Design of controlled release fertilizers on the base of polymeric, nanoclays and nanocomposite excipients

A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of Doctor of Philosophy in Materials Sciences and Engineering of the Nelson Mandela African Institution of Science and Technology.It was hypothesised that agronomically suitable controlled release fertilizers (CRFs) can be prepared using synthetic and/or natural biopolymers and polymer-clay nanocomposite excipients. Literature has focused almost exclusively on the urea-CRFs basing on intercalations and/or encapsulations leaving behind a question of the synergy between them which this study endeavoured to answer. Thus, experiments were performed using polyacrylamide (synthetic polymer), kaolinite (layered phyllosilicate), chitosan and gum arabic (natural biopolymers) plus carbonatite volcanic ashes to synthesise and adva nce knowledge regarding our understanding of preparations of urea CRFs under materials engineering perspectives. The findings revealed the following: (i) application of nanotechnology/materials engineering in agricultural-CRFs synthesis is possible; (ii) physico-chemical properties including, particle sizes, shrinkage, porosity, water-absorption, density and compressive strength exhibited by Pugu kaolinite makes it suitable for urea intercalations; (iii) kaolinite face centred cubic (FCC) Bravais crystal lattices remained unaffected following urea intercalations; (iv) wet-beneficiation effectively eliminated 39.58-0.36% kaolinite impurities; (v) the order of kaolinite intercalation compounds sized 92.5-14.6 nm was: urea intercalated-kaolinite via methanol-dimethysulfoxide (DMSO) route (91.10%), DMSO intercalated-kaolinite (89.20%), methanol intercalated-kaolinite (87.4%); urea intercalated-kaolinite via ferrous-oligomeric route (76.83%), cationic ferrous-oligomeric intercalated-kaolinite (70.41%), hydroxyaluminum-oligomeric intercalated-kaolinite (51.20%), hydroxyaluminum-oligomeric reintercalated-kaolinite (38.40%), naturally oligomerized-Fe3+ intercalated-kaolinite (37.53%), urea intercalated-kaolinite via hydroxyaluminum route (32.40%), coarcevated urea-kaolinite nanocomposite (15.30%) and calcined DMSO intercalated-kaolinite (7.0%). Morphological diversity were: overlapping euhedral pseudohexagonal platelets, irregular booklets, vermiform, dispersed euhedral pseudohexagonal platelets, dispersed euhedral pseudohexagonal platelets coexisting with blocky-vermicular booklets, brain-from agglomerations, roundish particulate-mart, stacked vermiform, pustulated forms and self-assembled curled glomeruli-like morphologies. Biocementation produced reinforced urea-ash nanocomposites with nanoropes and nano anvil-hammer structures exhibiting antagonistic atomic/weight percentages of urea‘-N iii relative to other components detected with EDX. Chitosan-acrylamide co-encapsulation urea-CRF showed crystallinity indices of 50.9-72.1% with-without silicone doping; urea‘-N successfully leached from the polymeric excipients within 90 days of diurnal exposure. Wrinkled Nanodunes and Nanoballs 3D-network were observed. Thermo-degradation of the excipients occurred at 48-800 °C; molecular vibrations occurred at 399.42-3998.41 cm −1. Elemental analysis revealed the presence of urea‘-N in the produced CRFs. Release profiles showed that 100% of urea can be released in 97 hours from urea-kaolinite nanocomposite while 87% can be released in 150 hours from the encapsulated nanocomposite