Adhesive Contact in Surface Layers of Low-Density Polyethylene Irradiated in Air

The formation of adhesive bond was studied for bulk low-density polyethylene irradiated in air. It was shown that the amount of the gel fraction over the depth of the surface layer is a signature of the relative contribution of degradation and crosslinking to the structure of the material at a given depth and makes it possible to determine its minimal depth below which the polymer has a sufficient strength required for the formation of an adhesive joint.     

Adhesive behavior of UV pre‐treated polyolefins

The effect of surface modification of polyolefin, mainly isotactic polypropylene and low‐density polyethylene, by UV irradiation and phosphoryl chloride on its adhesive behavior was investigated. A non‐linear increase of the surface free energy, its polar component and strength of adhesive joint to more polar polymer was observed. The effect of modification of polyolefins was strongly depended on the intensity of the UV radiation. The obtained values of the strength of adhesive joints to polyvinyl acetate correspond with the measured level of hydrophilicity of modified polyolefin.     

Influence of free surface energy of polymers on formation of their interphase contact with oxyethylated isononylphenol

The interconnection of the surface energy characteristics of polymers in a wide range of acid-base constituents of the free surface energy and their adhesive interaction with adducts of ethylene oxide and isononylphenol was investigated. It was shown that the content of the polar groups in the polymer surface layer and the length of the oxyethylene chain additively influence the wetting ability and the work of adhesion. The peculiarities of the adhesive interaction of high pressure polyethylene with oxyethylated compounds depending on the thermal oxidation of polymer and the acidity parameters of the surface were revealed.     

Polymer microchips bonded by O2-plasma activation

This paper presents a fabrication of polymer microchips with homogeneous material technique due to surface treatment by plasma before sealing. UV laser photoablation was used for fast prototyping of microstructures, and oxygen plasma was used as a surface treatment for both the microfabricated substrate and the polymer cover. It was found that with an oxidative plasma treatment, successful bonding could be achieved without adhesive material between polymer sheets substantially below the glass transition temperature of the polymer. Homogeneous polyethylene terephthalate (PET) microstructures were characterized by scanning electron microscopy (SEM) and analyzed by X-ray photoelectron spectroscopy (XPS) surface analyses after different surface treatments. The electroosmotic flow characteristics including the velocity and the stability over 20 days have been tested and compared to composite channels, in which the cover presents a polyethylene (PE) adhesive layer. Capillary zone electrophoresis in both homogeneous and composite microanalytical devices were then performed and compared in order to evaluate the separation efficiency. In preliminary experiments, a plate height of 0.6 microm has been obtained with homogenous microchannels. The surface analysis pointed out that the surface chemistry is of prime importance for the performance of microfluidic separation.     

Effect of polymer surface morphology on adhesion and adhesive joint strength. II. FEP Teflon and nylon 6

Heterogeneous nucleation and crystallization of FEP Teflon and nylon 6 melts against high energy surfaces (i.e., gold) produce an interfacial region, in these polymers, of high mechanical strength. Dissolution of the metal substrate rather than removal by mechanical means results in a polymer surface which is amenable to conventional structural adhesive bonding. Nucleation and crystallization of the polymer melts in contact with phases of low surface energy (e.g., vapor) result in the generation of weak boundary layers.     

Application of the Scanning Kelvin Probe for the study of the corrosion resistance of interfacial thin organosilane films at adhesive/metal interfaces

The Scanning Kelvin Probe is introduced as a real time non-destructive in situ technique for the detection of de-adhesion at adhesive/metal oxide interfaces. Iron substrates and an epoxy adhesive served as model systems. Iron surfaces were coated with ultra-thin organosilane plasma polymer films from a microwave discharge and 3-(trimethoxysilyl)-propylamine films from dilute water based solutions. Surface and film characterisation was done by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS). The effect of these interfacial films on the stability of the adhesive/metal joint was studied in corrosive environments. The Scanning Kelvin Probe allows the measurement of electrode potentials at buried polymer/metal interfaces with a spatial resolution of about 100 m. The electrode potential characterises the reactivity of the interface. Moreover, by the variation of the oxygen partial pressure in the measurement chamber, local anodes and cathodes underneath the polymer can be distinguished. The kinetics of electrochemical de-adhesion can be effectively slowed down by thin 3-(trimethoxysilyl)-propylamine films at the interface. The effect of the adhesion promoter can be further improved when a thin SiO_x layer, which inhibits electron transfer reactions, and is deposited on the iron surface prior to coating with the adhesion promoter.This paper is dedicated to Mike Owen on occasion of his winning the DeBruyn medal, the first silicon chemist to do so.     

Photoinitiated polymerization on metal surfaces

Irradiation of acrolein vapors in the presence of films of nickel and other metals results in the formation of thin films of polyacrolein on the metal surface. The polyarcrolein film protects the metal surface from abrasion and corrosion. Polymer growth is more rapid on oxidized vs. unoxidized metal surfaces indicating a role for surface oxide sites in the polymerization process. Several other monomers investigated fail to form adhesive polymer films on metal films, but can be copolymerized with acrolein.     

Surface Energy and Adhesive Properties of Polyamide 12 Modified by Barrier and Radio-Frequency Discharge Plasma

Summary. The polyamide 12 foil with sufficient surface and adhesive properties to other substrates can be prepared by discharge plasma modification. For improvement of bonding and printing of polymer a surface barrier discharge plasma in N₂ and O₂ as well as a radio-frequency discharge plasma in air has been studied. A significant increase in surface energy of the polymer as well as in strength of adhesive joint to more polar polymer was found. The chemical changes of PA 12 modified by plasma were analyzed using fourier transform infra red – attenuated total reflection (FTIR–ATR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurements. The observed changes of surface properties of the polymer due to aging were not important.     

Surface Energy and Adhesive Properties of Polyamide 12 Modified by Barrier and Radio-Frequency Discharge Plasma

The polyamide 12 foil with sufficient surface and adhesive properties to other substrates can be prepared by discharge plasma modification. For improvement of bonding and printing of polymer a surface barrier discharge plasma in N₂ and O₂ as well as a radio-frequency discharge plasma in air has been studied. A significant increase in surface energy of the polymer as well as in strength of adhesive joint to more polar polymer was found. The chemical changes of PA 12 modified by plasma were analyzed using fourier transform infra red – attenuated total reflection (FTIR–ATR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurements. The observed changes of surface properties of the polymer due to aging were not important.     

The influence of processing in discharge with a closed drift of electrons on the adhesion properties and the strength of polymer adhesive joints

Results obtained in studying the influence of processing in gas-discharge plasma with a closed drift of electrons on the surface free energy of polymers (polyethylene terephthalate, polyvinylidene fluoride, polysulfone, and polyimide) and the strength of adhesive joints formed by polymer materials and adhesion of paint-and-lacquer coatings.     

Effect of Atomic Oxygen on the Surface Morphology of Polyethylene

The chemical species created in a low-pressure electrical discharge in oxygen attack the polymer at the surface, converting it to gaseous products. This process is interesting because: 1) the chemical changes on the resulting surface facilitate the formation of strong adhesive bonds and provide sites for the chemical attachment of other molecules, 2) significant morphological features lying below the surface may be revealed, 3) polymer can be cleanly removed from surfaces which are resistant to oxidation, and 4) dielectric breakdown frequently is preceded by the attack on the polymer of chemical species created in a corona discharge. Atomic oxygen is an important chemical species created in such a discharge. It reacts with organic substances rapidly at room temperature, but lives long enough in the low-pressure gas that it can be separated from many other reactive species created in the discharge. “Titration” with NO₂ provides a straightforward chemiluminescent means for determining the concentration of atomic oxygen to which the sample is exposed. This paper characterizes the attack of atomic oxygen, perhaps in the presence of long lived but less reactive species such as excited O₂molecules, on polymer surfaces, using electron microscopic observations of known morphological features of polyethylene to observe the changes produced by atomic oxygen. Lamellar polyethylene crystals were attacked both at the edges and the fold surfaces. Layers many microns thick were removed from spherulitic samples and replicas obtained from the surfaces thus exposed. Thick samples were thinned to the point at which they were transparent to an electron beam and interior morphological features were directly observed.     

Flame surface modification of polyethylene sheets

High density polyethylene sheets 2 mm thick were flame treated to modify the surface properties. Sheets treated using a flame with air to gas (methane) ratio ∼ 10:1 at different distances between the inner cone tip of the flame and the polymer surface were investigated. Grafting of selected monomers as maleic anhydride, acrylamide and glycidyl methacrylate was attempted by flame treatment of sheets covered with a monomer layer. Good grafting results were obtained with acrylamide and maleic anhydride. The surface temperature-time dependence during the flame treatment was measured with a high resolution thermocouple. Scanning Electron Microscopy (SEM) allowed evidencing a modified thickness of about 120 μ. The chemical surface modification was studied by X ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT). The hydroxyl, carbonyl and carboxyl content was measured after derivatization with reagents containing an elemental tag to facilitate XPS analysis of surface functional groups. In comparison to the untreated polyethylene, wetting tension and contact angle of the flamed materials showed a strong variation. This variation was almost independent of the distance between the flame and the polymer surface. Adhesion between treated polyethylene and a polyurethane adhesive was determined using T-peel test measurements. High adhesion levels were found with flame treated polyethylene at 5 mm distance. XPS results indicate that when adhesion is high, the hydroxyl is in excess compared to the other measured functions, i.e. carbonyl and carboxyl species.     

Characterisation of pure or coated metal surfaces with streaming potential measurements

In the field of corrosion prevention, the characterisation of metal surfaces is useful to obtain information about the necessary preparation of the surface and about the quality of thin coatings of coupling and protective agents. Electrokinetic measurements can be used to determine the properties of modified polymer surfaces, metal sheets, and different surface preparations. However, it was necessary first to create special conditions for measuring the streaming potential, such as electrical isolation of the sample sheets together with the use of inert systems, as shown by the example of aluminium. According to the usual procedure the metal was first coated with a thin layer of a coupling agent. The effect of this adhesive agent depends on the degree of its adsorption by the metal surface. The quality of this layer can be characterised by streaming potential measurements, which can show the degree of coverage, the adhesive strength of the coated layer, and the effective chemical properties of the treated surface. These results were confirmed by wetting measurements. The production of surfaces which allow us to couple a coating varnish to the adhesive agent in good quality was demonstrated. Received: 24 June 1996 / Revised: 30 January 1997 / Accepted: 30 January 1997     

过硫酸铵水溶液对聚乙烯表面作用的研究

本文利用X光电子能谱(XPS)及其它技术对过硫酸铵水溶液处理聚乙烯表面改进粘合性的作用机理进行了研究。结果表明,过硫酸铵的氧化作用使聚乙烯表面引入酮、醛、羧基等含氧基团,使其粘合强度显著提高。高密度聚乙烯表面的氧化深度小于40,低密度聚乙烯的均匀氧化深度在40—90之间。处理后的聚乙烯表面未发现明显的交联产物。     

Mechanical and morphological investigations of UHMWPE/Fe composites

Ultra-high molecular weight polyethylene/iron composites were investigated. The specimens were obtained by pressing in a steel die and sintering at different temperatures. By means of porosimetry, microscopy, microhardness, density, and partial volumes of the components it is shown that there are no microcavities. The microhardness does not depend upon the weight % content of the metal in the composites. It also neither depends on the pressure nor the temperature of sintering. For low metal content within the composites, microhardness Mayer equations are linear. For high metal content the dependence is nonlinear. With the increasing of the iron content tensile strength weakly decreases. However, plane-strain compression, dimension steadiness, Vicat softening temperature, and tribometric characteristics of the composites are improved. It is shown that the polymer is a well-dispersive medium. The particles of the components have a good mechanical compatibility. The polymer wets the surface of the iron; this is probably connected with the surface oxidation of the metal particles.     

Adhesive properties of plasma-modified polytetrafluoroethylene films

A procedure was developed for the determination of the adhesion characteristics of the modified surface of thin polymer films, including those treated in a low-temperature plasma, with the use of the Scotch® 810 adhesive tape. The procedure comprises coating the surface to be studied by physical vapor deposition with an aluminum layer of ～100 nm thickness, making an adhesive joint of the film with the Scotch® 810 tape, and T-peel testing of the specimen. Using this procedure, the peel resistance of the initial PTFE film and the film modified at the cathode and the anode in dc discharge was measured.     

Polymer surface science

Molecular level studies of the structure and mechanical properties of polymer surfaces have been carried out by sum frequency generation (SFG) surface vibrational spectroscopy and atomic force microscopy (AFM). The surfaces of different grades of polyethylene and polypropylene have been characterized-including during the glass transition and when mechanically stretched. Copolymers that have hard and soft segments with different glass transition temperatures show phase separation, an effect of hydrogen bonding between the hard and soft segments, that influences their adhesive and friction properties. AFM and SFG show that low surface energy additives migrate to the surface and alter the surface mechanical properties. Polymers, where the chemical nature of the end groups is different from the backbone, show surface segregation of the hydrophobic part of the chain in air and the hydrophilic part in water. Likewise, in miscible polymer blends, surface segregation of the more hydrophobic component in air and the more hydrophilic component in water is observed. This area of surface science requires increased attention because of the predominance of polymers as structural materials and as biomaterials.     

Study of physicochemical interactions in metal–polymer systems

This article deals with the investigation of adhesive joints of unlike metals separated by layers of thermoplastics. Experimental data are presented on electrical conductivity of polymers at temperatures of 333–573 K in the electric field of 1–10² V/cm. Infrared (IR) spectroscopy data have been used to establish correlation between the parameters of the voltage generated on the metal–polymer specimens and the existence of groups that can form hydrogen bonds. Adhesive strength of the adhesive joints is discussed in connection with the performance of a metal–polymer–metal voltaic couple when the adhesive joints are being formed. The results presented allow a conclusion that polymeric dielectrics exhibit properties of electrolytes when heated in contact with metals. Therefore electrochemical interactions between components of metal–polymer systems should be taken into consideration when predictions are made of performance characteristics of industrial materials based on polymers and metals.     

Influence of colloidal structure of polymer mixes on adhesion strength of polyolefin compositions

Mixtures of low-density polyethylene and ethylene-vinyl acetate (EVA) copolymer are studied. It is shown that the adhesion value is defined by the polymer that forms a dispersion medium in the adhesive compositions and the type of fracture depends on the competing influence of the physical and mechanical parameters and the reduced acidity parameter of the polymer, which forms a continuous phase.     

Planarizing surface topography by polymer adhesion to water-soluble templates with replicated null pattern

Water-soluble polymer templates are replicated from flat master surface patterns by spin-casting a poly(vinyl alcohol) film-forming solution that solidifies at standard ambient conditions in less than 1 min. The fabricated water-soluble templates are coupled to substrates with surface topography by polymer adhesion with an intervening reactive or photocurable liquid layer. After curing, the resulting two-layer solid structure is subjected to water thereby dissolving the soluble template to expose the underlying polymer adhesive layer with flat surface topography. The results demonstrate a reduction of surface topography from several micrometers to less than 100 nm. The chemical interactions involved in bonding the soluble template to the polymer adhesive and then dissolving are measured by Raman spectroscopy to demonstrate that the constituents comprising the water-soluble template are absent from the surface of the planarization material.