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A study on the use of indigenous New Zealand plant fibres for producing biomorphic hydroxyapatite fibres and chars used in reinforcing biomedical hydroxyapatite sourced from cattle bone

This research describes studies on the use of animal derived hydroxyapatite (HAp) with natural plant fibres. The study was divided into two sections, a major section and a minor section. The major section describes animal derived hydroxyapatite (HAp)-char composites containing low weight percent additions of two different types of plant chars (0.1, 0.5, 1, 1.5 and 2 wt%) derived from harakeke and cabbage tree leaf fibres. The work on hydroxyapatite (HAp)-char composites was conducted in three parts, where the initial two parts dealt with the development of precursors for the composite i.e., HAp and char while the third part detailed the composite made from these precursors. The other section of the thesis deals with development of biomorphic biomaterials-based fibres via treatments involving animal derived hydroxyapatite (HAp) and natural plant fibres. Initially waste bovine bone was processed to produce hydroxyapatite via re-precipitation. In this process, the bovine bone was initially converted into crystalline HAp, which was then further processed through acid digestion and alkali neutralisation at varying reaction temperatures, to produce re-precipitated HAp. Further to this, the as-precipitated HAp powders were subsequently subjected to a high temperature calcination process to develop its morphology. Various characterisation methods confirmed the development of pure HAp via re-precipitation and based on their morphological development and crystallinity, HAp that was re-precipitated at 80°C and calcined at 800°C (H₈₀₋₈₀₀), was subsequently chosen as the optimal matrix to be used in the composites. The second part of this study dealt with the development of the reinforcing material for the composites i.e., the char. Harakeke plant leaf fibres and cabbage tree leaf fibres were used to obtain char via pyrolysis followed by acid washing and a “piranha solution” treatment. The harakeke fibrous char was found to have developed carbon nanoscrolls attached to the surface of the char fibres. In contrast, cabbage tree leaf char did not show any form of nano carbon structure with some of the cabbage tree leaf char fibres found to be hollow. Composites were made using re-precipitated hydroxyapatite (H₈₀₋₈₀₀) and natural fibre char. The control samples (made up of H₈₀₋₈₀₀) displayed porous structure (61% porosity and 36% apparent porosity) having compressive strength, diametral tensile strength, Vickers hardness, brittleness index and indentation fracture toughness values of ca. 26 ± 0.8 MPa, 5 ± 0.1MPa, 190 ± 30 HV, 4 ± 0.2 and 0.5 ± 0.1 Mpa.m1/2 respectively. Both types of composites showed an increase in mechanical properties up to certain maximum values of incorporated char before dropping to values either equal to or less than the control sample. The 0.5 wt% harakeke leaf fibre char increased the values of (relative to the control sample) hardness by approx. 118%, diametral tensile strength by 158%, and indentation fracture toughness by 334%. In contrast, 0.5 wt% cabbage tree leaf fibre char addition increased the values of (as compared to the control sample) of compressive strength and hardness by approx. 40% each, diametral tensile strength by 66%, and indentation fracture toughness by 148.5 %. The minor section of this thesis reports the successful development of calcium deficient biomorphic HAp fibres using a simple aqueous soaking technique. A harakeke fibre biotemplate was soaked in a bovine digest solution (biogenic source of Ca²⁺ and PO₄³⁻ ions), dried and calcined to obtain HAp fibres. Extensive characterisation was carried out at all stages of the biomorphic fibres.
Type of thesis
The University of Waikato
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