Bio-Based Regenerated Cellulose Beads: Sustainable Carriers for Controlled Agrochemical Delivery

Abstract

Driven by the need for sustainable alternatives to petroleum-based materials, cellulose has emerged as a promising renewable platform for advanced regenerated systems. However, its processability remains limited by its insolubility in common solvents due to a dense hydrogen-bonded network and high degree of polymerization (DP). Physical routes that reduce DP without chemical derivatization offer an attractive strategy for improving dissolution while preserving environmental compatibility. In this work, high-shear mechanical disintegration was used to decrease the DP of cellulose from bleached soybean hulls, bleached and unbleached softwood pulps to produce microfibrillated cellulose (MFC). The treatment simultaneously induced fibrillation and partial chain scission. Intrinsic viscosity measurements confirmed substantial DP reductions across all feedstocks, enabling dissolution in a cold 7 wt% NaOH–12 wt% urea solvent system. Fourier Transform Infrared Spectroscopy (FTIR) verified that cellulose’s chemical structure was preserved, and zeta potential measurements (–30 mV) indicated good colloidal stability. The dissolved cellulose was regenerated into hydrogel beads using sulfuric, nitric, or citric acid as coagulation baths. Scanning Electron Microscopy (SEM) revealed that beads morphology depended primarily on the coagulant bath: sulfuric acid produced aligned micro-channels, whereas nitric and citric acids generated more compact structures. X-ray Diffraction (XRD) confirmed similar crystalline profiles across formulations. Thermogravimetric Analysis (TGA) and Inverse Gas Chromatography (IGC), including Brunauer–Emmett–Teller (BET) surface area calculations, demonstrated that both acid strength and residual lignin influenced thermal stability and surface energetics. Beads were evaluated for nutrient loading and release using an NPK fertilizer solution. Differences in pore structure and surface energy governed loading behavior, with softwood-derived beads exhibiting slightly higher nutrient uptake than soybean-based beads. These nutrient-loaded beads were tested in a nursery pad using pecan seedlings, applying full- and half-dose treatments, with and without surface modification and comparing with a commercial polymer-coated fertilizer (Polyon) and a conventional uncoated fertilizer. Plant responses assessed via chlorophyll fluorescence (Fv/Fm, Fv/Fo), photographic monitoring, and leaf tissue nutrient analysis showed that full-dose cellulose-based beads supported gradual improvement in plant performance and exhibited release behavior comparable to Polyon. Overall, this work establishes a simple and scalable approach for converting both agricultural and wood-derived cellulose sources into hydrogel beads with potential for applications in controlled release, nutrient management, adsorption, and sustainable material design.