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AZ9RBAYCAN KIMYA JURNALI № 4 2017
UDC 678-1:53-19; 532.135
STRENGTH AND RHEOLOGICAL PROPERTIES OF THREE-COMPONENT POLYMER BLENDS BASED ON POLYOLEFINS
N.T.Kakhramanov, Z.N.Huseynova, N.B.Arzumanova, U.M.Mammadli
Institute of Polymer Materials, NAS of Azerbaijan [email protected] Received 12.12.2016
The influence of the composition and concentration of polymers and structurants in three-component polymer blends on breaking stress, elongation of the composite material has been considered. In evaluating rheological properties of polymer blends are investigated the dependence of viscosity and shear rate on shear stress. The foundational results of the research and conclusions regarding the rheological characteristics of complex polymer blends are offered.
Keywords: breaking stress, elongation, shear rate, shear stress, viscosity, spherulites.
Introduction
The polymers are blended to obtain polymer materials with new improved properties and to expand the assortment of polymer materials. Due to mixing it is possible to improve most diverse properties of polymers: mechanical, rheological, thermophysical, friction, diffusion, and others. Blending of polymers does not yet have such broad opportunities to change the properties of the polymers like the chemical synthesis, but the blending of polymers is a simpler way to create the new polymer materials. As polymer blends they understand systems obtained by mixing two or more of polymers under conditions in which the mixing components can be irreversibly deformed. These conditions include the mixing at temperatures above the glass transition temperature or melting temperature, mixing in the solution with subsequent removal of solvent, mixing of oligomers with subsequent increase of their molecular mass. For the purposeful creation of new polymer materials with desired properties by blending of polymers it is necessary to know regularities that bind the composition, mixing conditions, structure and properties of polymer blends [1-5].
For a long time rheology was considered mainly as a theoretical basis of polymer processing. However, conducted studies in this direction showed that the rheological characteristics, particularly dependence of the shear rate on melt viscosity and the temperature dependence of viscosity in Arrhenius coordinates give complete picture of the processes occurring in the material cylinder of the mixer - of the extrusion machine
[6, 7]. Of particular interest are the studies aimed at investigating the influence of mixing process on the compatibility of three-component mixture on their rheological characteristics of the melt flow. It should be noted that very fragmentary information was available for rheological studies of multicomponent mixtures, which do not allow organizing them into a single theory [8]. Many authors relate the situation not only with the difference in the structure and behavior of polymer blends melt-in mode, but also their level of technological compatibility [9]. The studies on the influence of the structurants on the compatibility of polymer blends and on their rheology are very limited.
Thus, it becomes obvious that the problems associated with the establishment of the influence of the structural features of polymer blends on their technological properties are not given sufficient attention in the literature. The absence of a systematic approach to conducting research in this area does not allow for a comprehensive analysis of the mechanism of formation and orientation of the aggregates in the melt of polymer-polymer compositions.
In connection with this, the aim of the research is a detailed study of the rheological properties of polymer blends based on processes occurring in the viscous-flow state.
Experimental part
As an object of research there were used a low density polyethylene (LDPE), polypropylene (PP) and ethylene-propylene rubber (EPDM-40):
STRENGTH AND RHEOLOGICAL PROPERTIES OF THREE-COMPONENT
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LDPE of 10604-007 grade melt flow index (MFI) is equal to 0.72 g/10 min, breaking stress (op) 14.3 MPa, elongation 525%;
PP 21030 grade MFI is equal to 3.5 g/10 min, breaking stress 31.0 MPa, elongation 440%;
EPDM-40 - ethylene-propylene synthetic rubber.
Alizarin C14H8O4 - 1,2-dihydroxy anthra-quinone, colorant - red crystals with molecular mass of 240.2, melting temperature 562 K. The structural formula of alizarin is following:
Polymer compositions were prepared by mechanical and chemical modification (hot rolling) at temperature of 150-1550C and rolling time 10-15 min.
For carrying out the physico-mechanical tests the polymer compositions were compressed at 2000C. Of them samples were cut to determine breaking stress and elongation of the polymer compositions. Breaking stress and elongation were determined in accordance with the GOST 11262-80 (State Standard).
The melt indexes of the composites were determined on IIRT device at temperature of 1900C and load of 5 kg.
Rheological studies of polymer materials were carried out on MELT FLOW TESTER, CEAST MF50 (INSTRON, Italy) in the temperature range of 190-2500C and in the range of loads - 2.16-21.6 kg.
Results and discussion
Before the beginning to study the rheological properties of polymer composite materials, it would be proper to consider first the possible options of the occurrence in their structural formations, a schematic illustration of which is shown in Figure 1. According to the data shown in this figure, the process of forming supramolecular structure in mixtures containing two crystallizing polymer components (LDPE and PP) is there generally formed matrix structure. Such structure differs in that each crystallizing component in the cooling
process independently of each other forms its own spherulite formation. That is, PP macro-chains may not be incorporated into the crystalline phase of LDPE and vice versa. It is explained by the fact that the mechanism of crystallization of PP and PE macromolecules from the melt is different for each of them. Furthermore, it should be taken into account that the temperature beginning crystallization of PP makes up 1450C, while for LDPE it is 95-970C. From this it follows that in the cooling process of the polymer blend at the beginning polypropylene component is crystallized and at 500C below begins the crystallization of polyethylene component. Introduction of an amorphous component (EPDM) into the composition of the mixture reduces the microheterogeneity and degree of crystallinity of the whole composition, providing, thereby, essential influence on the process of changing its crystallization mechanism. For example, during the growth of spherulitic structures, the latter contributes to ousting of the amorphous component in the interfacial region (Figure1, I). As a rule, amor-phization of interfacial area leads to its loosening, lowering the sample density, blocking motility of feedthrough macrochains and, as will be demonstrated below, the comparative deterioration of elongation.
The introduction of alizarin into the polymer mixture as structurant component leads to the formation of additional "heterogeneous" crystallization nuclei in polymer matrix, which ultimately contribute to the formation of fine spherulitic supramolecular structures (Figure 1, II). The latter circumstance, according to the data in Table 1, has a positive effect on improving the physicomechanical properties of polymer blends.
By analyzing the data cited in Table 1, it is possible to establish that the introduction of synthetic rubber into the composition leads to the expected lowering of breaking stress, elongation, and MFI of samples. However, with increasing concentration of alizarin in the composition of polymer blend there is expected tendency to increasing the above stated properties. These data are in good agreement with our ideas, illustrated in Figure 1.
m
Fig. 1. Schematic illustration of the formation processes of structures in polymer blends in the solid (I and II) and viscous (III and IV) states.
IV
Influence of the ratio of components on physico-mechanical properties of polymer blends
Samples Composition formulation, weight parts Breaking stress, MPa Elongation, % Melt flow index, g/10 min
1 100 PE+15 PP 15.3 360 2.91
2 100 PE+15 PP+20 EPDM 12.4 260 1.52
3 100 PE+15 PP+40 EPDM 9.5 130 1.02
4 100 PE+15 PP+40 EPDM+0.3 alizarin 11.5 460 1.56
5 100 PE+15 PP+40 EPDM+0.5 alizarin 12.0 500 1.83
6 100 PE+15 PP+40 EPDM+0.7 alizarin 12.2 500 2.45
7 100 PE+15 PP+40 EPDM+1.0 alizarin 12.9 500 2.94
I
II
After being identified the main criteria for predetermining the structural organization of three-component polymer blends, it was of interest to begin studing melt flow characteristics of the composite materials. In addition, for comparative analysis as an object of research have been were used samples 3 and 7.
Figures 2 and 3 show the flow curves of the original polymer blend (sample 3) and their
IgY 2.5 -
2 ■
1.5 -
1 -
modified by alizarin compositions (sample 7). By comparing the curves in these figures can be established that in taking temperature interval (190-2500C) the dependence of the shear rate on shear stress varies according to certain regularities. As seen in Figure 2, at the temperature 190-23 00C flow curves change their straightness at the shear stress equal to 4.2 MPa or higher.
lg Y 2.5 -
2 -1.5 -
0.5 -
1
4 4.3 5 lgr 4 4.5 5 igx
Fig. 2. Flow curve of the PE+PP+ Fig. 3. Flow curve of the PE+PP+
+EPDM (example 3) at: 1 - 250, +EPDM+alizarin (example 6) at: 1 -
2 - 230, 3 - 210, 4 - 1900C. 250, 2 - 230, 3 - 210, 4 - 1900C .
STRENGTH AND RHEOLOGICAL PR
Only at the temperature 2500C flow curve has a straightforward character. To answer this question it will be correctly to turn to the theory of Frenkel-Eyring, according to which in a uniaxial direction polymer flow is the aggregates flow, spontaneously formed and decaying under the influence of temperature and shear stress [6, 7]. Under conditions of steady flow thermofloating theory of decay and recovery of aggregates is in equilibrium. In case of violation of this equilibrium in the curve of dependence of shear rate on shear stress appear breaks. The fact of existence of these breaks at relatively high shear stresses confirms the ability of the macromolecules of mixed polymers to preserve the structure aggregated in the melt (Figure 1, III and IV). Moreover, it is not excluded that the break in the flow curves means an approximation to the area of the lower Newtonian viscosity of the melt. In this area viscosity is independent of the applied shear stress, i.e. the rate of decomposition and recovery of aggregated structures are in equilibrium.
1 1,5 2 2,5 lgy
Fig. 4. Dependence of viscosity vs. shear rate in logarithmic coordinates for the samples PE+PP+EPDM at different temperatures: 1 -190, 2 - 210, 3 - 230, 4 - 2500C.
By comparing the curves for the dependence in Figure 5 can be established that over the entire temperature range (190-2500C) on the curves of dependence of viscosity on shear rate breaks occur. Unlike the previous figure
ERTIES OF THREE-COMPONENT..........25
Analysis of the data in Figure 3 shows that in the entire range of temperatures and shear stresses on the flow curves break occurs confirming the ability of heterogeneous structural aggregates in the melt at high shear stresses to equalize rates of decay and recovery, characteristic for the region lower Newtonian region.
To confirm our inferences about the processes procceding in the melt of the polymer blend, let us turn to dependence of viscosity on shear rate in logarithmic coordinates. Figures 4 and 5 show the dependence of the viscosity on shear rate for the original polymer blend PE+PP+EPDM and its modified compositions with alizarin. By analyzing the data in this figure it can be established that at relatively high shear rates the curves are close to the line parallel to the x-axis. This regularity is particularly evident in the temperature range of 190-2300C. At high temperature (25 00C) thermofloating decay of aggregated structures prevails over the recovery, which affects by the existence almost linear dependence of viscosity on shear rate.
Fig. 5. Dependence of viscosity vs. shear rate in logarithmic coordinates for the samples PE+PP+EPDM+alizarin at different temperatures: 1 - 190, 2 - 210, 3 -230, 4 - 2500C.
these breaks in curves are most clearly manifested at relatively high temperatures. The latter circumstance is clearly indicates that the heterogeneous aggregation centers formed by alizarin particles in the melt, are prone to the
formation of more stable structures. Ultimately, this is manifested in the preservation of stable equilibrium rates of decay and recovery of aggregated structures in the melt of the modified composite material.
Thus, it becomes obvious that the study of the rheological characteristics of the flow of multicomponent polymer blends in a wide range of temperatures and shear stresses allows competently to approach to the interpretation of physicochemical processes occurring in the melt and thus scientifically to substantiate the technological features of their processing in various types of construction products.
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POLЮLEFiNLЭR ЭSASINDA UCKOMPONENTLi POLiMER QARI§IQLARININ MбHKЭMLiK
VЭ REOLOJi XASSЭLЭRl
N.T.Qэhrэmanov, Z.N.Hйseynova, N.B.Arzumanova, U.M.MэmmэdИ
и^котропепШ роИтег qaп§lglnda ро11тег1эг1п tэrkibinin уэ qatl1lglmn уэ qurulu§эmэlэgэtiricinin kompozisiya таГейаЬтп dagldlcl gэrgin1iyinэ, nisbi uzanmasшa tэsiri nэzэrdэn ke5iri1mi§dir. Po1imer qarl§lq1arlmn гео1о_д xassэ1эrinin qiymэt1эndiri1mэsi zamam бz1u1uyun уэ yerdэyi§mэ surэtinin yerdэyi§mэ gэrgin1iyindэn asl1l1lgl tэdqiq edi1mi§dir. Murэkkэb po1imer qarl§lq1arln reo1oji xйsusiyyэt1эrinэ dair tэdqiqatln пэйсэ1эп уэ xus1asэsi уеиМ^и-.
Адаг sдzlэr: йа^йт gэrginlik ,nisbi uzanma, yerdэyщmэ yerdэyщmэ gэrginliyi, 6zluluk, sferoШlэr.
ПРОЧНОСТНЫЕ И РЕОЛОГИЧЕСКИЕ СВОЙСТВА ТРЕХКОМПОНЕНТНЫХ ПОЛИМЕРНЫХ
СМЕСЕЙ НА ОСНОВЕ ПОЛИОЛЕФИНОВ
Н.Т.Кахраманов, З.Н.Гусейнова, Н.Б.Арзуманова, У.М.Мамедли
Рассмотрено влияние состава и концентраций полимеров и структурообразователя в трёхкомпонентной полимерной смеси на разрушающее напряжение, относительное удлинение композиционного материала. При оценке реологических свойств полимерных смесей исследовали зависимость вязкости и скорости сдвига от напряжения сдвига. Приводятся основополагающие результаты исследования и выводы относительно реологических характеристик сложных полимерных смесей.
Ключевые слова: разрушающее напряжение, относительное удлинение, скорость сдвига, напряжение сдвига, вязкость, сферолиты.
