Photostabilization Of Polymers Research Articles

Surface modification to enhance photo-stability of polymers

Surface modification to enhance photo-stability of polymers

Surface modification to enhance photo-stability of polymers

Photo-degradation is an irreversible alteration in the chemical, mechanical and physical properties of polymers, these alterations are a result of photon absorption from sunlight. UV-light is considered to be the main factor for initiating photo-degradation process of polymers. To extend the lifetime of polymers, their durability, overall minimization of the rate of photo degradation and protection of polymers against environmental factors, stabilizers are introduced to polymers. In addition, since the interaction of the polymer with its environment occurs mainly at the surface of the polymer, therefore surface modification of polymers is used to enhance the UV photo-stabilization. This method can also provide a more durable, weather resistant and photo-stable polymers.

A Review on Graphene’s Light Stabilizing Effects for Reduced Photodegradation of Polymers

Graphene, the newest member of the carbon’s family, has proven its efficiency in improving polymers’ resistance against photodegradation, even at low loadings equal to 1 wt% or lower. This protective role involves a multitude of complementary mechanisms associated with graphene’s unique geometry and chemistry. In this review, these mechanisms, taking place during both the initiation and propagation steps of photodegradation, are discussed concerning graphene and graphene derivatives, i.e., graphene oxide (GO) and reduced graphene oxide (rGO). In particular, graphene displays important UV absorption, free radical scavenging, and quenching capabilities thanks to the abundant π-bonds and sp2 carbon sites in its hexagonal lattice structure. The free radical scavenging effect is also partially linked with functional hydroxyl groups on the surface. However, the sp2 sites remain the predominant player, which makes graphene’s antioxidant effect potentially stronger than rGO and GO. Besides, UV screening and oxygen barriers are active protective mechanisms attributed to graphene’s high surface area and 2D geometry. Moreover, the way that graphene, as a nucleating agent, can improve the photostability of polymers, have been explored as well. These include the potential effect of graphene on increasing polymer’s glass transition temperature and crystallinity.

QSPR studije karbonilnih, hidroksilnih, polienskih indeksa i prosječne molekulske težine polimera pod fotostabilizacijom pristupom ANN i MLR

One of the main disadvantages of the use of synthetic or semi-synthetic polymeric materials is their degradation and aging. The purpose of this study was to use artificial neural networks (ANN) and multiple linear regressions (MLR) to predict the carbonyl, hydroxyl, and polyene indices (ICO, IOH, and IOP), and viscosity average molecular weight (MV) of poly(vinyl chloride), polystyrene, and poly(methyl methacrylate). These physicochemical properties are considered fundamental during the study of photostabilization of polymers. From the five repeating units of monomers, the structure of the polymer studied is shown. Quantitative structure-property relationship (QSPR) models obtained by using relevant descriptors showed good predictability. Internal validation {R2, RMSE, and Q2LOO}, external validation {R2, RMSE, Q2pred, rm2, Δrm2, k, and k’}, and applicability domain were used to validate these models. The comparison of the results shows that the ANN models are more efficient than those of the MLR models. Accordingly, the QSPR model developed in this study provides excellent predictions, and can be used to predict ICO, IOH, IOP, and MV of polymers, particularly for those that have not been tested.

Effects of the Reduction and/or Fluorination of the TT‐Units in BDT‐TT Polymers on the Photostability of Polymer:Fullerene Solar Cells

Polymer solar cells have a promising future for applications in our day to day usage of energy in small appliances and portable devices. However, their performance in terms of efficiency is limited by a number of factors, among which is their low open circuit voltage (Voc). It is, therefore, understandable that much effort is channeled by the scientific community in improving the Voc. One way to achieve this goal is the development of novel materials, for example, polymers, through chemical structure modification. Typical examples are addition (chlorination, fluorination, or sulfonylation) and/or reduction (from alkyl‐ester to ketone substituents) mechanisms. This paper reports on the study of the effect of these structural changes for Voc enhancement on the performance of the polymers in polymer:fullerene solar cells. In particular, it looks at seven polymers of the polybenzodithiophene‐thienothiophene family, identifying the structural changes in the thienothiophene units or their moieties as a function of Voc behavior in relation to their UV‐stability. The findings reveal that the fluorination of the TT‐units or having alkyl‐ester groups as substituents on the TT‐units is bad for photostability. However, when these alkyl‐ester groups are reduced into ketone substituents, the photostability behavior improves.

Side chain structure and dispersity impact the photostability of low band gap polymers

A series of eight low band gap polymers based on benzodithiophene - diketopyrrolopyrrole (BDT-DPP) skeleton were designed with side chain variation on the benzodithiophene unit. The effect of different side chains, including -H, alkyl, alkoxy, and aryl moieties, over polymer stability is examined. Thin films were processed and submitted to photooxidative degradation. We experimentally confirm that alkoxy side chains are the most promising candidates for designing soluble and photo-resistant polymers. This conclusion is modulated by the polymer dispersity which also plays an important role: a low dispersity value being synonymous of higher photostability. The reasons why the side chain structure and dispersity value drive the polymer photostability are discussed. For the design of photo-resistant polymers and devices, side chain selection must go hand in hand with the control of the synthesis meaning a low dispersity.

Effects of Backbone Planarity and Tightly Packed Alkyl Chains in the Donor–Acceptor Polymers for High Photostability

The photostability of donor–acceptor (D–A) polymers remains a critical issue despite recent improvements in the power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. We report the synthesis of three highly photostable polymers (PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF2) and their suitability for use in high-performance OPV cells. Under 1 sunlight of illumination in air for 10 h, these polymer films demonstrated remarkably high photostability compared to that of PTB7, a representative polymer in the OPV field. While the PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF2 polymer films maintained 97, 90, and 96% photostability, respectively, a PTB7 film exhibited only 38% photostability under the same conditions. We ascribed the high photostability of the polymers to both the intrinsically photostable chemical moieties and the dense packing of alkyl side chains and planar backbone polymer chains, which prevents oxygen diffusion into the PDTBDT-BZ films. This work demonstrates the high photostability of planar PDTBDT-BZ series polymers composed of photostable DTBDT and BZ moieties and suggests a design rule to synthesize highly photostable photovoltaic materials.

Nanostructured oxyhydroxide niobium (NbO2OH) as UV radiation protector for polypropylene

In this study a novel approach for improving the photo-stabilization of polymers by incorporation of nanoparticles of a new niobium compound is reported.

Poly(vinyl chloride) derivatives as stabilizers against photodegradation

The photo-stabilization of polymers derived from poly(vinyl chloride) (PVC) films was investigated. The PVC and modified PVC films were produced by the casting method from tetrahydrofuran (THF) solvent. The photostabilization activities of these compounds were determined by monitoring the carbonyl, polyene and hydroxyl indices with irradiation time. The changes in viscosity average molecular weight of PVC with irradiation time were also tracked (using THF as a solvent). The quantum yield of the chain scission (Φcs) of these complexes in PVC films was evaluated and found to range between 4.79×10−8 and 7.50×10−8. Results obtained showed that the rate of photostabilization of PVC in the presence of the additive followed the trend:P1>P2>P3>P4>P5

Synthesis and properties of multifunctional hindered amine light stabilizers

Abstract A series of multifunctional hindered amine light stabilizers (HALSs) for monomers were designed and synthesized from cyanuric chloride, allylamine, 2,2,6,6-tetramethylpiperidine-4-ol or 1,2,2,6,6-pentamethylpiperidine-4-ol, and 2-(2-hydroxyphenyl)-1,2,3-benzotriazole derivatives through nucleophilic substitution. The new stabilizers were confirmed by 1H NMR, 13C NMR, FT-IR, ESI-HRMS and elemental analysis. The synthesized compounds 5a–f were evaluated for their antioxidant and anti-aging properties. The results indicate that the new HALSs can considerably improve polymer photostability.

Photodegradation and photostabilization of polymers, especially polystyrene: review.

Exposure to ultraviolet (UV) radiation may cause the significant degradation of many materials. UV radiation causes photooxidative degradation which results in breaking of the polymer chains, produces free radical and reduces the molecular weight, causing deterioration of mechanical properties and leading to useless materials, after an unpredictable time. Polystyrene (PS), one of the most important material in the modern plastic industry, has been used all over the world, due to its excellent physical properties and low-cost. When polystyrene is subjected to UV irradiation in the presence of air, it undergoes a rapid yellowing and a gradual embrittlement. The mechanism of PS photolysis in the solid state (film) depends on the mobility of free radicals in the polymer matrix and their bimolecular recombination. Free hydrogen radicals diffuse very easily through the polymer matrix and combine in pairs or abstract hydrogen atoms from polymer molecule. Phenyl radical has limited mobility. They may abstract hydrogen from the near surrounding or combine with a polymer radical or with hydrogen radicals. Almost all synthetic polymers require stabilization against adverse environmental effects. It is necessary to find a means to reduce or prevent damage induced by environmental components such as heat, light or oxygen. The photostabilization of polymers may be achieved in many ways. The following stabilizing systems have been developed, which depend on the action of stabilizer: (1) light screeners, (2) UV absorbers, (3) excited-state quenchers, (4) peroxide decomposers, and (5) free radical scavengers; of these, it is generally believed that excited-state quenchers, peroxide decomposers, and free radical scavengers are the most effective. Research into degradation and ageing of polymers is extremely intensive and new materials are being synthesized with a pre-programmed lifetime. New stabilizers are becoming commercially available although their modes of action are sometimes not thoroughly elucidated. They target the many possible ways of polymer degradation: thermolysis, thermooxidation, photolysis, photooxidation, radiolysis etc. With the goal to increase lifetime of a particular polymeric material, two aspects of degradation are of particular importance: Storage conditions, and Addition of appropriate stabilizers. A profound knowledge of degradation mechanisms is needed to achieve the goal.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-398) contains supplementary material, which is available to authorized users.

Study on Photoluminescence Quenching and Photostability Enhancement of MEH-PPV by Reduced Graphene Oxide

In conjugated polymer based photovoltaic devices, efficient charge transfer and photostability of the fluorescence polymer are two essential properties, which could be responsible for better performance and longer lifetime of the device. Hence, it is of great importance to explore strategies that can enhance the exciton separation and improve the photostability of polymers. In this work, composites of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) participated by appropriate amounts of reduced graphene oxide (r-GO), which leads to a significant photoluminescence quenching as well as superior photostability of MEH-PPV, have been investigated. The photoluminescence quenching and photostability of MEH-PPV/r-GO composites have been observed by UV–visible and fluorescence spectroscopy. From transient fluorescence spectrum, the mechanism of photoluminescence quenching has been confirmed to be static quenching, which is caused by electron transfer at the interface of the composite. Furthermore, we propose that this very efficient photoinduced excitation electron transfer from MEH-PPV to r-GO results in protecting MEH-PPV from further chemical degradation reaction. This work shows that graphene is promising as both an electron acceptor and light stabilizer for applications in optoelectronics devices.

Design and synthesis of highly photostable fluorescence sensing 1,8-naphthalimide-based dyes containing s-triazine UV absorber and HALS units

Two novel highly photostable yellow-green emitting 1,8-naphthalimide-based dyes, containing active fragments of both a hindered amine radical scavenger (HALS) and an s-triazine UV absorber were designed as multifunctional additives capable of simultaneously chemically fluorescent dyeing and photostabilization of polymers. They showed substantially higher photostability in respect to other similar fluorescent dyes, not containing either UV absorber or HALS component in their molecules. Novel compounds were also configured as “fluorophore-spacer-receptor” systems based on photoinduced electron transfer by incorporation a tertiary cation receptor at the C-4 position of the 1,8-naphthalimide fluorophore. The ability of the new compounds to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions and protons. The presence of metal ions and protons was found to disallow a photoinduced electron transfer leading to an enhancement in the dye fluorescence intensity. The results obtained indicate the potential of the novel compounds as highly photostable and efficient “off–on” pH switchers and fluorescent detectors for metal ions with pronounced selectivity towards Cu2+ ions.

Synthesis of highly photostable blue-emitting 1,8-naphthalimides and their acrylonitrile copolymers

Two novel highly photostable blue-emitting 1,8-naphthalimides, containing active fragments of a hindered amine radical scavenger and an s-triazine UV absorber were designed as multifunctional additives capable of simultaneous fluorescent brightening and photostabilization of polymers. Their light absorption and fluorescence properties have been determined and discussed. The ability of the combined fluorescent brighteners to copolymerize with acrylonitrile was demonstrated by obtaining acrylonitrile copolymers with an intense blue fluorescence. Photodegradation of the new fluorophores and their influence on the photostability of the fluorescent copolymers have been studied and compared to other similar 1,8-naphthalimides, not containing either UV absorber or hindered amine fragment in their molecules as well as not containing both of them. Novel fluorophores showed the best photostability in both solution and polymer. A significant photostabilizing effect towards photodegradation of polyacrylonitrile was found.

Photo-stability of yellow-green emitting 1,8-naphthalimides containing built-in s-triazine UV absorber and HALS fragments and their acrylonitrile copolymers

Two novel 1,8-naphthalimide dyes, containing active fragments of both 2-(2-hydroxyphenyl)-1,3,5-triazine UV absorber and 2,2,6,6-tetramethylpiperidine radical scavenger as well as a polymerisable allyl group, were designed as multifunctional yellow-green emitting fluorophores capable simultaneously of chemically fluorescent dyeing and photo-stabilisation of polymers. Their basic photo-physical characteristics have been determined and are discussed. It was shown that combination of different structural units in the 1,8-naphthalimide molecule does not result in their interaction through intramolecular fluorescence quenching due to an electronic energy transfer. The ability of the combined dyes to copolymerise with acrylonitrile was demonstrated as polyacrylonitriles stable to solvents and with an intense colour and fluorescence were obtained. Photo-degradation of the new fluorophores and their influence on the photo-stability of the coloured copolymers have been studied and compared to other similar fluorescent dyes, not containing either UV absorber or hindered amine fragment in their molecules as well as not containing both of them. Novel fluorophores showed the best photo-stability in both solution and polymer. A significant photo-stabilising effect towards photo-destruction of polyacrylonitrile was found, which might be caused by a possible “synergism” of two stabiliser fragments differing in their action.

Factors affecting accelerated testing of polymer photostability

The effect of components of the atmosphere on photostabilized polymers and development of degradation phenomena is outlined. The processes are characteristic of heterogeneity in distribution of products of polymer degradation and stabilizer transformation or consumption. Concentration gradients of the products indicate preferential surface and near-surface changes having U-shaped characteristics and affected by the polymer material or sample thickness due to limited penetration of oxygen. Increased intensity of radiation in artificial sources induces material changes different from those resulting from natural weathering, complicating correlation between the two processes and lifetime prediction. Surface and near-surface analyses of tested samples provide a realistic insight into heterogeneity characteristic of photodegradation.

Ciba Specialty Chemicals launches UV absorber for powder coatings

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.

Polymer Weathering: Photo-Oxidation

As the polymer industry evolved, considerable effort was made to understand the degradation processes of high polymers during weathering and ways were found to inhibit or at least retard their chemical modification and loss of their physical and mechanical properties. Weathering is particularly severe for polymers because it combines the photophysical and photochemical effects of ultraviolet radiation with oxidative and hydrolytic effects of the outdoor environment. This article discusses photo-oxidation degradation (the behavior of polymers as a result of outdoor factors) and mainly concentrates on the photo-oxidative degradation of polyolefins and poly(vinyl) chloride. Polymer photostabilization with ultraviolet screeners, quenchers, hydroperoxide decomposers, and radical scavengers is also described.

Photodegradation of polycarbonate under narrow band irradiation at 172 nm

Photostability of polymers is an important issue since most polymers tend to loose their original properties upon exposure to light, especially to ultraviolet radiation. Polycarbonates are widely used industrial materials because of their excellent properties, which includes transparency, high tensile strength, impact resistance and rigidity. In this paper, we present results on 172 nm photodegradation of polycarbonate (PC) films. PC films of 50 μm thickness were irradiated for up to 20 min using a Xe 2 ∗ excimer lamp system. Ex situ UV visible spectroscopic investigation of the treated films revealed the appearance of two strong absorption bands at 279 and 317 nm and a third broad band centred around 380 nm whose intensity increased linearly with illumination time. The morphological changes were characterised by atomic force microscopy and resulted in a gradually increasing roughness, being a linear function of irradiation time. The interpretation of the observed chemical degradation is based on attenuated total reflection IR and X-ray photoelectron spectroscopic measurements which show cleavage of the aromatic C–C and carboxylic CO–O bonds together with some nitrogen incorporation into the surface layer of the irradiated films.

Curing and Photostabilization of Thermoset and Photoset Acrylate Polymers

The light-stability of thermosetting acrylate and UV-cured acrylate polymers has been tested in an accelerated QUV weatherometer. Infrared spectroscopy was used to monitor in situ the chemical changes occurring upon both curing and photoageing of 35 μm thick clearcoats. The curing was shown to proceed more extensively in photoset than in thermoset acrylate polymers which contain 6 and 20% unreacted functional groups, respectively. During photoageing, the loss of the binder structural groups is accompanied by the production of oxidation products (carbonyl and hydroxyl groups). The UV-cured polyurethane-acrylate coating was shown to be more resistant to accelerated weathering than the melamine/acrylate thermoset currently used as automotive finishes. The addition of a hydroxyphenyltriazine UV-absorber and a hindered amine light stabilizer (HALS) radical scavenger was found to increase substantially the light stability of acrylate clearcoats.