Design of voltage stabilizers for high breakdown strength materials

High breakdown strength material in the cable insulation layer is a key enabler for high voltage power transmission. In this work, we seek to design high-performance voltage stabilizers to be compounded into polyethylene to improve its breakdown strength. We hypothesize that electron affinity (EA) and HOMO-LUMO gap are two key factors that affect the performance of voltage stabilizers. To achieve larger EA and smaller HOMO-LUMO gap, we propose to use aromatic molecules decorated with electron acceptors and donors. A search of an internal chemical database narrows down to 529 molecules using structure, ClogP, and H-phrases (hazard statement) as criteria. The EA and HOMO-LUMO gap of these molecules are then calculated and experiments are carried out to measure the performance of 20 molecules. The performance improvement does not show a significant correlation with either EA or HOMO-LUMO gap. However, the best performers have an EA of 1.3–2.3 eV and HOMO-LUMO gap of 3.2–5.2 eV. The experimental study shows that adding side groups to voltage stabilizers will typically degrade their performance because side groups will generally increase the distance between the HOMO-LUMO orbitals and polyethylene backbone, and therefore decrease the electron/hole tunneling effectiveness.     

Photooxidative ageing of low density polyethylene. Kinetics determined by an electrical method

The efficiency of light stabilizers is investigated by electric methods in the initial stage of photooxidative ageing of low density polyethylene (LDPE). Three types of UV light stabilizers are tried to improve the UV stability of LDPE: a phosphite type (3,9-bis-[(2,4-di-tert-butyl)phenoxy]-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane) a benzophenone type [2-hydroxy-4-octyloxy-benzophenone] and a stabilizer based on chelate salt [2,2′-thiobis(4-tert-octyl phenolato) (n-butylamine) nickel (II)]. LDPE is very susceptible to ultraviolet light. UV light stabilizers improve the stability of low density polyethylene for electrical applications, especially the UV stabilizer based on chelate salt.     

High-temperature stabilization of polyolefines with hydroxides of alkali metals

Hydroxides of alkali metals are shown to be high-temperature stabilizers of polyethylene. Potassium hydroxide is found to be most efficient. The reaction mechanism of alkali metal hydroxides as thermal stabilizers is considered.     

Effect of mesogenic modifiers on the physicomechanical properties and supramolecular structure of polyethylene films

Substituted formyl azobenzenes are effective light and thermal stabilizers of polyethylene even in concentrations 20 times lower than for industrial stabilizers. X-ray structural analysis showed that the presence of mesogens in the LDPE matrix prevents crystallization of the polymer as a result of exposure to light and heat, preserving the strength indexes of film material.     

The preparation and performance of “Cage” diphosphites as secondary antioxidants in the stabilization of polyolefins

“Cage” diphosphites, a new family of phosphorus antioxidants, are discussed in regard to their preparation, properties, and effectiveness in polyolefins, particularly, with phenolic stabilizers, in respect to their ability to control melt flow and color during processing. These trivalent phosphorus compounds have two different types of phosphite functionalities in their structure. One phosphorus is part of an eight membered (1,3,2-dioxaphosphocine) ring system while the other is part of a tricyclic cage of carbon and oxygen atoms. This structures can contribute to improved hydrolytic stability over rather similar aryloxy-alkoxy phosphites and show competitive stabilization effectiveness in the processing of polyolefins. The possible modes of formation and of hydrolysis are discussed.     

Behaviour of regenerated polyethylene,recovered from worn out packaging,to artificial ageing and under natural climate conditions

This paper presents the efficiency of styrenated phenol and dian (bisphenol A) stabilizers in high density polyethylene regenerated from worn out packaging samples, by following up the regenerates' behaviour under artificial ageing as well as in natural climate conditions. The efficiency of the stabilizers was assessed by following up the characteristic physical-mechanical modifications and the formation of carbonyl groups in the stabilized, regenerated polyethylene samples, as compared with the primary polyethylene and the unstabilized regenerated samples.     

Delocalized aromatic molecules with matched electron-donating and electron-withdrawing groups enhancing insulating performance of polyethylene blends

Seven delocalized aromatic molecules with electron-donating and electron-withdrawing groups are applied as voltage stabilizers to improve the insulation properties of polyethylene blends. Voltage stabilizers 1 wt% are added into the blends (90 wt% low-density polyethylene and 10 wt% high density polyethylene) by diffusion loading method. Electrical measurements including electrical treeing, space charge distribution, and direct current conductivity are conducted to disclose their effects. The results show that the co-existence of matched electron-donating and electron-withdrawing groups in the molecules is favorable for the insulation properties. A 50% increase of tree initiation voltage is achieved with the addition of 3-aminobenzoic acid, which is also able to inhibit the space charge and decrease the conductivity at lower temperature. Besides, the grafting sample of the optimal molecule is successfully prepared and displayed enhanced electrical properties. Finally, the common internal mechanism of the delocalized molecules on different electrical properties is revealed.     

Electron‐beam irradiation of low‐density polyethylene in the presence of phenolic stabilizer,carboxylic acid stabilizer,or both

The effects of Irganox 1010 and citric acid as antioxidants and modifiers of the network structure and mechanical and thermal properties of low‐density polyethylene (LDPE) during electron‐beam crosslinking with different irradiation doses (up to 120 kGy) were investigated. The results showed that the addition of these stabilizers had a retarding effect on the gel fraction of LDPE within the investigated range of electron‐beam‐irradiation doses. However, a noticeable effect on the gel fraction was found for the LDPE formulations compounded with citric acid alone or with its mixture with Irganox 1010 (in an equal ratio), as illustrated by a study of the gel‐fraction/dose relationships. Tensile testing measurements showed that the addition of both stabilizers caused a slight reduction in the stress at break and an increase in the strain at break. On the other hand, the thermal properties of the LDPE batches crosslinked with electron‐beam irradiation were greatly improved as a result of the compounding with these stabilizers, as shown by thermogravimetric analysis studies. In this respect, the temperatures at different weight losses, the temperatures of the maximum rate of thermal decomposition, and the activation energies indicated that compounding with citric acid was more effective for stabilization against thermal decomposition than compounding with Irganox alone or a mixture. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1275–1286, 2005     

Photooxidative Destruction and Stabilization of Polycaproamide by Bis-Aroilenbenzimidazole Derivatives

Abstract

Some derivatives of bis-naphthoylenebenzimidazoles have been studied as light stabilizers of polyamide-6 and polyethylene terephtalate. These stabilizers are stable in the melts of these polymers for long times at 260–280°.

The light-stabilizing effect of compounds studied is discussed.     

Urethane-based stabilizers for radiation-crosslinked polyethylene

Unsaturated urethane-based stabilizers for use in radiation-crosslinked polyethylene were synthesized. Aromatic amine moieties were attached to allylic and acrylic monomers by means of aromatic or aliphatic diisocyanates. The synthesized stabilizers were incorporated in high-density polyethylene films which were subjected to electron beam irradiation. The oxidative stability of the films prior to and after extraction was determined by DTA in the temperature range 185–210°C and compared with samples treated with commercial amine-bearing antioxidants. Tensile strength and gel content were also determined. Best results were obtained with a stabilizer prepared from equimolecular amounts of allyl alcohol, tolylene-2,4-diisocyanate and N-phenyl-1,4-phenylenediamine. Estimated lifetimes at 70°C of stabilized irradiated polyethylene samples were calculated.     

Photoinitiated crosslinking of low density polyethylene. IV: Continuous extrusion application

A new continuous method is developed to crosslink polyethylene, based on a photoinitiated radical reaction. An experimental production line for low density polyethylene (LDPE) extrudate is constructed with a Brabender^® extruder and an “Irradiation Unit” on line. Some new initiators of benzophenone derivatives are prepared to overcome the volatility of benzophenone and increase its compatibility with the polymer matrix. Extraction and gel swelling experiments are performed to characterize the crosslinking of the product and the results are quite satisfactory: under the conditions used, crosslinking can be optimized to about 65% gel content within 5 to 15 s irradiation time, corresponding to a production rate of about 1.5 to 0.5 m/min, respectively. The dynamic mechanical properties of the crosslinked polymer are measured through the melting region and the effects of crosslinking are demonstrated. Without affecting the rate of crosslinking, the stability against thermal oxidation of the crosslinked products is greatly improved by adding stabilizers to the compounds before crosslinking.     

聚乙烯材料耐候性能研究进展

综述了聚乙烯材料耐候性能的影响因素,包括自身结构因素及外部环境因素;系统分析了聚乙烯的老化机理,主要有热氧老化、光氧老化和环境应力开裂,其中前两者都与自由基链式反应有关;最后概括了改善聚乙烯材料耐候性能的方法,主要为添加抗氧剂、光稳定剂和控制加工工艺。     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

Use of reactable light stabilizers to prevent migration and to improve durability of coatings on plastic substrates

One of the challenges of coating plastic substrates for exterior automotive applications involves the tendency for light stabilizers, which inhibit UV degradation of the coating, to migrate out of the topcoat and into the underlying plastic substrate. The consequent depletion of the stabilizer from the topcoat could account for significantly poorer durability for coatings applied on plastic than on a nonpermeable substrate such as steel. These studies investigate the migration of both nonreactable and reactable UV absorbers (UVAs) and hindered amine light stabilizers (HALS) in fully formulated 2K urethane coatings applied on thermoplastic olefin (TPO) and steel substrates. Extensive migration of the nonreactable stabilizers occurs during accelerated exposure of the cured coating, and this migration correlates with poorer performance on TPO. Functionalization of the stabilizer with a group which covalently reacts into the coating will prevent much of this migration, and the improved degree of retention of the reactable light stabilizers in the topcoat correlates with improved performance on TPO substrates. In addition, stabilizer variables, such as the type and extent of functionalization as well as their chemical structure, have an effect on both the migration and performance of the stabilizers.     

Retention of thermal antioxidants in polyethylene by silane coupling agents. III. Copper deactivators

Stabilizer activity has been correlated with physical retention and state of dispersion in aged polyethylene films. Incompatibility and poor state of dispersion were found to limit long-term performance of otherwise chemically efficient stabilizers. A practical method to improve compatibility and state of dispersion of stabilizers involves complexation of nonfunctional stabilizer phenolic groups with N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane. Substantial improvement in retention and state of dispersion may be realized with antioxidant–silane weight ratios of 1:1.     

聚酯热氧化降解的速度和机理

本文推导了求PET热氧化降解速度常数的公式。采用热重法、粘度法和羧端基法,对不同催化稳定体系的PET,求出了热氧化降解速度常数。根据实验结果,讨论了热氧化降解机理。     

Synthesis of polyethylene terephthalate in the presence of 4-carboxybenzaldehyde

Conclusions Contamination of terephthalic acid with 4CBA causes a decrease in the whiteness of the finished polyethylene terephthalate and the appearance of branched structures due to reactions of the aldehyde group.To obtain high-quality polyethylene terephthalate with good color characteristics, it is very advisable to use stabilizers which reduce the aldehyde group in 4CBA, phosphites for example.Translated from Khimicheskie Volokna, No. 4, pp. 9–11, July–August, 1983.     

Stabilization of vulcanized polyethylene

Some polyaminedisulphides were studied as thermal stabilizers of polyethylene vulcanized by dicumyl peroxide. The effects of temperature, time, and concentration were investigated. A reaction mechanism is suggested.     

多功能复合助剂在HDPE中的应用

针对高密度聚乙烯(HDPE)合成树脂,采用多种国产高效抗氧化稳定剂、热加工稳定剂,同时配以加工润滑剂和分散剂改善助剂分散性及树脂加工性,进行HDPE树脂用多功能复合助剂的研制。实验表明:该多功能复合助剂中各单剂间存在协同效应,不同比例的用量直接影响树脂的抗老化性能。     

Degradation of chlorinated polyethylene—III: Effect of additives on dehydrochlorination and oxygen absorption

Degradation of chlorinated polymers takes place via two simultaneous reactions; namely, dehydrochlorination and oxygen absorption. The dehydrochlorination and oxygen absorption of five grades of chlorinated polyenthylenes were studied at temperatures varying between 120 and 180°C. The chlorinated polyethylene grades varied in both molecular weight and chlorine content, the latter being in the range of 24.0 to 45.2 percent chlorine. Dehydrochlorination measurements on the pure polymers in both nitrogen and oxygen atmospheres showed that the rate of dehydrochlorination increases with an increase in the degree of chlorination of the polymer. The oxygen absorption rate, however, showed a decrease with higher chlorine content of the polymer. Dehydrochlorination and oxygen absorption studies were also carried out on chlorinated polyethylene containing dehydrochlorination stabilizers, antioxidants, antimony oxide, and other metal salts and metal oxides. Retardation of both oxygen absorption and dehydrochlorination was observed in the presence of antioxidants. More significant, however, was the observed action of some dehydrochlorination stabilizers as efficient antioxidants in the polymer.