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Prof. James Njuguna
Robert Gordon University, Aberdeen, UK

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0 Energy & the Environment
0 Nanocomposites
0 Composite Materials and Structures
0 Product Design & Development
0 Automotive Materials

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Short Biography

Professor James Njuguna is the Academic Strategic Lead (Research) at School of Engineering and also leads the Centre for Advanced Engineering Materials at Robert Gordon University. PhD and MSc in Aeronautical Engineering from City, University of London. Former Research Councils United Kingdom (RCUK) Fellow and Marie Curie Fellow. Research focus on composites materials toughness and mechanical properties optimisation to improve impact resistance & thermo-mechanical performance

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Journal article
Published: 24 August 2021 in Journal of Natural Gas Science and Engineering
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This paper proposes a novel way to study the casing structural integrity using two approaches of finite element analysis (FEA) and machine learning. The approach in this study is unique, as it captures the pertinent parameters influencing the casing buckling and the evaluation of the magnitude of each. In this work, the effect of combined loading using multiple parameters to establish the relationship and effect of each on stress, displacement and ultimately casing safety factor is revealed. The optimised result show remarkable improvement in reducing the total deformation, the von Mises and increasing the safety factor of the casing under combined loading condition. The optimised casing shows 89% reduction in total deformation and 87% reduction in von Mises in comparison to unoptimised simulation result. In addition, the safety factor of 3.3 is obtained against the initial predicted stress of 932.46 MPa with a corresponding safety factor of 0.8129. Real time parametric prediction and optimisation using Lunar and Quasar (ODYSSEE software package) enabled the examination of the casing structural responses based on the pertinent parameters. In effect, a very good agreement was found between “KNN” and Lunar predictions on parameters influencing casing buckling phenomena and the corresponding Mises stress. Lunar optimisation provided the ideal parameter values for the attainment of pre-define von Mises stress as a function of other factors. This quick approach shows both accuracy and validation of the two independent procedures arriving at the same conclusion. We found that concurrent investigation of the casing buckling attributing factors and optimisation using FEA and ODYSSEE package is sufficient to maintain casing structural integrity during shale gas extraction process.

ACS Style

Auwalu I. Mohammed; Mark Bartlett; Babs Oyeneyin; Kambiz Kayvantash; James Njuguna. An application of FEA and machine learning for the prediction and optimisation of casing buckling and deformation responses in shale gas wells in an in-situ operation. Journal of Natural Gas Science and Engineering 2021, 104221 .

AMA Style

Auwalu I. Mohammed, Mark Bartlett, Babs Oyeneyin, Kambiz Kayvantash, James Njuguna. An application of FEA and machine learning for the prediction and optimisation of casing buckling and deformation responses in shale gas wells in an in-situ operation. Journal of Natural Gas Science and Engineering. 2021; ():104221.

Chicago/Turabian Style

Auwalu I. Mohammed; Mark Bartlett; Babs Oyeneyin; Kambiz Kayvantash; James Njuguna. 2021. "An application of FEA and machine learning for the prediction and optimisation of casing buckling and deformation responses in shale gas wells in an in-situ operation." Journal of Natural Gas Science and Engineering , no. : 104221.

Journal article
Published: 06 July 2021 in Journal of Petroleum Science and Engineering
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Hydrogenated nitrile butyl rubber (HNBR) elastomers are highly resistant to chemicals and degradation, and they are good candidates to be adopted in aggressive environmental conditions of high temperature and pressure. As these service parameters are common in oil and gas applications, HNBR is popular in applications such as elastomer packers in wellhead installations. This study investigated the thermal ageing behaviour of HNBR elastomers to better predict the long-term sealing performance of the packers. Elastomer compounds were thermally aged and FTIR-ATR and differential scanning calorimetry techniques were used to indicate dominant chemical reactions during ageing. Furthermore, the mechanical performance of the aged compounds were studied to investigate the effect of dominant ageing reactions on performance. It was indicated that crosslinking reaction was dominant in the ageing process of HNBR compounds up to 150 °C. This resulted in increased stiffness and alleviated elongational strains at the break. However, compounds behaved brittle at ageing temperatures above 150 °C, and from the thermal analysis, it was concluded that at those temperatures chain scission reactions overtook the ageing mechanism. Finally, an approach for life-long prediction of mechanical characteristics of the specimens showed while long-term ageing promotes elastic failure, ageing temperatures above 150 °C facilitate rupture because of the brittle response of the compounds.

ACS Style

Farzaneh Hassani; Nadimul H. Faisal; Ryan Nish; Stuart Rothnie; James Njuguna. The impact of thermal ageing on sealing performance of HNBR packing elements in downhole installations in oilfield wellhead applications. Journal of Petroleum Science and Engineering 2021, 109200 .

AMA Style

Farzaneh Hassani, Nadimul H. Faisal, Ryan Nish, Stuart Rothnie, James Njuguna. The impact of thermal ageing on sealing performance of HNBR packing elements in downhole installations in oilfield wellhead applications. Journal of Petroleum Science and Engineering. 2021; ():109200.

Chicago/Turabian Style

Farzaneh Hassani; Nadimul H. Faisal; Ryan Nish; Stuart Rothnie; James Njuguna. 2021. "The impact of thermal ageing on sealing performance of HNBR packing elements in downhole installations in oilfield wellhead applications." Journal of Petroleum Science and Engineering , no. : 109200.

Journal article
Published: 26 March 2021 in Upstream Oil and Gas Technology
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To convert the hazardous oil-based mud waste into a resource, this study has addressed reclaimed nanoclays and its application as a filler material for reinforcing polyamide 6 polymer matrix into a novel polymer composite material. This work focuses on the synergistic effect of complex mixture of various clay minerals reclaimed from oil-based mud waste on different mechanical properties in polyamide-6 (PA6)/oil-based mud fillers (OBMFs) nanocomposites. PA6/OBMFs nanocomposites were manufactured through the melt compounding of OBMFs with PA6 in a twin-screw extruder followed by injection moulding. The study shows significant improvement for mechanical properties. For instance, the tensile properties increased with the incremental loadings of OBMFs in PA6 matrix. The Young's moduli were increased by 42% and 35% in PA6 with 7.5 and 10 wt% OBMFs nanocomposites respectively whereas the tensile strengths were increased by 24% and 16% in PA6 with 7.5 and 10 wt% OBMFs nanocomposites respectively. The flexural strength increased by 26% with the addition of OBMFs from 0 to 10 wt% in PA6. The storage modulus of the nanocomposite containing 10 wt% OBMFs was 16% higher than the storage modulus of neat PA6 at 30 °C, whereas at 60 °C (glass transition temperature, Tg of neat PA6) the storage modulus of PA6 with 10 wt% OBMFs was 56% higher than that of neat PA6. The study shows that the oil-based mud waste can be appropriately management to develop a new raw materials resource for polymer technology.

ACS Style

Shohel Siddique; Pak Sing Leung; James Njuguna. Drilling oil-based mud waste as a resource for raw materials: A case study on clays reclamation and their application as fillers in polyamide 6 composites. Upstream Oil and Gas Technology 2021, 7, 100036 .

AMA Style

Shohel Siddique, Pak Sing Leung, James Njuguna. Drilling oil-based mud waste as a resource for raw materials: A case study on clays reclamation and their application as fillers in polyamide 6 composites. Upstream Oil and Gas Technology. 2021; 7 ():100036.

Chicago/Turabian Style

Shohel Siddique; Pak Sing Leung; James Njuguna. 2021. "Drilling oil-based mud waste as a resource for raw materials: A case study on clays reclamation and their application as fillers in polyamide 6 composites." Upstream Oil and Gas Technology 7, no. : 100036.

Journal article
Published: 15 December 2020 in Composite Structures
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Polyester fibres reinforced with glass fibres hybridised polyester resin composite (PFR/GFHC) is a unconventional complex high-molecular weight crosslinked network polymer composite. This novel composite can be used in the manufacture of structural body parts for lightweight vehicles, armour vest for body protection as well as armours for vehicles. For body armour applications, it is important to determine the dynamic behaviour of PFR/GFHC during high velocity impact. In this work, we propose a method of calculating Gurneisen parameter from the measured Hugoniot in shock velocity – particle velocity of polyester based composites product by high velocity actuated nail gun impact. Several high-velocity impacts were conducted on pultruded plates using a power actuated nail gun with different cartridges and varying nail sizes. The experimentally measured Hugoniot in shock velocity – particle velocity space was determined as Us = 2.872 + 1.22Up (ρ0 = 1.25 g/cc) and low gradient observed for Gruneisen parameter as calculated from measured Hugoniot against V0/V shows higher shock absorption of PFR/GFHC for impact velocity.

ACS Style

Arindam Mukherji; James Njuguna. Shock propagation behaviour and determination of Gruneisen state of equation for pultruded polyester/glass fibre-reinforced composites. Composite Structures 2020, 262, 113444 .

AMA Style

Arindam Mukherji, James Njuguna. Shock propagation behaviour and determination of Gruneisen state of equation for pultruded polyester/glass fibre-reinforced composites. Composite Structures. 2020; 262 ():113444.

Chicago/Turabian Style

Arindam Mukherji; James Njuguna. 2020. "Shock propagation behaviour and determination of Gruneisen state of equation for pultruded polyester/glass fibre-reinforced composites." Composite Structures 262, no. : 113444.

Review
Published: 13 November 2020 in Polymers
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There is a rising demand for replacement, regeneration of tissues and organ repairs for patients who suffer from diseased/damaged bones or tissues such as hip pains. The hip replacement treatment relies on the implant, which may not always meet the requirements due to mechanical and biocompatibility issues which in turn may aggravate the pain. To surpass these limitations, researchers are investigating the use of scaffolds as another approach for implants. Three-dimensional (3D) printing offers significant potential as an efficient fabrication technique on personalized organs as it is capable of biomimicking the intricate designs found in nature. In this review, the determining factors for hip replacement and the different fabrication techniques such as direct 3D printing, Fused Deposition Modelling (FDM), Selective Laser Sintering (SLS) and stereolithography (SLA) for hip replacement. The study also covers surface modifications of 3D printed implants and provides an overview on 3D tissue regeneration. To appreciate the current conventional hip replacement practices, the conventional metallic and ceramic materials are covered, highlighting their rationale as the material of choice. Next, the challenges, ethics and trends in the implants’ 3D printing are covered and conclusions drawn. The outlook and challenges are also presented here. The knowledge from this review indicates that 3D printing has enormous potential for providing a pathway for a sustainable hip replacement.

ACS Style

Obinna Okolie; Iwona Stachurek; Balasubramanian Kandasubramanian; James Njuguna. 3D Printing for Hip Implant Applications: A Review. Polymers 2020, 12, 2682 .

AMA Style

Obinna Okolie, Iwona Stachurek, Balasubramanian Kandasubramanian, James Njuguna. 3D Printing for Hip Implant Applications: A Review. Polymers. 2020; 12 (11):2682.

Chicago/Turabian Style

Obinna Okolie; Iwona Stachurek; Balasubramanian Kandasubramanian; James Njuguna. 2020. "3D Printing for Hip Implant Applications: A Review." Polymers 12, no. 11: 2682.

Journal article
Published: 08 October 2020 in Fibers
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The ever-increasing demand for environmentally friendly biocomposites for use in various engineering applications requires a strong understanding of these materials properties, especially in automotive applications. This study focused on investigating how the stacking sequence and fibre orientation impacts the damping properties of hybrid flax/carbon fibre-reinforced composites. Different hybrid carbon fibre/flax fibre-reinforced composites using epoxy resin as the matrix were manufactured using vacuum-assisted resin infusion moulding technique. Each composite material was then tested for tensile properties using a universal testing machine, and the damping experiment was conducted using an impulse hammer and a Laser Doppler Vibrometer. The tensile study found out that adding a flax layer to the external layers of carbon fibre laminate reduced Young’s modulus by 28% for one layer and 45% for two layers. It was noted that when the fibre orientation of the internal layer of [C/F2/C]s was replaced with two ±45° layers, this had a very little effect on Young’s modulus but reduced the ultimate tensile strength by 61%. This experimental study also showed that the most important layer when it comes to damping properties is the external layers. By adding an external flax layer into an epoxy/carbon fibre-reinforced composite considerably enhanced its damping ratio by 53.6% and by adding two layers increased it by 94%. The results indicated a high potential for the automotive semi-structural applications to improve damping properties of the vehicle.

ACS Style

George Fairlie; James Njuguna. Damping Properties of Flax/Carbon Hybrid Epoxy/Fibre-Reinforced Composites for Automotive Semi-Structural Applications. Fibers 2020, 8, 64 .

AMA Style

George Fairlie, James Njuguna. Damping Properties of Flax/Carbon Hybrid Epoxy/Fibre-Reinforced Composites for Automotive Semi-Structural Applications. Fibers. 2020; 8 (10):64.

Chicago/Turabian Style

George Fairlie; James Njuguna. 2020. "Damping Properties of Flax/Carbon Hybrid Epoxy/Fibre-Reinforced Composites for Automotive Semi-Structural Applications." Fibers 8, no. 10: 64.

Journal article
Published: 14 August 2020 in Journal of Aerosol Science
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Researchers and legislators have both claimed the necessity to standardize the exposure assessment of polymer nanocomposites throughout their life cycle. In the present study we have developed and compared three different and independent operational protocols to investigate changes in particle emission behavior of mechanically degraded polypropylene (PP) samples containing different fillers, including talc and two types of nanoclays (wollastonite-WO- and montmorillonite-MMT-) relative to not reinforced PP. Our results have shown that the mechanical degradation of PP, PP-Talc, PP-WO and PP-MMT samples causes the release of nano-sized particles. However, the three protocols investigated, simulating industrial milling and drilling and household drilling, have produced different figures for particles generated. Results suggest that it is not possible to describe the effects of adding nano-sized modifiers to PP by a single trend that applies consistently across all different protocols. Differences observed might be attributed to a variety of causes, including the specific operational parameters selected for sample degradation and the instrumentation used for airborne particle release characterization. In particular, a streamlined approach for future assessments providing a measure for released particles as a function of the quantity of removed material would seem useful, which can provide a reference benchmark for the variations in the number of particles emitted across a wider range of different mechanical processes.

ACS Style

María Blazquez; Verónica Marchante; Laura Gendre; Kristof Starost; James Njuguna; Jurg A. Schutz; José María Lacave; Ainhoa Egizabal; Cristina Elizetxea; Miren P. Cajaraville. Particle emission measurements in three scenarios of mechanical degradation of polypropylene-nanoclay nanocomposites. Journal of Aerosol Science 2020, 150, 105629 .

AMA Style

María Blazquez, Verónica Marchante, Laura Gendre, Kristof Starost, James Njuguna, Jurg A. Schutz, José María Lacave, Ainhoa Egizabal, Cristina Elizetxea, Miren P. Cajaraville. Particle emission measurements in three scenarios of mechanical degradation of polypropylene-nanoclay nanocomposites. Journal of Aerosol Science. 2020; 150 ():105629.

Chicago/Turabian Style

María Blazquez; Verónica Marchante; Laura Gendre; Kristof Starost; James Njuguna; Jurg A. Schutz; José María Lacave; Ainhoa Egizabal; Cristina Elizetxea; Miren P. Cajaraville. 2020. "Particle emission measurements in three scenarios of mechanical degradation of polypropylene-nanoclay nanocomposites." Journal of Aerosol Science 150, no. : 105629.

Research article
Published: 28 July 2020 in Waste Management & Research: The Journal for a Sustainable Circular Economy
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Oil-based mud (OBM) waste from the oil and gas exploration industry can be valorised to tailor-made reclaimed clay-reinforced low-density polyethylene (LDPE) nanocomposites. This study aims to fill the information gap in the literature and to provide opportunities to explore the effective recovery and recycling techniques of the resources present in the OBM waste stream. Elemental analysis using inductively coupled plasma–optical emission spectrometry (ICP-OES) and X-ray fluorescence analysis, chemical structural analysis by Fourier transform infrared (FTIR) spectroscopy, and morphological analysis of LDPE/organo-modified montmorillonite (LDPE/MMT) and LDPE/OBM slurry nanocomposites by scanning electron microscopy (SEM) have been conducted. Further analysis including calorimetry, thermogravimetry, spectroscopy, microscopy, energy dispersive X-ray analysis and X-ray diffraction (XRD) was carried out to evaluate the thermo-chemical characteristics of OBM waste and OBM clay-reinforced LDPE nanocomposites, confirming the presence of different clay minerals including inorganic salts in OBM slurry powder. The microscopic analysis revealed that the distance between polymer matrix and OBM slurry filler is less than that of MMT, which suggests better interfacial adhesion of OBM slurry compared with the adhesion between MMT and LDPE matrix. This was also confirmed by XRD analysis, which showed the superior delamination structure OBM slurry compared with the structure of MMT. There is a trend noticeable for both of these fillers that the nanocomposites with higher percentage filler contents (7.5 and 10.0 wt% in this case) were indicated to act as a thermal conductive material. The heat capacity values of nanocomposites decreased about 33% in LDPE with 7.5 wt% MMT and about 17% in LDPE with 10.0 wt% OBM slurry. It was also noted, for both nanocomposites, that the residue remaining after 1000°C increases with the incremental wt% of fillers in the nanocomposites. There is a big difference in residue amount (in %) left after thermogravimetric analysis in the two nanocomposites, indicating that OBM slurry may have significant influence in decomposing LDPE matrix; this might be an interesting area to explore in the future. The results provide insight and opportunity to manufacture waste-derived renewable nanocomposites with enhanced structural and thermal properties.

ACS Style

Shohel Siddique; Kyari Yates; Kerr Matthews; Laszlo J Csetenyi; James Njuguna. Oil-based mud waste reclamation and utilisation in low-density polyethylene composites. Waste Management & Research: The Journal for a Sustainable Circular Economy 2020, 38, 1331 -1344.

AMA Style

Shohel Siddique, Kyari Yates, Kerr Matthews, Laszlo J Csetenyi, James Njuguna. Oil-based mud waste reclamation and utilisation in low-density polyethylene composites. Waste Management & Research: The Journal for a Sustainable Circular Economy. 2020; 38 (12):1331-1344.

Chicago/Turabian Style

Shohel Siddique; Kyari Yates; Kerr Matthews; Laszlo J Csetenyi; James Njuguna. 2020. "Oil-based mud waste reclamation and utilisation in low-density polyethylene composites." Waste Management & Research: The Journal for a Sustainable Circular Economy 38, no. 12: 1331-1344.

Research article
Published: 03 June 2020 in ACS Applied Electronic Materials
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Polymer-metal oxide nanocomposite is a key in developing a high temperature insulation material for power electronics and HVDC and MVDC subsea cables having capability of transmitting offshore renewable energy with lower losses and higher reliability. To achieve higher operation voltage level and larger power capacity at reduced cable size, weight and volume, the lighter material offering improved electrical insulation at high operating temperature is required. Addition of metal oxide ceramics in the polymer is shown to improve the insulating properties of the polymer used in the cable and power electronic applications, however, their performance deteriorates at elevated temperature as thermal energy facilitates the electron injection to the bulk material following conduction according to Schottky emission. In this work, the heat insulating Al2O3 nanoparticles are added to the MgO-polyethylene nanocomposite to observe the effect of interface between mix oxide nanoparticles on current density and breakdown strength of the nanocomposite compared to the MgO-Polyethylene nanocomposite at room and elevated temperature (90○C). The concentration of the MgO and MgO+Al2O3 mixture were varied from the 1 wt% to 12 wt% to find out that the nanocomposite containing MgO showed best response than MgO+Al2O3 at elevated and room temperature. There is no unified trend was observed in the leakage current density and breakdown strength results for the MgO+Al2O3 nanocomposite indicating absence of the interface formation between MgO and Al2O3 . Decrease in interaction radius, calculated using numerical simulation of nanoparticle dispersion state, resulted in the high breakdown strength. Addition of 12 wt% MgO helped achieving highest breakdown strength but overall breakdown strength for MgO+Al2O3 nanocomposite improved at elevated temperature. All nanocomposite showed improved electrical insulating properties compared to virgin LDPE (pure).

ACS Style

RanjeetKumar Gupta; Lindsay Smith; James Njuguna; Alan Deighton; Ketan Pancholi. Insulating MgO–Al2O3–LDPE Nanocomposites for Offshore Medium-Voltage DC Cables. ACS Applied Electronic Materials 2020, 2, 1880 -1891.

AMA Style

RanjeetKumar Gupta, Lindsay Smith, James Njuguna, Alan Deighton, Ketan Pancholi. Insulating MgO–Al2O3–LDPE Nanocomposites for Offshore Medium-Voltage DC Cables. ACS Applied Electronic Materials. 2020; 2 (7):1880-1891.

Chicago/Turabian Style

RanjeetKumar Gupta; Lindsay Smith; James Njuguna; Alan Deighton; Ketan Pancholi. 2020. "Insulating MgO–Al2O3–LDPE Nanocomposites for Offshore Medium-Voltage DC Cables." ACS Applied Electronic Materials 2, no. 7: 1880-1891.

Journal article
Published: 01 June 2020 in Atmosphere
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Graphene oxide (GO) nanoparticles are increasingly being used to tailor industrial composites. However, despite the advantages, GO has shown conceivable health risks and toxicity to humans and the environment if released. This study investigates the influence that GO concentrations have on nanoparticle emissions from epoxy-reinforced carbon fiber hybrid composites (EP/CF) during a lifecycle scenario, that is, a drilling process. The mechanical properties are investigated and an automated drilling methodology in which the background noise is eliminated is used for the nanoparticle emissions measurements. Real-time measurements are collected using a condensation particle counter (CPC), a scanning mobility particle sizer spectrometer (SMPS), a real-time fast mobility particle spectrometer (DMS50) and post-test analytical methods. The results observe that all three nanoparticle reinforced samples demonstrated a statistically significant difference of up to a 243% increase in mean peak particle number concentration in comparison to the EP/CF sample. The results offer a novel set of data comparing the nanoparticle release of GO with varying filler weight concentration and correlating it the mechanical influence of the fillers. The results show that the release characteristics and the influence in particle number concentration are primarily dependent on the matrix brittleness and not necessarily the filler weight concentration within the nanocomposite.

ACS Style

Kristof Starost; James Njuguna. The Influence of Graphene Oxide on Nanoparticle Emissions during Drilling of Graphene/Epoxy Carbon-Fiber Reinforced Engineered Nanomaterials. Atmosphere 2020, 11, 573 .

AMA Style

Kristof Starost, James Njuguna. The Influence of Graphene Oxide on Nanoparticle Emissions during Drilling of Graphene/Epoxy Carbon-Fiber Reinforced Engineered Nanomaterials. Atmosphere. 2020; 11 (6):573.

Chicago/Turabian Style

Kristof Starost; James Njuguna. 2020. "The Influence of Graphene Oxide on Nanoparticle Emissions during Drilling of Graphene/Epoxy Carbon-Fiber Reinforced Engineered Nanomaterials." Atmosphere 11, no. 6: 573.

Review article
Published: 19 January 2020 in European Polymer Journal
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According to a survey conducted by Grand View Research, the market demand for medical grade UHMWPE has raise remarkably from 60.9 kilotons up to 204.8 kilotons during 2015- 2024 valued at $1.36 billion (USD) with a compound annual growth rate of 15%. There are various materials available for medical implants comprising of metals, ceramics and polymers among them UHMWPE has been used widely. The wide impact of UHMWPE in medical field is due it’s superior biocompatibility, chemical resistance, low wear volume (0.68 mm3), ultimate tensile strength (41.3 MPa), low coefficient of friction [In dry condition (0.12-0.15)] and high crystallinity (more than 90%). However, wear debris, oxidative degradation due to generation of free radicals when subjected to irradiation with gamma rays and low ageing of implant are some critical problems observed in UHMWPE based implants in human body. These severe problems have been resolved using various innovative methodologies to enhance the properties of UHMWPE, comprising of surface modification techniques for pure UHMWPE as well as composite reinforced UHMWPE. The enhancement in properties of pure UHMWPE is achieved using electron beam or atmospheric cold plasma treatment. The reinforced composites are majorly developed by reinforcement of materials such as hydroxyapatite, Multi walled carbon nanotubes, Vitamin E (α-tocopherol), graphene oxide, DLC films, Gallic acid and Dodecyl gallate along with base UHMWPE matrix material. Based on the recent studies, Comparative study of these functionalization techniques along with the ameliorated surface or bulk properties along with it’s diverse application in medical implant fields (Total hip arthroplasty, joint implants, bone tissue engineering) has been discussed extensively. Descriptive study of pure UHMWPE along with it’s composite to functionalize the properties of the medical implants has been included in this review along with it’s future scope succeeding the review.

ACS Style

Nikhil Avinash Patil; James Njuguna; Balasubramanian Kandasubramanian. UHMWPE for biomedical applications: Performance and functionalization. European Polymer Journal 2020, 125, 109529 .

AMA Style

Nikhil Avinash Patil, James Njuguna, Balasubramanian Kandasubramanian. UHMWPE for biomedical applications: Performance and functionalization. European Polymer Journal. 2020; 125 ():109529.

Chicago/Turabian Style

Nikhil Avinash Patil; James Njuguna; Balasubramanian Kandasubramanian. 2020. "UHMWPE for biomedical applications: Performance and functionalization." European Polymer Journal 125, no. : 109529.

Research article
Published: 19 December 2019 in SN Applied Sciences
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The application of superabsorbent polymer hydrogels is gaining much research attention. Industrial applications include agriculture, environmental engineering, biomedical and tissue engineering, oilfield, construction and electrical products, personal care products, and wastewater treatment. In this study, the swelling performance and adsorption kinetics of two commercial superabsorbent polymer hydrogels were evaluated based upon their stimuli response to pH and salinity at varying temperature and reaction time periods. Characterisation and evaluation of the materials were performed using analytical techniques—optical microscopy, scanning electron microscopy, thermal gravimetric analysis, and the gravimetric method. Experimental results show that reaction conditions strongly influence the swelling performance of the superabsorbent polymer hydrogels considered in this study. Generally, increasing pH and salinity concentration led to a significant decline in the swelling performance of both superabsorbent polymer hydrogels. An optimal temperature range between 50 and 75 °C was considered appropriate based on swell tests performed between 25 c to 100 °C over 2-, 4- and 6-h time periods. These findings serve as a guideline for material technologist and field engineers in the use of superabsorbent polymer hydrogels for a wide range of applications. The study results provide evidence that the two superabsorbent polymer hydrogels can be used for petroleum fraction-saline water emulsions separation, among other applications. Graphic abstract Highlights The swelling performance of the two superabsorbent polymer hydrogels experimentally studied showed a maximum absorbency in the range of 270 to 300g/g. Thermal gravimetric analysis curves show that both superabsorbent polymer hydrogels are stable at high temperatures. Commercially available superabsorbent polymer hydrogels can be used in industrial water absorption applications.

ACS Style

Ruissein Mahon; Yakubu Balogun; Gbenga Oluyemi; James Njuguna. Swelling performance of sodium polyacrylate and poly(acrylamide-co-acrylic acid) potassium salt. SN Applied Sciences 2019, 2, 1 -15.

AMA Style

Ruissein Mahon, Yakubu Balogun, Gbenga Oluyemi, James Njuguna. Swelling performance of sodium polyacrylate and poly(acrylamide-co-acrylic acid) potassium salt. SN Applied Sciences. 2019; 2 (1):1-15.

Chicago/Turabian Style

Ruissein Mahon; Yakubu Balogun; Gbenga Oluyemi; James Njuguna. 2019. "Swelling performance of sodium polyacrylate and poly(acrylamide-co-acrylic acid) potassium salt." SN Applied Sciences 2, no. 1: 1-15.

Journal article
Published: 12 November 2019 in Journal of Petroleum Science and Engineering
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Casing deformation during volume fracturing in shale gas horizontal wells is caused by both existing and induced stresses. These stresses jointly alter and compound the stress field around the casing leading to inefficient well stimulation as planned, lack of access into the well for recompletion, future workovers and present imminent danger of well integrity. Using two simulation scenarios, casing structural integrity was investigated in both radial and axial configurations under the mechanics of a combine system - casing, cement and formation rock. Results obtained show that time dependent rock slippage - creep during stimulation lead to an increase transverse displacement and corresponding stresses on the casing. In addition, the effect of combined loading results in significant increase in both displacements and stresses that can cause radial and axial permanent failure of the casing. This explains the lack of access into the casing during multi-stage hydraulic fracturing and future well intervention and recompletions and increased current understating of the downhole dynamics and casing structural integrity during volume fracturing. This new understanding is a major breakthrough in establishing casing health status during shale gas well stimulation.

ACS Style

Auwalu I. Mohammed; Babs Oyeneyin; Mark Bartlett; James Njuguna. Prediction of casing critical buckling during shale gas hydraulic fracturing. Journal of Petroleum Science and Engineering 2019, 185, 106655 .

AMA Style

Auwalu I. Mohammed, Babs Oyeneyin, Mark Bartlett, James Njuguna. Prediction of casing critical buckling during shale gas hydraulic fracturing. Journal of Petroleum Science and Engineering. 2019; 185 ():106655.

Chicago/Turabian Style

Auwalu I. Mohammed; Babs Oyeneyin; Mark Bartlett; James Njuguna. 2019. "Prediction of casing critical buckling during shale gas hydraulic fracturing." Journal of Petroleum Science and Engineering 185, no. : 106655.

Review article
Published: 09 October 2019 in Frontiers in Materials
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The two-dimensional macro molecule graphene and its derivatives have widely been investigated for their application as nanofiller in carbon fiber-reinforced composites (CFRC). Research has progressed from techniques that disperse graphene as a mixing constituent within the composite material to more complex examples where graphene is covalently bonded to fiber, matrix or both via multiple reaction steps. This field of research is multi-disciplinary whereby branches of materials, engineering, polymer science, physics and chemistry often overlap. From the materials engineering perspective, the desire is to discover the novel materials targeting industrial applications and obtain a full understanding of the graphene oxide chemistry and interaction of graphene oxide with a polymer matrix. To date, most of the research is targeted at (i) improving the fiber/matrix interface properties and/or (ii) improving the dispersion of nanofiller within the matrix; both factors ultimately improve composite performance. Organizing that information critically can lead to emergence of a generalization of material design. Therefore, the objective of this work is to critically review current state of art in the field of graphene oxide/epoxy CFRCs and propose the design rules based on current scientific trend and common themes for future works.

ACS Style

John Keyte; Ketan Pancholi; James Njuguna. Recent Developments in Graphene Oxide/Epoxy Carbon Fiber-Reinforced Composites. Frontiers in Materials 2019, 6, 1 .

AMA Style

John Keyte, Ketan Pancholi, James Njuguna. Recent Developments in Graphene Oxide/Epoxy Carbon Fiber-Reinforced Composites. Frontiers in Materials. 2019; 6 ():1.

Chicago/Turabian Style

John Keyte; Ketan Pancholi; James Njuguna. 2019. "Recent Developments in Graphene Oxide/Epoxy Carbon Fiber-Reinforced Composites." Frontiers in Materials 6, no. : 1.

Review
Published: 04 October 2019 in European Polymer Journal
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Recent research in soft materials is an exhilarating category which has been transcending boundaries for variety of functional applications. This category also stems liquid crystals whose stimuli-responsive feature has fantasized researchers for application arrays in actuators and biomedical. Liquid crystals evince dual characteristics of liquid and solids empowering them to reversibly transit on external actuation. The after-effect of irradiating photons on liquid crystals (LC) facilitate outlying functioning and are engineered with gold nanorods, dyes, graphene and carbon nanotubes among others which greets to incoming stimulus and participates in transference of light energy to perceivable transformation through heat drive. This is progressively explored in medical domain for drug delivery, tissue engineering, cancer treatment, and other disciplines of medicine and bio-mimicking. Additionally, photothermal trigger equips localized punctilious treatment outshining diffusion assisted heating and enables spot treatment. However, LC utilization is burgeoning towards 3D printing, characterizing it as 4D Printing. Present review framework probes LC and its photothermal actuation chemistry in the medical domain. Furthermore, it reflects on LC potential in smart manufacturing in 3D/4D printing, its challenges (limited concentration of filler, its miscibility, and actuation cycle fatigue) and future likelihood.

ACS Style

Prasansha Rastogi; James Njuguna; Balasubramanian Kandasubramanian. Exploration of elastomeric and polymeric liquid crystals with photothermal actuation: A review. European Polymer Journal 2019, 121, 109287 .

AMA Style

Prasansha Rastogi, James Njuguna, Balasubramanian Kandasubramanian. Exploration of elastomeric and polymeric liquid crystals with photothermal actuation: A review. European Polymer Journal. 2019; 121 ():109287.

Chicago/Turabian Style

Prasansha Rastogi; James Njuguna; Balasubramanian Kandasubramanian. 2019. "Exploration of elastomeric and polymeric liquid crystals with photothermal actuation: A review." European Polymer Journal 121, no. : 109287.

Journal article
Published: 02 July 2019 in JOM
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This work reports the development and testing of a magnetic polymer (Polyamide 6, PA6) nanocomposite capable of melting when exposed to an external magnetic field. Addition of high concentrations of iron oxide nanoparticles (NPs) can induce quick melting but is detrimental to the mechanical properties of the polymer. To reduce the amount of NPs required for achieving efficient melting, they should be well dispersed in the polymer. In this study, the oleic acid loading on the surfaces of the NPs was varied to study the effect of variations in coatings on the dispersion in the polymer and on the polymer melting time. The NPs functionalized with oleic acid were added to melted monomer ε-caprolactam and polymerized using ring-opening polymerization. The resulting PA6 nanocomposite was characterized by Fourier-transform infrared spectroscopy, differential scanning calorimetry, x-ray diffraction and transmission electron microscopy. The results confirmed that the PA6 nanocomposite showed a decrease of 8–10% in its glass-transition temperature compared to commercial PA6. The crystallinity of the synthesized samples were found to vary between 42% and 57%. The 55 wt.% oleic acid-loaded NPs were found to disperse most efficiently in the PA6 matrix; however, some large agglomerates were formed due to excessive oleic acid. Therefore, the 22 wt.% oleic acid coating showed overall superior dispersion. Additionally, the magnetic induction response was tested by observing a melt-characteristic of the magnetic polymer composite using a model set-up. Oleic acid concentration is found to affect the dispersion, melting time and crystallinity of the nanocomposite.

ACS Style

RanjeetKumar Gupta; Ketan Pancholi; Rulston De Sa; Duncan Murray; Dehong Huo; Ghazi Droubi; Maggie White; James Njuguna. Effect of Oleic Acid Coating of Iron Oxide Nanoparticles on Properties of Magnetic Polyamide-6 Nanocomposite. JOM 2019, 71, 3119 -3128.

AMA Style

RanjeetKumar Gupta, Ketan Pancholi, Rulston De Sa, Duncan Murray, Dehong Huo, Ghazi Droubi, Maggie White, James Njuguna. Effect of Oleic Acid Coating of Iron Oxide Nanoparticles on Properties of Magnetic Polyamide-6 Nanocomposite. JOM. 2019; 71 (9):3119-3128.

Chicago/Turabian Style

RanjeetKumar Gupta; Ketan Pancholi; Rulston De Sa; Duncan Murray; Dehong Huo; Ghazi Droubi; Maggie White; James Njuguna. 2019. "Effect of Oleic Acid Coating of Iron Oxide Nanoparticles on Properties of Magnetic Polyamide-6 Nanocomposite." JOM 71, no. 9: 3119-3128.

Review
Published: 04 June 2019 in Journal of Natural Gas Science and Engineering
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This paper focus on factors attributing to casing failure, their failure mechanism and the resulting failure mode. The casing is a critical component in a well and the main mechanical structural barrier element that provide conduits and avenue for oil and gas production over the well lifecycle and beyond. The casings are normally subjected to material degradation, varying local loads, induced stresses during stimulation, natural fractures, slip and shear during their installation and operation leading to different kinds of casing failure modes. The review paper also covers recent developments in casing integrity assessment techniques and their respective limitations. The taxonomy of the major causes and cases of casing failure in different well types is covered. In addition, an overview of casing trend utilisation and failure mix by grades is provided. The trend of casing utilisation in different wells examined show deep-water and shale gas horizontal wells employing higher tensile grades (P110 & Q125) due to their characteristics. Additionally, this review presents casing failure mixed by grades, with P110 recording the highest failure cases owing to its stiffness, high application in injection wells, shale gas, deep-water and high temperature and high temperature (HPHT) wells with high failure probability. A summary of existing tools used for the assessment of well integrity issues and their respective limitations is provided and conclusions drawn.

ACS Style

Auwalu I. Mohammed; Babs Oyeneyin; Bryan Atchison; James Njuguna. Casing structural integrity and failure modes in a range of well types - A review. Journal of Natural Gas Science and Engineering 2019, 68, 102898 .

AMA Style

Auwalu I. Mohammed, Babs Oyeneyin, Bryan Atchison, James Njuguna. Casing structural integrity and failure modes in a range of well types - A review. Journal of Natural Gas Science and Engineering. 2019; 68 ():102898.

Chicago/Turabian Style

Auwalu I. Mohammed; Babs Oyeneyin; Bryan Atchison; James Njuguna. 2019. "Casing structural integrity and failure modes in a range of well types - A review." Journal of Natural Gas Science and Engineering 68, no. : 102898.

Original paper
Published: 01 June 2019 in Journal of Polymer Research
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In this study, a novel reclaimed clay nanofiller was used to manufacture low-density polyethylene (LDPE)/Oil based mud filler (OBMF) nanocomposites by a melt compounding process. The mechanical testing samples were manufactured using injection moulding. The effect of reclaimed clay minerals influencing the crystallinity and the dispersion characteristics of this clay in LDPE matrix affecting the structural and thermal properties of the nanocomposites was investigated. It was observed that OBMFs were compatible with LDPE matrix which implies a strong interfacial interaction between the clay layers and polymer and that the influence of clay minerals present in OBMFs formed chemical bonds within the microstructure of the nanocomposites. The char yields of nanocomposites increased with OBMFs content. The TD5% and TD50% (onset degradation temperature at 5 wt% loss and 50 wt% loss, respectively) of the LDPE nanocomposite with 10.0 wt% OBMFs was the highest (27 °C higher in TD5% and 54 °C higher in TD50%) among the nanocomposites. Viscoelastic analysis data showed a sharp decrease in the storage modulus of OBMFs reinforced LDPE nanocomposites. The tan δ spectra presented a strong influence of the filler contents on the relaxation process of LDPE and its nanocomposites. An enhancement of mechanical properties of composites was identified which showed a gain of 14% Young’s modulus and a gain of 18% tensile strength at 10.0 wt% OBMFs loading compared to those properties of neat LDPE. The effect of filler dispersion in LDPE polymer matrix in relation to thermal stability was investigated and heat capacity data is employed to characterise changes in thermal characteristics relating to the nanomorphology of the materials.

ACS Style

Shohel Siddique; Grant David Smith; Kyari Yates; Ajay Kumar Mishra; Kerr Matthews; Laszlo Csetenyi; James Njuguna. Structural and thermal degradation behaviour of reclaimed clay nano-reinforced low-density polyethylene nanocomposites. Journal of Polymer Research 2019, 26, 154 .

AMA Style

Shohel Siddique, Grant David Smith, Kyari Yates, Ajay Kumar Mishra, Kerr Matthews, Laszlo Csetenyi, James Njuguna. Structural and thermal degradation behaviour of reclaimed clay nano-reinforced low-density polyethylene nanocomposites. Journal of Polymer Research. 2019; 26 (6):154.

Chicago/Turabian Style

Shohel Siddique; Grant David Smith; Kyari Yates; Ajay Kumar Mishra; Kerr Matthews; Laszlo Csetenyi; James Njuguna. 2019. "Structural and thermal degradation behaviour of reclaimed clay nano-reinforced low-density polyethylene nanocomposites." Journal of Polymer Research 26, no. 6: 154.

Full paper
Published: 19 March 2019 in Advanced Engineering Materials
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This study investigat the effectiveness of reduced graphene oxide as nanofiller in enhancing epoxy/carbon fiber‐reinforced composite at varying temperature conditions. The graphene oxide is synthesized using modified Hummer's method and then is chemically reduced to yield reduced graphene oxide (rGO). The rGO is dispersed in epoxy matrix system through combination of mechanical and sonication methods. The flexural and shear test samples are manufactured using resin infusion technique. These samples are then tested to determine their shear and flexural properties at varying temperatures (−10 °C, 23 °C, 40 °C) and the results correlate to neat samples. It is found that the composites’ flexural strength and flexural modulus increase with rGO wt% content up to 62% and 44%, respectively. The shear testing results show improvement on the shear strength and modulus at maximum of 6% and 40%, respectively. The rGO improvements advantage is lost for flexural strength, shear strength, and modulus at elevated temperatures while flexural modulus withheld at 40% improvements over virgin epoxy/carbon fiber‐reinforced composite. An interesting observation is that all samples with rGO exhibit reduced damage characteristics superior to the neat samples under flexural and shear loading conditions. This study indicates that the addition of rGO significantly alter the flexural and shear properties, failure modes, damage characteristics, and they are overall sensitive to elevated temperature conditions.

ACS Style

Paddy Jenkins; Shohel Siddique; Samrin Khan; Aliyu Usman; Kristof Starost; Allan MacPherson; Pravin Bari; Satyendra Mishra; James Njuguna. Influence of Reduced Graphene Oxide on Epoxy/Carbon Fiber‐Reinforced Hybrid Composite: Flexural and Shear Properties under Varying Temperature Conditions. Advanced Engineering Materials 2019, 21, 1 .

AMA Style

Paddy Jenkins, Shohel Siddique, Samrin Khan, Aliyu Usman, Kristof Starost, Allan MacPherson, Pravin Bari, Satyendra Mishra, James Njuguna. Influence of Reduced Graphene Oxide on Epoxy/Carbon Fiber‐Reinforced Hybrid Composite: Flexural and Shear Properties under Varying Temperature Conditions. Advanced Engineering Materials. 2019; 21 (6):1.

Chicago/Turabian Style

Paddy Jenkins; Shohel Siddique; Samrin Khan; Aliyu Usman; Kristof Starost; Allan MacPherson; Pravin Bari; Satyendra Mishra; James Njuguna. 2019. "Influence of Reduced Graphene Oxide on Epoxy/Carbon Fiber‐Reinforced Hybrid Composite: Flexural and Shear Properties under Varying Temperature Conditions." Advanced Engineering Materials 21, no. 6: 1.

Journal article
Published: 10 November 2018 in Polymer Degradation and Stability
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The crystallinity and thermal degradation behaviours of Polyamide 6/Oil Based Mud Fillers (PA6/OBMFs) nanocomposites have been investigated using DSC and TGA. TGA indicates the onset decomposition temperature of D1/2 (half-decomposition) is 16 °C higher for PA6 with 10.0 wt% of OBMFs than that of PA6, whereas the lowest onset decomposition temperature difference among the nanocomposites and neat PA6 is 8 °C for PA6 with 7.5 wt% of OBMFs. However PA6 with 5.0 wt % OBMFs nanocomposite has taken the longest time (1 min 36 s more than neat PA6) to reach D1/2. It can be deduced in this study that PA6 with 5.0 wt % OBMFs nanocomposite provided the maximum heat resistant property whereas PA6 with 7.5 wt % OBMFs nanocomposite showed the maximum heat absorbance property among different nanocomposites and PA6 with 10.0 wt % exhibited the maximum thermal stability. There is a sigmoidal curve generated based on the TIF and wt% filler content value which shows three significant points at intersections of 50% TIF line which are highlighted as exfoliation (4.2 wt%), intercalation (6.8 wt%) and agglomeration (9.0 wt%) points. These TIF values explained the investigated heat resistant, heat capacity and thermal stability properties of PA6/OBMFs nanocomposites illustrating the ratio of TIF and MAF is the key measure which can be considered as an effective approach to identify the nanomorphology of PA6/OBMFs nanocomposites.

ACS Style

Shohel Siddique; Lorraine Kwoffie; Kofi Addae-Afoakwa; Kyari Yates; James Njuguna. The crystallinity and thermal degradation behaviour of polyamide 6/Oil Based Mud Fillers (PA6/OBMFs) nanocomposites. Polymer Degradation and Stability 2018, 159, 139 -152.

AMA Style

Shohel Siddique, Lorraine Kwoffie, Kofi Addae-Afoakwa, Kyari Yates, James Njuguna. The crystallinity and thermal degradation behaviour of polyamide 6/Oil Based Mud Fillers (PA6/OBMFs) nanocomposites. Polymer Degradation and Stability. 2018; 159 ():139-152.

Chicago/Turabian Style

Shohel Siddique; Lorraine Kwoffie; Kofi Addae-Afoakwa; Kyari Yates; James Njuguna. 2018. "The crystallinity and thermal degradation behaviour of polyamide 6/Oil Based Mud Fillers (PA6/OBMFs) nanocomposites." Polymer Degradation and Stability 159, no. : 139-152.