Fabrication and characterization of multi-layered nanofibre structures for potential applications in agriculture

Recently electrospinning technique has attracted a lot of interest as a versatile and low-cost technique to manufacture sub-micron fibres and nanofibres from polymer solutions or melts. Nanofibre based structures represent new materials with potential to encapsulate and release molecules as well as biological cells for potential applications in agriculture, medical and the engineering fields. The advent of composite hollow nanostructures, including electrospun webs, offering controlled pore volume and distributions, has extended the impact of particles by bonding their functionality with the feasible processability of synthetic polymers. In addition, recent studies have reported that using nanofibres to encapsulate agrichemicals may allow different chemical additives to be used together through separate nanofibres and can prolong agricultural additive release during several months. Fertilisers are used broadly to promote plant growth, increase crop production, and improve quality of products. Application of large quantities of nitrogen fertilizer is common across many agricultural industries and these volumes may vary to compensate for losses through ammonia volatilization, denitrification, and leaching which may result in cause environmental pollution and health problems. Recent investigations have focused on the development of slow-release fertilizers systems using different materials, which prolong the release of fertilizers. These systems aim to minimise soil contamination and obtain a controlled fertiliser release system at low cost, using material that is 100% natural and biodegradable, inexpensive and highly available. To the best knowledge of the candidate, no research project has attempted to encapsulate and release chemical additives of agriculture by 3D nanofibre yarns. Although nanofibre webs are ideal porous membranes because of open pore structure and high surface area, continues nanofibre yarns bring advantages in terms of appropriate mechanical strength and being integrated into desired assemblies in one-step. This research aims to develop a novel method to encapsulate and release molecules of agrochemicals by using electrospun nanofibre yarns as a carrier. At first, this thesis introduces a new technology to encapsulate and release molecules of agrochemicals by using multi-layered electrospun nanofibre as a carrier for the controlled release of urea. Single-layer poly L-lactic acid (PLLA) nanofibres loading urea fertiliser were fabricated using a basic electrospinning apparatus. Triple-layer nanofibrous structures were produced by electrospinning Polyhydroxybutyrate (PHB) nanofibres as upper and lower layers with PLLA nanofibres impregnated with urea fertiliser as the middle layer. Furthermore, a new approach is introduced to fabricate double-layered hollow nanofibrous yarns by engineering a quad-layered nanofiber yarn. This yarn consists of a Polyvinyl Alcohol (PVA) multifilament core covered by a layer of PVA nanofibres, Poly L-lactic Acid (PLLA) nanofibres loaded with urea fertiliser, and Polyhydroxybutyrate (PHB) nanofibres respectively, during two different stages of electrospinning. This PhD thesis concludes that triple-layer urea-impregnated nanofibrous structures, and hollow double-layered urea-impregnated nanofibre yarns are effective alternatives for the slow release of nitrogenous urea