Adhesion promotion of thick fire-retardant melamine polymer dip-coatings at polyolefin surfaces by using plasma polymers

Melamine and melamine resins are widely used as fire retardants for polymer materials used in pharmaceutical, plastic, textile, rubber, and construction industry. Melamine-based flame retardants act by blowing off intumescent layers, char formation, and emission of quenching ammonia gas and diluent molecular nitrogen. Special advantages are: low cost, low smoke density and toxicity, low corrosive activity, safe handling, and environmental friendliness. Methylated poly(melamine-co-formaldehyde) (mPMF) was used as thick (≥40?μm) fire-retardant coating for plasma pretreated polymers. A combined low-pressure plasma pretreatment consisting of oxygen plasma exposure followed by deposition of thin poly(allylamine) (ppAAm) and poly(allyl alcohol) (ppAAl) plasma polymers as adhesion promoters have improved the adhesion of thick mPMF coatings strongly. Chemical structure and composition of deposited polymer films were characterized by infrared-attenuated total reflectance and X-ray photoelectron spectroscopy (XPS). After peeling, the peeled layer surfaces were also investigated for identification of the locus of failure and their topography using optical microscopy and XPS. Often the adhesion promotion was so efficient that the peeling of coating was not possible. Thermal properties of plasma polymers and dip-coating films were analyzed by thermogravimetric analysis. Significant improvement of fire-retardant properties of coated polymers was confirmed by flame tests.     

Characterisation of flame retardant plasma polymer deposited BOPP film

Abstract

Flame retardancy of polypropylene films was studied by plasma polymerisation technique. The surface of BOPP film was modified by boron containing plasma polymers at different plasma conditions. Plasma polymer coated polypropylene films were examined by flame retardancy test (limiting oxygen index, LOI) and TGA. Boron containing plasma polymer deposition on the film surface showed an improvement of flame retardancy. Furthermore, TGA thermograms pointed out that the first degradation temperature of treated polypropylene film was increased from 331 to 396°C, and the second degradation temperature was shifted from 401 to 455°C. Also, the plasma polymers were characterised by FTIR spectroscopy and XPS. According to XPS results, the BOPP surfaces treated with TMB showed significant difference in the composition with respect to the untreated sample. The FTIR spectra of plasma polymers obtained indicated that when the treatment time was increased to 60 min with a constant discharge power at 80 W, the absorption intensities of all the functional groups increased. As a result, boron containing plasma polymer treatment was found to be an effective method in enhancing the flame retardancy of BOPP film.     

Plasma polymerization of organoisothiocyanates. I. Characterization of deposition process and deposited materials

Thin polymer films were produced from methyl-, n-propyl-, allyl-, and phenyl isothiocyanates in an RF plasma, induced in an electrodeless flow system. The deposition rate of polymer film as well as its composition was found to be dependent on the substrate position in the reactor tube. The distinct effect of the monomer structure and the monomer saturated vapor pressure on the polymer deposition rate suggest a molecular nature for the plasma polymerization process and an important role for adsorption in the deposition process, respectively. The surface free energy data, evaluated by contact angel measurements, reveal the polar character of the organoisothiocyanate plasma polymers. The polar component of the surface appears to increase with the sulfur concentration in the polymer film.     

Thin ZrO2 coatings on polymers: role of interfacial adhesion

The interfacial characteristics between thin layers of zirconium dioxide and different thermostable polymers - polyimide, poly(ether ether ketone), and poly(ethylene terephthalate) - were studied. These layers, with a thickness ranging from a few nanometers to a few micrometers, were deposited by means of magnetron sputtering from a ZrO₂ target. In some cases, the polymers were subjected to plasma treatment (in the presence of different gases: air, Ar, and CO₂) prior to ZrO₂ deposition. X-ray photoelectron spectroscopy (XPS) analyses indicated clearly that zirconia coatings can be considered uniform when their thickness exceeds c. 10 nm. No interfacial covalent bonds between zirconia and polymers, such as Zr-O-C, were demonstrated. The level of adhesion at the coating-substrate interface was determined by a fragmentation test. The interfacial shear strength, related to the thermodynamic aspects of the polymer surfaces, i.e. their surface energy, was estimated. The result was in good agreement with the existence of physical interactions only, like van der Waals interactions, as shown by the XPS investigation.     

Plasma surface modifications for improved biocompatibility of commercial polymers

This report describes work using low pressure gas plasma techniques for the fabrication of surfaces designed for compatibility with biological tissue and fluids. The smoothness of the surfaces was investigated using scanning tunnelling microscopy (STM) and the wettability was assessed by measurement of air/water contact angles. Plasma surface treatment rendered fluorocarbon polymers wettable by polar liquids, but the wettability decreased with time during storage of the samples in air. Plasma polymerization, on the other hand, allowed the deposition of thin coatings which were more stable with time. STM of plasma polymers, which were coated with a sputtered film of platinum or gold, showed that these coatings were smooth and continuous. The attachment and growth of human umbilical artery endothelial cells was used to assess the biocompatibility of several plasma polymer surfaces. There was some correlation between the ability of a surface to grow cells and the wettability of that surface with polar liquids, but significant differences in cell growth on surfaces with very similar hydrophilicity indicated that other factors are at least as important.     

Enhanced adhesion of steel filaments to rubber via plasma etching and plasma-polymerized coatings

Zinc-plated steel filaments were coated with RF plasma polymers of acetylene or butadiene in order to enhance adhesion to rubber compounds. Plasma polymerization was carried out as a function of the plasma power, deposition time, and gas pressure. In order to maximize adhesion, argon plasma etching was performed and carrier gases such as argon, nitrogen, and oxygen were used. Plasma polymer coatings were characterized by FT-IR, Alpha-Step, and a dynamic contact angle analyzer. The adhesion of steel filaments was evaluated via a tire cord adhesion test (TCAT). The best results were obtained from a combined process involving argon etching (90 W, 10 min, 30 mTorr) and acetylene plasma polymer coating (10 W, 30 s, 30 mTorr) with argon carrier gas (25/5, acetylene/argon). These samples exhibited a pull-out force of 285 N, which is comparable to that from the brass-plated steel filament (290 N).     

The relationship between the oxidative polymers of soybean oil and flavor reversion

Summary The polymers formed during the autoxidation of soybean oil at 60°C. were isolated by a solvent-extraction method, using diethyl ether and pentanehexane as solvents. The more polar polymer fraction was further oxidized by air at 30°C., and the volatile material obtained was fractionated and characterized. It contained the same carbonyl compounds as the volatile material which has previously been obtained from reverted soybean oil, namely acetaldehyde, propionaldehyde, n-hexanal, and 2-pentenal. The more polar polymer fraction contained 21.04% of oxygen and degraded to volatile carbonyl compounds under vacuum as well as under oxygen-free nitrogen. Depolymerization and ethanolysis of these polymers were carried out in ethyl alcohol which had been adjusted to a normality of 3.5 with anhydrous hydrogen chloride. The polymeric substance formed on the filter presses of a soybean oil refinery could be depolymerized in a similar manner. It is therefore evident that oxidative polymers could be unintentionally introduced into soybean oil in various ways and serve as precursors of reversion compounds. Presented at the 27th fall meeting of the American Oil Chemists’ Society, November 4, 1953, in Chicago, Ill. Funds for this study were furnished by a grant-in-aid from Armour and Company, Chicago, Ill.     

Composition of gaseous combustion products of polymers

The gaseous products generated by the flaming combustion of ten kinds of synthetic polymers and a kind of wood (cedar) under the same conditions (sample weight, 0.1 g; temperature, 700°C air flow rates, 50 and 100 l./hr) were quantitatively analyzed by infrared spectrophotometry, gas chromatography, and colorimetric tube method. The main hydrocarbons generated were methane, ethylene, and acetylene. The amount of acetylene generated by the flaming combustion of polymers was much larger than the amount of acetylene formed by pyrolysis at 700°C in nitrogen. Acetylene increased in quantity with increasing air. For nitrogen compounds, hydrogen cyanide was generated from every polymer containing nitrogen used, but ammonia was detected only for nylon 66 and polyacrylamide. Nitrogen monoxide and nitrogen dioxide were detected only in small amounts. Nitrous oxide was detected in the gaseous products generated by the nonflaming combustion of urea resin and melamin resin. It was also found that about 70% of the nitrogen in N-66 and PAA was converted into nitrogen gas (N₂) by combustion under the conditions described above.     

Surface analyses of corona-treated poly(ethylene terephthalate)

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

Influence of operating parameters on plasma polymerization of acrylic acid in a mesh-to-plate dielectric barrier discharge

Plasma polymerization of acrylic acid is an interesting research subject, since the obtained coatings can have significant biomedical applications due to their high surface density of carboxylic acid groups. In this work, plasma-polymerized acrylic acid (PPAA) films are synthesized using a mesh-to-plate dielectric barrier discharge operated at medium pressure (10.0 kPa). Results clearly show that this reactor setup is able to deposit uniform PPAA films in contrast to the commonly used parallel plate reactor. Moreover, carefully planned experiments are conducted to study the influence of discharge power and monomer concentration on the chemical composition and thickness of the PPAA films. Results clearly show that input power strongly influences the properties of the deposited films: with increasing discharge power, monomer fragmentation in the discharge increases leading to a decrease in carboxylic acid functional groups and a lower polymer deposition rate. The effect of monomer concentration is less pronounced: only at very low monomer concentration (0.1 g/h), a decrease in carboxylic acid functional groups can be observed. The chemical composition and thickness of the PPAA films can thus be tailored by adjusting the operational parameters of the discharge.     

Reactive polymers. XII. Bead macroporous methacrylate terpolymers containing aldehyde groups

Bead macroporous terpolymers of methacrylaldehyde with methyl methacrylate and ethylene dimethacrylate were prepared. Preparation conditions (composition of the monomer mixture, of the inert components, concentration of the initiator and of the suspension stabilizer, and the rate of stirring) were discussed with respect to the properties of the terpolymers (porosity and concentration of reactive aldehyde groups). Concentration of reactive groups in the polymer was controlled by adding a third monomer. The analytically determined differences in the concentration of the reactive groups in the batch and in the polymer were interpreted (a) by the inaccessibility of the groups within the polymer bulk (for polymers with 30–50 mol-% of crosslinking agent), (b) by the presence of tetrahydropyran rings or acetate bonds between the chains, and (c) by the formation of extractable soluble polymers or copolymers, or by not reacting of parts of the monomers (observed predominantly with low-crosslinked polymers containing 10 mol-% of crosslinking agent).     

Surface modification of coil coatings with thin plasma polymer films structure and stability

Plasma deposition of a thin top layer with tailored properties is an effective strategy of modification of the organic coating surface. Thin plasma polymer layers are candidates and can provide superior hardness, scratch resistance, modified surface hydrophobicity and easy to clean properties.The present work studies the stability of thin plasma polymer films deposited as top layer on polyurethane coil coating systems. Microwave, hollow cathode and radio frequency plasma polymerization reactors were employed in order to deposit a thin SiO_x based plasma polymer layer.The plasma film stability was studied using surface analysis techniques, ex situ and in situ atomic force microscopy and scanning electron microscopy. Energy dispersive spectroscopy, FTIR spectroscopy and optical measurements confirm the composition and plasma layer properties. The structure of the plasma layers was investigated by means of transmission electron microscopy.The surface morphology together with composition evolution allows the study of the stability of the different coatings. The structure examination of the formed plasma polymer film offers good clarification for coating failure. Decrease of the operating pressure during plasma polymerization and oxygen concentration in precursor mixture lead to formation of compacter layer with higher stability. Introduction of fluorine-containing precursor also increases the anti-weathering performance of the plasma polymer films.     

Experimental study of the spontaneous thermal homopolymerization of methyl and n‐butyl acrylate

This article presents an experimental study of the spontaneous thermal homopolymerization of methyl acrylate (MA) and n‐butyl acrylate (nBA) in the absence of any known added initiators at 120 and 140°C in a batch reactor. The effects of the solvent type, oxygen level, and reaction temperature on the monomer conversion and polymer average molecular weights were investigated. Three solvents, dimethyl sulfoxide (DMSO; polar, aprotic), cyclohexanone (polar, aprotic), and xylene (nonpolar) were used. The spontaneous thermal polymerization of MA and nBA in DMSO resulted in a lower conversion and higher average molecular weights in comparison to polymerization in cyclohexanone and xylene under the same conditions. The highest final conversion of both monomers was obtained in cyclohexanone. The high polymerization rate in cyclohexanone was most likely due to an additional initiation mechanism where cyclohexanone complexed with the monomer to generate free radicals. Bubbling air through the mixture led to a higher monomer conversion during the early stage of the polymerization and a lower polymer average molecular weight in xylene and cyclohexanone; this indicated the existence of a distinct behavior between the air‐ and nitrogen‐purged systems. Matrix‐assisted laser desorption/ionization time‐of‐flight analysis of the polymer samples taken from nitrogen‐bubbled batches did not reveal fragments from initiating impurities. On the basis of the identified families of peaks, monomer self‐initiation is suggested as the principal mode of initiation in the spontaneous thermal polymerization of MA and nBA at temperatures above 100°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Novel thermally stable and chemically resistant epoxy polymers derived from phenylene oxides

Thermogravimetric and differential thermal analysis data are presented for three novel bisepoxy monomers and formulated coatings derived therefrom. The coatings were insensitive to impact in liquid oxygen and showed excellent resistance to liquid nitrogen tetroxide, concentrated nitric acid, and a variety of organic solvents. All coatings showed excellent adhesion to metals and oxidation resistance superior to any known commercial epoxy polymer. Thermal resistance was excellent at 500°F. for periods of at least 500 hr. in air. Other data on these novel epoxy polymers are also presented.     

Modification of wettability of a stainless-steel plate by cathodic plasma polymerization of trimethylsilane–oxygen mixtures

Wettability (by water) of a stainless-steel plate was modified by depositing an ultrathin layer of a plasma polymer of trimethylsilane (TMS) and an oxygen mixture. Plasma polymerization was carried out by cathodic glow discharge polymerization, in which a substrate stainless-steel plate was used as the cathode of the de glow discharge. The plasma polymer of TMS (oxygen mol fraction = 0) is very hydrophobic, but the addition of oxygen in the monomer mixture increased the hydrophilicity of the plasma polymer. The value of cos θ (θ: advancing contact angle of water) linearly increased with the mol fraction of oxygen in the monomer mixture. Oxygen in the monomer mixture acts as (1) an ablating agent of a carbon-based plasma polymer and (2) a comonomer for a silicon-based plasma polymer. The atomic composition of a plasma polymer, which can be expressed as SiC_xO_y, changes (x decreases and y increases) as the mol fraction of oxygen increases. © 1995 John Wiley & Sons, Inc.     

Preparation of nanocrystalline titanium carbonitride coatings using Ti(N(Et)<Subscript>2</Subscript>)<Subscript>4</Subscript>

Titanium carbonitride films with a thickness of 80–150 nm have been synthesized by low pressure chemical vapor deposition from a gas mixture of tetrakis(diethylamino)titanium and ammonia at temperatures of 773–973 K. The film properties have been studied by spectroscopy (IR, XPS, and EDS), scanning electron and atomic force microscopy, and ellipsometry. The studies have shown that the films consist of polycrystals with a size of 15–80 nm; their structure contains chemical bonds of titanium with atoms of carbon, nitrogen, and oxygen. The film composition is consistent with the data of the previously performed thermodynamic modeling of the deposition of different condensed phases in the Ti-C-N-H-O system. As the deposition temperature increases in the range under study, the refractive index of the films increases from 2.1 to 2.7.     

Transformation of polymers in a stream of low-temperature arc discharge plasma

Spraying of polymer materials in a low-temperature plasma stream is a very efficient way of depositing polymer coatings on large surfaces. The deposition of powdered polymers by an arc discharge plasma flow and spraying from the bulk have been compared. The properties of powdered polymers do not change considerably during transportation by the stream because of the short residence of the particles in the plasma. When spraying from the bulk, polymers are transported in the form of melt droplets (polyethylene, polycarbonate) or in gaseous phase (polytetrafluoroethylene); autohesion of the droplets or secondary polymerization occurs, respectively, on the substrate surface. This process offers high-quality thin films and coatings whose structure depends significantly on the characteristics of the substrate as well as on the structure of the source polymer. Obtained polymer coatings contain nitrogen and oxygen entrapped from the atmosphere as well as (on the glass surface) the products of glass etching. This fact enables one to vary widely the properties of the coatings. Furthermore, the problem of obtaining combined protective coatings in which polymer melt fills the pores between metal particles can be solved successfully in a united technological cycle including plasma spraying of the polymer and the metal. © 1995 John Wiley & Sons, Inc.     

Organometallic polymer-derived interfacial coatings on carbon and SiC fibers

Organosilicon and organogermanium polymers containing unsaturated carbon–carbon bonds were used as precursors for the SiC-based interfacial coatings on commercially available carbon and silicon carbide fibers and fabrics. The approach based on usage of the organometallic polymer solutions allowed to obtain uniform, adherent, crack-free and non-bridging SiC-based interfacial coatings on carbon and SiC fibers. The coated fibers retain their tensile strength. The morphology, composition, structure of coated fibers were evaluated by various analytical techniques. The drop-like germanium-containing phase was detected in the organogermanium polymer-derived coating on carbon and SiC fibers.     

Analysis of annealed thin polymer films prepared from dichloro(methyl)phenylsilane by plasma polymerization

Thin plasma polymer films were deposited from a mixture of dichloro(methyl)phenylsilane (DCMPS) vapor and gaseous hydrogen in an rf (13.56 MHz) capacitive coupling deposition system on pieces of silicon wafers. Some of samples were annealed in a vacuum to temperatures ranging from 450 to 700°C. The chemical composition, structure, and surface morphology of the annealed samples and those stored in air at room temperature were studied by FTIR, XPS, SEM, and optical microscopy. The thermal stability and decomposition of the plasma polymer with increasing temperature were characterized using thermogravimetry together with mass spectrometry. The plasma polymer was stable to a temperature of 300°C. Above that temperature, the material started to decompose together with additional crosslinking due to the incorporation of extra oxygen atoms forming new siloxane bonds. The plasma polymer was tough at room temperature but much more brittle after annealing. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2106–2112, 2001     

Plasma deposition of adhesion-promoting polymer layers onto polypropylene for subsequent covering with thick fire retardant coatings

Melamine resins were used as 50-μm-thick fire retardant coatings for polypropylene (PP). Preceding deposition, low-pressure plasma polymer films of allyl alcohol were coated onto PP to improve the adhesion between PP and melamine resin coatings. The efficiency of such fire retardant coatings was confirmed by flame tests. The plasma-deposited polymer and the dip-coated melamine resin films were characterized by Fourier transform infrared-attenuated total reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS). The adhesion of coatings was measured using a 90° peel test with a doubled-faced adhesive tape. To detect the locus of failure, the peeled layer surfaces were inspected using optical microscopy and XPS. Thermal properties of PP thick melamine resin-coated films were analyzed by thermogravimetric analysis.