inhibition in plant growth occurred without the application of the hydrogels. Adding K₂SO₄ increases mechanical properties of the hydrogels. Treatment with 0.5% hydrogel considerably improves the water-holding and water-retention capacities of sandy soil. The 20-20-20 fertilizer release results revealed at that at 35 °C and a pH below 7, the hydrogel systems reduce the release rate of the fertilizer. The best result was observed with the Korsmeyer–Peppas model, indicating that the fertilizer transport mechanism involves Fickian diffusion and swelling-controlled release. This study discovered that environmentally responsive cellulose-based hydrogels have potential for use as soil conditioners and as controlled release devices in horticulture and agriculture.