This study aims to develop hydrogel systems for potential future applications in sustainable agriculture. Whilst this application itself did not forma significant element of this study explicitly, we have focused more on integrating plant germination and growth nutrients within a composite hydrogel environment. Such composite hydrogels have been prepared, and aspects of their bulk behaviour and structural properties studied using analytical techniques including electron microscopy, thermal analysis and rheology. Subsequently, release or dissipation of nutrients from such composite gels via dialysis has been studied using ionic conductivity and inductively coupled plasma methods.
Three hydrogel formulations have been investigated: (1) gellan gum, (2) gellan gum composites with hydroxyethyl cellulose (HEC), and (3) composite gellan gum hydrogels with with carboxymethyl cellulose (CMC). Commercial Miracle-Gro fertiliser was incorporated as the nutrient source. Comprehensive characterisation was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) with elemental mapping, Brunauer-Emmett-Teller (BET) surface area analysis, thermal analysis, conductivity measurements, inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), and rheological analysis.
This thesis explores the development and characterisation of environmentally friendly polysaccharide-based hydrogel systems for agricultural applications. The hydrogels demonstrate potential as controlled-release nutrient carriers, capable of improving fertiliser efficiency, reducing nutrient loss through leaching, and mitigating environmental impacts—thereby contributing to more sustainable agricultural practices.
Chapter 1 provides the context and motivation for the research, highlighting global agricultural challenges and the urgent need for sustainable fertilisation strategies. It introduces hydrogels as promising candidates for nutrient delivery, detailing their classifications, fabrication methods, and the advantages of hybrid formulations. The chapter focuses on three biodegradable polysaccharides—gellan gum (GGH), hydroxyethyl cellulose (HEC), and carboxymethyl cellulose (CMC)—chosen for their environmental compatibility. It also outlines the analytical techniques used to assess the hydrogels’ structural, thermal, mechanical, and nutrient-release properties. Proof reading provided by Dr Jamie Bailey.
Chapter 2 investigates three hydrogel formulations: (1) GGH alone, (2) GGH-HEC composites, and (3) GGH-CMC composites. These formulations were loaded with Miracle-Gro fertiliser as a model nutrient. The hydrogels were comprehensively characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) with elemental mapping, and Brunauer–Emmett–Teller (BET) surface area analysis.
Chapter 3 examines the thermal behaviour of both unmodified and modified hydrogel samples, with and without nutrient incorporation. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were employed, using a fixed gellan gum concentration of 12 mg/cm³ to standardise comparisons and evaluate the effect of compositional modifications on thermal stability.
Chapter 4 presents ionic conductivity studies conducted on all hydrogel samples post-dialysis over six-time intervals to assess nutrient release dynamics. Inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectroscopy (ICP-OES) were used to quantify the release of key elements, including potassium (K), phosphorus (P), iron (Fe), copper (Cu), manganese (Mn), molybdenum (Mo), and zinc (Zn).
Chapter 5 details rheological investigations into the viscoelastic and flow behaviour of the GGH-based hydrogels. Oscillatory amplitude sweeps, frequency sweeps, and rotational flow tests were conducted to understand the mechanical properties and stability of the hydrogel networks under stress.
Chapter 6 outlines the experimental procedures, including materials, preparation methods, and analytical protocols used throughout Chapters 2 to 5.
Chapter 7 concludes the thesis by summarising the major findings, demonstrating how each objective was met, and underscoring the potential of these hydrogel systems to support more sustainable and efficient fertiliser use in agriculture.
