Polyethylene thermal destruction

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...

At the first stage of polyethylene thermal destruction the metallizing of polyethylene macroradical by the metal radical takes place. 

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... 

Upon thermal destruction of polyethylene the chain transfer reactions are predominant, but depolymerization proceeds to a much lesser extent. As a result, the products of destruction represent the polymeric chain fragments of different length, and monomeric ethylene is formed to the extent of 1-3% by mass of polyethylene. C—C bonds in polypropylene are less strong than in polyethylene because of the fact that each second carbon atom in the main chain is the tertiary one. 

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... 

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. 

Polyethylene cured by the chemical and radiation-chemistry methods undergoes thermal destruction upon heating as in normal polyethylene. Thermoslabiliz-... 

A series of polyamine disulphides (polyaniline disulphide, polyamine disulphide, and polyparaphenylenedi-amine disulphide) represent effective thermostabilizers of cured polyethylene, and provide a decrease in gel fraction 2.5-3 times as large as that in case of inhibited thermal destruction. Stabilizers of normal polyethylene (Neozone D , Santonox R ) are inefficient as stabilizers of cured polyethylene, these substances decompose and even initiate thermal destruction 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. 

Polyamine disulphides as inhibitors of thermal destruction of cured polyethylene are effective over a long period of time. 

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

Optionally, in the case of Fe- and Co-containing nanoparticles, the mineral oil was substituted for a mineral oil-low density polyethylene (LDPE) solution-melt. The thermal destruction was carried out at vigorous stirring at a constant temperature in the argon flow. The MCC solution was introduced into the reaction system dropwise at a constant rate. The black material produced after the addition of all the MCC solution was stirred at the synthesis temperature for 0.5 h and cooled down to room temperature. The product was extracted via rinsing the mixture with hexane. The calculated concentrations of metal-containing nanoparticles in the product resulted varied from 1 to 50 wt.%. 

Effect of thermostabilizers on the polymer properties was studied by different physicochemical methods. For example, in the work [260] method of DSS (differential spectroscopy) was used to define the effect of polyester-imide on thermo-physical properties of PETP. By this method it was found out that polyester-imide reduces PETP ability to crystallization. Methods of thermogravimetric analysis (TGA) and infrared spectroscopy in the nitrogen atmosphere were used in the work [261] to define thermal stability of the mixture of PETP and polyamide with the additive - modifier - polyethylene. It has been found that introduction of the additive decreases activation energy which positively tells on the ability of PETP to thermal destruction. 

Experimental and theoretical studies are presented from a laboratory-scale thermal destruction facility on the destructive behavior of surrogate plastic and nonplastic solid wastes. The nonplastic waste was cellulosic while the plastic waste contained compounds such as polyethylene, polyvinyl chloride, polystyrene, polypropylene, nylon, rubber, and polyurethane or any of their desired mixtures. A series of combustion tests was performed with samples containing varying composition of plastic and nonplastic. Experimental results are presented on combustion parameters (CO, excess air, residence time) and toxic emissions (dioxin, furan, metals). 

THERMAL DESTRUCTION OF POLYPROPYLENE, POLYSTYRENE, POLYETHYLENE, AND POLYVINYL CHLORIDE... 

Isomerization of the radicals formed is also possible. Thus, it has been shown in a number of studies [14, 15] that isomerization of the polymer radicals formed occurs in the thermal destruction of polypropylene and polyethylene oxide. 

The thermal destruction of resins based on 4,4 -dihydroxydiphenyl-2,2 -propane (resin ED-6, unhardened and hardened with polyethylene-polyamine and maleic anhydride) was studied in [1-4]. The thermal decomposition of these resins begins at temperatures above 200°C and is characterized by substantial gas evolution (the kinetics of the gas evolution was studied on a special setup, described in [1]). 

One additive that improves both long-term photo and thermal stability of polyethylene Is carbon black. The ability of carbon black to retard destructive thermal oxidation In polyethy-lenes at elevated temperatures Is well known(17) and, as was seen In the earlier section of this paper on photo oxidation. It Is effective at lower temperatures also. Our studies of the thermal oxidation of low-density polyethylene show black samples to be outstanding, even In the presence of copper. For example black low-density polyethylene wire Insulation Is still Intact after 7 years at 80°C while all other colors. Including unplg-mented, failed mechanically due to oxidation after only about 3 months. 

At the present time there is a comparatively large number of works in the literature studying the mechanism of the photooxidative destruction of polyolefins. Unfortunately, most of them are devoted to high-pressure polyethylene, in view of which it does not seem possible to make any comparison between individual types of this class of polymers. However, the general picture of the photooxidation possesses much in common with the thermal process of oxidation and differs from the latter mainly in the stage of initiation. 

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