Surface Modifications Produced by N2 and O2 RF Plasma Treatment on a Synthetic Vulcanized Styrene-Butadiene Rubber

A low-pressure gas RF plasma-treatment has been used to improve the adhesion of a synthetic vulcanized rubber to polyurethane adhesive as an environmentally friendly alternative surface treatment to the conventional chemical treatments. A sulfur vulcanized styrene-butadiene rubber (R2) containing a noticeable amount of zinc stearate and paraffin wax (both providing a lack of adhesion) in its formulation was used. Two different gases (oxygen and nitrogen) were used to generate the RF plasma, which was performed at 50 Watt for 1–15 min. The modifications produced on the R2 rubber surface by the RF plasma treatments were assessed by using advancing and receding contact angle measurements, ATR-IR spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Force Microscopy (SFM), and Scanning Electron Microscopy (SEM). Adhesion evaluation was obtained from T-peel tests of joints produced between plasma treated R2 rubber and a polyurethane adhesive. The plasma treatment produced a decrease in advancing and receding contact angle values on R2 rubber, irrespective to the gas used to generate the RF plasma. The treatment with RF plasma produced the partial removal of hydrocarbon moieties from the rubber surface and the generation of oxygen moieties. An increase in surface roughness was also produced. The degree of oxidation and the amount of hydrocarbon-rich layer removed from the R2 rubber surface was more important by treating with oxygen plasma. The treatment of rubber in oxygen plasma for 1 minute was enough to noticeably increase adhesion of R2 rubber to polyurethane adhesive. However, an extended treatment (15 min.) was needed when nitrogen plasma was applied to R2 rubber. The loci of failure in the joints produced between the plasma treated R2 rubber and the polyurethane adhesive was assessed by using ATR-IR spectroscopy. A mixed failure (partially adhesional and partially cohesive failure in the rubber) in the joints produced with plasma treated R2 rubber joints was always obtained.     

Interactions at the interface between thermoplastic rubber and polychloroprene adhesive

The interface produced between a chlorinated thermoplastic styrene‐butadiene‐styrene rubber and a polychloroprene (PCP) adhesive has been studied and compared to the interface produced using a polyurethane (PU) adhesive. Chlorination of the rubber was produced by spin coating solutions of trichloroisocyanuric acid in methyl ethyl ketone. The adhesive solution was spin coated on to the chlorinated rubber and the interface between the chlorinated rubber and the adhesive was analyzed by infrared spectroscopy. Chlorination of the rubber produces cross‐linking of the outermost chlorinated and oxidized rubber surface, which becomes insoluble in toluene. The chlorinated rubber chains are able to migrate through the chlorinated rubber/adhesive interface and produce a cross‐linked interface. Similar interfaces are obtained with PU or PCP adhesive. However it is the addition of a thermoreactive phenolic tackifier resin to the PCP adhesive, which imparts appropriate rheological properties to the PCP adhesive, responsible for the increased adhesion properties. Copyright © 2008 John Wiley & Sons, Ltd.     

Properties of solvent based polyurethane adhesives containing fumed silicas

Five hydrophilic and two hydrophobic fumed silicas of different surface area and particle size were added to solvent based polyurethane adhesives. Silica addition produced a noticeable increase in the adhesive viscosity, imparted negative thixotropy, increased the storage modulus (G') and improved the green adhesion of chlorinated rubber/PU adhesive/chlorinated rubber joints. Those modifications were more pronounced in the adhesives which contain hydrophilic silicas.     

Influence of Rubber Formulation on Surface Modifications Produced by RF Plasma

The effectiveness of nitrogen, oxygen and air Radio Frequency (RF) plasma treatments on two styrene-butadiene vulcanized rubbers with a different formulation has been studied. The presence of an antiadherent surface layer containing low-molecular weight ingredients (sulfur-rich vulcanization agents and wax) from SW (Sulfur-Wax) rubber formulation requires an extended plasma treatment capable of removing this surface layer. When the percentage of antiadherent moieties is reduced in ZS (Zinc Stearate) rubber formulation, shorter plasma treatment times are enough to modify rubber surface and increase its polarity by the creation of C–O and C=O polar groups that enhance adhesion towards a polyurethane adhesive. Air and oxygen plasma treatments are more aggressive than nitrogen plasma and therefore they are more effective in removing the antiadherent layer of the outermost rubber surface layer prior to oxidation of the rubber surface.     

Chemical nature of adhesion: Plasma modified styrene-butadiene elastomer and polyurethane adhesive joints

A study of the mechanism of gluing between plasma-modified styrene-butadiene elastomer (SBS) surfaces and polyurethane (PU) adhesives is presented in this paper. The plasma treatment was carried out employing low-pressure O₂ plasma generated by an RF discharge (13.56 MHz). FTIR-ATR spectroscopy and peel tests were utilized to characterize the SBS surfaces before and after the plasma treatment. It was found that hydroxyl groups are mainly created on the SBS surface by the plasma treatment and their concentration reveals very good linear correlation with the peel strength of the SBS-PU joints. The grafting of phenyl isocyanate (analog of the PU curing agent) into the plasma-treated SBS surface was also investigated. The process was performed at 353 K, that is at temperature in which the adhesive-bonded joints were made. It was shown that all hydroxyl groups on the SBS surface react with isocyanate groups forming carbamate bonds. The results obtained in this work strongly confirm the conception of the adhesion by chemical bonding between SBS and PU.     

Effect of surface modification on the properties of plasma-polymerized hexamethyldisiloxane thin films

Plasma-polymerized hexamethyldisiloxane (pp-HMDSO) thin films have been deposited in a radiofrequency (RF) remote plasma-enhanced chemical vapor deposition (PECVD) system, on different types of substrates: silicon wafers, glass, quartz crystals, and chemiresistor structure. The as-grown thin films have been post treated in two types of reactive plasmas produced in SF₆ and O₂ gases. The effect of this surface modification on different properties of the as-grown pp-HMDSO thin film (chemical structure, elemental composition, surface morphology, film density and thickness, optical bandgap, and electrical resistivity) has been investigated. It is found that SF₆ plasma and O₂ plasma surface modifications of the as-grown pp-HMDSO thin film induce property changes different from each other. SF₆ plasma converted the as-grown pp-HMDSO film to a more porous material and caused a narrowing of its optical band gap of about 33%, while O₂ plasma induced a lowering of film electrical resistivity of about two orders of magnitude.     

Features of composites prepared by radical graft-polymerization of styrene to a hydrophilic macromer adsorbed on ultrafine colloidal particles

Polymer modifications of ultrafine monodispersed colloidal metal oxide particles, smaller than 80 nm in diameter, by the graft-polymerization of styrene to a hydrophilic macromer adsorbed on the surface were investigated. The polymerization in ethanolic silica and titania colloid solution, which had negatively larger ζ-potentials, ?30 and ?42 mV in neutral aqueous solution respectively, gave poly(styrene)–silica or titania composite, being of nonspherical shape. The modifications of colloidal particles, having lower surface energy, such as Al(OH)₃ and CeO₂–TiO₂–SiO₂ complex, led to the formation of spherical composites, ranging in size from 500 to 3000 nm, of scattered metal oxide or hydroxide particles.     

Low-pressure plasma chlorination of styrene-butadiene block copolymer for improved adhesion to polyurethane adhesives

Studies concerning plasma-surface chlorination of a styrene-butadiene block copolymer (SBS), improving its adhesion to polyurethane adhesives (PU), are presented in this paper. The plasma was generated by an RF discharge (13.56 MHz, plate electrode reactor) in CCl₄ under low pressure. The 180°-peel test, contact angle measurements and XPS spectroscopy were utilized to investigate the SBS surface. A drastic increase in the adhesion (the peel strength 5-7 times higher than that for the non-treated surface) was observed after only a few seconds of the plasma treatment. It was shown that CCl, COH and >CO are the most important functional groups formed as a result of the plasma treatment and they play the crucial role in the chemical bonding between the SBS surface and the adhesive. H₂O molecules strongly attached to the SBS surface were also found. It was determined, however, that they reduce the gluing power. A very good correlation between the concentration of the functional groups and the peel strength was established. On the other hand, no correlation between the peel strength and the surface free energy (estimated from the contact angle measurements) was observed. It indicates that the thermodynamic adhesion is unimportant in this case and confirms the dominant role of the chemical adhesion.     

Synthesis of Maleated Ionomers via Ring‐Opening Reaction of Epoxidized (Styrene‐Butadiene‐Styrene) Triblock Copolymer with Potassium Hydrogen Maleate and Study of their Properties

A novel method for synthesizing maleated ionomer of (styrene‐butadiene‐styrene) triblock copolymer (SBS) from epoxidized SBS was developed. The epoxidized SBS was prepared via epoxidation of SBS with performic acid formed in situ by 30% H₂O₂ and formic acid in cyclohexane in the presence of polyethylene glycol 600 as a phase transfer catalyst. The maleated ionomer was obtained by a ring‐opening reaction of the epoxidized SBS solution with an aqueous solution of potassium hydrogen maleate. The optimum conditions for the ring‐opening reaction and some properties of the ionomers were studied. It is necessary to use phase transfer catalyst, ring‐opening catalyst and a pH regulator (dipotassium maleate) for obtaining the epoxy group conversion over 90%. The product was characterized by FTIR spectrophotometry and transmission electron microcroscopy (TEM) to be an ionomer with domains of maleate ionic groups. With increasing ionic groups, the water absorbency and the dilute solution viscosity of the ionomer increase, whereas the oil absorbency decreases. The tensile strength and ultimate elongation of ionomers increase with ionic group content and are higher than those of the original SBS without using any ionic plasticizer, which is usually used with the sulfonated ionomer. The ionomers with 1.2–1.7 mmol ionic groups/g exhibit optimum mechanical properties and behave as thermoplastic elastomers. The ionomer can be used as a compatibilizer for the blends of SBS with oil resistant chlorohydrin rubber (CHR). Addition of 3 wt% ionomer to the blend can increase the tensile strength and ultimate elongation of the blend optimally. The compatibility of the blends enhanced by adding the ionomer was shown by scanning electron microscopy (SEM). The blend of equal weight of SBS and CHR compatibilized by the ionomer behaves as a toluene resistant thermoplastic elastomer.     

Enhancement of polymer hydrophobicity by SF6 plasma treatment and argon plasma immersion ion implantation

In this study sulphur hexafluoride (SF₆) plasmas and argon plasma immersion ion implantation (ArPIII) techniques have been applied to improve the hydrophobicity of poly(tetrafluoroethylene) (PTFE), polyurethane and silicone surfaces. As evaluated by water contact angle measurements, all the treatments resulted in a significant enhancement in the hydrophobicity of the polymers. However, exposure of the treated samples to air induced a strong variation in their hydrophobicity as a consequence of post‐plasma reactions between atmospheric species and remnant surface free radicals. X‐ray photoelectron spectroscopy results strongly suggest that for polyurethane and silicone the surface fluorination by SF₆ plasmas and the creation of new carbon bonds and radicals are the main agents for hydrophobicity enhancement. The PTFE exposed to ArPIII revealed increases in the contact angles after exposure to air. A significant incorporation of oxygen and the formation of new carbon bonds were revealed by XPS measurements. Copyright © 2003 John Wiley & Sons, Ltd.     

Dynamic mechanical and dielectric properties of epoxidized SBS triblock copolymer

The morphological and dynamic properties of epoxidized styrene–butadiene–styrene block copolymers were studied and compared with their parent styrene–butadiene–styrene block copolymer (SBS). Two peaks were observed in the mechanical loss (tan δ) curve which can be attributed to segmental motion of epoxidized polybutadiene (EPPB) and polystyrene. Analysis by DSC thermograms also showed the linear increase of glass transition temperature for EPPB domain with the epoxy group content. Phase separated structures of epoxidized SBS as observed by TEM suggests a considerable degree of mixing occurred between phases after 80 mol % of the double bonds in SBS were epoxidized. The interfacial region displays a third peak and causes much steeper drop in modulus at higher temperature than T_g of EPPB. Parallel dielectric relaxation measurements were also made in the frequency range of 30 Hz–1 KHz as a function of temperature. In each dielectric constant (?′) curve, there is a maximum near the T_g of EPPB determined from the dielectric loss tangent curve. The shift in T_g of EPPB versus epoxy group content was consistent with that measured by the thermal and dynamic mechanic analysis. These findings indicated an 8°C shift in glass transition temperature as the epoxy group content in EPPB increased 10%.     

Surface modification of ethylene‐co‐tetrafluoroethylene films by remote plasmas

The surface modifications of ethylene‐co‐tetrafluoroethylene (ETFE) surfaces by six plasmas (direct H₂, Ar, and O₂ plasmas and remote H₂, Ar, and O₂ plasmas) were investigated with two questions in mind: (1) what plasma could effectively modify ETFE surfaces and (2) which of the CF₂? CF₂ and CH₂? CH₂ components in ETFE was selectively modified? The plasma exposure led to a weight loss from the ETFE surfaces and changes in the chemical composition on ETFE surfaces. The weight‐loss rate showed a strong dependence on what plasma was used for the modification. The remote H₂ plasma led to the lowest rate of weight loss in the six plasma exposures, and the direct O₂ plasma led to the highest rate of weight loss. During exposure to the plasmas, defluorination occurred, and two new C_1s components [? CH₂? CHF? CH₂? and ? CH₂? CH(O? R)? CF_x? , and ? CH₂? CHF? CF₂? , ? CH₂? C(O)? CF_x? , and ? CF_x? C(O)? O? ] were formed on the modified ETFE surfaces. Defluorination was strongly influenced by what plasma was used for the modification. The remote H₂ and Ar plasmas showed high defluorinations of 55 and 51%, respectively. The remote O₂ plasma showed a low defluorination of only 25%. Conclusively, the remote H₂ and Ar plasma exposure effectively modified ETFE surfaces. With the exposure of these surfaces to the remote H₂ plasma, the CF₂? CF₂ component was predominantly modified, rather than the CH₂? CH₂ component. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2871–2882, 2002     

Surface characterization of plasma‐modified poly(ethylene terephthalate) film surfaces

Poly(ethylene terephthalate) (PET) film surfaces were modified by argon (Ar), oxygen (O₂), hydrogen (H₂), nitrogen (N₂), and ammonia (NH₃) plasmas, and the plasma‐modified PET surfaces were investigated with scanning probe microscopy, contact‐angle measurements, and X‐ray photoelectron spectroscopy to characterize the surfaces. The exposure of the PET film surfaces to the plasmas led to the etching process on the surfaces and to changes in the topography of the surfaces. The etching rate and surface roughness were closely related to what kind of plasma was used and how high the radio frequency (RF) power was that was input into the plasmas. The etching rate was in the order of O₂ plasma > H₂ plasma > N₂ plasma > Ar plasma > NH₃ plasma, and the surface roughness was in the order of NH₃ plasma > N₂ plasma > H₂ plasma > Ar plasma > O₂ plasma. Heavy etching reactions did not always lead to large increases in the surface roughness. The plasmas also led to changes in the surface properties of the PET surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surfaces decreased. Modification reactions occurring on the PET surfaces depended on what plasma had been used for the modification. The O₂, Ar, H₂, and N₂ plasmas modified mainly CH₂ or phenyl rings rather than ester groups in the PET polymer chains to form C? O groups. On the other hand, the NH₃ plasma modified ester groups to form C? O groups. Aging effects of the plasma‐modified PET film surfaces continued as long as 15 days after the modification was finished. The aging effects were related to the movement of C?O groups in ester residues toward the topmost layer and to the movement of C? O groups away from the topmost layer. Such movement of the C?O groups could occur within at least 3 nm from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3727–3740, 2004     

Surface Properties of Low Density Polyethylene upon Low-Temperature Plasma Treatment with Various Gases

The surface of a LDPE was modified by Ar, O₂, N₂, CO₂ gaseous plasma. The changes in surface morphology and surface wettability were investigated using AFM and SEM. The surface chemical changes of LDPE were also characterized by FTIR-ATR. The SEM and AFM results demonstrated variable changes in surface roughness for different types of plasma gas used, the changes being more for the Ar and N₂ plasma treatments. Considering the nature of the LDPE film, XRD studies were carried out to determine changes in the percentage crystalinity. The results showed that all low pressure O₂, Ar, N₂, CO₂ gas plasmas improved the wettability of LDPE films. Contact angles decreased significantly depending on the discharge powers and exposure times. Surface morphology was also found to vary with plasma discharge powers, exposure times, and the type of gas being used. Ar and N₂ gas plasmas in general produced more superior results.     

Microwave and RF surface wave sustained discharges as plasma sources for plasma chemistry and plasma processing

The surface wave produced plasma belongs to a class of RF and microwave induced plasmas. It results from the propagation of an electromagnetic wave which uses the plasma column it sustains and the plasma tube as its sole propagating media. This type of plasma offers several advantages compared to the positive column plasma of dc discharges or to other RF and microwave produced plasmas. Surface wave plasmas require no internal electrodes, and they can be applied over an extremely broad range of wave frequencies (27 MHz to 10 GHz demonstrated) and gas pressures (about 10^–4 Torr to a few times the atmospheric pressures). Using the surface wave plasma technique, a large variety of plasma column diameters have been created (0.5–150 mm demonstrated) and no limitation on plasma column length (column up to 6 m long demonstrated) has been found. The surface wave produced plasma is used in elemental analysis and to sustain emission in lasing media. This article is intended as a guide for potential users of surface wave plasmas in the field of plasma processing and plasma chemistry.     

Fluorine-based plasmas: Main features and application in micro-and nanotechnology and in surface treatment

Fluorine cold plasmas produced by an electrical discharge in SF₆, CF₄, CHF₃ or C₄F₈ gases, principally, have two main fields of application. The first and historical application is etching of materials for microelectronics and later for micro- and nanotechnology. The second concerns the modification of surface properties, mostly in terms of reflectance and wettability. After an introduction to cold plasmas and plasma–surface interaction principles, the article aims at presenting successively the evolution of fluorine plasma etching processes since the origin with respect to other halogen-based routes in microelectronics, the important and raising application in deep etching and microtechnology, and finally some examples in surface treatment.     

Synthesis and Characterization of Crystalline Styrene‐b‐(Ethylene‐co‐Butylene)‐b‐Styrene Triblock Copolymers

By merit of dual catalysis of the cationic rare‐earth complex [(η⁵‐Flu‐CH₂‐Py)Ho(CH₂SiMe₃)₂(THF) (Flu = fluorenyl, Py = pyridyl) for the living polymerizations of butadiene (BD) and styrene (St), the crystalline styrene‐butadiene‐styrene (SBS) triblock copolymers consisting of elastic polybutadiene (PBD) sequences with suitable 1,4 regularity (about 70%) and crystalline syndiotactic polystyrene (sPS, [rrrr] > 99%) sequences were successfully synthesized through sequential addition of St, BD, and St monomers. The catalytic system showed high polymerization activities for St and BD in a controlled manner. The crystalline styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene (SEBS) triblock copolymers were obtained by hydrogenation of the above SBS copolymers. The observation of a strong endothermic peak at 266 °C in their differential scanning calorimetry (DSC) curves confirmed the existence of the sPS blocks in the crystalline SEBS different from the industrial product Kraton SEBS‐1652. Thermal degradation temperature of the crystalline SEBS (418 ± 2 °C) indicated the well thermostability and process window of this polymer. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1243–1249     

Alternating copolymerizations of styrene and acrylic monomers initiated with carbanions in the presence of ZnCl2

On electrochemical initiation of alternating copolymerizations of styrene–acrylonitrile (AN) and styrene–diethyl fumarate (DEF) in the presence of ZnCl₂, radical anions of AN–ZnCl₂ and DEF–ZnCl₂ complexes produced at the cathode were assumed to initiate copolymerization. In analogy with the cathode-initiated copolymerization, the radical anions of AN–ZnCl₂ and DEF–ZnCl₂, generated with the carbanions such as sodium naphthalene, disodium α-methylstyrene tetramer dianion, and butyllithium, were also found to produce alternating copolymers of styrene–AN and styrene–DEF. On the contrary, no polymers were obtained from methyl methacrylate (MMA)–styrene and methacrylonitrile (MAN)–styrene in the presence of ZnCl₂ either with carbanions or by electrochemical reduction. Styrene–MAN–ZnCl₂ yielded an alternating copolymer with carbanions upon introduction of oxygen.     

Effects of the processing sequence and critical interparticle distance in PA6-clay/mSEBS nanocomposites

Polyamide 6 (PA6) based nanocomposites were modified by maleinized styrene/ethylene-butylene/styrene (mSEBS) rubber through a modified processing with the aim of ameliorating the microstructure and performance of the nanocomposites, as well as examining the parameters that make the brittle/ductile transition of nanocomposites change. The studied parameters were the rubber and the organoclay contents. After the modified processing, the average dispersed particle size decreased and an overall increase in the impact performance occurred. This is attributed to a more effective reaction between the maleic groups of the rubber and the amine end groups of the PA6 when there is no surfactant present. The analysis of the variation of the critical interparticle distance (τ_c) indicates that it depends on the modulus of elasticity of the matrix (i.e., on the organoclay content) and on the interfacial adhesion, wherein higher modulus of elasticity and higher adhesion leads to smaller τ_c values.     

Fracture toughness of nylon‐6 blends with maleated rubbers

The fracture toughness of blends of nylon‐6 with maleated ethylene–propylene rubber and maleated styrene/hydrogenated butadiene/styrene triblock copolymer was investigated with a single‐edge‐notched three‐point‐bending instrumented Dynatup test. The blends for which the rubber particle size was less than 0.7 μm fractured in a ductile manner over the whole range of ligament lengths, whereas the blends with particles larger than 0.7 μm showed a ductile‐to‐brittle transition with the ligament length. In this regime, ductile fracture was observed for specimens with short ligaments, whereas brittle fracture was seen for those with long ligaments. The ductile fracture behavior was analyzed with the essential‐work‐of‐fracture model, whereas linear elastic fracture mechanics techniques were used to analyze the brittle fracture behavior. The fact that the ductile fracture energy was larger for the blends with the styrene/hydrogenated butadiene/styrene triblock copolymer than for those with ethylene–propylene rubber was due to the larger dissipative energy density of the blends based on the styrene/hydrogenated butadiene/styrene triblock copolymer. Both the critical strain energy release rate (G_IC) and the plane‐strain critical stress intensity factor (K_IC) increased as the rubber particle size decreased for both blend systems. The G_IC and K_IC parameters had similar values, regardless of the rubber type, when the rubber particle size was fixed. The transition ligament length was near the size criterion for plane‐strain conditions for both blend systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1739–1758, 2004