42 results for Pickering, Kim L.

  • A study of polyvinyl butyryl based binder system in titanium based metal injection moulding

    Thavanayagam, Gnanavinthan; Zhang, Deliang; Pickering, Kim L.; Raynova, Stiliana (Stella) Rousseva (2012)

    Conference item
    University of Waikato

    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.%.

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  • Optimising industrial hemp fibre for composites

    Pickering, Kim L.; Beckermann, Gareth; Alam, S.N.; Foreman, Nic J. (2007)

    Journal article
    University of Waikato

    The optimisation of New Zealand grown hemp fibre for inclusion in composites has been investigated. The optimum growing period was found to be 114 days, producing fibres with an average tensile strength of 857 MPa and a Young’s modulus of 58 GPa. An alkali treatment with 10wt% NaOH solution at a maximum processing temperature of 160o C with a hold time of 45 minutes was found to produce strong fibres with a low lignin content and good fibre separation. Although a good fit with the Weibull distribution function was obtained for single fibre strength, this did not allow for accurate scaling to strengths at different lengths. Alkali treated fibres, polypropylene and a maleated polypropylene (MAPP) coupling agent were compounded in a twin-screw extruder, and injection moulded into composite tensile test specimens. The strongest composite consisted of polypropylene with 40wt% fibre and 3wt% MAPP, and had a tensile strength of 47.2 MPa, and a Young’s modulus of 4.88 GPa.

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  • High performance aligned short natural fibre - Epoxy composites

    Pickering, Kim L.; Le, Tan Minh (2016-02-01)

    Journal article
    University of Waikato

    Aligned short harakeke fibre (New Zealand flax) mats were produced using dynamic sheet forming, impregnated with epoxy resin, then pressed and cured on a compression moulder to manufacture composite materials. These composites were found to have significantly higher tensile properties than planar random oriented short fibre composites; the tensile strength (136 MPa) obtained for the composites is higher than any seen in the literature to date for short natural fibre composites. Fibre orientation was not affected by fibre content despite the higher processing pressure required and fibre orientation factors obtained from Modified Rule of Mixtures equations for Young's modulus and tensile strength were found to be similar.

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  • Hemp fibre reinforced poly(lactic acid) composites

    Sawpan, Moyeenuddin Ahmad; Pickering, Kim L.; Fernyhough, Alan (2007)

    Journal article
    University of Waikato

    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.

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  • Comparison of harakeke with hemp fibre as a potential reinforcement in composites

    Efendy, M.G. Aruan; Pickering, Kim L. (2014-12-01)

    Journal article
    University of Waikato

    The objective of this study was to characterize the performance of untreated and chemically treated harakeke fibre (a leaf fibre from a plant native to New Zealand) and compare with hemp fibre to assess its use as potential reinforcement in composites. Alkali treatment is among the most popular treatments used to remove unwanted fibre constituents such as pectin, hemicellulose and waxes; it can enhance fibre properties, fibre separation, interfacial bonding and fibre dispersion within a composite. Physical and mechanical properties of untreated and alkali treated fibres were assessed using single fibre tensile testing, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis using thermogravimetric analysis (TGA). Untreated harakeke fibre was found to be lower in tensile strength compared to untreated hemp fibre. It was also found that the tensile strength of harakeke and hemp fibres treated with 5wt% NaOH/2wt% Na2SO3 and 5wt% NaOH was not significantly affected and these fibres had good fibre separation. However, alkali treatment was found to lead to higher crystallinity index (Ic) and better thermal stability for harakeke as well as hemp fibres.

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  • The manufacture and mechanical properties of aligned long harakeke fibre reinforced epoxy composites

    Le, Tan Minh; Pickering, Kim L. (2012-07-09)

    Conference item
    University of Waikato

    Aligned long harakeke fibre reinforced epoxy composites were prepared using hand lay-up followed by compression moulding. Densities of harakeke fibre and epoxy resin were determined for the purpose of composite design. The evenness of composites fabricated by two different size moulds was compared. It was found that more even composites were produced when using a small mould than a big mould. In this work, the dependence of tensile and flexural properties of harakeke/epoxy composites on fibre content was also investigated. The results showed that the addition of fibre enhanced tensile properties of epoxy. The tensile strength and Young’s modulus increased with the volume fraction of harakeke fibre. The flexural strength and flexural modulus increased as the fibre volume fraction increased up to 0.4. Further addition of fibre did not result in an improvement of composite flexural properties.

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  • 3D Printing of Natural Fibre Reinforced Recycled Polypropylene

    Stoof, David; Pickering, Kim L. (2017)

    Conference item
    University of Waikato

    The adverse effects that waste plastics are having on the environment is becoming increasingly apparent. However, the plastics recycling industry in New Zealand is entirely market driven, necessitating the development of new markets to account for increasing quantities of waste. Innovations in additive manufacturing (AM) have presented opportunities to recycle thermoplastics for use as AM feedstock material. Using waste thermoplastic materials to fabricate composites in this way, adds value to the polymer by enhancing mechanical and aesthetic properties. A range of composite filaments with differing fibre and gypsum weight contents were then produced using pre and post-consumer polypropylene (PP). The most successful filaments in terms of tensile properties consisted of 30 wt% harakeke in a post-consumer PP matrix which had a tensile strength and Young’s modulus of 41MPa and 3.8 GPa respectively. Comparing these results to those of plain PP filament, showed improvements in tensile strength and Young’s modulus of 77% and 275% respectively. Finally, a novel method of measuring shrinkage in 3d printed components was developed and used to compare relative shrinkage of different composites. The composite that showed the least shrinkage consisted of 30 wt% harakeke with a shrinkage value of 0.34% corresponding to a net reduction of 84% relative to plain PP.

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  • Interfacial modification of hemp fiber reinforced composites using fungal and alkali treatment

    Pickering, Kim L.; Li, Y.; Farrell, Roberta L.; Lay, Mark C. (2007)

    Journal article
    University of Waikato

    Increasing worldwide environmental awareness is encouraging scientific research into developing cheaper, more sustainable materials. Industrial hemp fiber is one of the strongest and stiffest available natural fibers [K. L. Pickering, M. Priest, T. Watts, G. Beckermann, and S. N. Alam, J. Adv. Mater. 37, 15 (2005)] and therefore has great potential in composite materials. Incorporated into a thermoplastic matrix, it gives a structural material that is cheap, lightweight, and recyclable. However, natural fibers are commonly incompatible with common molding thermoplastics such as polypropylene, which limits the performance of the composites produced. The main objective of the current work was to investigate the use of fungi to treat hemp fiber to create better bonding characteristics in natural fiber reinforced polypropylene composites. X-ray diffraction (XRD), ζ-potential, lignin testing, thermal analysis, and scanning electron microscopy (SEM) were used to characterize the effect of treatment on hemp fibers. A combined alkali and fungi treated fiber composite produced the highest tensile strength of 48.3 MPa, an increase of 32% compared to composites with untreated fiber.

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  • Damping properties and microstructure of magnetorheological composites based on iron sand and natural rubber

    Shuib, Raa Khimi; Pickering, Kim L. (2013)

    Conference item
    University of Waikato

    Material with high damping capability is desired from the viewpoint of vibration suppression in structures. Rubber is by far the most commonly used material for damping; here damping relies on the energy absorbed due to viscous flow that occurs during deformation in this viscoelastic materials. However, enhancement of damping through rubber modification or rubber selection to increase viscous flow, not surprisingly, generally results in a reduction in stiffness and strength [1]. More recently, a new class of damping materials, magnetorheological elastomers (MREs) have been developed such that inclusion of magnetic particles in rubber enables additional damping through magnetic particle interaction and interfacial friction. Furthermore, damping and stiffness can be varied by application of an applied magnetic field during fabrication or in service. MREs can be utilised for damping, either alone or within a composite structure such as those including steel plates.

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  • Comparison of dynamic properties of magnetorheological elastomers with existing antivibration rubbers

    Shuib, Raa Khimi; Pickering, Kim L. (2015-12-15)

    Journal article
    University of Waikato

    Tan δ and energy dissipated during hysteresis testing of isotropic and anisotropic MREs containing silane modified iron sand particles in a natural rubber matrix were compared with existing antivibration rubbers. Tan δ was measured using dynamic mechanical analysis (DMA) over a range of frequency (0.01–130 Hz), strain amplitude (0.1–4.5%), and temperature (−100–50 °C). Energy dissipated was measured using a universal tester under cyclic tensile loading. The chosen antivibration rubbers for comparison contained different contents of carbon black filler (30, 50 and 70 phr) in a natural rubber matrix. It was found that energy absorption for comparative samples was generally higher than isotropic and anisotropic MREs over the range of frequency and strain amplitude explored, as well as in hysteresis testing and this was believed to be largely due the presence of carbon black in the formulation. Further assessment was carried out on materials that were the same as anisotropic MREs except they had additions of carbon black. The energy absorption was found higher than comparative samples with the same carbon black contents, supporting the use of iron sand to improve damping. However, trends for energy absorption at around Tg were found to reverse which is considered to be due to the segmental motion of rubber chains being by far the most significant influence on energy absorption in the glass transition zone.

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  • Characterisation of hemp fibre reinforced Poly(Lactic Acid) composites

    Sawpan, Moyeenuddin Ahmad; Pickering, Kim L.; Fernyhough, Alan (2009)

    Journal article
    University of Waikato

    In this work, the mechanical properties including tensile strength, flexural strength, impact strength and fracture toughness of the PLA/hemp composites were investigated over a range of fibre content (0-30 wt.%). It was observed that, the tensile strength and Young's modulus of the composites increased with increased fibre content. The flexural strength did not increase with fibre reinforcement, however, the flexural modulus of the composites increased significantly. Impact strength of the composites increased up to 20 wt. % fibre loading, however, further increased fibre loading caused a reduction of impact strength. KIc and GIc values decreased with increased fibre content.

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  • Fibre orientation of novel dynamically sheet formed discontinuous natural fibre PLA composites

    Efendy, M.G. Aruan; Pickering, Kim L. (2016)

    Journal article
    University of Waikato

    This paper describes work carried out to fabricate and to assess the fibre orientation in PLA reinforced by aligned discontinuous harakeke and hemp fibre mats produced using a dynamic sheet former (DSF). These mats were combined with PLA sheets to make composites with fibre contents of 5–40 wt% using a hot press. It was found that the fibre orientation factors (Kθ) for both harakeke and hemp fibre composites were higher than those values seen in the literature for composites prepared using injection moulding and hot pressed using randomly oriented fibre mats, but slightly lower than the highest values obtained with aligned fibre nonwoven preform composites utilising more processing stages. The highest Kθ values for harakeke and hemp fibres in this work were found to be 0.58 and 0.44 respectively. Kθ decreased, reflecting increased fibre misalignment as fibre content increased, believed to be due to fibre agglomeration and the higher pressure required during processing.

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  • Microstructure and mechanical behaviour of ultrafine grained Al-4wt%Cu-(2.5-10) Vol.% SiC metal matrix composites produced by powder compact forging

    Gazawi, Amro Abdul-Karim; Zhang, Deliang; Pickering, Kim L.; Mukhtar, Aamir (2011)

    Journal article
    University of Waikato

    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%).

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  • Analysis of mechanical properties of hemp fibre reinforced unsaturated polyester composites

    Sawpan, Moyeenuddin Ahmad; Pickering, Kim L.; Fernyhough, Alan (2013)

    Journal article
    University of Waikato

    Different chemically treated hemp fibre reinforced unsaturated polyester composites were investigated over a range of fibre content (0–60 wt%). Although Young’s modulus of all the short fibre reinforced unsaturated polyester composites was found to be higher than that of unreinforced unsaturated polyester; however, tensile strength of the composites exceeded that of the unsaturated polyester matrix only for the combined alkali- and silane-treated fibre composites at 40 wt% fibre content. The decrease in tensile strength of the composites could be attributed to stress concentrations caused by the fibres in conjunction with the brittle matrix. Impact strength of all the treated fibre composites was higher than that of the untreated fibre composites at all fibre contents. KIc and GIc of the composites decreased initially and thenincreased as the fibre content increased because more and more fibres being available to pull-out. The mechanical properties of the composites were increased further due to the alignment of long fibres.

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  • Studying carbonisation with raman spectroscopy

    McDonald-Wharry, John; Ripberger, Georg; Manley-Harris, Merilyn; Pickering, Kim L. (2013)

    Conference item
    University of Waikato

    Raman spectroscopy can provide fast and non-destructive analysis of carbonaceous materials. As it is able to detect nanometre-sized structural features, Raman spectroscopy is widely used in the study of carbon nanotubes, fullerenes, graphenes, and many other carbon-rich materials. Raman analysis has previously shown potential for estimating the heat treatment temperatures (HTT) employed in the preparation of Japanese cedar charcoals which suggested future usefulness in quality control . In the current work, Raman spectroscopy was used to investigate the nanostructural development which had occurred within various chars prepared and carbonised at a range of heat treatment temperatures between ≈ 340°C and 1000°C. Chars were produced from sucrose sugar as standard precursor of high purity and two sources of biomass common in New Zealand (Radiata pine wood and Harakeke leaf fibres). In chars produced at lower HTTs, signals could be detected which were interpreted as representing hydrogen-rich amorphous carbon structures. In contrast, the Raman spectra of well-carbonised chars produced at higher HTTs featured signals consistent with graphene-like structures with coherent domains limited in size to below a few nanometres across. Measurement of such signals provides the ability to evaluate the extent of nanostructural development, identify char samples which are ‘undercooked’ when compared to other char samples, and estimate effective HTTs used in the production of a given char sample. More detailed Raman analysis of Radiata-derived chars was carried out, including analysis of chars produced from carbonising pyrolysis tars. Results of Raman analysis were correlated to H/C atom ratios obtained through elemental analysis for these chars produced from Radiata pine.

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  • Curing kinetics and effects of fibre surface treatment and curing parameters on the interfacial and tensile properties of hemp/epoxy composites

    Islam, Mohammad Saiful; Pickering, Kim L.; Foreman, Nic J. (2009)

    Journal article
    University of Waikato

    The curing kinetics of neat epoxy (NE) and hemp fibre/epoxy composites was studied and assessed using two dynamic models (the Kissinger and Flynn-Wall-Ozawa Models) and an isothermal model (the Autocatalytic Model) which was generally supported by the experimental data obtained from dynamic and isothermal differential scanning calorimetry (DSC) scans. The activation energies for the curing of composites exhibited lower values compared to curing of NE which is believed to be due to higher nucleophilic activity of the amine groups of the curing agent in the presence of fibres. The highest tensile strength, σ was obtained with composites produced with an epoxy to curing agent ratio of 1:1 and the highest Young's modulus, E was obtained with an epoxy to curing agent ratio of 1:1.2. Alkali treated hemp fibre/epoxy (ATFE) composites were found to have higher σ and E values compared to those for untreated hemp fibre/epoxy (UTFE) composites which was consistent with the trend for interfacial shear strength (IFSS) values. Composites σ and E were found to be higher for a processing temperature of 70°C than for 25°C for both UTFE and ATFE composites, but were found to decrease as the curing temperature was increased further to 120°C.

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  • Flexural properties of hemp fibre reinforced polylactide and unsaturated polyester composites

    Sawpan, Moyeenuddin Ahmad; Pickering, Kim L.; Fernyhough, Alan (2011)

    Journal article
    University of Waikato

    In this work, flexural strength and flexural modulus of chemically treated random short and aligned long hemp fibre reinforced polylactide and unsaturated polyester composites were investigated over a range of fibre content (0–50 wt%). Flexural strength of the composites was found to decrease with increased fibre content; however, flexural modulus increased with increased fibre content. The reason for this decrease in flexural strength was found to be due to fibre defects (i.e. kinks) which could induce stress concentration points in the composites during flexural test, accordingly flexural strength decreased. Alkali and silane fibre treatments were found to improve flexural strength and flexural modulus which could be due to enhanced fibre/matrix adhesion.

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  • Alignment of Short Fibres: An Overview

    Sunny, Tom; Pickering, Kim L.; Lim, Shen Hin (2017)

    Conference item
    University of Waikato

    Fibre orientation is a major factor influencing composite performance; research, largely on synthetic fibre composites, supports that the best mechanical performances are achieved in composites when fibres are aligned in the loading direction. Generally, with short natural plant fibre (SNPF) composites, randomly oriented fibre mats are used as reinforcements due to the innate limits of fibre length and the difficulty of aligning short fibre. However, there are a number of methods that have been developed for aligning short fibre, again largely employed for synthetic fibres. The two main approaches employed to align short fibres relate to whether dry or wet processing is used available in literature; in wet processes, fibres are generally suspended in a liquid medium and alignment of fibre trails the fluid flow direction, whereas in dry processes, dry fibres are aligned in the direction of an induced or applied force such as pneumatic or electric. An overview of different alignment methods with their working principles is presented in this paper. This paper also describes an alignment technique currently under development to improve the alignment obtained for SNPFs.

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  • The Effect of Aqueous Urea on the Processing, Structure and Properties of CGM

    Pickering, Kim L.; Verbeek, Casparus Johan R.; Viljoen, Carmen (2012-06)

    Journal article
    University of Waikato

    Corn gluten meal (CGM) is potentially a cost-effective raw material for producing a bioderivable thermoplastic. However, CGM disintegrates to a powder subsequent to processing with polar plasticisers, such as water. The hypothesis of this study was that aqueous urea could be used to denature protein within CGM and therefore encourage protein–protein interactions leading to consolidated bioplastics when using water as a plasticiser. To assess this, the effects of aqueous urea on structure and properties of CGM with particular focus on storage were assessed. Processing of CGM with aqueous urea produced consolidated materials. FTIR analysis showed secondary structure was modified during processing, leading to increased amounts of α-helices and random coils and reduction of the amount of intermolecular β-sheets and turns. Above 6 wt% free water, the plasticising efficiency of water in processed CGM increased as the amount of denatured proteins increased. Below 6 wt% free water, protein secondary structure did not have a significant influence on thermal and flexural properties. It was found that storage environment and urea concentration influenced the rate of drying, however, the final water content was constant relative to CGM, and not urea. The materials were resistant to cracking at urea concentrations above 8 M, provided the mass loss during storage did not exceed 15 wt%.

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  • A new method to predict optimum cure time of rubber compound using dynamic mechanical analysis

    Shuib, Raa Khimi; Pickering, Kim L. (2013)

    Journal article
    University of Waikato

    The degree of vulcanization of a rubber compound has a big influence on the properties of the final product. Therefore, precisely defining the curing process including optimum cure time is important to ensure the production of final products having high performance. Typically, vulcanization is represented using vulcanization curves. The main types of equipment used for producing vulcanization curves are the oscillating disc rheometer (ODR) and the moving die rheometer (MDR). These can be used to plot graphs of torque versus time at a constant temperature to show how cure is proceeding. Based on the results obtained, optimum cure time (t₉₀) is calculated as the time required for the torque to reach 90% of the maximum achievable torque. In this study, the use of Dynamic Mechanical Analysis (DMA) for assessment of t₉₀ was assessed. DMA was carried out using shear mode isothermal tests to measure the changes in material properties caused by vulcanization. The results revealed that the shear storage modulus (G′), shear loss modulus (G′′), and tan δ all reflect the vulcanization process, however, tan δ gave the best representation of level of vulcanization. Indeed, the curve of tan δ was able to be used to derive the t₉₀ for rubber compounds and showed good agreement with the results from an MDR.

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