Molecular polyethylene

Thermal destruction of low-pressure polyethylene with molecular weight of 34,800 and of high-pressure polyethylene is completely retarded by potassium hydroxide. The molecular weight of high-molecular polyethylene decreases by a factor of 1.8, and without an... 

In [332] it was noted that the strength of samples cut out at different locations of an article made from filled thermoplastics by pressure molding may differ widely — which is due to the non uniform orientation of the polymer at different locations of the mold. The very high strength parameters of composites with PMF in molded specimens are obviously also due to orientation effects, while for standard mixed samples of similar composition (that is, a matrix which, apart from the filler, contains some superhigh molecular polyethylene imitating the PMF coats) the... 

Large yields of polymer seem to be obtained only when polymerization proceeds on the outer catalyst surface, because the transport of high molecular polyethylene from catalyst pores is impossible (112). The working part of the specific surface of the catalyst can be expected to increase with diminishing strength of links between catalyst particles (112). Therefore, to obtain a highly active catalyst a support with large pore volume should be used (e.g. silica with pore volume >1.5 cm8/g). 

Pigment preparations are also marketed for coloring thermoplastic PUR. Their carrier materials range from vinyl chloride or vinyl acetate copolymers, such as are used for PVC, through low-molecular polyethylene to PUR itself. 

Rotation of the core (or its reciprocating rotary vibration) can be even more efficient in processing of high-viscous melts, for example, filled polymers, high- and superhigh-molecular polyethylene (with MM > 10s). We may assume that this is dependent upon two major causes. The introduction of a filler results in a changed spectrum of relaxation time H(9) 41-42-45). Thus, for example, introduction of 10% of chalk (by volume) into polyolefins shifts the spectrum along the axis of coordinates towards... 

Very recently. LET effects on fluorescence lifetimes of low molecular polyethylene model compounds (n-alkane) have been studied by many kinds of pulse radiolysis - methods such as electron beam, ion beam and synchrotron radiation (SR) [40] pulse radiolysis techniques [41]. Figure 10 shows time profiles of the fluorescence from neat n-dodecane liquids irradiated many kinds of radiation with different LET. The fluorescence lifetimes from irradiated neat... 

Very recently LET effects of ion beams on both standard polymers such as polystyrene and low molecular polyethylene model compounds (n-alkanes) have been studied by time-resolved spectroscopic methods, that is, ion beam pulse radiolysis techniques. Further basic studies are necessary so that the detailed mechanisms of ion beams on polymers can be clarified, especially LET effects and high density excitation effects. 

Today, the use of organic solvents, such as methylene chloride or chloroform is severely restricted, but nevertheless, small quantities of organic solvents are still used by most pharmaceutical companies. The most commonly used are ethanol, propylene glycol or low-molecular polyethylene glycol. Povidone is miscible in practically all proportions in these solvents and in water, though, above a certain concentration, the solution obtained has a high viscosity (see Section 2.2.3). 

Tilting disc Leaflet Delrin Pyrolytic carbon (carbon deposited on graphite substrate) ultra high molecular polyethylene (UHMPE)... 

In injection molding of semicrystalline thermoplastics, for example polyamide, polyoxymethylene, ultrahigh molecular polyethylene (very high melt viscosity), linear polyesters (PET, PBT), local variations in molecular orientation result in dimensional variations in the part (warpage, memory effect), especially if the toothed gear is exposed to a thermal stress load. 

Verfahren zur Herstellung von hochmolekularen Polyathylenen Process for Preparing High-Molecular Polyethylenes Karl Ziegler, Heinz Breil, Erhard Holzkamp, Heinz Martin Filed 18 November 1953, Published 14 April 1960... 

The crystalline fraction, C, is correlated with the chain length. High molecular polyethylene (HMPE) has a crystalline... 

Streicher RM. Ultra-high-molecular polyethylene as material for hip-joint cups. Stuttgart Georg Thieme Verlag 1986. 

Microporous polymer membranes are the most commonly used separators in lithium-ion batteries. Majority of the microporous polymer membrane separators are based on semicrystalline polyolefin materials, such as polyethylene (PE), polypropylene (PP), PE-PP blends and high-density polyethylene (HDPE)-ultrahigh molecular polyethylene (UHMWPE). 

For special parts, preference is given to using plastic, for the filter grids and the fdtrate pipes, for example polypropylene. The control and near plates are normally made of high-molecular polyethylene. These parts can optionally also be supphed in other materials, for example steel, stainless steel or cast iron. 

Turning to analogy about mediiuns with crystalline morphology of polymer matrices, let us note, that semicrystalline polymers (e.g., high-molecular polyethylenes) large strains, making 1000 2000%, are realized owing to... 

Beloshenko, V. A., Kozlov, G. V., Slobodina, V. G., Prut, E. U., Grinev, V. G. (1995). Thermal Shrinkage of Extrudates of Ultra-High-Molecular Polyethylene and Polymerization-Filled Compositions on its Basis. Vysokomolek. Soed. B, 37(6), 1089-1092. 

Kozlov, G. V, Beloshenko, V. A., Aloev, V. Z., Varyukhin, V. N. (2000). Microhardness of Ultra-High-Molecular Polyethylene and Componor on its Basis Produces by Solid-Phase Extrusion Method. Fiziko-Khimicheskaya Mekhanika Materialov, 36(3), 98-101. 

The orifice angle of the cone can signiflcantly influence the flow anomalies that are frequently found with high molecular polyethylene (PE). In such cases, changing the melt temperature has little effect. Computer programs are available to calculate the distribution of shear rate in the extrusion flow channel. It is important to ensure that the critical shear rate occurs near the die exit resp. is confined to as narrow a region as possible. With the accumulator head, the effects of flow anomahes can be influenced by the extrusion velocity. To achieve the shortest cycle times with continuous extrusion, the plastic usually exits from the orifice at close to critical shear rate. 

Polyethylene has been used in surgery since the 1950s. Experience shows that polyethylene cannot be used to replace soft tissue, but is a good substitute material for bone tissue (hip joint, pelvic bone). However, the first applications of PE-LD as bone tissue substitute resulted in high material wear. Subsequent developments in polymer synthesis led to a polyethylene with a higher molecular mass (PE-UHMW ultrahigh-molecular polyethylene (M, / = 4 10 g/mol)), that allowed wide application for pelvic prostheses. Table 5.129. 

Garcia RM, Kraay Ml, Messerschmitt PJ, Golberg VM, Rimnac CM. Analysis of Retrieved Ultra High Molecular Polyethylene Tibial Components From Rotating-Platform Total Knee Arthroplasty. J Arthroplasty. 2009 24 131-8. 

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