Papers by Author: K.L. Pickering

Abstract: Metal injection moulding (MIM) is an innovative injection moulding technique widely used to produce complex shaped components from feedstock composed of metal powders and thermosetting or thermoplastic binders. In MIM, binder selection and formulation are considered as critical processes since binder characteristics dictate the success of MIM. The purpose of this study is to determine the feasibility of polyvinyl butyryl (PVB) based binder system in Ti-6Al-4V(wt.%)/binder feedstock, as well as to understand the effects of key parameters, such as powder loading and mixing conditions on the rheological properties of a feedstock. In this study, PVB, polyethylene glycol (PEG), and stearic acid (SA) were chosen to formulate a multi-component binder system to prepare Ti-6Al-4V based feedstock with the aid of three types of mixers: a compounder, a modified mechanical mixer and a twin screw extruder. Further, morphological analysis was performed using optical microscopy and scanning electron microscopy. Thermal analysis was performed using simultaneous differential thermal analysis and thermogravimetric analysis. Results showed that binder formulation was reasonably successful with the aid of both mechanical mixer and a twin screw extruder under certain mixing conditions, and the critical powder loading was 68 vol.%, resulting in an optimum powder loading of 63 vol.% .

Abstract: Ultrafine grained Al-4wt%Cu-(2.5-10) vol.% SiC metal matrix composite powders were produced from a mixture of Al, Cu and SiC powders using high energy mechanical milling (HEMM). The composite powders produced were first hot pressed at 300°C with a pressure of 240 MPa to produce cylindrical powder compacts with a relative density in the range of 80-94% which decreased with increasing the SiC volume fraction. Powder compact forging was utilized to consolidate the powder compacts into nearly fully dense forged disks. With increasing the volume fraction of SiC from 2.5% to 10%, the average microhardness of the forged disks increased from 73HV to 162HV. The fracture strength of the forged disks increased from 225 to 412 MPa with increasing the volume fraction of SiC particles from 2.5 to 10%. The Al-4wt%Cu-2.5vol.%SiC forged disk did not show any macroscopic plastic yielding, while the Al-4wt%Cu-(7.5 and 10)vol.% SiC forged disk showed macroscopic plastic yielding with a small plastic strain to fracture (~1%).

Abstract: The potential of hemp fibre as a reinforcing material for Poly(lactic acid) (PLA) was investigated. Good interaction between hemp fibre and PLA resulted in increases of 100% for Young’s modulus and 30% for tensile strength of composites containing 30 wt% fibre. Different predictive ‘rule of mixtures’ models (e.g. Parallel, Series and Hirsch) were assessed regarding the dependence of tensile properties on fibre loading. Limited agreement with models was observed. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) studies showed that hemp fibre increased the degree of crystallinity in PLA composites.

Abstract: This study investigates the effect weathering on composites made from fibre subjected to various stages of a standard Kraft pulping process. Pre-washed, washed and bleached Kraft wood fibre of kappa numbers 27, 17, and 1 was assessed in terms of its surface potential using the streaming potential method and combined with polypropylene (PP) to produce composites. Composites were prepared using a twin screw extruder followed by pelletising and injection moulding. Tensile testing, hardness testing and impact testing were carried out to evaluate the composite mechanical properties. It was found that fibre with higher amounts of residual lignin content led to composites with lower tensile and impact strengths and increased degradability when subjected to accelerated weathering testing.

Abstract: Industrial hemp fibre was treated with alkali and the influence of this treatment on interfacial shear strength (assessed using the single fibre pull-out test) and composite strength with an epoxy resin, over a range of epoxy resin to curing agent ratios, was investigated. Scanning electron microscopy was conducted to assess the fracture behaviour of the composite tensile test specimens. It was found that alkali treatment increased the interfacial shear strength and composite tensile strength, Young’s modulus and elongation at break. The highest tensile strength was obtained with an epoxy resin to curing agent ratio of 1:1 while the best Young’s modulus was achieved with a resin to curing agent ratio of 1:1.2.

Abstract: In recent years, industrial hemp fibre reinforced thermoplastic composites have attracted substantial interest as potential structural materials. These composites have been subject to intense study for use in lightweight, recyclable and low cost applications. The aim of this research was to improve and evaluate the composite tensile strength and fibre/matrix interfacial adhesion by means of fibre treatment and addition of a coupling agent. Hemp fibre was digested in a small pressure vessel with a solution of 5wt% NaOH / 2wt% Na2SO3. Single fibre tensile tests were performed on treated and untreated fibres, and it was found that the alkali treatment resulted in an increase in fibre strength and an improvement in fibre separation. Composites containing either treated or untreated fibre, polypropylene and a maleic anhydride modified polypropylene (MAPP) coupling agent were then compounded in a twin-screw extruder and injection moulded into tensile test specimens. Tensile tests revealed that significant improvements in composite strength were made by using treated fibre and MAPP. The effect of MAPP on the interface of treated hemp fibre/polypropylene composites was assessed by means of the single fibre fragmentation test, and the interfacial shear strength was determined thereafter.

Abstract: Corn gluten meal (CGM) has potential as a bioderived polymer for use in composite materials. Previous work to improve the processability of CGM has focused on the use of plasticisers including water, polyethylene glycol, glycerol and octanoic acid, however, a common problem is that these leach from the material subsequent to processing [1]. It has been raised that a certain degree of denaturation must occur in order to make proteins processable [2]. The current work explores the use of aqueous urea as chemical denaturant in processing CGM into a biodegradable polymer material. Consolidated materials were obtained which showed increased resistance to cracking with higher urea concentration. FTIR analysis revealed that processing CGM with increased concentrations of aqueous urea resulted in the progressive transformation of the protein secondary structure from an ordered, clustered conformation to that of extended chains. Aqueous urea is assumed to promote protein-solvent interactions which stabilise the extended chain conformations.

Abstract: This study investigates the effect of recycling/reprocessing on the physical and mechanical properties of composites based on radiata pine (Pinus Radiata) fibre and polypropylene (PP) with a maleated polypropylene (MAPP) coupling agent, produced using a twin-screw extruder, followed by injection moulding. Composites containing 40wt% fibre and 4wt% MAPP were assessed mechanically and thermally, as well as for moisture absorption after being recycled up to eight times. Both the tensile strength (TS) and Young’s modulus (YM) of composites were found to decrease linearly from 41 MPa and 4556 MPa respectively to 31 MPa and 3800 MPa for composites recycled eight times. However, the elongation at break was found to increase with increased recycling due to fibre damage that occurred during reprocessing and the associated reduction of average fibre length, found to decrease from 2.36mm to 0.37mm after recycling eight times. Thermal stability and moisture resistance of composites improved with recycling due to the improvement of interfacial bonding between fibre and matrix.

Abstract: The aim of the current work was to investigate using fungi to treat hemp fibre to create better bonding characteristics in natural fibre reinforced polypropylene composites. X-ray diffraction (XRD), lignin testing and scanning electron microscopy (SEM), were used to characterise the effect of treatment on hemp fibres. A combined alkali and fungal treated fibre composite produced the highest tensile strength of 48.3 MPa, an increase of 32% compared to composites with untreated fibre.