Characterization of oxidation progress by chemiluminescence: A study of polyethylene with pro-oxidant additives

Non-isothermal chemiluminescence measurements in nitrogen and isothermal measurements in oxygen were used for the evaluation of degradation in pre-oxidized polyethylene either pure or containing Mn-based pro-oxidant additives. The results were compared with infrared spectroscopy data. Chemiluminescence measurements of pure polyethylene and polyethylene with additive made it possible to calculate the set of rate constants, based on the Bolland-Gee oxidation scheme. The oxidation rate constants of polyethylene with additive were significantly higher, while the activation energy of the process appeared lower (65 kJ mol⁻¹), than those of pure polyethylene. The method provides an access to study oxidation processes during the induction period of oxidation when infrared spectroscopy cannot provide sufficient information.     

Oxidation of polyethylene surface by corona discharge and the subsequent graft polymerization

Oxidation of a polyethylene (PE) surface by corona discharge and the subsequent graft polymerization of acrylamide (AAm) were studied. The maximum amount of peroxides introduced by corona treatment at a voltage of 15 kV was about 2.3 × 10^?9 mol cm^?2. The decomposition rate of peroxide and the dependence of graft amount on the storage period of the corona-treated PE films showed that there were several kinds of peroxides, the labile one being mainly responsible for the initiation of graft polymerization. When the corona-treated film was brought into contact with a deaerated aqueous solution of AAm, graft polymerization took place more strongly with the treatment time, but was reduced after passing a maximum. Although the x-ray photoelectron spectroscopic analyses of the corona-treated PE films showed homogeneous oxidation of the outer polymer surface by corona discharge, optical microscopy on the cross section of the grafted film revealed the graft polymerization to be limited to a very thin surface region.     

Polymer matrix of polyethylene porous films functionalized by electrical discharge plasma

The polyethylene porous films were treated by dielectric surface barrier discharge (DSBD) plasma at atmospheric pressure in oxygen (O₂) or nitrogen (N₂), and by radio-frequency discharge (RFD) plasma in air at reduced pressure 46 Pa. The surface energy of films was carried out by direct measurements of contact angles of six testing liquids. The strength of adhesive joints in the system modified polyethylene porous films - polyacrylate was measured by peeling of the joints under the angle of 90°. The significant increase of the surface energy and its polar component of polyethylene porous films modified by all types of plasma were observed. The higher strengths of adhesive joints were found for modification of polyethylene porous films by radio-frequency discharge plasma in comparison with modification of the films by barrier discharge plasma.     

Aqueous p-nitrotoluene oxidation induced with direct glow discharge plasma

A plasma induced degradation process has been studied to treat 4-nitrotoluene (4-NT) present as an aqueous pollutant. The plasma was locally generated from a glow discharge around a tip of a platinum anode in an electrolytic solution. The influence of initial pH and Fe²⁺ on the degradation was examined. Major intermediates resulting from the degradation process were identified. Amongst the aromatic intermediates, p-hydroxybenzoic acid was the predominant degradation product. The formation of oxalic acid, malic acid was also observed. The final products of degradation were NH ₄ ⁺ , NO ₃ ⁻ and CO₂. Based on the analysis of intermediates and the kinetic considerations, the degradation was shown to follow a pseudo-first order reaction hence, a possible reaction pathway was proposed.     

Oxidation of polyethylene surface by glow discharge and subsequent graft copolymerization of acrylic acid

Plasma-induced graft copolymerization of acrylic acid, which was incorporated into PE films, was investigated here. The influence of plasma conditions such as plasma treatment gases, power, pressure, time, monomer concentration, and graft copolymerization time on polymerization yield was determined. The samples were characterized by ESCA, IR, and water contact angle. A respective chemical shift of the C1s signal of Ar or O₂ plasmatreated and untreated PE films was revealed by ESCA, in which the presence of the grafted PAAc was also verified. An increase in polymerization yield with plasma treatment duration and power was found. That the grafted copolymerization was limited to a very thin surface region was revealed by optical microscopy on the cross section of the grafted film. © 1993 John Wiley & Sons, Inc.     

Remote atmospheric-pressure plasma activation of the surfaces of polyethylene terephthalate and polyethylene naphthalate

The surfaces of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were treated with an atmospheric-pressure oxygen and helium plasma. Changes in the energy, adhesion, and chemical composition of the surfaces were determined by contact angle measurements, mechanical pull tests, and X-ray photoelectron spectroscopy (XPS). Surface-energy calculations revealed that after plasma treatment the polarity of PET and PEN increased 6 and 10 times, respectively. In addition, adhesive bond strengths were enhanced by up to 7 times. For PET and PEN, XPS revealed an 18-29% decrease in the area of the C 1s peak at 285 eV, which is attributable to the aromatic carbon atoms. The C 1s peak area due to ester carbon atoms increased by 11 and 24% for PET and PEN, respectively, while the C 1s peak area resulting from C-O species increased by about 5% for both polymers. These results indicate that oxygen atoms generated in the plasma rapidly oxidize the aromatic rings on the polymer chains. The Langmuir adsorption rate constants for oxidizing the polymer surfaces were 15.6 and 4.6 s(-1) for PET and PEN, respectively.     

A study of heterogeneous recombination of chlorine atoms on aluminum and copper surfaces in glow discharge plasma

The absolute values of the rate constants for heterogeneous recombination of chlorine atoms on the surface of aluminum and copper in the positive column of a glow discharge in Cl₂ have been determined using the pulse relaxation technique.     

Gamma-, photo-, and thermally-initiated oxidation of linear low density polyethylene: A quantitative comparison of oxidation products

The detailed oxidation products from the initiated oxidation of linear low density polyethylene have been compared by the use of infrared spectroscopy combined with chemical derivatization. Oxidized films were treated with NO or SF₄ to allow the resolution of the various alcohol and hydroperoxides and of the carbonyl species, respectively. All types of initiation gave very similar products but in varying quantities. In photooxidation, hydroperoxide was clearly shown to approach a photostationary concentration either from below for fresh film or from above for samples that had been pre-oxidized by γ-irradiation, prior to UV exposure. Carboxylic acid groups, the main backbone scission product, dominated in photooxidations, possibly as the result of the further oxidation of sec-hydroperoxide sites.     

Surface oxidation of polyethylene using an atmospheric pressure glow discharge with liquid electrolyte cathode

This study investigated the action of an atmospheric pressure air glow discharge (APGD) with aqueous electrolyte cathode onto the surface of polyethylene (PE) films. Distilled water and aqueous solutions of KCl and HCl were utilized as a cathode. The surface properties of PE were characterized by contact angle measurement followed by surface free energy calculation, Fourier transform infrared by attenuated total reflectance (FTIR-ATR), and XPS. After treating the PE surface, we observed OH groups, CO groups in ester, ketone, and carboxyl groups, and CO groups in unsaturated ketones and aldehydes. For a treatment time of 20 min and a discharge current of 40 mA, atomic concentrations of O and N were 12% and 2%, respectively, under distilled water application. Modification processes were able to improve the surface free energy of PE.     

Thermoluminescence of a polyethylene surface after plasma treatment with a high-frequency glow discharge

The plasma treatment of polyethylene (PE) gives a specific pattern of thermoluminescence (TL). The qualitative difference between the TL curves of PE after plasma treatment and the curves for radioluminescence appears to be due both to specific features of the plasma treatment (attack on the surface of the sample and the unavoidable effect of photobleaching) and to the particular structure of the surface of the polymer (the existence or formation in the surface layer of special low-molecular structures). TL after plasma treatment can therefore be used to investigate the surface structure of polymers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1742–1744, August, 1990.     

基于火花放电等离子体部分氧化重整二甲醚制氢研究

应用自制的多级式等离子体富氢气体制备装置，进行了二甲醚部分氧化重整制氢实验。实验结果表明，常温常压下二甲醚的转化率和氢产率随占空比的增大先增大后减小，当占空比为80%时最大值分别为87.6%和39.4%。随着电源电压的增加，放电能量和持续时间逐渐增加，转化率和氢产率逐渐增加。当反应器采用保温措施或对反应物进行加湿时，转化率和氢产率均有明显提高，同时制氢能耗下降，热效率有一定提高。实验过程中附着在电极上的积炭主要是由于氧气不足造成，随空醚比的增大，积炭明显减少。     

Modification of surface properties of high and low density polyethylene by Ar plasma discharge

Structural changes induced by Ar plasma discharge in low and high density polyethylene (LDPE and HDPE) were studied by different techniques. AFM and SEM methods were used to determine surface morphology, the changes in chemical structure were followed using FTIR and UV-vis spectroscopy. The content and the depth profile of incorporated oxygen was determined by RBS method. The degree of polymer ablation was determined gravimetrically. Standard goniometry was used to determine contact angle and to follow aging of plasma modified polymer. As a result of plasma treatment a lamellar structure or spherulites appear on the surface of HDPE and LDPE, respectively. Pronounced increase of the surface roughness is observed on HDPE contrary to LDPE. Plasma treatment for 400 s leads to the ablation of the surface layer of about 0.6 and 1 μm thick for LDPE and HDPE, respectively. Plasma treatment results in oxidation of the polymer surface layer which is more pronounced in HDPE. Concentration maximum of incorporated oxygen lies 25 nm beneath the sample surface in both polymer types. After exposure to plasma discharge carbonyl, carboxyl and amide groups were detected in the polymer surface layer together with CC bonds either in aromatic or in aliphatic structures. Immediately after the plasma treatment strong decline of the contact angle is observed, the decline being larger in HDPE. Later, in aged specimens the contact angle increases rapidly. The increase, which may be due to rearrangement of degraded structures, is stronger in the specimens exposed to plasma for longer times.     

A direct method for preparing ethyldichlorosilane and its comparison with known alternative methods

Various methods, alternative to direct synthesis, for preparing an important commercial organosilicon monomer, ethyldichlorosilane, were studied in detail. The methods, including organomagnesium and organoaluminum procedures, hydrosilylation, and combined methods, were analyzed from the viewpoint of feasibility of laboratory and small-tonnage commercial production, and their advantages and drawbacks were revealed.     

ESCA study of polymer surfaces treated by plasma

Surfaces of polymers [polyethylene, polystyrene, poly(ethylene terephthalate), poly(oxymethylene), cellulose acetate, polyacrylonitrile, nylon 6, and polytetrafluoroethylene] treated with argon (inert) and nitrogen (reactive) plasma were examined by ESCA (electron spectroscopy for chemical analysis). Argon plasma treatment generally introduces oxygen functionalities into the polymer surface. Nitrogen treatment generally incorporates nitrogen and oxygen functionalities into the treated surface. The extent of oxygen incorporation is typically less than that produced by argon plasma. When nitrogen and oxygen functional groups are already in a polymer structure, the extent of additional incorporation of these two elements as a result of plasma treatment is very much less than with other polymers. Polymers which contain only one of the elements tend to incorporate the other element to much the same degree as polymers without either element initially present.     

Oxidation induction time and oxidation onset temperature of polyethylene in air

Oxidation induction times (OIT) and oxidation onset temperatures (OOT) of a low density polyethylene melt were evaluated in air using DSC. Good regression fits to OOT data were obtained using global values for the activation energy (E) that are specific for each antioxidant but assumed independent of concentration. Gimzewski’s postulate that OIT and OOT correspond to the same level of antioxidant depletion was tested by attempting to predict OIT values from OOT generated model parameters. The deviations between predicted and experimental OIT values were comparable in magnitude to the inherent scatter in the data. However, regression of the dynamic OOT data yielded statistically significant lower values for the activation energy than are obtained by direct regression of isothermal data.     

A survey of methods for the detection of thermal oxidation in high-density polyethylene pipes

Seven methods for the detection of thermal oxidation of the inner wall surface of high-density polyethylene (HDPE) pipes are presented. The methods presented include infrared spectroscopy, polarized light microscopy, differential scanning calorimetry, scanning electron microscopy, gloss measurements and uniaxial creep tests. These tests have been developed on the basis of earlier reported data for a large number of PE pipes. The tests are compared with each other and with the internal pressurizing test with respect to reliability of results, the time taken to determine whether or not a pipe is oxidized, the experimental difficulties, costs, etc.     

Radionuclide detection by inductively coupled plasma mass spectrometry: A comparison of atomic and radiation detection methods

Radionuclide detection by mass spectrometric techniques offers inherent advantages over conventional radiation detection methods. Since radionuclides decay at variable rates (half-lives) and via various nuclear transformations (i.e. emission of alpha-, beta-, and/or gamma-radiation) their determination via radiation detection depends not only on decay systematics but also on detector technology. Radionuclide detection by directatom measurement, however, is dependent only on technique sensitivity and is indifferent to decay mode. Evaluation of inductively coupled plasma mass spectrometry (ICP/MS) indicates this method to be superior to conventional radiation detection techniques for many radionuclides. This work discusses factors which influence detection by both methods. Illustrative applications of ICP/MS to the ultra-trace determination of several radionuclides, including¹²⁹I, are presented.Operated for the U.S. Department of Energy by Battelle Memorial Institute under contract De-AC06-76RLO 1830.     

Sulfur modification of polyethylene surfaces. II. Modification of polyethylene surfaces with fuming sulfuric acid

Previous work has shown that atomic sulfur irreversibility modifies polyethylene, presumably through an insertion reaction into carbon—hydrogen bonds with formation of surface thiol groups. The thiol groups were then oxidized to sulfonic acid surface groups, which were further reacted chemically as shown by wettability measurements. In this work the thiol group was bypassed and the surface sulfonic acid groups were obtained by exposing the polyethylene surface directly to fuming sulfuric acid. The sulfonic acid groups were reacted further. Critical surface tension values identical with those in the previous work with atomic sulfur were obtained, thus substantiating the previous work.     

Surface oxidation and degradation of polyethylene in a mixed argon-oxygen plasma

Changes in surface chemical composition and the rates of formation of gaseous degradation products under the action of a mixed argon-oxygen plasma on polyethylene (PE) were studied using multiple attentuated total internal reflection (MATIR) IR spectroscopy and mass spectrometry. It was found that the dilution of a gas mixture with argon decreased the rate of degradation of the material at argon contents higher than 30%. It was demonstrated that absorbance at the absorption bands of the main oxygen-containing groups in a PE film remained unchanged over an argon concentration range from 0 to 90%. Conceivable mechanisms of processes occurring in gas and solid phases, which allowed us to describe the phenomena observed, are discussed.