Improvement of paint adhesion to a polypropylene bumper by plasma treatment

Improvement of the paint adhesion to a polypropylene (PP) bumper has been investigated without using a primer by treating the bumper surface with O₂, H₂O, and acetylene plasmas. All the plasma treatments resulted in an increase of the adhesion strength in dry conditions. The adhesion strength could be increased up to a value comparable to that obtained by applying a primer. The treated surfaces were quite stable for 7 days in air. After exposure to wet conditions, however, the adhesion strengths for both O₂ and H₂O plasma-treated samples decreased significantly, while the adhesion strength for the acetylene plasma-treated sample did not change much.     

Surface coating protective against oxidative plasma etching of polypropylene

Polypropylene (PP) sheets were coated with the ultrathin polymer layers by plasma polymerization of hexamethyldisiloxane and two other Si-containing monomers, and the protection effects from oxidative plasma etching were investigated. Etching was evaluated by the weight loss of PP sheets after the exposure to an oxidative plasma of O₂ or air. The effects of plasma polymer coating on the etching resistance were investigated with respect to the type of plasma polymer, thickness of a coating layer, oxidative plasma etching conditions, etc. Weight of the coated PP sheets was less changed and the substrates remained stable after a certain period of oxidative plasma treatments, during which time the original PP film had prominently lost weight. The importance of the crosslinked network with —Si— MPO components in plasma polymers on the etching resistance was suggested from the results. Infrared spectra were taken and analyzed with the plasma polymers after O₂-plasma treatments, and the increase in the Si—O structure was indicated by the increase in the peak intensity at 1023 cm⁻¹. Stabilization against oxidative etching was attributed to the crosslinked Si—O structure on the surface layer. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1049–1057, 1997     

Ta and TaN adhesion to high-temperature fluorinated polyimides. Surface and interface chemistry

The practical adhesion of Cu/Ta to high-temperature fluorinated polyimides (FPIs) was initially good but failed after the reliability test involving treatment under the FPI curing condition five times (T₅). But a thin layer (40 nm) of TaN greatly improved the reliability of the Cu/Ta-to-FPI adhesion. Both CF₄ and in situ Ar plasma treatments of FPIs prior to metal deposition enhanced the metal-to-FPI adhesion strength. CF₄ plasma enriches the FPI surface with fluorine atoms and most of fluorine is bound to carbon as CF₃, CF₂, and CF. Ar plasma first destroys CF₃ and then C=O groups of the FPIs to yield a polar surface. The locus of failure by a 90° peel test was found to be within the Ar-plasma-modified FPI layer but it moved toward the bulk of FPI, i.e. away from the metal-polymer interface, after the T₅ reliability test. The locus of failure in the case of weak adhesion where no plasma treatment was done on FPI films was in the near-interface region within the FPI layer, and the failure seemed to occur in the weak boundary layers of FPI surfaces. Plasma treatment removes weak boundary layers and also increases FPI surface roughness. These two effects combined improved the metal-to-FPI practical adhesion.     

Adhesion Improvement by UV Grafting onto Polyolefin Surfaces

High Density Poly(ethylene) (HDPE) and Poly(propylene) (PP) were subjected to several surface treatments, namely UV grafting of hydroxyethylmethacrylate (HEMA), plasma deposition of HEMA and oxygen plasma treatment. Treated surfaces were subjected to two post-treatment routines (extraction with ethanol and high temperature aging). The effect of these treatments on the adhesion of HDPE and PP to epoxy coated studs was evaluated by a pull test. No adhesion at all was recorded on untreated samples. On the other hand, all the treatments yield high bond strength in the case of HDPE: an average bond strength of about 290 kg/cm² and of about 200 kg/cm² was observed after UV grafting and plasma treatments. The treated samples were practically insensitive to post-treatments. As to PP, which undergoes chain scission in plasma, it is best treated by the comparatively milder conditions of UV grafting, which yields an average bond strength similar to that observed on HDPE. O₂ and HEMA-plasma-treated PP show a mean bond strength close to 50 kg/cm², and are deeply affected by the post-treatment routines.     

Effect of oxygen functional groups of reduced graphene oxide on the mechanical and thermal properties of polypropylene nanocomposites

Reduced graphene oxide (rGO) with various surface structures was prepared by reducing graphene oxide (GO) with hydrazine hydrate (N₂H₄), sodium borohydride (NaBH₄) and l ‐ascorbic acid, respectively. The resulting rGO were used to fabricate rGO/polypropylene (PP) nanocomposites by a melt‐blending method. The surface structure of rGO as well as multifunctional properties of rGO/PP nanocomposites were thoroughly investigated. It was shown that rGO with highest C/O ratio could be obtained by reducing GO with N₂H₄. The crystallization behaviors, tensile strength, thermal conductivity and thermal stability of rGO/PP nanocomposites were significantly improved with the increase of C/O ratio of rGO. For example, with only 1 phr (parts per hundred PP) rGO reduced by N₂H₄, the degree of crystallinity, tensile strength, maximum heat decomposition temperature and thermal conductivity of PP nanocomposite were increased by 6.2%, 20.5%, 48.0 °C and 54.5%, respectively, compared with those of pure PP. Moreover, the thermal degradation kinetics indicated that the decomposition activation energy of rGO/PP nanocomposites could be enhanced by adding rGO with higher C/O ratio. © 2018 Society of Chemical Industry     

Adhesion of SiO2 thin films to plasma-treated SUS304 stainless steel substrates

The adhesion strength of the coated SiO₂ thin film to SUS304 stainless steel substrates with various surface treatment conditions is studied in this research. The surface of the SUS304 stainless steel substrate is first treated with 1000-W plasma and then a SiO₂ thin film is deposited onto the surface via radio-frequency magnetron sputtering. Scanning electron microscopy is employed to observe the surface and cross section of the coating and X-ray diffraction is used to analyze the crystallographic structure. Moreover, a nanoscratch test instrument was employed to examine the indentation, scratches, coating hardness, modulus of elasticity, coefficient of friction, and critical adhesion of the SiO₂ film and to obtain surface profiles. A comparison of the coating adhesion of the substrate surfaces with and without plasma treatment indicates that critical adhesion increases significantly after Ar/N₂/O₂ plasma treatment.     

Improving the adhesion properties of polypropylene using a liquid-phase sulfonation treatment

This work describes the effects of a stable, short-reaction time, liquid-phase sulfonation technique aimed at improving the adhesion properties of polypropylene. The relationships among SO₃ concentration (0.15, 0.2, and 0.3 N), treatment time, surface chemistry, and adhesion debond strength have been investigated for polypropylene (PP) sheets sulfonated with SO₃ dissolved in 1,1,2-trichloro 1,2,2-trifluoroethane and neutralized using ammonium hydroxide (NH₄OH) or polyethyleneimine (PEI). It was confirmed that PEI neutralized specimens, compared to untreated PP, exhibited a larger increase in debond strength (~269% increase) than similarly treated specimens neutralized with NH₄OH (~210% increase). ATR-FTIR spectroscopy indicates the formation of sulfonic acid, ethylenic, ketone and alcoholic hydroxyl groups. These results are supported by X-ray photoelectron spectroscopy (XPS) that show the O : C ratios increasing from 0.03 to 0.25 for both the NH₄OH and PEI, and the S : C atomic ratios increasing from 0.0 to 0.05 and 0.06 for the NH₄OH and PEI, respectively. Furthermore, XPS examination of PEI neutralized specimens revealed a nitrogenated surface (~6%), providing evidence that PEI had grafted onto the sulfonated surface. The observed increases in adhesion are attributed to formation of polar functionalities and increased wettability (as measured by water contact angle measurements). The neutralizing agent also affects degree of adhesion improvement: the PEI causes larger increases in adhesion compared to the NH₄OH. The physical effects of sulfonation were examined using environmental scanning electron microscopy (ESEM), which showed crack formation after 2 min of treatment. Sulfonation times beyond 5 min degraded the polymer surface (severe microcracking and sloughing of the surface layer) decreasing the adhesion debond strength.     

Effect of Cu2O thin film on Cu–Sn alloy coated steel surface in promoting interfacial adhesion with rubber

In the present study, effect of Cu₂O film deposited via successive ionic layer adsorption and corresponding chemical reaction (SILAR method) on Cu–Sn coated steel substrate was explored for the purpose of improving the adhesion of steel with rubber. The effect of the relative alkali concentration in the oxide film deposition bath and the number of immersion cycles on the interfacial adhesion affecting the nature of oxide film deposited, its thickness and surface coverage were investigated. In the current study, Cu–Sn coated steel bead wire with coated surface roughness (R_a) around 2 μm showed an improvement of 33% in adhesion (in terms of pull out force) with an optimum alkali/Cu ion concentration of 25:1 with single dipping cycle attributed to an optimum oxide coating thickness of ~70 nm. Surface morphology study exhibited formation of thicker coating with increase in number of dipping cycles. Satisfactory thermal stability of the Cu₂O film was confirmed as no re-oxidation of the Cu₂O film to CuO was observed in the 200 °C heat treated samples.     

Role of helium plasma pretreatment in the stability of the wettability,adhesion, and mechanical properties of ammonia plasma-treated polymers. Application to the Al-polypropylene system

The stability of a plasma-treated polymer surface is an important issue, but very often a surface rendered wettable by the treatment is found to revert to a less wettable state with time. The purpose of this work was to minimize the ageing phenomenon by stabilizing the surface layer via crosslinking using an inert gas discharge. The stability of the wettability, adhesion, and mechanical properties of treated polypropylene (PP) has been investigated by a comparative study of two different plasma treatments (i.e. an NH₃ plasma and a He plasma pretreatment carried out before the NH₃ plasma; He plasma is well known to crosslink polymer surfaces). The aluminium-polypropylene (Al-PP) interfaces present very different features depending on the gas treatment. The role of the treatment time has been pointed out and under our experimental conditions, a treatment time of the order of a few seconds seems to be an overtreatment leading to degradation of the adhesion and mechanical properties. A broad interphase was obtained for an NH₃-overtreated PP, in contrast to the abrupt one formed when pretreated with the helium gas followed by NH₃ treatment. Good correlations between wettability and mechanical properties with adhesion measurements were established.     

Surface modification of low‐density polyethylene (LDPE) film and improvement of adhesion between evaporated copper metal film and LDPE

To improve the interfacial adhesion between evaporated copper film and low‐density polyethylene (LDPE) film, the surface of LDPE films was modified by treating with chromic acid [K₂Cr₂O₇/H₂O/H₂SO₄ (4.4/7.1/88.5)]/oxygen plasma. Chromic‐acid‐etched LDPE was exposed to oxygen plasma to achieve a higher content of polar groups on the LDPE surface. We investigated the effect of the treatment time of chromic acid in the range of 1–60 min at 70°C and oxygen plasma in the range of 30–90 sec on the extent of polar groups created on the LDPE. We also investigated the surface topography of and water contact angle on the LDPE film surface, mechanical properties of the LDPE film, and adhesion strength of the evaporated copper metal film to the LDPE film surface. IR and electron spectroscopy for chemical analysis revealed the introduction of polar groups on the modified LDPE film surface, which exhibited an improved contact angle and copper/LDPE adhesion. The number of polar groups and the surface roughness increased with increasing treatment time of chromic acid/plasma. Water contact angle significantly decreased with increasing treatment time of chromic acid/plasma. Combination treatment of oxygen plasma with chromic acid drastically decreased the contact angle. When the treatment times of chromic acid and oxygen plasma were greater than 10 min and 30 sec, respectively, the contact angle was below 20°. With an increasing treatment time of chromic acid, the tensile strength of the LDPE film decreased, and the film color changed after about 10 min and then became blackened after 30 min. With the scratch test, the adhesion between copper and LDPE was found to increase with an increasing treatment time of chromic acid/oxygen plasma. From these results, we found that the optimum treatment times with chromic acid and oxygen plasma were near 30 min and 30 sec, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1677–1690, 2001     

Role of polymer chain end groups in plasma modification for surface metallization of polymeric materials

How to improve adhesion between poly(oxybenzoate‐co‐oxynaphthoate) (Vecstar OC and FA films) and copper metal by Ar, O₂, N₂ and NH₃ plasma modification was investigated. The mechanism of adhesion improvement is discussed from the viewpoint of chemical and physical interactions at the interface between the Vecstar film and copper metal layer. The adhesion between Vecstar OC film and copper metal was improved by chemical rather than physical interactions. Polymer chain end groups that occur at Vecstar OC film surfaces contribute effectively to adhesion. This improvement in adhesion is due to interactions between copper metal and O?C groups formed by plasma modification. Aggregation of the O?C groups to the copper metal/Vecstar OC film interface is a key factor for good adhesion. From this aspect, heat treatment of plasma‐modified Vecstar OC films on glass plates is effective in the aggregation, and the peel strength for the copper metal/Vecstar OC film system reached 1.21 N (5 mm)^?1. Copyright © 2009 Society of Chemical Industry     

Photochemical surface modification of polypropylene for adhesion enhancement by using an excimer laser

Polypropylene (PP) surface in water was photochemically modified to render it hydrophilic using ArF excimer laser radiation. The chemical stability of PP is attributed to the C-H and C-H₃ bonds present. Thus, it is considered that H atoms are selectively pulled out from the area irradiated with ArF excimer laser light and are replaced with OH functional groups in the presence of water. In this treatment, the irradiated sample becomes hydrophilic with enhanced adhesion properties. The experimental conditions for this surface treatment were ArF laser fluence of 12.5 mJ/cm² and a shot number of 10000. The treated PP and stainless steel were bonded with epoxy adhesive and the tensile shear strength was 46 kg/cm².     

Surface functionalization of polypropylene nonwovens by metallic deposition

In this study, melt‐blown polypropylene (PP) nonwovens were used as substrates for the metallic deposition of copper. The substrates were pretreated by O₂ plasma, followed by treatments such as sensitization, activation, and reduction. The effects of the copper sulfate concentration, reaction temperature, and plasma power on the conductivity and adhesion strength of the PP nonwovens were investigated after copper deposition. The morphology of the PP nonwovens after copper deposition, analyzed by scanning electron microscopy and atomic force microscopy, revealed that copper nanoclusters were deposited on the fiber surface with a smooth surface morphology and dense structure. X‐ray photoelectron spectroscopy indicated that the copper was present mainly in the form of the elementary substance, which coexisted with a little Cu²⁺. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Stability control of adhesional interaction in a protective coating/metal system

The adhesion failure area (_n) at the polymer coating/steel interface in aggressive media was measured using an a.c. impedance technique. A _n value of 0.2-5.0% of the total surface was found for different film-formers (epoxy, vinyl, divinyl acetylene) after 10 days' exposure in electrolyte. It was shown that the _n value and its changes during exposure [_n = f(τ)] depend on the nature of the film-former, the solution composition, and the dissolved oxygen (C_O2) and chloride ion (C_Cl-) concentrations. It was found that the epoxy coating adhesion stability was much higher in comparison with the vinyl and divinyl acetylene coatings. An increase in the chloride ion concentration resulted in an increase of _n for the coatings studied, i.e. destruction of adhesional bonds, but at the same time relative increments δ_n/δτ and δ_n/δCO₂, were confined within the same range. The mechanism of the observed processes is explained from the point of view of competitive adsorption of hydroxide and chloride ions at the metal surface and the activating effects of the chloride ions on the metal dissolution.     

Adhesion of Pseudomonas aeruginosa to contact lenses after exposure to multi-purpose lens care solutions

Elemental surface compositions of contact lenses were measured after exposure to different lens care solutions (LCS) using X-ray photoelectron spectroscopy and were related to adhesion and detachment of Pseudomonas aeruginosa. Etafilcon A and polymacon contact lenses, prior to and after exposure to LCS were fixed on the bottom plate of a parallel plate flow chamber after which P.aeruginosa #3 was allowed to adhere for 2 h. After adhesion, bacterial detachment was stimulated by perfusing the chamber with an LCS or by passing an air-bubble through the chamber. After exposure to an LCS, the adhesion of P.aeruginosa #3 could either be enhanced or decreased, depending on the contact lens and LCS involved. Initial deposition rates of P.aeruginosa #3 could not be related with changes in elemental surface composition of the contact lenses, but decreased with an increasing ratio of oxygen involved in O C bonds relative to oxygen in O C bonds. P.aeruginosa #3 adhered tenaciously to both types of contact lenses and the passage of an air-bubble through the flow chamber detached only up to 9% of the adhering bacteria. Alternatively, the LCS most effective in decreasing bacterial adhesion after exposure (LCS A), was least effective in detaching adhering P.aeruginosa #3 (8-15%), while the other LCS detached up to 42% of adhering bacteria. In conclusion, different LCS have different abilities to detach the adhering P.aeruginosa #3 from contact lens surfaces and all leave adsorbed components on the surface after soaking. Adsorbed components rich in O C bonds increased adhesion of P.aeruginosa #3 under the conditions used in this study and should, therefore, be avoided.     

Weatherability of polypropylene/waste tire dust blends: Effects of trans‐polyoctylene rubber and dynamic vulcanization

Two series of polypropylene (PP)‐based blends containing waste tire dust (WTD) from scrap tires were naturally weathered. From investigations of specimens after 3‐month and 6‐month weathering periods, the overall indication was that blends with trans‐polyoctylene rubber (TOR) and sulfur dynamic vulcanization (PP/WTD_T‐SDV) resisted the deleterious effects of atmospheric factors better than the blends without TOR and dynamic vulcanization (PP/WTD). Tensile test results showed that PP/WTD_T‐SDV blends exhibited higher tensile strength and elongation at break than PP/WTD blends. The PP/WTD_T‐SDV blends also recorded higher retention values of tensile strength and elongation at break than PP/WTD blends. An increment in the Young's modulus of PP/WTD blends was noticed, however, after both exposure periods. The morphology of the fracture surfaces showed that less WTD_T‐SDV than WTD was removed from the PP matrix, a result indicating the presence of improved interfacial adhesion in PP/WTD_T‐SDV blends. Micrographs of exposed surfaces showed the formation of easily removed layers on the surface of PP/WTD_T‐SDV, which might act as a protective covering and resist the deleterious effects of weathering on the internal parts of the PP/WTD_T‐SDV blends. Thermograms showed that the melting temperatures of the exposed PP/WTD_T‐SDV specimens were higher than those of PP/WTD samples after both outdoor exposures. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers.     

Plasma treatment of polymethyl methacrylate to improve surface hydrophilicity and antifouling performance

Surface modification of polymethyl methacrylate (PMMA) by O₂/CF₄ plasma is investigated to improve hydrophilicity and antifouling performance of PMMA. The PMMA surface before and after treatment is characterized by atomic force microscopy, contact angle measurement, and X-ray photoelectron spectroscopy. Antifouling properties are evaluated by protein adsorption and bacterial adhesion experiments using Staphylococcus aureus in vitro. Higher O₂ content in the mixture gas promotes hydrophilicity of the plasma-treated PMMA, while a hydrophobic surface forms at higher CF₄ content. Modifying PMMA improves antifouling performance regardless of the O₂/CF₄ volume ratio, and this improvement increases with rising CF₄ content in O₂/CF₄ plasma working gas. Functional groups C O and C F are detected in O₂/CF₄ plasma-treated PMMA surface and the ratio of C O to C F can be controlled by the O₂/CF₄ volume ratio in the plasma working gas.     

Surface modification of tetrafluoroethylene–hexafluoropropylene (FEP) copolymer by remote H2, N2, O2, and Ar plasmas

Tetrafluoroethylene–hexafluoropropylene (FEP) copolymer sheets were modified by remote H₂, N₂, O₂, and Ar plasmas, and the effects of the modification on adhesion between FEP sheets and copper metal were investigated. The four plasmas were able to modify the FEP surfaces' hydrophilicity. Defluorination and oxidation reactions on the FEP surfaces occurred with exposure to the plasma. The hydrophilic modification by H₂ plasma was best, followed by modification by O₂, Ar, and N₂ plasmas. The surface modification of FEP by all four remote plasmas was effective in improving adhesion with copper metal. The peel strength order of the FEP/Cu adhesive joints was H₂ plasma > Ar plasma > N₂ plasma > O₂ plasma. Mild surface modification is important for the adhesion improvement of FEP with Cu metal. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1258–1267, 2002     

Enhanced adhesion of epoxy-bonded steel surfaces using O2/Ar microwave plasma treatment

Steel surfaces have been modified using low pressure microwave plasma to enhance its adhesion with an epoxy adhesive. Optimization of the wettability of the surface was done using contact angle measurements for varying plasma parameters. Maximum wettability (19.9°) was obtained at 1000 W microwave power with 20 min of treatment time, −50 V sample bias and 1.67% O₂/Ar gas flow rate ratio. Enhanced wettability of the steel surface was attributed to increased surface roughness and oxide deposition. Using atomic force microscopy, surface roughness was observed to increase from 64.4 nm for the untreated surface to 76.7 nm for the O₂/Ar plasma treated surface. Deposition of oxides on the steel surface was also confirmed by the energy dispersive x-ray spectroscopy. Moreover, the increase in the total surface energy to 53.2 mN/m for the O₂ plasma treated steel surface supported the enhancement of its wettability, and hence, the adhesion with epoxy. Based on tensile test results, the adhesion strength of epoxy-bonded O₂/Ar plasma treated surfaces at optimum settings was increased to 3816.0 N, which is significantly higher compared to 3038.3 N for the epoxy-bonded untreated surfaces.     

Surface analysis of aminated polypropylene films as an adhesion promoter to polycarbonate film

The surface composition of aminated polypropylene films (PP‐g‐NH₂) and their adhesion to polycarbonate (PC) film were evaluated. The detection of amine groups on PP‐g‐NH₂ surfaces was obtained by X‐ray photoelectron spectroscopy (XPS). Contact angle measurements showed a decreased in the polarity on PP‐g‐NH₂ surface The adhesion between laminated films of PP‐g‐NH₂ and PC was evaluated by T‐peel test and optical microscopy. PC deposited on the PP‐g‐NH₂ surfaces was confirmed by FTIR‐ATR and SEM analysis of delaminated films, which is an indicative of an interaction between reactive sites of each polymer. The adhesion performance between PC and PP was improved by using amine modified polypropylene (PP‐g‐NH₂). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011