Hindered Amine Light Stabilizers Research Articles

Property Characterization of Anti-Aging Additives and Modified Asphalt Based on Long-Term Aging Behavior

In order to achieve the good application of hindered amine light stabilizer (HALS) in the long-term aging control of asphalt pavement material, Tinuvin770 and Tinuvin622 light stabilizers were selected as modifiers for asphalt. The microstructure and characteristics of hindered amine light stabilizers were characterized by FIB-SEM. The elemental composition and relative content of hindered amine light stabilizers were studied by means of EDS analysis. The functional group composition of hindered amine light stabilizers was analyzed based on Dynamic-FTIR. On this basis, light stabilizer modified asphalt was prepared, and the effect of hindered amine light stabilizer on the thermal rheological properties of asphalt binder during UV aging period was studied by dynamic shear rheology (DSR). The changing law of low temperature rheological properties of hindered amine light stabilizer modified asphalt was evaluated by low temperature bending beam rheological test (BBR). The results showed that the hindered amine light stabilizer could capture the free radicals formed during the photodegradation of asphalt when subjected to ultraviolet aging. Under the impact of ultraviolet aging, hindered amine light stabilizer could improve the high temperature performance of asphalt binder. Furthermore, HALS could achieve the improving effect on the low temperature rheological properties and long-term aging performance of asphalt pavement materials.

Constructing cross-functional intumescent flame retardants with UV resistance for polypropylene composites

Cross-functional additives were carefully designed for polypropylene (PP) composites to enhance the flame retardancy, UV resistance, and mechanical properties. In this work, first, ammonium polyphosphate (APP) was coated with polysiloxane to avoid the pyrolysis of APP under UV irradiation; second, the charring formation agent (CFA) with triazine groups was selected to enhance the absorbance of UV radiation. Hindered amine light stabilizer (TEMP) was reacted with sodium lignin sulfonate (SLS) to obtain SLS-TEMP. By using 19 wt.% (SiAPP/CFA)/2 wt.% SLS-TEMP, the limiting oxygen index of the PP composite was increased to 33.5 and the UL-94 grade was achieved to V-0. The peak heat release rate and peak smoke release rate were reduced by 76% and 74% compared with that of the control PP sample, respectively. Moreover, the aging process of the PP composite sample was delayed. The tensile and impact strength of the PP/19 wt.%(SiAPP/CFA)/2 wt.%SLS-TEMP sample was decreased by 13.4% and 27.8%, respectively after 60 h UV irradiation, which was significantly lower than that of control PP (50.9% and 68%). The change of limiting oxygen index before and after aging was minimal, and the sample still passed UL-94 V-0 grade after 100 h UV-aging test. It was proved that the SLS-TEMP has an excellent synergy effect on improving the flame retardancy and UV resistance of PP. This cross-functional additive strategy provides a good solution for obtaining high-performance PP composites.

The kinetic degradation of LDPE films subjected to aggressive environments

The effect of natural and thermo-oxidative aging on the structure and physicochemical properties of LDPE films stabilized with hindered amine light stabilizers (HALS) was investigated. Based on multiple linear regression analysis (MLRA) mathematical models to predict the lifetime of the LDPE were developed. Four statistical criteria were used to evaluate the developed models: residual variance, coefficient of determination, Student's test and the Fisher-Snedecor test. The half-life times predicted by the mathematical models were found to be statistically significant (p < 0.05).

Photodegradation and Photostability of Bamboo: Recent Advances

Bamboo and its products are widely used in indoor and outdoor fields. Photodegradation occurs easily on the surface when bamboo is exposed to ultraviolet (UV) light from solar radiation. This induces surface discoloration and degrades the physical properties of bamboo, which not only negatively affects its utility and aesthetic characteristics but also restricts its application in outdoor environments. In this work, we review the mechanism of bamboo photodegradation, in which the behavior of lignin is key. The changes in bamboo’s microstructure, surface color, and chemical composition during photodegradation are described in detail. Methods for enhancing its photostability, including the application of transparent coatings containing UV absorbers and hindered amine light stabilizer compounds on bamboo surfaces, are then systematically summarized, and potential approaches to combat the photodegradation of bamboo surfaces are discussed. On the basis of the recent advances of photodegradation and photostability of bamboo, this review provides new insights into the scientific application and protection of bamboo in the outdoor field.

Non-Arrhenius behavior: Influence of antioxidants on lifetime predictions for materials used in the cable and wire industries

Thermo-oxidation (70–160 °C) of peroxide cross-linked polyethylene (XLPE) formulations stabilised with different antioxidants were studied. In order to separately study the influence of three commonly used antioxidants, three formulations were prepared with only one antioxidant each (0.3% w/w): a sterically hindered phenolic antioxidant (Irganox 1010), an organosulfur antioxidant (Hostanox SE4) and an oligomeric, sterically hindered amine light stabiliser (HALS 94). The materials were characterised by infrared spectroscopy measurements and tensile testing. Results proved that the addition of antioxidants causes in each case an Arrhenius break, occurring at a different temperature depending on the nature of the added antioxidant. Interestingly, the study of the thermo-oxidation (50–105 °C) of a certified antioxidant-free polyethylene (non-cross-linked) revealed no Arrhenius deviation. In a previous paper, we reported an Arrhenius deviation at low temperature (50 °C) for two cross-linked PE and EPR, containing residual process antioxidants. These results strengthen our hypothesis that several Arrhenius deviations could be explained by the presence of antioxidants (residual process antioxidants or formulation antioxidants), which “activity” is extremely dependent on the temperature.

Comparison of Crosslinking Kinetics of UV-Transparent Ethylene-Vinyl Acetate Copolymer and Polyolefin Elastomer Encapsulants.

Encapsulants based on ethylene-vinyl acetate copolymers (EVA) or polyolefin elastomers (POE) are essential for glass or photovoltaic module laminates. To improve their multi-functional property profile and their durability, the encapsulants are frequently peroxide crosslinked. The crosslinking kinetics are affected by the macromolecular structure and the formulation with stabilizers such as phenolic antioxidants, hindered amine light stabilizers or aromatic ultraviolet (UV) absorbers. The main objective of this study was to implement temperature-rise and isothermal dynamic mechanical analysis (DMA) approaches in torsional mode and to assess and compare the crosslinking kinetics of novel UV-transparent encapsulants based on EVA and POE. The gelation time was evaluated from the crossover of the storage and loss shear modulus. While the investigated EVA and POE encapsulants revealed quite similar activation energy values of 155 kJ/moles, the storage modulus and complex viscosity in the rubbery state were significantly higher for EVA. Moreover, the gelation of the polar EVA grade was about four times faster than for the less polar POE encapsulant. Accordingly, the curing reaction of POE was retarded up to a factor of 1.6 to achieve a progress of crosslinking of 95%. Hence, distinct differences in the crosslinking kinetics of the UV-transparent EVA and POE grades were ascertained, which is highly relevant for the lamination of modules.

Weatherability of Bamboo Scrimber: Enhance in Photostability of Substrate and Coatings

Enhancing the weatherability of bamboo-based products is essential for increasing their application lifespan. In this study, a composite protective coating containing organic and inorganic UV absorbers and a hindered amine light stabilizer (HALS) was investigated for outdoor bamboo scrimber (OBS). The optical properties of weathered coated and uncoated samples were investigated by colorimetry and UV-Vis spectrophotometry. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) were used to determine the physicochemical properties of the coating. The addition of HALS improved the photostability of the coating and preserved the properties of OBS. Compared to resin-coated samples, alicyclic amines in HALS inhibit photooxidation reactions between bamboo lignin and the coating adhesive. This inhibition is critical for maintaining the UV-shielding performance of the coating. We have developed a photostable protective coating for bamboo-based products whose widespread use can significantly help conserve critical forest resources.

Enhancement of Ultraviolet Light Resistance of Colorless and Transparent Semi-Alicyclic Polyimide Nanocomposite Films via the Incorporation of Hindered Amine Light Stabilizers for Potential Applications in Flexible Optoelectronics.

Optically transparent polymer films with excellent thermal and ultraviolet (UV) resistance have been highly desired in advanced optoelectronic fields, such as flexible substrates for photovoltaic devices. Colorless and transparent polyimide (CPI) films simultaneously possess the good thermal stability and optical transparency. However, conventional CPI films usually suffered from the UV exposure and have to face the deterioration of optical properties during the long-term service in UV environments. In the current work, the commercially available hindered amine light stabilizers (HALS) were tried to be incorporated into the semi-alicyclic CPI matrix with the aim of enhancing the UV exposure stability. For this target, a CPI-0 film was first prepared from hydrogenated pyromellitic dianhydride (HPMDA) and 2,2′-dimethylbenzidine (DMBZ) via a one-step polycondensation procedure. Then, the commercially available HALS were incorporated into the CPI-0 (HPMDA-DMBZ) film matrix to afford four series of CPI/HALS composite films. Experimental results indicated that the Tinuvin® 791 HALS showed the best miscibility with the CPI-0 film matrix and the derived CPI-D series of composite films exhibited the best optical transmittances. The CPI-D nanocomposite films showed apparently enhanced UV exposure stability via incorporation of the 791 additives. For the pristine CPI-0 film, after the UV exposure for 6 h, the optical properties, including the transmittance at the wavelength of 350 nm (T350), lightness (L*), yellow indices (b*), and haze obviously deteriorated with the T350 values from 55.7% to 17.5%, the L* values from 95.12 to 91.38, the b* values from 3.38 to 21.95, and the haze values from 1.46% to 9.33%. However, for the CPI-D-10 film (791: CPI-0 = 1.0 wt%, weight percent), the optical parameters were highly maintained with the T350 values from 61.4% to 53.8%, the L* values from 95.46 to 95.36, the b* values from 1.84 to 1.51, and the haze values from 0.69% to 3.34% under the same UV aging conditions.

Mixing of hindered amine-grafted polyolefin elastomers with LDPE to enhance its long-term weathering and photo-stability

Polyolefins are a commodity plastic family known as low cost and recyclable material, that has displayed high potencies for wide variety of applications, resulting from their desired chemical, mechanical, and physical properties. However, further modifications are needed to improve their properties to extend their service lifetime, weathering resistance, and photostability for use in outdoor applications, which are due to their low thermal and photo-stabilities. In this research, hindered amine light stabilizers were used to enhance the photo-stability of low-density polyethylene (LDPE). For this purpose, unsaturated 4-amino-2,2,6,6-tetramethylpiperidine (UATMPP) was prepared by amidation reaction of amine groups in amino-2,2,6,6-tetramethylpiperidine with acryloylol chloride of 10-undecenoyl chloride in presence of triethylamine and 4-dimethylaminopyridine. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) exhibited successful preparation of UATMPP. UATMPP was grafted on polyolefin elastomer (POE) through melt free radical grafting method. FTIR and NMR confirmed the successful preparation of UATMPP-grafted POE. Finally, UATMPP-containing POE was mixed by LDPE through melt compounding. The results from the calculation of carbonyl index from FTIR and tensile testing after UV irradiation exhibited desired antiaging and UV-resistant properties of LDPE/POE blends, which were influenced by grafting degree of UATMPP as well as POE content (wt%).

Photochromic Microcapsules for Textile Materials by Spray Drying—Part 3: Application of Photochromic Microcapsules on Cotton Fabrics

Photochromic textiles, a class of functional textiles, have a color build up feature under ultraviolet light irradiation. However, photochromic dye application onto textile materials by conventional finishing techniques has difficulties due to their low water solubility and low affinity to the textile materials. Encapsulation technology could be used to overcome these problems in the production of photochromic textile materials. This article, which is the third in a three-part series, deals with the application of photochromic dye microcapsules produced by a spray drying method onto cotton fabrics. The photochromic dye microcapsules were applied onto cotton fabrics by a pad–dry–cure process. Color build up and ultraviolet transmittance of the resultant photochromic fabrics were evaluated after the application and consecutive washing. Moreover, the fatigue resistance of the photochromic fabrics was studied and the effects of the incorporation of hindered amine light stabilizers into microcapsules were investigated. Ultraviolet protection factor values of the samples were found to be 50+ even after 20 washing cycles. It was shown that the photochromic fabrics have a loss of 10% in ultraviolet protection factor values and 20% in color values after 20 ultraviolet irradiation cycles and the fatigue resistance of the photochromic dye capsules improved with the use of hindered amine light stabilizer compounds during microcapsule production.

The effect of nanoparticles on the loss of UV stabilizers in polyethylene films

The adverse environmental effects (UV radiation and oxidation) on polyethylene films' durability significantly shorten their service life. This work was aimed to study the influence of incorporation of nanoparticles (hydrophobic nanosilica and Na+ nanoclays) to UV stabilized films (by hindered amine light stabilizer – HALS) on sustaining their properties by delaying the loss of the HALS from linear low-density polyethylene (LLDPE) films under photo-oxidative and humid environments. Results demonstrated that the incorporation of nanoclays to the stabilized film increased the photo-oxidative degradation of the LLDPE due to enhanced loss of the HALS from the nanocomposite film. In contrast, the addition of nano-silica delayed the loss of HALS under the same harsh conditions. The slower loss of HALS was attributed to the introduction of a longer diffusion path for the HALS molecules provided by the well-dispersed hydrophobic nanosilica particles and the immobilization effect resulting from the chemical affinity between the hydrophobic nanosilica and the hydrophobic sites on the HALS molecules. The HALS's increased retention in the LLDPE/nanosilica nanocomposite film resulted in extended retention of the film's mechanical properties.

Evaluating efficacy of different UV-stabilizers/absorbers in reducing UV-degradation of lignin

Abstract Susceptibility of wood to UV degradation decreases the service life of wood products outdoors. Organic UV absorbers (UVAs) and hindered amine light stabilizers (HALSs), as well as inorganic UVAs, are added to coatings to improve the UV stability of coated-wood products. Although about 85% of UV radiation is absorbed by lignin in the wood, it is unclear which UV stabilizers can minimize lignin degradation. In this study, the photodegradation of softwood organosolv lignin was monitored over 35 days of UV exposure. Changes in lignin properties were assessed using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and phosphorus-31 nuclear magnetic resonance spectroscopy (31P NMR). It was found that the aromatic rings of lignin underwent significant degradation, resulting in increased glass transition temperature and molecular weight of lignin. Subsequently, 18 different additives were mixed with lignin and exposed to UV irradiation. The analysis of samples before and after UV exposure with FTIR revealed that inorganic UVAs (cerium oxide and zinc oxide) and a mixture of organic UVAs and HALSs (T-479/T-292, T-5248, and T-5333) were the most effective additives in reducing lignin degradation. This study can help coating scientists to formulate more durable transparent exterior wood coatings.

Effect of Stabilizers and Thermoplastic Polyurethane on the Properties of Three-Dimensional Printed Photochromic Wood Flour/Polylactic Acid Composites.

This study was aimed at investigating the photofatigue resistance and mechanical properties of photochromic wood-plastic composites using a stabilizer complex-AH (antioxidant 1010 and hindered amine light stabilizer HALS 770)-with different contents of thermoplastic polyurethane (TPU), which was prepared by the melt-blending extrusion process and three-dimensional (3D) printing. Photofatigue resistance, mechanical property, microtopography, and thermal analyses of 3D printed samples were performed. The results showed that the difference in surface color of composites improved by 26.7% with addition of AH after 10 days of accelerated aging, whereas the mechanical strength decreased. Upon adding TPU, composites' impact strength significantly increased by 25.48% and 87.87% with 10% and 20% addition, respectively. Meanwhile, the interface compatibilities between the components were enhanced. The differential scanning calorimetry and thermogravimetric analysis results indicated that 10% TPU could improve the thermal stability of composites.

Effect of Hindered Amine Light Stabilizer on Properties of HDPE/Kaolin Composites for Hydraulic Gate and its Mechanism Analysis

High density polyethylene (HDPE)/kaolin composites with different hindered Amine light stabilizers were prepared by blending granulation. The mechanical properties and dynamic thermodynamic changes before and after aging were discussed and studied. The precipitates were analyzed by FI-IR and H1-NMR, and the precipitation reason and anti-aging difference of different light stabilizers were discussed and compared. The results showed that the mechanical properties retention rates of light stabilizer 2020, light stabilizer 944, light stabilizer 123, light stabi-lizer 770 and light stabilizer 292 were 87.1%, 81.7% and 79.1%, respectively %Light stabilizer 2020 and light stabilizer 944 with large molecular weight are more easily compatible with the system, not easy to precipitate, and have a better an-ti-aging effect. At the same time, light stabilizer 2020 with dense hindered amine structure has excellent anti-aging effect. This study provides a reference for the selection of light stabilizer and failure analysis of light aging resistance of HDPE system.

Weatherability of different monomers in melamine-crosslinked polyester binders: Towards increasing renewable content in coil coatings

The stability of coil coatings towards exterior influences is one of their most important properties as it ensures substrate quality. The weatherability of eight melamine crosslinked polyester coatings was studied in accelerated aging in order to systematically examine the effect of individual monomers including phthalic anhydride and the bio-based monomers succinic acid, sebacic acid, 1,2-propanediol, 1,3-propanediol and glycerol. Coatings with and without hindered amine light stabilisers were characterised upon degradation through their gloss retention, infrared spectra, film thickness and μ-hardness.A greater susceptibility to radical degradation mechanisms forming new polar chain ends was observed for sebacic acid compared to succinic acid, and for 1,3-propanediol compared to 1,2-propanediol. On the other hand, μ-hardness results suggested that 1,2-propanediol and phthalic anhydride accelerate the formation of new crosslinks during degradation.As radical and hydrolytic bond scission compete with the formation of new crosslinks and each mechanism influences the others, both monomeric composition and overall structure have to be considered to understand the degradation behaviour. The presented findings can be used as a guide by those aiming to increase the bio-based content in coil coatings.

Thermal aging behavior characteristics of asphalt binder modified by nano-stabilizer based on DSR and AFM

Abstract In order to clarify the effect of thermal aging on the nano-stabilized modified asphalt binder, TINUVIN 770 (T770) hindered amine light stabilizer of nanoscale was selected as aging modifying agent to prepare modified asphalt. The impact of thermal aging on the rheological properties of T770-modified asphalt was investigated using dynamic shear rheological test of frequency sweep and multiple stress creep recovery test. The surface roughness variation of T770-modified asphalt was characterized by using atomic force microscope throughout the thermal aging process. Furthermore, the typical morphology and parameter features of T770-modified asphalt were identified. The results showed that with the extension of thermal aging time, the high temperature rutting resistance of T770-modified asphalt was improved, while the unrecoverable creep compliance was degraded. When the thermal aging time exceeded 6 h, the bee structure appeared on the surface of T770-modified asphalt. Meanwhile, with the increase in thermal aging time, the special structure formed on the surface of asphalt gradually became smaller. The surface fluctuation difference of T770-modified asphalt reflected the better thermal aging resistance property of T770-modified asphalt than 70# asphalt.

Photovoltaic modules encapsulated in composite material modified with ultraviolet additives

Photovoltaic modules were manufactured by vacuum resin infusion process using glass reinforced epoxy composite as encapsulant where the cells are embedded. Incorporation of ultraviolet absorber (UVA) and hindered amine light stabilizer (HALS) additives to the epoxy resin was studied, given their potential to enhance the performance stability of the modules under ultraviolet (UV) radiation exposure.

Construction of hierarchical Ti3C2TX@PHbP-PHC architecture with enhanced free-radical quenching capability: Effective reinforcement and fire safety performance in bismaleimide resin

The effect of hindered amine light stabilizer on free radical quenching can be combined with the cross-linked polyphosphazene containing PN structure to improve the flame retardant efficiency of titanium carbide (Ti3C2TX) in both gas phase and condensed phase. Here, a hindered amine and polyphosphazene modified Ti3C2TX (Ti3C2TX@PHbP-PHC) was obtained. With the loading of Ti3C2TX@PHbP-PHC in the bismaleimide resin (BMI) increased to 2 wt%, an 43% reduction was achieved in the peak heat release rate (PHRR), and a 47% reduction in the total heat release rate (THR).Meanwhile, the total gaseous products and total smoke production (TSP) exhibited a similar decreasing trend. Furthermore, 0.5 wt% BMI system exhibited the highest storage modulus (2629 MPa) and impact strength (13.7 MPa), which were 21% and 76% higher than pure BMI, respectively. Therefore, the developed functionalized Ti3C2TX can be effectively used in BMI matrix, thereby providing reliable source material for the design of high-performance BMI resins that meet various application scenarios.

Light stabilizer and diazo passivation of black phosphorus nanosheets: Covalent functionalization endows air stability and flame retadancy enhancements

As a new nano flame retardant, black phosphorus (BP) is easy to degrade and oxidize in the presence of water and oxygen, especially in the case of light, this process will be accelerated. In order to delay the oxidative degradation of BP and maintain its structure stability and flame retardant properties, the light stabilizer, free radical quenching type hindered amine is used to improve the ambient stability and the flame retardant efficiency of BP. In this work, BP was modified by diazotization to obtain active chlorine groups, and then the hindered amine light stabilizer was grafted onto the surface of BP through covalent reaction to form functionalized BP (BP-HAN). The fire risk of epoxy resin can be obviously reduced by introducing the BP-HAN into the matrix. The addition of 2 wt% BP-HAN can reduce the PHRR and THR value of epoxy by 56.0% and 48.2%, respectively. In particular, epoxy composites with only 0.5 wt% BP-HAN were able to achieve UL-94V-0 rating with an oxygen index of more than 30. In addition, compared with pure BP nanosheets, the ambient stability of BP modified by hindered amine was significantly improved. This work provides a reference for the application of BP in the field of flame retardant, and simultaneously achieves the improvement of the ambient stability and flame retardant performance of BP.

Photostabilization of polyethylene by a hindered amine light stabilizer in blooming conditions and impact of MDO processing

The effect of Machine Direction Orientation (MDO) processing on the photostabilization of LLDPE samples containing Tinuvin® 770 was studied. The amount of Tinuvin® 770 in the processed samples was deliberately chosen at a level higher than the reported solubility at ambient temperature for two main reasons: the first reason was to assess the equilibrium between the soluble and nonsoluble forms of this additive and the impact of the MDO process, and the second was to demonstrate the role of a higher temperature in accelerated artificial photoaging on the protective role played by the nonsoluble part. The results reported in this article show that at room temperature, a nonnegligible amount of Tinuvin® 770 precipitates at the surface, which is commonly termed blooming. However, the additive that bloomed at the surface can be dissolved within the polymer with increasing temperature, which is the case in the conditions of accelerated artificial photoaging but not the case of natural outdoor weathering. Such physical phenomena are responsible for a possible bias brought by temperature during accelerated photoaging, which can affect aging tests. This questions the representativeness of accelerated aging at higher temperatures for polymers containing a blooming stabilizer.