The kinetics of phenol decomposition under UV irradiation with and without H2O2 on TiO2, Fe–TiO2 and Fe–C–TiO2 photocatalysts

H₂O₂ used in the photo-Fenton reaction with iron catalyst can accelerate the oxidation of Fe²⁺ to Fe³⁺ under UV irradiation and in the dark (in the so called dark Fenton process). It was proved that conversion of phenol under UV irradiation in the presence of H₂O₂ predominantly produces highly hydrophilic products and catechol, which can accelerate the rate of phenol decomposition. However, while H₂O₂ under UV irradiation could decompose phenol to highly hydrophilic products and dihydroxybenzenes in a very short time, complete mineralization proceeded rather slowly. When H₂O₂ is used for phenol decomposition in the presence of TiO₂ and Fe–TiO₂, decrease of OH radicals formed on the surface of TiO₂ and Fe–TiO₂ has been observed and photodecomposition of phenol is slowed down. In case of phenol decomposition under UV irradiation on Fe–C–TiO₂ photocatalyst in the presence of H₂O₂, marked acceleration of the decomposition rate is observed due to the photo-Fenton reactions: Fe²⁺ is likely oxidized to Fe³⁺, which is then efficiently recycled to Fe²⁺ by the intermediate products formed during phenol decomposition, such as hydroquinone (HQ) and catechol.     

Investigation of radiation grafting of vinyl acetate onto (tetrafluoroethylene–perfluorovinyl ether) copolymer films

A study has been made of radiation-induced grafting of vinyl acetate (VAc) on to (tetrafluoroethylene–perfluorovinyl ether) copolymer (PFA). Effects of grafting conditions such as inhibitor and monomer concentrations and irradiation dose on the grafting yield were investigated. In this grafting system, ammonium ferrous sulphate (Mohr′s salt) was added to the monomer-solvent mixture to minimize the homopolymerization of VAc and the most suitable concentration was found to be 2.0 wt%. It was found that the dependence of the initial grafting rate on monomer concentration is of the order 1.5. The degree of grafting tends to level off at high irradiation doses due to the recombination of formed free radicals without initiating graft polymerization. Some properties of the prepared graft copolymer such as swelling behaviour, electrical conductivity, thermal and mechanical properties were also investigated. The electrical conductivity was improved by hydrolysis of poly(vinyl acetate) in the grafted chains to their respective vinyl alcohols. The tensile properties were improved by grafting; however, the elongation percent decreased. The DTA data showed thermal stability of such graft copolymers for temperatures up to 300°C, but stability decreased at higher temperatures.     

An analysis of the changes in the structure and tensile properties of polytetrafluoroethylene films under vacuum ultraviolet irradiation

The effect of 5–200 nm of vacuum ultraviolet (VUV) irradiation on the structure and tensile properties of polytetrafluoroethylene (PTFE) films was investigated. The change in structure before and after VUV irradiation was evaluated with differential scanning calorimetry (DSC) and electron spin resonance (ESR) analysis. DSC analysis results showed that the melting point, melting enthalpy, and crystallization enthalpy increased and the maximum crystallization temperature decreased a little with increasing VUV dose. It was deduced from the DSC data that the molecular weight of the PTFE films decreased and the destruction of the crystal structure took place under VUV irradiation. The ESR results showed that the radicals formed under VUV irradiation were chain‐end radicals and peroxy radicals, which may have been formed due to the scission of carbon‐to‐carbon bonds. The tensile fracture strength and elongation decreased with increasing VUV irradiation dose. Under the same irradiation dose, the tensile properties were more sensitive to the lower VUV intensity. The decrease in the molecular weight and the destruction of crystal structure might have been the major reasons for the deterioration of the tensile properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1494–1497, 2004     

Analysis of ultrasonically induced free radicals in the emulsion polymerization system by GC–MS

A specially designed gas chromatography–mass spectrometry (GC–MS) analytical method has been developed and applied to identify the source of free radicals that served as initiators in a new ultrasonically induced emulsion polymerization system with monomer methyl mathacrylate (MMA), surfactant sodium dodecylsulfate (SDS) and water. The results showed the radicals came from the dissociation of SDS under ultrasonic irradiation. A quantitative determination procedure has been also developed and utilized to investigate the effects of the polymerization parameters, such as the surfactant concentration, the acoustic intensity of ultrasound, and the argon flow rate on the concentration of the generated free radicals in the emulsion system under ultrasonic irradiation. The results were helpful to understand the mechanism and kinetics of the system. © 1994 John Wiley & Sons, Inc.     

Effect of gamma‐irradiation on the electret properties of poly(L‐lactide)

Electret stability of poly(L ‐lactide) (PLA) films, gamma‐irradiated up to 100 kGy has been investigated by measuring the surface potential during the storage period. PLA samples—40‐μm thick films—were prepared by the casting method and then irradiated in a ⁶⁰Co radiation facility at a dose rate of 0.25 kGy/h. The structural changes during the irradiation were estimated by viscometric, differential scanning calorimetry and scanning electron microscope measurements. Random chain scission and appearance of end radicals are the most probable results of the irradiation process. After irradiation, the samples were charged in a corona discharge system and surface potential was measured by the method of the vibrating electrode with compensation. The values of the surface potential of the irradiated samples were higher in comparison with the non‐irradiated samples. This effect could be related to the degradation of the macromolecules and changes in the crystal state of PLA during the irradiation. Both of the mentioned factors lead to structural defects that increase the number of discrete trapping levels. The effect of low pressure on the surface potential drop was also investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electron beam and UV cationic polymerization of glycidyl ethers – PART I: Reaction of monofunctional phenyl glycidyl ether

Investigations of electron beam (e‐beam) and ultra violet (UV)‐induced cationic polymerization kinetics of a mono‐functional epoxy system, phenyl glycidyl ether (PGE), were conducted using real time in situ near infrared (NIR) spectroscopy. Effects of processing variables such as temperature and dose rate on initiation and propagation rate constants have been assessed. The experimental results and results from a simple mathematical model developed to predict the reaction behavior under continuous irradiation showed very good agreement. This work provides a basis for investigating the cure behavior of more complex and industrially relevant crosslinking epoxy systems where diffusion limitations play an important role as discussed in PART II. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Applicability of coumarin for detecting and measuring hydroxyl radicals generated by photoexcitation of TiO2 nanoparticles

Applicability of coumarin (COU) as fluorescent probe to detect and measure hydroxyl radicals generated by UV irradiation of aqueous suspension of TiO₂ was investigated under aerobic and anaerobic conditions. The fluorescent 7-hydroxycoumarin (7HC) was formed in argon-saturated suspension when silver ion was used as electron acceptor. The luminescence intensity increased with irradiation time until the deposition of silver on the surface of TiO₂ was completed and then the luminescence intensity was constant and proportional to the initial concentration of the silver ion. The low yield of 7HC related to the deposited silver (0.32%) indicates the appearance of efficient side reactions of hydroxyl radicals and holes. It has also been demonstrated that efficient electron donors reacting directly with photogenerated holes such as oxalic acid significantly reduce the yield of 7HC. Using oxalic acid of relatively high concentration in aerated suspension leads to the production of hydroxyl radical in thermal reactions followed by primary electron transfer steps.     

Ion‐Beam‐Induced Chemical Mixing at a Nanocrystalline CeO2–Si Interface

Thin films of nanocrystalline ceria deposited onto a silicon substrate have been irradiated with 3 MeV Au⁺ ions to a total dose of 34 displacements per atom to examine the film/substrate interfacial response upon displacement damage. Under irradiation, a band of contrast is observed to form that grows under further irradiation. Scanning and high‐resolution transmission electron microscopy imaging and analysis suggest that this band of contrast is a cerium silicate phase with an approximate Ce:Si:O composition ratio of 1:1:3 in an amorphous nature. The slightly nonstoichiometric composition arises due to the loss of mobile oxygen within the cerium silicate phase under the current irradiation condition. This nonequilibrium phase is formed as a direct result of ion‐beam‐induced chemical mixing caused by ballistic collisions between the incoming ion and the lattice atoms. This may hold promise in ion beam engineering of cerium silicates for microelectronic applications e.g., the fabrication of blue LEDs.     

Effect of large dosage irradiation in vacuo on polyethylene

The effect of large dosage irradiation in vacuo on polyethylene was investigated by the method of double irradiation. Polyethylene was first irradiated with γ-rays to a dosage of several hundred Mrad in vacuo at 298°K. The formed radicals were destoryed, and the polymer, changed chemically and morphologically, was irradiated again in vacuo at 77°K with a dose of 12.7 Mrad. The thermal decay of radicals produced in polyethylene by the second irradiation was investigated. The results show that many double bonds are formed in the sample irradiated to several hundred Mrad on the first irradiation. Alkyl radicals produced by the second irradiation react with these double bonds yielded by the first irradiation to form a large number of allyl radicals. These allyl radicals are much more stable than alkyl radicals radicals in vacuo at 298°K. In a sample not exposed to the first irradiation, almost all radicals formed by the second irradiation decay to form stable products. Crosslinks formed by a large amount of irradiation make the polyethylene matrix more rigid. This rigidity slows down the radical decay. These results suggest that the rate of radical accumulation in polyethylene irradiated in vacuo increases as the dosage increases.     

Radiation‐induced oxygen scavenging activity in EVOH copolymers

Oxygen scavenging capacity has been observed for the first time in an ethylene‐vinyl alcohol (EVOH29, i.e., 29 mol % of ethylene) copolymer as a consequence of electron beam irradiation at doses of 30 and 90 kGy. This oxygen blocking activity is thought to arise from the reaction of oxygen with the free radicals formed during the irradiation process and it has been observed to be dependent of the irradiation dose, i.e., the higher the dose, the longer the time the polymer is able to react with oxygen. The characterization of the irradiated polymeric samples has been carried out through DSC and FT‐IR and the oxygen transmission rate has been measured as a function of time and compared with the properties of the nonirradiated material. A drop in the melting point and in the enthalpy of fusion and broader peaks were observed after irradiation, which indicated changes in the morphology of the copolymer. Through FT‐IR, a slight decrease in the crystallinity of the irradiated EVOH29 was observed at the highest irradiation dose and several bands arise which correspond to the formation of degradation products such as aldehydes and ketones after irradiation. Those radiolysis compounds were identified through gas chromatography coupled to mass spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Quantum study of hydrogen–oxygen–graphite interactions

Density functional calculations are used to study the reactions of hydrogen and oxygen atoms on the basal plane of graphite. Oxygen atoms can strongly bond to the graphite surface forming an epoxide-like structure. Hydrogen atoms can react with the adsorbed oxygen and form hydroxyl (OH) radicals. The low-energy OH radicals can be retained on the graphite surface and then they can undergo recombination with hydrogen to form water molecules which leave the surface. Both the formation of hydroxyl radicals and water molecules can occur through Eley–Rideal or Langmuir–Hinshelwood mechanisms. The Eley–Rideal mechanism is kinetically favored. The study on formation of OH radicals was completed with quantum molecular dynamics calculations (Verlet algorithm).     

Combined reactive extrusion–orientation of polyethylene

The objective of this work is to combine reaction, extrusion, and orientation together in a process so as to provide product in a form which is not limited to fiber or film. Three coupled problems form the focus of the work: (i) devising a practical, continuous extrusion-orientation method; (ii) generating low concentrations of free radicals in the polymer to tailor molecular weight distribution before orientation; (iii) generating high concentrations of free radicals in the polymer to form a network in the oriented polymer without destroying its superior properties after orientation. A continuous extrusion method for orienting polymer in forms other than fibers and films was devised based upon two melt pullers. Operation of a prototype of the equipment showed it capable of providing draw ratios of greater than ten. Injection of low initiator concentrations during extrusion (i.e., before orientation) directed at solving the second problem had an effect which depended upon the degree of branching, the molecular weight, and the degree of unsaturation of the polyethylene. Large increases in molecular weight could be obtained. However, in agreement with previous work, formation of branched molecules drastically limited draw ratios attainable by the extrusion-orientation process. To obtain high concentrations of free radicals, bench scale experiments demonstrated that a recently published method involving the use of a UV sensitizer and crosslinker followed by irradiation was directly adaptable to this process (with the irradiation applied after orientation) and provided significant improvements in creep resistance. Various attempts involving die design to obtain orientation and high initiator concentrations as well as gamma radiation to induce crosslinking after orientation were attempted and appear far less promising than the above methods.     

Effect of ultrasound on extrusion of polypropylene/ethylene–propylene–diene terpolymer blend: Processing and mechanical properties

The effects of ultrasonic irradiation on extrusion processing and mechanical properties of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM) blends are examined. Results show that appropriate irradiation intensity can prominently decrease die pressure and apparent viscosity of the melt, increase output, as well as increase toughness of PP/EPDM blends without harming rigidity. In case the blends are extruded with ultrasonic irradiation twice, the impact strength of the blend rises sharply at 50–100 W ultrasonic intensity, and amounts to more than 900 J/m, 1.5 times as high as that of blend without ultrasonic irradiation. Scanning electron microscopy observation shows that with ultrasonic irradiation, morphology of uniform dispersed EPDM phase and good adhesion between EPDM and PP matrix was formed in PP/EPDM blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3519–3525, 2003     

Electron beam effects on polymers: Structure–property behavior of radiation-cured bis-GMA

Structure–property relationships were investigated for the diglycidly methacrylate derivative of bisphenol-A crosslinked by electron beam irradiation. This material, commonly called bis-GMA, is a viscous liquid at room temperature which crosslinks to form a glassy network. The major parameters which were systematically varied in this study were radiation dosage, dose rate, aging time after irradiation, and post-cure annealing at higher temperatures. Measurements were conducted to quantify the crosslinking reaction and to characterize the physical properties of the resulting networks. Solvent extraction was done to determine the relative degree of network formation through the equilibrium swelling and the gel weight fraction after drying. Another method utilized FTIR to monitor the disappearance of double bonds as the crosslinking reaction proceeded. To characterize the thermal and physical properties, differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy were utilized. Network density was found proportional to the irradiation dosage, with an upper limit reached above some critical dosage. Over the range of dose rate studied, this variable was not found to influence the degree of cure greatly. The crosslinking reaction became diffusion limited as vitrification occurred. These phenomena were discussed in terms of the well-known time–temperature–transformation diagram. Free radicals trapped in these reacting networks due to vitrification exhibited a finite lifetime. Post-curing could be achieved by annealing at a temperature above the T_g of the initially cured network, as shown by the increase of the glass transition temperature from both DSC and dynamic mechanical results.     

Study of poly(vinyl chloride)/acrylonitrile–styrene–acrylate blends for compatibility,toughness, thermal stability and UV irradiation resistance

A novel rigid poly(vinyl chloride) (PVC)/acrylonitrile–styrene–acrylate (ASA) copolymer blend with good ultraviolet (UV) irradiation resistance and toughness was reported. ASA with good weatherability and toughness was mixed with PVC by conical twin‐screw extruder to improve the UV irradiation resistance and toughness of PVC. The blends were characterized using Fourier‐transform infrared spectra, dynamic mechanical analysis, and scanning electron microscope. Notch Charpy impact test was used to characterize the UV radiation induced changes in toughness. The results showed that ASA was able to toughen PVC with simultaneously improving heat resistance, thermal stabilization, and protecting PVC from irradiation photochemical degradation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2143–2151, 2013     

Study of γ-irradiated lithographic polymers by electron spin resonance and electron nuclear double resonance

The room temperature gamma irradiation degradation of the lithographic polymers, poly(methylmethacrylate) (PMMA), poly(methyl-α-chloroacrylate) (PMCA), poly(methyl-α-fluoroacrylate) (PMFA), and poly(methylacrylonitrile) (PMCN), have been studied by electron spin resonance and electron nuclear double resonance (ENDOR) to assess their molecular degradation processes of relevance to electron beam lithography. Two classes of radicals are found, chain radicals and chain scission radicals. PMMA and PMCA mainly form chain scission radicals consistent with degradation while for PMCN the resolution is poorer, and this is only probable. PMFA forms mainly chain radicals consistent with predominant crosslinking. The total radical yield is greatest in PMCA and PMCN. ENDOR is used to assess the compactness of the radiation degradation region for PMMA and PMCA and hence the potential resolution of the resist; this appears to be about the same for these methacrylate polymers.     

Preparation and characterization of Cu2O/TiO2 nano–nano heterostructure photocatalysts

Cu₂O/TiO₂ nano–nano heterostructures with different concentrations of Cu₂O were prepared by an alcohol-aqueous based chemical precipitation method, and were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV–vis diffuse reflection absorption spectra. The photocatalytic efficiency of the Cu₂O/TiO₂ heterostructures was evaluated by degradation of Acid Orange II in water under UV–vis light and visible light irradiation. The results show that the heterostructures have dramatically improved photocatalytic activity comparing with pure TiO₂ (P25). The prepared Cu₂O/TiO₂ heterostructures with the Cu₂O concentrations of 30% and 70% have the best photocatalytic efficiencies, which are 6 times and 27 times higher than that of pure TiO₂ (P25) under UV–vis light and visible light irradiation, respectively.     

Reactions between carbon and a reduced C–O–H fluid under diamond-stable HP–HT condition

Reactions between graphitic carbon and a reduced C–O–H fluid were investigated using a mixture of stearic acid C₁₈H₃₆O₂ and oxalic acid dihydrate C₂H₆O₆, as the fluid source at high pressure and temperature (HP–HT) of 7.7 GPa and 1500°C in a platinum sealed capsule. A reduced C–O–H fluid mainly composed of methane and water, was formed by the thermal decomposition of the fluid source before reaching the HP–HT condition. An exchange reaction between carbon and methane occurred and starting carbon was re-crystallized to flaky graphite crystals, but no diamond was formed for the duration up to 24 h. In the experiment for 48 h, octahedral diamond crystals of a few to a few tens of micrometers in size were observed along with the recrystallized graphite. These results show that reduced C–O–H fluid acts as a diamond forming catalyst, although a long incubation time is necessary for diamond formation.     

Photopolymerization kinetics,photorheology and photoplasticity of thiol–ene–allylic sulfide networks

BACKGROUND: Thiol–ene networks are of interest due to their facile photopolymerization and their open network structure. In this work, an allylic disulphide divinyl ether monomer is reacted with tetrathiol and divinyl ether monomers, which allows the network structure to permanently change in shape if stressed while under irradiation. We also study the photo‐differential scanning calorimetry (DSC) kinetics and photorheology during cure and the dynamic mechanical properties after cure. RESULTS: The heat of polymerization is similar for the thiol–ene systems and suggests ca 80% conversion of the vinyl ether groups. An increase in the initiator concentration increases the photocure rate as expected. The activation energy for photopolymerization is 7.6 kJ mol^?1. DSC and rheometry studies show that the polymerization kinetics is slowed by the addition of the allylic disulfide divinyl possibly due to the formation of less reactive radicals. However, as shown by dynamic mechanical thermal analysis, the network structure is not changed very much by addition of this monomer. If radicals are generated by irradiation of a photoinitiator in the network while a stress is being applied, the polymer will permanently deform depending on the fraction of 2‐methylenepropane‐1,3‐di(thioethyl vinyl ether) in the network, due to a bond interchange reaction. CONCLUSION: The rate of thiol–ene reaction is slowed by the addition of the allylic disulfide divinyl ether. Photoplasticity is observed in the networks containing the allylic disulfide groups. Further work is required to optimize the extent of photoplasticity in these systems. Copyright © 2007 Society of Chemical Industry     

Mechanism of initiation of graft polymerization of ionogenic nitrogen-containing monomers to irradiated polypropylene fiber

Chemical analysis (iodometric titration) and electron spin resonance showed that alkoxyl radicals formed in decomposition of hydroperoxide groups make the predominant contribution to initiation of graft polymerization of ionogenic nitrogen-containing vinylic monomers to previously irradiated polypropylene fiber. It was shown that the concentration of alkoxyl radicals and the rate of graft polymerization increase when polypropylene fiber containing copper phthalocyanine complex is used.Moscow State Textile Academy. Translated from Khimicheskie Volokna, No. 4, pp. 28–30, July–August, 1992.