Polymer compositions based on polyethylene and poly(1-hexene)

PE-poly(hexene-1) compositions were synthesized via successive polymerization of the corresponding monomers in the presence of a titanium-magnesium catalyst. It was shown that a PE-poly(1-hexene) diblock copolymer is formed along with homopolymers of ethylene and 1-hexene during the polymerization. Nascent samples of these polymer blends are characterized by exceptionally high melting temperatures and heats of melting of the PE component (up to 149°C and 278 J/g, respectively).     

The electrical properties of schungite-containing compositions based on polypropylene and high-density polyethylene

Variations in the dc and ac conductivities of schungite-containing compositions based on polypropylene-high-density polyethylene (PP-PE) blends were studied depending on the composition of the polymeric blend, the volume concentration of the filler, and the order of the introduction of the composition components during the preparation of compositions. It was shown that the conductivities of the compositions could depend on the order of the introduction of the components. The structure of initial and schungite-containing PP-PE blends of different compositions was studied by atomic-force microscopy. It was shown that the structure of the compositions depended on the composition of the initial PP-PE blends and the order of the introduction of the components into schungite-filled PP-PE compositions.     

Properties of in-situ filled polyethylene

Polyethylene-filler composites (kaolin, BaSO₄, and TiO₂) have been prepared by in-situ polymerization using a metallocene catalyst and by extrusion mixing in the melt. TiO₂ influences the polymerization process. In-situ polymerization was found to be advantageous with respect to encapsulation, dispersion of the filler particles leading to improved mechanical properties, except for TiO₂ containing composites. No significant influence on crystallization was observed.     

Photocrosslinking of polyethylene. II. Properties of photocrosslinked polyethylene

Some properties of photocrosslinked high density polyethylene (2 mm thick sheets) have been studied. The homogeneity of the network is greatly improved by the application of triallylcyanurate (TAC) as crosslinking agent. The role of TAC in promoting the crosslinking is discussed. The crosslinked PE is found to be durable towards immersion in boiling water. Oxygen permeability increases while density and melting point decrease with increasing degree of crosslinking. The network chain density is obtained using conventional swelling method in boiling xylene, which together with data from melting point depression show that contribution of chain entanglement is insignificant to the gel formation of PE in this work.     

Properties of adhesive compositions based on thiirane

Comparative investigations of adhesive composite materials based on thiirane and its oxirane analog are carried out. It is shown that compositions based on thiirane provide for a high rate of adhesion and cohesion strength gain. It is established that the maximal values of the adhesion strength for thiirane are reached at essentially lower concentrations of a curing agent than in the case of oxirane derivatives.     

Deformation and structure of doubly oriented polyethylene

Doubly oriented low-density polyethylene with parallel lamellae was compressed along the initial draw direction (i.e., at right angles to the lamellar surfaces) at 20°C. Wide- and low-angle x-ray diffraction were used to determine the changes in the molecular orientation and in the texture. During the compression, specimens previously annealed at or near 102°C were found to undergo changes in length, in long spacing, and in molecular orientation which were consistent with an (001) chain slip mechanism. In specimens annealed at higher temperatures x-ray diffraction indicated that during compression some series component of the long spacing was compressed by a much smaller amount than the remainder of the long spacing, which deformed by chain slip; in these cases it was found that the macroscopic strain along the compression axis (ε_y) was greater than the strain in the long spacing along that axis (ε_d). It is suggested that the missing strain which makes ε_y greater than ε_d is due to partial melting and the consequent development of amorphous regions between the stacks of lamellae.     

Relaxation processes and structure of ultradrawn polyethylene

Solid-state extruded polyethylene fibers have been prepared, with a wide range of draw ratios and constant processing temperature. The draw ratios vary from 4 up to 30, and the processing temperature was always 398 K. The extruded material behaves anisotropically, owing to the high degree of chain orientation in the drawing direction. The modulus and linear expansion coefficients in the fiber axis direction have been measured, over a wide temperature range, from 140 K up to 320 K. These two properties are closely related to the degree of structural continuity of the fibers. A fibrous structure model is proposed to explain the temperature effects and the values obtained for the modulus and expansion coefficients, in terms of crystallinity and volumetric fraction of extended-chains structure. At least three relaxation processes can be identified which cause the structural continuity of the fibers to change with temperature.     

Improvement of adhesion strength of compositions based on chlorosulfonated polyethylene to rubbers

In order to increase the adhesion strength to rubbers, chlorosulfonated polyethylene was modified with amino-containing compounds. It is shown that such modification increases the adhesion strength of the compositions to resins by two to five times.     

Properties of polyethylene before and after cold drawing

Summary Polyethylene at room temperature and at moderate rates of deformation fails in a tough manner, that is to say it fails in shear. This mode of response to an energy input is a principal and characteristic attribute of the liquid state and manifests itself as viscous flow. This is true even if the stress system is one of nominal uniaxial tension. By subjecting suitable specimens of polyethylene to various rates of elongation and hence to varying shear rates and noting the maximum (yield) stress developed in each case it is therefore possible, by plotting yeld stress vs. draw rate, to determine the tensile viscosity of the undrawn polymer in the neck region. experimental results indicated that a log-log plot gave a fair linear relationship and that the Power Law applies. This makes it possible to calculate the zero-shear-rate viscosity and the power index of the polymer and to predict the yield stress for a given strain rate. It is, however, recognized that isothermal conditions do not in fact exist and that this method must therefore be regarded as an approximation valid only for relatively low strain where the development of frictional heat is not excessive, unless further assumptions can reasonably be made.A successful attempt has been made to correlate the instantaneous recovery after draw with the crystallinity of the polyethylene rods.

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Zusammenfassung Bei Raumtemperatur und bei mäßiger Zugdehnungsgeschwindigkeit reagiert das Polyäthylen in zäher Art. Dies bedeutet, daß ein Scherungsmechanismus bei der Zugdehnung vorliegt. Diese Reaktion auf einen Energie-einsatz its ein charakteristisches Zeichen für viskosen Fluß, welcher auch für das vorliegende nominell einachsige Zugdehnungssystem gilt. Wenn man nun geeignete proben von Polyäthylenen bei verschiedenen Geschwindigkeiten der Zugdehnung unterwirft und di maximale-Zugspannung abliest, welche bei dem Nachgeben (yield) entwickelt wird, dann ist es möglich, durch Auftragen von Maximal-Zugspannung gegen Zugdehnungsgeschwindigkeit die Zugviskosität des Polymeren in der Schulterregion der kaltziehenden Probe zu bestimmen. Die Versuchsresultate gaben ziemlich gute Geraden im log-log Auftrag, so daß das Potenzgesetz gilt. Dies ermöglichte die Berechnung der Viskosität bei Null-Zugdehnungsgeschwindigkeit wie auch der charakteristischen Potenzkennzahl, wonach die für Nachgeben der Probe notwendige Zugspannung bei beliebiger (doch nicht allzu großer) Zugdehnungsgeschwindigkeit bestimmt werden kann. Es its dabei zu bedenken, daß diese Methode wegen erheblicher Wärmeentwicklung nur bei mäßigen Zugdehnungsgeschwingdigkeiten eingesetzt werden kann, da die durch Scherung entwickelte Wärme sonst nicht als vernachlässigbar klein angesehen werden kann.Es wurde ein erfolgreicher Versuch gemacht, die Sofort-Rückschnellung nach Kaltzug mit der Kristallinität des Polyäthylens in quantitativen Zusammenhang zu bringen.

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With 8 tables     

Development of adhesive ozone-resistant compositions based on chlorosulfonated polyethylene for elastomeric materials

Chlorosulfonated polyethylene (CSPE) is modified by a Diafen FP amine-containing compound. It is shown that compositions based on modified CSPE can be used as adhesive compositions for rubber splicing and coatings for rubber protection from ozone aging.     

Elastic moduli and structure of low density polyethylene

Summary Low density polyethylene film is drawn at room temperature four times the original length and subjected to thermal annealing at 60, 80, and 100 °C keeping the film length constant. Long spacing measured by SAXS increased with increasing temperature of annealing; the increase of the long spacing is presumed to be due to the decrease of the number of micelles through relaxation during the annealing. Simultaneous measurement of the changes of the long spacing and the film length by stretching is carried out and stress-extension curves are obtained. The values of the initial moduli of the long spacingE ₁ and the film lengthY are very near to each other. Elastic modulus of the crystal latticeE _c is known to be 235 GN/m² and that of the amorphous regionE _a is found to be 0.15 GN/m². When higher stress is applied than in the case of the initial modulus, the percentage of extension of film is much greater than that of the long spacing. The discrepancy is explained by the increase of the number of micelles through stress crystallization.Dedicated to Professor Dr. K. Ueberreiter on the occasion of his 70th birthday.     

Properties of adhesive compositions based on thiirane and oxirane mixtures

Deformation, strength, dynamic-mechanical, and adhesive properties of polymers based on thiirane and oxirane mixtures were studied. The character of changes in indicators of properties on the ratio of the components in a mixture, as well as the duration and temperature of curing, was found to be quite complicated.     

Piled-lamellae structure in polyethylene film and its deformation

The fine structure of polyethylene film has been investigated by using a high-resolution scanning electron microscope equipped with a field emission source. The original film surface of a-axis-oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled-lamellae units, each pile containing three to ten lamellar crystal sheets. The piled-lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled-lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress-strain curves of films drawn the machine direction and perpendicular to it.     

Nanoporous structure of ultrahigh-molecular-weight polyethylene reactor powder

The influence of the catalyst system and synthesis conditions on the morphology and molecular dynamics of reactor (nascent) powders of ultrahigh-molecular-weight PE synthesized over supported Ziegler-Natta catalysts in laboratory reactors was studied by means of electron microscopy and ¹H broadline NMR spectroscopy. For comparison, commercial reactor powders were studied as well. The type of the catalyst system and the temperature of slurry polymerization have a substantial effect on the supermolecular structure of the nascent polymer. The proton NMR spectra of the reactor powders synthesized at low temperatures display a narrow component. An analysis of its behavior at low temperatures and different humidities led to the conclusion that the signal is due to water localized in nanopores of 2–4 nm in size in the nascent polymer. The role of nanopores in the sintering of reactor particles is discussed.     

Radiation-Induced degradation of polyethylene: Polymer structure and stability

The radiation-stability of annealed and quenched polyethylene (PE) was estimated by gel, FTIR, and mechanical property (elongation at break) measurements. Although both types of PE showed an equal probability in gel and carbonyl formation, the resistance to γ-ray irradiation as probed by elongation at break (%) was superior in quenched PE compared to annealed PE. This difference is discussed from the viewpoint of polymer structure, especially the number of the tie molecules, of annealed and quenched PE.