Browsing by Author "Militký, Jiří"
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- ItemA novel method for producing bi-component thermo-regulating alginate fiber from phase change material microemulsion(SAGE PUBLICATIONS LTD, 1 OLIVERS YARD, 55 CITY ROAD, LONDON EC1Y 1SP, ENGLAND, 2019-11) Wang, Yan; Yao, Juming; Zhu, Guocheng; Militký, Jiří; Marek, Jaromír; Venkataraman, Mohanapriya; Zhang, GuoqingA novel method for fabricating thermo-regulating alginate fiber by wet spinning from phase change material (PCM) microemulsions was proposed and carried out. In order to synthesize the PCM microemulsion successfully, different emulsifiers (alkylphenol polyoxyethylene ether (OP-10), sodium dodecyl sulfate (SDS) and their mixture) were added into the stock solution system. The solution systems with emulsifiers were observed under optical microscope and evaluated by using a differential scanning calorimeter (DSC); the results showed that only the solution system with the mixture of OP-10 and SDS transformed into PCM microemulsion, corresponding to the success of fiber formation by wet spinning. In addition, the microemulsion had a stable thermal property based on the DSC result, in which the latent heat capacity remained at 97.3% after 100 cycles of heating and cooling. The thermo-regulating alginate fiber was evaluated in terms of morphology, thermogravimetric (TG) analysis and differential scanning calorimetry. The results showed that the fiber had a smooth surface and porous structure in the cross-section, the bimodal TG curve of alginate fiber indicated that the PCM was successfully embedded into fiber and the DSC results demonstrated that the thermo-regulating alginate fiber had a comfortable phase change temperature of 25-35celcius, and an acceptable phase change enthalpy of about 20 J/g.
- ItemAkustické moduly speciálních vláken(Technická Univerzita v Liberci, 2013) Šebelová, Zdeňka; Militký, JiříV rámci této diplomové práce bylo zpracována literární rešerše na téma akustické moduly speciálních vláken. Jsou zde uvedeny základní vlastnosti a obecné charakteristiky NiTiNOLových, skleněných a čedičových vláken. Cílem je zjistit dynamický a statický modul pružnosti těchto vláken. Ke zjištění dynamického modulu pružnosti je použito zařízení DMT, založené na stanovení rychlosti šíření zvuku ve vláknech. Statický modul pružnosti je měřen na dynamometru LabTech při tahové zkoušce. Práce obsahuje porovnání výsledků dynamického a statického modulu. Na přístroji DSC jsou vlákna testována, aby se zjistilo, jak se mění transformační fáze během ohřívání a ochlazování vzorku u vláken NiTi.
- ItemAn experimental evaluation of convective heat transfer in multi-layered fibrous materials composed by different middle layer structures(SAGE PUBLICATIONS INC, 2455 TELLER RD, THOUSAND OAKS, CA 91320 USA, 2019-10) Xiong, Xiaoman; Venkataraman, Mohanapriya; Jašíková, Darina; Yang, Tao; Mishra, Rajesh; Militký, Jiří; Petrů, MichalIn this work, three types of multi-layered fibrous materials with different middle layer structures, including Struto nonwoven, Struto nonwoven with air pockets and Struto nonwoven with air pockets filled by aerogel particles, were prepared based on laser engraving technique and laminating method. A custom-built new device was fabricated to evaluate convective thermal behaviour of the multi-layered materials in cross flow. It was found that in cross flow the heat transfer coefficient of the multi-layered material with encapsulated aerogels is directly proportional to Reynolds number. There are considerable variances in heat transfer rates of the three structures at low airflow velocity (less than 10 m/s), but the values are very close at high airflow velocity. It is concluded that the air pockets and aerogels present in the multi-layered fibrous material have significant effect on convective thermal behaviour of the overall structure in cross flow. The finding is a new contribution to the field of aerogel-based fibrous materials as thermal insulators in building and industrial facilities.
- ItemAn analysis of effective thermal conductivity of heterogeneous materials(Technical University of Lodz, 2014) Zhu, Guocheng; Křemenáková, Dana; Wang, Yan; Militký, Jiří; Mazari, Funda BuyukEffective thermal conductivity (ETC) is a very important index for evaluating the thermal property of heterogeneous materials, which include more than two different kinds of materials. Several analytical models were proposed for predicting the ETC of heterogeneous materials, but in some cases, these models cannot provide very accurate predictions. In this work, several analytical models and numerical simulations were studied in order to investigate the differences among them. In addition, some factors which would influence the ETC of heterogeneous materials were investigated by numerical simulation. The results demonstrated that the numerical simulation can provide very accurate prediction, indicated that different analytical models should be selected to predict specific problems based on their assumptions, and suggested that more variables need to be considered in order to improve these analytical models, such as inclusion shape, inclusion size, distribution of inclusions and contact area. Besides, numerical method could be an effective and reliable way to obtain the ETC of heterogeneous materials with any kind of complicated structures. © AUTEX.
- ItemAnomalous electrical resistance of hybrid yarns containing metal fibers(Hong Kong Polytechnic University, 2011) Militký, Jiří; Šafářová, VeronikaThe total electric resistance R is theoretically linearly increasing function of the conductive wire length L, because the electric conductivity K or electric resistivity r is independent on L. It was found [7] that for yarns containing the conductive metal fibres the dependence of electric resistance R on L is highly nonlinear. Main aim of this contribution is creation of the simple mechanistic model describing this anomalous length dependence. Characteristic parameter of this model is so called specific resistivity .
- ItemBadanie właściwości zasysania wody (efekt knota) tkanin bawełnianych(Institute of Biopolymers and Chemical Fibres, 2015) Zhu, Guocheng; Militký, Jiří; Wang, Yan; Sundarlal, Bele Vijay; Křemenáková, DanaIn order to study the heat and moisture comfort, the wicking property of textiles has been used as an important and effective index. In this paper, the wicking behaviour of cotton fabric in the warp and weft directions was investigated in terms of the wicking height, rate of wicking, mass increment distribution per centimetre of the wicking height, and the durative wicking height after removal of the wicking liquid reservoir. The results showed that the wicking height square had a good correlation with the time in both the warp and weft directions. The wicking rate was higher in the weft direction than that in the warp, especially at the beginning of the wicking process. The mass increment of fabric per centimetre of the wicking height was inversely proportional to the wicking height; the mass of water absorbed in the fabric did not have a significant difference in the weft and warp directions. © 2015, Institute of Biopolymers and Chemical Fibres. All rights reserved.
- ItemBasalt fibres a new prospectus of old material(The Textile Institute, Manchester, UK, 1997) Militký, Jiří; Kovačič, Vladimír; Kvíčala, JaroslavBasalt fibers similarly as a glass fibers are used for production of high ttemperature resistant and chemically inactive products. Basalt is used mainly for molded productss (flag stones, pipes) with increased abrasion resistance, temperature resistance and chemical resistance or in a form of short fibers for insulation purposes (basalt wool). Application of the technology of continuous spinning leads to the sufficiently even basalt filament yarns applicable in the textile branch. It is possible to use these yarns for production of planar or 3D textile structures for composites, special knitted products and also as the sewing threads. In this contribution the selected properties of basalt fibers in the comparison with glass ones are presented. The properties are investigated after tempering to the 50, 100, 200, 300 °C. The ultimate strength, deformation at break and sound wave spread velocity are compared. Structural changes of fibers are identified by scanning electron microscopy. Thermal properties are investigated by the TMA apparatus. The thermal expansion and compressive creep are investigated. The sewing threads from basalt filament fibers were prepared. Their applicability for sewing of filtering bags from glass fabrics was verified. It was evaluated that the basalt sewing thread have generally a little mechanical resistance (due its brittleness). Improving of theirs performance can be made by the surface coating with suitable polymeric materials. Good results were obtained by using of the resin from polyethyleneterephthalate. The analysis of fibrous fragment evolved during abrasion of basalt weave is presented. The basalt particles are too thick to be directly respirable but their length/diameter ratio is higher that 3 and therefore the handling of basalt fibers must be carried out with care.
- ItemBasalt hybrid woven textile materials for advanced thermal applications(NATL INST SCIENCE COMMUNICATION-NISCAIR, DR K S KRISHNAN MARG, PUSA CAMPUS, NEW DELHI 110 012, INDIA, 2019-03) Jamshaid, Hafsa; Mishra, Rajesh; Militký, Jiří; Hussain, SajidThe thermal properties of hybrid basalt-polypropylene (B/PP), basalt-polyester (B/PET) and basalt-jute (B/J) as well as non-hybrid structures have been studied. The fabric structures have been developed as plain weave (PW) for B/PP, B/PET & B/J; matt weave (MW) for B/PP, B/PET & B/J; and 1/3 twill weave (TW) for basalt-PP, basalt-PET, and basalt-Jute along with the non-hybrid fabrics. The thermal properties of the fabrics, such as thermal conductivity and thermal resistance are studied along with the physiological behavior. Thermal properties are measured by Alambeta and TCi. Correlation between theoretical and experimental measurement of thermal conductivity are also studied. Air permeability is tested by air permeability tester. Based on the results, the influence of fabric structure on specific thermal insulation parameters are analyzed. The findings show that there is a significant impact on thermal properties of basalt hybrid woven structures by geometrical parameters of weave. Structure and fibre type have strong influence on thermal properties. Twill weave structures show higher air permeability and thermal resistance in all combinations.
- ItemBio-Composites Reinforced with Natural Fibers: Comparative Analysis of Thermal, Static and Dynamic-Mechanical Properties(KOREAN FIBER SOC, KOREA SCIENCE TECHNOLOGY CTR #501 635-4 YEOGSAM-DONG, KANGNAM-GU, SEOUL 135-703, SOUTH KOREA, 2020-03) Mishra, Rajesh; Wiener, Jakub; Militký, Jiří; Petrů, Michal; Tomková, Blanka; Novotná, JanaIn the present study, flax, jute and glass woven fabric samples were developed as reinforcement for composites with bio-epoxy resin. Flax fabrics were developed with plain weave, twill weave (different areal densities) and unidirectional (UD) structure. Jute fabrics were woven with three different structures i.e. plain, matt and twill respectively. For comparison purpose, glass woven fabric with plain weave and 3D orthogonal weave were used in this study. Static mechanical properties like flexural strength and impact resistance were studied. Dynamic mechanical properties were investigated by DMA 40XT RMI equipment.. Thermal conductivity has been studied for all composite samples. It is observed that the static mechanical properties of glass fabrics reinforced composites are superior but the flax & jute fabric reinforced composites are more flexible. The specific flexural strength as well as specific impact strength of the flax & jute fabric reinforced composites are competitive. The dynamic mechanical properties are comparable to that of glass fabric reinforced composites. They can be used in relatively lower load bearing applications as they are a sustainable source of materials for bio-composites which reduce the environmental burden and reduce the manufacturing cost.
- ItemBreaking strength distribution of basalt filaments(1996) Militký, Jiří; Kovačič, VladimírThis paper presents the results of an experimental analysis of the breaking strength distribution of basalt filaments. It outlines the composition and basic physical characteristics of glass and basalt fibres, and provides a statistical analysis of the fracture of fibres. The paper details the methodology and findings of the experiment, concluding, in particular, that the brittle fracture of basalt filaments is probably due to volume defects and can be described by the three parameter Weibull distribution.
- ItemBuilding And Statistical Interpretation Of Nonisothermal Kinetic-Models(Elsevier Science Bv, 1992) Militký, Jiří; Šesták, JaroslavMain features of building non-isothermal kinetic models are discussed. The possibilities of evaluation of kinetic and temperature terms are described. Statistical methods for parameter estimation under more realistic assumptions about the nature of data are presented.
- ItemCationization of cellulose fibers for composites(2017-01-04) Maqsood, Hafiz Shahzad; Bashir, Uzma; Zubair, Muhammad; Wiener, Jakub; Militký, JiříIn this work, composites were made by improved bonding of the cationized cellulosic fabric and some anionic matrix like Carboxymethyl Cellulose (CMC). Mercerized cotton fabric was cationized using cationization agent, TEXAMIN ECE with varying percentage from 1 to 10%. Those cationized cotton samples were incorporated in anionic matrices and the resultant composites were tested for mechanical properties on Universal Textile Tensile Testing machine. In the case of CMC as the matrix for the cationized reinforcement, the increasing trend in the tensile strength and elongation at break was observed. Scanning Electron Microscope images showed no extraordinary changes in the physical appearance of the cationized samples. Thermograms derived from Differential Scanning Calorimetry were informative for the evaluation of the thermal behavior of composites. © 2016 The Textile Institute
- ItemCharacteristics of Woven Basalt and Hybrid Structures as Composite Reinforcement(TEXTILE BIOENGINEERING & INFORMATICS SOCIETY LTD, TBIS 2010 SECRETARIAT MN104, HONG KONG POLYTECHNIC UNIV, HONG KONG SAR, 0000, PEOPLES R CHINA, 2018) Jamshaid, Hafsa; Mishra, Rajesh; Militký, JiříIn this study, experimental investigations are carried out to check the thermal and mechanical behavior of woven Basalt/PET and Basalt/PP fiber hybrid woven fabric epoxy composite laminates. Fabricated composite samples are subjected to mechanical and thermal characterization. Results are discussed in terms of fiber effect, weave geometry and the resin effect. The results reveal that the hybridization of basalt in different weaves leads to significant improvement in the mechanical properties of composites. The modulus is significantly increased in composites due to interfacial bonds between fibers and resin. Thermal behavior of fiber and composite was observed by Thermal Gravimetric Analysis. Thermal properties are also affected by hybridization. Thermal conductivity is strongly affected by resin properties. Fractography studies of the damaged surface are also demonstrated.
- ItemCo-solvent free interfacial polycondensation and properties of polyurea PCM microcapsules with dodecanol dodecanoate as core(Elsevier Ltd, 2020-03) Cai, Changwei; Ouyang, Xu; Zhou, Lan; Liu, Guojin; Wang, Yan; Zhu, Guocheng; Yao, Juming; Militký, Jiří; Venkataraman, Mohanapriya; Zhang, GuoqingA kind of eco-friendly micro-encapsulated phase change materials (MEPCM) with dodecanol dodecanoate as core material were synthesized via the interfacial polymerization of toluene-2, 4-diisocyanate (TDI) and diethylenetriamine (DETA). During the preparation, a facile solvent free synthesis route was developed owing to the good compatibility of TDI and dodecanol dodecanoate. The synthesized MEPCM were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Particle Size Distribution (PSD) analyzer, Differential Scanning Calorimetry (DSC), Thermogravimetric/Infrared spectrometry (TG-IR) and thermal constants analyzer. It is found that the resultant MEPCM in nearly spherical shape are in the size scope from 10.0 to 40.0 μm, have the average latent heat in the range of 103.4–140.3 J/g, and exhibit high temperature resistance with an onset evaporation temperature at 234.0 °C. Moreover, the MEPCM possess good thermal conductivity from 0.17 W/m K to 0.21 W/m K. Therefore, it is confirmed that the prepared MEPCM can be regarded as a promising thermal energy storage material appropriate to the thermo-regulating fields such as renewable solar heating system.
- ItemComparison of effective thermal conductivity of hollow fibers by prediction models and FE method(Trans Tech Publications Ltd, 2013) Zhu, Guocheng; Militký, Jiří; Wang, Yan; Huang, Juan; Křemenáková, DanaIn order to evaluate the effective thermal conductivity (ETC) of hollow fibers, three theoretical models (the parallel/series model, quadrate model and cylindrical model) and finite element method carried out by ANSYS simulation were studied. The results showed that different theoretical models gave quite different effective thermal conductivities. The results from theoretical models and simulations were completely identical in the case when models had regular structures and the heating surface was the same kind of material. The ETC of hollow fibers from all of theoretical models and simulations decreased exponentially with the increase of air volume content. In addition, the ETC of hollow fibers from the first theoretical model were a bit higher than the results from simulation, whereas those from the second theoretical model were smaller than the results from simulation, and those from the third theoretical model were identical to the results from simulation. © (2014) Trans Tech Publications, Switzerland.
- ItemComparison of methods for evaluating the electromagnetic shielding of textiles(2012) Šafářová, Veronika; Militký, JiříMaterials with electromagnetic shielding efficiency are widely used to attenuate the strength of electromagnetic fields as functional elements in electrotechnic devices and also as supporting elements for electromagnetic interference reduction. One of modern application is not only technical protection, but also protection of human being while operating specific electric equipments. In these days, instead of metallic shields it is more common to use various types of textile materials due to their desirable flexibility and lightweight. The results of shielding effectiveness measurements depend on the method, frequency and properties of the material itself. The current state of work in the field of standardization and measurement methods for the shielding effectiveness of thin planar materials is presented in this paper. Testing of textile samples shielding was performed by different methods and scope of application, their limitations and possibilities for comparison of results are discussed.
- ItemCompression resilience and impact resistance of fiber-reinforced sandwich composites(2019) Mishra, Rajesh; Wiener, Jakub; Militký, Jiří; Petrů, Michal; Tomková, Blanka; Novotná, JanaThis paper presents an experimental investigation on the compression behavior of fiber-reinforced sandwich composites. In this study, five different types of sandwich composites were prepared with warp knitted spacer fabric as middle layer. Four different types of woven Kevlar fabric structures were used as outer layers (skin) along with one sample of woven basalt fabric. The middle layer used is 100% polyester spacer fabric. Sandwich composites were fabricated using epoxy resin by wet lay-up method under vacuum bagging technique. Compression behavior, ball burst, and knife penetration were tested for all samples. The effect of outer layer of these composites on the mechanical performance was studied using the compression stress-strain curves. It is known that spacers have excellent compression elasticity and cushioning. Maximum knife penetration resistance is obtained with twill weave on surface because of maximum yarn cohesion and resin impregnation. Higher amount of cohesive friction results in higher resistance against penetration of sharp objects like the knife edge. Plain and twill fabrics offer sufficient resistance again ball burst. The yarn deformation allows formation of dome shape after ball impact. Maximum impact resistance in ball burst is obtained for plain weave because of highest level of interyarn binding. The results provide new understanding of knitted spacer fabric-based sandwich composites under compression and impact loading condition.
- ItemComputer estimation of dissociation constants. Part 6. Diagnostics in regression analysis of absorbance-pH curve(Springer-Verlag, 1994) Meloun, Milan; Militký, JiříNonlinear regression program DCMINOPT is introduced for numerical analysis of a set of {A, pH} data expressing a dependence of absorbance of a mixture of variously protonated light-absorbing species L, LH,..., LHR on pH. Efficiency of the program has been examined on simulated A-pH data corrupted with artificial (generated) errors namely for a case of closely overlapping protonation equilibria. An accuracy and precision of parameters estimates have been examined and compared with those determined by another three standard algorithms DCFIT, DCMINUIT and PSEQUAD. Goodness-of-fit test brings various regression diagnostics, 3D-plots and statistical measures enabling to test and prove a reliability of a regression process and accuracy and precision of parameter estimates. © 1993 Springer-Verlag.
- ItemComputer Estimation Of Dissociation-Constants 5. Regression-Analysis Of Extended Debye-Huckel Law(Springer-Verlag Wien, 1992) Meloun, Milan; Javůrek, Milan; Militký, JiříNonlinear regression program DHMINOPT has been used for an analysis of a set of values expressing the dependence of mixed dissociation constant on ionic strength according to the extended Debye-Hueckel law. Efficiency of program has been examined on simulated data loaded with generated random errors. Goodness-of-fit brings various regression diagnostics enabling to prove a reliability of a regression process and parameter estimates. For five selected sulphonephtalein indicators, i.e. Bromocresol Green, Bromophenol Red, Bromocresol Purple, Bromothymol Blue and Phenol Red, the thermodynamic dissociation constant has been determined at 25-degrees-C together with the ion-size parameter and the salting-out coefficient.
- ItemCopper electroless plating of cotton fabrics after surface activation with deposition of silver and copper nanoparticles(Elsevier Ltd, 2020-02) Ali, Azam; Baheti, Vijay; Vik, Michal; Militký, JiříIn this work, surface metallization of cotton fabrics was performed by electroless plating using a shorter route than is conventional. The fabric surface was activated by deposition of silver and copper nanoparticles, and then a thin layer of copper was coated using electroless plating. The performance of coated fabrics was compared in terms of electrical conductivity, electromagnetic interference (EMI) shielding, Joule heating and antibacterial properties with another sample coated with conventional electroless plating. The orthogonal array testing strategy was adopted to optimize the various factors of the electroless plating bath. The samples prepared by electroless plating of copper showed greater performance for the fabric first deposited with silver particles than those first deposited with copper particles or conventionally treated. Samples of copper electroplating over silver had surface resistivity of 20 Ω, EMI shielding of 75.53 dB and Joule heating of 83.1 °C. Moreover, samples with modified electroless plating showed better attachment of the metal layer and therefore longer durability.