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CHEMICAL PROBLEMS 2020 no. 1 (18) ISSN 2221-8688
33
UDC 541.68
EFFECT OF ALUMINUM HYDROXIDE CONCENTRATION ON PROPERTIES AND CRYSTALLIZATION REGULARITIES OF COMPOSITE MATERIALS BASED ON HIGH AND LOW DENSITY POLYETHYLENE MIXTURES
F.A. Mustafayeva
Institute of Polymer Material, ANAS S. Vurgun str. 124, AZ 5004, Sumgayit, Azerbaijan, e-mail: nnistafayevafatimaamail. ru
Received 01.08.2019
Abstract: The article presents results of research into the influence of aluminum hydroxide concentration on properties and crystallization regularities of composite materials based on mixtures of high and low density polyethylene. Studies were carried out with samples containing 1, 3, 5 and 10 % wt. aluminum hydroxide. All composite materials were based on mixtures of high and low density polyethylene, taken in 50/50 ratio. Dilatometric studies were carried out on an IIRT-1 device in the course of stepwise cooling of samples with a load of 5.3 kg. Temperature dependence of the specific volume, density and free volume of composite materials established. Also, density of compositions at a temperature of 190°C was identified on a capillary rheometer of CEASTMF50 brand. Onset temperature of crystallization and approximate glass transition temperature of composite materials were determined. Physical-mechanical properties of composites, such as ultimate tensile stress and elongation at break, were studied.
Keywords: crystallization, dilatometry, specific volume, mixture of polymers, high-density polyethylene DOI: 10.32737/2221-8688-2020-1-33-39
Introduction
At present, polymer composites are increasingly attracting attention of scientists and experimenters to obtain on their basis the high-quality structural materials with high strength, lightness, resistance to aggressive media, low cost, etc. These materials are available in the form of physical mixtures of polymers filled with mineral fillers of polymer composites, which are distinguished by high technology and ability to be processed in various plastics processing equipment. Through varying the concentration or ratio of mixture components, it is possible to vary properties of composite polymeric materials in a fairly wide range. It is these features of polymer composites that make it possible to obtain materials on their basis that can be widely used in engineering, aircraft engineering, auto industry, ship-building, as well as in space and military equipment. Interest in these materials has increased mainly due to the ability to change mechanical properties and adapt them to specific operating conditions. The process of mixing polymer with polymer has always been one of effective
methods for producing compositions with predetermined properties [1-3].
In recent years, polyethylene-polyethylene mixture has been the subject of great scientific and practical interest, in which not only quality problems were solved, but also the cost of products derived from them [4,5]. Scientific and technical progress requires a constant expansion of the range and applications of polymers. In particular, one of the most important requirements for polymeric materials is fire safety. Given that polyethylene is the largest and most widespread polymer, the development of ways to increase its fire resistance is one of the most important tasks requiring special attention. Metal hydroxides have long been considered cheap fillers for the development on their basis of fire-resistant polyolefins [6-8]. At the same time, great attention is paid to composite materials characterized by minimal shrinkage in the course of the molding machine injection. This circumstance makes it possible to select the composition of the composite material in such a way that it is possible to significantly
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CHEMICAL PROBLEMS 2020 no. 1 (18)
reduce changes in its volume in the process of structural product casting. To control the crystallization process and change the volume of the material in the process of closed volume cooling, the most effective method is the method of dilatometric measurements [9].
In this regard, the purpose of this study was to determine the effect of the concentration of aluminum hydroxide (AH) on the crystallization regularity of composite materials based on mixtures of high and low density polyethylene.
Experimental part
Industrial samples of high-density polyethylene (HDPE) of HD 52518 brand, low-density polyethylene (LDPE) of 17703-01 brand, and filler - aluminum hydroxide (GOST 11841-76, OKP 631887 repacked by VEKTON) were used as the object of research.
LDPE- density- 912 kg/m3, ultimate tensile stress- 10.3 MP a, elongation at break-250%. HDPE - density- kg/m3, ultimate tensile stress- 25.0 MPa, elongation at break-500%.
Aluminum hydroxide Al(OH)3 - a colorless solid, insoluble in water, has amphoteric properties, is a part of many bauxite. Amorphous aluminum hydroxide has a variable composition AhO3 • nH2O. When heated above 180-200°C it decomposes depending on the size of particles.
Composite materials based on HDPE and LDPE mixture in a 50/50 ratio and with different concentrations of AH (1, 3, 5, 10 % wt.) were obtained by mixing the components on laboratory rollers at a temperature of 150°C
within 8-10 minutes. Then, at a pressing temperature of 170-180°C, the plates were molded to cut down appropriate samples for testing.
Research into dilatometric characteristics of the composites was carried out on IIRT-1 device during stepwise cooling in the temperature range of 25-180°C, with a load of 5.3 kg.
The density and melt flow index (MFI) of the compositions at a temperature of 190°C and a load of 5 kg were determined on a capillary rheometer of MELT FLOW TESTER, CEAST MF50 (INSTRON brand, Italy).
The melting point was determined on a Q-1500 D derivatograph of the MOM company (Hungary) of Paulik, Paulik, and Erdei systems.
Ultimate tensile stress (a, MPa) and elongation at break (s, %) were determined in accordance with GOST 11262-80.
Results
In our previous works, the results of studies of physicomechanical, thermophysical, rheological properties, kinetic regularities of crystallization of composite materials based on mixtures of high and low density polyethylene in various ratios were published [10,11]. As is known, a feature of the polyethylene structure is a combination of crystalline and amorphous phases there in. Many of its physicochemical and mechanical properties depend on their quantitative ratio in polyethylene. But it will be shown below that they also have a significant impact on regularities of changes in the specific volume of composites depending on temperature and filler's quantitative ratio. The filler' particles can increase or reduce the crystallization rate of the semi-crystalline polymer, affect the growth of polymer matrix
and discussion
crystals, as well as the nucleation effect in the melt [12]. It was interesting to study the effect of AH concentration in the properties and crystallization regularities of composite materials based on mixtures with high and low density polyethylene.
The practical application of polymers is determined by the state in which the polymer (viscous, highly elastic, glassy) is in operating conditions. The temperature regions of existence of various physical states of polymers are determined by the dependence of the specific volume on temperature.
Figure 1 shows the crystallization isotherms, the initial mixture of LDPE and HDPE in a 50/50 ratio, and composite materials based on it at various concentrations of AH. The analysis of dilatometric curves in
this figure shows that with increasing AH concentration, the specific volume of composite materials decreases, that is, material compaction is observed, the results of which are summarized in table1.
Table 1 presents the results of research
into the effect of AH concentration at a temperature of crystallization which characterizes a first-order phase transition. Loading of 1% wt. AH has almost no effect on the crystallization temperature of the initial LDPE / HDPE mixture and is equal to 114°C.
Table 1. Effect of AH concentration on the density and crystallization onset temperature of
composites based on high and low density polyet îylene mixture
№ Composition formulation, % wt. Crystallization onset temperature, 0C Density, g / sm3
At 25°C At190°C
1 HDPE / LDPE 114 0.941 0.730
2 HDPE / LDPE +1 AH 114 0.945 0.766
3 HDPE / LDPE +3 AH 110 0.954 0.782
4 HDPE / LDPE +5 AH 110 0.962 0.790
5 HDPE / LDPE +10 AH 110 1.053 0.801
a mixture of HDPE and LDPE were taken in a 50/50 ratio, AH - aluminum hydroxide
With an increase in AH concentration to 10%, the temperature at which the composites begin to crystallize does not undergo any changes and corresponds to a value of 110°C.. Phase transitions of the first kind arecharacterized by constancy of temperature and volume changes. A comparison of maximum and minimum
specific volume of samples under study at the phase transition temperature (Fig. 1) says that as AH concentration in composites rises, the difference between these values first increases, and for samples containing 5% and 10% wt. AH decreases at index rate.
Vo, sm3/g Vi, sm3/g
Figure 1. Graphic dependence of specific volume on temperature: x- initial mixture of 50 % wt. HDPE + 50 % wt. LDPE, o- HDPE / LDPE + 1% wt. AH, • - HDPE / LDPE + 3% wt. AH, □- HDPE / LDPE + 5% wt. AH, ■- HDPE / LDPE + 10% wt. AH
The data obtained show that AH smaller crystallization process; however, at concentrations contribute to fuller concentrations of 5-10% wt. the crystallization
process in filled composites is somewhat constrained.
It has to be kept in mind that the method of dilatometric measurements makes it possible to approximate estimate a crystallization temperature of composite materials. Approximate values of the glass transition temperature of the studied samples were found at the intersection point of the upper and lower branches of the dilatometric curves (Fig. 1). The glass transition temperature of the initial HDPE / LDPE and composites thereon containing 1, 3, 5, 10% wt. AH is equal respectively to -73, -84, -128, -100, -84°C. From the data obtained, it follows that with AH loading to 3% wt. there is reduction in the negative area glass transition temperature. When the AH concentration is over 3% wt. the glass transition temperature rises. All the data above suggest that at AH low concentrations, the latter in the material
melt exhibits properties of nucleating agents thereby obtaining samples with a fine-spherical structure that favorably affect the improvement of these properties. At higher temperatures, the filler particles are accumulated in the amorphous regions impeding the conformational mobility of passing chains and increasing the fragility of the material and, accordingly, decreasing the glass transition temperature of composite materials.
According to the derivographic analysis data, the melting point of the composites under consideration changed as follows: HDPE / LDPE - 120°C; HDPE / LDPE + 1% AH -120°C; HDPE / LDPE + 3% AH -120°C; HDPE / LDPE + 5% AH- 120°C; HDPE / LDPE +10% AH - 125°C. In this case, a decrease in conformational mobility of highly filled composites is due to a certain increase in their melting point.
Figure 2. Dilatometric curves of changes in the free specific volume of the absolute temperature: x- initial mixture of 50 % wt. HDPE + 50 % wt. LDPE, o- HDPE / LDPE + 1% wt. AH, • - HDPE / LDPE + 3% wt. AH, □- HDPE / LDPE + 5% wt. AH, ■- HDPE / LDPE + 10% wt. AH
Since the experimental determination of free specific volume is a difficult task, it is usually calculated using the graphical dependence of the specific volume of the polymer on temperature.As the temperature of absolute zero (0 K) is approached, the free volume becomes zero, therefore the value of the occupied volume (Vo) is obtained by
extrapolation to the ordinate axis (Figure 1). Using the specific volume (Vi) at a given temperature, the free specific volume (Vf) of the test samples was calculated from the difference (Vi-Vo). Figure 2 shows the dependence of the free specific volume on the absolute temperature at various concentrations of AH.
A comparative analysis of the dependency curves shows that the value of the free specific volume for AH-filled composites is higher than in case with the initial HDPE / LDPE blend. This can be explained as being due to the fact that AH particles can create steric hindrances for complete crystallization of macromolecules in the phase transition thereby facilitating the loosening of the material and reducing its density. Due to the incompatibility of the polymer mixture of polyethylene with AH, their contact in the interfacial layer becomes weak. AH reducing the packing density of macromolecules contributes to the loosening of its structure. To
this can also be attributed to a decrease in the ultimate tensile stress of composites with a relatively high content of AH, the results of which are summarized in table 2.
From table 2 it can be seen that the loading of AH does not lead to a noticeable change in melt flow. Basically, the effect of AH appears on the change in mechanical properties. The results of the study are in good agreement with the data of dilatometric measurements, according to which AH contributes to loosening the structure of the composite, which in a certain way affects the deterioration of the ultimate tensile stress and the elongation at break of the composites.
Table 2. The effect of the AH concentration on physical-mechanical properties of composites _based on high and low density polyethylene mixture__
№ Composition formulation, % wt. Ultimate tensile stress, MPa Elongation at break, % MFI, g /10 min
1 HDPE / LDPE 22.2 56 11.784
2 HDPE / LDPE +1 AH 20.0 37 11.300
3 HDPE / LDPE +3 AH 20.1 36 10.387
4 HDPE / LDPE +5 AH 18.5 36 10.222
5 HDPE / LDPE +10 AH 18.7 28 11.733
* a mixture of HDPE and LDPE were taken in a 50/50 ratio, AH - aluminum hydroxide
Thus, the method of dilatometric measurements makes it possible to obtain sufficiently complete clarity for determination of the influence of filler particles on the nature of changes in the structure and properties of composites. On the basis of the data obtained, it is possible to evaluate the regularity of cooling of the polymer composite into the product in the mold and thereby predetermine
the main trends affecting their quality. Therefore, quantifying these properties through the use of dilatometry is crucial. By dilatometry, it was found that as AH concentration rises, the specific volume of composites decreases and a regular increase in density is observed. The lower and upper limits of the temperature used in these samples were determined.
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ALÜMiNiUMHiDROKSiDiNMiQDARININ YÜKSdK Vd AÇAGISIXLIQLI POLiETiLEN QARIÇIGI dSASINDA OLANKOMPOZiTMATERÎALLARIN XÜSUSiYYdTLdRINd VdKRISTALLAÇMA QANUNAUYGUNLUQLARINA TdSiRi
F.d. Mustafayeva
AMEA Polimer Materiallari înstitutu, AZ 5004, Sumqayit §, S. Vurgun kûçdsi, 124 e-mail: mustafayevafatima@mail. ru
Mdqalddd alüminium hidroksid miqdarinin yüksdk vd a§agi sixliqli polietilen qariçigi dsasinda olan kompozit materiallarin xüsusiyydtldrind vd kristallaçma qanunauygunluqlarina tdsiri tddqiqatlarinin ndticdldri tdqdim olunmuçdur. Tddqiqatlar tdkibindd 1, 3, 5 vd 10 kütld % alüminium hidroksid olan nümundldrld aparilmi§dir. Bütün kompozit materiallar 50/50 nisbdtindd götürülmü§ yüksdk vd açagi sixliqli polietilen qariçigi dsasinda olmuçdur. Dilatometrik tddqiqatlar ÏÏRT-1 qurgusunda, nümundldrin 5.3 kq yük altinda pilldli soyutma prosesindd aparilmi§dir. Kompozit materiallarin xüsusi hdcminin, sixliginin vd sdrbdst hdcminin temperatur asililigi müdyydn edimiçdir. Kompozitldrin 190°C uygun sixliqlari CEAST MF50 markali kapilyar reometrdd müdyydn olunmuçdur. Kompozit materiallarin kristallaçmasinin baçlangic temperaturu vd tdxmini §ü§dld§md temperaturu müdyydn olunmuçdur. Kompozitldrin dartilmada möhkdmlik hdddi vd nisbi uzanmasi kimi fiziki-mexaniki xüsusiyydtldri tddqiq edilmiçdir.
Açar sözlw. kristallaçma, dilatometriya, xüsusi hdcm, polimer qariçigi, yüskdk sixliqli polietilen, açagi sixliqli polietilen, alüminium hidroksid.
ВЛИЯНИЕ КОНЦЕНТРАЦИИ ГИДРОКСИДА АЛЮМИНИЯ НА СВОЙСТВА И ЗАКОНОМЕРНОСТЬ КРИСТАЛЛИЗАЦИИ КОМПОЗИТНЫХ МАТЕРИАЛОВ НА ОСНОВЕ СМЕСЕЙ ПОЛИЭТИЛЕНА ВЫСОКОЙ И НИЗКОЙ ПЛОТНОСТИ
Ф.А. Мустафаева
Институт Полимерных Материалов Национальной АН Азербайджана AZ5004, г. Сумгайыт, улица С.Вургуна, 124; e-mail: mustafayevafatima@mail. ru
В статье приводятся результаты исследований влияния концентрации гидроксида алюминия на свойства и закономерность кристаллизации композитных материалов на основе смесей полиэтилена высокой и низкой плотности. Исследования проводились с образцами, содержащими 1, 3, 5 и 10 % масс. гидроксида алюминия. Все композитные материалы были на основе смесей полиэтилена высокой и низкой плотности, взятых в соотношении 50/50. Дилатометрические исследования проводились на приборе ИИРТ-1, в процессе ступенчатого охлаждения образцов при нагрузке 5.3 кг. Установлена температурная зависимость удельного объёма, плотности и свободного объёма композитных материалов. Плотность композиций при температуре 190°С была идентифицирована на капиллярном реометре марки CEAST MF50. Определены температура начала кристаллизации и приближенные значения температуры стеклования композитных материалов. Исследованы такие физико-механические свойства композитов, как разрушающее напряжение и относительное удлинение. Ключевые слова: кристаллизация, дилатометрия, удельный объем, смесь полимеров, полиэтилен высокой плотности, полиэтилен низкой плотности, гидроксид алюминия.
