Prevention of degradation of γ-irradiated EPDM using phenolic antioxidants

The mitigation of oxidative degradation under γ-irradiation promoted by eight commercial antioxidants: Ethanox 330, Hostanox O3, Irganox 1010, Topanol OC, Ionox 220, Santonox R, Santowhite, Cyanox 2246 loaded onto ethylene-propylene terpolymer at the concentration of 0.5 phr in respect of a pristine polymer was studied. The polymer samples were exposed to various doses up to 500 kGy. The kinetic parameters of oxidations: oxidation induction times, onset oxidation temperature, oxidation rates were evaluated by CL measurements. They validated the differences in the stabilisa-tion activities by limitation of the oxidation gradient. The high efficiency of some of the antioxidants studied, such as Ionox 220 and Santowhite, ensured the delay in degradation even at a high irradiation dose (500 kGy). For the environments with γ-radiation exposure, a relevant sequence in the increasing protection efficiency could be established: Topanol OC; Hostanox O3; Irganox 1010; Cyanox 2246; Santonox R; Ionox 220; Santowhite. The FT-IR spectra were recorded for the calculation of the radiochemical yields resulting from the modifications occuring in the concentrations of oxygenated structures. The accumulations of hydroxyl- and carbonyl-containing products were calculated to evaluate the irradiation effects in EPDM-based products during a severe accident. The options for EPDM stabilisation are discussed based on chemiluminescence and FTIR analyses.     

The effects of gamma irradiation on the fate of hindered phenol antioxidants in food contact polymers. Analytical and 14C-labelling studies

The extractable levels of two hindered phenol antioxidants (Irganox 1076 and Irganox 1010) present in PVC, polyethylene and polypropylene, have been monitored by HPLC techniques following progressive exposure of the polymers to ⁶⁰Co γ radiation. There is a gradual diminution in the extractable levels of each antioxidant as irradiation progresses as a result of transformation of the antioxidants in the oxidation reactions ensuing during irradiation. Experiments involving the use of a ¹⁴C-labelled sample of Irganox 1076 in polyolefins have provided evidence of covalent binding of antioxidant degradation products to the polymer following gamma irradiation. However, there is also evidence of the formation of extractable degradation products, the identity of which is as yet unknown.     

耐辐射致色聚烯烃的研究

研究了在γ射线辐照条件下受阻胺光稳定剂 (简称HALS)、各种抗氧剂对聚丙烯 (PP)和聚乙烯 (PE)的黄度 (YI)的影响。结果表明五甲基HALS比相应的四甲基HALS更能有效地阻止聚烯烃的辐射致色。抗氧剂Irganox 10 76比Irgafos16 8或IrganoxPS 80 2更有效。当抗氧剂和HALS并用时显示出协同效应 ,10 76和PDS并用时聚丙烯的黄度比单独添加 10 76或PDS的聚丙烯的黄度都低。     

Investigation of antioxidant and electron beam radiation effects on the thermal oxidation stability of low-density polyethylene

Effect of various antioxidants on the thermal oxidation stability of LDPE and X-LDPE has been investigated. To achieve this purpose, miscellaneous commercial grade antioxidants such as Irganox 1010, Irganox1076, Irgafos168, Irganox B225, and Chimassorb 944 were selected. Then, formulations based on different content of antioxidant were prepared. The samples were crosslinked by exposure to electron beam irradiation. To assess the thermal oxidation stability of samples, oxidation induction time (OIT) test was accomplished on both the irradiated and unirradiated specimens. Ageing tests were carried out in order to evaluate the thermal oxidation stability of irradiated X-LDPE. The results indicate that Irganox 1010 is the most effective antioxidant amongst the selected ones, concerning thermal oxidation stability of LDPE, before and after aging test.     

Structural and physico-chemical studies on modification of polypropylene and its polyphenolic antioxidant by electron beam irradiation

As polypropylene (PP) is widely used in medical and pharmaceutical fields, the effect of sterilization on both the polymer and its additives must be taken into account. In this study, PP and its antioxidants Irganox 1010 and 1076 were electron beam irradiated in order to evaluate by Fourier transform infrared spectroscopy, differential scanning calorimetry and size exclusion chromatography, their structural and physico-chemical modifications. A good correlation between those analytical techniques has indicated the formation of oxidation products, chain scissions as well as crosslinking. The effect of the absorbed dose is underlined.     

Determination of antioxidants in polyolefins by pressurized liquid extraction prior to high performance liquid chromatography

The effect that a high amount of mineral filler might have on the extraction process of antioxidants from polyethylene and polypropylene was investigated. Extraction of Irganox 1010, Irganox 1076 and Irgafos 168, along with its oxidation product 2,4-di-tert-butylphenol, from freeze ground polyethylene–based (PE–based) and polypropylene–based (PP–based) mineral concentrates of 85 w/w calcium carbonate (CaCO₃) and 75 w/w talc was carried out by pressurized fluid extraction (PLE) prior to high performance liquid chromatography (HPLC). Results indicate that 85 w/w CaCO₃ did not affect the extraction process from PE or PP. For talc concentrates, additive recovery from PE and PP was considerably lower. The relation of recovery yield and mixing time was investigated for the talc concentrates and it was concluded that the presence of talc seemed to accelerate the rate of antioxidant consumption during sample processing, thus, less antioxidant was left to be extracted from the polyolefin; rather than talc has limited the extraction process. The method developed in this work has been applied to determine these compounds in several commercial samples.     

Evaluation of long‐term performance of antioxidants using prooxidants instead of thermal acceleration

Evaluation of stabilization efficiencies of different antioxidants in polymers at low temperature and relatively short time was performed using incorporation of a prooxidant for catalytic oxidation. Comparisons were made between polypropylene films stabilized with primary antioxidants (Irganox 1076, Irganox 1010, and α‐tocopherol), with or without the prooxidant manganese stearate at different temperatures. A faster degradation was obtained in the presence of a prooxidant than without it. The relative efficiency of the antioxidants at prooxidant acceleration correlated better to low temperature long‐term test than at the thermal acceleration. The results were affected by initial differences in the amounts of the antioxidants present after the processing of the films. These differences were corrected for by a recalculation using microwave‐assisted extraction (MAE) and high performance liquid chromatography analysis from the exponential decrease in the amount of antioxidant in the films. The fastest comparison of the antioxidants efficiency was obtained from oxidation induction times, using total luminescence intensity measurements, but reliable results could also be obtained from the time to apparent failure. © 2005 Wiley Periodicals,Inc. J Polym Sci Part A: Polym Chem 43: 4537–4546, 2005     

HALS和抗氧剂对PE辐射致色的影响

聚乙烯;稳定剂;HALS和抗氧剂对PE辐射致色的影响     

The extractability of phenolic antioxidants into water and organic solvents from polyethylene pipe materials - Part I

Three commercial anti-oxidant systems have been studied regarding migration and chemical reaction in different polyethylene pipe materials during extraction in organic solvents and in hot water, 95-100 °C, under anaerobic and aerobic conditions. Materials made of crosslinked and non-crosslinked high density polyethylene, low density polyethylene and blends thereof were stabilized with different phenolic antioxidants: Irganox 1330, Irganox 1010, and Irganox 1076. The loss in stability with increasing extraction times was followed by oxidation induction time (OIT) measurements and by measuring the residual amounts of anti-oxidant by extraction. A gradual decrease in OIT and amount of anti-oxidant with increasing treatment time in water was observed for all samples. However, the behaviour of the three antioxidants was dissimilar. For materials containing Irganox 1330 three new species, possibly transformation products of the anti-oxidant, were found within the material. Larger decrease in anti-oxidant content in the polymer compared to corresponding loss in OIT indicates that the new species still have anti-oxidant capacity. On the other hand, corresponding transformation species could not be found within materials stabilized with Irganox 1010 or 1076. It is suggested that these antioxidants, which both contain ester groups, are hydrolyzed and that the new species migrate out into the surrounding water. Solvent extractions showed that crosslinking did not affect the extractability of the antioxidants. Actually, even with water as the extracting media, the network did not show any obstructive effect of the migration of the anti-oxidant. For peroxide crosslinked samples part of the anti-oxidant could not be extracted with solvent but we believe that grafting of antioxidants onto the polymer backbone is the most plausible explanation in this case. Additionally, we see a clear decrease in anti-oxidant loss with increasing crystallinity.     

Determination of antioxidants in polyolefins using total dissolution methodology followed by RPLC

Antioxidants are added to polyolefins to improve the stability of the resin from oxidation and degradation during processing of the finished article and to increase product lifetime. Without antioxidants, polyolefins would quickly degrade during and after the extrusion or thermoforming process, which would cause inferior appearance and physical properties. The proper level must be added to protect the polymer and to minimize cost. Antioxidants are usually extracted from the resin and the extract is analyzed by RPLC, GC, or Fourier transform infrared spectroscopy. Unfortunately, many of these procedures require significant manual labor, time, and solvent, rendering them impractical for high-throughput work processes. In addition, they may not provide complete extraction of the additives depending upon the type of resin. A validated analytical method was needed for the determination of three common antioxidants, Irganox(?) 1010, Irganox(?) 1076, and Irgafos(?) 168 in polyolefin resins. This paper shows the determination of these antioxidants using dissolution followed by precipitation with o-xylene and methanol. Direct analysis of the solution is achieved in 8?min using RPLC.     

Extraction of polypropylene additives and their analysis by HPLC

Summary The polypropylene additives were extracted by dissolution-precipitation and Soxhlet. The Soxhlet method was adapted for the extraction of phosphorous antioxidants. The RP HPLC method with quaternary gradient elution separated five chemical groups of additives: lower molecular mass di-tert-butyl phenol (D.T.B.P.), hindered amine light stabilizers (Tinuvin 326), hindered phenolic antioxidants (Irganox 1010) and phosphorous antioxidants (Irgafos 168 and Ultranox 626) with their degradation products.     

TMP与受阻酚Irganox 1010在异辛烷溶液中并用时光稳定作用的研究

本文研究了2,2,6,6-四甲基哌啶醇(简称TMP)和2,2,6,6-四甲基哌啶醇氮氧自由基(简称TMPO·)分别与四[3-(3,5-二叔丁基-4-羟基苯基)丙酸]季戊四醇酯(简称Irganox 1010)在异辛烷溶液中并用时的光稳定作用。结果表明:TMP与Irganox 1010的并用体系有反协同作用:Irganox 1010对异辛烷溶液的光氧化有敏化作用;TMP与Irganox 1010并用时,TMPO·的累积速率变慢,浓度极大值比只含TMP的样品低;TMPO·与Irganox 1010并用时,TMPO·的衰减比只含TMPO·的样品快得多。根据实验事实提出:TMPO·与Irganox 1010之间起了某种反应,该反应引起的氮氧自由基浓度的降低可能是受阻胺与受阻酚并用时产生反协同效应的主要原因。     

Gel permeation chromatography – Atmospheric pressure chemical ionization – Mass spectrometry for characterization of polymer additives

The study presents the possibility to use gel permeation chromatography (GPC) with atmospheric pressure chemical ionization (APCI)-mass spectrometry for the analysis of polymer additives having molecular weights up to 2,000?g?mol^?1. Irganox 1010, Irganox 1035, Irganox 1076, and Irganox 3114 were analyzed in chloroform using 2.1-mm-internal-diameter GPC columns at the optimum flow rate of 50?µL min^?1. Based on the chemical formula, the APCI interface combined with chlorine ionization enabled us to predict the expected mass spectrum and to build libraries without needing to inject each additive separately. Quantification limits of about 100?µg of additive in 1?g of polymer (100?ppm) can be reached using single-ion-monitoring methods based on the calculated isotope distribution.     

Thermal oxidation and molding feasibility of cycloolefin copolymers (COCs) with high glass transition temperature

Cycloolefin copolymers (COCs) with high glass transition temperature (T_g = 203 °C) have been synthesized and pelletized by extrusion molding. However, their colors change from transparent to yellow during extrusion molding because of thermal oxidation and generation of alkene groups. We have successfully blended several antioxidants (Irganox 1010, Irgafos 168, Irganox HP2225 and Irganox HP2921) into lab-made COCs to avoid the discoloration. The experimental results show that Irganox HP2921 is the best antioxidant among the antioxidants used and can effectively not only suppress thermal oxidation but also eliminate the color stain.     

LDPE protected by secondary amines of dehydroabietic methyl ester derivatives

The thermal degradation of low density polyethylene in the presence of several esters—methyl-12N-(phenyl)amino-14-amino-dehydroabietate (A 8), methyl-12N-(2-methoxyphenyl)amino-14-amino-dehydroabietate (A 9), methyl-12N-(4-methoxyphenyl)amino-14-amino-dehydroabietate (A 11) and methyl-12N-(phenyl)amino-14-nitro-dehydroabietate (A 12)—was investigated by chemiluminescence at three temperatures: 180, 200, and 220 °C. Kinetic parameters that depict the stability of polymers—temporal characteristics (oxidation induction times, half-period of oxidation and maximum oxidation time), oxidation rates and activation energies—were calculated from the dependencies of chemiluminescence intensity on thermal degradation time. The stabilization effectiveness of the compounds tested and other antioxidants, namely 4010 (amine compound) and Irganox 1010 and 1076 (hindered phenols), is presented for comparison. Experimental data have demonstrated that two members of the studied series, A 8 and A 11, are more efficient than good commercial hindered phenols.     

Separation of hydrophobic polymer additives by microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) has been applied to the separation of some phenolic antioxidants [Irganox 1024, Irganox 1035, Irganox 1076, Irganox 1010, Irganox 1330, Irgafos 138, Irganox 168 and 2,6-di-tert.-butyl-4-methylphenol (BHT)]. Due to the extremely hydrophobic nature of these analytes, they could not be separated using standard MEEKC conditions and two alternative approaches were investigated. Using an acidic buffer (phosphate, pH 2.5) to effectively suppress the electroosmotic flow, the addition of 2-propanol to the aqueous phase of the microemulsion buffer to improve partitioning of the analytes, and a negative separation voltage, separation of five of the analytes in under 10 min was possible. The second approach, using a basic buffer (borate, pH 9.2) and a positive separation voltage resulted in complete resolution of all eight analytes. A mixed surfactant system comprising the anionic sodium dodecyl sulfate (SDS) and neutral Brij 35 was used to reduce the overall charge and with it the mobility of the droplets, and hence the separation time. Using an optimised MEEKC buffer consisting of 2.25% (w/w) SDS, 0.75% (w/w) Brij 35, 0.8% (w/w) n-octane, 6.6% (w/w) 1-butanol, 25% (w/w) 2-propanol and 64.6% (w/w) 10 mM borate buffer (pH 9.2) the eight target analytes were baseline separated in under 25 min. For these analytes, MEEKC was found to be superior to micellar electrokinetic chromatography in every respect. Specifically, the solubility of the analytes was better, the selectivity was more favourable, the analysis time was shorter and the separation efficiency was up to 72% higher when using the MEEKC method. Detection limits from 5.4 to 26 microg/ml were obtained and the calibration plot was linear over more than one order of magnitude. The optimised method could be applied to the determination of Irganox 1330 and Irganox 1010 in polypropylene.     

Kinetics and structure-activity relationship of dendritic bridged hindered phenol antioxidants to protect styrene against free radical induced peroxidation

A series of dendritic poly(amido-amine) (PAMAM) bridged hindered phenols antioxidants were synthesized. The active antioxidant group (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) was attached to two generations of PAMAM dendrimers, and their structure was verified by nuclear magnetic resonance (NMR) and fourier transform infrared spectra (FT-IR). The antioxidant abilities of the dendritic phenols to inhibit the oxidation of styrene were evaluated and the relationships between the length of core, the generation of dendrimers and the antioxidant activities were established. The reaction kinetics of scavenging peroxyl radicals was followed by oxygen consumption. The inhibition time (t_inh) values showed the dendritic phenols had the ability of scavenging peroxyl radicals, and that the antioxidant ability increased with the increasing length of the core and the generation. The kinetic analysis demonstrated that dendritic phenols could slow the rate of styrene peroxidation induced by AIBN, as shown by the number of trapping ROO· (n), and this role was in accordance with that of the t_inh values.     

A Straightforward Route to Potent Phenolic Chain‐Breaking Antioxidants by Acid‐Promoted Transposition of 1,4‐Benzo[b]oxathiines to Dihydrobenzo[b]thiophenes

The transformation of simple phenols with limited antioxidant activity into potent chain‐breaking antioxidants was achieved by a three‐step protocol, consisting of the conversion of phenols into 1,4‐benzo[b]oxathiines followed by an unprecedented acid‐promoted transposition to o‐hydroxydihydrobenzo[b]thiophenes, or dihydrobenzo[de]thiochromenes, starting from phenols or naphthols, respectively. These derivatives, bearing a benzo‐fused heterocycle with a sulfide sulfur ortho to the phenolic OH, have a rate constant of reaction with alkylperoxyl radicals (k_inh) comparable to that of α‐tocopherol. A solid rationale for the transposition mechanism as well as for the structure‐antioxidant activity relationship is presented.     

Solvent exchange using hollow fiber prior to separation and determination of some antioxidants by high performance liquid chromatography

This study presents a simple and rapid solvent exchange procedure using a hollow fiber. Antioxidants (Irganox 1010, Irganox 1076 and Irgafos 168) and solvents such as tetrahydrofuran (THF), carbon tetrachloride and toluene were selected as model compounds and sample solvents, respectively. After injection of the sample solution into the hollow fiber and solvent evaporation, the precipitated analytes in lumen and pores of the fiber were washed with methanol (the mobile phase for separation and determination by HPLC-diode array detection) and good chromatographic peaks were obtained. The effect of different parameters such as fiber length, volumes of sample and washing solvents were investigated and the optimum conditions were selected. The repeatability of the method was tested and it was found that the relative standard deviation (R.S.D.) was less than 10% for all analytes. Also enrichment factors of 3.03, 2.21 and 1.19 times were obtained for Irganox 1010, Irganox 1076 and Irgafos 168, respectively, when 200 μL sample and 50 μL methanol (washing solvent) were used.