Surface modification of polyolefine by UV light/ozone treatment

The surface modification of polyethylene (PE) and polypropylene (PP) was investigated by UV light/ozone (UVO) treatment. The surface oxygenation was determined by electron spectroscopy for chemical analysis (ESCA). As shown from ESCA spectra, after UVO treatment, oxygen-containing functional groups, such as carbonyl, carboxyl, and ether groups, were produced in the sample surface. The dependence of oxygenation extent (as measured by O_1s/C_1s value of ESCA spectra) on different experimental conditions, such as irradiation time, temperature, and O₂ flow rate, was obtained. It was shown that after UVO treatment at suitable conditions the surface properties of polyolefine samples, such as hydrophilicity, adhesion property, and dyeability, were improved remarkably. Furthermore, UVO treatment in short time does not have notable effect on the ageing property. It was concluded that UVO treatment is a promising technique to modify polyolefine surface properties. © 1996 John Wiley & Sons, Inc.     

Photooxidation of polystyrene. Effect of stabilizers

The effect of commercially available stabilizers such as Tinuvin-327, Tinuvin-770, and Irganox-1024 on the photooxidation of polystyrene (PS) was investigated by following the changes in molecular weight and molecular weight distribution. Structural changes during degradation were studied by ¹H-NMR- and IR-Spectroscopy and by Electron Spectroscopy for Chemical Analysis (ESCA). Neat PS films became very brittle and yellow on exposure to UV light. Tinuvin-770 stabilized the PS films towards discolouration and brittleness. The ESCA studies of surface photooxidation of polystyrene indicate the formation of ketonic and methylene ether groups in the initial stages (? 100 h). At later stages ester and carbonate groups are formed.     

Surface and structural characterization of multi-walled carbon nanotubes following different oxidative treatments

Six commonly used wet chemical oxidants (HNO₃, KMnO₄, H₂SO₄/HNO₃, (NH₄)₂S₂O₈, H₂O₂, and O₃) were evaluated in terms of their effects on the surface chemistry and structure of MWCNTs using a combination of analytical techniques. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDX) were used to characterize the extent of surface oxidation, while chemical derivatization techniques used in conjunction with XPS allowed the concentration of carboxyl, carbonyl, and hydroxyl groups at the surface to be quantified for each MWCNT sample. Our results indicate that the distribution of oxygen-containing functional groups was insensitive to the reaction conditions (e.g., w/w% of oxidant), but was sensitive to the identity of the oxidant. MWCNTs treated with (NH₄)₂S₂O₈, H₂O₂, and O₃ yielded higher concentrations of carbonyl and hydroxyl functional groups, while more aggressive oxidants (e.g., HNO₃, KMnO₄) formed higher fractional concentrations of carboxyl groups. IR spectroscopy was unable to identify oxygen-containing functional groups present on MWCNTs, while Raman spectra highlighted the frequently ambiguous nature of this technique for measuring CNT structural integrity. TEM was able to provide detailed structural information on oxidized MWCNT, including the extent of sidewall damage for different oxidative treatments.     

Behavior of aqueous solutions of poly(ethylene oxide-b-propylene oxide) copolymers containing a hydrotropic agent

The effect of the hydrotropic agent, sodium p-toluenesulfonate (NaPTS), was evaluated on the micelle formation process and on phase behavior of aqueous solutions containing poly(ethylene oxide-b-propylene oxide) (PEO–PPO) copolymers. We have studied monofunctional diblock copolymers coupled with hydrocarbons groups (R—PEO—PPO—OH and R—PPO—PEO—OH, where R length is linear C₄ and C_12–14). The critical micelle concentration (CMC) and critical micelle temperature (CMT) values of the aqueous copolymers solutions were obtained from both surface tension versus concentration plots and the dye solubilization method. The influence of the hydrocarbons groups length and PPO segment position in the structure of the copolymers were also analyzed. The same measures were obtained for the aqueous solutions of hydrotropic agent which, in turn, also presented molecular aggregation. The presence of the hydrotropic agent in the aqueous copolymers solutions altered the surface tension of these solutions and the occupied molecular area per copolymer molecule at air–water interface and CMC and CMT values of the copolymers. On the other hand, the aggregation points and the surface tension of the NaPTS solutions were dependent on the copolymer structure and composition. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2459–2468, 1998     

Nitric acid oxidation of vapor grown carbon nanofibers

Vapor grown carbon nanofibers (Pyrograf III™) with 100–300 nm diameters and ∼10–100 μm lengths were oxidized in 69–71 wt.% nitric acid (115 °C) for various times (10 min to 24 h). These fibers were remarkably oxidation-resistant. XPS (O_1s) showed that the surface atomic oxygen percent increased from 6.3 to 18.3–22.5% for 10–90 min oxidations followed by a drop to 14–15% after 10–24 h oxidations. No damage was observed by TEM. Little change in surface area was observed by N₂ BET but CO₂-DR measurements exhibited an increase from 20–25 m²/g to 41–73 m²/g after 10–90 min of oxidation followed by a decrease to 35–22 m²/g after 10 h, consistent with the XPS findings. Shallow ultramicropore formation could account for the surface area increase. NaOH titrations showed ∼3-fold increase in surface acidic functions (∼27 to 76 μmol/g) occurring after 10 min of oxidation. Then this level remained constant through 24 h of oxidation. XPS (C_1s), O_1s) confirmed that carboxyl groups were removed and ester, anhydride, quinoid and phenolic hydroxyls appeared upon HNO₃ oxidation. Oxidized fibers dispersed when shaken in water, demonstrating wettability had increased. A model for this oxidation behavior is proposed.     

Surface analysis by ESCA of sulfite post-treated CTMP

Handsheets of post-treated chemithermomechanical pulps (CTMP) and a sample of Whatman paper no. 1 were analyzed using an ESCA spectrometer. All of these samples revealed the presence of the C₁, C₂, and C₃ components in the carbon (1s) peak and the O₂ component in the oxygen (1s) peak; the O¹ peak component which was present in the other samples was missing from the Whatman paper. Pulp sulfonation produced a reduction in C₁ representing the group of carbon not bonded to oxygen, and an increase in C₂ with C₃ remaining relatively constant. These changes imply reductions in lignin and extractives and a corresponding increase in cellulose content on the fiber surface. Extrapolation of the C₁, C₂, C₁/C₂, and O/C curves of CTMP to zero percent sulfonation yielded the same values as those obtained for pure TMP. ESCA analysis allows us to monitor the increase of sulfur content as a function of sulfonation in accordance with results obtained from bulk pulp sulfonate content titration.     

ESCA spectroscopy of poly(methyl methacrylate) grafted onto wood fibers

The incompatibility of hydrophilic wood fiber and hydrophobic polymers is the main difficulty with wood thermoplastic polymer composites. To overcome this issue, many researchers suggest grafting polymer onto wood fiber for improving the interfacial adhesion during mixing. A systematic ESCA study of chemi-thermo-mechanical pulp (CTMP) grafted fiber has been performed to provide chemical information about surface composition modification. The material analyzed included initial CTMP fiber, the pure polymer i.e., poly(methyl methacrylate) (PMMA) as reference material, and grafted fiber at different polymer loadings. Interest is focused on the carbon and oxygen spectra. Samples at high polymer loading or high grafting level have an O/C, C₁, C₂, C₄, O₁, and O₂ intensities much similar to those of the PMMA but a little different since some wood fiber sites have still not fixed the polymer. ESCA spectra provide information on about 1–5 nm depth. The ESCA technique allows the monitoring of grafting polymer onto wood fiber as a surface phenomenon.     

ESCA study of the solid residues of supercritical extraction of Populus tremuloïdes in methanol

A systematic ESCA study of the solid residues of supercritical critical extraction of Populus tremuloïdes prepared in various conditions has been performed. Reference materials also examined by ESCA included the initial wood, Whatman no. 1 paper, and two lignins prepared by different procedures. Interest has been focused on the C_ls and O_ls spectra and on the determination of surface O/C atomic ratio. A difference between bulk O/C values measured by chemical analysis and surface O/C ratios obtained from ESCA data is considered diagnostic of a difference in chemical composition of the bulk and the surface. In the C_ls peaks of wood and its constitutive polymers, the usual components peaks C₁, C₂, and C₃ were observed. For the solid residues, however, a fourth peak designated as C₀ appears, the importance of which increases steadily when the temperature of extraction is raised from 250 to 350°C. The component C₀ was ascribed to polyaromatic constituants. Its proportion is correlated with the fraction of the carbon in the residue comprised in the recondensed material and determined independently. The O_ls peak shows also a complex structure with three components in the wood-derived reference materials and four in some of the solid residues. These structures have not been discussed previously in the literature and a tentative assignment for the component peaks is proposed.     

Evidence of selective oxidation in surface layers of graphite-like thin sheets by mild oxidation

Graphite-like thin sheets (GLSs) contained in globular aggregates of carbon nanohorns have few oxygenated groups; therefore, they are suitable for studying how oxidation can be finely controlled. We found that mild oxidation in GLSs with H₂O₂ solution at room temperature for 7–28 days enabled GLS surface layers to be selectively oxidized, where carboxyl, quinone, carbonyl, and hydroxyl groups were created. The inner layers were little oxidized and almost no exfoliation occurred as was suggested by the lack of change in the layer–layer distances and the histogram of layer numbers in the GLS. The other evidence was that the quantity ratio for the surface and inner layers, viz., oxidized and not-oxidized layers, was estimated to be about 2:1 from thermogravimetric analysis, and this value largely coincided with the surface and inner ratio of layer numbers estimated from the histogram for the layer number.     

Maximizing the number of oxygen-containing functional groups on activated carbon by using ammonium persulfate and improving the temperature-programmed desorption characterization of carbon surface chemistry

The number of oxygen-containing functional groups (OCFGs) on the surface of a commercial activated carbon (AC) was maximized using ammonium persulfate ((NH₄)₂S₂O₈, APS) as an oxidant. Effects of the oxidation conditions, including temperature, time and concentration of APS, on physical and chemical properties of the treated AC were examined to develop a relationship between the oxidation conditions and surface chemistry of AC. A maximum amount of oxygen, 18.7 mmol/g, on the AC was achieved by oxidation with 2.0 mol/L APS solution and an APS/AC weight ratio of 9.1 at 60 °C for 3 h. Temperature-programmed desorption coupled with mass spectrometry (TPD–MS) was used to identify and quantify OCFGs on the AC samples. It was found that using the TPD–MS method currently reported in the literature to quantify various OCFGs on the carbon surface on the basis of TPD–CO₂ and TPD–CO profiles may significantly underestimate the number of carboxyl groups, and overestimate anhydrides and lactones due to some in situ reactions of OCFGs during the TPD–MS analysis. The amount of H₂O and CO released in the temperature range corresponding to decomposition of carboxyl groups should be taken into account when estimating the amount of carboxyl groups on AC.     

Effects of polymer molecular weight and chemical modification on the gas transport properties of poly(2,6‐dimethyl‐1,4‐phenylene oxide)

Poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) of different intrinsic viscosities has been studied to understand the effect of polymer molecular weight on the permeability and permeability ratio of CO₂/CH₄ and O₂/N₂ gas pairs. The increase in permeability of dense films prepared from higher molecular weight PPO was explained in terms of increased free volume. Gas permeability for the high molecular weight was further improved by attaching bulky bromine groups to the phenyl ring of the PPO backbone. Permeability ratio of PPO was greatly improved by attaching polar groups such as —COOH or —SO₃H. The loss in permeability because of the presence of the polar groups was compensated by using PPO that was brominated and sulfonated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1137–1143, 2000     

A study of the performance and chemical characteristics of composite reverse osmosis membranes prepared by plasma polymerization of allylamine

A study has been carried out of the performance and chemical characteristics of composite reverse osmosis membranes prepared by plasma polymerization of allylamine in a radio-frequency electric discharge. It has been shown that membranes can be prepared which simultaneously exhibit a high rejection for sodium chloride and a high water flux. The primary factors influencing the quality of the membranes are the choice of substrate material, the deposition time, and the power supplied to the discharge. Variations in rejection and flux as a function of applied pressure indicate that water flows through the membrane by both diffusive and bulk flow. A reduction in rejection and an increase in flux are observed when membranes are operated for prolonged periods or at higher temperatures (up to 60°C). Elemental analysis of plasma-polymerized allylamine shows that it can be represented by the stoichiometry C₃H_3.8N_0.9O_0.1. Infrared spectra show evidence for N? H, C?N, C?N, and C? H bond vibrations. ESCA spectra of the polymer surface show that the surface contains substantial amounts of both nitrogen and oxygen and that the nitrogen is present as either a nitrile or an imine group but not as an amine group. ESCA spectra of membranes used for reverse osmosis show that the surface loses nitrogen and gains oxygen with time and that this phenomenon is accelerated at higher operating temperatures. A decrease in rejection and an increase in flux accompanies these changes. It is postulated that most of the nitrogen in the polymer is present in the form of RR′C?NH or RR′C?NR″ type structures. The loss of nitrogen and gain in oxygen observed in the ESCA spectra of membranes run at elevated temperatures is explained by the hydrolysis of the proposed structures.     

Effect of wet chemical treatments on the distribution of surface oxides on carbonaceous materials

The properties of carbonaceous materials are often modified using wet chemical treatments; however, the detailed changes in the oxide distribution that accompany different chemical treatments have not been clearly elucidated. To illustrate how this information can be obtained, we have employed chemical derivatization in conjunction with X-ray photoelectron spectroscopy (XPS) to quantify changes in the concentration of hydroxyl, carbonyl, and carboxylic acid groups on the surface of a modified wood char following several different wet chemical treatments (H₂O₂, HNO₃, ammonium persulfate, O₃, and NaBH₄). Results from the present investigation highlight the fact that changes in surface oxide distributions are sensitive to the chemical treatment. For example, ammonium persulfate selectively increases the carboxylic acid group concentration. In contrast, O₃ increases the concentrations of hydroxyl, carbonyl, and carboxylic acid groups with roughly equal propensity. These oxide distributions were further modified by reduction with NaBH₄, which generally converts carbonyl and carboxylic acid groups to hydroxyl groups. A comparison of results obtained from XPS and chemical analysis reveal that the oxidative effects of wet chemical treatments are restricted to the char’s surface.     

Electrocatalytic decomposition of hydrogen sulfide

Cu/ZSM-5 catalysts prepared by impregnation of Cu acetate are active for NO reduction. In mixtures containing both NO and O₂, reductants such as CO or CH₄ preferentially react with O₂, but propane reacts preferentially with NO. Small amounts of O₂ actually increase the reduction of NO by C₃H₈. The N₂ yield reaches a maximum near an O₂ /C₃H₈ ratio=5, i.e. the stoichiometry of total C₃H₈ oxidation. At much higher than stoichiometric O₂ contents for total C₃H₈ oxidation the N₂ yield with C₃H₈ (54%) is still substantially higher than, for instance, with CO of the same or larger concentration. The hypothesis that an intermediate of C₃H₈ oxidation is responsible for the enhanced NO reduction is discussed. Temperature-programmed reduction shows that after reaction with NO+C₃H₈ and sub-stoichiometric amounts of O₂ Cu in the catalyst is mainly metallic, but CuO particles appear to be formed in the presence of an excess of O₂.     

Structure and morphology of isotactic polypropylene functionalized by electron beam irradiation

The structure and morphology of isotactic polypropylene (iPP), functionalized by electron beam irradiation at room temperature in air, are investigated by elementary analysis, FT‐infrared (FTIR) spectroscopy, electron spectroscopy for chemical analysis (ESCA), polariscope, and static contact angle. Elementary analysis reveals that the element oxygen has been introduced onto iPP chains after electron beam irradiation. In addition, as shown from FTIR spectra, oxygen‐containing groups, such as carbonyl, carboxyl, and ether groups, are introduced onto iPP molecular chains. The dependence of oxygenation extent (as measured by O_1S/C_1S value of ESCA spectra) on electron beam dose is obtained. Under polariscope, it can be observed that the dominant alpha phase appears to become more enhanced, and there is no crystalline phase transition. The static contact angle of iPP decreases with increasing dose. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 75–82, 2000     

Oxidation of Ldpe in the Molten State in the Presence of Tetrabutyl Ammonium Permanganate and Potassium Permanganate

Of the various oxidizing agents available. never have the tetrabutyl ammonium permanganate or the potassium psrmanganate been used for the oxidation of polyolefins in the molten state. The effects of time and temperature on the oxidation reaction were studied using an internal mixer. The reaction was performed in the presence of traces of hexadecyl alcohol as an accelerator. In certain cases, biphenyl was uscd as a conipatibilizing agent in the molten state. The oxidized polyethylene was purified by sol-ubilization in order to eliminate the MnO_l formed from the reaction between KMnO₄, tetrabutyl ammonium permanganate, and low-density polyethylene (LDPE). The presence of MnO₂ was confirmed by chemical tests and by electron spectroscopy for chemical analysis (ESCA).

Infrared and ESCA analyses were conducted in order to determine the presence of carboxylate ester. and ketonic or alcoholic groups as well as the amount of carbonyl groups. The mechanical and physical properties were determined. A diluted H₂SO₄ solution was used to hydrolyze the ester groups. The results are compared with virgin LDPE as well as with a commercial oxidized polyethylene. A reaction mechanism of oxidation of the LDPE in the molten state is proposed.     

Effect of oxygen functional groups on synthetic carbons on liquid phase oxidation of cyclohexanone

Synthetic carbons from phenolic resins were used as catalysts for the aqueous phase oxidation of cyclohexanone to C₄-C₆ dicarboxylic acids (adipic, glutaric and succinic acids) at 413 K under 50 bar total air pressure. The changes in microporous structure and surface chemistry, produced as a consequence of activation or heat treatment processes, were analyzed. Using CO₂ or air as activating agent increased significantly the surface area and the total pore volume responsible for the activity. The surface chemistry of the samples was also modified and was characterized by titration with bases of different strength and with HCl, by temperature programmed desorption, and by X-ray photoelectron spectroscopy. To determine the role of surface oxygen functionalities on the catalytic behavior of the carbons, heat treatments in nitrogen at different temperatures were used to selectively eliminate oxygenated groups. Thus, treatment at temperatures of 1173 K eliminating the carbonyl/quinone groups decreased the selectivity to adipic acid and dicarboxylic acids. Introducing quinone groups during the synthesis of the carbons also improved the selectivity to adipic acid, proving that the mechanism of oxidation involves the quinone type groups on the carbon surface.     

Direct Aerobic Oxidation of Secondary Alcohols Catalysed by Pt(0) Nanoparticles Stabilized by PV2Mo10O40 5− Polyoxmetalate

Pt(0) nanoparticles stabilized by the H₅PV₂Mo₁₀O₄₀ polyoxometalate were prepared in water by a sequence of redox reactions and supported on α-alumina. Characterization by TEM showed an average particle size of 2.6 nm with an approximate size dispersion of about ±25%. EDS analysis confirmed the amounts of metal and polyoxometalate as indicated from the reaction stoichiometry. These nanoparticles were further used as catalysts for the oxidation of secondary alcohols with molecular oxygen to the corresponding carbonyl products. The oxidation of secondary alcohols was further improved by the use of Pt nanoparticles stabilized by Rh_1.7PV₂Mo₁₀O₄₀.     

Reaction and Surface Characterization Studies of Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for CO Preferential Oxidation in Reformed Gas

In order to investigate the reasons the activation of a Ru/Al₂O₃ catalyst by heating in a H₂/N₂ mixed gas improves the CO preferential oxidation (PROX) activity, the oxidation state of the Ru on the catalyst surface was studied by using ESCA. As the ratio of Ru(0) to total Ru on the surface was increased, the temperature window of the Ru catalyst, where CO was reduced to below 10 ppm, was expanded to the lower temperature side. The activity of CO oxidation by O₂ of the Ru catalyst at lower temperatures was improved by increasing the ratio of Ru(0). However, the selectivity for CO oxidation hardly varied with the change in the surface Ru(0) ratio at these low temperatures. It is considered that O₂ activation on Ru(0) plays an essential role in CO PROX activity on the Ru catalyst at low temperatures.     

In vitro monocyte adhesion and activation on modified FEP copolymer surfaces

The functional group content and the ionic state of functional groups present on a series of surface modified poly(tetrafluoroethylene/hexafluoropropylene) (FEP) copolymers were characterized by electron spectroscopy for chemical analysis (ESCA), contact angle, and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Additionally, after a protein was preadsorbed on these surfaces, in vitro cell (monocyte) adhesion and activation were analyzed. The two proteins in this study were fibrinogen and immunoglobulin-G (IgG). Four modified FEP surfaces were prepared with increasing concentration of carboxyl groups relative to amide groups; ESCA was used to quantify the functional group content. To characterize the ionic state of the functional groups at physiological pH (7.1), the ATR-FTIR spectra were collected at various pH levels. Collectively, the contact angle, ESCA, and ATR-FTIR results suggested that the amide groups were unprotonated and the carboxyl groups were ionized at the physiological pH. The results from the in vitro studies showed that on the fibrinogen preadsorbed surfaces, monocyte adhesion was higher and monocyte activation was lower on the three surfaces that contained carboxyl groups compared to the FEP surface that had only amide groups. Conversely, the results indicated that the surface chemistry had no significant effect on monocyte adhesion or activation on the IgG preadsorbed surfaces. © 1995 John Wiley & Sons, Inc.