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  • 51.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Palmeira Belotti, Luca
    Effect of surface roughness and hygrothermal aging of multiscale carbon reinforced UHMWPE-composites2018Conference paper (Other academic)
  • 52.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ramanenka, Dmitrij
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Enqvist, Evelina
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mechanical and thermal characterisation of novel UHMWPE-nano composite: A copmarrative study against virgin UHMWPE2012Conference paper (Refereed)
  • 53.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sin, Jorge Rituerto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Bryant, Micheal
    University of Leeds, 2Institute of Functional Surfaces, School of Mechanical Engineering,, United Kingdom.
    Neville, Anne
    University of Leeds, 2Institute of Functional Surfaces, School of Mechanical Engineering,, United KingdomLeeds University, UK.
    Modelling the repassivation kinetics of CoCrMo alloys in simulated body fluids2016In: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016, Frontiers Media S.A., 2016Conference paper (Refereed)
    Abstract [en]

    CoCrMo alloys used for biomedical applications are often exposed to the combined effect of mechanical wear and electrochemical corrosion. Tribocorrosion tests have been performed in this work to investigate the repassivation kinetics of a HC CoCrMo alloy in four different solutions commonly used to simulate body fluids. The repassivation kinetics are analysed by fitting two different exponential equations. The comparison of the different equations reveals that that a second order exponential equation models the repassivation currents more closely than a first order exponential equation. A repassivation model based on a second order exponential equation is suggested. The repassivation currents are divided in two main phases, a ’coverage’ phase and a ’film thickening’ phase. At the initial stage, when part of the surface is exposed to the corrosive media, higher potentials lead to faster repassivation rates. By contrast, potential does not have a clear effect at the thickening phase, when the material is protected by the oxide film formed on top of the surface.Conclusions The repassivation kinetics of a CoCrMo alloy have been investigated.

  • 54.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Söderholm, Karl-Johan M.
    University of Florida.
    How filler properties, filler fraction, sample thickness and light source affect light attenuation in particulate filled resin composites2005In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 21, no 8, p. 721-730Article in journal (Refereed)
    Abstract [en]

    The way by which variables such as filler type, filler surface treatment and light source affect light attenuation in particulate filled resin composites was presented. Mixture of 50 wt% bisGMA and 50wt% TEGDMA consisting of a photo-initiatior and a co-initiator was prepared. Three different filler types, HBB, SBB, and KU, which were either silane surface treated or not, were added to that mixture in eight different volume percentage. It was observed that of the two light sources, more light was absorbed by the composite when the laser light was used. It was also observed that the HBB filler absorbed most light and the KU filler the least.

  • 55.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, K J
    University of Florida, Gainesville.
    Young's modulus and degree of conversion of different combination of light-cure dental resins2009In: The Open Dentistry Journal, E-ISSN 1874-2106, Vol. 3, p. 202-207Article in journal (Refereed)
    Abstract [en]

    Objectives: To evaluate Young's modulus and degree of conversion of several combinations of bisGMA,To evaluate Young's modulus and degree of conversion of several combinations of bisGMA, UEDMA, TEGDMA light-cure dental resin.Methods: Young's modulus and DC% were studied for 21 different resin combinations of bisGMA, TEGDMA and Young's modulus and DC% were studied for 21 different resin combinations of bisGMA, TEGDMA and UEDMA. Small universal testing machine and photo-calorimetry were used for the tests. The results were evaluated using ANOVA and Duncan's multiple range tests and regular t-test. Results: Young's modulus varied between 2.37±0.2 GPa (100% TEGDMA) and 4.15±0.2 GPa (100% bisGMA). By adding Young's modulus varied between 2.37±0.2 GPa (100% TEGDMA) and 4.15±0.2 GPa (100% bisGMA). By adding TEGDMA to bisGMA or UEDMA, the Young's modulus decreased significantly (p<0.05). Degree of conversion was significantly (p<0.05) higher when the wt% of TEGDMA was high in the mixtures than for highly concentrated bis-GMA (resin mixtures with TEGDMA in comparison to mixture with bisGMA had higher degree of conversion). DC% was significantly higher (p<0.05) for binary mixtures of UEDMA and TEGDMA, and significantly lower for 100 wt% bis-GMA´(p<0.05). The DC% values were between 53.1%±0.9% (100% bisGMA) and 85.6%±1% (80% UEDMA-20% TEGDMA). The concentration of bisGMA, in the monomer mixture, affected DC% and Young's modulus oppositely. Conclusions: The differences in the values for DC% were mostly justified by the differences in the molecular structures of The differences in the values for DC% were mostly justified by the differences in the molecular structures of the different monomers. It was also revealed that higher DC% does not always result in a higher Young's modulus, because molecular and network structural parameters play major roles in the final physical properties of the mixtures.

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  • 56.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan
    Florida University.
    Cure kinetic behavior of light-cure dental composites2003In: Journal of Dental Research, ISSN 0022-0345, E-ISSN 1544-0591, Journal of Dental Research. Meeting abstracts: , no Suppl.Article in journal (Other academic)
    Abstract [en]

    Objective: To investigate differences in cure kinetic behaviours of different photo and co-initiator systems used in dental light-cure composites. Method: A resin system (50 wt.% of bisGMA and 50 wt.% of TEGDMA) was mixed with either campherquinone (CQ) or 1-phenyl-1,2-propanedione (PPD) as photo-initiator. N,N-dimethyl-p-aminobenzoic acid ethylester (DABE), N,N-cyanoethylmethylaniline (CEMA), N,N-diethanol-p-toluidine (DEPT) and 2-dimethylaminoethyl methacrylate (DMAEMA) were used as co-initiators respectively. Complex cure behaviour of 24 experimental mixtures made from 2 photoinitiators, 4 co-initiators, 3 curing light/time was studied with differential Scanning Calorimetery (DSC). Six specimens of each composition were cured either with 800 mW/cm2 for 40 s, soft start curing for 60 s or LED for 40 s. The DSC results were analysed using ANOVA and Duncan's multiple range test and regular t-test. Result: Rate of polymerisation was significantly (p<0.05) higher when materials were cured with 800 mW/cm2 compare to soft start and LED curing methods when the final degree of conversion values did not differ significantly (p>0.05). Compared to campherquinone, the photo-initiator PPD reduced the maximal DC% and rate of the polymerisation significantly (p<0.05). PPD was not a suitable photo-initiator when cured with LED since the blue spectra emitting from the used LED lamp does not cover the optimal activation wavelength for PPD properly. The highest DC% measured at the end of curing was for CQ & DABE 74%±1 cured with 800 mw/cm2 for 40s and the lowest was for PPD&DMAEMA 22%±1.1 when material was cured with LED for 40s. Use of DEPT resulted in significant decreases in degree of conversion (p<0.05). Conclusion: It was concluded that intrinsic slow cure might be obtained with certain compositions of photo & co-initiators and curing methods without impairing the final extent of degree polymerzation.

  • 57.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan
    University of Florida.
    How light irradiance and curing time affect monomer conversion in light-cured resin composites2003In: European Journal of Oral Sciences, ISSN 0909-8836, E-ISSN 1600-0722, Vol. 111, no 6, p. 536-542Article in journal (Refereed)
    Abstract [en]

    We tested the hypothesis that the degree of conversion of a light-cured dental composite relates to the calculated (s × mW cm-2 = mJ cm-2) rather than to the irradiance value (mW cm-2) of the light source. Two light-curable composite resins were cured with three different light irradiance values over different curing times. The specimens tested were 2, 4 or 6 mm thick, and the degree of conversion values were measured with Raman spectroscopy on the top and the bottom surfaces of the specimens. The highest conversion value of one of the materials was just below 60%, while the maximal conversion value of the other material was just below 65%. That difference in conversion values could be related to differences in monomer systems used in the two composites. By considering light energy per square centimeter (J cm-2) rather than light irradiance (mW cm-2), we found that equivalent energy values gave similar conversion values for a certain sample thickness. From these findings, we conclude that our experimental results support our hypothesis.

  • 58.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan
    Florida University.
    Berglund, Lars
    Kungliga tekniska högskolan, KTH.
    Effect of light intensities variations on bulk curing of dental composites2002In: Journal of Dental Research, ISSN 0022-0345, E-ISSN 1544-0591, Vol. 81, no Suppl. 1Article in journal (Refereed)
    Abstract [en]

    The light intensity used during curing of light curable dental composites is believed to affect the residual stress level. In this study we tested the hypothesis that low light intensity and long but clinically acceptable light curing time, can produce composites with physical/clinical properties (e.g. volumetric shrinkage, linear contraction stress, degree of conversion (DC%) and Young's modulus) comparable to those of high light intensity cured composites. Methods: Two dental composites, Z100 and Z250, were investigated. Specimens were cured with light intensities of 200, 450 and 800 mW/cm2 for 140, 60 and 35 s from a distance of 7 mm. Linear contraction strains were measured with strain-gages attached to stainless steel rings serving as molds (8 mm in diameter and 4 mm high). DC% was measured at the top and the bottom of samples as well through the bulk using FTIR. Volumetric polymerization shrinkage was determined using a water displacement method. Young's modulus was determined in tension on composite specimens with dimensions of 8 x 50 x 1 mm. Results: Polymerization stress level decreased significantly (p<0.05) when cured with 200 mW/cm2 rather than with 800 mW/cm2. Reduction in light intensity did not decrease the DC% values significantly, nevertheless the most dramatic differences existed between top and bottom surfaces (p<0.05) rather than among curing groups. Measured modulus and volumetric shrinkage values were no significantly different (p>0.05) between different light intensity groups. Conclusion: Low light intensity decreased the residual stress and DC% values (through the depth of cure) significantly (p<0.05), but did not significantly affect the Young's modulus and the volumetric shrinkage values. The lower residual stress values, reflected by lower strain levels in the metal rings used during measurement, suggest that more stress relaxation occurs in the low light intensity group during cure. Our results support the proposed hypothesis

  • 59.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan
    Florida University.
    Berglund, Lars
    Kungliga tekniska högskolan, KTH.
    Effect of light-intensity variations on bulk curing of dental composites2002In: Journal of Dental Research, ISSN 0022-0345, E-ISSN 1544-0591, Vol. 81, no Suppl 1, p. A-407-Article in journal (Other academic)
  • 60.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan
    Florida University.
    Berglund, Lars
    How light-intensity and cure-time affect monomer conversion in light-cured composites2002In: Journal of Dental Research, ISSN 0022-0345, E-ISSN 1544-0591, Vol. 81, no Suppl 1Article in journal (Refereed)
  • 61.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan
    Florida University.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Quantitative measurements of dental light beam (halogen versus LED)2005Conference paper (Other academic)
  • 62.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan M.
    Department of Dental Biomaterials, University of Florida.
    Dynamic mechanical thermal analysis of two light-cured dental composites2005In: Dental Materials, ISSN 0109-5641, E-ISSN 1879-0097, Vol. 21, no 10, p. 977-983Article in journal (Refereed)
    Abstract [en]

    ObjectivesClinical observations suggest that some composite resins are more often linked to post-operative sensitivity than others. These differences may relate to differences in modulus of elasticity and polymerization rates among materials. The aim of this study was to identify viscoelastic behavior of two light curable composites and determine whether significant differences in viscoelastic behavior exist between the two materials when light cured at each of three different irradiance values.MethodsTwo composites (Z100 and Z250 by 3M ESPE) were evaluated. Six specimens per composite and irradiance value (250, 500 and 850 mW/cm2) were made. The curing times were chosen to produce a fixed energy value of 30 J/cm2 independent of irradiation value. Dynamic mechanical thermal analysis (DMTA) was performed in single cantilever clamped mode.ResultsThere were significant differences in transition temperatures between the two materials and the three frequencies at their glass transition temperatures, while significant differences did not exist at the lower transitions. The glass transition of Z250 was lower and narrower than that of Z100. Z250 exhibited lower storage modulus values. The irradiance values did not affect any of the transition temperatures significantly.SignificanceThe lower and more distinct Tg of Z250 suggests that Z250 cures more efficiently than Z100. The lower storage modulus of Z250 suggests that Z250 develops less stress in the tooth than Z100 during curing if shrinkage is the same for the two materials. The findings suggest that the material chosen, rather than irradiance, determines the stress level developed during light curing.

  • 63.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan M.
    How degree of conversion and E-modulus of light-cure dental-resins interact2006In: 84th General Session and Exhibition of the IADR and 1st Meeting of the Pan-Asian-Pacific Federation: Brisbane Convention and Exhibition Centre, Brisbane, Queensland (Australia), 28 Jun-1 Jul 2006, IADR , 2006Conference paper (Other academic)
    Abstract [en]

    Objectives: To investigate how E-modulus, degree of conversion (DC%) and rate of polymerization of the most used monomer resins in dental light-cure composites interact. Methods: Young's modulus and DC% were studied for 21 different resin combinations of three commonly used dental monomers, bis-GMA, TEGDMA and UEDMA (combinations of 0, 20, 40, 60 and 100 wt% as it is illustrated in the figure). For each resin combination 6 specimens were tested. Small Instron and differential scanning calorimetry (photo-calorimetry) were used as testing machines. The results were tested using ANOVA and Duncan's multiple range tests and regular t-test. Results: Rate of polymerization was significantly (p<0.05) higher when the wt% of the TEGDMA was high in the mixtures compare to highly concentrated bis-GMA. DC% was significantly high (p<0.05) for binary mixture of UEDMA and TEGDMA. The DC% was significantly lower for 100 wt% bis-GMA (p<0.05). The calculated values for DC% were between 53.1%± 0.9% and 85.6%±1%. Young's modulus values varied between 2.37± 0.15 GPa and 4.15± 0.2 GPa. It was noticeable that by adding TEGDMA to bisGMA or UEDMA, the Young's modulus decreased significantly (p<0.05). There were no significant (p>0.05) differences between Young's modulus values when the monomer mixtures contained bis-GMA, TEGDMA and UEDMA at different concentration levels. The higher the concentration of bisGMA in the monomer mixture, the lower was the degree of conversion. However, Young's modulus increased at higher concentration of bis-GMA. Conclusions: The differences in the values for degree of conversion were mostly justified by the differences in the molecular structures of the different monomers. It was also revealed that higher degree of conversion does not always result in a higher Young's modulus, because molecular and network structural parameters play major roles in the final mechanical/physical properties of the mixtures.

  • 64.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Söderholm, Karl-Johan M.
    Department of Dental Biomaterials, University of Florida.
    Influence of light-curing procedures and photo-initiator/co-initiator composition on the degree of conversion of light-curing resins2005In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 16, no 1, p. 47-52Article in journal (Refereed)
    Abstract [en]

    Objective: The hypothesis that the degree and rate of conversion can be modified favourably by using different light-curing procedures and different photo initiator/co-initiator combinations was tested.Method: A photo-initiator (0.02 mM/g resin); either camphorquinone (CQ) or 1-phenyl-1,2-propanedione (PPD), was mixed with bisGMA:TEGDMA (50:50 by weight). In addition, a co-initiator (0.04 mM/g resin); either N,N-dimethyl-p-aminobenzoic acid ethylester (DABE), N,N-cyanoethylmethylaniline (CEMA), or 2-dimethylaminoethyl methacrylate (DMAEMA), was added. These six combinations were subjected to three curing conditions (standard curing, soft-start curing or LED curing). The conversion levels (DC) were determined with differential scanning calorimetry (DSC). The DSC results were analysed using a general linear model (GLM) and Duncans multiple range test and regular t-test.Results: The fastest conversion initially was obtained by standard curing, followed by LED curing and soft-start curing. After 40 s of curing, conventional curing and soft-start curing produced a higher DC than LED curing. However, strong interactions occurred between the different variables (curing method, initiator and co-initiator). Initially, CQ was more efficient than PPD, but after 40 s, this difference was insignificant.Conclusion: By using soft-start curing and an appropriate photo initiator/co-initiator combination it is possible to achieve slow curing and a high DC at within a curing time of 40 s.

  • 65.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Applied Physics and Mechanical Engineering.
    Söderholm, Karl-Johan M.
    Department of Dental Biomaterials, College of Dentistry, Florida University, FL, USA.
    Berglund, Lars A.
    Luleå University of Technology, Department of Applied Physics and Mechanical Engineering.
    Effect of light power density variations on bulk curing properties of dental composites2003In: Journal of Dentistry, ISSN 0300-5712, E-ISSN 1879-176X, Vol. 31, no 3, p. 189-196Article in journal (Refereed)
    Abstract [en]

    Objective. The hypothesis that low light intensity and long but sufficient curing time can produce composites with volumetric shrinkage, degree of conversion (DC%) and Young's modulus (E-modulus) comparable to those of high light intensity cured composite was tested, when the contraction strain and heat generation were lower with low light intensity curing. Methods. Dental composites (Z100 and Z250, 3M ESPE) were investigated. Specimens were cured with light intensities of 200, 450 and 800 mW/cm2 for 140, 60 and 35 s from a distance of 7 mm. Strain-gages were used for contraction strain measurements. DC% was measured at the top and the bottom of 4 mm thick samples using FT-Raman spectroscopy. Volumetric polymerization shrinkage was determined using a water displacement method. E-modulus was determined in tension on composite specimens. Results. The results were analyzed using ANOVA and Duncan's multiple range tests and regular t-test. Polymerization stress level decreased significantly (p<0.05) when cured with 200 mW/cm2 rather than with 800 mW/cm2. Temperature rises were significantly different (p<0.05) for different composites and light intensity values. Reduction in light intensity did not decrease the DC% values significantly at the top surfaces. The most dramatic differences existed between top and bottom surfaces (p<0.05) rather than among curing groups. Measured E-modulus and volumetric shrinkage values were not significantly different (p>0.05) between different light intensity groups. Conclusion. DC%, E-modulus and the volumetric shrinkage values in cured composites were not affected by low light intensity, however, the contraction strain and polymerization's exotherm were decreased. Thus our results support the proposed hypothesis.

  • 66.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tavassoli, Sara
    Department of Carilogy and Preventive Dentistry, Tehran.
    Mehran, Majid
    Department of Carilogy and Preventive Dentistry, Tehran.
    Shear bond strength of sealant to primary and permanent enamel2010Conference paper (Refereed)
    Abstract [en]

    Objectives: The purpose of this study was to compare the effect of phosphoric acid, one-bottle adhesive and self-etching adhesive on shear bond strength (SBS) of light-curing sealant to ungrounded primary and permanent enamel.Methods: In this in vitro study 30 primary molars and 30 permanent premolars were cleaned and divided to 6 groups (n=10). The following materials used on flattest, peripheral surface (mesial or distal) of permanent (groups 1,3,5) and primary (groups 2,4,6) teeth. Group 1&2 (control): acid etching + light-Curing sealant (Concise 3M-ESPE). Group 3&4 (SB): acid etching +2 layer bonding agent (Single Bond 3M-ESPE) + sealant. Group 5&6 (PLP): self etching adhesive (Prompt L-Pop 3M-ESPE) +sealant. The teeth were thermocycled 500 cycles between 5„a and 55„a with a dwell time of 30s. For shear bond strength testing, the load was applied vertically from the Zwick universal testing machine with load cell 10KN to the base of the mold at a cross-head speed of 5 mm/min. Then two way variance analysis (Between-Subject Effect) and multiple comparisons (Post Hoc Test-LSD) were performed. Failure mode was determined in a stereomicroscope at x20. Result: There was no significant difference in SBS between control (1&2), and PLP (5&6) groups, neither between SB (3&4) and PLP (5&6) groups (P>0.5). But there was significant difference in SBS between control and SB (3&4) groups (P=0.22). However, the SBS to primary enamel were lower than those to permanent enamel (P<0.5). Conclusion: The self-etching adhesive Prompt L-Pop, is as effective as conventional acid-etching in mediating a bond between a light-curing sealant and ungrounded human enamel. Applying Single Bond adhesive under fissure sealant would be beneficial for increasing the bond strength.

  • 67.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tavassolie, Sara
    Dental Faculty, Shahed University.
    Mehran, M
    Dental Faculty, Shahed University.
    Sealant microleakage study of two-component self-etch and one-component total-etch adhesives2009Conference paper (Other academic)
  • 68.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vadivel, Hari
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological behavior of carbon filled hybrid UHMWPE composites in water2017Conference paper (Refereed)
  • 69.
    Emami, Nazanin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Vadivel, Hari
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Golchin, Arash
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribological performance and thermal characteristics of UHMWPE multifunctional hybrid composites2017Conference paper (Refereed)
  • 70.
    Enqvist, Evelina
    et al.
    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.
    Nanodiamond reinforced ultra high molecular weight polyethylene for orthopaedic applications: Dry versus wet ball milling manufacturing method2014In: Tribology - Materials, Surfaces & Interfaces, ISSN 1751-5831, E-ISSN 1751-584X, Vol. 8, no 1, p. 42564-Article in journal (Refereed)
    Abstract [en]

    Nanodiamonds (NDs) were investigated as reinforcement for ultra high molecularweight polyethylene (UHMWPE). Dry and wet mixing with planetary ball milling was compared and analysed by scanning electron microscopy (SEM), differential scanning calorimerty (DSC), X-ray diffraction (XRD) and contact angle measurements. The composites were mixed from one to four hours to study the dispersion of the nanoparticles. It was concluded that wet mixing is more effective at distributing nanodiamonds in comparison to dry mixing. It could also be concluded that dry mixing increases the temperature by 20°C more than wet mixing which resulted in a more distinct welding process of the UHMWPE powder.

  • 71. Enqvist, Evelina
    et al.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grácio, José
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Gonçalves, Gil
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Marques, Paula
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Optimisation of manufacturing process of UHMWPE/nanoHA/MWCNTs2010Conference paper (Other academic)
    Abstract [en]

    Hip- and knee replacements are amongst the most common performed surgical operations performed today. Ultra high molecular weight polyethylene (UHMWPE) is frequently used for joint-replacements due to its excellent properties such as high impact strength, toughness and low friction. Wear debris produced when UHMWPE is sliding against a metal counter face is one of the major causes of total failure of implant as an effect of wear debris induced osteolysis. The nano scale dimensions of Carbon nanotubes (CNTs) give them unique physical and chemical properties. Their high aspect ratio makes them perfect as reinforcement in composite materials. Hydroxyapatite (HA) is similar in chemical composition and structure to apatite naturally occurring in human bone tissue and is thus positively affecting bone integration. However the brittleness and poor strength of HA limits the use of HA in load-bearing areas. This work focuses on the manufacturing of a new CNT and HA reinforced UHMWPE bio nanocomposite, using solvent casting and a melt-mixing method. Hot press was used to fabricate the final sample. The produced bio-nanocomposite was characterized by use of differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and micro-Raman spectroscopy. Nanoindentation was used to study the hardness and elastic modulus of samples containing CNTs and different HA loading.

  • 72.
    Enqvist, Evelina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Marques, Paula
    TEMA – NRD, Mechanical Engineering Department, University of Aveiro, 3810-193 Aveiro, Portugal. Aveiro Institute of Nanotechnology (AIN).
    Grásio, José
    TEMA – NRD, Mechanical Engineering Department, University of Aveiro, 3810-193 Aveiro, Portugal. Aveiro Institute of Nanotechnology (AIN).
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Nanoparticle reinforced UHMWPE for orthopaedic applications: Parameters affecting the manufacturing process2012Conference paper (Refereed)
  • 73.
    Enqvist, Evelina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ramanenka, Dmitrij
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Marques, Paula A.A.P.
    TEMA—NRD, Mechanical Engineering Department, Aveiro Institute of Nanotechnology (AIN), University of Aveiro, 3810-193 Aveiro, Portugal.
    Grácio, José
    TEMA—NRD, Mechanical Engineering Department, Aveiro Institute of Nanotechnology (AIN), University of Aveiro, 3810-193 Aveiro, Portugal.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The effect of ball milling time and rotational speed on ultra high molecular weight polyethylene reinforced with multiwalled carbon nanotubes2016In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 37, no 4, p. 1128-1136Article in journal (Refereed)
    Abstract [en]

    Ultra high molecular weight polyethylene (UHMWPE) composites reinforced with multiwalled carbon nanotubes (MWCNT) were produced using planetary ball milling. The aim was to develop a more wear resistant composite with increased mechanical properties to be used in stress bearing joints. The manufacturing technique, using ball-milling to incorporate MWCNT into UHMWPE matrix was investigated. The effect of manufacturing parameters such as effect of ball milling time and rotational speed on final composite was analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), particle size distribution and contact angle measurements. Ball milling as mixing technique for UHMWPE based composites is not a new approach but yet, the effect of time, rotational speed, loading of milling jar and type of ball mill has not been reported properly for UHMWPE. 0.5 and 1 wt% UHMWPE/MWCNTs were manufactured at different rotational speed and mixing time. The results indicate that rotational speed rather than mixing time is important for dispersing MWCNTs

  • 74.
    Gangwani, Prashant
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Laboratory for Tribology and Interface Nanotechnology, University of Ljubljana, Ljubljana, 1000, Slovenia.
    Kalin, Mitjan
    Laboratory for Tribology and Interface Nanotechnology, University of Ljubljana, Ljubljana, 1000, Slovenia.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Does a Compatibilizer Enhance the Properties of Carbon Fiber-Reinforced Composites?2023In: Polymers, E-ISSN 2073-4360, Vol. 15, no 23, article id 4608Article in journal (Refereed)
    Abstract [en]

    We have evaluated the effectiveness of compatibilizers in blends and composites produced using a solvent manufacturing process. The compatibilizers were two different types of polyethylene (linear low-density and high-density) grafted with maleic anhydride (MAH) and a highly functionalized, epoxy-based compatibilizer with the tradename Joncryl. The selected material combinations were an ultra-high-molecular-weight polyethylene (UHMWPE) with MAH-based materials as compatibilizers and a polyphenylene sulfide plus polytetrafluoroethylene (PPS-PTFE) polymer blend with an epoxy-based compatibilizer. The findings revealed that while the compatibilizers consistently enhanced the properties, such as the impact strength and hardness of PPS-based compositions, their utility is constrained to less complex compositions, such as fibrous-reinforced PPS or PPS-PTFE polymer blends. For fibrous-reinforced PPS-PTFE composites, the improvement in performance does not justify the presence of compatibilizers. In contrast, for UHMWPE compositions, compatibilizers demonstrated negligible or even detrimental effects, particularly in reinforced UHMWPE. Overall, the epoxy-based compatibilizer Joncryl stands out as the only effective option for enhancing mechanical performance. Thermal and chemical characterization indicated that the compatibilizers function as chain extenders and enhance the fiber–matrix interface in PPS-based compositions, while they remain inactive in UHMWPE-based compositions. Ultimately, the incompatibility of the compatibilizers with certain aspects of the manufacturing method and the inconsistent integration with the polymer are the main reasons for their ineffectiveness in UHMWPE compositions.

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  • 75.
    Golchin, Arash
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Villain, Alexis
    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 Nanodiamond Reinforced UHMWPE in Water-Lubricated Contacts2017In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 110, p. 195-200Article in journal (Refereed)
    Abstract [en]

    In this study, the tribological behaviour of nanodiamond reinforced UHMWPE composites was investigated in water-lubricated sliding contacts. A significant reduction of 72% in wear and 24% in friction of UHMWPE was observed with incorporation of 1 wt% nanodiamond in the polymer matrix. Various bulk and surface characterization techniques were utilised to reveal the main mechanisms involved in the friction and wear response of the polymeric materials. The improved tribological behaviour of UHMWPE upon incorporation of various loadings of nanodiamond in the polymer matrix was mainly attributed to the boundary lubricating action of nanodiamonds and the polishing effect of the nanodiamond reinforced UHMWPE composites on the counter surfaces in water-lubricated sliding contacts.

  • 76.
    Golchin, Arash
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Wikner, Alfred
    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.
    An Investigation into Tribological Behaviour of Multi-Walled Carbon Nanotube/Graphene Oxide Reinforced UHMWPE in Water Lubricated Contacts2016In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 95, p. 156-161Article in journal (Refereed)
    Abstract [en]

    In this study, the influence of incorporation of carbon based nano fillers, namely multi-walled carbon nanotubes and graphene oxide on the tribological behaviour of ultra-high molecular weight polyethylene was investigated in water lubricated sliding contacts. Further investigations were carried out to study the influence of γ-irradiation and hygrothermal aging on the friction and wear response of the polymeric materials. It was found that regardless of the treatment, GO/MWNT reinforced composites consistently exhibited a lower friction and higher wear resistance in comparison to the unfilled UHMWPE. This was mainly attributed to the lubricating action of the carbonaceous nano fillers in water lubricated sliding contacts.

  • 77.
    Goncalves, Gil
    et al.
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Marques, Paula
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Barros-Timmons, Ana
    CICECO, Department of Chemistry, University of Aveiro.
    Bdkin, Igor
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Singh, Manoj
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gracio, Jose
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Graphene oxide modified with PMMA via ATRP as a reinforcement filler2010In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 40, no 44, p. 9927-9934Article in journal (Refereed)
    Abstract [en]

    Graphene is a two-dimensional new allotrope of carbon, which is stimulating great curiosity due to its superior mechanical, electrical, thermal and optical properties. Particularly attractive is the availability of bulk quantities of graphene (G) which can be easily processed by chemical exfoliation, yielding graphene oxide (GO). The resultant oxygenated graphene sheets covered with hydroxyl, epoxy and carboxyl groups offer tremendous opportunities for further functionalization opening plenty of opportunities for the preparation of advanced composite materials. In this work poly(methyl methacrylate) (PMMA) chains have been grafted from the GO surface via atom transfer radical polymerization (ATRP), yielding a nanocomposite which was soluble in chloroform. The surface of the PMMA grafted GO (GPMMA) was characterized by AFM, HRTEM, Raman, FTIR and contact angle. The interest of these novel nanocomposites lies in their potential to be homogenously dispersed in polymeric dense matrices and to promote good interfacial adhesion, of particular relevance in stress transfer to the fillers. PMMA composite films were prepared using different percentages of GPMMA and pristine GO. Mechanical analysis of the resulting films showed that loadings as low as 1% (w/w) of GPMMA are effective reinforcing agents, yielding tougher films than pure PMMA films and even than composite films of PMMA prepared with GO. In fact, addition of 1% (w/w) of GPMMA fillers led to a significant improvement of the elongation at break, yielding a much more ductile and therefore tougher material. Thermal analysis showed an increase of the thermal stability properties of these films providing evidence that strong interfacial interactions between PMMA and GPMMA are achieved. In addition, AFM analysis, in friction force mode, is demonstrated to be an effective tool to analyse the surface filler distribution on polymer matrices

  • 78.
    Gonçalves, Gil
    et al.
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro, University of Aveiro, Nanotechnology Research Division, University of Aveiro.
    Vila, Mercedes
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Bdikin, Igor
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    de Andres, Alicia
    Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ferreira, Rute A.S.
    Physics Department and CICECO, University of Aveiro.
    Carlos, Luis D.
    Physics Department and CICECO, University of Aveiro.
    Gracio, Jose
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Marques, Paula A.P.A.
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation2014In: Scientific Reports, E-ISSN 2045-2322, Vol. 4, article id 6735Article in journal (Refereed)
    Abstract [en]

    Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform

  • 79.
    Gonçalves Nunes, Stephanie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Riga Technical University, Institute of Mechanics and Mechanical Engineering, Latvia; Federal University of Rio Grande do Sul, Materials Engineering Department, Brazil.
    Saseendran, Sibin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Research Institutes of Sweden, Department of Polymer Materials and Composites, Sweden.
    Fernberg, Patrik
    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.
    Esposito, Antonella
    Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, France.
    Campos Amico, Sandro
    Federal University of Rio Grande do Sul, Materials Engineering Department, Brazil.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Riga Technical University, Institute of Mechanics and Mechanical Engineering, Latvia.
    Shift factor dependence on physical aging and temperature for viscoelastic response of polymers2022In: 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. 431-438Conference paper (Other academic)
    Abstract [en]

    As polymeric resins are used as matrix in reinforced composites, understanding of their viscoelastic-viscoplastic response is critical for long-term performance design. However, during service life, thermosets are not in a thermodynamic equilibrium state, resulting in physical aging, which affects failure and viscoelastic (VE) properties, becoming a concern for industries. In this paper, an alternative methodology for testing and parameter determination for aging polymer, at different temperatures (TA) and times (tA), is proposed. The experimental data analysis was performed using a Schapery&apos;s type thermo-aging-rheologically simple VE model with constant coefficients in Prony series and the effect of temperature and aging included by two shift factors (aT, aA). Results showed that the shift factor can be presented as the product of shifts aT and aA. Furthermore, for short tA the change rate of the aA with tA does not depend on TA, whereas for long tA at high TA the rate increases.

  • 80.
    Gonçalves Nunes, Stephanie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Riga Technical University, Institute of Mechanics and Mechanical Engineering, Latvia.
    Swar, Roshan
    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.
    Varna, Janis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Riga Technical University, Institute of Mechanics and Mechanical Engineering, Latvia.
    The effect of short carbon fibers on viscoelastic behavior of UHMWPE2022In: 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. 314-321Conference paper (Other academic)
    Abstract [en]

    At service temperatures, ultra-high molecular weight polyethylene (UHMWPE) is a highly viscoelastic (VE) material due to its low glass transition temperature (≈-113 °C). Since the mechanical response changes over time, the ability to predict and improve its performance over lifetime is an engineering concern. Adding short carbon fibers (SCF) as reinforcement (10 wt%) is expected to improve the material instant and long-term properties. VE relaxation functions for UHMWPE and composite at different temperatures (25-100 °C) are obtained from experimental data used to find parameters in a Schapery&apos;s type linear VE model. Then, relaxation functions of the SCF (randomly distributed) composite are predicted using the quasi-elastic approach. The results show that fibers affect positively the VE properties of UHMWPE and that the temperature- and time-dependent matrix behavior affects the stress transfer to fibers However, due to uncertainty regarding the input parameters, limiting the applicability of the chosen quasi-elastic approach, the quantitative agreement is not perfect.

  • 81.
    Henriques, Bruno
    et al.
    CESAM & Department of Chemistry, University of Aveiro.
    Gonçalves, Gil
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro, University of Aveiro, Nanotechnology Research Division, University of Aveiro.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Pereira, Eduarda
    CESAM & Department of Chemistry, University of Aveiro.
    Vila, Mercedes
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Marques, Paula A.P.A.
    TEMA-NRD, Mechanical Engineering Department, University of Aveiro.
    Optimized graphene oxide foam with enhanced performance and high selectivity for mercury removal from water2016In: Journal of Hazardous Materials, ISSN 0304-3894, E-ISSN 1873-3336, Vol. 301, p. 453-461Article in journal (Refereed)
    Abstract [en]

    This work explores the preparation of three-dimensional graphene oxide macroscopic structures, shaped by self-assembling single graphene oxide (3DGO) sheets with control of its surface chemistry by combining with nitrogen functional groups (3DGON), or with nitrogen and sulphur functional groups (3DGOSN), and their application in the removal of mercury (Hg(II)) from aqueous solutions. The chemical structure of the materials was assessed by using different characterization techniques: SEM, XPS and BET. Adsorption studies conducted in Hg(II) contaminated ultra-pure water reveal the enhanced ability of 3DGON for the adsorption of this metal, when compared to the other GO foams. A small dose of 3DGON (10 mg L−1) allows to remove up to 96% of Hg(II) after 24 h of contact time, leading to a residual concentration in solution close to the guideline value for drinking water (1 μg L−1). The ability of this material to adsorb Hg (II) was evaluated relatively to different experimental parameters such as pH, sorbent dose, time and effect on different competing metal ions. Real application was also evaluated by testing its performance in two different natural matrices, river and sea water, with very promising results.

  • 82.
    Homayoun, Mohammad Reza
    et al.
    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.
    Effect of hygrothermal aging on wear mechanism and friction behavior of PTFE composites2017Conference paper (Refereed)
  • 83.
    Homayoun, Mohammad-Reza
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Golchin, Arash
    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.
    Effect of Hygrothermal Ageing on Tribological Behaviour of PTFE-Based Composites2018In: Lubricants, E-ISSN 2075-4442, Vol. 6, no 4, article id 103Article in journal (Refereed)
    Abstract [en]

    The present study investigates the influence of hygrothermal ageing on the tribological behaviour of polytetrafluoroethylene (PTFE) polymer composites. Three PTFE composites along with unfilled PTFE were tested in sliding contact against Inconel 625 (a Ni-based alloy) plates in both dry and water-lubricated conditions, utilising a unidirectional pin-on-disc tribometer. The tribo-tests were performed at a constant sliding speed of 0.13 m/s with a normal load of 84N providing an apparent contact pressure of 5 MPa. Hygrothermal conditioning was carried out at two different temperatures, and the water absorption evolution and kinetic parameters were estimated. Various characterisation methods were used to identify the wear mechanisms and influence of hygrothermal ageing on the degradation of the filler/matrix. The different tribological behaviour for different PTFE composites was observed within the ageing timeframe. The wear resistance of the fibre-filled samples was reduced compared to the non-aged ones over the ageing timeframe. However, the friction and wear resistance of the bronze-filled PTFE were enhanced by hygrothermal ageing.

  • 84.
    Hu, Xinming
    et al.
    School of Mechanical Engineering, University of Leeds.
    Sin, Jorge Rituerto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, Anne
    School of Mechanical Engineering.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tribocorrosion behaviour of Hf in Simulated Body Fluids2012Conference paper (Refereed)
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  • 85.
    Jain, Ayush
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Somberg, Julian
    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.
    Development and Characterisation of Multi-Scale Carbon Reinforced PPS Composites for Tribological Applications2019In: Lubricants, E-ISSN 2075-4442, Vol. 7, no 4, article id 34Article in journal (Refereed)
    Abstract [en]

    Polymer-based materials show to be of increasing interest in replacing metal based materials in tribological applications due to their low weight, cost and easy manufacturability. To further reduce the environmental impact of these bearing materials recyclability is becoming more crucial, stimulating the need for high performing thermoplastic materials. In this study, polyphenylene sulfide (PPS) composites were prepared in an effort to enhance its tribological properties. Short carbon fibres (SCFs), graphene oxide (GO) and nano diamonds (NDs) as well as polytetrafluoroethylene (PTFE) were used as micro and nano reinforcements. The addition of SCFs especially decreased the linear coefficient of thermal expansions while enhancing the micro hardness and wettability of the polymer. Under water lubricated conditions, a decrease in friction up to 56% and a reduction of wear rate in the order of 103 was observed by the addition of SCF. The reduction in friction and wear was further enhanced by the addition of NDs, providing a synergistic effect of the reinforcements in micro and nano scale. By testing the individual reinforcements under dry conditions, PTFE and SCFs were especially effective in reducing friction while the release and consequent abrasion of NDs and SCFs increased the wear under a higher contact pressure.

  • 86.
    Janis, Ayush
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Somberg, Julian
    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.
    Development and Characterisation of Multi-Scale Carbon Reinforced PPSManuscript (preprint) (Other academic)
    Abstract [en]

    Polymer-based materials show to be of increasing interest in replacing metal based materials in tribological applications due to their low weight, cost and easy manufacturability. To further reduce the environmental impact of these bearing materials recyclability is becoming more crucial, stimulating the need for high performing thermoplastic materials. In this study, polyphenylene sulfide (PPS) composites were prepared in an effort to enhance its tribological properties. Short carbon fibres (SCFs), graphene oxide (GO) and nano diamonds (NDs) as well as polytetrafluoroethylene (PTFE) were used as micro and nano reinforcements. The addition of SCFs especially decreased the linear coefficient of thermal expansions while enhancing the micro hardness and wettability of the polymer. Under water lubricated conditions, a decrease in friction up to 56% and a reduction of wear rate in the order of 103 was observed by the addition of SCF. The reduction in friction and wear was further enhanced by the addition of NDs, providing a synergistic effect of the reinforcements in micro and nano scale. By testing the individual reinforcements under dry conditions, PTFE and SCFs were especially effective in reducing friction while the release and consequent abrasion of NDs and SCFs increased the wear under a higher contact pressure.

  • 87.
    Khan, Sharjeel Ahmed
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Department of Mechanical Engineering, CEMMPRE, ARISE, University of Coimbra, Rua Luis Reis Santos, 3030-788 Coimbra, Portugal.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ramalho, Amilcar
    Department of Mechanical Engineering, CEMMPRE, ARISE, University of Coimbra, Rua Luis Reis Santos, 3030-788 Coimbra, Portugal.
    Custom-tailored cross-cylinder tribotest to emulate wear mechanism in drilling of CFRP-Ti stacks2023In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 186, article id 108589Article in journal (Refereed)
    Abstract [en]

    While drilling of CFRP-Ti stacks, tool experiences complex tribomechanical interaction due to dissimilar workpiece constituents. For emulating tool wear behavior, the typical tribotest configuration such as reciprocating and pin-on-disc test are not representative for imitating contact scenario underwent during the drilling operation. Cross-cylinder tribotest is an effective test configuration to emulate contact in different manufacturing processes by providing fresh contact surface during sliding. In this work, for the first-time, tool wear of WC-Co cylinders was analyzed in cross-cylinder configuration against multi-material stack arrangement. Moreover, cross-cylinder testing against multi-material [CFRP-Ti]n workpiece showed cyclic variation in coefficient of friction against different workpiece constituents and wear mechanism is a combination of adhesive and abrasive wear on WC-Co tool, comparable to actual drilling operation.

  • 88.
    Khan, Sharjeel Ahmed
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. Department of Mechanical Engineering, CEMMPRE, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal.
    Oliveira, João
    Department of Mechanical Engineering, CEMMPRE, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal.
    Ferreira, Fabio
    Department of Mechanical Engineering, CEMMPRE, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ramalho, Amilcar
    Department of Mechanical Engineering, CEMMPRE, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal.
    Surface Roughness Influence on Tribological Behavior of HiPIMS DLC Coatings2023In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 66, no 3, p. 565-575Article in journal (Refereed)
    Abstract [en]

    The application of diamond-like carbon (DLC) coatings in dry machining of difficult-to-machine materials has been gaining popularity due to high inertness, low coefficient of friction (COF), and high hardness of these coatings. Although the effect of surface roughness on the tribological properties of DLC coatings is of paramount importance, usually it is overlooked and coatings performance analysis was accomplished generally on highly polished substrates. The generation of polished surfaces is a time-consuming, labor-intensive process and, in most cases, not feasible for the industry due to its high cost. This article focuses on determining the effect of substrate (cemented carbide, WC-Co) surface roughness on the load-bearing capacity and tribological properties of DLC coatings deposited by High Power Impulse Magnetron Sputtering (HiPIMS) in Ne–Ar gas plasma. The DLC films were deposited onto WC-Co substrates with three different surface roughness profiles and their tribological performance were evaluated using a reciprocating tribotest. The high surface roughness resulted in increased wear rate due to high levels of asperities and increased potential for premature delamination of the coatings, while also causing severe damage to the counterbody due to inhibition of transfer film formation.

  • 89.
    Kneissl, Lucas M.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. aboratory for Tribology and Interface Nanotechnology, Faculty of Mechanical Engineering, University of Ljubljana, Bogišićeva 8, Ljubljana, 1000, Slovenia.
    Gonçalves, Gil
    Centre for Mechanical Technology and Automation, Department of Mechanical Engineering, University of Aveiro, Campus Universitário de Santiago, Aveiro, 3810-193, Portugal.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kalin, Mitjan
    Laboratory for Tribology and Interface Nanotechnology, Faculty of Mechanical Engineering, University of Ljubljana, Bogišićeva 8, Ljubljana, 1000, Slovenia.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mechanical properties and tribological performance of polyoxymethylene/short cellulose fiber composites2023In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 128, article id 108234Article in journal (Refereed)
    Abstract [en]

    Natural fibers are promising bio-based materials to use as reinforcements in polymer composites as often more affordable and accessible alternatives to fossil-based fibers, especially because of their superior sustainability. Polyoxymethylene (POM) is a widely used engineering thermoplastic, which has a melting temperature suitable for processing with natural fibers. In this study, such composites consisting of POM and regenerated cellulose fibers have been developed and studied in terms of their mechanical, thermal, tribological and structural properties. Tensile and flexural moduli increased with incorporation of 30 wt% fibers up to 89% and 79% respectively, crystallinity increased as well by a maximum of approx. 11% at 30% fiber content. Furthermore, the specific wear rate was improved for the composite with 10 wt% fibers, showing a decrease of roughly 80%. This study investigates the processing parameters and tribo-mechanical performance of POM-based natural fiber composites as an important route towards future sustainable polymer composites in load bearing applications.

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  • 90.
    Li, Bin
    et al.
    Department of Mechanical Engineering, Wichita State University.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Gong, Guan
    Swerea SICOMP AB, Box 271, 941 26, Piteå.
    Song, Weidong
    Department of Mechanical Engineering, Wichita State University, PD Materials, Boeing Commercial Airplanes, Seattle, WA 98124.
    Applications of Nanomaterials in Multifunctional Polymer Nanocomposites2016In: Journal of Nanomaterials, ISSN 1687-4110, E-ISSN 1687-4129, Vol. 2016, article id 5790194Article in journal (Other academic)
  • 91.
    Lindberg, A.
    et al.
    Public Dental Health Clinic, Skellefteå, Seminariegatan, Sweden; Department of Odontology, Dental School Umeå, Umeå University, Umeå, Sweden.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    van Dijken, JW.
    Department of Odontology, Dental School Umeå, Umeå University, Umeå, Sweden; .
    A Fourier transform Raman spectroscopy analysis of the degree of conversion of a universal hybrid resin composite cured with light-emitting diode curing units2005In: Swedish Dental Journal, ISSN 0347-9994, Vol. 29, no 3, p. 105-112Article in journal (Refereed)
    Abstract [en]

    The degree of conversion (DC), of a universal hybrid resin composite cured with LED curing units with low and high power densities and a 510 mW/cm2 quartz tungsten halogen unit, was investigated with Fourier Transform Raman spectroscopy. Three curing depths (0, 2, 4mm) and 0 and 7 mm light guide tip - resin composite (LT - RC) distances were tested. The DC of the LED units varied between 52.3% - 59.8% at the top surface and 46.4% - 57.0% at 4 mm depth. The DC of specimen cured with a 0 mm LT- RC distance at 4 mm depth varied between 50.8% - 57.0% and with 7 mm distance between 46.4% - 55.4%. The low power density LED unit showed a significantly lower DC for both distances at all depth levels compared to the other curing units (p < 0.05). Significant differences between the other curing units were only found at the 4 mm depth level cured from 7 mm distance (p < 0.05). The reduction in DC by increasing LT- RC distance was less than 10% for all curing units. It can be concluded that the improved LED curing units could cure the studied resin composite to the same DC as the control unit.

  • 92.
    Lindberg, Anders
    et al.
    Umeå universitet.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    van Djiken, Jan
    Umeå universitet.
    Comparison of the effect of different LED curing units on depth of cure2005In: Swedish Dental Journal, ISSN 0347-9994, Vol. 29, no 3, p. 105-112Article in journal (Refereed)
  • 93.
    Marian, Max
    et al.
    Department of Mechanical and Metallurgical Engineering, School of Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile.
    Berman, Diana
    Department of Materials Science and Engineering, University of North Texas, Denton, United States.
    Nečas, David
    Department of Tribology, Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Ruggiero, Alessandro
    Department of Industrial Engineering, Faculty of Engineering, University of Salerno, Salerno, Italy.
    Rosenkranz, Andreas
    Department of Chemical Engineering, Biotechnology and Materials (FCFM), Universidad de Chile, Santiago, Chile.
    Roadmap for 2D materials in biotribological/biomedical applications:€“ A review2022In: Advances in Colloid and Interface Science, ISSN 0001-8686, E-ISSN 1873-3727, Vol. 307, article id 102747Article, review/survey (Refereed)
    Abstract [en]

    The human body involves a large number of systems subjected to contact stresses and thus experiencing wear and degradation. The limited efficacy of existing solutions constantly puts a significant financial burden on the healthcare system, more importantly, patients are suffering due to the complications following a partial or total system failure. More effective strategies are highly dependent on the availability of advanced functional materials demonstrating excellent tribological response and good biocompatibility. In this article, we review the recent progress in implementing two-dimensional (2D) materials into bio-applications involving tribological contacts. We further summarize the current challenges for future progress in the field.

  • 94.
    McLaren, H.
    et al.
    Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT.
    Bryant, M.
    Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neville, A.
    Institute of Functional Surfaces, School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT.
    High-Performance Polymer Composites for Extreme Conditions2017In: Book of Abstracts, Université de Lyon , 2017, p. 152-152, article id 140228Conference paper (Refereed)
  • 95.
    Melk, Latifa
    et al.
    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.
    Mechanical and thermal performances of UHMWPE blended vitamin E reinforced carbon nanoparticle composites2018In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 146, p. 20-27Article in journal (Refereed)
    Abstract [en]

    Ultrahigh molecular weight polyethylene (UHMWPE) is a known to be the material of choice for bearing components in joint arthroplasty. However, oxidation wear of UHMWPE components is considered to be a major drawback limiting the lifespan of implants. Vitamin E was considered as a promising antioxidant to prevent long-term oxidation and reduce the wear degradation of UHMWPE material. Nevertheless, there are limited results on the improvements of vitamin E on the mechanical and thermal properties of UHMWPE. In this study, we investigated the incorporation of 0.5–3 wt.% carbon nanoparticles: Multiwalled Carbon Nanotubes (MWCNTs), Graphene (GO) and Nanodiamonds (ND) on the mechanical and thermal properties of UHMWPE blended vitamin E (UHMWPE-E). Surface analysis of the composite powders showed well-dispersed carbon nanoparticles within the UHMWPE-E matrix. Thermogravimetric (TGA) and Differential Scanning Calorimetry (DSC) were used to study the thermal behavior of the nanocomposites. It was found that the addition of GO, MWCNTs and ND improved the thermal stability of the nanocomposites compared to neat UHMWPE-E. However, the addition of carbon nanoparticles had no significant effect on the crystallization parameters of the composites. In addition, the incorporation of MWCNT and ND improved significantly the fracture toughness of the composites. The addition of 0.7 wt.% ND and 1 wt.% MWCNT increased the fracture toughness from 5.93 MPa m1/2 for neat UHMWPE-E to 7.38 and 9.19 MPa m1/2 respectively. The enhanced fracture toughness and thermal stability of the nanocomposites could be due to the successful powder processing technique where an optimized mixing and ball milling parameters were used.

  • 96.
    Melk, Latifa
    et al.
    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, mechanical and thermal performances of UHMWPE blended vitamin E reinforced carbon nanoparticle composites2018Conference paper (Refereed)
  • 97.
    Moreno, Silvia Suñer
    et al.
    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.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    UHMWPE/GO nanocomposites for orthopaedic applications: thermal, mechanical and tribological characterization2014Conference paper (Refereed)
    Abstract [en]

    Metal-on-Polyethylene (MoP) is the bearing combination most commonly used in total joint replacements. However, the degradative oxidation behaviour of ultra high molecular weight polyethylene (UHMWPE) leads to high amounts of wear debris, which contributes to the development of aseptic loosening and eventually to the failure of the implant. In order to address this issue, investigations have focused on the development of novel materials with improved characteristics. Recently, Graphene oxide (GO) has generated great interest as reinforcement for polymer matrices due to its excellent mechanical properties. The aim of this study was to investigate the possibilities of UHMWPE/GO nanocomposites for their use in joint implants.UHMWPE/GO nanocomposites with different wt% GO content, up to 2 wt%, were manufactured under optimised conditions using a ball milling technique. Thermal, mechanical and structural characterizations of the UHMWPE/GO nanocomposites and conventional UHMWPE were carried out by means of Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), uniaxial tensile tests and High Resolution Scanning Electron Microscopy (HR-SEM). Contact angle measurements were carried out to investigate the wettability of the materials. In addition, the tribological performance of the novel nanocomposites will be assessed with a six-station multidirectional pin on plate wear simulator under hip kinematics.The results showed that GO has the ability to improve the performance of conventional UHMWPE. The incorporation of GO enhanced the thermal stability and oxidative resistance of conventional UHMWPE. Under optimised conditions, the mechanical properties and wettability of the nanocomposites were also improved. These findings suggest that UHMWPE/GO nanocomposites might be an interesting alternative to conventional UHMWPE for their use in orthopaedic aplications and more research concerning the biocompatibility and tribological performance of this material is currently under investigation.

  • 98.
    Moreno, Silvia Suñer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biological effects of wear particles generated in total joint replacements: trends and future prospects2011Conference paper (Refereed)
    Abstract [en]

    Joint replacements have considerably improved the quality of life of patients with joints damaged by disease or trauma. However, problems associated with wear particles generated due to the relative motion between the components of the bearing are still present and can lead to the eventual failure of the implant. The biological response to wear debris is directly related to prosthesis longevity. The identification of the mechanisms by which cells respond to wear debris and how particles distribute around the human body may provide valuable information for the long term success of artificial joints.During the last few decades, orthopaedic research has been focused on predicting the in vivo performance of joint replacements. However, the exact interrelationship between material physicochemical properties and inflammatory response is not fully understood to date. Laboratory wear simulators provide an accurate prediction of implant wear performance. However, particles generated from such wear simulators require validation to compare them with particles extracted from peri-implant tissues. The present work focuses initially on the advantages and disadvantages of the different bearing combinations (hard-on-soft and hard-on-hard bearings). In addition, the similarities between particles observed in vivo and those generated in vitro to predict the cellular response to wear debris is discussed. Finally, the biological effects of the degradation products generated by wear and corrosion are described.

  • 99.
    Moreno, Silvia Suñer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biological Response to Wear Debris and Wear Properties of Prosthetic Joint Materials: a review2013Conference paper (Refereed)
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  • 100.
    Moreno, Silvia Suñer
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Tipper, Joanne
    Institute of Medical and Biological Engineering, University of Leeds.
    Emami, Nazanin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Biological response to wear debris and wear properties of prosthetic joint materials: a review2012Conference paper (Refereed)
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