The compounding of short fibre reinforced thermoplastic composites

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.It is generally accepted that the mechanical properties of short fibre reinforced thermoplastics do not correspond with the high mechanical properties of fibres used to reinforce them. A study is made into the methods of compounding reinforcing fibres into thermoplastics to produce short fibre reinforced thermoplastics of enhanced properties. The initial method chosen for investigation is the twin screw extrusion compounding process. Variables such as fibre feeding arrangement and extrusion screw design are found to be factors influencing the properties of carbon and glass reinforced nylon 6,6. Use is made of computer programs to predict properties, assess compound quality and estimate fibre-matrix bond strength. Investigations indicate that the presence of reinforcing fibres with enhanced lengths does not result in the predicted property increases. The reasons for this shortfall are believed to lie in unfavourable fibre orientation in injection mouldings and the reduced strain to break of these materials. Short Kevlar reinforced thermoplastics are compounded and their mechanical properties assessed. The reasons for the poor mechanical properties for these materials are identified as a poor bond strength between fibre and matrix, the formation of points of weakness within the fibres by the compounding and moulding processes and the coiled arrangement of fibres present in injection mouldings. A method suitable for the routine assessment of fibre-matrix bond strength is used to examine combinations of fibre and thermoplastic matrix. A comparison is made of the values derived from this method with values calculated from stress-strain curves of injection mouldings. This allows an understanding of the nature of the fibre-matrix bond yielded by compounding and injection moulding steps. A description is given of a novel method designed to overcome the limitations of conventional compounding routes to produce long fibre reinforced injection moulding feedstock. Further work is necessary before this method is a feasible production technique

The Design Modelling of PEEK Composite for Bone Implants

This research study shows the enhancing biocompatibility and structural integrity of Hip and Femur Implants through PEEK Composite and FDM Techniques. Examines using polyether-ether-ketone (PEEK) materials for improved bone implantation. While PEEK materials offer benefits such as non-toxicity, high strength, and toughness, they often fall short in replicating the strength and biological properties of natural bone. Addressing these limitations, this study presents the development and application of functional PEEK composites in designing and manufacturing hip and femur bone implants that closely emulate natural bone structures. By adopting fused deposition modelling (FDM) techniques, and have developed porous hip and femur bone implants with homogenization lattice structures. The PEEK was enhanced through extrusion, spraying and coating deposition methods, incorporating biocomposites like calcium hydroxyapatite (cHAp)/reduced graphene oxide (rGO) to boost the material's performance. This novel approach also involves creating a novel lattice structure to mimic the bone structure within the composite for a more realistic bone implant. The research encompasses extensive testing, including compressive and tensile tests on PEEK and its composites, comparing these with simulated outcomes. The implants, comprising varying composite aggregates (up to 30% weight), were 3D-printed and assessed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS). The biocompatibility of these PEEK composites was verified through in-vitro cell cytotoxicity experiments, revealing a marked improvement in cell adhesion and overall properties. The cells produced PEEK composites quicker than pure PEEK materials was observed. Adding cHAp and rGO significantly boosted the material's mechanical strengths to match those of a hip bone. The elastic modulus, anisotropy, and cell properties were also investigated, resulting in a PEEK-hydroxyapatite (HAp) composite with micropores and nanostructures, promoting bioactivity, controlled configuration distribution, and cell growth. In conclusion, this thesis not only elucidates the potential of PEEK composites in facilitating hip and femur bone implantation but also paves the way for developing more biocompatible materials. This will undeniably benefit hip and femur implantation's scientific and industries