Highly sensitive determination of a polymeric hindered amine light stabilizer in polypropylene by reactive thermal desorption-gas chromatography using nitrogen-specific detection

Highly sensitive and specific determination of trace amounts of a polymeric hindered amine light stabilizer (HALS) in polypropylene (PP) materials could be established by improving reactive thermal desorption-gas chromatography (RTD-GC) in the presence of an organic alkali, tetramethylammonium hydroxide. By using nitrogen-phosphorus detection, highly selective detection of the HALS-related components was attained. In addition, the use of a polar poly(ethylene glycol) separation column alleviated the adsorption of minor specific pyrolysis products. This modified RTD-GC method allowed the determination of the polymeric HALS (Mr 1900) in PP even for trace concentrations between 100 and 500 ppm, through observing selectively the characteristic products containing a tetramethylpiperidine moiety, which had been impossible to detect under the previous RTD-GC conditions using a non-polar separation column and conventional flame ionization detection.     

Advances in the determination of hindered amine light stabilizers – A review

Within this paper we discuss analytical strategies for the characterization and quantitation of hindered amine light stabilizers (HALS) an important sub-group of polymer additives. For the determination of monomeric HALS a range of mature and reliable techniques exists, allowing their determination in polymer extracts. If qualitative or semi-quantitative information suffices, certain techniques are capable of sampling directly from the polymer surface with limited or no sample preparation. Different strategies for the determination of complex oligomeric HALS in extracts from polymer samples are discussed. Here, approaches providing only a sum parameter including all HALS oligomers have been distinguished from more sophisticated technologies allowing the determination of single oligomers, their degradation and by-products. Particularly, the latter issue is facing increased interest as it provides important information for polymers aging studies. A tabulated overview provides comprehensive information on different analytical techniques suitable for HALS determination.     

The effect of hindered amine light stabilizers on the photooxidative stability of high-density polyethylene

The photoprotective effectiveness of various polymeric and nonpolymeric hindered amine light stabilizers (HALS) was determined by exposing samples of high-density polyethylene (HDPE) containing these additives to ultraviolet (UV) light and measuring the resultant oxygen uptake characteristics. Values of the initial quantum yield for oxygen uptake calculated for these formulations indicate that the higher molecular weight HALS compounds are less effective photostabilizers than the nonpolymeric HALS, and this is partly attributable to their decreased mobility in the polymer matrix. It was further found that the addition of an ultraviolet absorber (UVA) to a formulation containing a polymeric HALS compound enhances its photostability, although this phenomenon may be partly due to synergism between the UVA and the antioxidant, the latter having been added as part of the base stabilization. The antagonism which exists between certain sulfur-containing antioxidants and HALS compounds was also investigated and it was found that the lower molecular weight sulfur-containing antioxidants exhibit the greatest degree of antagonism. The results confirm that the mobility in the polymer matrix of the stabilizer system can serve as an explanation of its effectiveness. The article provides evidence that the technique of oxygen uptake monitoring is a sensitive and rapid method of assessment of polymer photostability in the presence of stabilizer systems.     

HPLC technique for quantitation of Chimassorb 944, and its evaluation in analysis of real and standard samples of polyolefins

A high performance liquid chromatography (HPLC) method is presented for the determination of Chimassorb 944 in polymeric matrix. A reversed phase column octadecyl silane (ODS) is used as a stationary phase. As a mobile phase, a mixture of THF:methanol:triethanol amine (90:10:1.5) (v:v:w) is used. The HPLC system was equipped with an UV detector and the absorbance of the analyte was recorded at 240 nm. In the case of polymers, 0.5 g of them along with 100 mg Irganox 1010 (for preventing oxidation of Chimassorb 944) were dissolved in boiling xylene, and then extracted with sulfuric acid 1 M four times. The extract was neutralized with sodium hydroxide solution and the analyte was re-extracted into carbon tetrachloride and then injected to the HPLC system. This method is an accurate and relatively fast technique for determination of Chimassorb 944 in polymers.     

Determination of a polymeric hindered amine light stabilizer in polypropylene formulated with magnesium hydroxide flame retardant by reactive thermal desorption-gas chromatography.

A polymeric hindered amine light stabilizer (HALS), Tinuvin 622 (MW [symbol: see text] 4000), in PP materials formulated with a magnesium hydroxide flame retardant was determined by reactive thermal desorption (RTD) gas chromatography (GC). Two kinds of the HALS components that were formed through the RTD in the presence of tetramethylammonium hydroxide [(CH3)4NOH, TMAH] were clearly observed in the chromatograms of the PP samples, with negligible interference from the other additives and the PP substrate. Here, the coexisting flame retardant was proved to affect significantly the RTD process of the occluded HALS. As a result, the recovery of the HALS components in the RTD-GC chromatograms of the PP samples increased with increase in the content of the flame retardant. This enhancement of the HALS recovery is attributed mainly to the preferential exposure of the HALS on the surface of the ground PP sample through the interaction between the polymeric HALS and the flame retardant in the molten PP during kneading. In spite of such a considerable action of the flame retardant, the observed intensities of the characteristic peaks of HALS by RTD-GC showed a good linear relationship with the HALS content in the PP samples with constant content of the flame retardant (50 phr); this relationship could be used as the calibration line for the determination of the polymeric HALS in the PP materials containing the flame retardant.     

Quantitative analysis of hindered amine light stabilizers by CZE with UV detection and quadrupole TOF mass spectrometric detection

The current work describes the development of a CZE method with quadrupole QTOF‐MS detection and UV detection for the quantitation of Cyasorb 3529, a common hindered amine light stabilizer (HALS), in polymer materials. Analysis of real polymer samples revealed that the oligomer composition of Cyasorb 3529 changes during processing, a fact hampering the development of a straightforward method for quantitation based on calibration with a Cyasorb 3529 standard. To overcome this obstacle in‐depth investigations of the oligomer composition of this HALS using QTOF‐MS and QTOF‐MS/MS had to be performed whereby 22 new oligomer structures, in addition to the ten structures already described, were identified. Finally, a CZE method for quantitative analysis of this HALS was developed starting with a comprehensive characterization of a Cyasorb 3529 standard using CZE‐QTOF‐MS, subsequently allowing the correct assignment of most Cyasorb 3529 oligomers in an electropherogram with UV detection. Employing the latter detection technique and hexamethyl‐melamine as internal standard, peak areas obtained for the melamine could be correlated with those from the triazine ring, the UV‐absorbing unit present in the HALS. This approach finally allowed proper quantitation of the single oligomers of Cyasorb 3529, an imperative for the quantitative assessment of this HALS in real polymer samples.     

The determination of small amounts of organic hydroperoxides in the presence of hindered amine light stabilizers and their nitroxyls

A method for the quantitative determination of hydroperoxide (ROOH) in the presence of hindered amine light stabilizers (HALS) and/or their nitroxyl free radical derivatives has been elaborated. The method is based on the quantitative reduction of hydroperoxides by triphenyl phosphine. The resulting compounds (alcohols) are then determined by GLC using the internal standard technique. The method has been tested on the hydroperoxides derived from 2,4-dimethylpentane. Its sensitivity and reproducibility appear to be comparable with other methods for ROOH determination but, unlike the latter, it has the advantage that its results are not influenced by the presence of HALS and/or their nitroxyl radical derivatives in the analyzed medium.     

Natural weathering test for films of various formulations of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE)

Natural (outdoor) weathering test was performed to investigate the UV stability of thin films (0.06 mm) of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). The PE films were prepared from various formulations of LLDPE and LDPE resins. Some of these films contained a single high molecular mass HALS only, along with a primary antioxidant (i.e. Irganox 1010) and a secondary antioxidant (i.e. Irgafos 168 or Alkanox TNPP), while others contained HALS and UVA (i.e. Chimassorb 81 or Tinuvin P or Tinuvin 326) along with these antioxidants. The HALS used was either an oligomeric or a synergistic mixture of a high molecular mass (HMM) hindered amine stabilizer and co-additives. The UV stability was investigated by exposing the prepared films at 45° towards south in the direct sunshine up to 365 days. Fifty percent of tensile strength retention was determined for all these exposed films and it was found that the films containing a single HALS gained improved UV stability by about two to 12 fold over the pure films. On the other hand, films that contained a combination of HALS and UVA obtained further improved UV stability over the films containing a single HALS (both have antioxidants). Films containing a single HALS reached 50% TS retention within 205 days, whereas, films containing a combination of HALS and UVA reached 50% TS retention within 590 days, which is about three times further improvement in UV stability.     

Synergism of hindered amine light stabilizers and UV-absorbers

The synergism of hindered amine light stabilizers (HALS) and UV-absorbers is very important in the practical photo-stabilization of polymers. As very little is known, however, the relationship between the composition of the mixture of the two kinds of light stabilizer and its photo-stabilizing efficiency was investigated in four common polymers. A high level of synergism was observed in polypropylene, high density polyethylene and ABS resin. A moderate synergistic effect was obtained in polystyrene. The maximum efficiency was observed at mixing ratios of hindered amine light stabilizer to UV-absorber of about 75:25 in polypropylene and high density polyethylene, 90:10 in ABS resin and 80:20 in crystal polystyrene.The synergism is due to different stabilizing mechanisms of hindered amine light stabilizer and UV-absorber, and is explained by the diffusion of very effective hindered amine light stabilizer from the polymer bulk, which is protected by the UV-absorber, towards the surface layer where photo-oxidation proceeds.     

Photogeneration of carbon dioxide from polypropylene film stabilized by hindered amines

Infrared spectrometric measurements have been used to measure the amount of carbon dioxide generated by UVA irradiation of polypropylene film stabilized with 0.5% of three different hindered amine light stabilizers (HALS). The measurements were made in situ, using a specially constructed glass cell fitted with CaF₂ windows. In each case the amount of photogenerated carbon dioxide was less than that from a HALS-free polypropylene film of similar thickness. The amount of photogenerated CO₂ was greatest in oxygen that had been pre-saturated with water and the amount of CO₂ evolved depended on the grade of HALS. In dry oxygen, although the differences between the films containing different HALS were much reduced the amount of CO₂ continued to be smaller than that from the HALS-free polymer. The sensitivity of CO₂ photogeneration to the presence of HALS provides new evidence of the relevance of the CO₂ photogeneration method to the diagnosis of photosensitivity of polymers and the influence of stabilizing additives.     

Tailoring the desired optical and mechanical performance of polyester‐plasticized PVC films: the role of different light stabilizers on the photo‐degradation

Effect of hindered amine light stabilizer (HALS: C944) and ultraviolet absorbers (UVAs: UV326, UV531) on the photo‐stabilities of polyester‐plasticized poly(vinyl chloride) (PVC) and polyester‐plasticized PVC/pigment yellow (PY) films were studied systematically. Both ultraviolet absorbers (UVAs) and hindered amine light stabilizer (HALS) could slow down the discoloration of polyester‐plasticized PVC and polyester‐plasticized PVC/PY films. However, the addition of UVAs protected polyester‐plasticized PVC films from being discolored and its efficiency is higher than HALS. The specific order of stabilizing effect on the photo‐oxidation is UV326 > UV531 > C944. For the optical performance, both UVAs and HALS could help to maintain the transmittance of visible light after photo‐degradation. The former could effectively adsorb ultraviolet (UV) light and resulted in lower transmittance of UV light. For the polyester‐plasticized PVC/PY systems, even though HALS and UVAs cannot help to maintain the shielding ability in high‐energy visible region after UV irradiation, they can help prevent the loss in transmittance of visible light. The surface morphology exhibited small holes on the surface of the films that contain UV531 or UV326; while large and deep holes were observed on the surface of PVC films without additives, C944‐doped and C944/PY‐doped films, indicating the higher UV‐stabilizing effect of UVAs. With regard to mechanical properties, UVAs and HALS can help to prevent the loss. Our present study systematically revealed the role of different stabilizers on the polyester‐plasticized PVC and polyester‐plasticized PVC/PY systems and paved the way to offer PVC materials with functional optical performance and desired long‐term performance using different light stabilizers. Copyright © 2017 John Wiley & Sons, Ltd.     

Antagonism between hindered amine light stabilizers and sulfur-containing compounds

Antagonism between hindered amine light stabilizers (HALS) and sulfur-containing compounds has been examined using esr and uv spectroscopic techniques. Evidence is presented to show that formation of nitroxyl from HALS and/or its disappearance is not affected by a sulfur-containing compound itself, but considerably by its acidic transformation product. From the results obtained in this study, a new mechanism of antagonism is proposed.     

Chromatographic methods for the analysis of basic neurotransmitters and their acidic metabolites.

Chromatographic techniques for the determination of trace amounts of neurotransmitters were reviewed. The two techniques found to be most useful were GC-MS and the reversed-phase mode of HPLC with an electrochemical or fluorescent detector. For structure determination or unequivocal peak identification, GC-MS is the method of choice. In addition the limits of detection of GC-MS were better than those obtained by HPLC. However for routine analyses, HPLC is now being used in studies of mental illness and other diseases. Good resolution, reproducibility and sensitivity can be obtained without the derivatisation steps required for GC-MS, and catecholamines, serotonin, and their acidic metabolites can be concomitantly determined in one analysis.     

Rapid determination of oligomeric hindered amine light stabilizers in polymeric materials

Hindered amine light stabilizers are essential for the stabilization of synthetic polymers, particularly for materials used for outdoor applications. Although up to now a considerable number of studies dealing with the analytics of this class of stabilizers had been published, especially the determination of oligomeric hindered amine light stabilizers is still an analytical challenge. In the current work, a fast and simple liquid chromatographic method for the quantitative determination of oligomeric hindered amine light stabilizers is presented. A key aspect of this method is their completely different retention behavior depending on the pH, enabling a single peak elution approach by a pH gradient run. This allows a quantitation with simple UV detection independent of the actual oligomeric composition. Calibration curves within the concentration range relevant for the analysis of real polymer samples (LOQ = 70 mg/L) were constructed with R ² values above 0.99. Spiked extracts from polyolefin samples showed recovery rates between 97.3 and 102.9% for five different commercial hindered amine light stabilizers. Relative standard deviations were between 2.0 and 3.9%. Furthermore, it was demonstrated that the employed approach can be easily adapted for mass spectrometry detection.     

Determination of polymer additives using analytical pyrolysis

When analyzing a polymeric material using pyrolysis-GC, the majority of the peaks seen are degradation products from the polymer matrix, but there may be specific compounds present resulting from the presence of antioxidants, plasticisers, stabilizers, flame retardants and other additives. Some of these compounds may be volatile or semi-volatile and appear as intact molecules, while others are larger and only appear as fragments after the pyrolysis. In understanding the pyrolysis of the complete system, it is important to understand the behavior of such additives under the thermal conditions used to analyze the polymer matrix.This paper presents data for several polymer additives, showing their contribution to the analytical results when studying typical polymers using Py-GC/MS. Specific types of additives include phenolic antioxidants, hindered amine light stabilizers, phthalates and phosphites.It was determined that for some additives, especially when analyzing simple polymers, co-analysis of the polymer and additive was feasible. For other, more complex formulas, a multi-step approach permitted a thermal separation of compound families and simplified the analysis. For some additives, especially in the parts-per-million range, pyrolysis with selected or extracted ion mass spectrometry was the most informative.     

Application of normal-phase high-performance liquid chromatography followed by gas chromatography for analytics of diesel fuel additives

The paper presents the results of investigations on new procedures of determination of selected cleaning additives in diesel fuel. Two procedures: one-step analysis using gas chromatography with flame ionization detection (GC-FID) or mass spectrometry (GC-MS) and a two-step procedure in which normal-phase high-performance liquid chromatography (NP-HPLC) was used for preliminary separation of the additives, were compared. The additive fraction was collected using either simple elution or eluent backflush. Final determinations were performed by GC-FID and GC-MS. The studies revealed that it was impossible to determine the investigated analytes by one-step procedures, i.e. by using solely HPLC or GC. On the other hand, the use of a two-step procedure ensures reproducible results of determinations, and the limits of quantitation are, depending on the method of fraction collection by HPLC, from 1.4–2.2 ppm (GC-MS in SIM mode) to 9.6–24.0 ppm (GC-FID). Precision and accuracy of the developed procedures are compared, and possible determination errors and shortcomings discussed.

聚乙烯光引发交联过程中的表面光氧化和光稳定

通过测定凝胶含量并利用红外-光声光谱和光电子能谱对光交联聚乙烯表面氧化程度和氧化产物进行了研究.结果表明,聚乙烯光交联过程中随着光照时间的增加,表面光氧化加剧,氧化产物主要是氢过氧化物和含羰基的化合物.考察了预辐照和添加受阻胺型光稳定剂对聚乙烯光交联过程的影响,发现这两种方法都能有效地降低光交联聚乙烯(XLPE)的表面氧化,但有些光稳定剂会降低XLPE的交联度.     

Rapid identification and semi-quantitative determination of polymer additives by desorption electrospray ionization/time-of-flight mass spectrometry

A fast and simple method for the direct qualitative and semi-quantitative determination of a set of four polymer additives in plastic samples by desorption electrospray ionization time-of-flight mass spectrometry (DESI-TOF-MS) is presented. After evaluation of crucial DESI parameters such as composition of spray solutions and spray voltages, a series of lab-made polypropylene samples containing Chimassorb 81 (2-hydroxy-4-n-octoxybenzophenone), Tinuvin 328 (2-(2-hydroxy-3, 5-ditert-pentylphenyl)-benzotriazole), Tinuvin 326 (2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chloro benzotriazole), and Tinuvin 770 (bis(2,2,6,6,-tetramethyl-4-piperidyl)sebaceate) in concentrations between 0.02% and 0.2% were analyzed, resulting in calibration graphs with R ² better than 0.994. To demonstrate the applicability of the developed method for the investigation of real samples, liners for in-ground swimming pools and polypropylene granules were analyzed with respect to their content in the selected polymer additives. Two alternative methods, both well established in the fields of polymer additive analysis, namely HPLC with UV detection (after previous extraction) and thermodesorption gas chromatography/mass spectrometry have been employed for evaluation of the results from the DESI experiments.     

Development and Applications of an Automated In-Column Pyrolysis Gas Chromatography-Mass Spectrometry System

A novel system for sample introduction into a Gas Chromatograph (GC) using an automated in-column pyrolysis device has been developed. The in-column pyrolysis device is suitable for use with any GC or GC-MS system. Solid samples are dissolved or emulsions can be diluted and injected into the system. Because the system is designed for introducing liquid samples, a better control of the injected sample amounts is achieved. This leads to high reproducibility of the peak areas, offering new opportunities for quantitation of polymers or other high molecular weight materials. In addition, a better statistical representation of the material to be analyzed is given if the samples are dissolved in a solvent. The system can be operated both in a normal GC injection mode, and in the pyrolysis mode. As a conventional GC injector working in on-column or Programmed Temperature Vaporization (PTV) injection mode, (without the pyrolysis function), information on the volatile fraction of a sample can be obtained. Once the volatile materials in the sample have been separated, a second analysis on the non-volatile matrix can be performed by initiating the pyrolysis sequence, yielding information on the non-volatile fraction of the sample. Both features, on column or PTV injection mode and in-column pyrolysis can be used separately or in combination. This new technology is expected to be useful for the determination of additives, monomers, solvents and other volatile components in a non volatile matrix, such as polymers, as well as in the characterization of the non-volatile matrix itself, in a single run. Revised: 20 June and 21 July 2005     

Separation and characterization of oligomeric hindered amine light stabilizers using high‐performance liquid chromatography with UV and quadrupole time‐of‐flight mass spectrometric detection

Hindered amine light stabilizers are an important class of stabilizers that protect synthetic polymers from degradation and thus from changing mechanical and optical properties. The current study presents an HPLC method capable of separating oligomeric hindered amine light stabilizers on a commercially available stationary phase, employing an MS‐compatible novel mobile phase. Based on the exact masses observed with Q‐TOF‐MS, a comprehensive characterization of five different types of oligomeric hindered amine light stabilizers was achieved, leading to structural information not included in the datasheets provided by the suppliers. For the different investigated hindered amine light stabilizers, a number of recurring units up to 17 and a molecular weight of 5200 g/mol were detected. Furthermore, the analysis of stabilizer extracts of processed polypropylene samples containing different types of hindered amine light stabilizers revealed significant differences in the oligomeric pattern between standards and polymer samples. Thus, changes in the analytes’ oligomeric pattern resulting from processing or aging of polymer materials can be monitored with the presented method.