Thermal Oxidation Of Polyethylene Research Articles

Space Charge Behavior of Thermally Aged Polyethylene Insulation of Track Cables.

The interface of multi-layer insulation is a relatively weak point in the cable system during the long-term high-temperature service. Space charge is prone to continuously accumulate in the interface area, leading to the deterioration of electrical properties and even insulation failure in advance. The knowledge about thermal oxidation of polyethylene (PE) materials at the molecular level is still urgent to explore. Herein, single-layer and double-layer PE insulation, representing the typical insulation structure of frequency-shift pulse voltage track cables, were prepared and thermally aged in the oven for up to 360 h. Thermal, mechanical, electrical, and space charge characterizations were systematically carried out. Thermogravimetric analyzer and oxidation induced temperature (OIT) measurements confirmed that LDPE’s thermal-oxidative aging temperature range was the lowest among the three PE groups in the O2 atmosphere. After 360 h thermal aging, the tensile property of HDPE material kept relatively stable, while the elongation at break of the other two groups was lower than 50%. Unaged HDPE exhibits apparent charge injection and migration, leading to the severe electric field distortion of 20%. Noticeable charge accumulation can be observed at the unaged double-layer sample interface due to the mismatching of DC conductivity, which play a significant role in the aged double-layer samples. This work utilizes precise thermal analysis to provide new information about the resistance ability of thermal oxidation of LDPE, FPE, and HDPE, and its influence on space charge behaviors, which is helpful for the insulation design and evaluation in cable applications.

Chemical recycling of polyethylene in oxygen-enriched supercritical CO2

Thermal oxidation of polyethylene was carried out in oxygen-enriched sc CO2 and in pure oxygen under a pressure of 215 and 14 bar, respectively. Oxygen to polymer weight ratio was varied. At lower oxygen content, the products were brown to dark brown pastes; at higher oxygen content, the products were dark yellow to dark-brown liquids. For the oligomeric fraction of the products, the data on molecular weights obtained by means of diffusion-ordered NMR and gel permeating chromatography was compared. Thermogravimetric analysis demonstrated that oxygen content strongly affects the yield of volatile products. The volatile products were further analyzed by means of 1H, 13C NMR, gas chromatography-mass spectrometry and potentiometric titration. All the results obtained suggest that sc CO2 influence is more pronounced at lower oxygen to polymer mass ratio, which may be useful for carrying out chemical recycling of polyethylene through thermal oxidation while minimizing the amount of oxygen required.

The effect of graphite nanoslabs on thermal oxidative destruction of polyethylene

The impact of graphite nanoslabs on thermal oxidation of polyethylene is studied via the methods of dynamic thermogravimetry and isothermal oxidation. Graphite nanoslabs are shown to exert an inhibiting effect on thermal oxidation of polyethylene, which leads to an increase in the induction period and in the oxygen-absorption rate. That there is an abnormal effect of the nanofiller content on the resistance to thermal oxidative destruction of composites, mainly for diffusion reasons, is established as well.

Investigating effect of ferric stearate on stabilization efficiency of a phenolic antioxidant during thermal oxidation of polyethylene

This study aimed to achieve a formulation for an additive to produce oxo-biodegradable films that accelerates oxidative degradation of the films after preservation of properties over a span of desired service life. Thermal oxidation behavior of high-density polyethylene (HDPE) films (approximately 250 μm thick) containing various weight ratios of a commercially used phenolic antioxidant (Irganox 1010) to ferric stearate as pro-oxidant has been studied in both melt and solid states. Thermo-oxidative stability in melt state was studied using differential scanning calorimetry. The rate of thermal oxidation in solid state was investigated via oven aging experiments at 90 °C followed by measuring changes in tensile properties, gel content, carbonyl index and density. Comparing thermo-oxidative stability of the HDPE samples containing a combination of Irganox 1010 and ferric stearate with the samples containing Irganox 1010 alone confirmed that ferric stearate reduces the stabilization efficiency of the phenolic antioxidant in the polymer either in melt or in solid state. It was also shown that the efficiency of the phenolic antioxidant in thermo-oxidative stabilization of the polymer in both melt and solid states could be changed by altering weight ratio of Irganox 1010/ferric stearate. On the basis of the obtained results, it was concluded that weight ratio of 0.1/0.1 wt% of the antioxidant to the pro-oxidant is suitable for attaining desired stability during melt processing as well as retaining properties during a reasonable service life when is used as a film and a favorable rate of thermal oxidation after the service life.

Photo- and thermal-oxidation of polyethylene: Comparison of mechanisms and influence of unsaturation content

The behaviour of polyethylene with different contents in vinyl and t-vinylene groups have been studied by photooxidation with λ ≥ 300 nm light or by thermooxidation at a temperature of 100 °C. The oxidation was studied by infrared spectroscopy and it was shown that the same oxidation products were obtained, but with different relative concentrations depending on the conditions of ageing, i.e. photochemical or thermal conditions. The mechanisms by which the oxidation products are formed were recalled. The differences between photo- and thermo-oxidation were evidenced on the basis of the stability of ketones that do not accumulate in photochemical conditions, as a result of Norrish reactions. The influence of the initial amount of unsaturated groups on the rates of oxidation was characterized. It was shown that the concentration of unsaturations had no effect on the rate of photooxidation but dramatically influenced the stability in thermooxidative conditions.

One-pot synthesis of hexadecyl modified layered magnesium silicate and polyethylene based nanocomposite preparation

Talc-like filler with a layered structure having covalently bonded hexadecyl chain was synthesized and employed for the preparation of polyethylene nanocomposites. Thanks to the organic functionality, hexadecyl modified magnesium silicate melts at 44°C and this peculiar property (characteristic) improves the dispersion of inorganic layers into the polymeric matrix. Transmission electron microscopy supports the formation of exfoliated polyethylene nanocomposites. The organo-modified talc greatly improves the stability on thermal oxidation of polyethylene.

Co-oxidation kinetic model for the thermal oxidation of polyethylene-unsaturated substrate systems

The thermal oxidation of polyethylene (PE) impregnated by the methyl esters of unsaturated fatty acids (UFEs) was studied using chemiluminescence, and infra-red spectrophotometry. It was shown that the presence of UFEs accelerates the PE aging process. This can be interpreted as a co-oxidation phenomenon. In this study, the previously established models for PE and UFEs self-oxidation have been coupled in order to develop a co-oxidation model. Using the existing rate constants for the PE and UFEs self-oxidations, this model can simulate the complex shape of the kinetic curves of PE-UFE co-oxidation.

Influence of Copper on Oxidation of Polyethylene Containing Antioxidants

Thermal oxidation of polyethylene containing amine and phenolic antioxidants during contact with copper (metal support, powder) and the trends in variation of the antioxidant performance were studied.

High sensitivity of positron annihilation to thermal oxidation of polyethylene

We demonstrate the high sensitivity of positron annihilation to compositional changes related to the thermal degradation of polyethylene (PE). Positron annihilation γ-ray and lifetime measurements were conducted for PE films with and without antioxidant (1000-ppm Ciba® IRGANOX® 1076), subjected to heat treatment at 100 °C for different periods, to a maximum of 30 days. For the film without antioxidant, the positron Doppler parameter (S) and ortho-positronium formation probability (Io−Ps) appreciably decreased with increased heat treatment times, whereas they barely changed for the film with antioxidant. This, together with the Fourier transform infrared measurements, demonstrated that the variations of S and Io−Ps are caused by the thermal oxidation of PE. The S parameter was found to be sensitive to the early stage of degradation, where the carbonyl concentration is inferred to be lower than 100 ppm. The high sensitivity results from the large positron mobility in PE and from the high positron affinity of oxygen-containing polar groups. This work provides the basis for an application of positron annihilation to sensitive detection of the initial degradation of PE and other nonpolar polymers.

Thermal Oxidation of Polyethylene Films Containing Dispersed Copper and Amine Antioxidant

Thermal oxidation of polyethylene filled with dispersed copper and containing an amine antioxidant was studied. The concentration ranges in which the catalytic effect of the metal on the polymer oxidation or the stabilizing effect of the antioxidant prevails were determined. Under certain conditions, dispersed copper enhances the stabilizing effect of the antioxidant.

Re-examination of the thermal oxidation reactions of polymers 2. Thermal oxidation of polyethylene

Thermal oxidation of polyethylene (PE) shows many distinctive features with that of polypropylene (PP). This is largely a consequence of reduced intramolecular hydrogen abstraction by the peroxy radicals in polyethylene compared to polypropylene. Although the data from model compounds differ widely, some data from PE oxidation seem to indicate an upper limit of approximately 30% for intramolecular hydrogen abstraction in PE compared to 90% and more in PP. The reactions of the alkoxy radicals in PE and in PP show much more analogy than the corresponding reactions of the peroxy radicals. The dominant reaction of the alkoxy radicals is intramolecular hydrogen abstraction, in PE as much as in PP. The β-scission reaction of alkoxy radicals seems even less important in PE than in PP. It cannot even explain the limited amount of chain scissions usually observed in PE. Thermolysis of hydroperoxides in PE shows specific features resulting from the structure of the hydroperoxide group. The intermolecular bimolecular decomposition is concerted and involves both hydroperoxide groups. It proceeds without chain scission and yields essentially ketones. It is expected not only in the polymer melt where it involves locally high hydroperoxide concentration but even more so in solid phase PE. Pseudo-monomolecular hydroperoxide decomposition is important in the polymer melt and can be seen as the main initiation reaction in the absence of shear. The α-alkyl-hydroperoxy radical formed on free radical abstraction of the tertiary hydrogen in α-position to the hydroperoxide group is very labile. It is decomposing spontaneously into a ketone and a hydroxyl radical.

Identification of volatile compounds resulting from the thermal oxidation of polyethylene

AbstractThe migration of compounds from polymer‐based packaging may impart undesirable odors to foods. We, therefore, undertook a study of the volatile compounds produced during the heating of polyethylene (PE) in the presence of excess O2 at temperatures of 150–350°C and for heating times of 5–15 min. Eightyfour volatile compounds in the range of C5—C23 were identified by gas chromatography mass spectrometry. The major products were aliphatic hydrocarbons, aldehydes, ketones, and olefins. Changes in temperature and heating times affected the amount and type of compounds produced, with hexanal being found in the largest amount and 300°C resulting in the greatest quantity of volatile compounds. At 350°C, greater amounts and numbers of low‐boiling and fewer high‐boiling compounds were formed. Only small amounts of volatiles were produced at 150°C. Many of the compounds identified have been reported to have odor and/or toxicological significance. © 1993 John Wiley & Sons, Inc.

The comparative effectiveness of some commercial antioxidants as studied by lyoluminescence

Lyoluminescence is an interesting tool to study the reactivity of different antioxidants towards the free RȮ 2 radicals which are frequently involved in the oxidative processes of different polymeric materials. In the present paper we have used lyoluminescence to characterize the effectiveness of the following commercial phenolic antioxidants: Topanol OC, Irganox 1076, Ionox 220, Etanox 330, Cyanox 2246 and Irganox 1010. The antioxidant efficiency of these products in the thermal oxidation of polyethylene was compared on the basis of the results of oxyluminescence and thermal analysis methods.

Identification of odor-active compounds resulting from thermal oxidation of polyethylene

Thermal processing of synthetic polymers in the presence of oxygen into food-packaging materials can result in the formation of by products which impart off-odors or raise toxicological questions. Volatiles from the thermal oxidation of polyethylene were collected and anlyzed by gas chromatography/olfactometry (GCO; CharmAnalysis). Fourteen odor-active compounds, most of which occurred in amounts that were too low to be detected instrumentally, were present. Overallodor was waxlike but individual components were fruity, herbaceous, rancid, metallic, way, pungent, or orange

Synthesis and thermal and photooxidative behaviour of 1, n-bis(3-hydroxy-4-benzoylphenoxy) alkanes in polyolefin films

A series of light stabilizers based on the 2,4-dihydroxybenzophenone unit linked at each end of an alkane chain have been prepared via the Williamson ether synthesis and characterized. Six homologues were prepared in this way from propane to octane. The thermal and photooxidative stabilization activities of all six compounds have been examined and compared with those of 2,4-dihydroxybenzophenone (DHBZ) and 2-hydroxy-4- n-octoxybenzophenone (HOBZ) in medium density polyethylene and polypropylene films at 0·1% w/w concentration using IR absorption spectroscopy. In medium density polyethylene all the bis-benzophenone homologues are weak antioxidants, the propane derivative being the most effective. The commercial light stabilizers 2,4-dihydroxybenzophenone (DHBZ) and 2-hydroxy-4- n-octoxybenzophenone (HOBZ) were also weak antioxidants but less effective than the bisbenzophenone alkane homologues. In polypropylene, similar results were obtained but in this case the DHBZ was the most effective antioxidant and HOBZ was the least effective. In the presence of a hindered phenolic antioxidant, Irganox 1010, all the stabilizers except the HOBZ were synergistic in the thermal oxidation of polyethylene whereas in polypropylene the effects were antagonistic. In both polymers, with Irganox 1010, the BHB-alkane structures with odd numbered alkane links were superior to those with even numbered alkane links. On photooxidation, the effects were reversed with antagonism being observed in the case of polyethylene and synergism in polypropylene. Surprisingly, all the bis-benzophenone homologues were less effective as light stabilizers than the two simple commercial benzophenone stabilizers HOBZ and DHBZ despite a marked increase in their extinction coefficients. In polypropylene the bis-benzophenone stabilizers with an even numbered alkane chain were the most effective whereas the reverse was the case in polyethylene. In the presence of Irganox 1010, however, the effect was reversed in polypropylene but not in the case of polyethylene. Initial hydroperoxide concentrations in the polypropylene films with and without Irganox 1010 were found to match the trends in light stabilization, confirming earlier theories on the radical scavenging behaviour of these compounds as chain-breaking donors. The thermal and light stability data are discussed in terms of possible cis and trans conformational arrangements of the benzophenone terminal groups on the alkane chains. In the former case this would allow some degree of self quenching as well as the possibility of association with the hindered phenolic hydroxyl groups on Irganox 1010 to give improved stabilization efficiency.

Synthesis and thermal and photo-oxidative behaviour of novel aminated 2-hydroxybenzophenone stabilizers in polyolefin films

Three light stabilizers have been prepared and characterized, based on the substitution of a tertiary amine group into the 3- and 5-positions of 2,4-dihydroxybenzophenone (DHBZ) and 2-hydroxy-4-n.octoxybenzophenone (HOBZ) via the Mannich reaction. The derivatives prepared by this method were, the 3- N, N-diethylaminomethyl of the former and the 5- N, N-diethylaminomethyl and 5-morpholinomethyl derivatives of the latter. The thermal and photo-oxidative stabilization activities of the three compounds have been examined and compared with those of DHBZ and HOBZ in medium density polyethylene and polypropylene films at 0.1% w/w concentration using i.r. absorption and fluorescence spectroscopy and hydroperoxide analysis. In medium density polyethylene, all three aminated derivatives are weak antioxidants with the diethylaminomethyl derivative of DHBZ being the most effective. The commercial light stabilizers DHBZ and HOBZ were also weak antioxidants but less effective than the aminated derivatives. In polypropylene, similar results were obtained but in this case both the Mannich derivatives of HOBZ were effective. In the presence of a hindered phenolic antioxidant, Irganox 1010, all the stabilizers except the HOBZ were synergistic in the thermal oxidation of polyethylene whereas in polypropylene the effects were antagonistic. On photo-oxidation, the effects were reversed with antagonism being observed in the case of polyethylene and synergism in polypropylene but only in the case of the morpholinomethyl derivative of HOBZ. Surprisingly, the three aminated derivatives were less effective as light stabilizers than the two simple commercial benzophenone stabilizers HOBZ and DHBZ. Hydroperoxide formation is markedly reduced on oven-ageing of polypropylene by the aminated derivatives and is consistent with the ability of the tertiary amine group to scavenge oxygen and free radicals. Fluorescence quenching studies on the same polymer also show that the aminated derivatives are more effective quenchers than the corresponding commercial HOBZ and DHBZ stabilizers.

Thermo-Oxidation of Polyethylene Stabilized with Irganox 1010 and Tinuvin 622

Abstract Thermal oxidation of polyethylene stabilized with the mixture of Irganox 1010 and sterically hindered amine Tinuvin 622 confirmed that the occurrence of synergism or antagonism in the effect of sterically hindered amines towards antioxidants is concentration dependent. Provided that the concentration of phenolic antioxidant Irganox 1010 in polytheylene exceeds that of Tinuvin 622, synergism is observed at 185 and 190°C. Chemiluminescence, oxygen absorption method, nonisothermal differential scanning calorimetry (DSC) and differential thermal analysis (DTA) were used for testing of stabilizing efficiency of mixtures of stabilizers and the mutual correspondence of the results have been pointed out.

Findings pertaining to polyethylene photooxidation

AbstractThe kinetics and mechanisms of photolysis of the hydroperoxides formed on thermal oxidation of polyethylene have been investigated. The difficulties to explain the results by the generally accepted decomposition mechanism based on homolytic splitting of the hydroperoxy bond are discussed. New mechanisms of hydroperoxide photolysis are proposed. The intermolecular reactions considered account for the main products found experimentally, ketones and trans‐vinylene groups. They are also in agreement with the kinetics of product formation. The intramolecular photolysis reactions envisaged seem to involve a small amount only of the hydroperoxides present in polyethylene after thermal oxidation. However, they affect directly the mechanical properties of the polymer because they involve main‐chain scission.

The effect of bisthioacetylacetanato nickel(II) compounds on thermal oxidation of polyethylene

The effect of bisthioacetylacetanato nickel(II) compounds on thermal oxidation of polyethylene

Thermal analysis of composites based on crystalline polymers and metals

Differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and infrared (IR) spectroscopy have been used to examine the chemical and physical changes (crystallinity, accumulation of oxygen-containing groups, etc.) during thermal oxidation of polyethylene, polypropylene and Penton contained in coatings and metalfilled films, taking into account the thickness of the polymer layer and catalytic activity of the metal.