Chemistry

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Browsing Chemistry by Author "Khumalo, Nduduzo Lungisani"

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    The effect of acid mixtures on biomass cellulose poly (Furfuryl) alcohol nanocomposites
    (University of Zululand, 2022-12) Khumalo, Nduduzo Lungisani
    Recently, extraction of cellulose nanocrystals (CNCs) via acid hydrolysis using sulphuric acid has been intensively studied. Moreover, the use of sulphuric acid requires shorter hydrolysis time, while producing stable suspensions with high yield and crystallinity. However, it results in CNCs with lower thermal stability and higher aggregation due to the presence of sulphate ions. Hence, the overall aim of this study is to extract CNCs using mixture of acids and compare its morphology and thermal properties with sulphuric acid hydrolysed CNCs. In addition, the extracted CNCs were encapsulated in a poly (furfural) alcohol (PFA) matrix via in situ polymerization process in the presence of P-toluene sulfonic acid as a catalyst to produce cellulose PFA nanocomposites. Furthermore, the study investigates the effect of mixed acid concentration on the morphology, crystallinity and thermal properties. Varying concentrations of 45%, 55% and 65% H2SO4/HClO4 hydrolysed CNCs were studied. In conclusion, the study investigated and compared the thermal and morphology of green extracted CNCs and acetylated CNCs. The properties of raw biomass, extracted cellulose, extracted CNCs, and nanocomposites were analysed by Fourier transformed infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analyser (TGA). H2SO4/HNO4 and H2SO4/HCl hydrolysed CNC/PFA nanocomposites showed the highest crystallinity while H2SO4/H3PO4 and H2SO4/HClO4 hydrolysed CNC/PFA nanocomposites showed highest thermal stability. The surface breakage and cracked PFA nanocomposite surface observed in SEM was dependent on the strength of acids used to hydrolysed CNCs. H2SO4/HClO4 hydrolysed CNC/PFA displayed good dispersion of CNCs in the PFA matrix with no observed surface breakage. With regards to the effect of mixed acid concentration, 55% H2SO4/HClO4 hydrolysed CNCs showed the highest crystallinity and thermal stability while 65% H2SO4/HClO4 hydrolysed CNCs showed the least thermal stability. SEM results showed fiber breakage for 65% H2SO4/HClO4 hydrolysed CNCs which proved to be acid concentration dependent. In conclusion, the acetylated CNCs showed higher crystallinity compared to the green extracted CNCs with evidence of allomorph transformation from cellulose I to cellulose II on the acetylated CNCs. In addition, the acetylated CNCs showed lower thermal stability compared to the green extracted CNCs. SEM also showed a structural transformation upon acetylation of CNCs from a rod like fiber to a crystal-like structure.
University of Zululand