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UV Absorber (uv + absorber)
Selected AbstractsLayer-by-Layer Interference Lithography of Three-dimensional Microstructures in SU-8,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Andrés F. Lasagni We report on rapid fabrication of two-, two and a half-, and 3D planar periodic structures using layer-by-layer deposition and interference patterning of SU-8 photoresist. Complex structures with non-periodic vertical symmetry were fabricated controlling the cure depth by addition of a UV absorber. The fabrication method reported here can be applied for the high-volume manufacturing of solid structures for microelectromechanical systems and microfluidic devices. [source] Eco-friendly methodologies for the synthesis of some aromatic esters, well-known cosmetic ingredientsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 1 2005C. Villa Synopsis Solid,liquid solvent-free phase transfer catalysis (PTC) and acidic catalysis in dry media were applied, with noticeable improvement and simplification over classical procedures in a Green Chemistry context, to the synthesis of some aromatic esters useful as cosmetic ingredients: 3-methylbutyl 4-methoxycinnamate, 2-ethylhexyl 4-methoxycinnamate, 2-ethylhexyl 4-(dimethylamino)benzoate and 2-ethylhexyl salicylate, well-known ultraviolet B sunscreen filters; 4-isopropylbenzyl salicylate, UV absorber and cutaneous antilipoperoxidant; propyl 4-hydroxybenzoate and butyl 4-hydroxybenzoate (parabens), antimicrobial agents. The reactions were performed under microwave (MW) activation and conventional heating. The best results for the synthesis of cinnamic, salicylic and 4-(dimethylamino)benzoic esters were achieved by in situ preformed carboxylates alkylation with alkyl bromides using PTC. The 4-hydroxybenzoates were obtained in good yields by classical esterification of the acid with alcohols using a simple heterogeneous mixture of reagents with catalytic amounts of p -toluenesulfonic acid (PTSA). The comparisons of yields and thermal profiles under either MW or conventional heating were studied and reported. Résumé La catalyse par transfert de phase (CTP) solide-liquide sans solvant et l'estérification acido-catalysée en ,,milieu sec'' ont été appliquées, dans le cadre de la ,,chimie verte'', avec des nettes améliorations et simplifications par rapport aux méthodes classiques, à la synthèse de certains esters aromatiques, ingrédients cosmétiques: 3-methylbutyl 4-méthoxycinnamate, 2-éthylhéxyl 4-méthoxycinnamate, 2-éthylhéxyl 4-(diméthylamino) benzoate et 2-éthylhéxyl salicylate, filtres solaires UVB bien connus; 4-isopropylbenzyl salicylate, filtre UV et antilipopéroxydant cutané; propyl 4-hydroxybenzoate et butyl 4-hydroxybenzoate (parabens), agents antimicrobien. Les réactions ont été procédées sous irradiation micro-onde et par chauffage classique. Pour la synthèse des esters dérivés de l'acide cinnamique, salicylique et 4-(diméthylamino)benzoïque les meilleurs résultats ont été obtenus grâce à la CTP par alkylation des carboxylates (préformés in situ) avec des bromures d'alkyle. Les esters de l'acide 4-hydroxybenzoique ont été obtenus avec de bons rendements par simple mélange hétérogène des réactifs et d'acide p-toluènesulfonique (PTSA) comme catalyseur. Les rendements et les profils de montée en température sous micro-ondes et par chauffage classique ont été comparés. [source] In-line analysis of the influence of monomeric and oligomeric hindered amine on the hydrolysis of polycarbonate in a PC/ABS blendJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Vipin V. Rajan Abstract The polycarbonate/polyacrylonitrile butadiene styrene (PC/ABS) blends lose mechanical properties when exposed to outdoor conditions. This is due to the ultraviolet (UV) induced photo-oxidation of the PC phase and the polybutadiene portion of the ABS. It is known that ABS can be stabilised against terrestrial light by the use of hindered amine in combination with a UV absorber. However, such hindered amine cannot be used when PC is present in a multi component polymer blend. The hydrolysis of PC is accelerated when a small amount of hindered amine light stabilisers (HALS) is incorporated in the resin and is exposed to elevated temperature. In this article the effect of monomeric and oligomeric hindered amine on the hydrolysis of PC during the compounding of PC/ABS blend in a twin screw extruder at 240°C is observed by means of in-line UV-vis spectroscopy. Tinuvin 765 was used as monomeric hindered amine and Tinuvin 622 as oligomeric hindered amine. The molecular weight of the compounded sample was determined by gel permeation chromatography (GPC) and the rheological properties were observed using an online viscometer. It was found that the extent of hydrolysis induced by the oligomeric hindered amine is less compared to monomeric amine. It was also observed that polymeric hindered amine imparts better dispersion of the ABS phase into the polymer blend. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effect of the combination of a benzophenone-type ultraviolet absorber with thermal stabilizers on the photodegradation of poly(vinyl chloride)JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2010Xiuqin Xiang The effect of the combination of a UV absorber (Chimassorb 81) with different types of thermal stabilizers, including an organic calcium complex and an organotin mercaptide, on the photodegradation of poly(vinyl chloride) (PVC) was investigated by color difference measurements, UV,Vis spectroscopy, Fourier-transform infrared spectroscopy, thermogravimetric (TG) analysis, and viscosity-average molecular weight determination. Films of PVC containing 0.5 phr of Chimassorb 81, with and without 2 phr of a thermal stabilizer, were prepared by solution casting. Then the accelerated UV weathering of the films was carried out under xenon light with an irradiance of 0.51 W/(m2 · nm) at 65°C. The results showed that both Chimassorb 81 and the mixture of Chimassorb 81 with the organic calcium complex showed good behavior in inhibiting the photodehydrochlorination and photooxidation of PVC. In contrast, the combination of Chimassorb 81 and methyltin mercaptide significantly accelerated initial color development during the final 200 h of exposure because of the UV sensitivity of the organotin. Moreover, when Chimassorb 81 and the methyltin mercaptide were used together to stabilize PVC films, the expected antioxidant effect of the mixture was not observed, in contrast to the behavior found with other stabilized systems, perhaps because the Chimassorb 81 had been depleted by the methyltin mercaptide during the UV irradiation. The TG analysis revealed that ultraviolet irradiation had caused severe destruction of the PVC chains. However, addition of Chimassorb 81 or the combination of Chimassorb 81 with the organic calcium complex effectively prevented the destruction, as was demonstrated by changes in the activation energies for thermal degradation. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers [source] A radically new UV stabilizer for flexible PVC roofing membranesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2005Gerald Capocci Ultraviolet absorbers, such as those from the hydroxyphenylbenzotriazole and hydroxybenzophenone classes of compounds, are typically added to flexible PVC roofing membranes in order to protect the membranes during long-term exposure to sunlight. In this article a radically new UV stabilizer, one that is not just another UV absorber, is introduced. This new UV stabilizer, which is chemically a low-basicity hindered piperidine derivative, was found to dramatically increase the weatherability of PVC roofing membranes. The performance of the new light stabilizer is documented and compared to that of traditional PVC membranes containing just a UV absorber. Although the article focuses on PVC roofing membranes, examples are provided of other durable applications that could benefit from the new light stabilizer technology. J. VINYL ADDIT. TECHNOL., 11:91,94, 2005. © 2005 Society of Plastics Engineers [source] Effect of hindered piperidine light stabilizer molecular structure and UV-absorber addition on the oxidation of HDPE.JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2004Part 1: Long-term thermal, photo-oxidation studies This series of papers explores the effect of structural characteristics of 2,2,6,6-tetramethylpiperidine-based hindered amine light stabilizers (HALS) on the long-term (40 months) thermal (110°C in air) and photo-stabilization (Microscal unit wavelength >300 nm) performance characteristics of high-density polyethylene formulations. Possible synergism with a triazine functional UV absorber is also explored. Under thermal degradation (measured by carbonyl index) the polymeric HALS performed best, mainly because of reduced volatilization. Additionally, >N-methyl HALS generally showed superior performance under thermal degradation. There was no synergism between an N-CH3 polymeric HALS and the UV1164 triazine additive. However, the equivalent N-H polymeric HALS interacted in a complex manner with UV1164, giving synergism and antagonism, depending on HALS/UV1164 ratio. Strong synergism was evident with the monomeric HALS when the total stabilizer level was 0.2% w/w. Reduction in the overall stabilizer level to 0.05% w/w eliminated the synergism. The UV1164 alone led to rapid and intense yellowing; however, the rate and intensity of yellowing reduced dramatically upon combination with HALS, particularly when the UV1164 level was above 0.1% w/w. When the formulation was under UV attack, the molar mass and the type of N-substitution had no influence on stabilization performance because of the relatively low temperature of testing (leading to reduced volatilization), and the similarly effective UV-stabilization routes for N-methyl HALS and N-H HALS. Under UV attack, yellowing reached a maximum and then decreased to approximately the initial level, while HALS/UV1164 combinations generally showed weak antagonism. J. Vinyl Addit. Technol. 10:79,87, 2004. © 2004 Society of Plastics Engineers. [source] Evaluation of a UV absorber added to PET bottles for edible oil packagingPACKAGING TECHNOLOGY AND SCIENCE, Issue 1 2003Leda Coltro Abstract The photo-oxidation of lipids has significant effects on the quality of edible oils. The oxidation of oils and fats can begin due to the action of external energy sources such as light. Studies showed that the rate of photo-oxidation of the oil depends on the light transmission of the packaging, the product characteristics and the O2 barrier of the packaging. The UV absorber 2-(2,-hydroxy-3,-tert-butyl-5,-methylphenyl)-5-chlorobenzotriazole (Tinuvin 326Ô) has been used in PET bottles for oil, making possible the reduction of the photo-oxidation rates. This additive was approved recently by the European Union and included in the Positive List of Directive 2001/62/EC, with a limit of specific migration. This additive is also approved by the Mercosur legislation; nevertheless its restriction of use is being reviewed in Brazil. This study had the objectives of evaluating the efficiency of the additive through the determination of the light barrier properties of PET bottles with various levels of Tinuvin 326Ô and of verifying its suitability for use in direct contact with foods. Copyright © 2003 John Wiley & Sons, Ltd. [source] Sunscreens containing the broad-spectrum UVA absorber, Mexoryl® SX, prevent the cutaneous detrimental effects of UV exposure: a review of clinical study resultsPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 4 2008Anny Fourtanier Background: UVA exposure of human skin mainly produces reactive oxygen species (ROS) leading to DNA, cell and tissue damage. It alters immune function, pigmentation and it is certainly responsible for a large part of photoaging changes. Moreover UVA is implicated in the etiology of several photodermatoses. As a consequence, to provide adequate protection, sunscreens or skin care products for daily use protective products need UVA absorbers combined with UVB ones. Aim: To assess the efficacy of sunscreens containing a broad-spectrum UVA absorber the Mexoryl® SX or ecamsule and to compare formulations with and without it through a large number of clinical studies in human volunteers and patients. Methods: The following assessments were conducted: ,Prevention of excessive pigmentation induced by UV exposure in Caucasian and Asian skins using a method that measures pigmentation protection factors (PPF). ,Efficacy against DNA damage by measurement of pyrimidine dimer formation and p53 protein accumulation. ,Protection of immune system using delayed type hypersensitivity (DTH) reactions to recall antigens, isomerization of urocanic acid (UCA), alteration of Langerhans cells (LC) density, morphology and function. ,Reduction of epidermal and dermal alterations induced by repeated UVA or UV solar simulated radiation (SSR) using histology or immunohistology. ,Prevention of the polymorphous light eruption (PMLE) in patients prone to develop this disease. Results: Mexoryl® SX-containing formulations showed a dose-dependent level of protection against pigmentation. For a same sun protection factor (SPF) the higher the UVA protection was, the higher was the PPF. Pyrimidine dimer formation and p53 accumulation were significantly reduced by formulations with Mexoryl® SX. In the studies looking at the suppression of DTH reactions to recall antigens by the different UV spectra, the LC alterations and the cis UCA formation, Mexoryl® SX formulations always showed a higher protective potency than sunscreen without it even when the protection against erythema was similar (products with same SPF). Mexoryl® SX formulations also prevented or significantly decreased to minimal, ferritin, tenascin and lysozyme expression induced by repeated UVA or SSR exposure. It also reduced the enhancement of collagenase 2 mRNA expression induced by SSR exposure. Finally PMLE study demonstrated that UVA protection was essential for the prevention of this photodermatose. Conclusion: Mexoryl® SX formulated in sunscreens or daily use products have been shown to be an effective UV absorber, leading to an increased efficacy of these products against a large number of biological damage induced by UVA, SSR or sun exposure. [source] Exploitation of the complex chemistry of hindered amine stabilizers in effective plastics stabilization,JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2007J. Pospí Hindered amine stabilizers (HAS) remain a prominent class of stabilizers having a fortunate development with continuous interest in shaping the future properties of plastics: increase in polymer durability, application extension, reaching new effects. Commercial tests provided much information. Insufficient mechanistic interpretations of the complex effects of environmental factors (harshness of testing, penetration of radiation and oxygen, superposition of temperature, atmospheric impurities) and those of the microenvironment (morphology of the polymer matrix, physical relations of HAS,polymer, interference between HAS and other additives) are a drawback. Model experiments complement commercial studies and explain some phenomena. A careful transfer of information from model experiments must be done to avoid misinterpretation of mechanisms, particularly of the HAS regenerative cycle. A critical analysis of primary steps of the HAS activity mechanism in the polymer matrix based on HAS-related primary nitroxides, formation of their stationary concentration and concentration gradients influenced by polymer morphology, spatial competition between autoreactions, and oxidation of polymer-developed alkyl radicals and their scavenging by nitroxides (the key process of HAS efficiency) is outlined. Cyclic regeneration of nitroxides affected by the structure of the amino moiety in the HAS molecule, influence of acid environment, atmospheric ozone or singlet oxygen, cooperative mixtures of HAS with UV absorbers, combinations with additives increasing the thermal stabilization effect and improving color retention, assessment of the heat stabilization performance of HAS by proper testing, and influence of the molecular weight of HAS are mentioned together with examples of the chemical consumption of HAS in the final phases of their lifetime. lifetime. J. VINYL ADDIT. TECHNOL., 13:119,132, 2007. © 2007 Society of Plastics Engineers [source] Photostability of UV Absorber Systems in Sunscreens,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Bernd Herzog Sunscreens are used to protect the human skin against harmful UV radiation. Today there is a trend toward higher sun protection factors (SPF) and better UVA protection. Methods for the assessment of SPF and UVA protection involve irradiation of the product, and the photostability properties of the sunscreen have an influence on its performance. Sunscreens often contain more than one UV filter. Thus it is important to understand the photostability properties of the complete system. The filter combinations used may exhibit destabilizing, stabilizing or inert interactions. For that reason, besides assessment of the properties of the single filters, photostabilities of binary filter combinations are investigated. Destabilization occurs when two UV absorbers undergo a chemical reaction after absorption of UV radiation. Stabilization may be achieved when the optical density of the system is very high, giving rise to a self-protection effect of the sunscreen film. Photounstable UV absorbers may be additionally stabilized by employing triplet quenchers. Being aware of these mechanisms and applying them for specific UV filter combinations can help in designing efficient sunscreens. [source] | |||||||||||||