Effect of dicumyl peroxide on photo-oxidation of polystyrene films:1

The effect of dicumyl peroxide on polystyrene film photo-oxidation was studied. Comparison of the rate and quantum yield of long-chain PS photo-oxidation product formation was made between pure PS films and PS films containing dicumyl peroxide.     

Photo-oxidation of polystyrene film: 2. Photo-oxidation of polystyrene film with light absorbed by the polystyrene-oxygen complex

Photo-oxidation of polystyrene films prepared from carefully purified polymer, irradiated with light absorbed only by a polystyrene-oxygen complex has been studied. It was found that photo-oxidation of polystyrene under such conditions results in carbonyl compound and hydroperoxide formation. Photo-oxidation of polystyrene with light of a frequency abosrbed by the polystyrene-oxygen complex occurs throughout the whole volume of sample.     

XPS studies of poly(acrylic acid) grafted onto UV photo-oxidized polystyrene surfaces

UV photo-oxidation of polystyrene was achieved with 253.7 and 253.7/184.9?nm radiation in the presence of an atmospheric pressure of oxygen and analyzed by X-ray photoelectron spectroscopy as a function of treatment time. A methodical increase in the atomic percentage (at.%) of oxygen occurred during 253.7?nm activation up to 2?h of treatment time. Photo-oxidation with the 253.7/184.9?nm lamps resulted in a saturation level of ca. 35 at.% O. Initially, C–O and C=O groups were formed and then O–C=O type moieties. Poly(acrylic acid) was partially and/or thinly grafted onto the oxidized polystyrene surfaces.     

聚苯乙烯无氧化过程研究

本文通过对聚苯乙烯模型化合物２－苯基丁烷（简称２—ＰＢ）的光氧化过程和产物与聚苯乙烯的光氧化产物进行比较，利用质谱和红外光谱的数据证明了聚苯乙烯的光氧化主链断裂有两种形式：其一是主链断裂氧化成苯酚和联苯二酚类似的低分子化合物，其二是主链断裂后氧化成为脂肪酮类和带有苯基类的低分子化合物。     

Photo-Initiated Lamination of Polyethylene (PE) and Poly(ethylene terephthalate) (PET)

Besides plasma-based processes, photo-initiated surface modifications have an interesting potential for adhesion promotion. This is of special interest with applications ranging from classical finishing to composites. Photo-chemical processes using continuous UV sources — monochromatic as well as broad band — are based on radical activation and ensuing reaction with the atmosphere. Achievable effects are addition of atoms — e.g., introduction of oxygen (photo-oxidation) resulting in increased surface energy — or grafting of functional groups. Both have certain potentials for adhesion promotion in a physico-chemical way. Based on the fundamental scheme of these processes — i.e., a photon-initiated radical reaction at the substrate-atmosphere interface — a direct 'inter-linking' of coating polymer and substrate is presented in this paper. The principal idea is to apply a thin layer of coating polymer on the substrate and irradiate this composite system at certain UV wavelengths. Given a low absorption of the radiation by the thin coating and — at the same time — a high absorption by the substrate, the radiation will penetrate the coating layer and generate radicals at the interface, which will induce cross-linking between the coating polymer and substrate. It is shown that for the example of laminates of polyethylene (PE) film on fabrics made of poly(ethylene terephthalate) (PET), extremely high adhesion strenghths are achieved without any use of additional adhesion promoters.     

Mechanisms of antioxidant action: effect of processing conditions on the stabilizing effectiveness of metal xanthates and related dixanthogen in polypropylene

The effects of processing conditions, on the thermal and photo-oxidation of polypropylene containing different metal octyl xanthates (MOX) and the related dixanthogen (OX) have been examined. It is concluded that in the presence of a limited amount of oxygen the metal xanthates (e.g. nickel and cobalt) are better u.v. stabilizers than the dixanthogen, and their greater effectiveness is atrributed to a combination of complementary mechanisms, i.e., peroxide decomposition, u.v. absorption, u.v. screening and radical scavenging. Under severe processing conditions (excess oxygen), the activity of the metal xanthates is reduced and their effectiveness becomes very similar to that of the corresponding dixanthogen in both melt and u.v. stabilization. The main mechanism of action in this case is peroxide decomposition.     

聚苯乙烯光氧老化行为及其模型研究

研究了自然曝晒试验后的聚苯乙烯(PS)样品结构和性能的变化,同时对其拉伸强度保持率的变化进行回归拟合,并建立了光氧老化模型。结果表明:太阳辐照是影响PS光氧老化的主要因素,水分对其起促进作用;PS老化过程中有羰基基团生成;老化模型可以反映光、热、水综合作用的强弱。     

Photocatalytic oxidation of toluene over TiO2 catalysts supported on glass fiber

Titania-impregnated photocatalysts supported on glass fiber (GF) were prepared and employed in the photocatalytic oxidation of toluene. Amorphous titania sol (ATS) prepared from titanium isopropoxide was useful to impregnate titania on glass fiber in the shape of a thin film. TiO₂/GF catalysts prepared by using the ATS showed better stability against water and vibration, but lower catalytic activity in the photo-oxidation of toluene compared to crystalline anatase powder (CAP) impregnated catalyst. Photocatalytic activity of the ATS catalyst was considerably enhanced by the addition of hydrogen peroxide, resulting in high activity comparable to that of the CAP catalyst.     

Adhesion of copper to poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces modified by vacuum UV photo-oxidation downstream from Ar microwave plasma

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces were exposed to vacuum UV (VUV) photo-oxidation downstream from Ar microwave plasma. The modified surfaces showed the following: (1) an improvement in wettability as observed by water contact angle measurements; (2) surface roughening; (3) defluorination of the surface; and (4) incorporation of oxygen as CF—O—CF₂, CF₂—O—CF₂ and CF—O—CF₃ moieties. With long treatment times, a cohesive failure of copper sputter-coated onto the modified surface occurred within the modified FEP and not at the Cu–FEP interface.     

The Dynamic Roles of Interstitial and Surface Defects on Oxidation and Reduction Reactions on Titania

Defect sites in titania have a substantial effect on many thermal and photochemical reactions. Three common types of defects are titanium interstitials, oxygen vacancies and oxygen adatoms—all of which can react with organic molecules adsorbed on the surface. We look broadly at thermal reduction and photochemical oxidation reactions of oxygenates. In particular, we focus on the reductive coupling of benzaldehyde, the photo-oxidation of butyrophenone, the photostability of benzoic acid, and the photo-oxidative coupling of methanol to methyl formate. Methods used include temperature programmed reaction spectroscopy, scanning tunneling microscopy, and density functional theory.     

Photo-oxidation mechanisms of poly(2,6-dimethyl-1,4-phenylene oxide).

A re-examination of the photo-oxidation mechanism of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at both long and short irradiation wavelengths under accelerated conditions is reported. The formation rate of poly-2,6-dimethylphenoxy (PDMP) radicals, have been observed by esr spectroscopy, while benzylic-type radicals have been detected by spin trapping experiments using nitrosodurene under UV irradiation conditions. The changes of FTIR spectra obtained under accelerated photo-oxidative conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical cations and superoxide anions by a photo-induced electron-transfer reaction is suggested under our conditions. In addition, some results on the of photo-oxidation PPO/PS blends as a function of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend containing atactic polystyrene. This effect has been ascribed to the absence of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO with bromine gave a bromomethylated PPO with different amounts of CH₂ Br groups, which has been used for further substitution reactions with alkoxy sodium salts of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMPP). The accelerated photo-oxidation of a modified copolymer PPO-PMPP containing a 60% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a commercially available hindered amine light stabilizers (HALS) and a modified copolymer PPO-PMPP are also reported under the same photo-oxidative conditions.     

The final bleaching of eucalypt kraft pulps with hydrogen peroxide: relationship with industrial ECF bleaching history and cellulose degradation

BACKGROUND: The process of chemical pulp bleaching is based for the most part in chlorine dioxide within elemental chlorine free (ECF) technologies. The use of greener alternatives such as bleaching with hydrogen peroxide (P stage) is not widely used owing to selectivity concerns related to transition metal‐catalyzed decomposition reactions. Even at the final stage where peroxide is recognized to boost brightness and improve the brightness stability of the bleached pulp, cellulose degradation often overcomes these advantages. This paper presents the results of studies intended to optimize final peroxide bleaching performance considering two standard ECF industrial bleaching sequences: the conventional DED and the ECF‐light OQ(PO)D (stages name: D—chlorine dioxide; E—alkaline extraction; O—oxygen; Q—chelation, (PO)—hydrogen peroxide pressurized with oxygen). RESULTS: The addition of sodium diethylenetriaminepentaacetate (DTPA) was the most effective option in terms of DED pulp bleachability and selectivity with hydrogen peroxide, as well as in terms of brightness reversion. As regards the OQ(PO)D pulp, a blend of DTPA and magnesium was the most beneficial in those properties. CONCLUSIONS: The choice of the best hydrogen peroxide stabilizer, among the different tested combinations of magnesium and chelants (EDTA and DTPA) studied, in terms of pulp bleachability, bleaching selectivity and brightness reversion is dependent on the impact of the previous bleaching stages on metallic nature and content. The pulp Mg/(Fe + Cu) ratio was highlighted as a process parameter controlling cellulose degradation in peroxide bleaching. Copyright © 2010 Society of Chemical Industry     

神府镜煤光氧化产物的组成和结构研究

在紫外光照射下,用氧气对神府镜煤进行了光催化氧化研究。探讨了氧化时间对氧化煤中腐植酸含量的影响。通过溶剂抽提,FTIR分析及GC/MS分析对神府镜煤光氧化产物进行了组成和结构分析。研究表明:控制光氧化时间,可以获得不同腐植酸含量的光氧化产物,在光氧化4 h时,镜煤中腐植酸含量最高;镜煤在光氧化产物过程中,芳香结构较难打开,主要是醚键等含氧官能团发生反应,生成羧基和甲基等。     

Preparation of surface initiated polystyrenesulfonate films and PEDOT doped by the films

Various substrates such as glass slides and silicon wafers were modified by styrylethyltrimethoxysilane to attach double bonds to those surfaces. The double bond layer was initiated and capped by benzoyl peroxide (BPO) and 2,2,6,6-tetramethylpiperidirooxy (TEMPO), respectively, to form ‘living’ free radical layer from which polystyrene brushes were grown. The density of double bonds on the surface controlled the orientation of polystyrene brush or film. The polystyrene films were then sulfonated by fuming sulfuric acid (H₂SO₄·xSO₃) to obtain polystyrenesulfonic acid (PSS) films with controlled polymer chain alignment. The lower double bond density led to a lower degree of polymer chain alignment. 3,4-Ethylenedioxythiophene monomer was diffused into PSS film and then polymerized. A conductive polyethylenedioxythiophene (PEDOT)/PSS film was obtained. The films were characterized by four-point probe, AFM and UV-VIS. The conductivity of PSS/PEDOT film measured along the direction which is normal to polymer chain alignment, is lower than that from commercial PSS/PEDOT.     

Inorganic Protection of Polymer Nanocapsules: A Strategy to Improve the Efficiency of Encapsulated Optically Active Molecules

We demonstrate that the efficiency under ambient conditions of optically active molecules encapsulated in polymer nanocapsules can be significantly improved by depositing an inorganic layer onto the polymeric shell. A triplet-triplet annihilation upconversion (TTA-UC) system consisting of a porphyrin derivative and perylene is used as a representative case. Different inorganic materials are deposited on the surface of functionalized polymer nanocapsules synthesized by free-radical polymerization in miniemulsion. First, a silicate clay with formula [Si₈(Mg_5.45Li_0.4)O₂₀(OH)₄]Na_0.7 is deposited on the surface of positively charged polystyrene nanocapsules via layer-by-layer deposition. Second, controlled in situ mineralization of hydroxyapatite and cerium(IV) oxide are carried out on the surface of negatively charged polystyrene nanocapsules. In both cases the inorganic materials on the nanocapsule surface act as a scavenger and avoid the entry of oxygen from the external environment. By avoiding the entry of oxygen, the photo-oxidation process of perylene molecules is avoided within the system, and an increase in the TTA-UC properties occurs.     

Surface modification of Teflon® PFA with vacuum UV photo-oxidation

Surface modification of poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) with vacuum UV (VUV) photo-oxidation using radiation from excited Ar atoms downstream from an Ar microwave (MW) plasma shows: (1) an improvement in wettability as observed by water contactangle measurements; (2) surface roughening; (3) incorporation of oxygen as C=O, CF—O—CF₂ and CF₂—O—CF₂ moieties and (4) enhancement of the CF—O—C _n F_2n+1 concentration. Adhesion measurements of Cu sputter coated onto the photo-oxidized PFA surface results in failure within the PFA (cohesive failure) and not at the Cu–PFA interface.     

Effect of Thermal Aging on the Optical Properties of ABS Plastics

Poly(acrylonitrile/butadiene/styrene, ABS) is a two-phase material consisting of elastomer particles in a glassy polymer matrix of styrene and acrylonitrile (SAN) [1]. The photo-oxidation of ABS has been the subject of several studies [2, 3]. It was suggested that several processes will take place during photo-oxidation. These changes include the formation of hydroperoxide [4], chain breakage of the polystyrene, and the oxidation of the polymer as it was monitored by IR spectroscopy [4–6]. Also, photooxidation affects the polybutadiene in ABS and oxidizes it, which results in the formation of hydroperoxide. No data are available on the thermal degradation of ABS. In a previous study the thermal aging of recycled high-impact polystyrene was studied using UV-Vis spectroscopy [7]. It was found that this method provides very useful information about the degradation of several industrial polymers [8–12]. In the work reported in this paper, thermal degradation of ABS was followed by UV-Vis and IR spectroscopy.     

Plasma oxidation of polystyrene vs. polyethylene

Polyethylene and polystyrene film surfaces have been plasma-oxidized and subsequently characterized by X-ray core level and valence band spectroscopies. The extent of polyethylene surface oxidation was found to be dependent on the power of the oxygen glow discharge employed and the length of time that the treated sample was left exposed to air prior to analysis. In marked contrast to these observations, plasma-oxidized polystyrene surfaces were much less dependent on the oxygen glow discharge power and were also found to retain their oxygenated character over much longer periods of ageing. These differences in oxidative behaviour are explained in terms of the molecular structures of the respective polymers.     

Photo-oxidation of polystyrene film: 1. Photo-oxidation of polystyrene films with light absorbed by polymer

The photo-oxidation of polystyrene films irradiated with light absorbed by the polymer has been studied. The overall quantum yield of hydroperoxide as well as the relationship between the concentration of acetophenone-type carbonyl products and α,β-enone and diketone products were found. The spatial distribution of the different types of carbonyl products was investigated.     

Surface functionalization of multiwalled carbon nanotubes with UV and vacuum UV photo-oxidation

Multiwalled carbon nanotubes (MWNTs) were surface photo-oxidized at room temperature with UV (253.7 and 184.9 nm) and vacuum UV (VUV) (106.7 and 104.8 nm) radiation. X-ray photoelectron spectroscopy (XPS) showed rapid UV photo-oxidation during the first hour of treatment and then an increase that was directly proportional to the time of treatment up to 4 h where the oxygen concentration was 7.5 at%. VUV photo-oxidation resulted in an oxygen concentration up to 9.5 at% with exposure time for the initial 2 h of treatment. Beyond 2 h, the oxygen concentration decreased with exposure to VUV photo-oxidation. Curve fitting of the XPS C_1s spectra revealed mainly C–O–C, as ether or epoxy functional groups, with the presence of C=O, O–C=O and O=C–O–C=O or carbonate moieties. SEM micrographs showed no apparent effect on the structure or appearance of the MWNTs as expected from surface modification. Gas-phase UV and VUV photo-oxidation effectively functionalize MWNTs for potential adhesion improvement without resulting in liquid waste as from the traditional bulk processing method involving acidic oxidation.