Molding temperature nanocomposite samples

The Influence of the Molding Temperature on the Density of the Nanocomposite Samples Based on the Low-Density Polyethylene... 

As is known, the low-density polyethylene molding onset temperature under pressure is about 70 °C [21]. Evidently, this mechanical action also influences the density and porosity of a polymeric sample in the course of the molding. Our experiments were performed using the piston and spring producing a pressure 2.6 X 10 N/m. A series of the nanocomposite samples were molded from the same powdered material in the muffle oven at the various temperatures (70, 90,100,110, 120,130, and 150 °C). As a result, we obtained 14 polymeric nanocomposite samples with a 10% concentration of MnO and CdS and 7 pure low-density polyethylene samples molded at the indicated temperatures. A comparison to the pure polyethylene samples revealed the influence of the nanoparticles presence in the polymeric matrix on the density and porosity of obtained nanocomposite materials. Using this technology, it was possible to obtain the flat, parallel disk samples with a thickness of 0.3-1 mm and a diameter of 12-14 mm, which could be readily extracted from the press. 

Figure 7.3 The dependence of the density of the nanocomposite samples on the molding temperature for the following materials based on the matrix of a low-density polyethylene 1,...

Then with the help of the precision micrometer, we determined the thicknesses of the obtained samples and their volumes were calculated using the known values of the thickness and diameter. The sample mass was measured by the precision analytical balance. The known sample volume and mass allowed us to find the density of the nanocomposite material. By this way it was possible to determine the dependencies of the material density on the molding temperature. These dependencies are presented in Figure 7.3 for the following samples pure modified low-density polyethylene (1), and nanocomposite materials based on low-density polyethylene matrix with 10% concentration of nanoparticles CdS (2) and MnO (3). 

Thus, it was established that the nanocomposite materials based on low-density polyethylene with minimum porosity and maximum density are obtained by molding at temperatures 110-120 °C. The results open the way to controlled modification of the parameters of such samples by varying the molding temperature. Properties, which depend on the material porosity, include the permittivity, refractive index, and elastic modulus. 

Thus in the course of the investigations it was shown that for obtaining the nanocomposite samples based on the low-density polyethylene with the minimum porosity or maximum density, one should use the molding temperature which is in the range 110-120 °C. The obtained results also indicate the possibility to change some physical macroscopic parameters (density, permittivity, etc.) by changing the molding temperature. 

Thermal properties were measured by using a Shimadzu DTA-500 system in air from 30 to 600 °C at a heating rate of 10°Cmin h Tensile bars were obtained on a Van Dorn 55 HPS 2.8 F mini injection molding machine under the following processing conditions a melt temperature of 150 °C, a mold temperature of 25 °C, an injection speed of 40mms an injection pressure of 10 MPa and a holding time of 2 s, with a total cycle time of 30 s. Tensile measurements on injection molded samples of nanocomposites were performed... 

Tensile bars according to ASTM D-638 were prepared using the HAAKE mini-jet piston injection molder at a temperature of 360 C and mold temperature of 130 C. The injection pressure was 740 bars in each case. Prepared nanocomposites were compression molded into discs of 25 mm diameter and 2.2 mm thickness at 300 C using the Carver 4122 compression molding press, for the rheological measurements. The samples for electrical conductivity measurement were also compression molded into discs of 90 mm diameter and 1 mm thickness. 

CaCOj-polylactide nanocomposites can also be prepared via melt compounding technique using twin screw extruder [64]. The temperature of the mixing zone varied from 150°C at entry to 190° at exit at a mixing speed of 150 rpm. These samples were then injection molded to the desired shape. 

An amorphous polyester-montmorillonite nanocomposite prepared from condensation of 2,2,4,4-tetramethyl-l,3-cyclobutanediol, 1,3-propanediol, and dimethylterephthalate produced unexpected mechanical properties [45]. Cloisite 20A was melt blended with the polymer at 2.5,5, and 10 wt.% with a Haake HBI System 90 drive attached to a Rheomex CTW 100 twin-screw extruder. The r/min of the extruder was 60 and the temperature was 120°C. The test samples were prepared in two different injection molders. The test samples from the polyester-montmorillonite composite at 5% Cloisite 20A content were prepared with a Demag Ergotech 35 at 150°C with a pressure range of 10000 to 11000 psi. The test samples from the polyester-montmorillonite composites with 2.5, 5.0, and 10% Cloisite 20A content were prepared with a mini-jector molding machine at a temperature range of 190-200°C. 

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