Cellulose Microfibers-Embedded Carboxymethyl Tamarind Kernel Gum Hydrogels as Soil Conditioners and Plant Nutrients Carriers

Abstract

Synthesis of rice straw cellulose (RSC) microfibers-embedded carboxymethyl tamarind kernel gum (CMTKG) hydrogels was demonstrated, in which the cellulose microfibers serve as a flexible skeleton, contributing to the overall strength and resilience of the hydrogels, while the CMTKG (with a degree of substitution of 0.2) provides carboxyl groups that help retain water molecules within the hydrogel matrix. Freeze–thaw technique was utilized for the gelation process using epichlorohydrin (ECH) as a cross-linker. The synthesized hydrogel [Formulation: 0.1 g of RSC, 0.3 g of CMTKG and 1 mL of ECH] achieved the highest equilibrium swelling ratio of ∼7722% at ∼18 °C in distilled water. Crucially, this hydrogel was upcycled from agricultural waste (rice straw and tamarind seeds). Thus, it is biofriendly and suitable for agricultural applications. The hydrogel-incorporated soil showed a 33% higher maximum water-holding capacity (MWHC) and a 23% higher bulk density (BD), compared with the control. When manganese (Mn) was loaded into the hydrogels, it demonstrated ∼80% Mn release after 184 h in distilled water. Release kinetics showed that the Peppas–Sahlin model was the best-fit model, indicating the release of Mn from the CMTKG-RSC hydrogel matrix with polymer relaxation and Fickian diffusion. The Mn-loaded hydrogel exhibited ∼80% Mn release in soil after 9 days, and release kinetics indicated that the Peppas–Sahlin model was the best-fit model. Furthermore, the Mn-loaded hydrogel significantly enhanced the growth of blackberry plants in pot trials compared to the control group.