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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.

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.

With increase in sample density, corona treatment was found to be decreasingly effective in enhancing the autohesion of polyethylene sheets. The effect of higher density could be offset in part by an increase in temperature of lamination. This parallel behaviour suggests that similar molecular mechanisms govern the phenomena of thermally-induced and corona-induced autohesion.

Corona treatment of films, mainly polypropylene (PP)-copolymers, was studied at commercial levels in a 2.7 kVA treater. The films were produced on a flat-film extruder with chill rolls. Degree of treatment was characterized by power of the generator divided by web speed and width of film (m Ws/cm2). The effectiveness of the treatment was measured in terms of the polar and dispersion components of surface-energy, the peel adhesion of pressure sensitive tape (similar to ASTM Adhesion Ratio) and the peel adhesion of polyurethane adhesives. The polar component of surface energy is a measure of the effectiveness of corona pretreatment. For a given degree of treatment, the polar surface energy component becomes greater as the film cooling rate increases (and the degree of crystallization falls). A comparison of homopolymers and copolymers does, however, reveal that even where these have the same density or the same degree of crystallization one cannot count on them having equally-sized polar components...

Moisture absorption, dielectric properties, and x-ray crystallinity of cellulose handsheets and deacetylated cellulose acetate films have been determined. The moisture absorption of the treated samples was lower than that of the controls. Further, the changes of the electrical properties of the treated samples agreed with the observed decrease in the moisture absorptions of the treated samples: no significant change in their crystallinity was noted.

A systematic study was made of seven common polyolefin resin stabilizers. Surface analysis techniques were used to characterize the surfaces of films containing these additives. Films were evaluated before and after corona treatment. Results of this study showed that a surprising number of additives are surface active. In some cases these additives have a dramatic effect on the surface chemistry produced by corona treatment, yet they do not affect subsequent ink adhesion. Conversely, an additive may not significantly affect the corona treatment chemistry but yet still reduce the adhesion performance of the film product.

Corona treatment of viscose–cotton blends enhances sliver tenacity and wettability. The effects depend on the degree of treatment, which increases with the corona power, the time in the corona, and the number of passages through the corona.

This work reports adhesion behaviour of polyethylene on paper, and deals with the surface energy of the materials involved in the manufacture of these composites, and its influence on the adhesion strength, at constant roughness, for the paper substrates. The surface energy of different papers treated with various sizing agents was determined by measuring contact angles according to the Owens-Wendt method. The peeling energy was shown to follow a linear relationship versus the reversible energy of adhesion. This result is explained by the fact that rupture takes place at the interface and that the size of the defect at the interface depends on the spreading coefficient. Corona treatment, applied to strongly sized papers before making the composites, restored the adhesion strength to its original range of values, again demonstrating the thermodynamic character of adhesion in thermoplastic-paper composites.

Polymeric films, chiefly polyethylenes, were subjected to corona-discharge treatment in a continuous treater at commercial rates in a program covering wide ranges of the main processing factors. Electron-spin-resonance measurements on freshly treated films found no free radicals. We studied the reactions of the treated surfaces with a free-radical compound, diphenyl picryl hydrazyl (DPPH), focusing mainly on the rate effects. The evidence indicates that corona treatment produces fairly stable peroxide structures of the forms RO/sub 2/R and RO/sub 3/R on polyethylene surfaces. RO/sub 3/R reacts rapidly with DPPH alone, while RO/sub 2/R undergoes a slower reaction after addition of the catalyst, triethylene diamine. DPPH is capable of detecting as few as 10/sup 13/ peroxide groups per square centimeter. Activation energies were 12 kcal/mole for the uncatalyzed reaction and 16 kcal/mole for the amine-catalyzed reaction. As with the physical effects reported earlier, the production of peroxides is most strongly dependent on the energy delivered to the film during treatment. This energy is proportional to the quotient of corona current and web speed, I/S. Regression analysis showed that air-gap thickness, relative humidity, and number of electrodes used also were significant factors, while dielectric thickness and corona frequence were not. We found that ..gamma../submore » S//sup P/, the polar component of surface energy of the treated film, which is nearly zero for untreated polyethylenes, is exponentially related to the concentrations of both RO/sub 2/R and RO/sub 2/R with a correlation coefficient for 92 specimens tested of 0.88.We believe this is the first strong evidence linking treatment factors, at commercial levels of treatment, to chemistry of the treated surface and linking both of those to changes in physical behavior of the surface.« less

Poly(ethylene terephthalate) (PET) Mylar® samples were treated by corona discharge in order to improve their adhesive properties. The corona treatments were performed in different atmospheres including nitrogen, ammonia and air. X-ray photoelectron spectroscopy (XPS) was used to investigate the chemical modifications induced at the PET surface by these corona treatments. XPS results show that nitrogen incorporation takes place in the form of non-oxygenated nitrogen functionalities, like amine or cyano groups. These are present at the surface of all the corona-treated samples but in different concentrations depending on the gases used in the corona discharge. Furthermore, XPS analyses performed after heating of the treated samples show a higher thermal stability of the corona-induced surface modifications in the case of nitrogen and ammonia. Ion scattering spectroscopy (ISS) and static secondary ion mass spectroscopy (SIMS) analyses were also performed because of their higher surface sensitivity compared with XPS: ISS reveals that nitrogen is not present at the topmost surface layer of the treated samples but is incorporated just beneath. The outermost surface layer presents a composition rich in oxygen. Finally, static SIMS spectra show that corona treatment induces more surface degradation when performed in air compared with nitrogen or ammonia. These results are discussed in relation to adhesive properties of PET.

In order to improve the adhesion of the electrodes which are most often vacuum-evaporated, the surface of the polypropylene film has been subjected to a high-pressure corona discharge at a frequency of the order of 10 kHz or higher. This type of surface treatment is very easily used and does not produce any transformation of the material for short expositions. In certain atmospheres and for longer exposition times, appreciable, and sometimes important, transformations of the dielectric characteristics appear. The evolution of these properties has been studied as a function of various corona discharge parameters, at a frequency of 50 Hz. This frequency, which is low compared with frequencies usually chosen, causes a slowing down of transformations which remains qualitatively identical. In order to establish a correlation between the species created by the discharge, the superficial and volume chemical transformations, and the dielectric properties of the material, several types of measurement were made: multi-internal reflectance (MIR) IR spectroscopy, the tan delta variations as a function of frequency and measurement of dielectric strength.

The resultant surface activation of polymers by corona discharges has been found to be markedly influenced by the type and purity of gases used in the corona. In this work it is shown that for the nitrogen gas corona treatment (15 KV, 15 mins) of polyethylene and polypropylene, traces of oxygen, >0.5% and

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 pilot-scale corona reactor was adapted to process cotton sliver. Corona treatment improved cotton spinnability and increased yarn and fabric strength and abrasion resistance. Treatment effectiveness was greatest at 93-96°C with the injection of dilute chlorine gas into the corona cell. Dyeability was unaltered, cotton wax was not removed or oxidized, and fiber hand was unaffected by air corona treatments. Slight harshening occured in air-chlorine corona treatments, but this can be overcome by a softener.

The chemical changes produced by brief corona treatments of polypropylene films have been studied by attenuated total reflection (a.t.r.) infrared spectroscopy. Surface layers of different thicknesses were investigated by varying the reflection conditions. Changes in the surface spectra were quantitatively compared by the use of an internal correction method which compensated for irreproducible experimental conditions. Corona treatment in a nitrogen atmosphere produced thin surface layers (less than 500 Å) of C—C unsaturation. Nitrogen derivatives were not detected in the surface. Corona treatment in oxygen caused surface changes which depended markedly on the corona conditions owing to the generation of ozone in the discharge zone. At low ozone concentrations, both unsaturation and oxidation were found in surface layers of under 500 Å thickness. At higher ozone concentrations, extensive oxidation occurred at appreciable depths into the polymer (several microns). An oxygen corona appears to result in essentially the same surface changes as does a nitrogen corona treatment, followed by exposure to ozone.

Corona treatment improved bonding between sheets of cellulose and synthetic polymers. The bond strength increased at higher temperatures of pressing. Physical changes in the surface were detected microscopically after corona treatment in air. Sheets treated in pure nitrogen made strong bonds although the surface treated in nitrogen was indistinguishable from the untreated surface.

"Frictionizing" textile fibers by corona treatment produces larger effects than conventional chemical methods. A marked increase in wool fiber friction occurs, both with and against the scales. For wool, the increase in with-scale fric tion decays slowly with time after treatment; against-scale friction does not. Initial cohesiveness of air-corona treated wool roving increases 230%, but then, reflecting the decay of with-scale single-fiber friction, decreases slowly with time toa residual cohesiveness 32% above that of untreated roving. Residual cohesiveness is responsible for improved wool yarn spinnability and tensile strength. Untreated mohair fiber friction is much less than that of untreated wool, but after corona treatment the friction values become comparable. However, treated mohair differs from treated wool in that its with-scale friction after treatment does not decrease. Increased mohair fiber cohesiveness improves yarn tensile strength 31% Injection of dilute chlorine gas into the reactor greatly reduces the required corona treatment time and indicates the feasihility of high-speed corona processing of mohair. Cotton roving cohesiveness is increased initially by chlorine-corona treatment to four times its original value, but then its cohesiveness diminishes much more rapidly than in the case of wool. The residual cohesiveness increases cotton yarn tensile strength by 24%. It appears that the very high cohesiveness of wool and cotton roving immediately after treat ment, if followed by immediate processing, can be used to further improve spinning beyond that achieved when treatment is followed by delayed processing.

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.

Corona treatment of various substrates in nitrogen was found to markedly improve the adhesion between the substrate and polymeric coatings which were subsequently applied by in situ polymerization of the appropriate monomers. Sub strates included films, fibers, and fabrics of polymers such as polypropylene, polyethylene, polyelhylene terephthalate, polytetrafluoroethylene, and Saran. Condensation polymers employed as coatings included polyamides, polyesters, poly- sulfonamides, and poiyureas. Other polymer coatings were also applied by anionic and cationic polymerization. Com posites prepared after corona treatment of the substrate were shown to have superior interfacial adhesion and abrasion and solvent resistance, compared with composites which had been prepared without corona treatment. Electron micro copy was used to demonstiate the difference between differently treated samples of films and fabrics. The good interfacial adhesion exhibited by coatings on corona-treated films, even after extensive elongation of the composites, indicated the possibility of preparing bicomponent fibers from coated substrates which fibrillate on drawing.

It has been shown by use of the Allwörden reaction that epicuticle of wool is still intact following corona discharge treatments in air and air/chlorine atmospheres in sliver form. The surface protein of keratin fibers after electrical dis charge treatments can, therefore, be isolated and investigated in a manner similar to that for virgin wool. That the Allwörden reaction depends on more than the conversion of cystine to cysteic acid in epicuticle is discussed. Corona treatment appears to be a method of increasing resistance to felting shrinkage without disrupting the epicuticle of a keratin fiber.

Variations in refractive index (density) with growth temperature are taken as a rough measure of residual compressive stress in dry SiO2 films. This paper presents experimental data regarding the relaxation of these stresses by a low-temperature (600–900°C) oxygen corona discharge process. For an initial oxide layer of 1100 Å thickness grown at 800°C, relaxation is complete after a corona treatment of 10 minutes at -lμA. The dose of O− ions required is found to be about 1–1.5% of the total oxygen atoms in the initial layer. The difference in dose between oxide on (111) and (100) Si is found to be proportional to the respective density changes from the initial oxide to fully relaxed oxide.

A mass-spectrometric study of negative ions, extracted through small orifice in a plane electrode, was carried out in flowing ambient air, having relative humidities within the range of 40% to 50% and pressures from 5 kPa to 30 kPa. The effect of distance between the point and plane electrodes, as well as the effect of discharge current, on the mass spectra has been investigated. A most important observation was the presence of cluster ions CO 3 −·(H 2 O). Other ions were also found mostly in cluster forms. An unknown cluster ion having e/m = 126 was found, in agreement with earlier reported experiments (de Vries, et. al.). The increase of electrode gap distance caused a reduction of O 3 −·(H 2 O). groups and an increase of O 3 −·(H 2 O) i groups of ions as Observed in the mass-spectra. The efficiency of corona treatment of polymer materials in air will also be discussed in relation to the obtained results.

Dispersion coating layers consisting of hydroxypropylated starch, 0–30 pph of barrier-grade talc and 0–10 pph of styrene-butadiene latex were subjected to both positive and negative direct-current corona treatments utilizing a specially developed dynamic treatment unit. The effects of the surface composition (barrier coating) on the response to the direct current corona treatment were evaluated by measuring contact angles and determining the surface energy. The effects of corona treatment on the properties of the barrier coating were further determined by measuring the contact angle of rapeseed oil and the grease resistance. It was found that the grease resistance of the corona-treated barrier coatings was substantially lower than that of untreated samples, which was ascribed to holes caused by corona discharge strike-through and to chemical changes on the treated surfaces. The corona treatment lowered the surface energy of the coatings, as indicated by an increase in the contact angles of water and rapeseed oil. Changes in the dispersion part of the surface energy were recorded, particularly after positive treatment voltage, whereas a negative discharge led to greater changes in the polar part of the surface energy. X-ray photoelectron spectroscopy (XPS) tests revealed an increase in the proportion of talc at the surface after corona treatment, which indicates a migration caused by the applied electric field. The peak force tapping mode of an atomic force microscope revealed moderate topographical changes in the coatings and a decrease in surface elasticity, supporting the migration of talc particles. In addition, significant changes in the physicochemical properties of the untreated reverse side were observed.

The interplay between capillary and viscous forces plays a significant role for optimal part quality in fiber-reinforced composites manufactured by Liquid Composite Molding (LCM); these are however difficult to analyze during flow. Two approaches are proposed in this study: (i) a woven glass fabric’s surface was modified by corona treatment to improve its wetting characteristics without altering its permeability, (ii) flow of a UV-curable resin was stopped during LCM by fast radiation cure. Capillary rise experiments and unsaturated/saturated permeability measurements confirmed the wetting improvement by corona treatment. Flow front morphology analysis of cured pristine and treated fabrics, processed under various pressure differentials, revealed the enhancement of dual-scale flow at capillary-dominated regime and improvement of intra-tow flow in viscous-dominated regime. Furthermore, the obtained results provide insight into the so-called optimal capillary number to attain the minimal void content in composites and its alteration by surface treatment of fiber reinforcements.

Superhydrophobic nanoparticle coating was created on the surface of board using liquid flame spray (LFS). The LFS coating was carried out continuously in ambient conditions without any additional hydrophobization steps. The contact angle of water (CAW) of ZrO2, Al2O3 and TiO2 coating was adjusted reversibly from >150° down to ~10−20° using different stimulation methods. From industrial point of view, the controlled surface wetting has been in focus for a long time because it defines the liquid-solid contact area, and furthermore can enhance the mechanical and chemical bonding on the interface between the liquid and the solid. The used stimulation methods included batch-type methods: artificial daylight illumination and heat treatment and roll-to-roll methods: corona, argon plasma, IR (infra red)- and UV (ultra violet)-treatments. On the contrary to batch-type methods, the adjustment and switching of wetting was done only in seconds or fraction of seconds using roll-to-roll stimulation methods. This is significant in the converting processes of board since they are usually continuous, high volume operations. In addition, the creation of microfluidic patterns on the surface of TiO2 coated board using simple photomasking and surface stimulation was demonstrated. This provides new advantages and possibilities, especially in the field of intelligent printing. Limited durability and poor repellency against low surface tension liquids are presently the main limitations of LFS coatings.

Corona treatment in air and air/chlorine atmospheres, does alter the wool fiber so it appears visually significantly more yellow than the untreated wool. The yellowness of wool after corona treatment, particularly that done in the presence of chlorine, may be reduced to the yellowness associated with non-corona treated, unbleached wool by scouring or solvent treatment. The amount of material extractable from wool is not greatly increased by corona treatment, suggesting that corona treatment is restricted to the surface layer of keratin fibers.