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DOI: http://dx.doi.org/10.20534/AJT-17-1.2-30-35-37
Turaev Erkin, Ph. D. Independent researcher Tashkent chemical-technological institute, The faculty ojchemical technology of fuel and organic substances, Uzbekistan, Tashkent E-mail: turaev08@yahoo.com
Mikitaev Abdulahj
Doctor of Chemistry Professor ojKabardino-Balkarian State University named by H. M. BerbekovRussia Nalchik
Djalilov Abdulakhatj Doctor of Chemistry Professor, Director of Tashkent State Unitary Enterprise Research Institute, Uzbekistan, Tashkent
The properties of polyethylene nanocomposites based on organo-modified montmorillonite
Abstract: Research the possibility of obtaining nanocomposite materials by the process of melt-mixing using organo-modified montmorillonite. Studied the the effect of the organoclay on the physical and mechanical, thermal properties of high density polyethylene.
Keywords: Polyethylene; Organo-modified montmorillonite; nanoсomposite; Mechanical properties; Thermal stability.
Introduction
In recent decades, the task of developing new materials is achieved by the modification of the base grades of industrial polymers. One way of adjusting the properties of polymer materials, is to obtain composite materials filled with nano size particles. It's due to the fact that such composite materials have a number of significant advantages. When incorporating nanoscale fillers in a polymer matrix, there is an increase of modulus, impact strength, thermal stability, chemical stability to solvents, flammability and decrease gas diffusion and permeability in polymers occurs.
In connection of above mentioned, the development and study of the properties of nanocomposites based on high density polyethylene (PE) and nanoscale particles is a very urgent task that allows to expand the scope of PE.
Methods of organic modification of montmorillonite
It is known that the main problem of creating layered silicate nanocomposites is the incompatibility of the organic (polymer) and inorganic (layered silicate) constituent of composites. This problem can be solved by using organo-modified layered silicate as an alternative. This product is the replacement of inorganic cations in the galleries of the layered silicates with organic cations, as shown in fig. 1.
As a nanoscale PE filler, we used montmorillonite (MMT), which is derived from bentonite clay deposits of Gerpegezh (Kabardino-Balkarian Republic).
Organic modifier that has been used for modification of organic MMT is shown in table 1.
Fig. 1. Scheme of organic modification of montmorillonite
Section 3. Materials Science
Table 1. - Composition of organo-modified MMT
Table 2. - Influence of the nature of organoclay on the properties of PE
To achieve the maximum possible effect of increasing the properties of nanocomposites, the optimal content of organic modifier-Acrylate guanidine in MMT is 3-10 wt. %. It is determined that increase in the concentration of organic modifier in MMT above 10 % leads to the destruction of natural structure of layered silicates (disorients the silicate layers) and premature exfoliation of layered silicates reduces the physical and mechanical properties of nanocomposites [1].
Mechanical properties of PE/organoclay nanocomposites
Introduction oforganoclay in the PE changes the whole complex of its physical and mechanical properties. The observed effect is also found conformation in the comparison of developed organoclay with unmodified natural MMT.
Table 3.
Matrix Modulus, МPа Tensile yield strength, MPa Elongation at break, %
PE 950 24 500
PE + 5 % MMT 1020 24 330
PE + 5 % organoclay 1300 26 350
As the result of the experiments shows, introducing 5 wt. % natural MMT and organoclay increases the modulus of the PE to 10 % and 37 %, the yield strength is 0 % and 8 % respectively. Table 2 shows that, the presence of organomodifier in clay, leads to the increase in adhesion strength and modulus of nanocomposites.
To determine the optimal concentration of organoclay, by extrusion process it was obtained composites containing 3, 5, 7 wt. % organoclay and mixture of 5 % compoline (compatibilizer) with organoclay. The results
of this study are shown below. The physical and mechanical properties of nanocomposites depending on the content of organoclay
Polymer matrix Filler, wt. % MI, gr/10min 2.16 kg Izod impact, J/m Modulus, MPa Tensile yield strength, MPa Tensile yield at break, МPа Elongation at break, %
— 0.8 88 950 24 25 500
3 % organoclay 0.8 58 1180 24 23 480
5 % organoclay 0.85 51 1300 26 23 350
7 % organoclay 0.85 48 1330 25 23 330
5 % compoline 0.79 116 880 21 23 500
PE 3 % organoclay + 5 % compoline 0.8 82 1200 22 23 500
5 % organoclay + 5 % compoline 0.76 80 1250 24 23 450
7 % organoclay + 5 % compoline 0.78 62 1260 24 24 450
As can be seen from table 3, even at a low content of organoclay, there is observed a significant increase in modulus in tension with a tendency to increase with increasing organoclay content. For example, introducing 5 wt. % organoclay increases the modulus of the material to about 1.37 times. Thus an increase in yield strength by 8 %.
PE strength increases when the content of the organoclay is in an amount of up to 5 wt. % in the polymer matrix, which is probably due to the very resistance clay, which is a reinforcing element in the matrix.
Apparently, there is a threshold concentration at which the organo-modified silicate layer capable to be distributed at the nanoscale level, given the nature of the polymer to form a nanocomposite exfoliated structure.
Large concentrations of organoclay lead to the formation of intercalated structure [2].
Additional introduction in 5 % Compoline composition increases of the modulus by 24 %, thus further increasing the concentration of organoclay does not effect on modulus of nanocomposites, which is probably due to the nature of compoline. Introducing 5 % compoline contributes to the preservation ofthe elongation at break at the level of the base PE. Introducing 5 and 7 wt. % organoclay, nanocomposites elongation decreases slightly to 10 %. This suggests that, Compoline acts as an elastic bridge, thereby maintains high elongation values of nanocomposites.
Reduced elongation of 30 % with the introduction of organoclay in PE, it is assumed that, it's due to the blocking
of the mobility of the polymer segments of the layered silicates at the nanoscale. Meanwhile, the modulus increases monotonously in the entire range of concentrations.
Established fact of reduced izod impact strength of nanocomposites when introduction of organoclay in PE, can be explained by the blocked mobility of the polymer segments of the layered silicates at the nanoscale.
Structure of nanocomposites based on PE/or-ganoclay
One of the methods of studying the degree of dispersion of organically modified layered silicates in a polymer matrix is an X-ray analysis. Diffractogram of nanocomposites obtained by melt mixing with PE/organoclay, is shown in fig. 2.
Fig. 2. The X-ray diffraction data: a — MMT; b — organoclay; PE with x % of organoclay content:
at c — 0 %; d — 1 %; e — 3 %; f — 5 %; g — 7 %
From the diffractogram, it can be seen that, for unmodified clay the characteristic peak is observed in 20 = 7.0 ° (d = 1.19 nm), which corresponds to the organoclay in 20 = 3.0 ° (d = 2.47 nm ). When introduced into the polymer matrix PE organoclay in an amount of 5 wt. %, a characteristic peak for organoclay is absent, indicating the division of organoclay plates into separate silicate layers. The results of the analysis of the diffractogram suggest a complete exfoliation of the clay.
By increasing organoclay content to 7 wt. %, in the diffractogram in 20 = 5.0 ° a peak appears, the intensity of which is very small. The maximum intensity of this peak corresponds to d = 1.84 nm. This suggests that, in the resulting composite regions in which there was a complete exfoliation of organoclay, coexist with areas, which partially preserved the order in the arrangement oflayers ofpackages.
Based on these results, it can be concluded that the composites obtained by melt mixing using an organoclay, when its content in an amount up to 5 wt. %, inclusive, are exfoliated, and when the content of organoclay in an amount of 7 wt. % composites have a mixed structure comprising intercalated and exfoliated packets.
Thermal properties of nanocomposites based on PE/organoclay
The method of thermogravimetric analysis (TGA) confirmed an increase in the degradation temperature (the temperature of the beginning of the slump) of the nanocomposites with the content of 3, 5, 7 wt. % organoclay on 5, 8, 11°C respectively. This is connected with the effect thermo-protection, influencing on macromol-ecules of polymers from the side of silicate layers.
In contrast to the base PE, nanocomposites are degraded in air to the form of coke, the quantity of which increases with increasing organoclay content. The presence of carbon residue indicates a more complex characteristic of the process of thermal destruction of nanocomposites.
The complexity of the thermal destruction process can be the result of the organoclay which plays the role of initiator of coking due to the barrier and blocking effects rendered by them to the volatile products. These results of TGA nanocomposites are shown in table 4.
Table 4. - The results of TGA nanocomposites based on PE/organoclay.
Degradation The coke
Matrix temperature, residues at
°C 600 °C, %
PE 394 0
PE + 3 % organoclay 399 5
PE + 5 % organoclay 402 8
PE + 7 % organoclay 405 10
Conclusion
The experimental data allow to draw conclusions about the prospects of given direction of research, as the development of new polymer nanocomposite materials based on MMT and polyethylene, permits to modify the basic properties of polymer significantly. Such materials with a low content of organoclay (about 5.3 wt. %) possess a new set of improved and new properties comparing to the base unfilled polymers, including high rigidity in a wide temperature range and increased thermal properties.
References:
1. Khashirov S. Guanidine containing polymers and nanocomposites based on them. Doctoral dissertation.
Na-
lchik, 2009.
2. Alexandre M., Dubois Ph. Polymer/layered silicate nanocomposites: preparation, properties and uses of a new class of materials//Mater. Sci. and Eng. - 2000. - V. 28. - P. 1-63.
