An investigation of the surface by XPS photoelectron spectroscopy has shown that the process of production of cast contact lenses based on poly(2-hydroxyethyl methacrylateco-diethyleneglycol methacrylate) is accompanied by mass transfer at the lens-mold boundary. This phenomenon, which impairs the compatibility of the lens during its application, can be considerably suppressed by employing a suitable surface modification of polypropylene molds. The surface treatment consisting in the oxidation of the mold surface by an AC corona discharge in the oxygen atmosphere increased hydrophilicity of the material, thus facilitating separation of the lens from the mold. The results of the XPS study were also confirmed microscopically by employing the SEM method. © 1992 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/jab.770030406

During the past decade polylactide acid (PLA) polymer has been the subject of numerous researches aimed at comparing it with traditional petroleum based polymers for many packaging applications. PLA is biodegradable and derived from agricultural by-products such as corn starch or other starch-rich substances like maize, sugar or wheat.While PLA is currently being used in many packaging applications with well documented performance, little work has been done comparing printing processes and performance. This study presents PLA printing performance and sustainability findings using the common flexography printing process. Various analytical methods were used to evaluate performance and provide recommendations for optimized printing on PLA as compared to PET, oriented PP and oriented PS. Results of this study found that PLA films were comparable in printability and runnability to standard petroleum based flexible packaging films.

This paper, as the title underlines, will be focused on flame treatment technology applications, mainly on BOPP substrates.

After an introduction regarding flame chemistry and BOPP surface activation mechanisms, this paper will be focused on unique flame treatment oxidation performances, in comparison with other treatment methods actually used in the market.

Focus will then be moved to the characteristics and advantages of using flame treatment for film surface treatment. In particular, a comparison will be run with other surface treatment technologies (corona surface treatment and atmospheric plasma treatment) in terms of:

• q surface energy after treatment;
• surface oxidation mechanisms and chemical species involved;
• quantity of oxygen on treated surface (oxidation level);
• quality of oxygen on treated surface;
• adhesion;
• printability/print quality.

Typical and new applications of flame treatment will be presented, underlining benefits coming from flame usage for pretreating different types of skins. Finally, the paper will try to make rid of prejudices and misinformation concerning flame treatment process applications, especially to certain kind of webs and substrates.

Ti films were deposited onto high‐density polyethylene (HDPE) samples by electron‐beam evaporation. Prior to film deposition the samples were in situ pretreated by Ar ion bombardment using a sputter ion gun. The adhesion of the films, determined as the pull strength required for film failure, was measured as a function of ion dose. HDPE substrates processed at two different temperatures were examined. The adhesion of the Ti films to HDPE samples processed at ≊150 °C increased with the ion dose to a steady‐state value corresponding to the cohesive strength of the HDPE substrate. The adhesion to the samples processed at ≊200°C increased to a maximum and then decreased for further ion bombardment to a level of the same order as that for films deposited onto as‐prepared samples. The effects of the ion bombardment upon the HDPE surface chemistry were examined by means of x‐ray photoelectron spectroscopy (XPS). The ion bombardment resulted in dehydrogenation and cross linking of the surface region and for prolonged ion bombardment, a graphitelike surface was obtained. The film/substrate interface as well as the initial Ti film growth were examined by XPS analysis. A chemical interaction which resulted in Ti–C bonds was observed at the interface. The Ti film growth followed a pronounced three‐dimensional growth mode on as‐prepared surfaces whereas the ion bombardment resulted in a change toward a more two‐dimensional growth mode. The difference in adhesion behavior for the two types of HDPE substrates was found to be due to a difference in the amounts of low molecular weight products present within the substrates. The HDPE substrates processed at ≊200°C contained larger amounts of low molecular weight products and also had a lower degree of crystallinity and a less closely packed structure compared to those substrates processed at ≊150°C. This resulted in a segregation of low molecular weight products towards the surface of substrates processed at ∼200 °C. This segregation in turn is suggested to lead to a weak boundary layer, reducing the adhesion to as‐prepared samples and to substrates exposed to a high ion dose.

The wetting of cylindrical monofilaments by liquid polymers is a problem of much scientific and technological importance. In particular, the characterization of the physicochemical nature of interfaces is a key problem in the field of advanced fibrous composites. The macroscopic regime contact angle, which reflects the energetics of wetting at the solid-liquid interface, is difficult to measure by usual methods in the case of very thin cylindrical fibers.

In the present article a numerical method is proposed for the calculation of macroscopic regime contact angles from the shape of a liquid droplet spread onto a cylindrical monofilament. This method, which builds on earlier theoretical treatments by Yamaki and Katayama [1], and Carroll [2], very much improve the accuracy of the contact angle obtained. Experimental results with high-strength carbon, para-aramid, and glass fibers, are presented to demonstrate the high degree of accuracy of the method proposed.

The interfaces formed by evaporating copper, nickel, and chromium layers on polystyrene, polyvinyl alcohol, polyethylene oxide, polyvinyl methyl ether, polyvinyl acetate, and polymethyl methacrylate have been studied with x‐ray photoemission spectroscopy (XPS). The adhesion strengths of the metal films to the polymers were measured by a tensile‐pull test. At submonolayer coverages of the metals, the peak positions and widths of the metallic electron core levels measured with XPS vary significantly from one polymer substrate to another. Most of these variations can be accounted for in terms of changes in the atomic and extra‐atomic relaxation energies during the photoemission process. Much of this change is brought about when the metal atom deposited on an oxygen‐containing polymer interacts with the substrate oxygen and forms a metal‐oxygen‐polymer complex. The presence of this complex is verified by changes in the photoemission lineshapes of the substrate carbon and oxygen atoms. The XPS signatures of these various complexes are quite similar and suggest that they are chelate‐like complexes. The adhesion strength of any metal on an oxygen‐containing polymer is greater than on the oxygen‐free polystyrene. In general, the increased adhesion strength correlates with the presence of the metal‐oxygen chelate complexes.

The effect of ion implantation including ion species (N₂ and C₃H₈⁺) and the fluences (1x10¹⁴-5x10¹⁵ ions/cm²) on the surface energy of ultrahigh molecular weight polyethylene (UHMWPE) were investigated. The total surface energy increases significantly after implanting with the fluence of 1x10¹⁴ ions/cm² regardless of ion species, then, the total surface energy slightly increases for N₂⁺ implanted UHMWPE and decreases slightly for C₃H₈⁺ implanted UHMWPE with a further increase of fluence. The structural changes of UHMWPE with different fluence for different ion species are very similar. The linear chains of UHMWPE are damaged and cross linking is generated after implantation. As the fluence increases, the polymer surface becomes more disordered, and the surface becomes hydrogenated amorphous carbon when the fluence exceeds 1x10¹⁵ ions/cm². The surface roughness increases with the increase of the fluence regardless of ion implantation species.

This paper presents and discusses particle behavior at solidification fronts from a thermodynamic point of view. Engulfing or rejection of particles embedded in a melt by solidification fronts depends on whether such quantities as the free energy of adhesion or of engulfing are positive or negative. As the relevant energy balances contain solid‐liquid interfacial tensions which are difficult to determine, these studies may also be viewed as tests for the validity of such data and the underlying theories used to determine them. In this paper, solid‐liquid interfacial tensions are derived from contact angle data and the equation of state approach for interfacial tensions [Neumann et al., J. Colloid Interface Sci. 49, 291 (1974)]. The thermodynamic predictions obtained in this way for approximately 60 systems agree very well with microscopic observations with particles in the range of 10–200 mm in diameter.

A triode glow discharge system was used for the plasma treatment of polytetrafluoroethylene (PTFE) films and the formation of plasma polymerized hexamethyldisiloxane (PPHMDS) films on PTFE films. The nitrogen plasma increased the surface tension of the PTFE films to about 40 dyn/cm by applying an rf voltage to the substrate electrode. The contact angle of water on the PPHMDS films with the rf voltage was changed to 40°∼90° by corona discharge exposure for 30 s at 6 kV. This reduction is due to the decarbonization and the oxidation of PPHMDS films.

Experimental results on plasma treatments of polysulfone and polyetherimide to improve the wettability of these polymers are presented. The plasma is characterized by optical emission spectroscopy. The wettability of the polymer surfaces were checked by contact angle measurements and ESCA is used to compare the surfaces before and after plasma treatment. Correlations between contact angle, concentration of oxygen at the surface, and optical emission intensity of the OH radical have been established. Optimization of operational plasma parameters leading to the best wettability of the treated samples is reported.

Polypropylene–nylon 6 10 composites were prepared by the in situ polymerization of the nylon monomers on polypropylene films. The adhesion between the nylon and the polypropylene was markedly improved by a brief corona discharge treatment of the films in nitrogen prior to coating. This improvement was demonstrated by an increase in the peel strength of the nylon coating and a decrease in brittleness of photo-oxidized compesites when corona treatment was used. Adhesive bonding between the nylon and substrate was sufficiently strong to cause cohesive failure in the corona-treated polypropylene. Only interfacial failure was observed at untreated surfaces. These effects were demonstrated by electron microscopy of the surfaces produced in peel tests. The effects of corona treatment on adhesive bonding characteristics of surfaces are discussed in terms of the chemical and physical changes observed in treated surfaces.

The effect of a remote nitrogen plasma on polyethylene and polystyrene was studied. The gas flow rate, the dilution of reactant gas, exposure times, and reactor base pressure were all found to have a large impact on the efficiency of nitrogen incorporation. Optimum conditions caused 18 atom % nitrogen to be incorporated within 20 seconds for polyethylene and 10 seconds for polystyrene. Studying a remote nitrogen plasma treated polyethylene sample over a period of 1 month indicated that except for a drop in the % N on initial exposure to air the concentration of nitrogen on the surface remained steady within the experimental limits. Angle resolved photoelectron spectroscopy indicated that nitrogen is incorporated to a depth below the analysis depth of XPS.

The use of plasma deposition to introduce sulfonate groups to the surface of a polyurethane was attempted. In previous work, the bulk incorporation of sulfonate groups was found to improve the blood contacting properties of the base polyurethane but physical properties in the hydrated state were adversely affected. Plasma deposition schemes involving ammonia and sulfur dioxide were utilized in an attempt to incorporate sulfonate groups. Surface characterization by X-ray photoelectron spectroscopy (XPS) and contact angle measurements was used to follow polymer surface rearrangement dynamics and to address the issue of plasma chemistry specificity. Concerns of reaction specificity were alleviated by using the plasma as a pretreatment which is followed by a chemical surface derivatization.

The efficiency of different techniques of obtain improved adhesion in polyethylene-aluminum laminates have been studied. Both surface treatments, such as thermal oxidation and corona discharge, and the use of copolymers with polar comonomers, i.e., vinyl acetate (EVA) and butyl acrylate (EBA), have been included. Thermal oxidation performed by high temperature extrusion including an ozone shower seems to be more effective than corona discharge. In a model experiment thermal oxidation was studied in more detail. The adhesion, as measured by a T-peel test, increased with the content of carbonyl measured by reflexion IR, except for relatively long thermal treatments. In the latter case molecular scission gave a large fraction of low molecular weight material with low cohesive strength. For EBA and EVA the peel strength increased linearly with the bulk concentration of comonomer from about 100 N/m for untreated polyethylene to 450 and 300 N/m, respectively, at 5 mol % comonomer. Corona discharge treatment of these copolymers had, however, a most remarkable effect on the adhesion properties. The increases, relative to untreated EBA and EVA, were much more dramatic compared to polyethylene, e.g., three to four and less than two times, respectively. The higher values obtained with EBA are suggested to be due to the conversion of acrylate groups into carboxylic acid. In the case of EVA, loss of acetic acid might instead decrease the content of polar groups.

Polymers formed from plasma-polymerized methane were employed to modify the surface properties of silicone rubber membrane. Polymers were evaluated based on the energy input parameter W/FM, where W is the discharge power, F is the monomer flow rate, and M is the molecular weight of the monomer. Dealing with the characteristics of plasma polymerization and the deposited polymer film, the effect of pumping rate on deposition rate and the coating thickness, surface energy, and gas permeabilities of methane-plasma-polymer-coated silicone rubber membrane were investigated in three plasma regions. Because more reactive species are expelled at high pumping rates, the monomer-deficient region is reached at lower W/FM in the high pumping rate system than that in the low pumping rate system. The composite parameter W/FM had a strong influence on coating thickness, gas permeability, surface energy, and the polar component of the surface energy but little effect on its dispersion component. Examination of gas permeabilities indicated that coating thickness was another important controlling factor on the properties of plasma polymer.

Surface graft polymerization of a hydrophobic monomer, 2,2,3,3,3-pentafluoropropyl methacrylate (5FMA), onto hydrophilic poly(vinyl alcohol) (PVA) and cellulose films was studied after corona discharge of the films. It was found that grafting strongly depended on the reaction medium; especially, addition of alcohol to the monomer greatly accelerated graft polymerization. For instance, when an ethanol/ water /5FMA mixture (65/25/10, by volume) was used as the polymerization medium. the PVA and cellulose films corona-discharged for a few minutes exhibited a high contact angle up to 100° after 30 min polymerization, the graft density being approximately 170 μg/cm² for cellulose and 80 μg/cm² for PVA. © 1993 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1993.070481016

To draw a relationship between surface concentration of the siloxane segment and adhesion performance, surface properties of the polydimethylsiloxane—poly(methyl methacrylate) block copolymers(PDMS-b-PMMA) prepared via poly(azo-containing siloxaneamide)s and their PMMA blends have been studied by measurements of FT-IR spectra, water contact angle, ESCA spectra and 180° peel strength toward pressure-sensitive adhesive tape. The water contact angles of the chloroform-cast blend films increased abruptly with siloxane bulk concentrations, or siloxane contents, particularly, on the air-side surfaces to reach almost 100° in low siloxane content. A marked increase of the contact angle was observed in the blends containing siloxane chain length (SCL) of longer than 2000. ESCA data evidently confirmed for these blend systems that the siloxane segments with low surface energy were accumulated or enriched mainly on the air-side surface, and that, on the other hand, polar PMMA segments with high surface energy were oriented to the glass-side surface and the inside of the films. This surface accumulation behavior of the siloxane segments reflected the 180° peel strength, as a measure of adhesion performance. The water contact angle and 180° peel strength were unequivocally correlated to the siloxane surface concentration estimated from ESCA data. Conversely, in the compression-molded blend films made by a hydraulic press between a Teflon and a stainless steel plate, the extent of surface accumulation of the PDMS segment was lower than that of the chloroform-cast films, suggesting lower degree of segment migration in hot-press films, probably due to substrate surface energy and lower relaxation in the blend melts.

Polypropylene films were treated with chromic acid mixture. The change in the treated films was investigated by comparing change in amount of 2,4-dinitrophenylhydrazones formed in the treated films with their change in wettability with water. Oxidation of the film surface zone, partial breakdown of polymer in the film surface zone, and oxidation of surface zone bared from the film inner zone seemed to occur with increase in treatment time or with increase in treatment temperature.

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.

If a low-density polyethylene sheet is treated in a corona discharge and subsequently pressed to a similarly treated sheet at 45°C, the bond formed is much stronger than that between similarly pressed but untreated sheets. Several series of observations have indicated that this enhanced autohesion is not due to surface oxidation or to surface crosslinking (CASING). Evidence is presented that the effect may be related to some type of electret formation induced in the polymer sheet by the corona discharge.

A geometric method proposed by Kaelble and Moacanin for analyzing energetic characteristics of solid surfaces is discussed. It is shown that a number of characteristics can be presented in a visual geometric form. The method is applied to the analysis of adhesion in a three-component system. Results of the analysis, concerned with the problem of creation of biocompatible materials, support the Andrade hypothesis that materials with zero interfacial tension of their water–solid interface show maximum biocompatibility. Data are obtained on wetting of polyethylene by different liquids before and after glow discharge plasma treatment. The analysis of these data in terms of geometric method shows the plasma treatment increased the polar component of the polymer surface energy to change the surface adhesiveness toward probable enhancement of polymer biocompatibility. That is consistent with available data on glow-discharge-treatment enhancement of biocompatibility for a number of polymers. © 1993 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1993.070470705

Corona discharge (CD) treated polyethylene films were examined using X-ray photoelectron spectroscopy (XPS) and a variety of chemical derivatization techniques. The composition of the CD-treated surfaces were found to be relatively unaffected by aging at temperatures between 70 and 80°F. Ink adhesion testing of films treated under progressively more serve conditions indicated the efficiency of adhesion varied directly with the severity of treatment. Derivatization of CDtreated polyethylene films with pentaflurophenylhydrazine (PFPH) resulted in the formation of a stable hydrazone complex. The PFPH complex extends the detection limit for enolizable carbonyl groups ca. eight-fold and provides relative quantitation of the number of these groups on variously treated polyethylenes. Formation of the hydrazone complex destroyed ink adhesion, indicating that the complex had blocked the site responsible for chemical bonding to the ink. Adhesion of water-soluble printing inks to CD-treated polyethylene is a direct consequence of hydrogen bonding between enolic hydroxyls on the polymer surface and carbonyl groups of the ink.

Characterization of poly(ethylene terephthalate) (PET) films surfaces through wettability measurements and inverse gas chromatography techniques leads to a better knowledge of the potential interactions with a coating. An important case is the one relative to gelatin coatings for photographic films. In order to favor adhesion on PET, it is of interest to examine the problem in terms of acid–base interactions. PET is found amphoteric and gelatin rather basic. Several surface treatments on PET like orientation on water and flame or plasma treatment in air lead to an increase in surface acidity. Adhesion with gelatin as determined by the peel test is increased through a flame treatment, because of the higher acidity of PET and subsequent chemical bonding at the interface. Determination of acid-base surface properties of PET and gelatin appears to be an excellent tool for adhesion prediction.

The adhesion between a polymer and a solid substrate may be considered to be one type of complex liquid-solid interaction. Relationships between surface wettability and bulk properties of liquidlike polymers are discussed. A new and direct empirical relationship between the glass temperature (T_g) and critical surface tension of a polymer (γ_c) is established:

Coating of polyethylene (PE), poly(vinyl fluoride) (PVF), poly(tetrafluoroethylene) (PTFE), and poly(vinyl chloride) (PVC) films with flow discharge-polymerized acetylene was investigated. The influence of glow discharge experimental conditions on the nature of the coated layer, the films' wettability, surface roughness, and adhesive joint strength was determined. It was found that coating of these films with plasma-polymerized acetylene led to the formation of a rough, crosslinked, irremovable layer with an improved wettability. The presence of the plasma-polymerized acetylene on the film surface lead to a large improvement in the adhesive joint strength of these films with epoxy adhesive. Best results were obtained with films coated at a low acetylene flow rate. Increase in glow discharge power and treatment time lead to a further improvement.

Oxygen plasma treatment of polypropylene (PP) surfaces led to introduction of oxygencontaining functionalities, with consequent improvement of surface wettability. A combination of X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectroscopy (SSIMS), and contact angle measurements (water-in-air and air-in-water) allowed us to characterize the behavior of the treated surface in contact with air (low-energy surface) and water (high-energy surface).

The treated surface showed the tendency to rearrange itself to minimize its interfacial energy. When contacted with air (low-energy surface), polar groups were buried away from the polymer/air interface, while in contact with water (high-energy surface) polar groups remained at the polymer/water interface.

When contacted with air, the polymer surface layer rearranged by macromolecular motions within itself, since interdiffusion with the bulk polymer seems forbidden. These motions are thermally activated and it was possible to obtain an apparent activation energy (58.1 kJ/mol) close to those reported for other vinyl polymers.

XPS, SEM, SSIMS, FTIR-ATR, water-in-air, and air-in-water contact angle measurements have been used to unambiguously characterize the locus of failure of PP/epoxy joints. In the case of untreated PP, the fracture has been found adhesive, whereas in oxygen plasmatreated PP, it is cohesive, within bulk PP, but close to the modified PP-bulk PP interface. The smoothness of fracture surfaces allowed us to exclude mechanical interlocking effects. Shear-strength measurements showed that the mechanical strength of the joint was improved by plasma treatment. Preliminary thermal equilibration of the plasma-treated PP sample and changes in the curing cycle of the epoxy resin did not change either the locus of failure or the shear strength of the joint. The reason is probably because the number of polar functions left at the surface after thermal equilibration is sufficient to induce adhesion. The mechanical strength of the PP surface layer may be the determining factor. Fracture energy calculations showed that the observed locus of failure is the same as predicted on the basis of surface energy considerations.

Peroxides formed on the surface by corona treatment of low-density polyethylene film can be used to initiate grafting of polar vinyl monomers such as acrylic acid. Different types of peroxides are probably formed on the surface, but at least hydroperoxides could be detected by XPS analysis. The grafting reaction was carried out directly after corona treatment, by placing the corona-treated film above a solution of acrylic acid heated to 100°C. The grafting reaction takes place in a vapor phase of the monomer. After extracting the reacted films with hot methanol and drying, surface analysis by XPS, IR, and contact angle measurements were carried out. Effect of degree of corona treatment and reaction time have been studied. The conclusion from this work is that acrylic acid in vapor phase can successfully be grafted onto corona-treated polyethylene film by this method. © 1992 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1992.070460916

Irradiation of polystyrene by 15 Mrad gamma or exposure to a 254 nm ultraviolet (UV) light source leads to surface oxidation of the polymer to depths greater than 10 nm as opposed to ∼ 3 nm depth offered by either plasma or corona-discharge treatment. Oxidation increases linearly with UV irradiation time. More carboxyl (OCO) acid functionality, which increases with depth, was detected for UV-treated polymer. With 3 Mrad gamma irradiation, only hydroxyl (CC) groups were detected by XPS as the surface-oxidized species. ADXPS, GPC, and static SIMS data suggest that chain scission is the dominant degradation mechanism for polystyrene exposed to high gamma and UV radiation, respectively. © 1993 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1993.070471213

A method for measuring the surface energy of solids and for resolving the surface energy into contributions from dispersion and dipole-hydrogen bonding forces has been developed. It is based on the measurement of contact angles with water and methylene iodide. Good agreement has been obtained with the more laborious γ_c method. Evidence for a finite value of liquid-solid interfacial tension at zero contact angle is presented. The method is especially applicable to the surface characterization of polymers.

Corona-treated polyethylene films have been reported to exhibit strong self-adhesion when joined together under conditions of heat and pressure that give no adhesion with untreated films. The present study of this effect has shown that the adhesion is completely destroyed by the application of any hydrogen-bonding liquid to the adhesive joint and that the effects of liquids is completely reversible. Joints allowed to dry recover full strength. These facts together with the results of chemical reactions conducted on the treated film surface have established that the adhesive bond is a hydrogen bond. Corona treatment forms keto groups on the polyethylene chain; these groups enolize and the enolic hydrogens bond with carbonyl groups in the adjacent sheet of film when two sheets are heated together under pressure.

The ability of corona treatment to render polyethylene film self-adherent has been previously reported and the mechanism explained. A similar effect has now been found with corona-treated poly(ethylene terephthalate) film which adheres strongly to itself when joined under conditions of heat and pressure that give no adhesion with untreated film. Poly(ethylene terephthalate) films irradiated with short-wave UV light also become self-adherent. The behavior of the adhesive joints in both cases is the same as that reported for corona-treated polythylene film in that the joint strength is zero in the presence of hydrogen-bonding liquids, but recovers completely if the joint is allowed to dry undisturbed. Chemical and physical tests have shown that the adhesive bond is a hydrogen bond between the hydrogens of phenol groups created by corona or UV irradiation in one surface with carboxyl carbonyl groups in the other surface. Thin-layer chromatography of surface extracts from corona- and UV-treated films has shown the products of treatment to be practically identical for both types of treatment, supporting the conclusion that the mechanism of corona treatment resembles that of greatly accelerated photo-oxidation.

It was found that the treatment of the surfaces of wet pulp sheets (moisture content; up to 85%) in a corona discharge improved greatly the plybond strength of the paperboard obtained when the treated wet pulp sheets were laminated together, pressed, and then dried. Treatment was carried out by use of a corona apparatus which had variable driven roll electrodes for transporting the wet pulp sheets through a corona field and was attached to a high-voltage generator (∼ max 500 W, ∼ 16 kV at 5 kHz). The plybond strengths of the paperboards were examined by means of Tappi RC-273 and JIS P8139 methods. Some experiments regarding the chemical effects of the corona treatment on the surface modification of wet pulp sheets were made with the aid of dye adsorption methods. Both untreated and corona-treated pulps adsorbed basic dyes, methylene blue, etc., with the same extent of dyeing. This indicates that no measurable acidic sites (carboxyl groups) increased on the surfaces of the pulp sheets during the corona treatment. To detect aldehyde groups, the dyeing examination of the pulps with Schiff's reagent was made, and the results showed a higher dyeing ability for the corona-treated pulps compared to the untreated, indicating that aldehyde groups on the pulp surfaces increased with an increase in the degree of corona treatment. The corona treatment seems to produce on the surface layer lightly oxidized and fairly degraded polysaccharide chains, which will tend to swell in water and thus act as an adhesive in plybonding the pulp sheets.

Oxidative activation of resinous wood surfaces by a corona treatment to improve adhesive bonding was studied. It was found that the wettability of the veneers, including hardwoods, softwoods, and tropical woods increased with an increase in the degree of treatment, and the gluability increased rapidly after the initial mild treatment. To elucidate the nature of any chemical change occurring on the wood surface, the dyeing examination of the wood and its components with Schiff's reagent was made, and the results showed a higher dyeing ability for corona-treated samples compared to untreated ones, indicating that aldehyde groups increased by the corona treatment. The treatment affected the alcohol-benzene extractives, and oxidized them to produce aldehyde groups. Especially, the neutral fraction in the extractives was significantly affected. On the other hand, negligible chemical effects of the treatment on the surface modification of the wood's main components were seen. Both the untreated and corona-treated samples adsorbed basic dye to the same extent of coloration. Thus, no measurable carboxyl groups increased on the surface of the samples. It seems that an increase in the wettability of corona-treated wood veneers resulted mainly from the oxidation of the high hydrophobic surface layer of neutral fraction substances in the extractives, and from the reduction in their hydrophobicity. © 1993 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1993.070490714

Further studies of a new and highly effective method for the surface treatment of low surface energy polymers for adhesive bonding are reported. Mechanisms are suggested for the increase in the cohesive strength in the surface region of polyethylene when it is exposed to activated species of inert gases. The technique is unique because, in contrast with results obtained with other methods, bulk properties of the polymer such as color or tensile strength and elongation are unaffected and surface properties such as wettability and dielectric properties such as surface conductivity are essentially unchanged.

An effective surface treatment for adhesive bonding of polyethylene has been developed. It involves exposing the polymer to an environment of elemental fluorine or fluorine diluted in argon. By this treatment, extensive fluorination of the surface region is effected. The fluorinated surface permits formation of strong adhesive joints by conventional adhesive bonding techniques even though the wettability of the new surface is similar to polytetrafluoroethylene. We believe that treatment of the polymer with elemental fluorine effectively eliminates the weak boundary layer associated with polyethylene by either crosslinking or by increasing the molecular weight in the surface region.

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.

The surface contact angle of glycerol and of water on polystyrene (PS) films has been found to depend on the extent of uniaxial draw for atactic PS. The contact angle depends on direction for the smooth films of PS drawn by solid state coextrusion. Results as a function of draw ratio to values over 4 on these noncrystalline PS samples, M_w = 6 × 10⁵, have also been interrelated with other measures of orientation such as the anisotropy of surface and bulk properties measured, respectively, by dichroic reflectance infrared spectroscopy and by birefringence.

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.