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40 AZERBAIJAN CHEMICAL JOURNAL № 2 2022 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 678.01:532.135
RHEOLOGICAL PROPERTIES OF METAL-FILLED SYSTEMS BASED ON HIGH-DENSITY POLYETHYLENE AND ALUMINUM
1Kh.V.Allahverdiyeva, 1N.T.Kakhramanov, 2M.I.Abdullin, 3G.S.Martynova,
1D.R.Nurullayeva
institute of Polymer Materials, NAS of Azerbaijan
2Bashkir State University Institute Geology and Geophysics, NAS of Azerbaijan
najaf1946@rambler.ru
Received 20.09.2021 Accepted 25.10.2021
The paper considers the fundamental principles of the study of the rheological features of the melt flow of the initial high-density polyethylene and its filled compositions with aluminum powder, depending on the filler concentration, temperature and shear rate. To improve the compatibility of metal-polymer systems, a compatibilizer has been used, which is a graft copolymer of high-density polyethylene containing 5.6 wt. % maleic anhydride. The flow curves and the dependence of the effective viscosity on the shear rate of the initial high-density polyethylene and composites containing 0.5 wt. % and 5.0 wt. % aluminum powder has been determined. The regularity of the change in the effective viscosity of the melt on the temperature in Arrhenius coordinates has been established. Based on the curves obtained, the values of the activation energy of the viscous flow have been determined. A temperature-invariant characteristic of the composites viscosity properties has been drawn, which makes it possible to predict the change in the value of this indicator at high shear rates, close to their processing by extrusion and injection molding. The developed materials have been tested at the METAK LLC enterprise in Azerbaijan.
Keywords: viscosity, shear rate, shear stress, composites, polymer melt.
doi.org/10.32737/0005-2531-2022-2-40-46
In spite of the fact that the total number of polymers synthesized in the chemical industry practically did not change, in recent years the area of application of the polymer materials in such industries as machine construction, agriculture, shipbuilding, aircraft construction, military and space technology considerably has expanded. This has been stipulated by the fact that the various methods of chemical and mechanical-chemical modification, favoring the purposeful improvement of the complex physical-mechanical properties of polymers produced in the industry are being undertaken [1-3]. The most widely used method of polymers modification is the introduction of various types of mineral and metallic fillers directly in the process of their processing by extrusion or pressure casting. In this case, it is possible to obtain the composites, which essentially exceed the initial polymers [4]. At the same time, it should be noted that in the literature the investigations on the rheological characteristics of the polymer composites are very limited, although, the de-
tailed analysis of this problem allows to approach the prediction of their processing ability with greater accuracy [5, 6].
In this connection, in this work, we have paid main attention to a detailed study of the rheological peculiarities of the melt flow of metal-filled polymer systems, where the high-density polyethylene and aluminum powder were used as the main object of investigation.
Experimental part
The high-density polyethylene (HDPE) used as a polymer matrix has the following properties breaking stress - 31.3 MPa, the flex-ural modulus of elasticity - 753 MPa, specific elongation - 435%, density - 946 kg/m , melt flow index (MFI) is equal to 1.16 g/10min., heat resistance - 1190C, melting point - 1310C, degree of crystallinity - 80%.
Compatibilizer is a high-density polyethylene HDPE functionalized with maleic anhydride (MA). The degree of vaccination of MA contained in HDPE is 5.6% mass.
With the aim of modification of the HDPE properties, a compatibilizer was first introduced into HDPE the composition on hot rollers at 1700C, and then the fine-dispersed aluminum particles with a size of 1.0-2.0 mcm were added in parts to the molten polymer mixture. The quantity of aluminum powder in the composition of HDPE was varied within 0.5, 1.0, 5.0, 10, 20, 30 % mass.
The size of aluminum particles was determined on the device of model STA PT1600 Linseiz, Germany.
The rheological investigations were carried out on the (INSTRON, Italy) rheometer on the MELT FLOW TESTER, CEAST MF50 device in the temperature range of 170-2300C and at a load of 2.16-21.6 kg.
Results and discussion
It was known that during the polymers processing and at the high shear stresses, the melt deformation, accompanied by structural conversions and changes in the rheological characteristics of polymers occurs. The study of the rheological properties of the polymer materials at various temperatures and shear stresses enables to use of purposeful scientifically-based approaches and methods of estimation of the optimal technological regimes of their processing [7].
Earlier, in work [8], we have shown that the introduction of aluminum powder into the HDPE composition favors the essential improvement of strength indices and resistance to delamination of the polymer coatings from the aluminum surface. The adhesive strength is largely determined by the microrheological processes occurring in the polymer-substrate contact zone. Based on this, it was interesting to study the rheological peculiarities of the composite melt flow depending on the value of the shear stress, temperature and filler concentration. With the aim of improvement of the compatibility of the mixed components of the mixture, 5.0% of the mass of the compatibilizer, being HDPE graft copolymer with maleic anhydride, was introduced into the composition of the filled composite. It was important to elucidate the role of the compatibilizer in a change
of the composite melt flow based on HDPE+aluminum powder. It should be noted that the influence of filler is determined by a variety of such factors like the shape and size of the particles, the interaction between the filler particles and the macrochains of the polymer base, the filler quantity and the technological peculiarities of the filler introduction into the polymer matrix. During the introduction of fillers into the polymer at the interface of two phases between macrochains and filler particles, an adsorption interaction is possible. This interaction becomes stronger with the growth of the contact surface of the polymer with the filler, i.e., with a decrease in the size of the filler particles its surface grows correspondingly. The strong or weak adsorption interaction at the interface of phases is largely determined by the polymer and the filler nature depending on the properties of the filler surface [7, 8].
J, g /10 min
2 ■?
30C,wt%Al
Fig.1. Influence of the concentration of aluminum powder on MFI of composites on the basis of HDPE (1) and HDPE+5.0% mass of PEMA (2).
Let us preliminarily consider the dependence of the melt flow index (MFI) on the concentration of aluminum powder in the HDPE composition and the compatibilized HDPE. The filler concentration was varied in the range of 0.5-30% mass. The analysis of the curves in this figure showed that the introduction of 0.51.0% mass aluminum powder favors a sharp increase of the MFI samples based on the initial and modified HDPE. A further increase in the
concentration of aluminum powder leads to a natural decrease in the melt flow. Noticeable growth of the MFI composites containing a minimum quantity of aluminum powder (0.51.0% mass) indicates the appearance of heterogeneous nucleation centers with a special form of the macrochains stacking on the surface of the filler particles. The latter circumstance has a favorable effect on the increase of the melt flow. An introduction of a compatibilizer in a quantity of 5.0% mass retains the general regularity of changes in the MFI dependence on the filler concentration.
The difference has appeared only in the fact that independently of the aluminum powder concentration the compatibilized samples are characterized by relatively high values of MFI. This has been stipulated by the fact that the com-patibilizer itself has a relatively high MFI value equal to 13.4 g/10 min, the introduction of which favors an increase of the composites melt flow.
Figure 2 (a,b,c) shows the flow curves of the initial HDPE (a) and its composites with 0.5% mass and 5.0% mass of aluminum powders (b,c). A comparative analysis of the curves in this figure shows that if for the initial HDPE at the minimum shear stress, a curvature of the curves as they approach the region of the highest Newtonian viscosity is observed, then for composites such sharp changes of the flow curves are
c
very insignificant (b, c). This circumstance is interpreted by the fact that in infilled composites, along with homogeneous ones, the heterogeneous nucleation centers are formed as a result of the orientation of macrochains on the developed surface of aluminum particles. The existence of heterogeneous crystallization centers allows asserting the "structural flow" of composites in the uniaxial direction. The structural flow means the flow of heterogeneous nucleation centers in the composite melt [9]. Attention should be paid to the fact that the 0.5% mass composites have some growth of the shear rate in comparison with the initial HDPE. With the introduction of 5.0% mass aluminum powder, the shear rate of the composite melt decreases again. There is reason to assume that a part of the filler particles participates in the formation of the heterogeneous nucleation centers, and other parts, while redistributing in the polymer volume, creates certain steric difficulties for the melt flow in the uniaxial direction.
The study of the dependence of the effective viscosity on the shear rate allows obtaining additional information about the processes occurring in the polymer matrix melt.
Figure 3 (a,b,c) shows the dependence of the effective viscosity on the shear rate in logarithmic coordinates.
JO 4,5 ,gT
b
Fig.2. Flow curves of the initial HDPE+5.0 mass % of PEMA (a) and their filled with 0.5 mass % (b) and 5.0 mass % (c) composites with Al content at various temperatures: 1 -170, 2 - 190 3 - 210, 4 - 2300C.
It can be seen from the comparative analysis of the curves in this figure that the temperature, the filler concentration and the shear stress have a noticeable effect on the change of the dependence of the effective viscosity on the shear rate. From this figure, for the initial HDPE, this dependence is nonlinear under almost all temperature conditions (Figure 3, a). At the same time, the introduction of aluminum powder in a quantity of 0.5% mass contributes to the formation of a linear regularity in the change of the effective viscosity with the shear rate (Figure 3,b). This composite is characterized by some disturbance of the linear dependence only at 2300C, especially at high shear rates. This circumstance is very important, since it allows to assert that indeed, with the introduction of 0.5% mass aluminum powder, the heterogeneous nucleation centers favoring a uniform change in the effective viscosity of the composite melt with an increase of the shear rate are formed [9, 10]. It is characteristic that during introduction of 5.0% mass aluminum powder, the linear dependence of the viscosity on the shear rate is mainly retained. Only at low shear rates the linearity is disturbed.
The investigation of the dependence of the effective viscosity on the temperature in Ar-rhenius coordinates is one of the informative methods of analysis of the rheological characteristics of the polymer materials. From Figure 4 (a,b,c), the dependence of the effective viscosity on the reverse temperature has a certain character. And in this case, it can be established that the linear regularity of the effective viscosity dependent on the reverse temperature is advantageously retained in composites with 0.5% mass content of aluminum powder. It can be asserted from the comparative analysis of the data given in these figures that in non-linear areas, one can approve the "apparent" or "point" activation energy of a viscous flow. So, for example, if the apparent activation energy for the initial HDPE is 50-72 kJ/mol, for samples with 0.5% mass content of filler is 34-61 kJ/mol, then for composites with 5.0% mass content of aluminum powder, the value of this index is varied in the range of 63-95 kJ/mol. Analyzing the obtained data, it can be established that relatively low values of the activation energy are appeared in composites with 0.5% mass content of filler.
ig>i
5,0-
3,(1-1->-1-1-1-1-r—*
-1,5 -1 -0,5 0 0,5 1 1,5 Igy
a
'si
-1,5 -1 -0,5 0 0,5 1 1,5 lgy
c
ign
b
Fig.3. Dependence of the effective viscosity on the shear rate in logarithmic coordinates for the initial HDPE+5.0% mass of PEMA (a) and their filled composites with 0.5% mass (b) and 5.0% mass (c) content of aluminum powder at various temperatures: 1 -170, 2 - 190, 3 - 210, 4 - 2300C.
lg<l
c
Based on this, it can be concluded that the formation of nucleation centers in a melt favors the uniform dispersion of filler particles in the polymer matrix and the regulation of the structural flow process in the uniaxial direction [9, 11, 12].
One of the interesting directions in the investigation of polymer rheology from a practical point of view is the study of the temperature-invariant characteristics of the melt viscosity. The existence of a dependence, invariant in relation to the temperature allows estimating the dynamic state of the polymer material melt under the conditions of the established flow regime. The analytical approach to the estimation of rheological dependences gives reason for the determination of the melt viscosity at high shear rates close to the processing regime on the casting aggregate and extruder. In other words, as a result of carrying out a minimum number of experiments, it is possible to obtain sufficiently complete information about the rheological peculiarities of the polymer materials flow. Predicting the region of high shear rates, it is possible to obtain data on the viscosity of the pol-
Fig.4. Dependence of the effective viscosity on the reverse temperature in Arrhenius coordinates for the initial HDPE+5.0 mass % of PEMA (a) and their filled composites with 0.5 mass % (b) and 5.0 mass % (c) with the content of aluminum powder at various shear stresses (lgx): 1 - 3.55; 2 - 3.9; 3 - 4.2; 4 - 4.5.
ymer material close to the real conditions of polymer processing [7, 13-14].
M Igyn,
Fig.5. Generalized temperature-invariant characteristic of viscous properties of the initial composition of HDPE+5.0% mass of PEMA and their filled compositions with Al.
So, for example, in Figure 5 the results of the investigation of the temperature-invariant characteristics of the viscous properties of HDPE and its composites are presented. The presented function does not depend on temperature, and therefore, this dependence is presented as temperature-invariant. Analyzing the curves in this figure, it can be established that with an
increase of the presented shear rate yno, a natural decrease of the presented viscosity nv/no is observed. The ratio nv/no characterizes the degree of deviation of the melt viscosity from the highest Newtonian viscosity. According to the obtained data, the temperature-invariant characteristic of the composite melt once again indicates the qualitatively same nature of the occurrence and destruction of associates in the viscous state.
Thus, on the basis of the above-mentioned, it can be stated that the introduction of a metallic component into HDPE composition -aluminum powder with a particle size of 1-2 mc favors a considerable change in the rheolog-ical peculiarities of composites. With the aim of improvement of the compatibility of the mixed components, a graft copolymer of HDPE with maleic anhydride was used as a compatibilizer. The rheological measurements were carried out in the temperature range of 170-2300C. In the process of study of the rheology of composites, the modern theoretical approaches for interpretation of their melt flow and the mechanism of uniaxial deformation of the metal-polymer systems in a viscous-flow state were used. In a wide temperature range, the influence of shear stress and filler concentration on flow curves, the dependence of viscosity on the shear rate and the reverse temperature in Arrhenius coordinates with the subsequent estimation of the apparent activation energy of the viscous flow has been considered. A universal temperature-invariant characteristic of the viscous properties of HDPE and its filled composites has been considered. The developed metal-polymer composite passed the industrial tests at the plastic processing enterprise "METAK LLC" Azerbaijan.
Conclusion
The flow curves and the dependence of the effective viscosity of the melt on the shear rate in the range of 170-230°C for the initial HDPE and its composites with 0.5 and 5.0% mass content of fine-dispersed aluminum have been investigated.
The dependence of the effective viscosity on the reverse temperature has been drawn in
Arrhenius coordinates. The apparent activation energy of the viscous flow of filled composites has been determined.
A temperature-invariant characteristic of the viscous properties of HDPE and its composites allowing to predict the technological regime of the polymer processing at high shear rates has been drawn.
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YÜKSOK SIXLIQLI POLiETiLEN VO ALÜMiNiUM OSASLI METALLA DOLDURULMU§ SiSTEMLORiN REOLOJi XÜSUSiYYOTLORi
X.V.Allahverdiyeva, N.T.Qahramanov, M.i.Abdullin, Q.S.Martinova, D.R.Nurullayeva
Maqalada ilkin yüksak sixliqli polietilenin va onun alüminium tozu ila doldurulmu§ kompozisiyalarinin arintisinin axininin reoloji xüsusiyyatlarinin tadqiqinin asas prinsiplari nazardan kegirilmi§dir. Metal-polimer sistemlarinin uygun-lugunu yax§ila§dirmaq ügün 5.6 kütla % malein anhidridi tarkibli yüksak sixliqli polietilen calaq birga polimeri kompat-ibilizator olaraq istifada edilmi§dir. ilkin yüksak sixliqli polietilenin va 0.5 kütla % va 5.0 kütla % alüminium tozu tarkibli kompozitlarin axin ayrilari, effektiv özlülüyün yerdayi§ma süratindan asililiqlari müayyan edilmi§dir. Arrenius koordinatlarinda arintinin effektiv özlülüyünün temperaturdan asili olaraq dayi§masinin qanunauygunlugu müayyan edilmi§dir. Alinan ayrilar asasinda özlü axinin aktivla§ma enerjisinin qiymati müayyan olunmu§dur. Kompozitlarin ekstruziya va tazyiq altinda tökma üsullari ila emalina yaxin yüksak yerdayi§ma süratinda özlülük göstaricinin qiymatinin dayi§masini proqnozla§dirmaga imkan veran özlülük xüsusiyyatlarinin temperatur-invariant asililigi qurulmu§dur.
Agar sözlar: özlülük, yerdsyi§ms sürati, yerd3yi§m3 gsrginliyi, kompozitbr, polimer arintisi.
РЕОЛОГИЧЕСКИЕ СВОЙСТВА МЕТАЛЛОНАПОЛНЕННЫХ СИСТЕМ НА ОСНОВЕ ПОЛИЭТИЛЕНА ВЫСОКОЙ ПЛОТНОСТИ И АЛЮМИНИЯ
Х.В.Аллахвердиева, Н.Т.Кахраманов, М.И.Абдуллин, Г.С.Мартынова, Д.Р.Нуруллаева
В работе рассмотрены основополагающие принципы исследования реологических особенностей течения расплава исходного полиэтилена высокой плотности и его наполненных композиций с алюминиевой пудрой Для улучшения совместимости металлополимерных систем использовали компатибилизатор, представляющий собой графтсополимер полиэтилена высокой плотности с 5.6 масс. % содержанием малеинового ангидрида. Были определены кривые течения, зависимость эффективной вязкости от скорости сдвига исходного полиэтилена высокой плотности и композитов с 0.5 и 5.0 масс. % содержанием алюминиевой пудры. Установлена закономерность изменения эффективной вязкости расплава от температуры в Аррениусовских координатах. На основании полученных кривых определены значения энергии активации вязкого течения. Построена температурно-инвариантная характеристика вязкостных свойств композитов, позволяющая прогнозировать изменение величины этого показателя при высоких скоростях сдвига, близких к их переработке методами экструзии и литья под давлением.
Ключевые слова: вязкость, скорость сдвига, напряжение сдвига, композиты, расплав полимера.
