Polyethylene higher ethylene concentration

Fig. 18. A plot of the minimum of the cloud point curve against chlorine content for blends of chlorinated polyethylene with ethylene-vinyl acetate copolymers having A (40 % vinyl acetate), B (45 % vinyl acetate). It is seen that the higher concentrations of interacting groups, CHCl or C=0, give a larger temperature range of miscibility...

The reaction rate is typically regarded as approximately first order in ethylene in polyethylene manufacture with the Phillips catalyst [47,52,349, 379,560,637,727-729]. In the solution process, this relationship holds well, at least when normal commercial concentrations are encountered. However, in slurry or fluidized-bed polymerization, at lower temperatures when the induction time can be significant, the dependence of rate on the ethylene concentration becomes more complex. This complication results because the initiation reactions, reduction and alkylation, also show a strong dependence on ethylene concentration, in addition to the polymerization itself. As noted above for Cr/AIPO4 (Figures 171 and 172), these initiation reactions can exhibit higher reaction orders than first [637]. 

Fig. 6 Melt rheological behaviOT of polyethylenes polymerized with 4/MAO varying the ethylene concentration and polymerization time. Single points shown at the of the graph represent theoretical j/o values [102] expected for a linear polymer of corresponding M . A decrease in the Ce results in the strongly elevated p at low shear rates and significant shear thinning. Note that for the samples with very high viscosity, the true zero-shear viscosity value >/o would be much higher than the experimentally measured >/ (

Two unique features of a solution polymerization process is the need to operate at relatively higher ethylene pressures in order to maintain a sufficient ethylene concentration due to the higher temperatures used, and the need to utilize an organic solvent such as cyclohexane that readily dissolves polyethylene. For the Phillips catalyst, polymerization temperature was used to control polymer molecular weight. 

Dimerization in concentrated sulfuric acid occurs mainly with those alkenes that form tertiary carbocations In some cases reaction conditions can be developed that favor the formation of higher molecular weight polymers Because these reactions proceed by way of carbocation intermediates the process is referred to as cationic polymerization We made special mention m Section 5 1 of the enormous volume of ethylene and propene production in the petrochemical industry The accompanying box summarizes the principal uses of these alkenes Most of the ethylene is converted to polyethylene, a high molecular weight polymer of ethylene Polyethylene cannot be prepared by cationic polymerization but is the simplest example of a polymer that is produced on a large scale by free radical polymerization... 

It has been found that, for a fixed mineral filler content, the viscosity of PMF-based composites increases when the coat is made of polyethylene [164, 209, 293], poly(vinyl chloride) [316] and polypropylene [326, 327], The picture was different, however, for composites based on the ethylene/vinyl acetate copolymer to which kaolin with grafted poly (vinyl acetate) was added [336]. Addition of PMF with a minimum quantity of grafted polymer results in a sharp drop of flowability (rise of viscosity), in comparison to addition of unmodified filler but with a further increase of the quantity of grafted polymer the flow gradually increases and, depending on the kaolin content and quantity of grafted polymer, may even become higher than in specimens with unmodified filler, for equal concentrations. 

The solubility of ethylene in freshly prepared polyethylene, and its diffusion out of the latter were studied in relation to the formation of explosive ethylene-air mixtures in storage. Explosive mixtures may be formed, because the solubility of ethylene in its polymer (e.g. 1130 ppm w/w at 30°C) considerably exceeds the concentration (30 ppm at 30°C) necessary to exceed the lower explosive limit above the gas-containing polymer in closed storage, and the diffusion coefficient is also 30% higher than for aged polymer samples. 

The beneficial effect that the introduction of water has on the extraction of ethylene from low-density polyethylene is shown in Fig. 18. The reduction in the exit concentration of ethylene is substantial, especially at the higher pressures, and dramatically illustrates the increase in mass transfer rates which results from the introduction of an immiscible stripping agent. 

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