Hindered Amine Light Stabilizers Research Articles

The role of quinoid derivatives in the UV-initiated synergistic interaction mechanism of HALS and phenolic antioxidants

Within this work, UV-initiated interaction mechanisms between the phenolic antioxidant Irganox 1330 and nine commercially used hindered amine light stabilizers (HALS) were successfully studied using high-performance liquid chromatography (HPLC) coupled to UV and high-resolution mass spectrometric detection (MS). An analytical evaluation of the stabilizer performances in the polypropylene-mimicking solvent squalane revealed that all investigated HALS exhibited a strong synergism when combined with the phenolic antioxidant. Up to now, the synergistic interaction was described as a result of the hydrogen transfer from a hydroxylamine derived from HALS to the oxidized form of a primary antioxidant, whereby the phenol is regenerated. Investigations on degradation products, however, indicated that the proposed interaction mechanism cannot be applied to a sterically hindered phenol such as Irganox 1330. Instead, a completely new stabilization mechanism of phenolic antioxidants in the presence of HALS, involving the formation of quinoid derivatives, was discovered and confirmed by using a model compound.

Evaluation of hindered amine light stabilisers and their N-chlorinated derivatives as antibacterial and antifungal additives for thermoset surface coatings

N-Halogenated amines or ‘halamines’ have attracted recent attention as potential biocides for materials and surface coatings application. Facile N-chlorination of the hindered amine light stabiliser (HALS) Tinuvin®770, bis-(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, was achieved by reaction with sodium dichloroisocyanurate. The chlorinated product was incorporated into a polyester-based paint formulated for coil coating, applied to test panels and subjected to high temperature curing conditions characteristic of the coil coating process (55 s at 262 °C). Rapid detection of N-chlorinated Tinuvin®770 in the cured coating was confirmed, using liquid extraction surface analysis-mass spectrometry, by the characteristic fragmentation patterns of the halamines observed upon collision-induced dissociation. Antimicrobial activity of the coating was determined by testing against the bacterium Pseudomonas aeruginosa and the fungus Cladosporium sp., two organisms that are known to colonise both internal and external surfaces in building and cladding applications. The activity of HALS and halamine containing coatings were compared against a commercial product containing an antimicrobial additive as well as control surfaces without additives. Significant activity against the bacterium, but not against the fungus was demonstrated for the parent HALS and halamine containing coatings. The possibility of regeneration of the halamines was also tested and confirmed by mass spectrometry, post-chlorination of samples showed no significant differences in activity between corresponding pairs of samples.

Textile applications of commercial photochromic dyes. Part 6: photochromic polypropylene fibres

Two commercial photochromic dyes, a spirooxazine and a napthopyran, were successfully incorporated into polypropylene fibres by melt extrusion to produce fibres that showed intense photochromism. The technical performance of the photochromic dyes was investigated using a methodological approach that has been established and validated for the dyes applied by screen printing onto textiles in previous publications in this series. These parallel investigations allowed a comparison of the properties of the dyes in polypropylene and screen printed on cotton. The photocolorability of both dyes was found to be significantly higher in polypropylene compared with screen prints on cotton when applied at the same dye concentration. Of particular interest was the observation of positive solvatochromism, providing evidence that the photochromism is due to the colorants in solution in both media. The colour development rates during UV exposure of the dyes applied by screen printing cotton and by extrusion into polypropylene were similar. However, differences were observed in the thermal fading rates after removal of the UV source, in that the spirooxazine dye reverted more slowly in polypropylene, while the reverse was true in the case of the naphthopyran. Both dyes showed better photostability in polypropylene than in screen‐printed textiles. A UV absorber and two hindered amine light stabilisers were found significantly to enhance the photostability of the dyes in polypropylene, although the presence of the UV absorber reduced the degree of photocoloration.

Acid Is Key to the Radical-Trapping Antioxidant Activity of Nitroxides.

Persistent dialkylnitroxides (e.g., 2,2,6,6-tetramethylpiperidin-1-oxyl, TEMPO) play a central role in the activity of hindered amine light stabilizers (HALS)-additives that inhibit the (photo)oxidative degradation of consumer and industrial products. The accepted mechanism of HALS comprises a catalytic cycle involving the rapid combination of a nitroxide with an alkyl radical to yield an alkoxyamine that subsequently reacts with a peroxyl radical to eventually re-form the nitroxide. Herein, we offer evidence in favor of an alternative reaction mechanism involving the acid-catalyzed reaction of a nitroxide with a peroxyl radical to yield an oxoammonium ion followed by electron transfer from an alkyl radical to the oxoammonium ion to re-form the nitroxide. In preliminary work, we showed that TEMPO reacts with peroxyl radicals at diffusion-controlled rates in the presence of acids. Now, we show that TEMPO can be regenerated from its oxoammonium ion by reaction with alkyl radicals. We have determined that this reaction, which has been proposed to be a key step in TEMPO-catalyzed synthetic transformations, occurs with k ∼ 1-3 × 10(10) M(-1) s(-1), thereby enabling it to compete with O2 for alkyl radicals. The addition of weak acids facilitates this reaction, whereas the addition of strong acids slows it by enabling back electron transfer. The chemistry is shown to occur in hydrocarbon autoxidations at elevated temperatures without added acid due to the in situ formation of carboxylic acids, accounting for the long-known catalytic radical-trapping antioxidant activity of TEMPO that prompted the development of HALS.

Damp Heat Aging Behavior of a Polyamide-Based Backsheet for Photovoltaic Modules

This paper describes and evaluates accelerated aging of a titanium dioxide (TiO2) filled polyamide (PA) based backsheet film for photovoltaic (PV) modules. Damp heat exposure (85%RH, 85 °C) was carried out up to 2000 hrs. The backsheet was characterized using microscopic, spectroscopic, thermoanalytic, chromatographic, and mechanical methods. While Raman microscopy, infrared spectroscopy in attenuated total reflection mode (IR-ATR), scanning calorimetry (DSC), and thermal gravimetric analysis did not reveal aging-induced changes, significant yellowing was detected by ultraviolet visible near infrared (UV/VIS/NIR) spectroscopy. Depending on the stabilizer type (UV-absorbers, hindered amine light stabilizers (HALSs), and antioxidants), rather different consumption rates were ascertained by high-performance liquid chromatography (HPLC) and gas chromatography (GC). Although the ultimate mechanical properties decreased significantly, no full embrittlement was obtained after damp heat exposure of up to 2000 hrs. The observed physical and chemical aging mechanisms were classified as within the induction period without premature failure.

Development of complementary HPLC-DAD/APCI MS methods for chemical characterization of pharmaceutical packaging materials

The chemical characterization of plastics for pharmaceutical packaging has been subject to ever increasing regulatory scrutiny, the reasons for which being: a) plastic additives and degradation products can be extremely hazardous to the patients’ health (especially patients on chronic therapy) and b) they offer no therapeutic or formulatory benefit whatsoever. The last decade has seen the issuing of several books, monographs and guidelines dealing with extractables and leachables, however the amount of scientific work done so far is still fairly small (the majority of it performed by only a few research groups), with only a small number of methods published in the literature.This work focuses on developing a set of two complementary HPLC-DAD/APCI MS methods for simultaneous separation, detection, identification and quantification of a wide variety of packaging additives and degradants, the second method specifically targeting a group of compounds known as polymeric hindered amine light stabilizers (HALS), which are known to be notoriously difficult to separate and analyze with standard analytical techniques. The methods are capable of detecting plastic additives present in low ppb concentrations, from samples extracted in solvents with various polarities and pH values.Both methods were developed and optimized using system suitability mixtures comprised of 9 additives commonly encountered in plastic materials, and their practical applicability tested on a variety of extracts from low-density polyethylene (LDPE) and polypropylene (PP), where several additives were successfully separated, detected and identified.

Accelerated degradation of water borne acrylic nanocomposites used in outdoor protective coatings

In this study, the degradation of a water-borne acrylic coating and the influence of rutile-TiO2 (R–TiO2) nanoparticles and a hindered amine light stabilizer (HALS) on its photo-stability in accelerated aging environment has been quantitatively studied by monitoring the chemical modifications occurring upon aging conditions. By using non-destructive analytical methods, like IR and UV-visible spectroscopy, 3D laser microscopy, SEM observations and weight loss measurements, it was possible to follow continuously the formation of photo-oxidative products and the loss of the binder functional groups on a sample undergoing accelerated aging. For the first time, numerous dark spots, randomly dispersed on the whole surface of the sample upon UV/condensation exposure are successfully observed and explained by using a novel technique 3D laser microscopy. Our findings also confirm that HALS greatly improved photo-stability to the coating thank to its free radical and hydrogen peroxide scavenging capacity. This work provides some useful information for a better understanding of the degradation behavior of water-borne acrylic coating under accelerated aging conditions.

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.

Stabilization of Polypropylene for Rotational Molding Applications

Rotational molding (RM) is a useful process for making large hollow objects. Due to its relatively high toughness and forgiving thermal oxidative degradation behavior, polyethylene is a most widely used material. However, it has too low elastic modulus for some important applications which leads to adaptation of polypropylene (PP) as a RM material. PP requires specially tailored antioxidant (AO) packages if it is to have any chance of surviving the often long (up to ca. 30 minutes) cycle times associated with RM. During the study the addition of the following stabilizers and antioxidants (AO) to the PP copolymer were investigated: a hindered phenolic primary AO, a phosphite secondary AO, a thioester secondary AO and a hindered amine light stabilizer. Synergistic effects between the primary and secondary AOs, as well as optimum heating times, were investigated. During the investigation formulations were prepared by compression molding and bench-scale RM. The combination resulting in the most effective synergism is the hindered phenolic primary antioxidant combined with the phosphite secondary antioxidant. A gel silica controlled release agent for the stabilizers was also investigated but did not yield significant improvements in stabilization.

The effects of ultraviolet and visible light on common furs: Color changes, photooxidation and the use of Tinuvin 292 as a photoprotectant

Abstract In order to determine the light sensitivities of commonly encountered furs, 17 furs from 12 species were exposed to 1.97 Mlx hours of light from a xenon arc lamp, filtered either to simulate window-filtered daylight or to remove all ultraviolet (UV) radiation. Comparison with coexposed Blue Wools showed that most samples were relatively lightfast (Blue Wool 5 or better), with darker specimens being more lightfast. Examination of the Commission internationale de l'éclairage (CIE) L*a*b* values revealed fading but also other changes: some furs darkened, and other experienced changes in b* values. Removal of UV radiation prevented darkening and usually decreased the magnitude of ΔE76 but did not prevent color changes, and one species exhibited greater change under visible light. Changes in color were accompanied by photooxidation of the keratin of all species as assessed by attenuated total reflectance infrared spectroscopy; the extent of photooxidation was decreased by filtering out UV radiation. Pre-exposure treatment with a spray application of a 1% solution of Tinuvin 292, a hindered amine light stabilizer, offered some protection against both UV and visible light-induced changes. Tinuvin 292 pre-exposure also helped prevent keratin photooxidation and light-induced mechanical damage and thus may be an appropriate preventative treatment when light exposure is unavoidable.

Synthesis and photostabilizing performance of a polymeric HALS based on 1,2,2,6,6-pentamethylpiperidine and vinyl acetate

Polymeric hindered amine light stabilizers (polymeric HALS) have been extensively studied because they combine a high ability to protect the polymers against harmful effects of weathering with minimum physical loss. In this study a new polymeric N-methylated HALS was synthesized by the radical copolymerization of a cyclic tertiary amine with vinyl acetate (VAc). 4-Acryloyloxy-1,2,2,6,6-pentamethylpiperidine (APP), the cyclic tertiary amine, was prepared by the initial conversion of 2,2,6,6-tetramethyl-4-piperidinol derivatives via two different routes. The APP/VAc copolymer synthesized was characterized by size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR) and carbon-13 nuclear magnetic resonance (13C NMR). The photostabilizing performance, particularly the induction period of polypropylene (PP) films containing different concentrations of APP/VAc copolymer, when exposed to accelerated aging, was comparable to that of PP films compounded with commercial polymeric HALS.

Multi-functional hindered amine light stabilizers-functionalized carbon nanotubes for advanced ultra-high molecular weight Polyethylene-based nanocomposites

Hindered Amine Light Stabilizer (HAS) molecules have been covalently linked on the outer surface of multi-walled carbon nanotubes (CNTs), and the so-obtained multi-functional fillers (HAS-f-CNTs) have been compounded with Ultra High Molecular Weight Polyethylene (UHMWPE) to get composite films. The success of the grafting reaction of the HAS molecules has been confirmed through spectroscopic and thermo-gravimetric analyses. Morphological analyses reveal a segregated microstructure, in which CNT-rich channels surround the polymer domains. This morphology results in improved mechanical properties and appreciable electrical conductive features. More importantly, the addition of only 1 wt.% of HAS-f-CNTs brings about a significant improvement of the photo-oxidation resistance, which neither HAS nor CNTs can provide if used separately. The origin of this synergic effect is discussed. Overall, our results demonstrate the possibility of using properly functionalized CNTs as multi-functional fillers to get high-performance polymer composites.

Study on the performance of cooling composite materials for liquid-immersed concentrating photovoltaic systems

According to the aging phenomenon that di-methyl silicon oil working as a cooling material for liquid-immersed concentrating photovoltaic system for long time. In this paper, the method that enhances the weather-resistance of silicon oil by adding additives was proposed. Hydroxy-4-methoxy-benzophenone (UV-9) and a hindered amine light stabilizer named GW-783 were selected as additive to prepare composite materials. The performance of these composites was studied by accelerated life test (ALT). The results showed that the composites can inhibit the aging effect on flow and optic characteristics and did not affect the performance of solar cell. The most efficient one is the composite prepared by adding UV-9 and GW-783 together into silicon oil.

Synthesis and Application of Polymeric Fluorescent Compounds Based on Coumarin

In this work, a multifunctional yellowing inhibitor was synthesized by the Pechmann method. In order to obtain the target compound, 7-hydroxy-4-methyl coumarin was prepared by using the raw materials of resorcinol and ethyl acetoacetate, with toluene-p-sulfonic acid as the catalyst. New polymeric fluorescent compounds were synthesized by connecting the 7-hydroxy-4-methyl coumarin, the hindered amine light stabilizer 4-amion-2,2,6,6-tetramentylniperidine, and a series of polyethylene glycol segments into the same molecule with cyanuric chloride as a bridge. The structures of the synthesized molecules were confirmed by FT-IR, 1H NMR, and elemental analysis. The luminescent properties of the fluorescent compounds were studied by UV-vis spectroscopy and fluorescence spectroscopy. The integration effect between the fluorescent compounds and paper was tested by a scanning electron microscope. The light stability effect on the paper sheet was tested using an ultraviolet aging apparatus. The results indicate that the polymeric fluorescent compounds had a positive effect on the light stability of the high-yield pulp.

Influence of typical stabilizers on the aging behavior of EVA foils for photovoltaic applications during artificial UV-weathering

Ethylene vinyl acetate copolymer (EVA) is the most commonly used embedding material in crystalline silicon photovoltaics. It is responsible for fixing module components, electrical isolation and protecting cells against mechanical and environmental stresses. The degradation of EVA during weathering can cause adhesion loss, the so called delamination, and yellowing of the foil, resulting in a drop of module efficiency. In order to improve the long-term stability, several stabilizers including UV-absorber, hindered amine light stabilizer and phosphite are added to the polymer. However, the exact influence of the different stabilizers on failure mechanisms has not yet been identified in detail. Therefore, different EVA foils containing variable additive formulations were exposed to artificial UV-irradiation at 50 °C. As a result, delayed EVA degradation could be observed depending on stabilizers added. On the other hand, some of the tested additives were found to be involved in delamination and yellowing processes.

Exploitation of Acacia confusa heartwood extract as natural photostabilizers

Heartwood extracts of Acacia confusa (HEAc) were proven to have the capability of ameliorating wood photostability. However, the efficacy of photostability compared with that of commercial photostabilizers was unknown. The aim of this study was to examine whether HEAc can be used as commercial photostabilizers. Comparison was made among commercially available photostabilizers, UV absorber (Eversorb 80, EV80) and hindered amine light stabilizer (Eversorb 93, EV93). Photostability of wood slices soaked in 1, 5 and 10 % HEAc or 1 % commercial photostabilizers (EV80 or EV93) solutions was evaluated. The discoloration of 5 and 10 % HEAc-treated specimens was significantly reduced after UV irradiation. Furthermore, lignin degradation and carbonyl formation were concurrently inhibited by 5 and 10 % HEAc treatments after UV irradiation. Interestingly, 1 % HEAc treatment showed similar effectiveness compared with EV80 treatment, while 5 and 10 % HEAc treatments showed better effectiveness than EV80 treatment. HEAc can absorb UV light and quench radicals; hence, wood photodegradation was consequently prevented. These results revealed that HEAc has great potential to be developed as a natural photostabilizer.

Synthesis and properties of multifunctional nitroxyl radical hindered-amine light stabilizers

Abstract A series of novel nitroxyl radical hindered-amine light stabilizer monomers were designed and synthesized from 2,2,6,6-tetramethylpiperidine-N-oxyl-4-ol, cyanuric chloride, allylamine, and 2-hydroxyphenylbenzotriazole derivatives. Structures of the new stabilizers were confirmed by 1H NMR, 13C NMR, FT-IR, ESI-HRMS, and element analysis. The synthesized compounds 5a–f were evaluated for their antioxidant and antiaging properties, and a significant stabilizing effect against photodegradation was found.

Influência de estabilizantes na degradação foto-oxidativa de filmes de compósitos de SWy-1/poli(óxido de etileno)

Compósitos de poli(óxido de etileno) (PEO) com argila montmorilonita SWy-1 e estabilizantes (2-hidroxibenzofenona e tinuvin 770) foram preparados pelo método de intercalação em solução. Os filmes obtidos foram expostos a irradiação UV, e os produtos da fotodegradação foram monitorados por FTIR (Fourier Transform Infrared Spectroscopy, ou Espectroscopia no infravermelho por transformada de Fourier) e SEC (Size Exclusion Chromatography, ou cromatografia de exclusão por tamanho). O PEO puro apresentou maior coeficiente de degradação, kd, comparado com as demais amostras. O sistema que apresentou o menor valor para o coeficiente de degradação (kd = 1,9×10–6 mol g–1 h-1) foi o compósito de PEO/5%SWy-1 com 0,25% de tinuvin 770. Nesse caso, a estabilização da matriz de PEO pode ser atribuída à argila juntamente com o tinuvin 770. A argila dispersa e absorve a irradiação UV, e o tinuvin age como estabilizante do tipo HALS (do inglês hindered amine light stabilizer, ou estabilizantes à luz tipo aminas impedidas).

Effect of High pH Found in Low-Level Radioactive Waste Leachates on the Antioxidant Depletion of a HDPE Geomembrane

AbstractAntioxidant depletion from a high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) immersed in three different high pHs solutions is examined over a 3-year period. The three solutions had the same concentration of inorganic salts but a range of pH (9.5, 11.5, and 13.5) likely to encompass those found in low-level radioactive waste leachate and other geoenvironmental applications. Increasing the pH from 9.5 to 13.5 increased the antioxidant depletion rates detected by both standard and high-pressure oxidative induction time tests (Std-OIT and HP-OIT) and also increased the residual HP-OIT values. Arrhenius modeling is used to predict the length antioxidant depletion stage for each solution.

Property modification and process parameter optimization design of polylactic acid composite materials Part II: application of response surface methodology and multi-objective particle swarm optimization in the processing of polylactic acid composite fiber

Two biodegradable polymers (polylactic acid (PLA) and polybutylene succinate (PBS)) were mixed with ultraviolet absorbers and hindered amine light stabilizers to improve the durability of this composite fiber outdoors. Filament was obtained from this composite material under the optimum conditions by using melt spinning to investigate the effects of spinning temperature, spinneret rotation speed and take-up roller speed in the fiber spinning process on the quality characteristics of newly spun threads. The response surface method was used to build a regression model for different quality characteristics. Moreover, multi-objective particle swarm optimization was applied to optimize the model of these quality characteristics and parameter limits. According to experimental validation, the composite material of PLA/PBS was better than the composite material of PLA/polycaprolactone. The denier of the composite fiber obtained under the optimized conditions was 40.07 d, with an increase of 5.3% compared to the denier before optimization. The fiber strength after optimization was 1.69 (g/d), with an increase of 42%. The breaking elongation was 176.04% and increased 27% after optimization. The prediction error rate of an optimum regression model showed that the model has good reproducibility.