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AZ9RBAYCAN KIMYA JURNALI № 1 2018
53
UDC 532.135
RHEOLOGICAL CHARACTERISTICS OF NANOCOMPOSITES ON THE BASIS OF POLYPROPYLENE AND CLAY
G.Sh.Gasimova, N.T.Kakhramanov, N.B.Arzumanova, I.A.Ismailov, U.M.Mamedli, A.A.Gasanova, E.G.Iskandarova, Z.M.Orudzheva
Institute of Polymer Materials, NAS of Azerbaijan
ipoma@science.az
gulnara.qasimova.68@ mail.ru
Received 19.10.2017
Nanocomposites on the basis of clay and polypropylene have been prepared and their rheological properties have been studied. The results of investigation of influence of shift stress and temperature on flow rate, effective melt viscosity of nanocomposites and activation energy of viscous flow are presented. It has been shown that a use of natural mineral - clay as a filler favors essential improvement of fluidity of nanocomposites on the basis of polypropylene.
Keywords: polypropylene, rheology, nanocomposite, viscosity, fluidity.
On improvement of technique and technology of the industrial enterprises in the field of mechanical engineering, shipbuilding, automobile industry, military equipment, military and space equipment, etc., the more rigid requirements began to be made to quality of polymer materials. With the aim of improvement of quality of the polymer materials there are used the various methods of modification synthesized in the industry of polymers. Such large-tonnage polymers as polyolefins, which along with good physico-mechanical properties are most receptive to various methods of modification, attract the most interest. One of such effective methods of improving quality of the polyolefins are the introduction of mineral fillers by most simple and accessible mechanico-chemical method of modification immediately in melt of material cylinder of extruder. Now the scientists began to pay much attention to the investigations directed to the development of nanocomposites possessing unique combination of structure and properties. In this, the very great importance is given to the study of rheo-logical characteristics of nanocomposites, since this index determines the choice of the optimal conditions of their processing into various types of constructional products [1-3].
In this connection, the purpose of this work is the study of influence of concentration of filler, temperature and shift stress on basic rheo-logical characteristics of nanocomposite materials on the basis of clay and polypropylene.
Experimental
The polypropylene (PP) with the following physico-mechanical properties: breaking stress - 31.4 MPa, specific elongation - 185%, MFI = 3.8 g/10 min was used as an object of the investigation.
The thermoplastic block-copolymer of ethylene with propylene and mineral fillers was used as an object of the investigation.
Block-copolymer of propylene with ethylene of mark NV240R (BEP) with the following properties: breaking stress - 25.6 MPa, specific elongation - 200%, melting index -0.61 g/10 min, Vicat heat resistance - 1480C, melting temperature - 1550C.
BEP - this is the chain of molecule of propylene interrupted by chain of the ethylene-propylene copolymer. They have: high impact strength (at low temperatures) and high elasticity; higher long-term thermal stability; stability to thermooxidative destruction during production and polypropylene processing and also at exploitation of products from it.
Alizarin C14H8O4 - 1,2-dihydroxyan-thraquinone, dye with molecular weight - 240, melting temperature - 2890C. Structural formula of alizarin is presented below:
Clay is a black crystalline powder, greasy to the touch, hardness - 1.3 Mohs scale.
The clay nanoparticles were obtained in an analytical mill А-11 at maximum rotation rate 28000 rev/min. The size of nanoparticles was determined on apparatus of model STA PT1600 Linseiz (Germany) and was 14-110 nm. The nanopartilces were introduced into composition BEP on rolls at temperature 180-1900С for 7 min.
The rheological investigations of the polymer materials were carried out on capillary rheometer MELT FLOW TESTER, CEAST MF50 (INSTRON, Италия) in the temperature range of melt 190-2500С and in the interval of loads - 2.16-21.6 kg.
Results and discussion
In the process of industrial synthesis of polymers and flow line analysis of the melt fluidity it is usually used by melt flow index (MFI), which allows their labeling for specific information for specialists on the processing of plastics. However, the experimental investigations carried out by us showed that this index in spite of simplicity of its determination is not sufficiently informative for full evaluation of process ability of the thermoplastic polymers in the melt regime. Therefore, the investigation of the rheological characteristics of thermoplastics in a wide range of temperatures and shift stresses
allows to obtain sufficiently complete presentation of the physical and physico-chemical processes, which occur in the polymer melt in the process of their thermo-mechanical processing in the material cylinder of the molding or extrusion machine [4, 5].
The use of nanoparticles as fillers of the polymer materials makes some corrections for reguliarity of the melt flow of nanocomposites, which is not always possible to interpret, basing only on standard classical concepts and position in the field of polymer materials science [6, 7]. So, for example, in Figure 1(a,b,c) the results of investigation of influence of melting temperature and shift stress on shift rate of the initial PP (Figured) and its composites on the basis of clay and alizarin (Figure1b,c). The temperature regime in the melt was regulated in the ranges of 190-250°C Analyzing the flow curves in this figure one can establish that in all cases on increasing the shift stress and temperature a natural increase of shift rate of the considered composites is observed. The latter circumstance indicates that in the process of temperature effects in the melt of the composite do not occur the processes of cross-linking or thermal degradation, which could be favor change of character of flow curves. The rheological process proceeds in the regime of established flow, as a result of which a decay rate of associates of macrochains is equal to their establishment rate.
IgY 1.0
0.5
-0.5
-1.0
3.5
4.5
5 lgx
IgY 2
1.5
0.5
IgY
3.5
4.5
IgT
3.5
4.5
5 lgx
Fig.1. Influence of shift stress on melt shift rate for initial PP (a) and its composites: PP + 10% of clay (b) and PP+10% of clay+alizarin (c) at various temperatures, 0C : 1 - 190, 2 - 210, 3 - 230, 4 - 250.
1
1
1
b
a
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АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 1 2018
As can be seen from character of curves of the melt flow of PP in Figure1a, with minimum values of shift stress a small area having comparatively low angle of inclination to the x-axis is observed. A change of similar type in the regularity of polymer flow in shift stress (lgx) equal to 3.77 Pa indicates unambiguously the presence of a field of the greatest Newtonian viscosity. For initial PP at temperature 210-2500C a character of flow curves is slightly changed: linear dependence passes to curvilinear in the field of lgx=4.19-4.52 (Pa).
Comparing the curves of the melt flow of PP and its composites in Figure1 one can detect one very important peculiarity. It consists in the fact that the introduction of clay in composition of PP leads to the growth of the melt shift rate (melt fluidity) approximately in 7-12 times. In simultaneous introduction of clay and alizarin this effect is more intensified and reaches 20-30 times. Such sharp increase of the melt flow in the presence of filler in reality is an unusual phenomenon and contradicts to generally accepted ideas on rheology of the composite materials [7]. There are two possible explanations for the observed facts: firstly, in the intercalation process of low molecular parts of PP macrochains to the interlayer space of nanoclay leads to destruction - "exfoliating" of its structure into smaller particles accompanied by high melt fluidity in the uniaxial direction in the capillary; secondly, the exchange cations and anions, glycerin and surface-active substances (SAS) existing in the interlayer space of nanoclay, in the process of exfoliative migrate to the polymer matrix, favoring lubrication like the agent to improve the melt fluidity of nano-composites [8, 9].
The other peculiarity in the regularity of change of flow curves is in that an introduction of clay and clay mixture with alizarin in composition of PP leads practically to their linear dependence lgy from lgx. Only at temperature 2500C in composite of PP+10 mass % of clay linearity is rather disturbed (Figure1 b). We do not exclude that at comparatively high temperatures there can be occurred the processes of thermal destruction, making the certain contri-
bution to the character of change of the flow curves. In the studied temperature range and shift stress the Newtonian flow region in composites is not practically shown, i.e., an introduction of clay particles in the composition favors change of character of the melt flow. For composite PP+10 mass % of clay+1.0 mass % of alizarin in the considered temperature field a character of change of the flow curves is subjected to strictly linear dependence (Figure 1c). An absence of evidently expressed distortions in the curves of the dependence lg y from lg t can be interpreted as the result of the formation of more stable associates of macrochains in the presence of inorganic filler (clay). It is possible that in this case, along with the homogeneous crystallization centers in the melt of the composite the clay nanoparticles favor the formation of additional heterogeneous centers of crystallization. There is reason to assume that this circumstance influences certainly on mechanism of formation and destruction of the associates of macrochains of PP with simultaneous participation of homogeneous and heterogeneous centers of nucleation and crystallization in the composite melt [10].
However, in comparative analysis of flow curves in Figure 1(a,b,c) one can establish that an introduction of structure-forming agent - alizarin in composition independently of experience temperature favors equalization of flow curve i.e. the melt flow process occurs in strictly defined regularity. We do not exclude that, in this case, an introduction of alizarin as structure-forming agent in composition favors formation of greater number of additional heterogeneous centers of nucleation in the composite melt, which, as is known, favor increase of orientation process on its surface. The important point is that with introduction of structure-forming agent a growth of the shift rate of the composite melt approximately 4 times is observed.
In Figure 2 (a,b,c) in logarithmic coordinates the results of investigation of influence of temperature and shift rate on effective melt viscosity of nanocomposites are presented. Comparing the curves in this figure one can establish that in composite PP+10 mass % of clay
(Figure 2 a) it has nonlinear character. It has been established in this that at temperature 230-2500C an irregular jump in change of this dependence occurs. With increase of shift rate and temperature of test a sharp decrease of melt viscosity is observed. As we have noted above, a similar sharp decrease of effective viscosity at 230-2500C can be interpreted on the basis of the assumption of a possible proceeding thermal destruction. It should be paid attention to the fact that in the minimum and maximum value of shift stress there is correspondingly observed an appearance of the areas of the smallest and largest Newtonian viscosities. This is evidenced by the fact of the location of the curves parallel to the x-axis under certain values of shift rate. The obtained data confirm our assumption
ign
4,5
3,5
1 1
about the cooperative character of flow of associates of macrochains formed on homogeneous and heterogeneous centers of nucleation.
Analyzing the curves in Figure 2c one can see that an introduction of structure-forming agent of alizarin in composition of the nanocomposite on the basis of PP and clay favors essential change of dependence of viscosity on shift stress and temperature. The difference is that independently of temperature the alizarin favors establishment of practically linear dependence of viscosity on shift stress. The appearance of small horizontal section at relatively low values of the shift stress evidenced unambiguously about the initial demonstration of the areas of the greatest Newtonian viscosity.
igii
1.5
0.5
-1.0 -0.5 0 0.5 1.0 1.5 lgy
0 0.5 1 1.5
2 lgy
1.5
2.5
3.5 lgy
Fig. 2. Dependence of melt viscosity on shift stress for initial PP (a), samples of PP +10% of clay (b) and PP+10% of clay+alizarin (c) at various temperatures, 0C: 1 - 190, 2 - 210, 3 - 230, 4 - 250.
4.5
3.5
1 g 2
3
4
ign
3.5
2.5
ign 2
1.5
0.5
1.75
2.25 1000/T
1.75
2.25 1000/T
1.75
2.25 1000/T
Fig. 3. Dependence of melt viscosity of composites of the initial PP (a), PP + 10% of clay (b) and PP+10% of clay+alizarin (c) on temperature at various loads, kg: 1 - 3.8, 2 - 5.0, 3 - 10.0, 4 - 21.6.
4
4
a
c
1
2
3
a
c
A3EPEAH#^AHCKHH XHMH^ECKHH ^YPHA^ № 1 2018
In Figure 3(a,b,c) the results of investigations on study of influence of shift stress (lg y) on viscosity (lg n) at different temperatures are presented. A character of the curves shows that the temperature (especially at 230 and 2500C) plays an essential role (in equal shift values). With increase in shift stress value, the melt viscosity, as expected, falls. It is seen from Figure 3 c that for composites of PP+10 mass % of clay+1.0% of alizarin a dependence of viscosity on temperature at various temperatures has relatively linear character even at temperature 2500C. There is reason to assume that the alizarin is not only structure-forming agent, but also to a certain extent like thermostabilizer favors improvement of thermal stability of the nano-composite. Indeed, we have established on the basis of derivatographical analysis data that if for initial PP the beginning temperature of thermal decomposition is 220 C, in the samples of PP+10 mass % of clay and PP+10 mass % of clay +1.0 mass % of alizarin, it is equal to 226 and 2430C, respectively.
Thus, it can be concluded on the basis of the obtained results of the investigations that carrying out the rheological investigations of the polymer materials allows to obtain an enough complete and useful information not only about ability of the composite materials to the flow, but also enables to estimate the influence of fillers, modifiers and structure-forming agent on those processes, which occur in the material cylinder of equipments on plastics processing and as a result of which allows to make a correct selection of regime of the polymers processing depending on temperature and shift stress.
References
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POLIPROPILEN VO GiL OSASLI NANOKOMPOZiTLORiN REOLOJi XASSOLORi
G.§.Qasimova, N.T.Qahramanov, N.B.Arzumanova, i.A.ismayilov, U.M.Mammadli, A.A.Has3nova,
E.G.iskandarova, Z.M.Orucova
Polipropilen va gil asasli nanokompozitlar alinmi§ va onlann reoloji xassalari tadqiq edilmi§dir. Yerdayi§ma garginliyinin va temperaturun nanokompozitlarin axin süratina, arima özlülüyünün effektivliyina va özlülü axinin aktivla§ma enerjisina tasirinin tadqiqinin naticalari göstarilmi§dir. Müayyan edilmi§dir ki, gilin doldurucu qisminda istifadasi polipropilen asasinda nanokompozitlarin axiciliginin ahamiyyatli daracada yax§ila§masina kömak edir.
Agar sözlar: polipropilen, reologiya, nanokompozitlar, özlülük, axiciliq.
58
КИБОШОТСЛЬ СНЛКЛСТБШ8Т1С8 ОБ 1ЧЛ]Ч0С0МР08ГГЕ8
РЕОЛОГИЧЕСКИЕ ХАРАКТЕРИСТИКИ НАНОКОМПОЗИТОВ НА ОСНОВЕ
ПОЛИПРОПИЛЕНА И ГЛИНЫ
Г.Ш. Касумова, Н.Т. Кахраманов, Н.Б. Арзуманова, И.А.Исмаилов, У.М. Мамедли, А.А.Гасанова, Э.Г.Искандарова, З.М.Оруджева
Получены нанокомпозиты на основе глины и полипропилена и изучены их реологические свойства. Приводятся результаты исследования влияния напряжения сдвига и температуры на скорость течения, эффективную вязкость расплава нанокомпозитов и энергию активации вязкого течения. Показано, что использование природного минерала - глины в качестве наполнителя способствует существенному улучшению текучести нанокомпо-зитов на основе полипропилена.
Ключевые слова: полипропилен, реология, нанокомпозит, вязкость, текучесть.
АЗЕРБАЙДЖАНСКИЙ ХИМИЧЕСКИЙ ЖУРНАЛ № 1 2018
