Degradation of polyethylene during extrusion. II. Degradation of low‐density polyethylene,linear low‐density polyethylene,and high‐density polyethylene in film extrusion

The degradation of different polyethylenes—low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and high‐density polyethylene (HDPE)—with and without antioxidants and at different oxygen concentrations in the polymer granulates, have been studied in extrusion coating processing. The degradation was followed by online rheometry, size exclusion chromatography, surface oxidation index measurements, and gas chromatography–mass spectrometry. The degradations start in the extruder where primary radicals are formed, which are subject to the auto‐oxidation when oxygen is present. In the extruder, crosslinking or chain scissions reactions are dominating at low and high melt temperatures, respectively, for LDPE, and chain scission is overall dominating for the more linear LLDPE and HDPE resins. Additives such as antioxidants react with primary radicals formed in the melt. Degradation taking place in the film between the die orifice, and the quenching point is mainly related to the exposure time to air oxygen. Melt temperatures above 280°C give a dominating surface oxidation, which increases with the exposure time to air between die orifice and quenching too. A number of degradation products were identified—for example, aldehydes and organic acids—which were present in homologous series. The total amount of aldehydes and acids for each number of chain carbon atoms were appeared in the order of C5>C4>C6>C7?C2 for LDPE, C5>C6>C4>C7?C2 for LLDPE, and C5>C6>C7>C4?C2 for HDPE. The total amounts of oxidized compounds presented in the films were related to the processing conditions. Polymer melts exposed to oxygen at the highest temperatures and longest times showed the presence dialdehydes, in addition to the aldehydes and acids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1525–1537, 2004     

Susceptibility of starch-filled and starch-based LDPE to oxygen in water and air

The susceptibility of starch-filled and starch-based polyethylenes to oxygen in water and air was analyzed and compared. LDPE containing 7.7% starch and a pro-oxidant formulation in the form of masterbatch (LDPE-MB) was compared to pure LDPE, LDPE with 7.7% starch (LDPE-starch), and a blend with 70% starch and 30% ethylene maleic anhydride (starch-EMA). Thermal ageing at 80°C in air and water was followed by monitoring the molecular weight changes, the formation of carbonyl groups, and degradation products by SEC, FTIR, and GC-MS. It was demonstrated that LDPE-MB was the most susceptible material to degradation in both environments, although the degradation was faster in air than in water. The slower degradation in water is explained by a deactivation or leaching out of the pro-oxidant during the aging. The degradation of pure LDPE and starch-EMA is faster in water than in air. LDPE-starch was the only material that did not degrade during 11 weeks in water at 80°C. The addition of starch to LDPE made this material even more stable than pure LDPE to aging in water. The molecular weight distribution of LDPE-MB narrowed during aging in air. In water, on the other hand, the MWD of LDPE-MB, LDPE, and LDPE-starch broadened. The lower oxygen concentration in water increases the probability for molecular enlargement reactions in comparison to the case in air. Mono- and dicarboxylic acids were the major products identified in both environments. Ketoacids were formed in both air and water, but ketones and hydrocarbons were only identified after aging in air. Either these products are not formed or they remain in the polymer matrix rather than migrate out into the water. Lactic acid and 2-furancarboxaldehyde were only identified in the starch-EMA material degraded in water at 80°C. LDPE, LDPE-starch, and starch-EMA did not form any degradation products during 11 weeks at 80°C in air in agreement with the neglible molecular weight changes observed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 959–967, 1997     

Thermal oxidation of polypropylene in the temperature range of 120–280°c

Thermal oxidation of isotactic polypropylene films at 120–280°C in air was studied. Separation and identification of the volatiles formed was carried out by gas chromatography–mass spectrometry. Sixteen products were tentatively identified for the first time. Altogether, 50 compounds representing hydrocarbons, ethers, alcohols, aldehydes, ketones, and acids are reported. Oxygen deficiency is manifested in diffusion-limited products of olefines, dienes, and aromatic compounds. The relative amounts of acetaldehyde and acetone are almost temperature independent in the range of 120–280°C. This indicates a similarity of oxidative degradation of the polymer in a broad temperature range. Addition of an antioxidant to the polymer depresses the evolution of the main volatiles by 9–10 times at 280°C. The relative amounts of the volatiles formed are, nevertheless, the same as for the polymer without an antioxidant. The mechanism of formation of the degradation products is discussed.     

Liberation of aldehydes from alk-1-enyl glyceryl ethers by acid hydrolysis

Labeled alk-1-enyl glyceryl ethers were used in conjunction with thin layer chromatography to study the liberation of aldehydes from alk-1-enyl glyceryl ethers by two acid hydrolysis procedures. Both methods gave similar results, but neither liberated the aldehydes quantitatively. Only 75–85% of the alk-1-enyl glyceryl ether radioactivity was liberated as free aldehydes. Several nonaldehyde products were detected and one appeared to be a cyclic acetal. Under contract with the U.S. Atomic Energy Commission.     

Degradation of low density polyethylene during extrusion. III. Volatile compounds in extruded films creating off‐flavor

This study was aimed at finding a correlation between the experienced off‐flavor in packaged foods and the presence of specific degradation products in PE packaging films. The possibility to trap degradation products by chemical reactions with scavengers, that is, zeolites and maleic anhydride grafted LLDPE, were investigated. This trapping would prevent the degradation products from migrating to the polymer film surface and further into food in contact with the film. This work concludes that off‐flavor in water packed in LDPE‐films depends on extrusion temperature and the content of oxidation products in the polymer film. At lower extrusion temperatures, reactive additives to the LDPE material could control the release of off‐flavor giving components. Adsorbents, such as zeolites, which are able to adsorb degradation products, are effective also at higher extrusion temperatures. The amount of oxidized degradation products in the films correlated well to the perceived off‐flavor in the packed water. The presence of aldehydes and ketones have a clear impact on the off‐flavor. The best correlation between off‐flavor and oxidized components were found for C₇? C₉ ketones, and aldehydes in the range of C₅ to C₈. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 847–858, 2005     

Effect of alkyl chain length on the electrochemical perfluorination of n-alkane (C6–C10) carboxylic acid chlorides

Electrochemical perfluorination (ECPF) of n-hexanoyl, n-heptanoyl, n-octanoyl, n-nonanoyl and n-decanoyl chlorides was carried out under identical experimental conditions in liquid HF. The product distribution among perfluorinated carboxylic acids, perfluoro ethers, perfluoroalkanes, isomerised and fragmented products containing less number of carbon atoms was identified using ¹⁹F NMR. The selectivity of C₆–C₁₀ perfluoro carboxylic acid varied between 29 and 36%. The alkali insoluble perfluoro cyclic ether and perfluoro alkane fractions increased with increasing chain length. The increase of perfluoroalkane fractions is mainly due to decarboxylation. Cyclic ether fractions also decreased slightly with increase in chain length. Among the cyclic ethers α substituted oxolanes were the predominant products. Six membered cyclic ethers were always found to contain β substitution. The possible pathways for these products are also indicated. An erratum to this article can be found at     

Volatile components from tristearin heated in air

Tristearin was heated to 192 C in air, and its volatile oxidation products were collected directly on a cooled (−60 C) gas liquid chromatography column. Subsequently, the volatile products were separated by temperature programing up to 250 C and identified by mass spectrometry. Methyl ketones and aldehydes were the major degradation products along with minor amounts of monobasic acids, n-hydrocarbons, primary alcohols, and γ-lactones. Qualitative results indicated all the fatty acid methylene carbon atoms are susceptible to oxidation. Quantities of aldehydes and ketones were found to be in excess of their taste threshold concentrations, suggesting thermally oxidized saturated fatty acids may be precursors of some odors and flavors associated with heated lipids. Presented at the AOCS Fall Meeting, Philadelphia, September 1974. ARS, USDA.     

Conversion of organic oxygen compounds and their mixtures on H-ZSM-5

The conversion of a number of alcohols, ethers, ketones, aldehydes, carboxylic acids, esters, and cyclic compounds and their mixtures on H-ZSM-5 at 673 K was investigated. These compounds can be easily converted to aromatic hydrocarbons if the C/H ratio of the molecule fragment, remaining after elimination of oxygen as water, is less than 0.62. At higher C/H ratios, coking of the catalyst increases, thus reducing its lifetime, a difficulty which can be overcome by hydrogenation of these compounds prior to their conversion over H-ZSM-5. A procedure is proposed for converting at least a part of organic waste chemicals to valuable products instead of burning them.     

Degradation of low density polyethylene during extrusion. IV. Off‐flavor compounds in extruded films of stabilized LDPE

This study was aimed at finding a correlation between the experienced off‐flavor in packed foods and the presence of specific degradation products in LDPE packaging films. The possibility to trap degradation products by chemical reactions with scavengers, i.e., a zeolite additive or antioxidants, was investigated This would prevent degradation products from migrating to the polymer film surface and further into food in contact with the film. It was found that off‐flavor noted in water packed in LDPE films depended on extrusion temperature and exposure time for the melt to oxygen, that is, the parameters that influence the contents of oxidation products that are able to migrate from the polymer film. It was also found that adsorption of oxidative degradation products in a zeolite additive or protection of LDPE by using antioxidants could prevent off‐flavor in the packed product (water). However, the antioxidant should be selected with regard to extrusion temperature because thermal instability in the additive might jeopardize the intended effect. Multifunctional antioxidants seem to provide improved protection, the most effective one evaluated in this work being Irganox E201, i.e., vitamin E. Concentrations of oxidized degradation products are well correlated to the perceived off‐flavor in the packed water. The highest correlation between off‐flavor and oxidized components was found for ketones in the range of C₇ to C₉ and aldehydes in the range of C₆ to C₉. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 583–595, 2005     

Environmentally Degradable Blends of Low Density Polyethylene (LDPE) and Partially Carboxymethylated Starch (PCMS)

Abstract

Sodium - salt of partially carboxymethylated starch (Na-PCMS) with degree of substitution (DS) 0.21 and 0.58 was synthesized by etherification of starch. These starch ethers and low density polyethylene (LDPE) were mixed with and without poly(vinylacetate) (PVAc) in various proportions using Brabender mixer. FTIR confirmed the etherification reaction of starch and blending. Positive changes in the mechanical properties as a function of blending, and environmental degradation have been observed. Addition of 5 wt% PVAc improves the blend quality. Samples were exposed to direct sunlight for one month and environmental degradation was measured in terms of change in tensile strength and per cent elongation.     

Degradation of low density polyethylene during extrusion. I. Volatile compounds in smoke from extruded films

Many problems with odor and taste in food packaging can be traced to degradation of the packaging materials during processing. From this starting point, the degradation of polyethylene in a commercial extrusion coating process was studied by analyzing degradation products present in smoke sampled at the extruder die orifice. Two low‐density polyethylenes, A and B, with similar melt flow indexes and densities and obtained from different producers, were investigated. A third polymer, C, consisting of recycled material B, was also investigated. More than 40 aliphatic aldehydes and ketones, together with 14 different carboxylic acids, were identified in the smoke. The highest concentration was found for acetaldehyde, regardless of polymer and processing conditions. Increasing the extrusion temperatures in the range 280–325 °C increased the amounts of the oxidized products in the smoke. The extruded film thickness, 12 and 25 μm, influenced the concentrations of degradation products, with the thicker film giving higher amounts of product. The recycled polymer C generally gave lower concentrations of degradation products compared with the virgin polymer B. Differences in the product spectrum between the two virgin polymers may be related to differences in the manufacturing process. Many of the identified compounds have very characteristic taste and smell and are consequently of interest from an odor and taste point of view in food packaging applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1580–1586, 2002     

HDPE/LDPE复合交联物的热降解研究

采用热重分析仪（TG）考察了高密度聚乙烯（HDPE）／低密度聚乙烯（LDPE）复合交联物的热稳定性。结果显示，HDPE／LDPE复合交联物的热稳定性低于HDPE／LDPE共混物。FTIR分析证实，交联反应使聚乙烯（PE）的支化程度提高，取代基的位阻效应在一定程度上影响了PE的热降解过程。在N2气氛下，HDPE／LDPE共混物及交联物的热降解过程均为一步降解反应。Kissinger法求解HDPE／LDPE共混物及其复合交联物的热降解活化能发现，LDPE质量分数在20％～30％之间变化时，HDPE／LDPE交联物的热降解过程对温度的敏感性发生了突变。     

Synthesis and characterization of cleavable surfactants derived from poly(ethylene glycol) monomethyl ether

A series of noncyclic acetal-linked cleavable surfactants were simply prepared by condensation of aldehydes with poly(ethylene glycol) monomethyl ethers. All of the products were characterized by¹H nuclear magnetic resonance. Their hydrophile-lipophile balance, surface tension, cloud point, critical micelle concentration, and foam height were determined. Hydrolysis kinetic studies, followed by gas chromatography, showed that they had higher hydrolytic reactivity in acidic solution than cyclic acetal-linked cleavable surfactants.     

海南香草兰萃取物挥发性成分的GC／MS分析

用 90 %乙醇从香草兰豆荚中萃取香味物质 ,并用GC/MS分析其挥发性化学成分 ,鉴定出 19个已知化合物 ,其中醛类 5个 ,酯类 4个 ,醚类 2个 ,烷烃 4个 ,烯烃 2个 ,脂肪酸 2个。萃取物挥发性成分中 ,香兰素的相对含量最高 ,为2 9 .95 %。     

Studies on the preparation and analysis of glyceryl ether derivatives and the isolation and reductive ozonolysis of unsaturated glyceryl ethers

Glyceryl ethers were identified and quantified by the GLC analysis of their alkyl iodide (special conditions described), acetonide and allyl alkyl ether derivatives. The acetoxy-mercuri-methoxy derivatives of unsaturated glyceryl ether swere separated from saturated glyceryl ethers by TLC and the fractions were analyzed as alkyl iodides. Monoiodides from saturated glyceryl ethers and diiodides from unsaturated glyceryl ethers were also separated by TLC and then analyzed. Allyl alkyl ethers had small retention volumes and these derivatives were separated into pure fractions by preparative GLC. Ozonides were reduced either to alcohols with lithium aluminum hydrodie or to aldehydes with dimethyl sulfide. The alcohols were converted to mono- and diiodides which were separated by TLC and analyzed by GLC. The recovery of n-C₆ and n-C₇ monoiodides was not quantitative. Diiodides and aldehydes were both identified and quantified by GLC. Ozonolysis data suggest that the 16∶1 glyceryl ethers from dogfish liver oil contain 7,8 and 9,10 isomers and the 18∶1 glyceryl ethers contain 9,10 and 11,12 isomers. Presented in part at the AOCS Meeting, Philadelphia, October 1966.     

鸡肉及其酶解液挥发性风味成分的对比分析

为了研究酶解对鸡肉挥发性风味成分的影响,采用SPME法提取鸡肉及其酶解液中的挥发性风味成分,用气相色谱-质谱联用技术进行分离鉴定。结果显示:鸡肉酶解液共鉴定出63种挥发性风味成分,包括醛类19种、醇类7种、酸类2种、酮类6种、酯类2种、醚类2种、酚类3种、烃类8种、杂环化合物14种。水煮鸡肉的挥发性风味成分共19种,包括醛类11种、醇类3种、酮类1种、酯类1种、烃类2种、杂环化合物1种。两者共同鉴定出的物质有:己醛、辛醛、壬醛、(E)-2-辛烯醛、苯甲醛、苯乙醛、(E,E)-2,4-癸二烯醛、对甲氧基苯甲醛、1-辛烯-3-醇、右旋萜二烯。     

PET和关中麦秆共热解特性及其动力学研究

利用TG-FFIR技术研究陕西关中地区小麦秸秆(麦秆)、聚对苯二甲酸乙二醇酯(PET)及其两者混合物麦秆-PET(质量比1∶1)在20 K/min的升温速率下的热解行为、主要热解产物、协同效应和动力学.研究结果表明:PET热解初始温度为375℃,最大热失重速率处的温度为454.9℃,失重率为62.87％,其热解残余质量...     

Photolyse von 13(S)-Hydroperoxy-9(Z), 11(E)-octadecadiensäuremethylester in Gegenwart von Sauerstoff — Analyse der niedermolekularen Reaktionsprodukte

Photolysis of methyl 13(S)-Hydroperoxy-9(Z),11(E)-Octadecadienoate in the Presence of Oxygen — Analysis of the Low Molecular Reaction Products A solution of methyl 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate in n-pentane was irradiated in the presence of oxygen at 15°C with light at wavelengths greater than 230 nm. After 2 hours 3.5 mol-% volatile aldehydes and esters and in addition 5 mol-% low molecular acids were isolated. Four major products were identified: hexanal, caproic acid, azelaic acid monomethyl ester and methyl 6-heptenoate.     

Continuous distribution kinetics for the thermal degradation of LDPE in solution

Polymer degradation in solution has several advantages over melt pyrolysis. The degradation of low‐density polyethylene (LDPE) occurs at much lower temperatures in solution (280–360°C) than in conventional melt pyrolysis (400–450°C). The thermal degradation kinetics of LDPE in solution was investigated in this work. LDPE was dissolved in liquid paraffin and degraded for 3 h at various temperatures (280–360°C). Samples were taken at specific times and analyzed with high‐pressure liquid chromatography/gel permeation chromatography for the molecular weight distribution (MWD). The time evolution of the MWD was modeled with continuous distribution kinetics. Data indicated that LDPE followed random‐chain‐scission degradation. The rapid initial drop in molecular weight, observed up to 45 min, was attributed to the presence of weak links in the polymer. The rate coefficients for the breakage of weak and strong links were determined, and the corresponding average activation energies were calculated to be 88 and 24 kJ/mol, respectively. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 681–690, 2002; DOI 10.1002/app.2344     

Changes in fatty acids and volatile components in mackerel by broiling

Mackerel is known to be a rich source of omega‐3 family PUFAs. The acid value and conjugated dienoic acid value of mackerel, known as indices of oxidation, were determined. Fatty acids in both raw and broiled mackerels were analyzed by GC. PUFAs and saturated fatty acids were observed at a low level in broiled mackerel, possibly as a result of thermal degradation of the lipids. In addition, volatile components in mackerel extracted by solvent‐assisted flavor evaporation were analyzed by GC‐MS. In total, 38 volatile components were detected in raw mackerel, whereas 53 volatiles were found in broiled mackerel. Hydrocarbons and methyl‐ and/or ethyl‐substituted benzenes were quantitatively dominant. Levels of aldehydes and alcohols were significantly enhanced in broiled mackerel, as was the level of benzothiazole, which possibly forms as a result of the condensation of thermal degradation products from amino acids and/or proteins, and lipids.