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AZ9RBAYCAN KIMYA JURNALI № 1 2017
UDC 678.01:620:17
THE ROLE OF STRUCTURANTS IN THE PROCESS OF FORMATION OF STRUCTURE AND PROPERTIES OF POLYMER COMPOSITES BASED ON RANDOM POLYPROPYLENE AND MINERAL FILLERS
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N.T.Kahramanov, N.B.Arzumanova, V.S.Osipchik, Y.N.Kahramanly, F.M.Aliyeva, U.M.Mammadli, G.D.Heydarova, S.S.Aliyeva
Institute of Polymer Materials, NAS of Azerbaijan 1D.Mendeleev University of Chemical Technology of RF 2 Azerbaijan State University of Oil and Industry
Received 12.02.2016
The influence of the multifunctional organic structure forming and mineral fillers on the structural features and physico-mechanical properties of polymer composites based on statistical copolymer of ethylene with propylene - random polypropylene has been considered. The principal possibility of improvement of strength characteristics and fluidity of polymer composites in the process of joint use of mineral fillers and ingredients is shown.
Keywords: ultimate tensile stress, tensile strength at yield, the elasticity module at a bend, interfacial area, continuous chains, spherulites, crystallinity, crystallization, filler.
In recent years, scientists worldwide have all increasingly been attracted to researches aimed at studying the influence of the structure and composition of mineral fillers on the process of formation of crystalline permolecular organization in polymer materials [1-7]. Unique ability of finely dispersed particles of minerals to affect the mechanism of occurrence and growth of heterogeneous crystal nucleus in the polymer matrix has been detected in the process of mixing the polymers with the minerals. The latter circumstance has an essential impact on improving the properties of polymer composites filled with minerals.
The following are widely applied in order to implement a set of measures aimed at changing the mechanical properties of the original polymer matrix:
- technological additives that improve processing conditions;
- additives that modify the mechanical properties (structurants, plasticizers, armoured fillers etc.).
Therewith the efficiency of only once use of a number of additives has the combined action on the properties of the polymer composite. The mechanism of the coexistence of the components in the boundary areas of interphase area is predetermined by the physical and physico-chemical forms of interaction existing in the ad-
ditive-macrochain-filler system [7-10].
There are almost no systematic studies aimed at establishing the effect of multifunctional of organic origin structure forming on the structural characteristics and properties of filled polymer composites. The urgency of this problem is that the introduction of the minimum concentrations of organic structurants contributes not only to improving the deformation-strength characteristics of polymer composites, but also significantly facilitates the miscibility of the blend components and, as a consequence, their processability [11, 12].
We have repeatedly confirmed in our works [8-12] that the use of organic structurants significantly affects the formation of finely-divided spherulitic structures that contribute to the improvement of the technological compatibility of limited-compatible polymers [11], increasing the strength properties, melt flow index and processability of composite materials [12].
Investigations on the effects of finely-disperced particles of the organic structurants on mechanism of formation of permolecular structure in polymer composites and processes occurring in the interphase area and boundary areas of polymer-filler system still remain open. The occurrence of certain structures in the filled polymers and the consequential impact of filler
on the regularity of the changing of their properties are one of the most important criteria predetermining the degree of "strengthening" the polymer base. The increase in the elasticity coefficient and strength of the samples by dispersing the filler is considered as a form of "strengthening" of polymer composites.
Taking into account the complexity and the insufficient illumination of this problem in the literature, the purpose of this paper is to show how essential is the role of multi-functional structurants in the regularities of changes of main physico-mechanical and rheological properties of filled polymer composites is.
Experimental part
Random copolymer (REP) - the South Korean Industrial statistical copolymer of ethylene with propylene (ethylene content 2-4%), trade name RP2400 has been used as the polymer base. The properties of the polymer are given below:
ultimate tensile stress - 28.5 MPa,
the elasticity module at a bend (EMB) -
975 MPa,
tensile strain - 600%, fluidity limit of melt (FLM) - 0.36 g/10 min Vicat softening point - 1250C, melting point - 1380C.
Cement, chalk and silica flour have been used as the filler of polymer.
Cement. The main components of this building material are the binding materials of inorganic origin. The particle size varies in the range of 107-400 nm.
Silica flour. Typical chemical composition of the silica flour is: SiO2 (99.46%), Fe2O3 (0.048%), Al2O3 (0.21%), TiO2 (0.027%), CaO (0.021%). Bulk density - 653 kg/m3. The average particle size - 50-100 nm.
Chalk. The base of the chemical composition of the chalk is the calcium carbonate with a small amount of magnesium carbonate, but generally there is also non-carbonate part, mainly metal oxides. The average particle size - 200-400 nm.
Alizarin and zinc stearate have been used as organic structurants.
Zinc stearate (C17H35COO)2Zn - white amorphous powder, melting point - 403 K, used
concentration 0.3-1.0 wt.%, used as the lubricant agent in the processing of polymers by injection molding and extrusion.
Alizarin C14H8O4 - 1,2-dihydroxy an-thraquinone, colorant, red crystals with molecular mass - 240.2, melting point - 562 K. Below is the structural formula of alizarin:
The polymer compositions were prepared in the process of mechano-chemical modification (hot rolling) at temperature of 463 K, the rolling time - 10 min.
For carrying out physico-mechanical testing of the polymer composites they are subjected to pressing at temperature of 473 K. Samples were cut out from these to determine the elasticity module at a bend, ultimate tensile stress and tensile strain of filled composites. Ultimate tensile stress and tensile strain were determined in accordance with the GOST 11262-80 (State Standard). The elasticity module at a bend was (EMB) determined in accordance with the GOST 4648-71 (State Standard).
Melt index of composites was determined on the IIRT device at temperature of 1900C and load of 5 kg.
The crystallization temperature was determined on IIRT device fitted for dilatometric measurements [13].
Results and Discussion
Taking into account the complexity and insufficient study of this problem, it seemed interesting to carry out a phased approach to the study of regularity of changes in the structure and properties of polymer composites, depending on the type of filler and structurant. It should be noted that often in the literature zinc stearate is represented only lubricant agent, which improves the processing of polymer composites, but do not reveal the main reasons for the improvement of the quality of the products obtained with the participation of this ingredient. At the same time, alizarin is known as a colorant and therefore practically is not considered as a structurant in polymer composites.
For a more complete interpretation of detected regularities let's turn to the results of experimental studies, shown in Table 1. As can be seen from this table, the introduction of such fillers like cement, silica flour and chalk (without ingredients) contributes to continuous growth of flexural modulus. As regards ultimate tensile stress, the maximum value of its values is accounted for by the samples with 5-10 wt% filler content. Further increase in the concentration of these fillers leads to a natural decrease in ultimate tensile stress, tensile strain and melt index of samples. Reducing the strength of filled composites during uniaxial tension is the evidence to complex processes in the inter-spherulite area. We do not exclude that in small concentrations of the filler particles (5-10 wt.%), the latter predominantly involved in the formation of heterogeneous nucleation [14]. A further increase in the concentration of filler helps in the process of crystallization from the melt and the crystal growth of particles in excess pushed in inter-spherulite amorphous area. If the crystallinity of the polymer base is approximately 50%, the amount of filler in the amorphous field is doubled. In other words, if the polymer is introduced 20 wt.% filler, its concentration in the amorphous field of semi-crystalline REP is approximately 40 wt.%. Accumulating in this space, the filler particles reduce conformational mobility "continuous chains", increase the stiffness of the amorphous field, which immediately affects the deterioration of strength and tensile strain of polymer composites.
Attention shall be paid to the fact that the separate introduction of 1wt% alizarin and zinc stearate into the REP leads to serious changes in its qualitative characteristics. For example, in this case, it provided a significant increase in all its strength characteristics, tensile strain and MFI of REP. It is clear that such significant improvement in the quality characteristics of REP can be clearly interpreted based on the peculiarities of the formation of fine spherulitic permolecular structures.
The important aspect is that the simultaneous introduction of alizarin and zinc stearate into the composition of REP leads to even more improvement of final properties of po-
lymer composites. It is precisely this feature of joint participation of alizarin and zinc stearate towards improving the quality of REP that can be regarded as a "synergetic effect". Therefore, in our further investigations in all the filled composites of REP, these ingredients were introduced simultaneously in the amount of 1wt.% alizarin and 1wt. % zinc stearate.
According to the data given in Table 1, introduction of the described ingredients into composition of filled composites leads to a substantial improvement of their properties. Of pairwise comparing samples of filled composites with or without ingredients can establish that the maximum increase in the EMB is 2225%, ultimate tensile stress 15-21% and fluidity limit of melt FLM 4.0-4.8 times. There is a reason to assume that the smaller spherulite size, the fewer defects in crystalline formations and the more likely uniformly dispersing of the filler particles in inter-spherulite area and generally throughout the volume of the polymer matrix. On the other hand, we do not exclude that alizarin and zinc stearate may to some extent contribute to laying the grain of surface of filler particles, thereby creating favorable conditions for the aggregate flow of the melt and supporting maximum wall sliding in evaluating of FLM of samples. In view of nature of the filler and polymer, and mutual dispersion, the process of choosing the optimum ratio of components in the polymer matrix may be associated with certain difficulties. In several cases this circumstance is explained by a variety of approaches to the interpretation of the observed regularities [13, 14]. Depending on the type and concentration of filler, the latter has a significant structuring influence on polymer base both in solid and in viscous-flow state.
For example, Table 2 presents the results of investigations on the influence of type and concentration of the filler and organic structurants on the crystallization temperature of the polymer composites.
Analyzing the data contained in this table, it can be stated that the used organic structurants have a strong impact on the value of crystallization temperature of composites.
Table 1. The composition and the physico-mechanical properties of the filled composites based on REP containing
1wt.% alizarin and iwt. % zinc stearate
Sample Composition of polymer compound Ultimate tensile stress, MPa EMB, MPa Tensile strain, % Melt index, g/10 min
1 REP 28.5 975 600 0.36
2 REP+1% alizarin 29.8 1001 750 1.56
3 REP+1% zinc stearate 29.1 9SS 680 2.98
4 REP+alizarin+zinc stearate 30.4 100б 780 3.11
5 REP+5% cement 31.3 1010 560 0.44
б REP+5% cement+alizarin+zinc stearate 32.2 102S 640 1.94
7 REP+10% cement 31.5 1025 320 0.35
S REP+10% cement+alizarin+zinc stearate 34.6 117б 510 1.98
9 REP+20% cement 24.0 1075 85 0.25
10 REP+20% cement+alizarin+zinc stearate 32.3 119S 250 1.85
11 REP+30% cement 22.8 10S0 25 don't flow
12 REP+30% cement+alizarin+zinc stearate 24.6 1215 125 0.95
13 REP+5% silica flour 29.8 1015 240 0.35
14 REP+5% silica flour+alizarin+zinc stearate 31.4 1022 525 2.04
15 REP+10% silica flour 27.0 1020 180 0.30
1б REP+10% silica flour+alizarin+zinc stearate 30.8 1132 295 1.84
17 REP+20% silica flour 22.6 1040 70 0.11
1S REP+20% silica flour+alizarin+zinc stearate 27.3 1155 110 1.92
19 REP+30% silica flour 20.8 1050 35 don't flow
20 REP+30% silica flour+alizarin+zinc stearate 24.5 1175 70 0.73
21 REP+5% chalk 27.1 9S0 495 0.37
22 REP+5% chalk+alizarin+zinc stearate 30.3 1035 210 2.01
23 REP+10% chalk 25.8 1000 315 0.20
24 REP+10% chalk+alizarin+zinc stearate 27.9 1121 145 1.72
25 REP+20% chalk 19.8 1010 95 0.12
2б REP+20% chalk+alizarin+zinc stearate 24.7 1123 105 1.45
27 REP+30% chalk 18.2 1015 15 don't flow
2S REP+30% chalik+alizarin+zinc stearate 22.6 1155 65 0.69
Table 2. Influence of structurants and mineral fillers on heat resistance and crystallization temperature of REP
Sample Composition of polymer compound Chilling point, 0С Vicat softening point, 0С
1 REP 141 125
2 REP+1% alizarin 144 125
3 REP+1% zinc stearate 142 125
4 REP+alizarin+zinc stearate 146 125
5 REP+5% cement 142 127
б REP+5% cement+alizarin+zinc stearate 147 128
7 REP+10% cement 143 129
S REP+10% cement+alizarin+zinc stearate 147 130
9 REP+5% silica flour 143 127
10 REP+5% silica flour+alizarin+zinc stearate 148 129
11 REP+5% chalk 141 125
12 REP+5% chalk+alizarin+zinc stearate 142 126
Particularly, there is a strong influence of alizarin. The joint use of discussed organic structurants once again has confirmed the existence of "synergism" effect, which was expressed in the increase of crystallization temperature of composites 5-70C. It is characteristic that filler itself (except chalk) exhibits a struc-
ture-forming effect expressed in increase of the temperature of crystallization of polymer composites. As shown in this table, the most intensive crystallization process occurs in those samples in which cement and silica flour are used as a filler. Changing the crystallization temperature of the polymer matrix is only
possible when foreign finely dispersed particle of organic or mineral origin is capable of forming heterogeneous crystallization nucleus.
The filled polymer composites may have two types of crystallization nucleus: homogeneous and heterogeneous. In our view, homogeneous nucleus - the primary microcrystalline formations which emerged as a result of thermo fluctuation changes in the melt of polymer at the level of oriented segments of macro chains. In the process of further cooling these micro oriented areas grow into larger crystalline formations -spherulites. Heterogeneous crystallization nucleus is formed with the participation of solid foreign particles, which can orient macro segments of the polymer matrix on their surface. It is obvious that during polymer processing by extrusion or injection molding, the cooling process of products is accompanied, at first, by formation of heterogeneous crystallization nucleus and then homogeneous crystallization nucleus [13, 14].
Thus, on the basis of the foregoing, it can be concluded that the use of structurants with various mineral fillers has a positive impact on the improvement of physico-mechanical, thermal and rheological properties of filled polymer composites. It becomes obvious that the use of mineral fillers and structurants allows solving a number of problems related to improving the technological capabilities of processing of filled polymer composites. As a matter of fact, new polymer composites with improved operating and processing characteristics were generated in the process of modification of REP.
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RANDOM POLiPROPiLEN VO MiNERAL DOLDURUCULAR OSASINDA POLiMER KOMPOZiTLORiN QURULU§UNUN VO XASSOLORiNiN FORMALA§MASI PROSESiNDO QURULUSOMOLOGOTiRiCiLORiN ROLU
N.T.Qahramanov, N.B.Arzumanova, V.S.Osipfik, Y.N.Qahramanh, F.M.Oliyeva, U.M.Mammadli,
G.D.Heydarova, S.S.Oliyeva
Etilenin propilenla statistik birgapolimerinin - random polipropilenin asasinda polimer kompozitlarin qurulu§ xususiyyatlarina va fiziki-mexaniki xassalarina uzvi goxfunksiyali qumlu§amalagatiricilarin va mineral doldurucularin tasiri nazardan kegirilmi§dir. Mineral dolduruculann va inqridientlarin birga istifadasi prosesinda polimer kompozitlarin mohkamlik xassalarinin va axiciliginin yax§ila§dinlmasi imkani gostarilmi§dir.
Agar sozlar: dagidici garginlik, dartilma zamani axiciliq haddi, ayilma zamani elastiklik modulu, fazalar-arasi saha, kegici zancirlar, sferolitlar, kristalliq, kristalla§ma, doldurucu.
РОЛЬ СТРУКТУРООБРАЗОВАТЕЛЕЙ В ПРОЦЕССЕ ФОРМИРОВАНИЯ СТРУКТУРЫ И СВОЙСТВ ПОЛИМЕРНЫХ КОМПОЗИТОВ НА ОСНОВЕ РАНДОМ ПОЛИПРОПИЛЕНА И МИНЕРАЛЬНЫХ
НАПОЛНИТЕЛЕЙ
Н.Т.Кахраманов, Н.Б.Арзуманова, В.С.Осипчик, Ю.Н.Кахраманлы, Ф.М.Алиева, У.М.Мамедли,
Г.Д.Гейдарова, С.С.Алиева
Рассмотрено влияние органических многофункциональных структурообразователей и минеральных наполнителей на структурные особенности и физико-механические свойства полимерных композитов на основе статистического сополимера этилена с пропиленом - рандом полипропилена. Показана принципиальная возможность улучшения прочностных характеристик и текучести полимерных композитов в процессе совместного использования минеральных наполнителей и ингредиентов.
Ключевые слова: разрушающее напряжение, предел текучести при растяжении, модуль упругости при изгибе, межфазная область, проходные цепи, сферолиты, кристалличность, кристаллизация, наполнитель.
