Photo-oxidative Degradation Of Poly Research Articles

Computational and Experimental Study on the Mechanism of CO2 Production during Photo-Oxidative Degradation of Poly(butylene adipate-co-terephthalate): Differences between PBA and PBT Segments

Computational and Experimental Study on the Mechanism of CO₂ Production during Photo-Oxidative Degradation of Poly(butylene adipate-<i>co</i>-terephthalate): Differences between PBA and PBT Segments

Photo-oxidative degradation of poly(ethylene-co-vinyl acetate)/nisin antimicrobial films

The photo-oxidative behaviour of different antimicrobial blown films based on poly (ethylene-co-vinyl acetate) (EVA) was studied. In particular, two samples of EVA containing different level of vinyl acetate comonomer (namely 14% and 28%) were used as matrices while nisin at different concentrations was used as antimicrobial agent. The degradation was followed by analyzing the changes in the spectroscopic behaviour and of the elongation at break measured in tensile tests. Moreover, changes in the antimicrobial activity of the films were followed by measuring the inhibition halo in agar diffusion tests. The results indicate that nisin acts as an excellent UV stabilizer for both samples of EVA used and especially for the sample with the higher vinyl acetate content. The protective effect of nisin is accompanied by a progressive decrease of the antimicrobial properties as a function of the photo-oxidation time due to the photo-degradation of the additive, which causes the inactivation of the additive.

Influence of the microstructure on the photooxidative degradation of poly(3-hexylthiophene)

The influence of the microstructure of poly(3-hexylthiophene) (P3HT) on its photodegradation upon exposure to UV–visible light was studied. High-regioregular (>98%) and low-regioregular (<95%) P3HTs with different molecular weights, dispersities and purities were submitted to irradiation under accelerated artificial ageing conditions. While the molecular weight had no effect on the photodegradation rate, a linear relationship was observed between the photodegradation rate and the regioregularity. The higher photo-instability of low-regioregular P3HTs, which have low crystalline phase content, could be due to the fact that the radical chain oxidation occurs predominantly in the amorphous phase of the polymer. Low-regioregular P3HTs also have a higher number of impurities, especially Fe residues, which are well known for their photocatalytic effect. The results also show that, at low concentrations, oxidation products are able to quench the singlet state of P3HT by acting as electron traps, and that the shortest wavelengths of solar light are the most harmful. Finally, the photooxidation of P3HT leads to the formation of low-molecular-weight carboxylic acids that can easily diffuse and migrate out of low-regioregular P3HT thin films. These results are therefore relevant to the preparation, storage and lifetimes of P3HT-based organic solar cells.

Oxidative and photooxidative degradation of poly(acrylic acid)

The oxidative degradation of poly(acrylic acid) (PAA), a water soluble polymer, was studied at various temperatures with different concentrations of persulfates, potassium persulfate (KPS), ammonium persulfate (APS) and sodium persulfate (SPS). The photodegradation of PAA was also examined with APS as oxidizer. The degraded samples were analyzed for the time evolution of molecular weight distribution by gel permeation chromatography. A theoretical model based on the continuous distribution kinetics was developed that accounted for the polymer degradation and the dissociation of persulfate. The rate coefficients for the oxidative and photooxidative degradation of PAA were determined from the parametric fit of the model with experimental data. The rate of degradation increased with increasing amount of persulfate in both oxidative and photooxidative degradation. The rate of degradation also increased with increasing temperature in the case of oxidative degradation.

Photo-oxidative degradation mechanisms in styrene–ethylene–butadiene–styrene (SEBS) triblock copolymer

The photo-oxidative degradation of poly[styrene- b-ethylene- co-butylene- b-styrene], SEBS, has been studied at wavelengths cut-off below 290 nm, and monochromatic light of 254 nm and 365 nm, using a variety of spectroscopic methods including FTIR, UV and luminescence spectroscopy coupled with crosslinking and hydroperoxide analyses in order to understand the mechanisms involved. A study on polystyrene photodegradation is also compared at varying wavelengths in order to provide an understanding of the light sensitivity of the styrene vs the aliphatic phases in the SEBS. The increase in colour shows evidence for the presence of visible light absorbing chromophores. Hydroperoxide analysis reflects a rapid increase in the hydroperoxide concentration in the olefinic phase. Fluorescence spectroscopy shows a rapid disruption of the polystyrene excimers coupled with the formation of long-wavelength emitting polyconjugated stilbene-type chromophores. Phosphorescence analysis indicates the presence of acetophenone groups while GPC and sol/gel analysis showed that degradation occurs mainly due to chain scission. Changes in the FTIR spectra of the photo-oxidised samples show a predominant absorption associated with carboxylic acids and/or aliphatic esters at 1712 cm −1. Other species such as hydroperoxides, ketones and α,β-unsaturated carbonyls are also formed and mechanisms are proposed.

MALDI Investigation of Photooxidation in Aliphatic Polyesters: Poly(butylene succinate)

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS) has been found to be an excellent method to determine the structure of the molecules produced in the photooxidative degradation of poly(butylene succinate) (PBSu) at 60 °C in air. Over 20 compounds are present in the MALDI spectrum of the oxidized sample, as compared to only 4 in the original PBSu sample. The MALDI spectra present many new well-resolved peaks, which provide information on the structure and end groups of the oxidation products. The MALDI peaks correspond to sodiated ions of oxidized oligomers, and they have been assigned to polymer chains containing succinic and malonic acid, butyl ester, ethyl ester, and butyl formate end groups. These oligomers had not been revealed before. The mechanisms accounting for the formation of photooxidation products of PBSu involve the operation of several reactions: (i) oxidation of hydroxyl end groups; (ii) α-H abstraction decomposition; (iii) Norrish I photocleavage. Our results establish the photooxidation mechanisms of PBSu. The novelty of our approach consists of using a nonaveraging technique, such as mass spectrometry, which allows the detection of individual compounds formed during the oxidation process. This is a remarkable result, and it should be expected that future MALDI studies might have an impact on the current views on photooxidation processes of other polymer systems.

Application of spectroscopic ellipsometry to probe the environmental and photo-oxidative degradation of poly( p-phenylenevinylene) (PPV)

We report on the spectroscopic ellipsometry (SE) characterization and modeling of the light and environmental induced degradation of Poly( p-phenylenevinylene) (PPV) prepared by xanthate precursor route. We find a decrease in the refractive index as well as absorption coefficients after exposure to light in air ambient. Further, a decrease in film density and increase in film thickness is also observed on light exposure in air. On the other hand, optical constants are not affected by light exposure in vacuum.

Photo-oxidative degradation of poly(epichlorohydrin- co-ethylene oxide) elastomer at 254 nm

The photo-degradation of unstabilised poly(epichlorohydrin- co-ethylene oxide) was evaluated under accelerated ageing conditions by infrared spectrophotometry (FTIR), gel permeation chromatography (GPC) and scanning electron microscopy (SEM). The elastomer photo-degradation leads to the formation and increase of carbonyl containing products, hydroxyl and hydroperoxide groups. FTIR spectra after elastomer photo-degradation and derivatization in an inert atmosphere, indicate that hydroperoxides are the first products of the photo-oxidation and their photolysis produces carbonyl-containing products. These are subsequently photolyzed to produce carboxylic acids, alcohols, esters and others minor products. The study of the average molar mass by GPC shows that it decreases exponentially during the first 2 h of irradiation, with evidence for random chain scission. The SEM study shows that photo-degradation leads to the formation of micro-cracks on the polymer surface.

The influence of transition metal salts on photo-oxidative degradation of poly(ethylene oxide)

The influence of iron (III), cobalt (II) or nickel (II) chlorides on photo-oxidative degradation of poly(ethylene oxide) (PEO) has been investigated. The rates and efficiencies of photochemical reactions occurring in PEO containing small amounts (1–3%) of the transition metal chlorides were compared. The mechanism of reaction induced by UV-irradiation in doped PEO is discussed. The role of active Cl atoms and chlorine radical anion Cl 2 − (formed in the first step of metal salt photolysis) in initiation of polymer degradation is pointed out. The iron salt was found to be the most effective agent accelerating PEO photodegradation.

Photooxidative degradation of poly(alkyl methacrylate)s

Photooxidative degradation of four different poly(alkyl methacrylate)s: poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate), poly( n-butyl methacrylate) and poly( n-hexyl methacrylate) have been investigated using FTIR, UV–Vis spectroscopy and gel permeation chromatography. The influence of the ester group size on the course of photochemical reactions in poly(alkyl methacrylayte)s has been estimated. It has been found that PMMA undergoes slower photooxidation but faster photodegradation than those in higher poly(alkyl methacrylate)s. The different behavior of the polymers studied is caused by the different reactivity of the macroradicals influenced by the different flexibility and mobility of macrochains at room temperature.

Changes of poly(ethylene oxide) photostability by doping with nickel(II) chloride

The influence of small addition of nickel(II) chloride on photooxidative degradation of poly(ethylene oxide) (PEO) in solution and in solid state has been investigated. Gel permeation chromatography, viscometry, differential scanning calorimetry, infrared and UV–Vis absorption spectroscopy has been used in these studies. It was found that nickel salt accelerates photodegradation and photooxidation of PEO. Photoinduced changes of PEO crystallinity and influence of macrochains conformation on the efficiency of photodecomposition has also been discussed.

Cobalt(II) chloride catalysed oxidative degradation of poly(ethylene oxide) by a short wavelength UV-radiation

Photo-oxidative degradation of poly(ethylene oxide) with small amount (1 and 3wt.%) of cobalt (II) chloride was studied in acetonitrile solutions and in solid state. On the basis of FTIR, UV-Vis spectroscopy, GPC and viscometry measurements it was found that cobalt salt accelerates photodecomposition of PEO. DSC was applied for study of crystallinity changes in PEO and PEO+CoCl2 during UV-irradiation. The structure of PEO+CoCl2, mechanism of photoreactions and the influence of physical factors are discussed.

The photooxidative degradation of poly(vinylchloride)—2. The stabilising action of dibutyltin maleate and trisnitro (1,3-dihydroxyl-2-hydroxymethyl-2-nitropropane) on PVC from ultraviolet light radiation

The photooxidative degradation and stabilisation of poly(vinylchloride) (PVC) have been studied using dibutyltin maleate (DBTM) alone and mixed with varying amounts of trisnitro (1,3-dihydroxyl-2-hydroxylmethyl-2-nitropropane) compounds as stabilisers. Films of the unstabilised and stabilised PVC were exposed to ultraviolet (UV) light ageing at room temperature. The degradation reactions were monitored by IR, colour formation, tensile strength and elongation at break, as well as determination of time to embrittlement. The stabilising action of 7.2 × 10 −3 mol% DBTM mixed with 10 × 10 −4 mol% of the lauryl ester of the trisnitro compounds proved most effective in limiting photooxidative reactions in PVC.

Photo-oxidative degradation of poly(ethylene oxide)-copper chloride complexes

Poly(ethylene oxide) (PEO) forms with CuCl 2 a complex in acetonitrile (AN) solution as well as in solid phase (after evaporation of solvent). During u.v. or visible light irradiation it has been observed that a rapid photo-oxidative degradation of the PEO-CuCl 2 complex in AN is caused by free Cl ● and/or Cl ●− 2 radicals (formed from the photolysis of CuCl 2). With increasing degradation processes, there is also a pronounced change in the morphology of PEO-CuCl 2 complexes. They lose their capability to form spherulites. This results from changes in molecular weight and dispersity that affect crystallization conditions. Both wide angle X-ray spectroscopy and differential scanning calorimetry show that photodegraded PEO molecules are almost amorphous. Low-molecular fractions are formed as a result of chain scission processes. Photodegradation processes in AN solution do not cause crosslinking or formation of a gel fraction.

Photo-oxidative degradation of poly(2,6-dimethyl-1,4-phenylene oxide) in the presence of concentrated hydroxy peroxide: the role of hydroxy (HO .) and hydroperoxy (HO 2.) radicals

The reaction of poly(2,6-dimethyl-1,4-phenylene oxide) with hydroxy (HO .) and hydroperoxy (HO 2 .) radicals generated by the UV photolysis of concentrated hydrogen peroxide (H 2O 2) (35wt%) has been studied. The HO ./HO 2 . radicals accelerate the photo-oxidative chain-scission of a polymer, in comparison with photo-oxidative degradation in air or in water. However, both HO . and HO 2 . radicals undergo additional reactions to the aromatic phenyl rings in a polymer. Spectroscopic analyses suggest the presence of phenols and hydroxy-mucondialdehydes among the photo-oxidation products, indicating that HO . and HO 2 . addition occurs at the phenyl groups of the polymer. Rearrangement of hydroxy-phenyl radicals can also produce quinoide structures. Coloration of the polymer can result from formation both of quinone and hydroxy-mucondialdehyde structures in photo-oxidized polymer. The significance of HO . radicals formed from the thermolysis and/or photolysis of hydroperoxides in the polymer is considered.

Effect of lubricants on the photo-oxidative degradation of solid poly(vinyl chloride)

Various commercially employed lubricants, such as low molecular weight polyethylene (Type PA-520 Wax), hydroxystearic acid (Loxiol G-21), butyl stearate (Loxiol G-32) and di-stearyl phthalate (Loxiol G-60), have been examined for their active rôle in the photo-oxidative degradation of poly(vinyl chloride) (PVC). The results show that low molecular weight polyethylene has an obvious accelerating effect on the photo-oxidative degradation of PVC, whereas other lubricants reduce the effect of photo-oxidation. None of the lubricants used has an obvious rôle in the chain scission and crosslinking of PVC.

Effect of zinc diisopropyl dithiophosphate on the photooxidative degradation of poly(2,6‐dimethyl‐1,4‐phenylene oxide) films

AbstractThe effect of zinc diisopropyl dithiophosphate (ZnDTP) chelate over the range of 0.1 to 1.0 wt.% on the photostabilized degradation of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) films was examined. The degradation of the polymer was remarkably affected by the concentration of the ZnDTP which acted as photostabilizer at all concentrations.

Photo-degradation and photo-stabilisation of the two-phase system poly(vinyl chloride)-polybutadiene

The photo-oxidative degradation of poly(vinyl chloride) (PVC)/polybutadiene (PB) blends has been studied. After uv irradiation, photo-grafting of the PVC and PB phases was observed. Photolysis of PVC accelerates cis-trans isomerisation of PB. Both phases, PVC and PB, are photo-degraded according to free radical oxidation mechanisms. The rates of these processes can be decreased by the addition of metal chelates, such as commercially produced Cyasorb uv light absorber 1084 (2,2′-thiobis(4- t-octylphenolato)- n-butylamine nickel(II)) and Cyasorb uv light absorber 2548 (cobalt dicyclohexyldithiophosphinate).

Inhibitive effects of transition metal thiopicoline anilides on the photo-oxidative degradation of poly(2,6-dimethyl-1, 4-phenylene oxide) films

The changes of physical, chemical and mechanical properties of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) films under u.v. light were investigated. The inhibitive effects of transition metal (Zn, Cr) thiopicoline anilides on the photo-oxidative degradation, both in the presence and absence of copper stearate as oxidation accelerator, were examined. In both cases Zn(II) and Cr(III) thiopicoline anilides showed a pronounced inhibitive effect on the degradation of the polymer, especially the Zn compound. The inhibitive action of these additives is discussed from the viewpoint of molecular weight, elongation, gel, carbonyl and hydroperoxide content of the polymer.

Thermal, thermooxidative and photooxidative degradation of poly(2,6‐dimethyl‐1,4‐phenylene oxide). Review

AbstractThermal, thermooxidative and photooxidative degradations of polyphenylene oxide are reviewed. Emphasis is given to analytical data of volatile products formed during the thermal degradation. Changes of the solid substrate, such as the methyl group oxidation, crosslinking and chain scission, are of particular importance during the thermooxidative and photooxidative degradation.