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1

Novel rheological modelling of thermosets and unidirectional monotropic fibre-reinforced thermoset matrix composites

Klasztorny Marian, Nycz Daniel B.

Composites Theory and Practice

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2023

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R. 23, nr 1

3--21

EN

A refined, fully analytical rheological modelling of thermosetting polymers and unidirectional monotropic fibre-reinforced thermoset matrix (UFRT) composites is presented. New polymers and composites under normal conditions, fully relaxed from curing and post-curing stresses, are modelled. The theory includes quasi-static short-term/medium-term/long-term reversible rheological processes. Thermosets are isotropic materials exhibiting linearly viscoelastic shear strains and linearly elastic bulk strains. Fibres are monotropic (transversely isotropic) and linearly elastic materials. A generic function well reproducing the viscoelastic characteristics of thermosets and UFRT composites is a Mittag-Leffler fractional exponential function in an integral form. Coupled/uncoupled standard/inverse constitutive equations of linear rheology are formulated for thermosets and UFRT composites. The equations are mutually analytically transformable. New rheological models (coded H-R/H) for thermosets and UFRT composites are described by the smallest possible number of material constants. The thermoset is described by two independent elastic constants and three independent viscoelastic constants. The homogenized UFRT composite is described by five independent elastic constants and four independent viscoelastic constants, whereby two visco-elastic constants are common to the matrix and the composite. An improved homogenization theory of UFRT composites, based on analytical solutions of the selected tasks of the theory of linear elasticity, is formulated for monotropic fibres and positively validated experimentally. The viscoelastic constants of the thermoset are calculated analytically in an iterative loop using a long-term unidirectional tension creep experimental test. The viscoelastic constants of the UFRT composite are calculated analytically employing H-R/H shear/quasi-shear storage compliances and VECP (the viscoelastic-elastic correspondence principle) shear/quasi-shear storage compliances. The H-R/H rheological model was validated numerically for selected UFRT composites. The validation tests were performed on the enhanced reliability UFRT composites reported by Soden, Hinton, and Kaddour (Composites Science and Technology, 1998, 2002).

2

Rheological studies of high-density fracturing fluid using high-density brine and carboxymethyl hydroxypropyl guar (CMHPG) for high-temperature well condition

Raja Idris R.F.W., Rosli N.R., Mohammadian E., Hasan N.

Archives of Materials Science and Engineering

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2023

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Vol. 120, nr 2

49--59

EN

Purpose: This work investigated carboxymethyl hydroxypropyl guar (CMHPG) as a potential base polymer for a fracturing fluid used in deep tight gas wells, synonym to high-temperature reservoirs. Fracturing is a common method to improve oil production by creating fractures in potentially productive reservoirs using fracturing fluids. Fracturing fluids are typically composed of water, sand, proppant, and many different additives to alter the capabilities of the fluid. Design/methodology/approach: A stable high-density fracturing fluid (HDFF) was developed to cope with scorching good temperatures up to 350°F (177°C)as well as to reduce the surface treating pressure. The HDFF consists of NaBr heavy brine, CMHPG, clay stabilizers, and zirconium and borate crosslinkers. A linear gel fluid was prepared by combining NaBr brine with CMHPG before adding the additives. The resulting fluid was then tested using a high-pressure, high-temperature (HPHT) rheometer. Findings: The results showed that the performance of the HDFF was optimum in an alkaline environment between pH 10 to 12. The efficiency of zirconium and borate crosslinkers were optimum at 0.7 ppm and 1.5 ppt, respectively. Concentrations higher than these values are not only uneconomical but will cause the fluid to be overly crosslinked, consequently reducing efficiency. In actual field operation, this is disastrous when the fluid does not flow to the fracturing column but instead swirls around the drill string as the drill string rotates. On the other hand, a reduction of concentration below the optimum values can cause fluid instability at high temperature reservoirs. Research limitations/implications: The study was limited to using two different kinds of crosslinkers and various concentrations. Future studies can be conducted using other kinds of crosslinkers, as well as an investigation into the effects of varying temperatures, pressures, and pH on the HDFF using CMHPG. Practical implications: It can be concluded that HDFF using CMHPG as the base polymer can be a potential use in formulating fracturing fluids. Originality/value: Information on the rheological behaviour of HDFF using NaBr and CMHPG can provide a reference point for future scientists in developing a new formulation of fracturing fluid.

3

Experimental Study of Surface Roughness Effect on the Rheological Behavior of MR Fluid

Stępień Barbara, Horak Wojciech

Tribologia

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2022

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nr 4

73--83

EN

Magnetorheological (MR) fluids are classified as smart materials. They are non-homogeneous substances of complex composition and are characterised by complex rheological properties. In addition, the characteristics of their behaviour can be actively affected by the magnetic field, both in terms of its value and spatial orientation. This paper presents the results of shear stress measurements of a commercial magnetorheological fluid using a plate-plate type geometry with a modified working surface. The purpose of the study was to determine the effect of changing the roughness of the measuring plate on the obtained shear stress results. Controlled shear rate tests and Magneto Sweep measurements were carried out for three MR fluid layer heights. The tests were carried out at magnetic field induction in the range of 0 to 680 mT. The study showed that the measurement system's geometric parameters significantly affect the MR fluid's behaviour under test. It was shown that increasing the surface roughness can increase or decrease the measured value of shear stress depending on the test parameters.

PL

Ciecze magnetoreologiczne (MR) zaliczane są do grona materiałów inteligentnych. Są to substancje niejednorodne o złożonym składzie i charakteryzują się złożonymi właściwościami reologicznymi. Ponadto charakterystyki ich zachowania mogą być aktywnie kształtowane przez pole magnetyczne, zarówno ze względu na jego wartość, jak i orientację przestrzenną. W pracy przedstawiono wyniki pomiarów naprężenia stycznego komercyjnej cieczy MR z wykorzystaniem geometrii pomiarowej typu płytka–płytka o modyfikowanej powierzchni roboczej. Celem badań było określenie wpływu zmiany chropowatości płytki pomiarowej na uzyskiwane wyniki naprężeń ścinających. Przeprowadzono badania z kontrolowaną szybkością ścinania oraz pomiary typu Magneto Sweep dla trzech wysokości warstwy cieczy MR. Badania przeprowadzono przy indukcji pola magnetycznego w zakresie 0 do 680 mT. Badania wykazały, że parametry geometryczne układu pomiarowego istotnie wpływają na zachowanie się badanej cieczy MR. Wykazano, że w zależności od parametrów badania zwiększenie chropowatości powierzchni może powodować zwiększenie lub zmniejszenie rejestrowanej wartości naprężeń stycznych.

4

Pressure drops during the flow of solutions of cocamidopropyl betaine and cocamide DEA mixtures with the addition of ethylene glycol

Różańska Sylwia, Różański Jacek, Wagner Patrycja, Warmbier Ewelina

Polish Journal of Chemical Technology

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2022

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Vol. 24, nr 4

67--71

EN

The paper presents the results of experimental studies on pressure drops during the flow of cocamidopropyl betaine (CAPB) and DEA cocamide solutions with the addition of ethylene glycol. The degree of drag reduction during the flow of the CAPB/DEA aqueous solution and with the 10% addition of ethylene glycol was similar. A significant reduction in pressure drops was also observed at the 20% concentration of ethylene glycol. However, the increase in the concentration of ethylene glycol resulted in the reduction of flow resistance at higher temperatures. The resistance of the micellar microstructure of CAPB/DEA solutions to mechanical degradation depends strongly on the pH level. Significant changes in flow properties were observed when the initial pH was alkaline. The solution with initial pH close to neutral was stable over time, though reduced resistance to degradation with time was also observed.

5

Rheological behavior of sepiolite suspensions homogenized by ultra-turrax high-speed homogenizer

Tonkur Hatice, Can Muhammed Fatih, Sabah Eyüp

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 5

art. no. 153415

EN

The ability to disperse sepiolite suspensions is of great interest in various fields such as the production of cosmetics, pharmaceuticals, colors, etc., and in preparing the sample material for analytical purposes. In this study, the flow curves and time-dependent rheological behavior of sepiolite aqueous suspensions homogenized by Ultra-Turrax high-speed rotor-stator homogenizer were investigated under operating conditions. Forward and backward flow curves for homogenized sepiolite suspensions at different homogenization times and solid concentrations were plotted, and the amount of existing hysteresis loop was measured to determine the best conditions for the obtention of a suitable product having gel-forming properties for industrial and/or analytical applications. The results showed that the dispersed sepiolite suspensions exhibited a substantial increase in the viscosity values owing to gel formation, and thixotropic behavior that was rapidly improved by the increasing the solid content of suspension/ homogenization time, and their apparent viscosity decreased by the increasing the time of shearing, and flow characteristic was time-dependent. However, changing the distance between dispersing tool/bottom showed no favorable effect on preserving the rheological behavior of sepiolite suspensions, although the apparent viscosity decreased marginally due to increased distance between dispersing tool/bottom. Also, two time-dependent/independent models, namely the Power-law model and the Weltman model, were used to describe the thixotropy behavior, and different parameters of these models were analyzed. The Weltman model was found to be appropriate to fit the timedependency behavior of sepiolite suspensions and the most obtained value for model parameters A and B belonged to sepiolite suspension with 6 wt% at 25 min, which was considered as the optimized sample in the applied experiments, its final viscosity level increased from 0.82 to 12.55 Pas.

6

Effect of crystallinity and surface silanol groups on rheological properties of different sepiolites

Çınar Mustafa, Gülgönül Ilhan, Ozdemir Orhan, Çelik Mehmet S.

Physicochemical Problems of Mineral Processing

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2022

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Vol. 58, iss. 5

art. no. 153947

EN

In this study, differences in the rheological properties of three different types of brown sepiolites (K1, K2, and K3) along with one beige (B) sepiolite with different physicochemical properties were explained based on their crystallinity and level of surface silanol groups. Towards this aim, SEM images, XRD and chemical analyses, cation exchange capacity (CEC), and water absorption tests were conducted along with surface area measurements and time-dependent pH profiles. The pH profiles at 3% by wt. revealed that each sepiolite sample attained the equilibrium at different times. These differences showed a parallel behavior with the degree of crystallinity. While sepiolite with better crystallinity (K1) was rather slow in reaching the equilibrium pH, the sepiolites with poor crystallinity (B and K3) reached their equilibrium pH more quickly. The rheological studies conducted with different sepiolites at 3% solids concentration exhibited time-dependent flow of the Bingham plastic model and thixotropic. Differences observed in the rheological behavior of sepiolites were found to correlate with the fiber size, CEC, surface area, and water absorption. The results further indicated that sepiolites with low crystallinity or high level of surface silanol groups (K3 and B sepiolites) show the best rheological properties.

7

Improving the Quality of Clay Powders by Mechanoactivation

Bogoslavets Volodymyr, Voloshyn Yurii, Hrytsulyak Halyna, Yurych Lidiia

Journal of Ecological Engineering

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2022

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Vol. 23, nr 12

145--154

EN

The ability to effectively use mineral resources is the key to the sustainable development of industry in modern conditions of environmental protection. High-quality bentonites are rarely found in nature, so technologies for improving the quality of clay powders are quite relevant today. The article considers the possibility of improving the quality of clays obtained from candidate quarries for the purpose of further use as components of drilling fluids. The filtration and rheological characteristics of drilling fluids obtained on the basis of activated clay powder were also investigated by Benta Limited Liability Company.

8

Sztywność i podatność mostów z betonu

Machelski Czesław

Inżynieria i Budownictwo

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2022

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R. 78, nr 9-10

426--432

PL

W pracy sformułowano określenie sztywność mostu, stosowane w przypadku obciążeń doraźnych (krótkotrwałych) oraz podatność mostu przydatne do analiz długotrwałych zmian (reologicznych) w konstrukcji obiektu. Analizowano trzy ujęcia podatności na przykładzie mostów z betonu. Pierwsze dotyczyło deformacji doraźnej (krótkotrwałej). W drugim uwzględnia się fazę budowy i efekty reologiczne zachodzące w betonie. Trzecie ujęcie jest przydatne w sytuacji monitoringu obiektu. W pracy podano przykłady analiz obiektów z betonu.

EN

The paper defines the stiffness of the bridge, used in the case of a motion loads (short-term), and the flexibility of the bridge useful for the analysis of long-term (rheological) changes in the structure of the object. Three shots of flexibility were analyzed on the example of concrete bridges. The first concerned ad short-term deformity. The second takes into account the construction phase and rheological effects occurring in concrete. The third shot is useful in the situation of monitoring the object. The paper gives examples of analyses of concrete objects.

9

Monitoring przęseł mostowych wybudowanych metodą wspornikową

Machelski Czesław

Inżynieria i Budownictwo

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2022

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R. 78, nr 1-2

42--45

PL

Negatywną cechą mostów technologii betonowania wspornikowego są duże długotrwałe ugięcia jako wynik procesów reologicznych w betonie i stali sprężającej. W niniejszym artykule ugięcie jest reprezentowane jako funkcja czasu eksploatacji konstrukcji mostu, skalibrowana przez wyniki monitoringu. Analizy przedstawione w artykule zostaną wykorzystane do opracowania modeli reologicznych. W podsumowaniu podano funkcję pełzania.

EN

The negative feature ot the cantilever concreting technology bridges is a large long-term deflection, as a result of rheological processes in the concrete and in the pre-tensioning steel. In this paper the deflection is represented as a function of the service time ot the bridge structure, calibrated by the results of monitoring. Analyses presented in this paper will be used to develop rheological models. As the summary result of creep function.

10

10 lat eksploatacji i monitoringu mostu Rędzińskiego we Wrocławiu

Biliszczuk Jan, Teichgraeber Marco, Hawryszków Paweł

Inżynieria i Budownictwo

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2022

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R. 78, nr 1-2

14--18

PL

W sierpniu 2011 r. otwarto dla ruchu most Rędziński we Wrocławiu. Most został wyposażony w rozbudowany system monitorowania konstrukcji (SHM), wsparty dodatkowymi pomiarami geodezyjnymi. Obserwacje 10-letnie dostarczyły wielu interesujących danych dotyczących zachowania konstrukcji podczas jej eksploatacji. W pracy przedstawiono wybrane wyniki uzyskane z pomiarów SHM i geodezyjnych oraz oceniono wpływ zjawisk reologicznych na rozkład sił wewnętrznych i bezpieczeństwo konstrukcji.

EN

In August 2011, the concrete cable-stayed bridge with an atypical structure open to traffic - the Rędziński Bridge in Wrocław, Poland. The bridge has been equipped with an extensive structure monitoring system (SHM), supported by additional geodetic measurements. The 10-year observations provided a lot of interesting data on the behaviour of the structure during its operation. The paper presents selected results obtained from SHM and geodetic measurements, and assesses the influence of rheological phenomena on the distribution of internal forces and the safety of the structure.

11

Zawiesina nanorurek z surfaktantem, a właściwości reologiczne zapraw cementowych

Goldmann Eryk, Kostrzanowska-Siedlarz Aleksandra, Górski Marcin, Klemczak Barbara

Cement Wapno Beton

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2022

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R. 27, nr 4

275--284

PL

Dodatek nanomateriałów węglowych wpływa na szereg właściwości kompozytów cementowych. Pomimo wielu badań na temat właściwości stwardniałych materiałów cementowych, wpływ nanorurek węglowych [MWCNT, ang. Multiwall Carbon Nanotube] na właściwości reologiczne zapraw cementowych, wciąż nie jest wystarczająco opisany. Badania wykazały, że właściwości reologiczne zapraw z MWCNT, oznaczone Viskomatem NT, okazały się bardzo zależne od czasu sonikacji i ilości MWCNT. Wraz ze wzrostem czasu sonikacji zawiesiny z MWCNT i surfaktantem oraz wraz ze zmniejszeniem zawartości MWCNT płynność zaprawy jest większa, tym samym zmniejsza się zarówno granica płynięcia jak i lepkość plastyczna.

EN

The addition of carbon nanomaterials influences the variety of properties, of cementitious composites. Despite the multiple researches in the topic of properties of the hardened cement materials the influence of the Mutiwall Carbon Nanotubes [MWCNT] on rheological parameters of the cement mortars is not sufficiently described. Research shows that rheological properties of cement mortars with the MWCNTs, determined with the use of Viscometer NT, proved to be strongly dependent on the sonication time and amount of MWCNT, added. Increase of sonication time of MWCNT suspension with surfactant and decrease of amount of MWCNT caused increment in fluidity while yield stress parameter and plastic viscosity parameter decreased.

12

Wpływ mączki ze skorupek jaj kurzych i z wapienia, na właściwości reologiczne zaczynów cementowych

Grzeszczyk Stefania, Kaleta-Jurowska Alina, Jurowski Krystian

Cement Wapno Beton

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2022

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R. 27, nr 6

403--411

PL

Przedstawiono badania wpływu mączki, uzyskanej ze skorupek jaj kurzych oraz z wapienia, na właściwości reologiczne zaczynów cementowych. Mączki dodano do cementu portlandzkiego CEM I 42,5 R, w ilości 30%. Stwierdzono większe granice płynięcia i lepkości plastyczne dla zaczynów z cementów z dodatkiem mączki ze skorupek jaj kurzych, od zaczynów cementowych, z dodatkiem mączki z wapienia. Przyczyną jest wpływ budowy błonki jajka kurzego. Chłonąca wodę i pęczniejąca w zaczynie cementowym błonka, powoduje wzrost lepkości oraz zwiększenie tiksotropii w wyniku łączenia się cząstek, w porównaniu z klasycznym zaczynem oraz zaczynem z dodatkiem mączki z wapienia.

EN

The paper presents the effect of the powders obtained from eggshells and limestone on the rheological properties of cement pastes. Both powders were added to Portland cement CEM I 42.5 R, 30% by mass. The higher yield stress and plastic viscosity of the cement pastes prepared with the addition of eggshell powder, compared to the cement pastes made with limestone powder, were explained by the influence of the eggshell membrane and its chemical structure. The membrane, which absorbs water and expands in the cement paste, is causing an increase in rheological parameters. The membrane, which absorbs water and swells in the cement paste, causes an increase in viscosity and thixotropy compared to the neat cement slurry and slurry with limestone meal added as a result of particle bonding.

13

Evaluation of Repetitively Used Feedstock for Powder Injection Molding

Jang Jin Man

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 4

1511--1515

EN

This study investigates the effects of repetitive injection molding on the properties of feedstock using the AISI 4140 feedstock. The properties of feedstock are evaluated from the mixing homogeneity of powder and binder, rheological properties, and dimensional accuracy of parts sintered. The feedstock after the 1st injection molding shows a better homogeneity than as-received feedstock due to re-mixing effects between the screw and barrel during the injection molding process. As the number of recycling numbers increases, the homogeneity, viscosities ad shrinkage ratio of recycled feedstocks show slight differences with those of the as-received feedstock until the 6th molding injection. However, some rheological parameters like the moldability index sharply increased up to the 4th injection but shows a tendency to decrease thereafter.

14

Experiments and analysis of the limit stresses of a magnetorheological fluid

Horak Wojciech, Stępień Barbara, Sapiński Bogdan

Acta Mechanica et Automatica

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2022

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Vol. 16, no. 4

408--416

EN

This paper presents the results of a rheological test of a commercial magnetorheological (MR) fluid (MRF-132DG). The research includes the problem of measuring and interpreting limit stresses under conditions close to the magnetic saturation of the fluid. Four different limit stresses were determined, two related to the yield point and two related to the flow point. Methods for determining limit stresses, especially due to excitation conditions, were also analysed. The aim of this study is to determine the effect of selected parameters on the values of limit stresses of the selected MR fluid. An additional objective is to highlight the problems of defining and interpreting individual limit stresses in MR fluids, particularly in the context of selecting the values of these stresses for the purpose of modeling systems with MR fluids.

15

Method of Research on the Dynamic Viscosity of Magnetic Fluids at High Shear Rate

Szczęch Marcin, Horak Wojciech

Tribologia

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2021

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nr 1

53--63

EN

Magnetic fluids have an important position in the design of technical systems due to their unique properties. They are used primarily in mechanical energy dissipation systems, i.e. brakes and vibration dampers, as well as in the design of seals. In many applications, the magnetic fluid operates at high flow velocities through narrow slots. Therefore, there is a need to determine the rheological properties of this type of substance at high shear rates. Due to the high density of magnetic fluids and the associated occurrence of mass forces, as well as the requirements regarding the distribution of the magnetic field, the measurement of the viscosity of magnetic fluids at high shear rates is extremely difficult when conventional measuring systems are used. The paper presents a proposal for a new measuring system and a method to determine the viscosity of magnetic fluids at high shear rates, as well as the results of research on the possibility of using the presented structure in the case of ferrofluids.

PL

Ciecze magnetyczne ze względu na swoje unikatowe właściwości mają ugruntowaną pozycję w konstrukcji układów technicznych. Znalazły zastosowanie przede wszystkim w systemach dyssypacji energii mechanicznej, tj. hamulcach i amortyzatorach drgań, jak również w konstrukcji uszczelnień. W wielu aplikacjach ciecz magnetyczna pracuje w warunkach wysokich prędkości przepływu przez wąskie szczeliny. W związku z tym istnieje potrzeba wyznaczania właściwości reologicznych tego typu substancji przy wysokich szybkościach ścinania. Ze względu na znaczną gęstość cieczy magnetycznych i związane z tym występowanie sił masowych, jak również wymagania odnośnie do przestrzennego rozkładu pola magnetycznego pomiar lepkości cieczy magnetycznych w wysokich szybkościach ścinania w przypadku zastosowania konwencjonalnych układów pomiarowych jest istotnie utrudniony. W pracy przedstawiono propozycję nowego układu pomiarowego, metody pomiaru lepkości cieczy magnetycznych w wysokich szybkościach ścinania oraz wyniki badań dotyczących możliwości wykorzystania przedstawionej konstrukcji w przypadku ferrocieczy.

16

The effect of filler content on the viscosity of polymer composites

Markovičová Lenka, Zatkalíková Viera, Kojnoková Tatiana

Quality Production Improvement - QPI

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2021

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Vol. 3, Iss. 1

293--298

EN

Currently, research on materials containing magnetic magnetic particles give opportunity to the prepare and study of composites with interesting magnetic features. One possibility for producing such materials is the use of fillers with magnetic properties. The final properties of such composites depend mainly on characteristic polymer matrix. However, the addition of magnetic materials arose use of new technologies. Such builders include the magnetic ferrites. Metal hexaferrites represent well researched group of magnetic materials (Mallick, 1993). Their high values of magnetocrystalline anisotropy and saturation magnetization enable widespread application of these materials as permanent magnets. Low price and excellent chemical stability with suitable magnetic characteristics classified ferrites to one of the most important magnetic materials (Rigbi, 1988). The experimental material used was a composite formed by combining a polymer matrix (linear polyethylene HDPE), and the hard-magnetic strontium ferrite labeled FD 160S as a filler. Composites with different filler contents were prepared from the starting materials. The dependence of viscosity on the content of ferrite filler was determined by rheological measurements.

17

Effect of polyacrylic acid molar mass as a surface modifier on rheological properties of calcium carbonate suspensions

Selim Khaled Abdelaal, Farghaly Mohamed Galal, Abdallah Samah Saleh, Abdel-Khalek Mohamed Abdel-Dayem

Physicochemical Problems of Mineral Processing

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2021

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Vol. 57, iss. 4

18--26

EN

Suspensions of calcium carbonate are of a major concern in various fields, such as coating, painting and ceramics and their rheological properties are very important. The effect of polyacrylic acid (PAA) of different molecular mass as a surface modifier on the surface and rheological properties of the aqueous suspension of calcium carbonate was investigated. The effect of the volume fraction of particles and polymer concentration on the viscosity at lower shear rate was discussed. The flow behavior of the concentrated suspension in the presence of PAA can be explained by the difference of the repulsive force among particles, induced by the adsorbed polymer. The results showed that the dispersibility is more pronounced by the steric hindrance behavior rather than the electrostatic behavior.

18

Characteristics of physicochemical and rheological properties of chitosan hydrogels based on selected hydroxy acids

Zavyalova Olga, Gajewska Sandra, Dąbrowska-Wisłocka Dominika, Sionkowska Alina

Engineering of Biomaterials

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2021

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Vol. 24, no. 161

2--7

EN

Chitosan is a natural cationic polymer that dissolves in an acidic environment and forms gels. Its properties depend on the degree of deacetylation and molecular weight. It is a bioactive compound with antibacterial and film-forming properties that allow to increase the regenerative capacity of the skin. Moreover, it is biodegradable, biocompatible, non-toxic, and stable. In this research, chitosan was combined with mandelic and lactobionic acids which are characterized by biological activity and low toxicity. This combination not only has a positive effect on the chitosan solubility, but it also allows to obtain new biomaterials whose positive features of the base ingredients are enhanced by their synergistic effect. The obtained hydrogels were assessed regarding the interaction of chitosan and hydroxy acid molecules, and the stability of the resulting structures was examined. The research was performed by using rheological methods and IR spectroscopy. Chitosan hydrogels made with mandelic acid are characterized by higher viscosity values, as compared to hydrogels containing lactobionic acid. The samples of the obtained hydrogels stored for 7 days showed no signs of degradation and their viscosity values were constantly increasing, which proves the ongoing process of creating new bonds between hydroxy acid molecules and chitosan chains. After this time, the hydrogels with mandelic acid revealed higher viscosity values in comparison to hydrogels made with lactobionic acid. Based on the obtained IR spectra, the shifts of the characteristic chitosan bands as a result of interaction with the tested hydroxy acids were analyzed.

19

Targeted modification of the composition of polymer systems for industrial applications

Ondrušová Darina, Labaj Ivan, Pajtášová Mariana, Vršková Juliana, Božeková Slavomíra, Feriancová Andrea, Skalková Petra

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2021

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Vol. 69, nr 2

art. no. e136721

EN

The targeted modification of the material composition is a common procedure used to improve the parameters of the final products. This paper deals with the targeted modification of polymer systems composition using two various types of alternative fillers. The first type of alternative filler (SVD) has been obtained from energetics where it arises as a by-product of flue gas desulfurization. The second alternative filler used (KAL) is based on waste from glass production. The elastomeric systems designed for the production of car tires and solid wheels for transport systems were used in the role of modified polymer systems. Alternative fillers (SVD, KAL) have been applied as a substitution of commonly used fillers (carbon black, silica). The filler – elastomeric matrix interaction, rheology, cure characteristics, as well as hardness and rebound resilience of vulcanizates, which are important parameters for their industrial application, have been studied in the new prepared polymeric systems. The main output of the work is a new formulation of an elastomeric system for industrial applications with high rebound resilience and low rolling resistance, which is the subject of the international patent. The modification of composition using raw material substitution can also bring significant environmental and economic effects.

20

Creep damage model of rock mass under multi-level creep load based on spatio-temporal evolution of deformation modulus

Zhang Xing, Lin Hang, Wang Yixian, Zhao Yanlin

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

508--523

EN

To study the damage characteristics of rock mass under multi-level creep load, damage variable D was defined based on the spatio-temporal evolution characteristics of deformation modulus E, and the Kachanov damage theory is used to describe the damage evolution, then the damage evolution equation of the rock mass under multi-level creep load is obtained. Combining the damage evolution equation with the Lemaitre strain equivalence principle, the creep damage constitutive model of rock mass under multi-level creep load considering initial damage is obtained. By comparing the results of uniaxial and triaxial tests with the calculated values of the model, the rationality, reliability, application range of the model proposed in this paper is verified. According to the results of parameter inversion, obtain the relationship between damage, stress and time. Results show that time and stress are the important factors influencing the damage of rock mass under multi-level creep loading, the damage increases with time and stress level. However, the influence of time and stress on damage has a significant stress response characteristics: under low stress, the instantaneous damage Dis caused by the instantaneous stress loading is the main reason for the damage. With the increase of the load level, the main cause of the damage gradually changes from the instantaneous loading of the stress to the creep accumulation of the damage, and the greater the initial damage, the higher the time-dependent damage DiT proportion in the global damage.