Search results for "polymers"
showing 10 items of 3567 documents
DEGRADATION OF MATER-BI /WOOD FLOUR BIOCOMPOSITES IN ACTIVE SEWAGE SLUDGE
2009
The mechanical properties of Mater-Bi® are, in general, not adequate for certain applications and the addition of a filler is therefore necessary. Among the different fillers, natural fibres are particularly interesting because they potentially allow improving the performance of the material without compromising its biodegradability. In order to improve the basic mechanical properties of a Mater-Bi grade and to obtain a new, fully biodegradable material, wood flour based composites were prepared by different processing methods. To simulate actual and not laboratory bacterial attack on the prepared materials, in this work we studied the biodegradation of the composites in a real active sewag…
Durability of Basalt/Hemp Hybrid Thermoplastic Composites
2019
The Achilles heel of thermoplastic natural fibre composites is their limited durability. The environmental degradation of the mechanical properties of hemp and hemp/basalt hybrid-reinforced high-density polyethylene (HDPE) composites has been investigated with a special focus on the effects of water ageing and accelerated ageing, including hygrothermal and UV radiation. Modification of the matrix was carried out using a maleic anhydride high-density polyethylene copolymer (MAPE) as a compatibilizer. Hybridization of hemp fibres with basalt fibres and the incorporation of MAPE were found to significantly decrease the water uptake (up to 75%) and increase the retention of mechanical propertie…
Synthesis and activity of zirconocene catalysts supported on silica-type sol-gel carrier for ethylene polymerization
2001
Synthesis and activity of bis(cyclopentadienyl)zirconium dichloride catalyst supported on unconventional silica-type material obtained in sol-gel process and activated by organoaluminium co-catalyst were studied. The effect of support modification conditions (thermal dehydration and/or modification by organoaluminium compound) and a type of co-catalyst on an activity of the catalytic system in ethylene polymerization and properties of resulting polymers were investigated and compared with results obtained earlier for vanadium catalysts supported on mentioned sol-gel carrier. The most appropriate method of the sol-gel silica-type support preparation is thermal pre-treating (200°C) followed b…
A practical ethylene polymerization for vinyl-polyethylenes: synthesis, characterization and catalytic behavior of α,α’-bisimino-2,3:5,6- bis(pentame…
2016
A series of α,α′-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridyliron chlorides was synthesized in a one-pot reaction and characterized by FT-IR and elemental analysis as well as X-ray crystallography for one representative iron complex, where the Fe center adopts a distorted square pyramidal geometry with three coordinating nitrogen and two chlorine atoms. The iron precatalysts, upon treatment with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), exhibit high activities in the range of 107 g of PE per mol of Fe per h toward ethylene polymerization, yielding highly linear and, more importantly, vinyl-polyethylenes. The correlation between the structural features of iron…
Carboranyl Substituted Siloxanes and Octasilsesquioxanes: Synthesis, Characterization, and Reactivity
2008
Carboranyl-containing disiloxane, cyclic-siloxane and cage-like silsesquioxane have been prepared in high yields. Two routes are compared for their preparation, a classical hydrolytic process based on hydrolysis and condensation of the freshly prepared carboranylalkylchlorosilane and ethoxysilane precursors and a nonhydrolytic route based on the specific reactivity of chorosilane toward DMSO. Based on the typical reactivity of the carboranyl group toward nucleophiles, dianionic disiloxanes and octaanionic silsesquioxanes were obtained without modification of the siloxane bond. Products are fully characterized by FTIR, NMR and MALDI-TOF methods.
Finely tuned nickel complexes as highly active catalysts affording branched polyethylene of high molecular weight: 1-(2,6-Dibenzhydryl-4- methoxyphen…
2018
Abstract A series of unsymmetrical 1,2-bis(imino)acenaphthenenickel(II) halides containing N-2,6-dibenzhydryl-4-methoxyphenyl – a single bulky group with adjusted electron donating properties – has been synthesized and characterized. These compounds adopt distorted tetrahedral geometry and their 1H NMR spectra show the paramagnetically shifted peaks. On activation with a low amount of Et2AlCl or ethylaluminum sesquichloride (EASC), these nickel complexes display high activity in ethylene polymerization, yielding the polyethylene of high molecular weight. They are also stable at elevated temperature; superb activity of 2.51 × 106 g of PE (mol of Ni)−1 h−1 can be attained at 90 °C. The result…
The apparently anomalous effects of surfactants on interfacial tension in the IBA/water system near its upper critical solution temperature
2016
We studied the effect of anionic, cationic, and nonionic surfactants on the interfacial tension between the two phases of the isobutyric acid/water system using spinning drop tensiometry. It has been found that interfacial tension decreases with increasing concentration of the surfactant in the case of sodium dodecyl sulfate (SDS) and of dodecyltrimethylammonium chloride (DTAC). However, in the case of Triton X-100 an increase of surfactant concentration leads to an increase of the interfacial tension. Such results are consistent with the upper critical solution temperature (UCST) in the presence of these surfactants: the UCST decreases with increasing SDS and DTAC concentrations while it i…
Multi-Alkenylsilsesquioxanes as Comonomers and Active Species Modifiers of Metallocene Catalyst in Copolymerization with Ethylene.
2018
The copolymers of ethylene (E) with open-caged iso-butyl-substituted tri-alkenyl-silsesquioxanes (POSS-6-3 and POSS-10-3) and phenyl-substituted tetra-alkenyl-silsesquioxane (POSS-10-4) were synthesized by copolymerization over the ansa-metallocene catalyst. The influence of the kind of silsesquioxane and of the copolymerization conditions on the reaction performance and on the properties of the copolymers was studied. In the case of copolymerization of E/POSS-6-3, the positive comonomer effect was observed, which was associated with the influence of POSS-6-3 on transformation of the bimetallic ion pair to the active catalytic species. Functionality of silsesquioxanes and polymerization par…
Crosslinked α,β-Polyasparthydrazide Micromatrices for Controlled Release of Anticancer Drugs
1995
The preparation of new hydrogels by the reaction of α,β- polyasparthydrazide and glutaraldehyde is reported. A different crosslinking degree was obtained by varying the ratio crosslinking agent/polymer which influenced the swelling behavior of the gel. 5-Fluorouracil, was incorporated into the matrices during the crosslinking reaction and in vitro release studies were performed in simulated gastric juice (pH 1.1) and pH 7.4 buffer solution. The hydrogels prepared were chemically stable in the dissolution media. The observed data show the potential application of these new matrices for peroral administration of anticancer agents.
Spectroscopic studies of the stability of monolayers of 2-docosylamino-5-nitropyridine at the air/water interface
1991
Monolayers of 2-docosylamino-5-nitropyridine (DCANP) at the air/water interface were investigated by UV/Vis spectroscopy. The combination of this method with the classic constant-area relaxation technique yields insight into the longtime stability and the collapse behavior of monolayers. We have demonstrated that monolayers of DCANP are certainly stable under standard deposition conditions. At surface pressures above 20 mN/m monolayer instabilities lead to the formation of a three-dimensional head-to-head multilayered structure.