Grafting fluorocarbons to polyethylene in glow discharge

A systematic surface fluorination of high-density polyethylene was carried out using CF₄, CF₃H, CF₃Cl, and CF₃Br, in a radio-frequency glow discharge. Based on ESCA and wettability measurements, all of these compounds provided a fluorocarbon layer on high-density polyethylene surface, but the fluorine to carbon ratio and extractability of the films were strongly dependent on the starting materials and the location of the sample specimen in the reactor chamber as well as the duration of the reaction. The results with vertically held, CF₃H-treated samples showed a high level of nonextractable surface fluorination and very little change in wetting properties before and after extraction with CF₂ClCFCl₂.     

Immobilization of polyethylene oxide surfactants for non-fouling biomaterial surfaces using an argon glow discharge treatment

A non-fouling (protein-resistant) polymer surface is achieved by the covalent immobilization of polyethylene oxide (PEO) surfactants using an inert gas discharge treatment. Treated surfaces have been characterized using electron spectroscopy for chemical analysis (ESCA), static secondary ion mass spectrometry (SSIMS), water contact angle measurement, fibrinogen adsorption, and platelet adhesion. This paper is intended to review our recent work in using this simple surface modification process to obtain wettable polymer surfaces in general, and non-fouling biomaterial surfaces in particular.     

Surface crosslinking of polyethylene and adhesive joint strength

Exposure of polyethylene film to UV radiation at wavelengths of ≤2537 Å is sufficient to induce surface crosslinking and to facilitate the formation of strong adhesive joints to these surfaces with conventional adhesives. Reduction of the vapor pressure in the reaction vessel to about 1 torr apparently maximizes the efficiency of the crosslinking process. Examination of the treated films which have been exposed for times necessary to form strong adhesive joints has revealed an absence of surface oxidation. It appears that crosslinking to improve the mechanical strength of the surface region of the polyethylene is sufficient to allow the formation of strong adhesive joints.     

Spin trapping of radicals produced by glow discharge on low-density polyethylene

An electron spin resonance study of radicals produced by glow discharge on low-density polyethylene powder shows three kinds of radicals, depending upon experimental conditions. The first formed, alkyl radicals, are unstable at room temperature and react rapidly with oxygen to form peroxide radicals. If a spin trapping compound, N-tert-butyl--phenyl nitrone, is added to the polyethylene, before discharge, nitroxide radicals are formed in place of peroxide. The interest in forming nitroxide radicals is their stability at room temperature. This simple method can be helpful for the observation and identification of radicals produced in polymers, for example by electrical treeing.     

Surface morphology of polyethylene after treatment in a corona discharge

Corona treatment of low-density polyethylene in oxygen or oxygen-containing gases produced bumps on the surface, while treatment in nitrogen, hydrogen, argon, or helium caused no detectable surface change. Bumps made by an oxygen corona increased in size with time and temperature of the treatment. The bumps were removed when a treated polymer sheet was dipped into solvents such as CCl₄, ethanol, or 0.2% aqueous NaOH. Infrared analysis indicated that most of the oxidized layer was eliminated from the polymer surface by solvent dipping and that the degraded products contained a substantial proportion of ? CH₂? groups. It is suggested that the bumps are caused by the migration of low molecular weight degradation products to charged areas of the polymer surface.     

A study of the contact angle on RTV-silicone treated in a hydrogen glow discharge

A hydrogen glow discharge surface treatment followed by exposure to the atmosphere has been used to decrease the contact angle for distilled water on RTV-silicone. The change in contact angle has been studied in terms of vacuum ultraviolet irradiation, metastable bombardment, free-radical bombardment, and electrostatic charging. The study demonstrates that the decrease in the contact angle is caused by the interaction of the hydrogen atoms produced in the glow discharge with the polymer surface.     

Surface modification of a polyurethane film by low pressure glow discharge oxygen plasma treatment

Low pressure oxygen plasma has been used to improve the surface wettability of a polyurethane film. The modifications induced by the plasma treatment in the material were analyzed using contact angle measurements. X‐ray photoelectron spectroscopy technique was used for surface characterization of the plasma‐treated films. Atomic force microscopy and scanning electron microscopy were used to analyze topography changes due to the plasma‐etching mechanism. The results show a much better surface wettability of the film even for short exposure times, with a considerable increase in the surface energy values. As expected, functionalization with oxygen plasma is mainly because of surface oxidation with species like (C? O, C?O, OH, etc). An aging process with regard to polar groups rearrangement has been observed, thus promoting a partial hydrophobic recovery. Besides functionalization, the surface wettability of the material improves as a consequence of a slight increase in surface roughness because of the etching effect of oxygen plasma. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Surface crosslinking of high‐density polyethylene beads in a modified plasma reactor

High‐density polyethylene (HDPE) beads were successfully surface‐crosslinked in a modified plasma reactor. The modified plasma reactor treats large amounts of beads, which are uniformly surface‐crosslinked. In this study, effects of the gas pressure, radio‐frequency (RF) power, and the treatment time on the degree of surface crosslinking were systematically investigated. Degree of surface crosslinking was measured by solvent extraction method (boiling xylene method, BXM). The gel content of plasma‐treated HDPE increases from 0.0 to 1.05% within 10 min at 100 mTorr, 200 W. FTIR and DSC analyses show that the crosslinked layer after plasma treatment is limited only at HDPE surface without changing the bulk thermal property of HDPE. Through the analysis of FTIR, it was confirmed that main peaks corresponding to CH₂ bands were decreased and two peaks corresponding to CF₂ and CF₃ were observed after plasma surface modification. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2921–2929, 2002; DOI 10.1002/app.10295     

Surface structure of low density polyethylene films grafted with acrylic acid using corona discharge

Chemical composition, morphology, and crystalline structure of low density polyethylene (LDPE) films surface grafted with acrylic acid (AA) using corona discharge were studied by attenuated total reflection infrared (ATR-IR), electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD) techniques. The grafted film surface is covered with grafted chains. After grafting for 3.0 h in 20% aqueous solution of AA, the depth of the grafted layer is more than 10 nm. A grain structure was observed on the grafted surfaces which was probably caused by the isolated dispersion of active sites generated by corona discharge, and these active sites initiated the graft copolymerization. However, surfaces of grafted films were smoother than that of ungrafted ones. DSC curves of grafted films show a small peak at about 100°C due to vaporization of adsorbed water. The longer the graft copolymerization time, i.e. the higher the graft degree of AA on LDPE, the higher the amount of adsorbed water. The position of each peak in WAXD patterns, crystal axial length, crystal plane distance and crystal grain size remain almost unchanged during the graft copolymerization time of 2.0 h. However, when the graft copolymerization time reaches 3.0 h, twin peaks at about 21.4° and 22.0° are observed, indicating that a different crystal form is formed at longer copolymerization time, i.e. at a higher graft degree.     

Intercrystalline crosslinking of polyethylene

The heat distortion temperature (British Standards Method 102C) and DTA nominal melting point of high density polyethylene have been raised to 140°C by nonrandom crosslinking in which the crosslinks are superimposed on the existing semicrystalline structure. The crosslinking agent was a mixture of dicumyl peroxide and allyl methacrylate, and the crosslinking temperature was 120°C, just below the crystal melting range. In contrast, random crosslinking by the same system above the melting range at 160°C lowered the HDT (heat distortion temperature). Conventional peroxide crosslinking also lowered the HDT. The gel swelling of randomly crosslinked polyethylene was higher than that of nonrandomly crosslinked polyethylene having the same gel content. This dependence of the gel swelling on the crosslink distribution can be correlated with the HDT. The effect of γ-radiation and carbon black loading on the HDT has also been studied.     

Surface modification of polyethylene by diffuse barrier discharge plasma

Low‐density polyethylene (LDPE) modified by atmospheric dielectric surface barrier discharge plasma in oxygen was investigated to improve surface properties and adhesion of LDPE to more polar polymers. The process of plasma modification was investigated using several methods—surface energy measurements, Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance (FTIR‐ATR), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). The surface energy of LDPE increased significantly after activation by oxygen barrier plasma even at very short time of modification. The FTIR‐ATR spectra manifested the presence of carbonyl functional groups on the surface of polymer pre‐treated by oxygen barrier plasma. It was shown by SEM, and AFM, that the topography of modified LDPE was significantly changed and the surface of modified polymer exhibited higher roughness in comparison with unmodified polymer. The surface energy of treated LDPE diminished in the course of ageing especially during the first 10 days after modification by barrier plasma. Hydrophilicity of the modified LDPE surface was stabilized by photochemical post‐functionalization with 2,2,6,6‐tetramethylpiperidin‐4‐yl‐diazoacetate. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Adhesion of glow discharge polymers

Various reaction parameters in a propylene glow discharge polymerization were investigated with the objective of synthesizing films having good adhesion to metal and glass substrate. Monomer flow rate (at a constant pumping efficiency) was found to exert a significant effect on the quality of polymer adhesion to substrates. Good adhering polymeric films were obtained only at high flow rates where the deposition rate decreases with an increase in monomer flow rate. This observation applied also to ethylene, propane, allyl bromide, and ?-caprolactam. Transmission electron microscopy of the freshly deposited polymer films indicated a defect-free structure of the polymer surface obtained at high flow rates. The polymer surface obtained at low flow rates had a bead structure superimposed by uniformly placed circular defects.     

Wettability of glow discharge polymers

Treatment of good adhering glow discharge polymerized propylene (GDPP) coatings with reactive gas plasma from oxygen, nitrogen, or water (produced in a tubular reactor operation at 27.1 MHz) results in surfaces characterized by more hydrophilic interactions. Zisman's plots indicate a change in surface energy after such treatment. Transmission electron microscopy depicts that the pronounced improvement in wettability of GDPP polymer after oxygen plasma treatment in part results from the high surface development in the polymer. However, the effect is not permanent. The wettability of plasma-treated polymer diminishes with time and reaches a limiting value in 2–3 months indicating structural rearrangements at the polymer surface. Argon, carbon monoxide, or bromotrichloromethane plasma does not change the polymer surface wettability significantly. In contrast to the O₂ plasma-treated GDPP polymer, a glow discharged polymer synthesized from ?-caprolactam maintains its inherent hydrophilicily over an extended period of time.     

Surface modification of polyethylene by remote dc discharge plasma treatment

The surface modification of polyethylene in a remote nitrogen, oxygen, and hydrogen dc discharge plasma was investigated. In the case of the nitrogen plasma a strong correlation exists between the concentration of active nitrogen species, as detected by Langmuir probe measurements and plasma emission spectroscopy, and the time dependence of the polymer surface modification, as detected by contact-angle measurements. The obtained contact-angle data were interpreted in terms of the acid–base model for the interaction of the test liquid with the polymer surface. There was a great similarity in the functionalization of the polyethylene surfaces treated with nitrogen as well as with oxygen plasma, except in the intial stage, where in the former, mainly functional groups acting as electron acceptors were formed, whereas in the latter a sharp increase in the content of both electron donor as well as electron acceptor groups was detected. Thus, a determining influence of oxygen residues in the remote nitrogen plasma was indicated. The absence of such an effect in the case of the hydrogen plasma could result from direct quenching of reactive oxygen species and / or the chemical reduction of formed oxygen containing functionalities by hydrogen species. © 1993 John Wiley & Sons, Inc.     

Surface properties of polymers prepared from trimethylsilyldimethylamine and hexamethyldisilazane by glow discharge polymerization

Polymers prepared from the monomers trimethylsilyldimethylamine and hexamethyldisilazane by glow discharge polymerization were analysed by elemental analysis and infrared spectroscopy, and some surface properties were investigated. Although the polymers formed from both monomers have similar chemical structures involving CH₂, CH, Si---CH₃, Si---CH₂---CH---₂---Si, Si---O---Si, and Si---O---C groups, there is a significant difference in nitrogen residues. The nitrogen residues in polymers formed from trimethylsilyldimethylamine exist mainly as amide groups, and the residues in the polymers from hexamethyldisilazane exist as disilazanyl groups. This difference is evident in the surface energy, especially in the polar contribution. The relative ratio of polar and to dispersive contributions to the surface energy is higher for the polymers from hexamethyldisilazane (0.6) than for those from trimethylsilyldimethylamine (0.3). Adhesion between these plasma films and polymer substrates subjected to modification was also examined.     

Degradation of indole in aqueous solution using contact glow discharge plasma

Exhaustive indole oxidation in aqueous solution was studied using contact glow discharge plasma. The results indicated that the rate of indole degradation increases with the decrease in the solution conductivity. The degradation rate can be enhanced under the following situations. First, the increase in temperature. Second, introduce active carbon and hydrogen peroxide to the solution. Third, the degradation process is performed in alkaline or acidic media rather than the neutral media. Fourth, add Fe²⁺ to solution to undergo Fenton’s reaction. However, n-butanol was found decelerate the degradation of indole. Some major intermediates produced during the degradation were detected by using both HPLC and GC-MS.     

Polymerisation by glow discharge electrolysis

A glow discharge passed from a metal anode to the surface of aqueous solutions of acrylamide produces radicals which initiate polymerisation. The yield of polymer together with its relative molecular mass has been examined as a function of monomer concentration and pressure in neutral solutions. The form of the variations can be explained in terms of a simplified reaction scheme. On the basis of the proposed mechanism there are two reaction zones. In the primary reaction zone no polymerisation occurs, the radical concentration being too high. About 0·2% of the radicals escape into the secondary reaction zone to initiate polymerisation, the volume of this zone being about 0·4 cm³.In alkaline solutions the yields and relative molecular masses of the polymers are very low and this is attributed to chain termination by oxygen which rises from the destruction of hydrogen peroxide in alkaline solution.     

Benzoyl peroxide as a crosslinking agent for polyethylene

The efficiency of benzoyl peroxide (BPO) as a crosslinking agent for polyethylene (PE) was studied as a function of concentration and temperature in relation with the resin melt flow index and particle size. The investigation can lead to the selection of suitable materials and operating conditions for a proper crosslinking process. The decomposition characteristics of the initiator studied can be regulated in order to allow faster production rates when crosslinked PE are prepared by injection molding.     

Synthesis and characterization of superabsorbent composite by using glow discharge electrolysis plasma

A convenient and effective technique for polymerization to produce the poly(acrylic acid-co-acrylamide)/montmorillonite superabsorbent composite in aqueous solution was developed, in which the reaction was initiated by the glow discharge electrolysis (GDE) plasma rather than chemical initiators. The resulted superabsorbent has higher water absorbency, for example, 1024 g g⁻¹ for distilled water and 56 g g⁻¹ for 0.9% NaCl solution. To optimize the synthesis conditions, the following parameters were examined in detail: the discharge voltage, discharge time, ratio of acrylic acid to acrylamide, neutralization of acrylic acid, amount of crosslinking agent and montmorillonite added. The superabsorbent composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Results indicated that montmorillonite was effectively bonded with polymer. Moreover, the water absorbency, water retention and thermal stability of the superabsorbent composite prepared by GDE were higher than those of the superabsorbent composite by conventional chemical method under the same polymerization conditions.