Inhibition of polyethylene

Fiber glass provides effective inhibition of polyethylene thermal destruction up to 400°C. The inhibitive efficiency increases with increased content of sodium oxide from 0.7-16% (Table 5). 

Table 5 Inhibition of Polyethylene Thermal Destruction by Filler—Fiberglass of Varying Alkalinity...

Boric acid esters provide for thermal stabilization of low-pressure polyethylene to a variable degree (Table 7). The difference in efficiency derives from the nature of polyester. Boric acid esters of aliphatic diols and triols are less efficient than the aromatic ones. Among polyesters of aromatic diols and triols, polyesters of boric acid and pyrocatechol exhibit the highest efficiency. Boric acid polyesters provide inhibition of polyethylene thermal destruction following the radical-chain mechanism, are unsuitable for inhibition of polystyrene depolymerization following the molecular pattern and have little effect as inhibitors of polypropylene thermal destruction following the hydrogen-transfer mechanism. 

Inhibition of polyethylene thermal destruction by polypyrocatechin borate could be represented as follows. The initial molecular-chain scission of branched... 

At 300°C and in the presence of KOH an increase in the molecular weight is observed, i.e., the reaction of macropolymerization is realized [38,39]. Potassium hydroxide is effectively inhibiting thermal destruction of polyethylene at temperatures from 350-375°C. The per cent change in molecular weight is half or one-third as high as that without the use of an inhibitor. At 400°C the efficiency of inhibition is insignificant. Potassium hydroxide with an ABC carrier is effective up to the temperature of 440°C due to the increased contact surface of the inhibitor with macroradicals. 

A similar situation is observed when studying the effect of temperature on inhibition of thermal destruction of polyethylene by fiber glass of varying composition (Table 6). The molecular weight of polyethylene is practically unchanged when exposed over a period of 6 hours at 350°C with 30% of fiber glass containing 16%... 

The inhibitive efficiency of alkali metal hydroxides increases with increased branching of polyethylene. This is confirmed by more pronounced effect of these hydroxides diminishing the yield of propane and propylene than in case of ethane and ethylene. The decreased yield of propane and propylene is also conditioned by more efficient inhibition of the macroradical isomerization stage by alkali metal hydroxides. Upon thermal destruction of polyethylene with the use of inhibitors the... 

One would think that thermal destruction of polyethylene should be inhibited by hydroxides of alkali metals according to the following scheme, as with phenols ... 

Metallizing is supported by the fact that thermal destruction of polyethylene is inhibited by alkali metals. 

In the process of inhibition polypyrocatechin borate interacts with polyethylene macroradicals to form the B—O—C bonds. This is confirmed by the fact that the absorption spectrum of polyethylene inhibited with polypyrocatechin borate revealed the bands in the region of 1350 cm" characteristic for the B—O—C bond. There is no such a band in the spectrum of pure polypyrocatechin borate after heating under the same conditions. Chemical analysis of boron in polyethylene provides support for the IR-spectroscopy data concerning the presence of chemically bonded boron in polyethylene after destruction. 

Polypyrocatechin borate has a higher inhibitive efficiency relative to the reactions of the radical R2 than to that of the radical Ri, since the latter exerts a more severe decrease in the yield of propane and propylene than in the yield of ethane and ethylene, and favors an insignificant growth of polyethylene nonsaturation in the pro-... 

Po[yamine disulphides do not inhibit peroxide vulcanization of polyethylene, are stable in air up to 300-350°C, exhibit good compatibility and show no sweating out from the polyethylene mass. Table 8 gives the comparison between the efficiency of polyamine disulphides as thermostabilizers of cured polyethylene. 

An investigation into the effect of the concentration of polyaniline disulphide on inhibition of thermal destruction in case of cured polyethylene has demonstrated that polyaniline disulphide is efficient even at the concentration of 0.25%. An increase in the concentration over the range 0.25-1.0% results in the increased efficiency, while further increase in the concentration leads to a slight drop in inhibition. 

Table 8 Inhibition of Thermal Destruction of Low-Density Cured Polyethylene in Vacuum (10- torr)...

Other common poly glycol-based antifoams include certain derivatives of polyethylene glycol (PEG), which are condensation polymers of ethylene glycol. An example is polyethylene glycol-8 dioleate. Apart from its antifoam properties, PEG-8 dioleate is also used in cooling water inhibitor formulations as a surface cleaner, in the formation of a corrosion-inhibiting surface film. Additionally, it is employed as an oil-soluble emulsifier for other defoamer chemistries. 

Stearamide is one of many electron donors which donate an electron to the cationic moiety in excited MAH or in propagating -MAH chains. This results in the inhibition of the homopolymerization of MAH and decreases the crosslinking of polyethylene and the degradation of polypropylene which accompany the peroxide-catalyzed reaction of MAH with these polyolefins (8,9). ... 

Catalyst efficiency, estimated by polymer yield, eliminated several of the potential CSAs due to their inhibition of polymerization. For those combinations that produced a sufficient amount of polymer for characterization, the molecular weights and molecular weight distributions of the polyethylene samples were then compared to control polymers prepared with no added CS A. A reduction in the Mn in combination with a narrowing of the MJMn indicated a hit for chain shuttling behavior. 

Research in this field is ongoing aiming to understand the mechanism of action of kinetic inhibitors. Lee and Englezos (2005) showed that inclusion of polyethylene oxide (PEO) to a kinetic inhibitor solution was found to enhance by an order of magnitude the performance of the hydrate inhibitor. Binding of inhibitor molecules to the surface of hydrate crystals was considered to be the key aspect of the mechanism of kinetic inhibition (Anderson et al.,... 

EP-4 developed by ERDL is a very flexible polyester based on polyethylene glycol with molecular weight-200 (PEG-200), isophthalic acid (IPA) and maleic anhydride (MAn). Before its use, it is blended with styrene monomer (1 1) and cured at room temperature using cobalt naphthenate (as an accelerator) and methyl ethyl ketone (MEK) peroxide (as a catalyst). This meets the requirements of the main inhibitor and is used for inhibition of DB and CMDB propellants after the application of a barrier coat (generally a rigid polyester such as PR-3). However, it is observed during manufacture of EP-4 that there is a lot of batch-to-batch variation in properties in spite of the strict quality control measures adopted during its manufacture. 

Dintaman JM, Silverman JA. Inhibition of P-glycoprotein by D-a-tocopheryl polyethylene glycol 1000 succinate (TGPS). Pharm Res 1999 16 1550-1556. 

Hugger, E.D., et al. 2003. Automated analysis of polyethylene glycol-induced inhibition of P-glycoprotein activity in vitro. J Pharm Sci 92 21. 

The third side reaction is formation of a small amount of polyethylene during the growth step. The quantity of polyethylene does not represent a significant yield loss, but does present serious processing problems. The polymer deposits on reactor surfaces, inhibits heat transfer, plugs valves, and must be cleaned out periodically. A Conoco patent (9) indicates this problem can be prevented by addition of small quantities of carbon monoxide to the feed ethylene. 

Romson JL, Haack DW, Lucchesi BR (1980b) Electrical induction of coronary artery thrombosis in the ambulatory canine a model for in vivo evaluation of anti-thrombotic agents. Thromb Res 17 841-853 Ruebsamen K, Kirchengast M (1998) Thrombin inhibition and intracoronary thrombus formation effect of polyethylene glycol-coupled hirudin in the stenosed, locally injured canine coronary artery. Coron Artery Dis 9 35-42 Sullivan J, Hansen P, Rahko PS, Folts JD (1992) Continous measurement of left ventricular performance during and after maximal isometric deadlift exercise. Circulation 85 1406-1413... 

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