Various aspects of electrical and thermophysical properties of nanocomposites based on low‐density polyethylene matrix filled with nanostructuralized expanded graphite (EG) and standard, microsized graphite are presented in this article. A periodical method developed in the laboratory was used to measure simultaneously thermal conductivity, specific heat, and diffusivity of composites at room temperature. The effect of micro‐ and nanosized fillers on the final thermophysical and electrical behavior is investigated. It was found that the electrical conductivity of composites strongly depends not only on the filler content but also on the filler size. When the microsized graphite was used, the percolation concentration of the filler was found to be 15 vol%, whereas the percolation concentration of the filler in nanocomposites filled with EG of large sizes was significantly lower. Similarly, it was shown that the graphite significantly improves the thermophysical behavior of composites filled with micro‐ and nanofiller sizes. The thermal conductivity measured values were also compared with some theoretical models for the prediction of the thermal conductivity. POLYM. COMPOS., 2012. © 2013 Society of Plastics Engineers

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IntroductionTitanium containing active species in supported Ziegler-Natta catalysts are not accessible to direct observation. Therefore, special methods are utilized to describe the structure and characteristic properties at least of a fraction of the titanium amount.Electron spin resonance (ESR) measurements were used extensively for this purpose and attempts were made to reveal the relations between the ESR-active Ti(II1) population and the polymerization Chien and H u t ) studied the propene polymerization with a highly active MgCI, supported catalyst and found that isotactic poly(propy1ene) (PP) is formed on the ESR-active Ti(II1) species and atactic PP on the ESR-silent sites. The reaction of TiCl, with Al(i-C,H& was studied recently') by means of the ESR spectroscopy with the result that clusters of TiCl, are formed in the solution even at very low temperatures.In this paper, we carried out the propene polymerization with the simplified onephase catalyst SiO,/TiCl,/Al (i-C4H9)36) and the active sites for both atactic and isotactic polymerizations were correlated with the ESR results of the catalyst. Experimental partMaterials, preparation of the catalysts, polymerization and analytical procedures are described in a preceding paper ').The silica gel, grade 952 (Fuji Davison Co., Japan; Grace GmbH, Germany) and 175 (Grace GmbH, Germany), was dehydrated in a quartz glass vessel in a nitrogen stream at 400 or 600 "C for 6 h, then pumped for 1 h and cooled under nitrogen. The specific surface area of the silica gel was measured using the Brunauer-Emmett-Teller method to obtain 306 f 4 m2/g (grade 952) and 750 f 8 m2/g (grade 175). The pore volumes calculated using a nitrogen desorption isotherm were 1,6 * 0,l and 0,4 f 0,l cm3/g, respectively; the range of pore diameter distribution was 6 -30 nm with a mean value of 20 nm. The amount of ethane evolved during the reaction of these silica gel samples with a surplus of a triethylaluminium solution (0,5 mol/L) at 25 "C was 1,22 and 1,45 mmol/g, respectively, which can be equivalents of the surface hydroxy groups. The isotactic poly(propy1ene) fraction was determined by extraction with boiling heptane for 8 h using a Soxhlet type extractor. Results and discussionThe polymerization of propene was conducted on the one-phase catalyst system 6, SiO,/TiCI,/AI (i-C4H9), using different mole ratios AI/Ti (see Tab. 1). All polymerization runs exhibited a decay type of kinetic pattern with a maximum rate reached in 10-20 min, and practically a stationary rate in 2 h after starting the polymerization. The catalyst prepared at Al/Ti = 2, which showed the highest activity for the ethylene polymerization, gives also the highest activity for the propylene polymerization.Further increase in the AVTi mole ratio causes a decrease in activity accompanied by a remarkable increase in catalyst stereospecifity. Judging from the change of the catalyst color together with these results, it may be considered that most of the titanium species are separately located on the silica gel surface b...

Active one‐phase Ti‐based supported catalysts were prepared by interacting the activated silica gel (0.8 mmol OH groups/g) with RxAlCl3–x (x = 1–3, Al/OH = 0.9–1.0), then with TiCl4 and R2Mg (Mg/Ti = 1–16), and finally with R3Al (Al/Ti = 0–16). The catalyst activity in the fluid bed ethylene polymerization varied between 40 and 540 kg PE/g Ti h, depending on the component used and preparation conditions employed. A mechanism of the polymerization‐active species formation was proposed.