Maria de Fátima V. Marques

Binary metallocene supported catalyst for propylene polymerization

Abstract The binary silica supported catalyst system comprising the Cp2ZrCl2 and SiMe2(Ind)2ZrCl2 metallocene compounds was prepared with different immobilization methods and evaluated at different propylene polymerization conditions. The performance results of the homogeneous isolated catalysts and also the homogeneous catalyst mixture were also included for comparison. High activities were obtained with the supported systems and the molecular weight of the produced polypropylene was invariably higher than that obtained using the homogeneous precursor.

Polyethylene synthesis using zeolite as support for metallocene catalyst

Abstract Zeolite sodic mordenite was evaluated as support for bis(cyclopentadienyl) zirconium dichloride catalyst in the synthesis of polyethylene. The zeolite was calcinated at 300°C under heating rate of 2°C/min before treatment with methylaluminoxane (MAO) and Cp 2 ZrCl 2 solutions. The supported catalysts were prepared under different conditions of Cp 2 ZrCl 2 impregnation temperature and MAO and Cp 2 ZrCl 2 concentrations. The performance of the heterogeneous catalyst systems was evaluated in terms of polymerization activities and the characteristics of the produced polyethylene. Although not expected, it was observed in this work that high amounts of zirconium incorporated on the support leaded to catalysts with lower catalyst activity. The obtained polyethylene with these supported catalysts presented very high molecular weights.

Thermal and Mechanical Properties of Sustainable Composites Reinforced with Natural Fibers

Chemically modified natural fibers were introduced into a commercial biodegradable poly(butylene adipate-co-terephthalate) (PBAT) matrix to obtain composite materials in a mini-extruder. Influence of the fiber introduction on thermal and mechanical properties of the composites were studied. A decrease of the crystallinity degree of the composites was observed upon addition of the hydrolyzed-fibers, but the addition of the acetylated ones resulted in the opposite behavior. Thermal stability of the matrix was not affected by introduction of the treated fibers. However, an improvement of mechanical properties of the composites was found by means of dynamic mechanical thermal analysis and tensile tests, particularly for those containing acetylated fibers. Scanning electron micrographs of cryofractured surfaces of the composites showed stronger adhesion of the acetylated fibers to the PBAT matrix. No interfacial gaps or signs of the fiber pullout from the matrix were observed.

Polypropylene nanocomposites using metallocene catalysts supported on commercial organophilic clays

In this work, different organophilic clays were employed as supports for the preparation of heterogenized metallocene catalysts to be evaluated for propylene polymerization. The supports employed were Viscogel B8, Claytone HY and Cloisite 15A. These supports were chemically pre-treated with methylaluminoxane (MAO) and then impregnated with SiMe2(2-Me-Ind)2ZrCl2 complex. The prepared catalysts performed much worse than the homogeneous precursor system. Those organoclays, as well as the prepared metallocene catalysts, were analyzed by X-ray diffractometry (XRD), showing the displacement and broadening of the clay peak to lower angles. The polymers were also characterized by XRD, infrared absorption spectrometry (FTIR) to determine the isotactic index, by thermogravimetric analysis (TGA) to determine the degradation temperatures, by differential scanning calorimetry (DSC) to determine the thermal characteristics of the polypropylene produced, and by transmission electron microscopy (TEM) to examine the morphology of the materials obtained.

Copolymerization of ethylene and butadiene with a ziegler catalyst based on MgH2/TiCl4

Abstract The copolymerization of ethylene and butadiene by a MgH2/TiCl4-AlEt3 catalyst system was studied. The influence of diene concentration in the reaction medium and time of polymerization were described. The distribution of repeating units in the copolymers was random. The diene units were substantially in trans-1,4 configuration at lower diene content and longer polymerization times. The butadiene showed no tendency for homopolymerization with the catalyst system which was studied.

Silane Crosslinked Polyethylene from Different Commercial PE’s: Influence of Comonomer, Catalyst Type and Evaluation of HLPB as Crosslinking Coagent

In the present work, the synthetic route to obtain crosslinked polyethylene (PEX) was studied using vinyltrimethoxy silane (VTMS) as crosslink agent and commercial polyethylene (HDPE and LLDPE). Materials were processed with increasing amounts of VTMS (2.5, 5.0 and 7.5 wt.%). After insertion of silane onto polymer chain in solid state, samples were molded by compression. Gel content was used to measure the extension of crosslinking. Melting temperature and degree of crystallinity were evaluated using differential scanning calorimetry (DSC). The microstructure of the starting polyethylene was correlated with the effectiveness of crosslinking and the resultant thermal and mechanical properties of the PEX. Hydroxylated liquid polybutadiene (HLPB) was employed to improve crosslink efficiency, as well as mechanical properties of the material.

Catalisadores metalocênicos: aspectos gerais e heterogeneização

Este trabalho apresenta uma discussao sobre aspectos gerais da nova tecnologia de sintese de polimeros com microestrutura e propriedades controladas, obtidos via sistema catalitico metaloceno/MAO. Mostra a importância da heterogeneizacao desses sistemas para possibilitar o seu emprego na producao industrial de uma ampla classe de materiais polimericos. Sao discutidas ainda as principais caracteristicas dos suportes mais empregados para esses catalisadores.

Influence of the elastomeric polypropylene addition on the properties of commercial metallocenic polypropylene

Polypropylene with special properties can be obtained by metallocenic catalysts. These catalytic systems represent the beginning of a new age in polyolefins technology. In this work, the influence of the addition of a syndiotactic polypropylene (s-PP) on the processability and mechanical properties of a commercial isotactic polypropylene (i-PP) obtained by metallocenic catalysts was evaluated. Increasing addition of s-PP promoted better processability, with an increase in the impact strength and a decrease in the stress at break. A reduction of the crystallinity in the polymeric blends was verified. The more significant influence of the s-PP addition was observed for the mi-PP, compared to the ZNi-PP.

Magnesium chloride supported metallocene catalysts in olefin polymerizations

Abstract MgCl 2 supported systems and homogeneous Cp 2 ZrCl 2 and Et(Flu) 2 ZrCl 2 catalysts were used to investigate their behavior in ethylene and propylene homopolymerization. MgCl 2 was activated by vigorous ball milling with ethyl benzoate. Two types of catalysts were prepared: immobilizing the metallocene catalyst directly on the carrier and also immobilizing the metallocene catalyst on the carrier pretreated with methylaluminoxane (MAO). Polymerization was carried out in toluene at 50°C and 60°C. MAO was employed as cocatalyst in all polymerizations. Molecular weight, molecular weight distribution, melting point and crystallinity were determined. It is important to report that the molecular weight distribution of polymers, obtained from MgCl 2 supported metallocene catalysts, remained narrow (around 2).

Co- and terpolymerizations of α-olefins and dienes with MgH2-supported Ziegler catalyst

Copolymerizations of ethylene or propylene with butadiene, 1,5-hexadiene or 1,7-octadiene by MgH2/TiCl4-AlEt3 catalyst system were carried out. The effect of diene concentration in the reaction medium for each polymerization system on catalytic activity was observed. The compositions of the obtained copolymers were evaluated and the reactivity ratios were determined. Ethylene-propylene-diene terpolymerizations with the same catalyst system were also investigated.