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The Influence of Flame, Corona and Atmospheric Plasma Treatments on Surface Properties and Digital Print Quality of Extrusion Coated Paper
Abstract
Polymer and paper structures have been successfully utilized in several fields, especially in the packaging industry. Together with barrier properties, printability is an important property in packaging applications. From the point of view of printing, the dense and impervious structure of extrusion coatings is challenging. Flame, corona and atmospheric plasma treatments were used to modify the surface of low density polyethylene (LDPE) and polypropylene (PP) and the influence of these surface modifications on print quality, i.e., toner adhesion and visual quality was studied. The traditional surface treatment methods, i.e., flame and corona treatments, increased the surface energy by introducing oxygen containing functional groups on the surfaces of LDPE and PP more than helium and argon plasma treatments. Only in the case of flame treatment, the higher surface energy and oxidation level led to better print quality, i.e., toner adhesion and visual quality, than the plasma treatments. The morphological changes observed on LDPE surface after flame treatment are partly responsible for the improved print quality. Atmospheric plasma treatments improved the print quality of LDPE and PP surfaces more than corona treatment. The electret phenomenon observed on LDPE and PP surfaces only after corona treatment is the most likely reason for the high print mottling and low visual quality of corona treated surface.
... Surface treatment is conducted in order to make functional groups with high binding capacity to create interaction and bonds with other functional groups. It may increase surface energy, introduce surface crosslinking, modify surface morphology by increasing or reducing its roughness and crystallinity, and remove dirt and weak boundary layers (Gooch, 2011;Tuominen et al., 2010;_ Zenkiewicz, 2008). Corona discharge may occur in air atmosphere or in an atmosphere of various inert or active gases. ...
... In the case of some polymer materials, low-molecular-weight oxidized materials (LMWOM) emerge on the upper layer. If it is not bound with the substrate permanently, then it may cause problems with adhesion and lead to problems with blocking during printing of the material (Brzezi nski et al., 2009;Chan, 1999;Kusano, 2014;Stepczy nska & _ Zenkiewicz, 2014;Tuominen et al., 2010). ...
... These oxidants in combination with free radicals, which are on the surface of the material, create oxidizing groups such as hydroxyl, carboxyl, carbonyl, and ester groups. Corona treatment effectively oxidizes thin layers of the material (Tuominen et al., 2010;_ Zenkiewicz, 2008). As a result of corona discharges, low-temperature plasma is created. ...
This chapter describes a method of polymer treatment with the use of corona discharge. This is the most common industrial method to improve the wettability of nonabsorbent printing substrate before printing processes or to improve its properties before laminating or metalizing. This chapter describes treatment process and devices, as well as the factors that influence the effectiveness of modification. This chapter also characterizes the changes that occur on the upper layer of material, as a result of corona treatment, as well as the methods used to determine their characteristics. Based on the results of own research on polylactide (PLA) films, there is a presentation of application for surface topography examination, surface chemistry, and wettability to determine changes occurring in polymers during corona discharge and their impact on printability of this substrate. There is also a wide review of literature that was the basis for describing the changes resulting from treatment of polypropylene, polyethylene, polyethylene terephthalate, polyvinyl chloride, ethylene vinyl acetate, and PLA.
... Previously, the APT unit has been used to modify the surface properties of papers [16][17][18]29], extrusion coated papers [30,31], polymer films [32] and non-woven materials [33,34]. In addition, the APT unit has been used to deposit a siloxane coating on LDPE coated paper [35]. ...
... The contact angle of water (surface tension 72.8 m N / m [19,30]) was measured using a KSV CAM 200 Optical Contact Angle Meter (KSV Instruments Oy, Helsinki, Finland) and a Pocket Goniometer PG-3 meter (Fibro System AB, Sweden). The samples were stored and the measurements were performed at controlled atmosphere (50 ± 2% RH, 23 ± 2°C) one day after the treatments. ...
... It is also known that the surface chemistry of sub strates has a significant effect on the performance of plasmas, par ticularly on paper surfaces, which usually possess heterogeneous and complicated surface chemistry [13,[16][17][18][19]. For example, in our other studies [30,31] argon and helium plasma treatments decreased the CAW of low density polyethylene (LDPE) and poly propylene (PP) coated papers quite equally. ...
In the first part of our studies, pigment coated and machine glossed papers were plasma pre-treated and extrusion coated with low density polyethylene (LDPE). The plasma treatment was performed roll-to-roll at atmospheric conditions, using dielectric barrier discharge (DBD). The effects of treatments on the surface properties and LDPE adhesion to different papers were studied. The argon plasma treatment decreased the contact angle of water (CAW) of both paper grades more efficiently than helium plasma or corona treatment. The lower electron density is the probable reason for the poor performance of helium plasma, whereas the treatment uniformity and efficiency of corona are reduced by the streamers present in the filamentary DBD. The treatments altered the surface roughness of papers but the increased wetting of the papers was mainly caused by the surface oxidation. Contrary to the plasma treatments, the corona treatment led to the unwanted treatment of the reverse side of papers. The argon plasma treatment increased the surface wetting more efficiently than the corona treatment, but the adhesion between LDPE coating and machine glossed paper was enhanced by both treatments quite equally. The adhesion was enhanced already at low treatment efficiency, and the additional treatment did not further promote the LDPE adhesion to machine glossed paper. The argon plasma treatment improved the LDPE adhesion to pigment coated paper more than the corona treatment. The effect of treatment efficiency depended on the thickness of LDPE coating. Presumably, thicker coating led to the increased contact area between the coating and pigment coated paper.
... Unique electrode design, suitable power supply, automatic impedance matching, and controlled gas flow in APT unit minimize the filamentary discharges, which are typical in a corona discharge [8]. More information about the APT unit can be found in the previous study [33]. Photographs of flame, corona, plasma, and LFS units are presented in Figure 1. ...
... The contact angles were determined using KSV CAM 200 Optical Contact Angle Meter (KSV Instruments Oy, Helsinki, Finland). The treated samples were stored and the measurements were performed in controlled atmosphere (50 ± 2% RH, 23 ± 2°C) one day after the [14,33]. Each contact angle value was an average of five simultaneous measurements taken from the centre line of substrate or coating. ...
... From wettability point of view, the top of the fibers is the most relevant. In other reported studies, the filamentary discharges of corona have caused low print uniformity on polyolefin surfaces [33], reduced moisture barrier of board [37] or even damage to porous nonwoven materials [38]. Another interesting point is that no saturation of hydrophilicity is observed on the surface of MG paper, whereas the CAW decreases quite linearly as a function of treatment efficiency. ...
Corona, flame, atmospheric plasma, and liquid flame spray (LFS) techniques were used to create highly hydrophilic surfaces for pigment-coated paper and board and machine-glossed paper. All the surface modification techniques were performed continuously in ambient atmosphere. The physical changes on the surfaces were characterized by field emission gun-scanning electron microscopy (FEG-SEM), atomic force microscopy and Parker Print-Surf surface roughness. The chemical changes were analysed by X-ray photoelectron spectroscopy. The superhydrophilic surfaces, i.e. contact angle of water (CAW) <10°, were created mainly by modifying the surface chemistry of the paper and board by argon plasma or SiO2 coating. The nano- and microscale roughness existing on paper and board surfaces enabled the creation of the superhydrophilic surfaces. Furthermore, the benefits and limitations of the surface modification techniques are discussed and compared. For example, the SiO2 coating maintained its extreme hydrophilicity for at least six months, whereas the CAW of argon plasma-treated surface increased to about 20° already in one day.
... The treatment induces oxidation on the surface of the specimen in the presence of oxidizing agents such as atomic oxides, oxygen-free radicals, and ozone. Due to oxidation, the surface of the specimen is cleansed while also increasing its mechanical characteristics (Tuominen et al. 2010). Corona treatment improves the bonding and compatibility of fibres and fillers, as Gholshan Tafti et al. (2018) concluded in their study. ...
... Corona treatment improves the bonding and compatibility of fibres and fillers, as Gholshan Tafti et al. (2018) concluded in their study. Tuominen et al. (2010) found that corona treatment improved the oxidation level and surface energy of the specimen. After the corona treatment, Gassan and Gutowski (2000) found fibre and matrix compatibility and specimen surface oxidation increased. ...
The development of natural fiber (NFr) composites for a variety of applications is on the rise. The optimization of the interfacial bonding (IFB) between the reinforcing NFr and polymer matrix is perhaps the single most critical aspect in the development of natural fibre polymer composites (NFPCs) with high mechanical performance. While the IFB is critical in determining the mechanical properties of the NFPCs, such as stress transfer, it is one of the least understood components. This article offers a summary of IFB mechanisms, different modification approaches targeted at lowering incompatibility and improving IFB, and evaluation of the impact of IFB. It has been found that 1) In general, interdiffusion, electrostatic adhesion, chemical reactions, and mechanical interlocking are accountable for the IFB; 2) the incompatibility of the fibre and matrix, which results in poor dispersion of the fiber, weak IFB, and ultimately worse composite quality, may be addressed through strategic modifications; and 3) Interfacial interactions between polymers and nanoparticles (NPs) are significantly improving their performance in areas like thermal, mechanical, robust IFB, and moisture absorption. As a result, this review study could be an important resource for scholars interested in coating and treating NFr to further enhance their surface characteristics.
... The treatment induces oxidation on the surface of the specimen in the presence of oxidizing agents such as atomic oxides, oxygen-free radicals, and ozone. Due to oxidation, the surface of the specimen is cleansed while also increasing its mechanical characteristics (Tuominen et al. 2010). Corona treatment improves the bonding and compatibility of fibres and fillers, as Gholshan Tafti et al. (2018) concluded in their study. ...
... Corona treatment improves the bonding and compatibility of fibres and fillers, as Gholshan Tafti et al. (2018) concluded in their study. Tuominen et al. (2010) found that corona treatment improved the oxidation level and surface energy of the specimen. After the corona treatment, Gassan and Gutowski (2000) found fibre and matrix compatibility and specimen surface oxidation increased. ...
Due to growing environmental consciousness and the depletion of oil supplies, numerous efforts have been made to replace synthetic fibers in fiber-reinforced composites with natural fibers (NFr). The low cost and abundance of NFr and its biodegradability and low density have encouraged researchers worldwide to study their potential applications in several industrial sectors. However, NFr has several disadvantages: excessive moisture absorption and subsequent swelling and degradation, low chemical and fire resistance, and insufficient interfacial interactions with polymers. Consequently, there is great interest in modifying the surface of NFr using a variety of methods. This chapter presents an overview of the NFr, its characterization, the problems associated with adding NFr to polymer composites. This literature survey suggests an in-depth review of photocatalysis by utilizing photocatalysts nanoparticle (PHNPs) aimed at increasing the hydrophobicity and interfacial bonding between the NFr and the matrix Using a photo-induced oxidation mechanism to disassemble water molecules, pollutants, and bacteria in a wet environment. Additionally, we reviewed the effects of these PHNPs on the moisture absorption, mechanical characteristics, and dimensional stability of NFr composites. As a result, this review article may make a valuable contribution to researchers interested in coating and treating NFr to further enhance their surface characteristics.
... The treatment supports oxidation on the specimen's surface in the presence of oxidizing agents like atomic oxides, oxygen-free radicals, and ozone. The specimen's surface gets cleaned due to oxidation while also improving the mechanical properties [32]. Enhanced bonding and fibre matrix compatibility can be seen in fibres and fillers with corona treatment, concluded H. R. G. Tafti et al [33] in their research. ...
... Enhanced bonding and fibre matrix compatibility can be seen in fibres and fillers with corona treatment, concluded H. R. G. Tafti et al [33] in their research. Mikko Tuominen et al [32] conclude that improvements were seen in the oxidation level and the surface energy of the specimen after corona treatment. Gassan et al [34] concluded that the fibre matrix compatibility and specimen's surface oxidation was increased after the corona treatment. ...
Fibers obtained from fruits, stem, and plant leaves are nature-based fibers and are known as natural fiber. Due to their versatile properties such as good mechanical behavior, low cost, eco-friendly, less dense, biodegradable, etc. natural fibers are getting focus amongst researchers. Since the density of bio-composites reinforced by natural fiber is significantly inferior to other traditional materials they satisfy the automotive need of high-performance vehicle parts/components of lightweight. To decrease the cost and weight of the vehicle automotive manufacturers are extensively utilizing the natural fibers (as interior insulation, seat bottom, door panels, dashboard, body panels, boot liner, etc.). Although, the composite of natural fiber has few shortcomings like poor chemical and fire resistance, poor interfacial bonding among matrix and fiber, moisture intake. Thus, natural fiber is required to be surface treated. Among the finest method for physical treatment is plasma treatment. Herein plasma which participates within surface modification directly is produced within the vacuum chamber by the ionization of the gas. The improved interfacial bonding in fiber composite is obtained as a result of surface treatment of plasma, which results in increase mechanical strength. Effect of surface treatment of plasma on several natural fiber is included in this paper and the aim of this review paper is to occupy the literature gap through this paper.
... To address this dilemma, membrane surface treatments have been applied aimed at altering the surface wettability and chemical properties. A wide range of methods have been deployed for altering the surface properties, such as plasma [3][4][5][6][7][8][9], UV irradiation [3], ion irradiation [4] and chemical coating [5,6]. These treatments have been used to attain the following goals: produce special functional groups at the surface for interactions with other functional groups, amend surface energy, change hydrophobicity or hydrophilicity, and alteration of surface morphology [7]. ...
... A wide range of methods have been deployed for altering the surface properties, such as plasma [3][4][5][6][7][8][9], UV irradiation [3], ion irradiation [4] and chemical coating [5,6]. These treatments have been used to attain the following goals: produce special functional groups at the surface for interactions with other functional groups, amend surface energy, change hydrophobicity or hydrophilicity, and alteration of surface morphology [7]. The PPM has been used as a bioinspired substrate for separation applications [8]. ...
Radio frequency plasma is one of the means to modify the polymer surface namely in the activation of polypropylene membranes (PPM) with O2 plasma. Activated membranes were deposited with TiO2 nanoparticles by the dip coating method and the bare sample and modified sample (PPM5-TiO2) were irradiated by UV lamps for 20–120 min. Characterization techniques such as X-ray diffraction (XRD), Attenuated total reflection technique- Fourier transform infrared spectroscopy (ATR-FTIR), Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM) and water contact angle (WCA) measurements were applied to study the alteration of ensuing membrane surface properties which shows the nanoparticles on the sample surface including the presence of Ti on PPM. The WCA decreased from 135° (PPM) to 90° (PPM5-TiO2) and after UV irradiation, the WCA of PPM5-TiO2 diminished from 90° to 40°.
... The board was then plasma treated before to be wet laminated and the adhesion between the two layers was reevaluated. Plasma treatment, which is industrially used, increase the surface energy of the board and so the adhesion between two layers, especially for printing applications (Pykönen et al. 2008(Pykönen et al. , 2009Tuominen et al. 2010). ...
The packaging industry is undergoing a major turn in its history looking for biobased, recyclable and biodegradable alternatives to petrobased products. Cellulose based materials such as paper and board can be a good solution, however, they present poor barrier properties, which are mandatory for packaging applications. In this study, all cellulose packaging with good barrier properties to grease, oxygen, water and water vapour were produced combining two innovative technologies: the wet lamination of microfibrillated cellulose (MFC) and the chromatogeny grafting. First, a thin layer of MFC (10 to 25 g/m²) was applied on a board without the use of glue in one pass. The influence of the MFC grade on the minimum MFC coat-weight required to develop grease barrier properties was investigated. Secondly, the MFC wet laminated board was grafted by chromatogeny at pilot scale. The MFC covered produced samples present excellent grease barrier properties with an oil absorption lower than 2 g/m² after 1800s (Cobb oil 1800s), a kit test of 12 and very good oxygen barrier properties. The chromatogeny grafting of fatty acids on the MFC hydroxyl groups confers barrier properties to water and water vapour to the MFC wet laminated board with a water vapour transmission rate around 36 g/(m².d). Finally, the mechanical properties of the samples and the adhesion of the MFC layer on the board were evaluated.
... This heating source oxidizes the surface, improving its wettability and adhesion properties. The technique is commonly used in the packaging industry, for instance, in the treatment of bottle caps to improve the adherence of inks and labels [159]. Flame treatment also finds an interest in the automotive industry for pre-treating polymer components, such as polypropylene before painting or bonding [160]. ...
This comprehensive review begins by tracing the historical development and progress of cold plasma technology as an innovative approach to polymer engineering. The study emphasizes the versatility of cold plasma derived from a variety of sources including low-pressure glow discharges (e.g., radiofrequency capacitively coupled plasmas) and atmospheric pressure plasmas (e.g., dielectric barrier devices, piezoelectric plasmas). It critically examines key operational parameters such as reduced electric field, pressure, discharge type, gas type and flow rate, substrate temperature, gap, and how these variables affect the properties of the synthesized or modified polymers. This review also discusses the application of cold plasma in polymer surface modification, underscoring how changes in surface properties (e.g., wettability, adhesion, biocompatibility) can be achieved by controlling various surface processes (etching, roughening, crosslinking, functionalization, crystallinity). A detailed examination of Plasma-Enhanced Chemical Vapor Deposition (PECVD) reveals its efficacy in producing thin polymeric films from an array of precursors. Yasuda’s models, Rapid Step-Growth Polymerization (RSGP) and Competitive Ablation Polymerization (CAP), are explained as fundamental mechanisms underpinning plasma-assisted deposition and polymerization processes. Then, the wide array of applications of cold plasma technology is explored, from the biomedical field, where it is used in creating smart drug delivery systems and biodegradable polymer implants, to its role in enhancing the performance of membrane-based filtration systems crucial for water purification, gas separation, and energy production. It investigates the potential for improving the properties of bioplastics and the exciting prospects for developing self-healing materials using this technology.
... One is a deposition of molecular films with the pronounced hydrophilic property on the substrate; for example, thiols are commonly used to enhance the surface hydrophilicity of gold, silver, and copper materials [9][10][11][12][13]. The second hydrophilic technique is the hydrophilic treatment by plasma, photons, electrons, ions, and ozone [14][15][16][17][18], which often exhibit disadvantages in both the mechanical strength and the time aging, thus actually impeding their practical applications. ...
The acquiring of superhydrophilic surfaces attracts the strong interest in self-cleaning, anti-fogging and anti-icing fields based on the unique features. However, the persistent time of su-perhydrophilic surfaces is still facing a big challenge because of easily adsorbing hydrophobic groups. Here, we propose a strategy to achieve a superhydrophilicity persisting for an unprece-dently long time on sapphire surfaces, by compounding the femtosecond laser-induced hierarchical structures and the subsequent varnish of TiO2. The superhydrophilic effect (with a contact angle of CA = 0°) created by our method can be well prolonged to at least 180 days, even for its storage in air without additional illumination of UV lights. Based on comprehensive investigations, we attribute the underlying mechanisms to the coordination of laser-induced metal ions on the material surface via TiO2 doping, which not only prevents the adsorption of the nonpolar hydrocarbon groups, but also modulates the photo-response properties of TiO2. In addition, further experiments demonstrate the excellent anti-fogging properties of our prepared samples. This investigation provides a new perspective for further enhancing the durability of superhydrophilicity surfaces.
... The corona derived reactive oxygen species which include ozone, atomic oxygen, superoxide anion radical (O 2 − ), singlet oxygen ( 1 O 2 ), hydroxyl radical ( · OH) and hydroperoxyl radical (HO 2 · ) [13], introduce new functional groups at the surface of polymer films. Hydroxyl, carbonyl, carboxyl and ester groups are most commonly found on the surfaces of polymers after plasma treatments, which increases the surface energy and improves the wetting and adhesion properties of polymer films [14]. ...
Polyethylene terephthalate (PET) is a thermoplastic polyester with numerous applications in industry. However, it requires surface modification on an industrial scale for printing and coating processes and plasma treatment is one of the most commonly used techniques to increase the hydrophilicity of the PET films. Systematic improvement of the surface modification by adaption of the plasma process can be aided by a comprehensive understanding of the surface morphology and chemistry. However, imaging large surface areas (tens of microns) with a resolution that allows understanding the surface quality and modification is challenging. As a proof-of-principle, plasma-treated PET films were used to demonstrate the capabilities of X-ray ptychography, currently under development at the soft X-ray free-electron laser FLASH at DESY, for imaging macroscopic samples. In combination with scanning electron microscopy (SEM), this new technique was used to study the effects of different plasma treatment processes on PET plastic films. The studies on the surface morphology were complemented by investigations of the surface chemistry using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). While both imaging techniques consistently showed an increase in roughness and change in morphology of the PET films after plasma treatment, X-ray ptychography can provide additional information on the three-dimensional morphology of the surface. At the same time, the chemical analysis shows an increase in the oxygen content and polarity of the surface without significant damage to the polymer, which is important for printing and coating processes.
... The authors concluded that, in future, plasma treatment of wool can replace the wet pretreatment processes for wool printing. In addition, different research papers have been published regarding the application of plasma treatment in the printing of polyester [71][72][73][74][75][76][77][78], silk [79] and PP [80,81] textile substrates. ...
Nowadays, cold plasma technology is highly involved in textile processing either to assist conventional wet-chemical processing and/or create innovative products. Plasma surface treatment is an ergonomically simple process, but the plasma process and its effect on the fibre surface are more complex due to the interplay of many concurrent processes at a time. The efficiency of plasma treatment mainly depends on the nature of textile material and the treatment operating parameters. The main objective of this review paper is to summarise and discuss the application of plasma treatment and its effect on the pre-treatment, dyeing, printing and finishing of natural and synthetic textile fibres. However, the application of plasma technology to different types of textile substrates has not been fully addressed.
... 19 Current technologies for preparing polymeric materials for printing often rely on surface treatment, such as plasma or corona discharge, to modify the top polymer layer, remove the dirt, and change the wettability and roughness. 20,21 Strong chemical interactions and surface bonding are facilitated by such surface treatments that induce a high concentration of reactive surface functional groups. 22 These treatments increase the surface free energy and improve the adhesive properties by eliminating pendant bonds from the surface. ...
High-resolution inkjet printing of a hydrophobic polymer surface (polystyrene, PS) was accomplished using a patterned coating of cellulose nanocrystals (CNC) that prevents the ink from bleeding. A periodically crack-free, wrinkled (wavelength around 850 nm) stamp was prepared by surface oxidation of an uniaxially stretched polydimethylsiloxane (PDMS) elastomeric substrate, and was used as a template to transfer aligned patterns of cellulose nanocrystals (CNC) onto PS surfaces by wet stamping. The morphology of the aligned CNC coatings on PS was then compared with randomly deposited CNC on PS using atomic force microscopy (AFM). The wettability of the CNC and polymer surfaces with water and ink was measured and analyzed in the context of inkjet printing. This biomaterial coating technique enables high resolution printing of modern water-based inks onto hydrophobic surfaces, for applications in renewable packaging and printing of biomolecules for high throughput diagnostics. Further, with suitable modifications, the technology is scalable to roll-to-roll manufacturing for industrial flexo printing.
... Plasma, corona, flame, photons, electrons, ions, X-rays, g-rays, and ozone are methods that were investigated to alter the chemistry of polymer surfaces without affecting their bulk properties (Chan, Ko, and Hiraoka 1996;Ozdemir, Yurteri, and Sadikoglu 1999). Oxidation of polymer surfaces can be carried out using plasma treatment, in air or oxygen environment (Liston, Martinu, and Wertheimer 1993;Siow et al. 2006) corona (O'Hare, Leadley, andParbhoo 2002;Strobel et al. 2003) and flame (Farris et al. 2010;Strobel et al. 2003;Tuominen et al. 2010). ...
Wettability of a material’s surface plays a significant role in how fluids interact with such surfaces. Wetting behavior is universal but can vary depending on the chemical nature of the solid and liquid phases. Plants and animals adapt to their environment by having evolved special properties. These properties are such as hydrophilic and hydrophobic. Hydrophilic surface has a strong affinity to water and spreading of water on such surface is preferred. The degree of hydrophilicity of the substance can be measured by measuring the contact angle between the liquid and solid phases. Hydrophobic materials are known as non-polar materials with a low affinity to water, which makes them water repelling. A contact angle of less than 90° indicates hydrophilic interaction where as an angle greater than 90° indicates a hydrophobic interaction. More recently, superwetting such as superhydrophilicity has been receiving an increased focus in the literature due to its potential significance. Superhydrophilic surface has a contact angle of less than 5°.
The fabrication of hydrophilic materials can be carried out in two main ways: depositing molecules on surfaces or modification of surface chemistry. Both methods have been successful historically in achieving their intended purposes. Hydrophobic and superhydrophobic materials can be produced with many fabrication methods such as layer-by-layer assembly, laser process, the solution-immersion method, sol-gen techniques, chemical etching, and Hummer’s method.
The applications of such an important property are significant. For example, hydrophilic surfaces can be used in anti-fogging applications, biomedical, filtration, heat pipes, and many others. Hydrophobic and superhydrophobic materials have been successfully applied in many sectors, such as: (I) the removal of petroleum from aqueous solutions, (II) applied to plastic, ceramics, and mesh to contribute to the oil removal from aqueous solutions, (III) hydrophobic layers have a strong self-cleaning effect on plastics, heat pipes, metals, textiles, glass, paints, and electronics, (IV) hydrophobic layers improve the anti-freezing behavior of heat pipes which prevents unwanted build-up and (V) they function as a water and dust protecting coat on electronics.
The presence of this property is historic but there is still a huge potential for development for its applications in many sectors such as water treatment, heat transfer applications, biomedical devices, and many more.
... Unusually high treatment levels were chosen, since preliminary trials showed only a very minor effect on surface energy with a treatment efficiency typical of industrial converting processes (approx. 50 W*min/m 2 ,Tuominen et al. 2010). ...
Changes in consumer habits and the replacement of solid trans fats in foodstuffs with
unsaturated fats have increased the demand for low-cost grease-resistant packaging materials worldwide. Taking into account the global aim to reduce our dependence on oil-based plastics, new bio-based solutions are needed to meet the demand for sustainable packaging solutions, and the development of such materials was the focus of the work reported in this thesis.
Pigmented dispersion barrier coatings were prepared using a blade-coating technique on
commercial solid bleached sulphate paperboard. The coatings consisted of a bio-based
component, hydroxypropylated starch or hydroxypropyl cellulose, a styrene-butadiene latex binder, and talc. The grease resistance in terms of time taken for a model grease to penetrate the coated paperboard varied between a few hours and several days, depending on the coating composition and on the ambient temperature during the test. Particular attention was given to coatings that prevented oil to penetrate the whole 24 h test period described in ISO 16532-1.
The feasibility of producing barrier-coated boards was studied from the viewpoints of the
finishing and converting processes and their end-use applications. The findings suggested that corona treatment should be used with caution if the board is to be printed, since it may cause a drastic decrease in oil penetration time due to strike through that occur if the voltage of the discharge is sufficiently high to change the electrical conductivity of the sample. The oil barrier was impaired regardless of whether the uncoated or the coated side of the board was treated with corona. Moreover, the coatings did not prevent the occurrence of reverse side effects. Unexpectedly, contact angle determinations suggested that exposure to heat in converting processes may even improve the oil repellency of dispersion coatings containing pigments due to the migration of latex towards the outer surface. Migrated latex also induced self-healing of
the coating, according to scanning electron microscope (SEM) images that indicated the
disappearance of pinholes. The oil and grease resistance (OGR) was, however, dependent on the oil viscosity and fatty acid composition. Particularly with moderately grease-resistant samples, the penetration time of pure coconut and rapeseed oils was considerably longer than that of their mixtures. Finally, press forming of paperboard led to a decrease in oil penetration time, but none of the studied coating compositions completely lost their barrier properties.
The developed coating formulations seem to have a potential in many commercial sustainable packaging applications in a transitional period before implementation of completely bio-based coatings on an industrial scale. Potential uses may include e.g. instant meal trays and fast food packages, but particular attention should be paid to the effects of converting and finishing processes on the physical and barrier properties of the materials.
http://urn.fi/URN:ISBN:978-952-335-009-0
... The surface treatment applications include oxidation, etching, etc. Cold plasma treatment could transform the hydrophobic surfaces into hydrophilic and also aids in the deposition of hydrophilic layers over different surfaces (Kim et al., 2006). Other applications of cold plasma include treatment of polythene package films for enhancement of surface charge and ink adhesion properties (Tuominen et al., 2010). Of late, cold plasma is being used for biological decontamination of inert surfaces as well. ...
... Tuominen et al. [10] evaluated how corona, flame, and atmospheric plasma treatments modified the surface of extrusion-coated LDPE and PP and also the influence of these surface modifications on the print quality, that is, toner adhesion and the visual quality of the extrusion coatings. ey concluded that flame treatment contributed beneficially to the print quality, on LDPE surfaces in particular, and it produced the best toner adhesion and visual quality on LDPE surfaces. ...
Poor adhesion continues to be a problem for manufacturers of laminated packaging. Therefore, the aim of this research was to study the effect of flame treatment, the type of coating, and starch application on the adhesion force of polyethylene/paperboard. The force of adhesion was determined using the peel test method; the paper surface energy was assessed by contact angle analysis; and paperboard roughness was determined by profilometer. The flame treatment did not affect the surface roughness but significantly increased the paperboard surface energy. The paperboard coated with polar latex showed much higher surface energy than the paperboard coated with nonpolar latex. The adhesion force of polyethylene presented a linear correlation to the surface energy of the paperboard. Therefore, the surface energy of paperboard is an excellent indication of its adhesion force to polyethylene, and this represents a very reliable and practical method in terms of quality control in the paper industry for producing laminated packages.
... Corona treatment is very effective as a pretreatment for fibers surfaces. In addition to surface "cleaning", the plasma treatment promotes surface activation and improves the adhesion properties and surface roughness, leading to surfaces that are easier to functionalize without changing the whole material's mechanical properties [31,32]. ...
This paper provides new insights regarding jute fibers functionalization with silver nanoparticles (Ag NPs) with improved conductivity values and highlights the sustainability of the processes involved. These NPs were applied onto jute fabrics by two different sustainable methods: ultraviolet (UV) photoreduction and by using polyethylene glycol (PEG) as a reducing agent and stabilizer. Field Emission Scanning Electron Microscopy (FESEM) images demonstrated that the Ag NPs were incorporated on the jute fibers surface by the two different approaches, with sizes ranging from 70 to 100 nm. Diffuse reflectance spectra revealed the plasmon absorption band, corresponding to the formation of metallic Ag NPs, in all samples under study. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) was used to characterize the obtained samples, demonstrating NPs adsorption to the surface of the fibers. The resistivity value obtained by the two-point probe method of the jute fabric without functionalization is about 1.5 × 107 Ω·m, whereas, after NPs functionalization, it decreased almost 15,000 times, reaching a value of 1.0 × 103 Ω·m. Further research work is being undertaken for improving these values, however, 1000 Ω·m of resistivity (conductivity = 0.001 S/m) is already a very reasonable value when compared with those obtained with other developed systems based on natural fibers. In summary, this work shows that the use of very simple methodologies enabled the functionalization of jute fibers with reasonable values of conductivity. This achievement has a huge potential for use in smart textile composites.
... This treatment effectively oxidizes only the thin surface layers, without negatively affecting bulk mechanical properties. Moreover, etching and ablation processes are important for increasing surface roughness [28][29][30][31][32]. These oxidation and surface roughness changes lead to improved wettability and adhesion characteristics of the polymer surfaces [33,34]. ...
Polymers/metal laminates are often used to improve physical and mechanical properties,
especially those required in building applications. A flat aluminum composite panel (ACP)
consisted mainly of two thin metal sheets usually made of aluminum (Al) and a non-metal core,
such as polyethylene (PE). The lack of adhesion associated with the low wettability of PE is a
serious problem. An eco-friendly, dry, non-destructive corona treatment technique can be
applied to solve this problem. In this work, the use of a corona treatment to enhance the
adhesion properties of linear low-density polyethylene (LLDPE) was studied. The changes in
surface and adhesion properties were thoroughly analyzed using various analytical techniques
and methods to obtain the optimal parameters for corona discharge using contact angle
measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron
spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy
(AFM). AFM force adhesion measurements were used to analyze the effect of the corona
treatment on the adhesion enhancement of LLDPE, and the peel tests confirmed a significant
increase in peel resistance in the LLDPE/Al laminate. A synergy effect from using the corona
treatment in combination with an ethylene acrylic acid dispersion primer was observed.
Keywords: Corona Treatment, Wettability, Adhesion, Polyethylene, Laminates
... Unusually high treatment efficiency values were chosen, since preliminary trials showed only a very minor effect with the treatment efficiency (approx. 50 W*min/m 2 ) typical for industrial converting processes 32 . In addition, high treatment levels allowed breakdown effects to be studied. ...
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 utilising 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.
... Such parameters are: setting time, extruder and chill roll temperature profiles, press roll pressure [31] line speed, applied coating thickness and intensity of pretreatments (e.g. corona, plasma or flame) of the paper surface [32]. ...
Extrusion coating expts. of flame retarded low d. polyethylene (LDPE) onto a std. machine finished Kraft paper have been carried out. A pilot extrusion coating line was used in order to investigate the potential of halogen-free flame retardant system based on azoalkanes such as azocyclohexane (AZO) and 4',4-bis(cyclohexylazocyclohexyl)methane (BISAZO) for fire resistant coating applications. In comparison, expts. were performed using FlameStabNOR116, magnesium dihydroxide (MDH) and a brominated additive Luvogard MB81/PE as ref. flame retardants. The concn. of azoalkane flame retardants was varied between 0.5 and 1 wt.%. The max. extrusion temp. was varied between 260 and 290 °C and the coating layer wt. from 12.9 to 25.0 g/m2. The obtained multilayer facings contg. azoalkanes exhibited significantly improved flame retardant properties, esp. at the low coating wt. of 12.9 g/m2. Under all of the used exptl. conditions the runnability on the pilot line was flawless for azoalkane formulations. In c
... 114,115 Plasma treatment, in air or oxygen environment, 116,117 corona 118,119 and flame 118,120 treatments are the most designated techniques in oxidation of surfaces of polymers. 121 In both plasma and corona treatments, the accelerated electrons bombard the polymer with energies 2-3 times that necessary to break the molecular bonds, producing free radicals which generate cross-linking and react with surrounding oxygen to produce oxygen-based functionalities. 116 Polar groups being typically created on the surface are hydroxyl, peroxy, carbonyl, carbonate, ether, ester, and carboxylic acid groups. ...
The term superhydrophilicity is only 11–12 years old and was introduced just after the explosion of research on superhydrophobic surfaces, in response to the demand for surfaces and coatings with exceptionally strong affinity to water. The definition of superhydrophilic substrates has not been clarified yet, and unrestricted use of this term to hydrophilic surfaces has stirred controversy in the last few years in the surface chemistry community. In this review, we take a close look into major definitions of hydrophilic surfaces used in the past, before we review the physics behind the superhydrophilic phenomenon and make recommendation on defining superhydrophilic surfaces and coatings. We also review chemical and physical methods used in the fabrication of substrates on surfaces of which water spreads completely. Several applications of superhydrophilic surfaces, including examples from the authors' own research, conclude this review.
... The standard deviation is very small, proving that the flame treatment is homogeneous. Some reactive functions such as hydroxyl functions are created on the sample surface, [25] which allow a better compatibility with the coating and thus a better adhesion of the coating. ...
An innovative way to improve fire-retardant properties of different polymers by applying intumescent coatings on their surface has been studied. Two polymers have been investigated: polypropylene and polycarbonate. The surfaces were first subjected to a flaming treatment in order to clean them and to increase their wettability and thus improve the adhesion of the coatings. Two different formulations were then applied: a transparent intumescent varnish, based on an acrylic resin, and an intumescent coating based on polyvinylacetate resin. Different parameters have been obtained using several fire tests. The cone calorimeter, the limiting oxygen index and UL94 tests have been carried out to evaluate the fire-retardant properties obtained for both the intumescent coating and the intumescent varnish. Results clearly evidence an outstanding improvement of the fire-retardant properties using intumescent coatings without any incorporation of flame retardants in the bulk. Copyright © 2010 John Wiley & Sons, Ltd.
... The substrate to be treated is fed through the plasma. Electrode design, suitable power supply, impedance matching and controlled gas flow help to minimise the filamentary discharges, which are typical for a corona discharge [34]. Both corona and plasma were run at low and high power levels. ...
In this study, the influence of different surface characteristics of dispersion-coated barrier layers on top layer coatability is examined. The barrier layer consisted of platy pigments, such as talc and kaolin, combined with different amounts and types of latexes. Coating of the top coat was carried out using the reverse gravure technique in which a dispersion consisting of mineral pigments and latex is applied under slight pressure onto the barrier-coated substrate. Wettability and coatability were measured as a function of surface energy and surface roughness of the barrier layer and the surface tension of the top coat dispersion. Plasma and corona surface treatments were used to increase the surface energy and wettability without affecting the surface topography. The most important aspect for predicting the coatability was the wettability, especially the water contact angle, because the top coat is an aqueous suspension. Decreasing the surface tension of the top coat dispersion also improved the coatability, whereas roughness had only a minor effect.
... The substrate to be treated is fed through the plasma. The electrode design, suitable power supply, impedance matching and controlled gas flow help to minimize the filamentary discharges, which are typical for a corona discharge [35]. Both the corona and plasma treatments were run at low and high power levels.Table 2 lists the treatment parameters. ...
The influence on top layer coatability by different surface characteristics of dispersion coated barrier layers was studied. The barrier layer consisted of platy pigments such as talc and kaolin combined with different amounts and types of latexes. Coating of the top coat was carried out using reverse gravure technique where the dispersion consisting of mineral pigments and latex is applied under slight pressure onto the barrier coated substrate. Wettability and coatability were measured as a function of surface energy and surface roughness of barrier layer and surface tension of the top coat dispersion. Plasma and corona surface treatments were used for increasing surface energy and wettability without affecting surface topography. The most important aspect to predict coatability was the wettability and especially the water contact angle since the top coat is an aqueous solution. Decreasing the surface tension of top coat dispersion also improved coatability whereas roughness had only a minor effect.
... Treatment with cold plasma can modify hydrophobic surfaces to render them hydrophilic, or can be used to deposit a hydrophilic coating on various surfaces (Kim et al. 2006). Plastic packaging films and papers treated with cold plasma had improved performance, including surface charge and ink adhesion (Tuominen et al. 2010). Biological decontamination of inert surfaces is also an application of cold plasma; applications to food surfaces are the subject of the bulk of this review. ...
Cold plasma is a novel nonthermal food processing technology that uses energetic, reactive gases to inactivate contaminating microbes on meats, poultry, fruits, and vegetables. This flexible sanitizing method uses electricity and a carrier gas, such as air, oxygen, nitrogen, or helium; antimicrobial chemical agents are not required. The primary modes of action are due to UV light and reactive chemical products of the cold plasma ionization process. A wide array of cold plasma systems that operate at atmospheric pressures or in low pressure treatment chambers are under development. Reductions of greater than 5 logs can be obtained for pathogens such as Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus. Effective treatment times can range from 120 s to as little as 3 s, depending on the food treated and the processing conditions. Key limitations for cold plasma are the relatively early state of technology development, the variety and complexity of the necessary equipment, and the largely unexplored impacts of cold plasma treatment on the sensory and nutritional qualities of treated foods. Also, the antimicrobial modes of action for various cold plasma systems vary depending on the type of cold plasma generated. Optimization and scale up to commercial treatment levels require a more complete understanding of these chemical processes. Nevertheless, this area of technology shows promise and is the subject of active research to enhance efficacy.
Over the course of the COVID-19 pandemic, people have realized the importance of wearing a mask. However, conventional nanofiber-based face masks impede communication between people because of their opacity. Moreover, it remains challenging to achieve both high filtration performance and transparency through fibrous mask filters without using harmful solvents. Herein, scalable transparent film-based filters with high transparency and collection efficiency are fabricated in a facile manner by means of corona discharging and punch stamping. Both methods improve the surface potential of the film while the punch stamping procedure generates micropores in the film, which enhances the electrostatic force between the film and particulate matter (PM), thereby improving the collection efficiency of the film. Moreover, the suggested fabrication method involves no nanofibers and harmful solvents, which mitigates the generation of microplastics and potential risks for the human body. The film-based filter provides a high PM2.5 collection efficiency of 99.9 % while maintaining a transparency of 52 % at the wavelength of 550 nm. This enables people to distinguish the facial expressions of a person wearing a mask composed of the proposed film-based filter. Moreover, the results of durability experiments indicate that the developed film-based filter is anti-fouling, liquid-resistant, microplastic-free and foldability.
In this study the influence of matrix type on plasma-treated high tenacity polypropylene fiber reinforced cementitious composites were investigated. The fibers were subjected to low frequency cold plasma of oxygen gas. Power rate of the generator was 50, 100 and 200 W, and duration was 0.5, 2 and 20 min. 25 × 60 × 300 mm prismatic samples were prepared with two type of matrices, and plasma-treated/untreated fibers. Scanning electron microscope was used to determine physical modifications on the fibre surface. Four point bending tests were conducted on prismatic samples. Matrices with treated and untreated fiber reinforcement were compared by means of flexural properties. Analysis of variences was applied to the plasma treated fiber reinforced groups. Test results showed that the flexural behaviour of composites was affected by plasma power and duration. There was physical modification for each plasma power and duration. The influence of plasma treatment on fiber-matrix bond properties was mainly affected by matrix type: weak matrix showed better flexural properties with low power and short duration plasma-treated fibers, whereas comparatively stronger matrix expressed greater flexural properties at higher power and longer durations when compared to untreated fiber reinforced composites.
We have studied the chromatographic separation of solvents and dyes after deposition of a dye solution on a paper substrate. Due to their larger molecular size, dyes typically exhibit a stronger interaction with the paper constituents. Consequently, the imbibition process of the dye is usually delayed compared to that of the solvent. This impacts the achievable resolution and color homogeneity in inkjet printing. We present experiments and a comprehensive numerical model to illustrate and quantify these effects. The model accounts for the solvent evaporation, heat transfer, multicomponent unsaturated flow, and dye adsorption, as well as the presence of permeable fibers in the paper substrate. We identify the key parameters that can be tuned to optimize the pattern fidelity of the printing process.
Three different types of paper with different coatings have been used in order to study the influence of gaseous plasma treatment on surface properties of paper. Radio frequency (RF) oxygen plasma was used for treatment of papers that contain different parts of organic and inorganic components in their coatings. Surface properties like surface morphology, roughness, surface energy, wettability, and chemistry were studied. The influence of plasma modification was also studied in terms of printability and paper gloss, which are one of the key parameters that dictate the use of such paper in desired applications. The results indicate that plasma modification of different types of coatings indeed influences paper printability as well as gloss function, which was shown to be highly connected with surface morphology, as micro-and nanopores were opened or formed due to selective plasma etching of organic part of the coating. Moreover, significant increase in surface energy was observed on all plasma treated papers, however this seemed not to influence much on the printing and gloss properties.
The aim of this investigation was to determine the role of negative direct current and alternating current (plasma) corona treatments in modification of bio-based dispersion barrier coatings and the response of replacing fossil-based binder with a thermoplastic bio-based binder (starch). The study emphasizes the importance of understanding and optimizing electric corona discharge in order to obtain high oxidation level without harming the substrate and causing unintentional treatment of the reverse side. The coatings were exposed to different corona treatment conditions using a novel developed sheet-fed laboratory-scale device. Corona-induced topographical, mechanical and surface chemical changes were observed from atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle and surface energy measurements. XPS results indicated further that partial starch decomposition occurred after plasma treatment. Coated surfaces became substantially smoother after both treatments suggesting that nanoparticle migration and re-orientation effects occurred. Additionally, reverse side effects and strike through were also discussed.
Actually flame treatment technology is a mature one, but still characterized by high improvements margin, as last process developments are demonstrating. Moreover esseCI has recently focused on what have been traditionally considered weak points as influence of room conditions on flame and as mixture composition control/monitoring system. Flame treater system can actually be fully integrated in any converting line, both from a mechanical and electrical/electronical point of view. There is no machine able to do everything. Starting from this consideration it is anyway out of any question that flame treatment can warrant higher quality on film treated surfaces, respect to corona, thanks to its higher surface adhesion and surface energy. This is particularly true in applications as: • extrusion coating. • metallisation: where flame treated surfaces, compared to corona, allow significantly increased barriers to water vapour (WVTR) and to oxygen (OTR), as well as improved and longer lasting adhesion of metal to the film, as widely demonstrated by REXAM tests; • printing: where flame treated surfaces allow, compared to corona, to get better printing quality, improved toner adhesion and improved visual quality, as well as improved rub-off and abrasion resistance in f lexo, rotogravure and digital printing applications; • tapes films.
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.
This study shows the sensitivity of the performance of a 30 nm Al2O3 barrier layer deposited by atomic layer deposition (ALD) on biaxially oriented polypropylene (BOPP) film to material processing. The most detrimental effects were caused by the contact between the rollers and the deposited layer during web handling and the surface contamination of the substrate prior to the deposition process. The shipment of the material as sheets and the atmospheric corona treatment of the coated surface had also a minor effect on the barrier performance. The results obtained show the importance of carrying out protective actions during both pre- and post-processing of the material in order to maintain the barrier performance of an ALD-Al2O3 layer.
Polymer and paper structures have been used in several fields, especially in the packaging industry. This study shows how flame and corona treatment modify the most important properties of fiber-based packaging materials: printability, sealability, and barrier effectiveness against water vapor, oxygen, and grease. A high level of wetting or oxygen content of the surface after flame or corona treatment did not lead to improved print quality (i.e., better toner adhesion and high visual quality for the extrusion coatings). Flame treatment improved visual quality and toner adhesion of low-density polyethylene (LDPE) coating, but increased minimum sealing temperatures and reduced seal strengths of the coating. The reduced sealability likely resulted from cross-linking of the LDPE surface, which reduced chain mobility and limited the amount of chain interdiffusion across the seal interface. Polypropylene (PP) coating sealability was enhanced by flame treatment, whereas corona treatment improved the sealability of both coatings. The reason for the improved sealability was chain-scission, not cross-linking, which is the dominant reaction for flame-treated PP and corona-treated LDPE and PP coatings. Flame treatment also improved the water vapor and oxygen barrier ability by increasing the surface crystallinity of coatings.
The target of this study is to investigate the correlation between surface properties and heat sealability of flame-treated low-density polyethylene (LDPE) coating because it is vital to know how to modify the surface properties of LDPE coating without losing the heat sealing properties. Flame treatment showed a significant effect on the heat sealing properties of LDPE-coated paper. For example, the heat sealing temperature of LDPE coating decreased or alternatively doubled, depending on the equivalence ratio (air-propane ratio) of flame treatment. In addition, the hot tack strength was significantly enhanced by flame treatment, which broadened the hot tack window of LDPE-coated paper. The reason for the heat sealing performance of flame-treated LDPE coating was believed to be related to the simultaneous reactions, that is, cross-linking and chain scission, occurring on the LDPE surface. The molecular weight of LDPE surface increased or decreased, depending on the dominating reaction during flame treatment. This affected the chain mobility and the amount of chain interdiffusion across the seal interface and finally defined the heat sealing performance of LDPE-coated paper. Copyright © 2012 John Wiley & Sons, Ltd. The study shows how the heat sealability of LDPE-coated paper can be enhanced or alternatively deteriorated, depending on the equivalence ratio of flame treatment. For example, the increased seal strength at the hot tack temperatures of 50 °C to 80°C expanded the hot tack window of LDPE-coated paper significantly, even at the line speed of 300 m/min. The reason for the heat sealing performance of flame-treated LDPE coating is believed to be related to the simultaneous reactions, that is, cross-linking and chain scission, on the surface of LDPE-coated paper. Copyright © 2012 John Wiley & Sons, Ltd.
Polymer and paper structures have been successfully utilized in several fields, especially in the packaging industry. Besides barrier properties, printability and sealability are the most important properties of fiberbased packaging materials. This second part of our study shows how atmospheric plasma and corona treatments modify surface properties of low density polyethylene (LDPE) and polypropylene (PP) coatings and what is the effect of these surface modifications on the printability, sealability, friction, gloss and barrier (moisture and grease) properties of these extrusion coatings. Plasma and corona treatments increased the surface energy mainly by introducing oxygen containing functional groups onto the surfaces of LDPE and PP coatings. Helium and argon plasma treatments improved the print quality of extrusion coatings more than corona treatment. The electret phenomenon was observed on LDPE and PP surfaces after corona treatment and it is the most likely reason for the high print mottling and low visual quality of corona treated surfaces. Plasma and corona treatments affected the sealability properties of LDPE and PP coatings by decreasing the heat sealing temperature and hot tack strength of the extrusion coatings. The reason for the altered sealability properties of LDPE and PP coatings is probably related to the changes in the surface molecular weight of the extrusion coatings. Low-molecular-weightoxidized- compounds (LMWOCs) observed on the surface of plasma and corona treated LDPE coating are the most likely explanation for the increased hot tack strength of the LDPE coating at the high treatment level. In addition, plasma and corona treatments increased the friction of LDPE and PP surfaces, whereas no significant changes were observed in surface gloss or barrier property of the extrusion coatings. © 2013 Scrivener Publishing LLC. All rights reserved.
Summaries The effect of air dielectric barrier discharge plasma treatment on the chemical structure and morphology of polypropylene
(PP) film was studied using UV-VIS (ultraviolet-visible), FT-IR, (Fourier transform infrared), SEM (scanning electron microscopy)
and AFM (atomic force microscopy). Polypropylene samples were printed using solvent-based gravure ink. An evaluation of the
print quality criteria of the treated PP films included measurement of print density and print gloss. SEM investigated the
ink laydown on the modified PP film. The results showed that after a few seconds of plasma treatment, both the surface energy
and the surface roughness of the treated PP film increased. There was an increase in the absorbance at the almost-visible
range, and C=C and C=O bands were found after the air discharge plasma treatment. A short plasma treatment of 15 seconds was
found to bring about a dramatic increase in the print density readings, but a decrease in print gloss. The time of the air
discharge plasma treatment was found to have no effect on the print density or print gloss at a high ink film thickness. The
results showed that air dielectric barrier discharge plasma treatment, for a few seconds, is effective in printing and is
economical for industrial use (this will be studied in detail in future work).
The comparison of corona-treated and flame-treated polypropylene (PP) films provides insight into the mechanism of these surface-oxidation processes. Atomic force mi-croscopy (AFM), contact-angle measurements, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize surface-treated biaxially oriented PP. While both processes oxidize the PP surface, corona treatment leads to the formation of water-soluble low-molecular-weight oxidized materials (LMWOM), while flame treatment does not. Computational modeling of the gas-phase chemistry in an air corona was performed using a zero-dimensional plasma-chemistry model. The modeling results indicate that the ratio of O to OH is much higher in a corona discharge than in a flame. Chain scission and the formation of LMWOM are associated with reactions involving O atoms. The higher ratios of O to OH in a corona are more conducive to LMWOM production. Surface-oxidized PP exhibits considerable thermodynamic contact-angle hysteresis that is primarily caused by microscopic chemical heterogeneity.
Of the several techniques available for the surface modification, plasma processing has proved to be very appropriate. The low temperature plasma is a soft radiation source and it affects the material only over a few hundred deep, the bulk properties remaining unaffected. Plasma surface treatment also offers the advantage of greater chemical flexibility. PET films are widely used for packaging and electrical insulation. The studies of adhesion and printability properties are important. In the present study PET films are treated in air plasma for different time of treatment. The improvement in adhesion is studied by measuring T-peel and Lap shear strength. In addition, printability of plasma treated PET films is studied by cross test method. It has been found that printability increases considerably for plasma treatment of short duration. Therefore it is interesting to study the surface composition and morphology by contact angle measurement, ESCA and AFM. Surface energy and surface roughness can be directly correlated to the improvement in above-mentioned surface related properties. It has been found that the surface oxidation occurs containing polar functional groups such as C-O, COO. A correlation of all such observations from different techniques gives a comprehensive picture of the structure and surface composition of plasma treated PET films.
Poly mer Interface and Adhesion provides the critical basis for further advancement in thisfield. Combining the principles of interfacial science, rheology, stress analysis, and fracturemechanics, the book teaches a new approach to the analysis of long standing problemssuch as: how is the interface formed; what are its physical and mechanical properties;and how does the interface modify the stress field and fracture strength of the material.The book offers many outstanding features, including extensive listings of pertinent references, exhaustive tabulations of the interfacial properties of polymers, critical reviews ofthe many conflicting theories, and complete discussions of coupling agents, adhesion promotion, and surface modifications. Emphasis is placed on physical concepts and mechanisms, using clear, understandable mathematics.Polymer Interface and Adhesion promotes a more thorough understanding of the physical, mechanical, and adhesive properties of multiphase, polymer systems. Polymer scientistsand engineers, surface chemists, materials scientists, rheologists, as well as chemical andmechanical engineers interested in the research, development or industrial applications ofpolymers, plastics, fibers, coatings, adhesives, and composites need this important newsource book.
Digital printing is suitable for short runs of highly personated packagings. The obvious benefit of digital printing is low waste amount and print-on-demand. The status of digital printing, at least in packaging sector, is still quite moderate, but the future is bright and it has been estimated that this method will increase more than the traditional printing techniques. The quality of digital printing will also approach that of offset. The aim of this study was to evaluate printability of various extrusion coatings used for packaging boards and to map out important material and process parameters.
One of the first applications of the study of flame spectra was for qualitative analysis, and indeed some elements were first discovered from their characteristic flame spectra, e.g. rubidium by Bunsen and Kirchhoff in 1861. Quantitative spectrochemical analysis now has frequent and important applications in both industry and research, especially for trace elements. The main sources for excitation of spectra are arcs, sparks and flames. The spectrum of an element, as developed in a flame, is relatively simple, consisting normally of only a few resonance lines; identification of the lines is thus much easier than with the more complicated arc or spark spectra, and confusion with lines of other elements is less likely. With such simple spectra it is often sufficient to use spectrographs or monochromators of low resolving power, or even in some cases just interference colour filters. Also flames are much steadier sources than arcs or sparks and are capable of higher precision for quantitative measurements. Since the previous edition of this book was written there have been major improvements in the techniques of flame photometry, especially in the use of atomic absorption and atomic fluorescence by C. T. J. Alkemande, A. Walsh, T. S. West and J. B. Willis and their colleagues, and these techniques are commented on here.
Atomic force microscopy was used to study the surfaces of oxygen-plasma-treated polypropylene (PP), kraft pulp, filter paper, and wood. The effect of plasma treatment on the adhesion properties between PP film and wood was evaluated by means of a peel test. The highest adhesion to wood resulted from the shortest treatment times used. The effects of plasma on the adhesion properties were more pronounced when both the PP film and the wood surface were treated. Oxygen plasma caused changes in the morphology of the materials: the treated PP surface was covered by a nodular structure, which was not seen on the untreated film. A similar nodular structure was also seen on the lignocellulosic materials. These nodules seemed to have poor interaction with the PP surface, resulting in a weak interface between the plastic film and wood.
The relationship between surface chemistry and morphology of flame treated low-density polyethylene (LDPE) was studied by various characterization techniques across different length scales. The chemical composition of the surface was determined on the micrometer scale by X-ray photoelectron spectroscopy (XPS) as well as with time of flight secondary ion mass spectrometry (ToF-SIMS), while surface wettability was obtained through contact angle (CA) measurements on the millimeter scale. The surface concentration of hydroxyl, carbonyl and carboxyl groups, as a function of the ``number'' of the flame treatment passes (which is proportional to the treatment time) was obtained. Moreover, a correlation was found with chemical composition and polarity, emphasizing the role of oxygen-containing functional groups introduced during the treatment. Carboxyl functional groups were specifically identified by fluorescent labeling and the results were compared with the ToF-SIMS data. In addition, atomic force microscopy (AFM) was used to evaluate changes in surface topography and roughness on the nanometer to micrometer length scales. After flame treatment, water-soluble low molecular weight oxidized materials (LMWOM), which were generated as products of oxidation and chain scission of the LDPE surface, agglomerated into small topographical mounds that were visible in the AFM micrographs. After rinsing the flame treated samples with water and ethanol, bead-like nodular surface structures were observed. The ionization state of flame treated LDPE surfaces was monitored by chemical force microscopy (CFM). The effective surface pKa values of carboxylic acid ( COOH) obtained by AFM were revealed by chemical force titration curves and the effective surface pKa values were found to be around 6.
The flame treatment of polypropylene (PP) film involves the use of impinging, conical flames to oxidize the surface of the PP.Depending on treatment conditions, the PP film can be exposed to an inhomogeneous environment because of the conical shape of the flames. This environment can lead to cross-web variations, or 'lanes', in the wettability of the film. We have developed a simple method to quantify these non-uniformities using the information provided by the Wilhelmy plate technique of dynamic contact angle measurement. Both surface-averaged and spatially resolved surface-energy data can be obtained by this technique. In the case of our PP film, the spatial nonuniformities were found to be caused by variations in surface chemistry, not topography. These nonuniformities are not observed on untreated PP. Use of this method enables a quantitative evaluation of the effects of flame-treatment process variables on treatment uniformity.
Contact-angle measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated biaxially oriented polypropylene (PP) films. While the surface of PP treated in a fuel-lean flame is highly oxidized, no watersoluble low-molecular-weight oxidized material (LMWOM) is formed by the flame treatment. A new computational model, SPIN, was used to determine the chemical composition of the impinging flames used to modify the PP. The SPIN model indicates that the species primarily responsible for the surface oxidation of the PP are OH, HO2, H2O2, and O2. Because the concentration of atomic O in the flame is low, there is little scission of the PP chains and no formation of LMWOM. AFM indicates that a 'nodular' surface topography is generated during the flame oxidation of the PP. The surface topographical features generated by flame treatment are probably the result of the agglomeration of intermediate-molecular-weight materials.
Contact-angle measurements, the ASTM standard wetting test for polyolefin films, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated polypropylene (PP) films. Two combustion models, STANJAN and PREMIX, were then used to determine the chemical and physical properties of the flames used to treat the PP films. Both the flame equivalence ratio and the position of the PP film in the flame are important variables in determining the extent of oxidation and improvement in wettability obtained by flame treating. The optimal equivalence ratio for the flame treatment of PP is 0.93, while the optimal luminous flame-to-film distance is 0-2 mm. Modeling of the combustion processes occurring in the flame provides evidence that the extent of treatment correlates closely with the concentrations of H, O, and OH radicals present in the flame. The extent of surface modification of the flame-treated PP does not appear to correlate with either the flame temperature or the concentraion of oxygen molecules. The mechanism of surface oxidation by flame treatment probably involves polymer-radical formation by O and OH, followed by rapid reaction of the polymer radicals with O, OH, and O2.
The flame treatment of a rubber-modified polypropylene has been studied using XPS, contact angle measurement, SEM, vapour-phase derivatisation, and a composite butt adhesion test. Optimum air-to-gas ratio and the distance from the inner cone tip to the polymer surface were found to be ∼ 11:1 and ∼ 0.5 cm, respectively. The lack of correspondence between contact angle and surface oxygen concentration was proposed to be due to the reorientation/migration of surface functional groups that had been incorporated during flame treatment. SEM shows changes in surface topography induced by intense flame treatment. Trifluoroacetic anhydride (TFAA) was found to derivatise-OH groups selectively by using model polymers. About 30% of the incorporated oxygen on flame-treated polypropylene surfaces was found to be present as-OH. Under most flame conditions studied, the interfacial adhesion with an epoxy adhesive or a polyurethane paint was found in excess of the polymer's cohesive strength. The results obtained are compared with those from a propylene homopolymer and an ethylene/propylene copolymer.
Specific reactions for the derivatization of oxygen-containing functional groups in polymer surfaces have been developed in order to improve the precision of analysis by X-ray photoelectron spectroscopy (xps). These have been used to probe the chemical composition of low density polyethylene (ldpe) surface-modified by electrical discharge treatment. Simultaneously the effect of derivatizing particular groups on the auto-adhesive behaviour of these surfaces has been examined. Two independent specific interaction mechanisms have been identified.
In this paper, polyester (PET) and polypropylene (PP) films are modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 kPa). The plasma-modified surfaces are characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS) as a function of energy density. The polymer films, modified in air, helium and argon, show a remarkable increase in hydrophilicity due to the implantation of oxygen-containing groups, such as C–O, O–CO and CO. Atomic oxygen, OH radicals, UV photons and ions, present in the discharge, create radicals at the polymer surfaces, which are able to react with oxygen species, resulting in the formation of oxygen-containing functionalities on the polymer surfaces. It is shown that an air plasma is more efficient in implanting oxygen functionalities than an argon plasma, which is more efficient than a helium plasma. In an air plasma, most of the created radicals at the polymer surface will quickly react with an oxygen particle, resulting in an efficient implantation of oxygen functionalities. However, in an argon and helium plasma, the created radicals can react with an oxygen particle, but can also recombine with each other resulting in the formation of an oxidized cross-linked structure. This cross-linking process will inhibit the implantation of oxygen, resulting in a lower efficiency. In argon plasma, more ions are present to create radicals, therefore, more radicals are able to react with oxygen species. This can explain the higher efficiency of an argon plasma compared to a helium plasma.
After the atmospheric pressure plasma treatment of polypropylene (PP) film surface, we measured the contact angle of the surface by using polar solvent (water) and nonpolar solvent (diiodomethane). We also calculated the surface free energy of PP film by using the measured values of contact angles. And then we analyzed the change of the contact angle and surface free energy with respect to the conditions of atmospheric pressure plasma treatment. Upon each condition of atmospheric pressure plasma treatment, the contact angle and surface free energy showed optimum value or leveled off. Through AFM analysis, we also observed the change of surface morphology and roughness before and after plasma treatment. The surface roughness of PP film showed the highest value when the plasma treatment time was 90 s. Finally, we analyzed the change of chemical compositions on the PP film surface through XPS. As the result of analysis, we observed that polar functional groups, such as –CO, –C=O, and –COO were introduced on the PP film surface after atmospheric pressure plasma treatment.
X-ray photoelectron spectroscopy (XPS) has been used to study the effects of flame treatment on three propylene polymers, i.e. a homopolymer, an ethylene-propylene copolymer and a rubber-modified polypropylene. Angle-resolved XPS has shown an enrichment in oxygen concentration at the near surface for all three propylene polymers when treated with a mild flame. A depletion in oxygen has been shown at the near surface of the rubber-modified polypropylene treated with an intense flame. The use of simple surface composition models shows that the oxidation depth induced by a mild flame treatment is around 50 Å, and that oxygen-containing functional groups may have reoriented or migrated a few ångströms away from the near surface of the rubber-modified polypropylene during the treatment with an intense flame.
Digital printing is increasingly being used for package printing. One of the major techniques of digital printing is dry-toner electrophotography. This paper evaluates the printability of three different extrusion coatings used for packaging boards: low-density polyethylene (PE-LD), ethylene methyl acrylate (E/MA) and polyethylene terephthalate (PET). Extrusion coatings in general have an impervious, chemically inert, nonporous surface with low surface energies that cause them to be non-receptive to bonding with toners. The most common methods used in improving the adhesion properties of polymer coatings are different surface treatments. These increase the surface energy and also provide the polar molecular groups necessary for good bonds between the toner and polymer molecules. The polymer coatings have been modified with electrical corona discharge treatment. The effects of corona on polymer surfaces and the correlation between surface modification and print quality have been evaluated. Results show that sufficiently high surface energy and surface-charge uniformity are necessary for even print quality and toner adhesion. E/MA and PET have the required surface-energy level without the corona treatment, but PE-LD needs surface modification in order to succeed in the electrophotographic process. E/MA also has exceptional surface-charge properties compared with PET and PE-LD. Polym. Eng. Sci. 44:2052–2060, 2004. © 2004 Society of Plastics Engineers.
Polymers have been applied successfully in fields such as adhesion, biomaterials, protective coatings, friction and wear, composites, microelectronic devices, and thin-film technology. In general, special surface properties with regard to chemical composition, hydrophilicity, roughness, crystallinity, conductivity, lubricity, and cross-linking density are required for the success of these applications. Polymers very often do not possess the surface properties needed for these applications. However, they have excellent bulk physical and chemical properties, are inexpensive, and are easy to process. For these reasons, surface modification techniques which can transform these inexpensive materials into highly valuable finished products have become an important part of the plastics and many other industries. In recent years, many advances have been made in developing surface treatments to alter the chemical and physical properties of polymer surfaces without affecting bulk properties. Common surface modification techniques include treatments by flame, corona, plasmas, photons, electron beams, ion beams, X-rays, and γ-rays.
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.
The surface free energy is an essential paper property affecting liquid/ink interaction with the ink-jet paper surface. Different ways of calculating surface energy components for ink-jet papers is introduced. The results given by the very useful van Oss–Chaudhury–Good (vOCG) bi-bidentate model are compared with simpler mono-bidentate and mono-monodentate models. The unbalance in the acid–base (AB) values of the vOCG-model is compensated for, and occasional negative roots obtained are removed when applying the simpler mono-bidentate- and mono-monodentate models. The simple and elegant mono-monodentate model produces comparable values with the other models, and is thus recommended. The calculated percent work of adhesion between the probe liquids and substrates correlates well with surface energy component values. Also the percent work of adhesion between the inks and substrates correlates with surface energy values.
Atomic force microscopy was used to study the surfaces of oxygen-plasma-treated polypropylene (PP), kraft pulp, filter paper, and wood. The effect of plasma treatment on the adhesion properties between PP film and wood was evaluated by means of a peel test. The highest adhesion to wood resulted from the shortest treatment times used. The effects of plasma on the adhesion properties were more pronounced when both the PP film and the wood surface were treated. Oxygen plasma caused changes in the morphology of the materials: the treated PP surface was covered by a nodular structure, which was not seen on the untreated film. A similar nodular structure was also seen on the lignocellulosic materials. These nodules seemed to have poor interaction with the PP surface, resulting in a weak interface between the plastic film and wood.
Adhesion between two substrates is a complex phenomenon which at present is still not well understood. The important existing adhesion models (electrical, diffusion, thermodynamic adsorption, chemical, etc.) are reviewed in order to try to explain their mechanisms. Thermodynamic adsorption is now believed to be one of the most importnat mechanisms by which adhesion is achieved. Difusion and wetting are kinetic means in attaining good adsorption of a polymer at the interface. In the case of this model (thermodynamic adsorption), the notion of surface energy is developed and the importance of this property in the understanding of adhesion phenomena is emphasized. The methods of determining the surface characteristics of low and high energy solids are presented. The role played by acid-base interactions in adhesion is also mentioned.
Corona discharge treatment (CDT) is a surface modification technique commonly used to treat plastic films prior to adhesive bonding, printing with inks, lamination to other films and other coating applications. In this study, the treatment conditions are, in energy terms, representative of those used in industrial and laboratory coating applications.
The physicochemistry of the surface of untreated and corona-discharge-treated biaxially oriented polypropylene (BOPP) film was investigated using a number of complementary surface analytical techniques: contact angle analysis; x-ray photoelectron spectroscopy (XPS); atomic force microscopy (AFM). This report describes the surface energetics, chemical functionality and morphology of polypropylene film before and after CDT. Both AFM and XPS were utilized, along with washing experiments, to investigate the presence of a weak boundary layer.
The surface energy was found, as expected, to increase with increasing energy of the corona. The functional groups incorporated onto the surface have been identified as hydroxyl [C–OH], peroxy [C–O–O], carbonyl [CO], ester [C–O–CO], carboxylic acid [HOCO] and carbonate [OC(O)O]. These groups are present in varying relative concentrations, depending on the energy of the corona utilized.
The morphology of the film changed after CDT. Initially, a fibrillar crystalline structure was observed, whereas after CDT a globular morphology became apparent. These globular features were attributed to low-molecular-weight oxidized material (LMWOM) created by CDT. The roughness of the film was not found to increase under the corona conditions employed.
Formation of LMWOM was found to be independent of treatment energy. However, two mechanisms have been suggested for its formation, dependent on the energy of treatment: below a threshold energy of ∼4 kJ m−2, oxidation and scission of the inherent low-molecular-weight boundary layer present on polyolefin films is the dominant means for the formation of LMWOM; above 4 kJ m−2, oxidation and scission of the polymer backbone is the main process.
This work provides a comprehensive reference around CDT of polypropylene film for industrial applications, while also informing how the optimal level of treatment can be determined. In the case of adhesion of silicones, it would be expected that optimal adhesion would be obtained where the maximum amount of oxygen incorporated was in a water-insoluble form. Copyright
Morphological and chemical changes of the surface of low-density polyethylene (LDPE), linear middle-density polyethylene (L-MDPE), and their 80/20 blend were studied by different techniques after corona-discharge treatment in air and subsequent annealing. The surface tension was determined by wetting; the roughness was measured by atomic force microscope (AFM), and the surface chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS), whereas the low-molecular-mass fraction washed off by chloroform by FTIR. The surface tension of the films increases with the electrode current. The surface roughness depends primarily on the polymer type and is less affected by the corona treatment. At the initial stage of annealing, posttreatment-type oxidation and hydrophobic recovery are competing. The former is more pronounced in L-MDPE, the latter in LDPE. After annealing at 50°C for 160 days, hydrophobic recovery becomes predominant in each film studied, which is accompanied by significant smoothening of the surface. According to XPS and FTIR results, this is due to the migration of low-molecular-mass components (oligomers, oxidized polymer fractions, and additives) to the surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1529–1541, 2000
This paper reviews recent studies on the mechanism of corona treatment of polyolefin films, specifically the chemical and physical changes of this process and the self-adhesion mechanism. Corona discharge of polymeric films introduces polar groups into the surfaces, which increases the surface energy and, as a consequence, improves substrate wettability and adhesion. The main chemical mechanism of corona treatment is oxidation. In addition, corona treatment can crosslink surface regions and increase the film cohesive strength.
Modification of polyolefin surfaces is often necessary to achieve improved printability, lamination, etc. Although corona discharge and flame treatments can produce the higher surface energy needed for these applications, the properties of the resulting surfaces are not always optimal. Atmospheric pressure plasma is a surface modification technique that is similar to corona discharge treatment, but with more control, greater uniformity, and higher efficiency. Using an atmospheric pressure plasma unit with a dielectric barrier discharge generated using an asymmetric pulse voltage, the effects of different gases, powers, and linespeeds on polyethylene surface treatment were studied. Our results show that atmospheric pressure plasma can be used to achieve higher long-term wettability, higher surface oxygen and nitrogen, and a greater range of surface chemistries with better robustness versus standard corona treatment. Atomic force microscopy results suggest significant differences in the mechanism of surface functionalization versus etching and ablation depending on the gases used. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 319–331, 1999
In a number of automotive applications of polypropylene (PP) good paint adhesion is essential. For industrial applications, the initially poor adhesion properties of PP compounds are often improved by flame treatment, resulting in good paint adhesion on the PP parts. For control purposes, intensive and time consuming paint tests are required. To relate adhesion behaviour with the parameters used in the flame treatment modification, several methods are applied such as simple surface tension tests with inks (wetting tests), contact angle measurements and standard XPS(ESCA) measurements. Unfortunately a good correlation is rarely obtained between these tests and the desired adhesion behaviour under rigid test conditions. Good wetting, for example, is necessary, but is no guarantee for good adhesion. In this paper results are presented on the characterisation of flame treated PP compounds by XPS, as well as the predictive information obtained from the XPS study concerning the paint adhesion behaviour of the modified PP surfaces.
Static secondary ion mass spectroscopy (fast atom bombardment mass spectroscopy), (SIMS (FABMS)) and Fourier transform infrared-photo-acoustic spectroscopy (FTIR-PAS) studies have been performed on samples of polypropylene subjected to different numbers of flame treatments. SIMS spectra allowed us to identify unambiguously the site of oxidation in the methyl pendant groups, because of the striking decrease in the intensity of the methyl fragment in positive-ion spectra. The behaviour of the surface concentrations of hydroxyl, formyl and carboxyl groups as a function of the number of flame treatments has also been observed, leading us to an hypothesis supporting the effectiveness of hydroxyl groups in promoting paint adhesion. FTIR-PAS spectra did not show evident changes on passing from untreated to flame-treated samples. This negative evidence is also important: it implies a limited depth of oxidation. In the light of previous XPS results and FTIR-PAS characteristics (thickness of the observed layer and sensitivity) we suggest a depth of oxidation of some 10 to 20 nm.
X-ray photoelectron spectroscopy showed that a normal flame treatment caused a high level of oxidation in low-density polyethylene. 0.02% of the antioxidant 2,6-ditertbuty-p-cresol did not reduce the degree of oxidation or the level of adhesion in contrast to the extrusion of low-density polyethylene. It is estimated that the depth of oxidation is between 40 and 90 which is much less than for a moderate chromic acid treatment or with extrusion. There were no significant changes in the XP-spectra or adhesion levels of flame treated samples after 12 months.
Oxidative (oxygen and air) RF-plasma treatment of HDPE was found as an effective tool for improving wettability, as well as for increasing its surface micro-hardness. The latter plasmas generate wide range of reactive species in the system, which undergo consecutive chemical reactions, creating thus several oxygen based functionalities at the interface (carbonyl, carboxyl, ether, peroxide etc.) as were detected by ATR FTIR and XPS analysis. An increased negative surface charge of plasma treated polyethylene (PE) confirms the presence of functional ionogenic groups containing oxygen. Simultaneously, the vigorous increase of the surface roughness was found as a result of the successful plasma etching.
Polypropylene (PP) samples have been treated in an ECR-rf plasma with several gases and at different treatment times and rf-potentials. Modifications of the surface topography have been analyzed by AFM and the results were correlated with previous XPS measurements of the surface chemistry. Plasma treatments with reactive gases (N2, O2) lead to the incorporation of new chemical species in the PP surface, whereas plasma treatments with noble gases (He, Ar, Xe) induce a desorption of hydrogen and a graphitization. The untreated PP sample has a rough surface with a granular structure. Plasma treatments with reactive gases induce weak morphology changes, but no new defined structures. Moreover, the modifications of the surface roughness are very sensitive to the treatment conditions. Noble gas plasma treatments, on the contrary, create a completely new surface morphology, which consists of a network of chains of 40–100 nm in diameter oriented in a random way. The size and the shape of these structures are very sensitive to the nature of the gas and to the treatment conditions (ion energy and dose, total energy deposition).
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