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  • 1.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gong, Guan
    RISE SICOMP AB, Fibervägen 2, 943 33 Öjebyn, Sweden.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mechanical Performance of PE Reinforced with Graphene Nanoplatelets (GNPs): Effect of Composition and Processing ParametersManuscript (preprint) (Other academic)
  • 2.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gong, Guan
    Rise Sicomp AB, Fibervägen 2, SE-941 26 Öjebyn, Sweden.
    Nyström, Birgitha
    Podcomp AB, Skylvägen 1, SE-943 33 Öjebyn, Sweden.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Characterization of Wood and Graphene Nanoplatelets (GNPs) Reinforced Polymer Composites2020In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 9, article id 2089Article in journal (Refereed)
    Abstract [en]

    This paper investigates the utilization of commercial masterbatches of graphene nanoplatelets to improve the properties of neat polymer and wood fiber composites manufactured by conventional processing methods. The effect of aspect ratio of the graphene platelets (represented by the different number of layers in the nanoplatelet) on the properties of high-density polyethylene (HDPE) is discussed. The composites were characterized for their mechanical properties (tensile, flexural, impact) and physical characteristics (morphology, crystallization, and thermal stability). The effect of the addition of nanoplatelets on the thermal conductivity and diffusivity of the reinforced polymer with different contents of reinforcement was also investigated. In general, the mechanical performance of the polymer was enhanced at the presence of either of the reinforcements (graphene or wood fiber). The improvement in mechanical properties of the nanocomposite was notable considering that no compatibilizer was used in the manufacturing. The use of a masterbatch can promote utilization of nano-modified polymer composites on an industrial scale without modification of the currently employed processing methods and facilities.

  • 3.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Jantel, Ugo
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological Study on Wood and Graphene Reinforced High Density Polyethylene2022In: ECCM 2022 - Proceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability / [ed] Vassilopoulos, Anastasios; Michaud, Véronique, Lausanne: EPFL Lausanne, Composite Construction Laboratory , 2022, Vol. 1, p. 585-592Conference paper (Other academic)
    Abstract [en]

    Wear rate (WR) and coefficient of friction (COF) for high-density polyethylene (HDPE)and its composites of wood flour (WF) and/or graphene nanoplatelets (GNPs) are studied. Theinvestigation is performed by pin-on-disc test configuration on samples with different moisturecontents (dry, and samples saturated at RH of 33% and 79% in room temperature). The effect ofthe different scales of reinforcement (GNPs and WF) on these properties is discussed. Themorphological/microstructural changes in the materials induced by the motion in contact and/ormoisture content are investigated by differential scanning calorimetry (DSC). Results show thatreinforcing the polymer with WF or GNPs reduces the WR significantly, compared to neat HDPE.The hybrid reinforcements contribute to maximum improvement in wear resistance (>98%) andin the reduction of COF (>11%). The improvement in the tribological behavior of bio-basedmaterials has a significant impact on sustainable development through the improved design,durability, and environmental impact.

  • 4.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Synergistic Effect of Multiscale Reinforcement on Wear of Wood Polymer Composites2022In: PolyTrib 2022, 2022, p. 34-35Conference paper (Other academic)
  • 5.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ouarga, Ayoub
    High Throughput Multidisciplinary Research Laboratory, Mohammed VI Polytechnic University (UM6P), Lot 660—Hay Moulay Rachid, 43150 Benguerir, Morocco.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Chouhan, Shailesh Singh
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Landström, Anton
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hajlane, Abdelghani
    Laboratory of Crystallography and Materials Sciences, National Graduate School of Engineering of Caen, 6 Boulevard Maréchal Juin, 14000 Caen, France.
    Conductive Regenerated Cellulose Fibers for Multi-Functional Composites: Mechanical and Structural Investigation2021In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 14, no 7, article id 1746Article in journal (Refereed)
    Abstract [en]

    Regenerated cellulose fibers coated with copper via electroless plating process are investigated for their mechanical properties, molecular structure changes, and suitability for use in sensing applications. Mechanical properties are evaluated in terms of tensile stiffness and strength of fiber tows before, during and after the plating process. The effect of the treatment on the molecular structure of fibers is investigated by measuring their thermal stability with differential scanning calorimetry and obtaining Raman spectra of fibers at different stages of the treatment. Results show that the last stage in the electroless process (the plating step) is the most detrimental, causing changes in fibers’ properties. Fibers seem to lose their structural integrity and develop surface defects that result in a substantial loss in their mechanical strength. However, repeating the process more than once or elongating the residence time in the plating bath does not show a further negative effect on the strength but contributes to the increase in the copper coating thickness, and, subsequently, the final stiffness of the tows. Monitoring the changes in resistance values with applied strain on a model composite made of these conductive tows show an excellent correlation between the increase in strain and increase in electrical resistance. These results indicate that these fibers show potential when combined with conventional composites of glass or carbon fibers as structure monitoring devices without largely affecting their mechanical performance.

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  • 6.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Riga Technical University, Kalnciema Iela 6, Rīga, LV-1048, Latvia.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Analysis of long-term performance of wood polymer composites with added multifunctionality2022In: 80th International Scientific Conference of the University of Latvia - Advanced Composites and Applications: Book of Abstracts, Riga: University of Latvia , 2022, p. 9-Conference paper (Other academic)
  • 7.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Time-dependent properties of graphene reinforced HDPE2019In: Proceedings of 9th International Conference on Composite Testing and Model Identification: Book of Abstracts / [ed] R. Joffe; L. Pupure; J. Varna; L. Wallström, 2019, article id 163Conference paper (Other academic)
  • 8.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Department of Structural Engineering,Riga Technical University, Rīga, Latvia.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Time-dependent properties of high-density polyethylene with wood/graphene nanoplatelets reinforcement2023In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 44, no 1, p. 465-479Article in journal (Refereed)
    Abstract [en]

    The effect of graphene nanoplatelets (GNPs) on the long-term performance of wood fiber/high-density polyethylene (HDPE) composite is investigated by using short-term creep tests with an efficient, faster data analysis approach. Previously, it was shown that the addition of GNPs at 15 wt% into HDPE reduces the viscoplastic (VP) strain developed during 2 h creep by ~50%. The current study shows that 25 and 40 wt% wood content in HDPE reduce the VP strains developed during 2 h creep time by >75% with no noticeable effect of the increased wood content. However, further addition of GNPs results in more than 90% total reduction in the VP strains. The current study shows that the development of the VP strains in the hybrid composites follows Zapas model. Viscoelastic (VE) response of these composites is nonlinear and thus is described by Schapery's model. Parameters for VP and VE models are obtained from the creep experiments and were validated in a separate loading-unloading test sequence. Results show a very good agreement between experiments and predictions for the studied materials as long as the micro-damage is not present.

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  • 9.
    Al-Maqdasi, Zainab
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pupure, Liva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Riga Technical University, Institute of Construction and Reconstruction, Riga, Latvia.
    Gong, Guan
    RISE SICOMP AB, Composite materials and product development, Piteå, Sweden.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Time‐dependent properties of graphene nanoplatelets reinforced high‐density polyethylene2021In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 138, no 30, article id 50783Article in journal (Refereed)
    Abstract [en]

    The deformation of polymers at constant applied stress is one of their major drawbacks, limiting their use in advanced applications. The study of this property using classical techniques requires extensive testing over long periods of time. It is well known that reinforced polymers show improved behavior over time compared to their neat counterparts. In this study, the effect of adding different amounts of graphene nanoplatelets (GNPs) on the time‐dependent properties of high‐density polyethylene (HDPE) is investigated using short‐term creep tests and load/unload recovery tests. The results are discussed in terms of the test profile and the influence of loading history. Viscoplasticity/viscoelasticity analysis is performed using Zapas model and by comparing creep, creep compliance and pure viscoelasticity curves. The results show that the reinforcement of 15 wt% GNP have the most significant effect on the time‐dependent behavior, reducing the strain by more than 50%. The creep compliance curves show that nano‐reinforced HDPE behaves nonlinearly viscoelastically even at very low stresses. In addition to demonstrating the effect of nano‐reinforcement, the discussion of the results concludes that the influence of loading history can be quite significant and should not be neglected in the design and evaluation of material behavior.

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  • 10.
    Almeida, Nuno A.F.
    et al.
    Mechanical Engineering Department & TEMA, University of Aveiro, Campus Universitário de Santiago.
    Rodrigues, Joana
    Physics Department & I3N, University of Aveiro, Campus Universitário de Santiago.
    Silva, Patricia
    Mechanical Engineering Department & TEMA, University of Aveiro, Campus Universitário de Santiago.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Soares, Manuel J.
    Physics Department & I3N, University of Aveiro, Campus Universitário de Santiago.
    Monteiro, Teresa
    Physics Department & I3N, University of Aveiro, Campus Universitário de Santiago.
    Lopes-da-Silva, José A.
    Chemistry Department & QOPNA, University of Aveiro, Campus Universitário de Santiago.
    Marques, Paula A.A.P.
    Mechanical Engineering Department & TEMA, University of Aveiro, Campus Universitário de Santiago.
    Pressure dependent luminescence in titanium dioxide particles modified with europium ions2016In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 234, p. 137-144Article in journal (Refereed)
    Abstract [en]

    Particles of titanium dioxide were prepared in the presence of europium ions (TiO2:Eu) by a solvothermal method and thermal annealed in air at 500 °C. The spectroscopic properties of TiO2:Eu particles were analyzed indicating that the Eu3+ ions are likely distributed at the surface or near the surface of the titanium dioxide particles. The photoluminescence analysis showed that the intraionic emission was strongly sensitive to reduced pressure conditions, as seen by its absence under vacuum conditions. The ion emission was re-established as soon as the atmosphere was restored. Additionally, the ion integrated emission intensity follows a linearly dependence with pressure in the range of 150 to 800 mbar revealing a high sensitivity to small variations in pressure, which is an unprecedented result. This innovation will allow the study of new technologies in the area of low vacuum sensors where TiO2:Eu may act as the active element of an optical sensor for a pressure device.

  • 11.
    Almqvist, Andreas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pellegrini, Barbara
    Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy; CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Verona, Italy.
    Lintzén, Nina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Holmberg, H-C
    Luleå University of Technology, Department of Health, Learning and Technology, Health, Medicine and Rehabilitation. School of Kinesiology, University of British Columbia, Vancouver, BC, Canada.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    A Scientific Perspective on Reducing Ski-Snow Friction to Improve Performance in Olympic Cross-Country Skiing, the Biathlon and Nordic Combined2022In: Frontiers in Sports and Active Living, E-ISSN 2624-9367, Vol. 4, article id 844883Article in journal (Refereed)
    Abstract [en]

    Of the medals awarded at the 2022 Winter Olympics in Beijing, 24% were for events involving cross-country skiing, the biathlon and Nordic combined. Although much research has focused on physiological and biomechanical characteristics that determine success in these sports, considerably less is yet known about the resistive forces. Here, we specifically describe what is presently known about ski-snow friction, one of the major resistive forces. Today, elite ski races take place on natural and/or machine-made snow. Prior to each race, several pairs of skis with different grinding and waxing of the base are tested against one another with respect to key parameters, such as how rapidly and for how long the ski glides, which is dependent on ski-snow friction. This friction arises from a combination of factors, including compaction, plowing, adhesion, viscous drag, and water bridging, as well as contaminants and dirt on the surface of and within the snow. In this context the stiffness of the ski, shape of its camber, and material composition and topography of the base exert a major influence. An understanding of the interactions between these factors, in combination with information concerning the temperature and humidity of both the air and snow, as well as the nature of the snow, provides a basis for designing specific strategies to minimize ski-snow friction. In conclusion, although performance on “narrow skis” has improved considerably in recent decades, future insights into how best to reduce ski-snow friction offer great promise for even further advances.

  • 12.
    Belotti, Luca
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vadivel, Hari Shankar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Influence of counter surface topography on the tribological behavior of hybrid UHMWPE composites2018Conference paper (Refereed)
  • 13.
    Bryant, M.
    et al.
    Institute of Functional Surface, University of Leeds, Leeds, UK.
    Sin, Jorge Rituerto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, A.
    Institute of Functional Surface, University of Leeds, Leeds, UK.
    Effect of proteins and phosphates on the degradation and repassivation of CoCrMo alloys under tribocorrosion conditions2020In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 14, no 4, p. 207-218Article in journal (Refereed)
    Abstract [en]

    Cobalt-chromium-molybdenum alloys are commonly used for biomedical applications such as dental implants and joint implants. Once the material is implanted into the body it is exposed to the corrosiveness of biological fluids and, in some cases, to mechanical loading that can lead to the combined action of wear and corrosion; better known as tribocorrosion. The effect of four different simulated body fluids on the tribocorrosion behaviour of a CoCrMo alloy has been investigated. The degradation of the studied CoCrMo alloys due to tribocorrosion shows a great dependence on the chemical composition of the media. Phosphate-buffered saline (PBS)-based solutions tend to show higher mass loss than the solutions prepared with distilled water. Phosphates present in PBS tend to accumulate on the surface of the alloy and change its tribological performance. In addition, proteins show a lubricating effect reducing the coefficient of friction of the system in the boundary lubrication regime.

  • 14.
    Bryant, M.
    et al.
    Institute of Functional Surfaces, UK.
    Sin, Jorge Rituerto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, A.
    Institute of Functional Surfaces, UK.
    Exploring the oxide reformation kinetics of CoCrMo alloys in simulated body fluids2016Conference paper (Refereed)
  • 15.
    Clegg, Benjamin A.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shrestha, Dilesh Raj
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribo-Mechanical Properties and Bioactivity of Additively Manufactured PAEK Materials for Load Bearing Medical Applications: A Systematic Review2023In: Biotribology, ISSN 2352-5738, Vol. 35-36, article id 100263Article, review/survey (Refereed)
    Abstract [en]

    Additive manufacturing (AM) holds significant potential in transforming medical applications, with a particular focus on polyetheretherketone (PEEK) and its derivatives, collectively known as poly-aryl-ether-ketone (PAEK) materials. Advances in AM precision have paved the way for the successful 3D printing of high-performance thermoplastics like PEEK, offering new prospects in load-bearing medical applications. This systematic review comprehensively assesses recent scientific literature concerning the tribo-mechanical properties and bioactivity of additively manufactured PAEK materials, with a specific emphasis on PEEK, for load-bearing medical uses. Despite substantial research into AM of metallic biomaterials, knowledge gaps persist regarding AM processing parameters, structure-property relationships, biological behaviours, and implantation suitability of PAEKs. This review bridges these gaps by analysing existing literature on the tribo-mechanical properties and bioactivity of additively manufactured PAEK materials, providing valuable insights into their performance in load-bearing medical applications. Key aspects explored include printing conditions, strength limitations, and outcomes of in-vitro and in-vivo evaluations. Through this systematic review, we consolidate current knowledge, delivering essential information for researchers, clinicians, and manufacturers involved in advancing additively manufactured PAEK materials for load-bearing medical applications.

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  • 16.
    Coelho, Margarida
    et al.
    Department of Mechanical Engineering, University of Aveiro.
    Torrao, Guilhermina
    Department of Mechanical Engineering, University of Aveiro.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gracio, Jose
    Department of Mechanical Engineering, University of Aveiro.
    Nanotechnology in automotive industry: research strategy and trends for the future – small objects, big impacts2012In: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, E-ISSN 1533-4899, Vol. 12, no 8, p. 6621-6630Article in journal (Refereed)
    Abstract [en]

    The goal of this paper is to emphasize and present briefly the nanotechnology science and its potential impact on the automotive industry in order to improve the production of recent models with an optimization of the safety performance and a reduction in the environmental impacts. Nanomaterials can be applied in car bodies as light weight constructions without compromising the stiffness and crashwortiness, which means less material and less fuel consumption. This paper outlines the progress of nanotechnology applications into the safety features of more recent vehicle models and fuel efficiency, but also emphasis the importance of sustainable development on the application of these technologies and life cycle analysis of the considered materials, in order to meet the society trends and customers demands to improve ecology, safety and comfort.

  • 17.
    Dhakal, Nayan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT Leeds, United Kingdom.
    Espejo, Cayetano
    Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT Leeds, United Kingdom.
    Morina, Ardian
    Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT Leeds, United Kingdom.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance of 3D printed neat and carbon fiber reinforced PEEK composites2024In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 193, article id 109356Article in journal (Refereed)
    Abstract [en]

    This work investigates the tribological behavior of neat and carbon fiber-reinforced polyether-ether-ketone (PEEK) materials processed using the fused filament fabrication (FFF) technique. The reciprocating sliding behavior of printed polymers against stainless steel (SS) under dry and water-lubricated conditions was studied. The running-in behavior and evolution of friction were dependent on the material combination and sliding conditions. PEEK reinforced with 10 wt% carbon fibers was optimal considering tribological performance. Neat PEEK exhibited a combination of abrasive and adhesive wear mechanisms, while composites primarily showed fiber-matrix debonding and delamination during sliding. The outcome of this work has significance in improving the processing design of PEEK-based materials in extrusion-based 3D printing for tribological applications.

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  • 18.
    Dhakal, Nayan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behaviour of UHMWPE composites lubricated by polyvinylpyrrolidone‐modified water2022In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 34, no 1, p. 42-53Article in journal (Refereed)
    Abstract [en]

    Tribological characteristics of ultra-high molecular weight polyethylene (UHMWPE) composites with 10% short carbon fibres (SCF) lubricated in water with polyvinylpyrrolidone (PVP) as a modifier were investigated. The aqueous solutions with varying concentrations of PVP were prepared, and their viscosity-enhancing action, friction-reducing properties and anti-wear performances were studied under different loading conditions equivalent to 10 and 20 MPa of contact pressures at a constant sliding speed of 20 mm/s. The results showed that PVP is an excellent viscosity modifier for water. PVP-modified water exhibited excellent performance compared to distilled water, reducing the wear and friction coefficient of neat UHMWPE up to 25%. The anti-wear properties of UHMWPE-SCF composite were also improved with PVP modified water lubrication, yielding a maximum reduction of wear up to 45%. PVP seems to be a promising additive of modifying the lubricating properties of distilled water for water-based lubrication. 

  • 19.
    Dhakal, Nayan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT, Leeds, United Kingdom.
    Wang, Xiaolong
    State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, CAS, Lanzhou, 730000, China.
    Espejo, Cayetano
    Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT, Leeds, United Kingdom.
    Morina, Ardian
    Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, LS2 9JT, Leeds, United Kingdom.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Impact of processing defects on microstructure, surface quality, and tribological performance in 3D printed polymers2023In: Journal of Materials Research and Technology, ISSN 2238-7854, Vol. 23, p. 1252-1272Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM), also known as three-dimensional (3D) printing, of polymer-based materials is growing as a time-efficient, economical, and environmentally sustainable technique for prototype development in load-bearing applications. This work investigates the defects arising from the processing in material extrusion-based AM of polymers and their impact on the part performance. The influence of raster angle orientation and printing speed on tribological characteristics, microstructure, and surface finish of acrylonitrile butadiene styrene (ABS) fabricated in a heated build chamber was studied. Comprehensive analysis with fractography and tomography revealed the formation, distribution, and locations of internal voids, while surface defects were studied with the topography analysis of as-printed surfaces. Surface roughness and tribological results show that printing speed can be optimally increased with a minimal impact on interlayer bonding and part performance. Increased printing speed allowed up to 58% effective reduction in printing time obtaining comparable mechanical properties at varying process parameters. 3D printed ABS exhibited dry sliding friction coefficients in the range of 0.18–0.23, whilst the maximum specific wear rate was 6.2 × 10−5 mm3/Nm. Higher surface roughness and increased printing speed exhibited delayed running-in during dry sliding, while insignificant influence was observed for steady-state friction and wear behaviors. The findings indicate that improved surface finish and reduced internal defects can be achieved with a controlled build environment allowing for higher printing speed. The observations in this study are evidence that 3D printing can be adapted for the sustainable manufacturing of polymeric components for tribological applications.

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  • 20.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biocompatibility, Mechanical and Tribological properties of GO reinforced thermoplastic polymer2018Conference paper (Other academic)
  • 21.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biointerface characterization of metal on metal implant materials using XPS and ToF-SIMS: comparison of human serum, synovial fluid, MEM and water2008Conference paper (Other academic)
  • 22.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biomaterials and biotribology2009In: Thule: Kungl. Skytteanska samfundets årsbok 2009, Umeå: Kungl. Skytteanska samfundet , 2009, p. 117-127Chapter in book (Other (popular science, discussion, etc.))
  • 23.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biotribological behaviour of reionforced UHMPWE2010Conference paper (Refereed)
  • 24.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Design and manufacturing of Graphene Oxide reinforced high performing thermoplastics hybrid composites for Tribological applications2018Conference paper (Other academic)
  • 25.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Effect of light power density variation on dental light-cure resin composites2001Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dental resin based composites are tooth-colored filling materials composed of synthetic resins and particulate ceramic reinforcing filler particles. The resin system also contains molecules that promote and/or modify the polymerisation reaction of the dimethacrylate resin monomers. The filler is bonded to the cured polymer with a film of silane coupling agent covering the filler particles. That silane film is also bonded to the reinforcing filler particles. Dental composites have been used as restorative materials for anterior applications since the 60s. Their tooth matching ability, ability to bond to tooth tissues and their lack of mercury have also promoted them as an alternative to dental amalgam for use in posterior teeth. Favourable results from long-term clinical trails demonstrate that when placed correctly, composites can produce esthetical posterior restorations with acceptable longevity ( el-Mowafy et al., 1994: Taylor et al., 1994 ), although not yet comparable to amalgams (Mjor). Significant problems still remain to be solved and limit their usefulness in the routine practice of dentistry. One of the most significant problems today relates to large material contraction during intra-oral polymerisation of composites. The hardening of composites is the result of polymerisation reactions involving dimethacrylate monomers. A rigid and heavily cross-linked polymer network is produced which surrounds the inert filler particles. The extent of this reaction, the degree of conversion, dictates many of the physical and mechanical properties of the composites. The degree of cure is influenced by many factors, including the light energy used to activate the reaction (Rueggeberg and Jordan, 1993). A reduction in volume, here termed shrinkage, occurs when the monomer polymerises. That shrinkage, which is more than 10-20 times higher in microns than what occurs when an amalgam sets, is caused by a change from van der Waal bonding to covalent bond formation. During that reaction, the monomer molecules rearrange and move closer together (Oleinik, 1986). The magnitude of the shrinkage is dictated by the extent of the reaction, as well as by the nature of the monomers. Research program In the currently ongoing study we are studying the effect of light intensity on polymerisation-induced strain, degree of conversion, volumetric changes and modulus of elasticity of two commercial dental composites. The objective is to test the hypothesis that low light intensity and increased curing time can be used to cure composites with better performance than high intensity cured composites. The benefits with the low intensity long time cure could be improved marginal integrity without loss of mechanical and physical properties. MethodsPolymerisation strain: Small ring shape samples were prepared and cured with three different light intensities (800, 450 and 200 mW/cm2). The polymerisation strain was measured by strain gages. The temperature increase was also measured. The sources of increased temperature are heat generated from the lamp as well as exothermal heat from curing. Volumetric shrinkage: The overall volumetric shrinkage was measured using water and mercury displacement methods. Degree of conversion: The effect of light intensity irradiation time on degree of conversion was measured by spectroscopy (FT- Raman). Modulus of Elasticity: One important factor influencing residual stresses is the stiffness of the dental composite. A miniature tensile machine for small sample size was used to measure the Young's modulus for two materials cured with different light intensities. ResultsA decrease in light intensity decreased the residual strain for the different material systems being evaluated. As long as the lower light intensity was compensated with an increased curing time, degree of conversion, Young's modulus and volumetric shrinkage were compared to high intensity cure for shorter time. The temperature increase, though, was lower for the low intensity cure than for the high intensity cure, even if longer time was used for the low intensity cure. DiscussionThe above results support the proposed hypothesis. A lower light intensity delays gelation, allowing the material to flow more initially. Such flow decreases the induced strain. Another important factor is the lower increase in temperature, which also decreases the thermal shrinkage that occurs during cooling back to room temperature. Differences between the two materials can also be related to differences in molecular structures between the two composites. An important conclusion is that for these materials, the polymerisation reaction is controlled by the total light energy supplied to the dental composite.

  • 26.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Graphene oxide reinforced UHMWPE composites in Tribological applications2016Conference paper (Refereed)
  • 27.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Improved tribological performance of water lubricated bearings: using hybrid nanodiamond polymeric composites2016Conference paper (Refereed)
  • 28.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Investigation of the mechanical and the thermal properties of HMWPE-blended vitamin E/nanofillers composites2017In: The 9thInternational Biotribology Forum. The 9thChinese Biotribology and Implant Engineering Satellite Forum of 6th World Tribology Congress (WTC), 2017Conference paper (Refereed)
  • 29.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Manufacturing of bionano-composite: CNT reinforced UHMWPE composite2007Conference paper (Other academic)
  • 30.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Manufacturing parameters and Tribological characterisation of carbon reinforced UHMWPE composites-in orthopaedic applications2015Conference paper (Refereed)
  • 31.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Nanoparticle reinforced UHMWPE for orthopaedic applications “parameters affecting the manufacturing process and mechanical properties”2015In: 7th UHMWPE International Meeting, October 22-23, 2015, Philadelphia, PA, Implant Research Center , 2015, p. 73-73Conference paper (Refereed)
  • 32.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Overview on carbon reinforced UHMWPE composites “in orthopaedicapplications”2014In: Abstract Book, Universidade de Aveiro , 2014, p. 295-295, article id 381Conference paper (Refereed)
  • 33.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Processing of high performance thermoplastic multiscale composites for tribological applications2018In: 45th Leeds-Lyon Symposium on Tribology, 2018Conference paper (Refereed)
  • 34.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Reactivity of XPS Ion-etched CoCrMo and TiAlV alloys in physiological medium2009Conference paper (Other academic)
    Abstract [en]

    Introduction: Osteolysis induced by wear particles in metal-on-polyethylene hip implants has been the key motivation to look for alternative bearings and in fact emergence and development of new metal-on-metal (MOM) implant materials for joint replacement. However, while the volume of wear particles produced in metal-on-metal articulations is lower in MOM implants, it is clear that the smaller size of the metal wear particles has a dramatic effect on the number of particles produced per unit volume of wear. Although various surface and interface characterization methods have been applied to study the physical wear, corrosion and implant surface interactions with biological environments, presently the local and systematic effects of metal debris in body are poorly understood. Materials and Methods: Cobalt-chromium-molybdenium (CoCr) and titanium-aluminum-vanadium (TiAlV) alloys have been used in MOM implants extensively. Metallic samples were cut and mirror polished. In the present study the samples were immersed in four different biological lubricants (Human serum, synovial fluid and MEM) for 10 min, 1 hr, and 5 days of immersion and then studied by X-ray Photoelectron Spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). XPS determined the chemistry of elements located whit in the top few nanometers of materials. Significant differences in the absorbed layers and differences in the corrosive nature of CoCr implant substrates immersed in different media were found. Results and discussion: Spectra from P2p3/2, O1s, Ca2p3/2, C1s and N1s were collected. Metallic substrates behaved differently when immersed in the same lubricant for different time intervals. The three lubricants reacted different with metallic surfaces. Larger calcium deposits occurred in supersaturated physiological solutions. Deposition of calcium phosphate was different on CoCr and TiAlValloys depending on the lubricant and the immersion period. Specimens immersed into synovial fluid gave thinner oxide layers and lower calcium phosphate deposits. For all specimens, water immersion resulted in thicker oxide layer. Conclusion: Passivation of the metal surface is fundamental to corrosion resistance where a metallic oxide (like chromium oxide) barrier protects the underlying metal from further corrosion. The amount and purity of the oxide layer on immersed specimens depends on the density and thickness of the overlying deposits of calcium phosphate (Figure 1), proteins and other adsorbed molecules, as well the contaminations. The ration of Cr2O3 to Cr was calculated for CrCo alloy and was related to the thickness and/or concentration of the oxide in different lubricants. The lower calcium phosphate deposit in synovial fluid might be due to the present of components such as GAG and associated proteins, which stop the calcium deposition due to the circulation of the fluid in the effective joint space. ToF-SIMS measurements showed that the resulting corrosion products depend upon the nature of the environment. The thickness of the calcium phosphate deposits was different for different metal substrate.

  • 35.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological characterisation of carbon reinforced UHMWPE composites in orthopaedic applications2015In: ANM Abstracts, ANM2015 , 2015, p. 166-167, article id 571Conference paper (Refereed)
  • 36.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    UHMWPE composites for bearing applications; manufacturing and tribological characterisation2016Conference paper (Refereed)
  • 37.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Variables affecting stress development and resin conversion in light-cured dental composites2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The general aim of this dissertation was to identify and investigate factors that can be used to minimize stress development in light cured dental resins without compromising the conversion level of the polymer. Modulus of elasticity, polymerization contraction strain, degree of conversion and shrinkage of light-cure dental composites were determined after curing with three different light power densities where total irradiated energy (J/cm2) kept constant. FT-Raman spectroscopy was employed to determine the degree of conversion. The cure kinetic of light cured resins was studied by use of photocalorimetry (photo-DSC). Dynamic mechanical thermal (DMTA) analysis was used to investigate how different light curing methods affected glass transition and tangent delta of light curable dental resins when the temperature changed from 0 to 200°C. Optical properties of dental composites were studied. Three different filler types, two different surface treatments and eight different filler fractions per filler type and surface treatment were investigated. Light transmission was measured for the different composite compositions at sample thicknesses of 1 to 5 mm by use of a universal power meter. As long as the total light energy remained the same, the modulus of elasticity remained constant for each composite, even though the power density differed. Composite thickness, irradiance time, composition of the light cure composite and irradiation value had significant impact on degree of conversion. The irradiance value did not significantly affect on the transition temperature value. Initiator, co-initiators and light irradiance value had all significant impact on cure behavior. Different filler types and filler surface treatments had significant effects on light absorption. In general, light absorption increased linearly with filler fraction and sample thickness of the cured composites. Conclusion: Low rather than high light irradiance values decrease stress levels in composites, and comparable conversion levels are reached as long as the total light energy value remains the same for low versus high irradiance. By increasing the composite thickness above 2 mm but not exceeding 6 mm, energy levels exceeding 30 J are needed to achieve acceptable levels of degree of conversion. Different irradiance values do not affect the final Tg of tested composites as long as the total light energy remains the same. By using appropriate photo initiator/co-initiator combination and soft-start curing it is possible to achieve slow curing and high DC within a 40 s. As expected, different filler particle properties have significant effects on light absorption during curing making it important to consider these differences when one tries to develop a general light curing strategy for light curable dental resins.

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  • 38.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Enqvist, Evelina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grácio, José
    Nanotechnology Research Division, University of Aveiro.
    Gonçalves, Gil
    Nanotechnology Research Division, University of Aveiro.
    Marques, Paula
    Nanotechnology Research Division, University of Aveiro.
    Biotribolological behaviour of reinforced UHMWPE2010Conference paper (Other academic)
    Abstract [en]

    Carbon nanoforms exhibit exceptional physical and chemical properties due to their nano-scale dimensions. They also have very high aspect ratio which makes them an excellent reinforcement material for polymer composites. Hydroxyapatite (HA) is the prime constituent of bone generation because of its ability to bond chemically with living bone tissues and positively affect the osteoblasts; this is due to its similar chemical composition and crystal structure to apatite in the human skeletal system. Ultra high molecular weight polyethylene (UHMWPE) is already used as implant material in high stress bearing areas such as hip and knee prosthesis. Wear debris of ultra high molecular weight polyethylene cause osteolysis which is a major reason of long-term failure of total hip replacements. In this study carbon nanoforms together with hydroxyapatite (HA) nanoparticles were used as reinforcement in UHMWPE matrix in order to produce high strength and wear resistant biocomposite with better bioactivity character. Solvent casting and melt blending methods were used during the preparation of this bio-nano composite. The manufacturing process was studied using different characterization methods such as diferencial scanning calorimetry (DSC), scanning electron microscopy (SEM) and Raman-spectroscopy. The tribological behaviour of the manufactured bio-nano composite was studied using pin-on-plate method. Wear and friction of the produced novel composite were studied in different biological lubrications. Different lubrication affected the friction rate and wear, though the results were not statistically different. The reinforced UHMWPE showed superior tribology behaviour in comparison to pure UHMWPE (p>0.05).

  • 39.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Enqvist, Evelina
    Larsson, Roland
    Gracio, José
    University of Aveiro.
    Kumar, Sunil
    University of South Australia.
    Friction, wear and surface characterization of metal-on-metal implant in protein rich lubrications2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    Although various surface and interface characterization methods have been applied to study the physical wear, corrosion and implant surface interactions with biological environments, presently - in metal on metal (MOM) hip implant- the local and systematic effects of interaction between metal surfaces and protein rich lubrication in body are poorly understood. Materials and Methods: Cobalt-chromium-molybdenium (CoCrMo) alloys have been used in MOM implants extensively. In the present study the samples were immersed in four different biological lubricants (Human serum, synovial fluid, MEM and distill water) for 10 min, 1 hr, and 5 days of immersion and then studied by X-ray Photoelectron Spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). XPS determined the chemistry of elements located whit in the top few nanometers of materials. Friction and wear behavior of CoCrMo substrate in different biological lubricatin were also studied. Results and discussion: Spectra from P2p3/2, O1s, Ca2p3/2, C1s and N1s were collected. Metallic substrates behaved differently when immersed in the same lubricant for different time intervals. The four lubricants reacted differently with metallic surfaces. Larger calcium deposits occurred in supersaturated physiological solutions. Deposition of calcium phosphate was different on CoCrMo alloys depending on the lubricant and the immersion period. Specimens immersed in synovial fluid gave thinner oxide layers and lower calcium phosphate deposits. For all specimens, water immersion resulted in thicker oxide layer. Synovial fluid gave lowest coefficient of friction when distill water gave the highest value. Generally wear was higher for disc in comparison to the pin (in the pin on plate test).

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  • 40.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fernberg, Patrik
    Evaluation of manufacturing schemes for carbon nanotube doped epoxy resins and composites2005Report (Other academic)
  • 41.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gomez, Alvaro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lindström, Kristoffer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ultra high molecular weight polyethylene based nano-composite in medical application: thermal, mechanical and tribological properties before and after aging and gama irradiation2016In: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016, Frontiers Media S.A., 2016Conference paper (Refereed)
    Abstract [en]

    Introduction: Osteolysis due the wear particles release at implant surfaces is one of the most important reasons for the failure of the polymer on metal implant devices in hip and knee prosthesis. Today the polymer on Metal/cermic composition is one of the most comon desgin used in clinic.

    Materials and Methods: In most of the polymer on metal (soft on hard) hip implant devices, Ultra High Molecular Weight Polyethylene (UHMWPE) is used as acetabluar liner. In the presented study, Surface functionalized Multi walled carbon nanotubes (MWCNTs), graphene oxide (GO) and nanodiamond (ND) were used to develop UHMWPE based nanocomposites. Effects of the reinforcement weight% were investigated (lowest of 0.1 wt% and highest of 2 wt% of different reinforcement were tested). Mechanical, thermal and tribological properties of different wt% of UHMWPE composites were characterised for all composites as manufactured, aged and gamma irradiated. The mentioned nanocomposites were compared to virgin UHMWPE as reference material. combination of ball milling and ultrasonication with controlled parameters were used to manufacture the nanocomposites.

    Results: In thermal properties, the degree of the crystalinity was not significantly affected, whereas the oxidation degradation was delayed significantly for as developed 3 different nanocomposites. The youngs’ modulus were increased by 10-15% for all nanocomposites and fracture stress reduced (from 0wt% to 0.5wt%) by 35%. Wear resistance was increased for UHMWPE/MWCNT nanocomposites at 0.5wt% for up to 30% and thereafter reduced when higher wt% of MWCNTs were added to the polymeric matrix. However, the UHMWPE/GO nanocompostes showed the maximum wear reduction at 2wt% of the reinforcement. For UHMWPE/ND nanocomposites, the wear mechanism showed the most improvement at 0.5 and 0.7 wt% of the reinforcement. The wear particles from wear tests for all different nano composites were collected and analysed via scanning electron microscopy (SEM). No significant differences in particle size distribution and shape among nanocomposites in comparison to the virgin UHMWPE were observed.   Gamma irradiation at 90 KGy affected the thermal, mechanical and tribological properties positively (in comparson to the virging UHMWPE). Whereas the aging reduced the wear resitance by 20% and tensile properties decreased by 30%. In general aging affected the performance of the nanocomposites negatively.

    Conclusion: Ball milling was successful method for preparation of nanocomposites. The addition of carbone based nano particles showed positive effect of thermal, mechanical and tribological properties of the developed nanocomposites in comparison to virgin UHMWPE.

  • 42.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Griesser, H.
    Ian Wark Research Institute, University of South Australia.
    Biotribocorrosion: time dependence of the surface chemistry of metal-on-metal implants in biological environment2009In: 8th World Biomaterials Congress 2008: Amsterdam, the Netherlands, 28 May - 1 June 2008 ; [WBC 2008], Red Hook, NY: Curran Associates, Inc., 2009, Vol. 4, p. 1978-Conference paper (Refereed)
  • 43.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Jain, Ayush
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    High performance hybrid PPS polymer composites for tribological applications2017Conference paper (Refereed)
  • 44.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Höglund, Erik
    Biotribology: surface chemistry characterization of metal-on-metal implants in rich environment2008In: Proceedings of NORDTRIB 2008, 13th Nordic Symposium on Tribology: Scandic Rosendahl Hotel, Tampere, Finland, June 10 - 13, 2008 / [ed] Jaakko Kleemola; Arto Lehtovaara, Tampere: Tampere University of Technology, 2008Conference paper (Refereed)
    Abstract [en]

    Introduction: Osteolysis induced by wear particles in metal-on-polyethylene hip implants has been the key motivation to look for alternative bearings and in fact emergence and development of new metal-on-metal (MOM) implant materials for joint replacement. However, while the volume of wear particles produced in metal-on-metal articulations is lower the number of particles produced is higher per volume of wear, due to the reduced size of wear particles. Although various surface and interface characterization methods have been applied to study the physical wear, corrosion and implant surface interactions with biological environments, presently the local and systematic effects of metal debris are poorly understood. Materials and Methods: Cobalt-chromium-molybdenium (CoCr) alloys have been used in MOM implants extensively. Metallic samples were cut and mirror polished. In the present study The samples were immersed in four different biological lubricants (Human serum, synovial fluid, MEM and Milli-Q water) for 10 min, 1 hr, and 5 days of immersion and then studied by X-ray Photoelectron Spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). XPS determined the chemistry of elements located whitin the top few nanometers of materials. Significant differences in the absorbed layers and differences in the corrosive nature of Ti and CoCr implant substrates and wear particles were found. Results and discussion: Spectra from P 2p3/2, O1s, Ca2p3/2, C1s and N1s were collected. Metallic substrates behaved differently when immersed in the same lubricant. The four lubricants reacted different with metallic surfaces. Larger calcium deposits occurred in supersaturated physiological solutions. Deposition of calcium phosphate was different on CoCr alloys depending on the lubricant and the immersion period. Specimens immersed into synovial fluid gave thinner oxide layers and lower calcium phosphate deposits. For all specimens, water immersion resulted in thicker oxide layer. For many reactive metals, dissolution of ions from the metal surface takes place along with thickening of the metal oxide during passivation, or surface corrosion.Conclusion: Glycoaminoglycans (GAG) and related proteins may hinder calcium phosphate deposition on samples immersed in synovial fluid. ToF-SIMS measurements showed that the resulting corrosion products depend upon the nature of the environment. The thickness of the calcium phosphate deposits was different for different metal substrate.

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  • 45.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Lindberg, A.
    Umeå universitet.
    van Dijken, J.W.V.
    Umeå universitet.
    The effect of flow-composite on interfacial-chemistry and morphology of dentin/bonding2008Conference paper (Other academic)
    Abstract [en]

    Objectives: to study the interfacial bond of self-etching primer to coronal and root dentin with and without the use of flow composite. Methods: morphology, structural characteristics and interaction at the interfaces were studied with Raman micro-spectroscopy and SEM. Coronal (superficial) dentin and root (deep) dentin were prepared from eight non-carious extracted premolars. Immediately after extraction, teeth were carefully cleaned and stored in chlorhexidine digluconate solution prior to preparation. Smear-layer was generated by wet grinding with 600 grit silicon carbide polishing paper for 10 s. A self etching primer Xeno III (Dentsply) was applied according to manufacturer instruction. Half of the specimens were covered with a thin layer of Tetric flow (Ivoclar Vivadent) prior to curing. A 1mm slice was cut of the mesial and distal surface of the teeth with a low speed diamond saw to uncover the interfacial margins and hybrid layer. A modified Nakabayashi method, using HCl and HNO3 followed by NaOCl, was used to show the penetration depth of the monomers. SEM images from 750 to 6000 magnification were collected from dentin/bonding interfaces. Raman spectrums were collected at 1µm intervals across the dentin/bonding interface and provided chemical information. Degree of demineralization as function of depth was calculated. Results: No difference in degree of demineralization was seen between coronal and root dentin. It was slightly lower by using a thin layer of flow prior to curing. The thickness of the dentin/bonding hybrid layer was less for samples with flow and its morphology of hybrid layer and interfacial structure was significantly different. Conclusion: Flow composite had an undesirable affect on the physical-chemistry structure of dentin bonding with a self etching primer. HL and bonding tags morphology was significantly different by using flow composite. No significant different were observed between root and coronal dentin interfaces.

  • 46.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marques, Paula
    University of Aveiro.
    Gracio, Jose
    University of Aveiro.
    Enqvist, Evelina
    Gonçalves, Gil
    University of Aveiro.
    Novel bio nano-composite for biomedical application2010In: 14th Nordic Symposium on Tribology: NORDTRIB 2010 : Storforsen, Sweden, June 8-11, 2010, Luleå: Luleå tekniska universitet, 2010Conference paper (Refereed)
    Abstract [en]

    Carbon nanoforms exhibit exceptional physical and chemical properties due to their nano-scale dimensions. They also have very high aspect ratio which makes them an excellent reinforcement material for polymer composites. Hydroxyapatite (HA) is the prime constituent of bone generation because of its ability to bond chemically with living bone tissues and positively affect the osteoblasts; this is due to its similar chemical composition and crystal structure to apatite in the human skeletal system. Ultra high molecular weight polyethylene (UHMWPE) is already used as implant material in high stress bearing areas such as hip and knee prosthesis. Wear debris of ultra high molecular weight polyethylene cause osteolysis which is a major reason of long-term failure of total hip replacements.In this study carbon nanoforms together with hydroxyapatite (HA) nanoparticles were used as reinforcement in UHMWPE matrix in order to produce high strength and wear resistant biocomposites with better bioactivity character. Solvent casting and melt blending methods was used during the preparation of this bio-nano composite. The phase compositions and the surface morphology of the nanocomposite material have been studied using X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), and micro-Raman spectroscopy. Nanoindentation technique was used to determine the elastic modulus and hardness of the nanocomposites with different weight% of HA and carbonnanoforms concentrations. The tribologic behaviour of this nano composite was studied using pin-on-plate method. Wear and friction of the produced nano-composites were studied in different biological lubrications.

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  • 47.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    McLaren, Heather
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Surface functionalisation of MWCNTs to Improve Behaviour of UHMWPE-Based Nanocomposites2015In: 7th UHMPWE International Meeting October 22-23, 2015 Philadelphia, PA, Implant Research Center , 2015, p. 74-74Conference paper (Refereed)
  • 48.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    McLaren, Heather
    Leeds University, UK.
    Neville, Anne
    Leeds University, UK.
    Bryant, Micheal
    Leeds University, UK.
    Tribological performance of PEEK and a PEEK composite in reciprocating sliding under various conditions2018Conference paper (Refereed)
  • 49.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Melk, Latifa
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Fracture toughness and thermal characterisation of GO based UHMWPE composites2018Conference paper (Other academic)
  • 50.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Nilsson, Greger
    SICOMP AB, Swedish Institute of Composites.
    Undersökning av rotstift av kompositmaterial2004Report (Other academic)
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