Improvement of Adhesion Between Liquid Crystalline Polyester Films by Plasma Treatment

Surface modification of thermotropic liquid crystalline aromatic polyester (LCP) films was carried out by low-pressure plasma treatment to improve the initial adhesion as well as the long-term adhesion reliability, a measure of durability between the LCP films used as substrates for printed circuit boards. Plasma irradiation was carried out in various plasma gases with different plasma modes such as reactive-ion-etching, and direct-plasma (DP) with pressures ranging from 6.7 Pa to 26.6 Pa. The introduction of polar groups on the film surface such as phenolic hydroxyl groups and carboxyl groups enhanced the initial adhesion by increased chemical interaction. However, if the concentration of polar groups became too high, the longterm adhesion reliability estimated by the pressure cooker test was degraded due to the acceleration of the penetration of water molecules into the interface. A large surface roughness was also effective in preventing the decrease in the long-term adhesion reliability. However, too much increase in surface roughness decreases the long-term adhesion reliability. The DP-treatment in the O₂ atmosphere at a gas pressure of 6.7 Pa was found to be the best plasma condition for both the initial adhesion as well as the long-term adhesion reliability between the LCP films.     

Atomic force microscopy analysis of cellulose triacetate surface modified in low temperature argon plasma and its adhesion behavior

The surface of cellulose triacetate (CTA) film was modified with gaseous plasma of several discharge power in the presence of Argon (Ar) gas at 0.5 torr pressure. After gas plasma etching, the surface structure of the films is analyzed by atomic force microscopy (AFM) and measured with peel strength. Furthermore, the wetting properties of the CTA film treated with Ar plasma are studied by contact angle measurement. Peel strength after plasma treatment was increased with increasing plasma treatment time. However, treatments of plasma greater than 7 min did not find an additional increase in peel strength, similarly to roughness and morphological changes of AFM. The water contact angle decreased for an initial treatment time due to the improved wettability of the film, but showed an increasing trend for a higher treatment time (7 min). These results show that Ar plasma treatment is a convenient tool for improving the adhesive properties of CTA film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3963–3971, 2006     

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     

The effect of atmospheric‐pressure air plasma discharge power on adhesive properties of aramid fibers

After exposure to the atmospheric‐pressure air plasma at different discharge powers, the adhesion characteristics of Twaron aramid fibers were investigated. For the 12 s‐300 W plasma treatment, the interlaminar shear strength of Twaron fiber reinforced thermoplastic poly(phthalazinone ether sulfone ketone) was increased from 46.0 to 61.7 MPa by 34.1%, and the diffusion of water molecule into the resulting composites was proved to be effectively prevented. These results showed that surface adhesive properties of the plasma‐treated aramid fibers were improved. At the power level of 300 W, X‐ray photoelectron spectroscopy analysis revealed the increases in concentrations of oxygen and nitrogen polar groups on the fiber surface, and atomic force microscopy observations led to the conclusion that the fiber surface morphology was changed and the surface roughness was greatly increased. These new polar and irregular surface structures accounted for the better adhesion between the fiber and the matrix, while due to the reasonability of this discharge power level applied to the surface modification, the measured fiber tensile strength only decreased by 2.0%. POLYM. COMPOS., 37:620–626, 2016. © 2014 Society of Plastics Engineers     

Adhesion behavior of different annealed polyphenylquinoxaline foils treated using low pressure plasma

The aim of this study was to investigate the adhesion behavior of polyphenylquinoxaline (PPQ) foils. PPQ foils were initially produced and then annealed in vacuum furnace at different temperatures. The surface of PPQ was activated with GHz‐low pressure plasma (lp‐plasma) using oxidative (O₂) and noble (Ar, Ar/He) gases. An epoxy adhesive was used to glue the PPQ foil with a sheet of steel. The adhesions of foils were examined using 90°‐peel test. Observations from scanning electron microscopy (SEM) and atomic force microscopy (AFM) in addition to the gravimetry measurements were used to interpretate the effects of plasma treatment of adhesion of foils. The results showed that the peeling resistance values were significantly dependent on plasma treatment time and power as well as annealing conditions. In case of PPQ foils where the adhesion was significantly enhanced, it was observed that the fracture changed from adhesion mode at the interface between the adhesive layer and the PPQ foil to cohesive mode, which was seen either in the layer nearby the PPQ surfaces or in the foil itself. Furthermore, furrowed structures were observed at the fracture surface and they were oriented transversely to the peeling direction. SEM and AFM graphs showed that the surface roughness of PPQ foils increased significantly with increasing plasma treatment time and it was more pronounced when using oxidative than noble gas. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39949.     

Effects of surface modification by oxygen plasma on peel adhesion of pressure‐sensitive adhesive tapes

Surfaces of poly(isobutylene) (PIB) and poly(butylacrylate) (PBA) pressure‐sensitive adhesive tapes were treated by oxygen plasma, and effects of surface modification on their adhesive behavior were investigated from the viewpoint of peel adhesion. The peel adhesion between PIB and PBA pressure‐sensitive adhesive tapes and stainless steel has been improved by the oxygen plasma treatment. The surface‐modification layer was formed on PIB and PBA pressure‐sensitive adhesive surfaces by the oxygen plasma treatment. The oxygen plasma treatment led to the formation of functional groups such as various carbonyl groups. The treated layer was restricted to the topmost layer (50–300 nm) from the surface. The GPC curves of the oxygen plasma‐treated PBA adhesive were less changed. Although a degradation product of 1–3% was formed in the process of the oxygen plasma treatment of the PIB adhesive. There are differences in the oxygen plasma treatment between the PIB and PBA adhesives. A close relationship was recognized between the amount of carbonyl groups and peel adhesion. Therefore, the carbonyl groups formed on the PIB and PBA adhesive surfaces may be a main factor to improve the peel adhesion between the PIB and PBA adhesive and stainless steel. The peel adhesion could be controlled by changing the carbonyl concentration on the PIB and PBA adhesive surfaces. We speculate that the carbonyl groups on the PIB and PBA adhesive surface might provide an interaction with a stainless steel surface. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1392–1401, 2000     

常压等离子体改善高性能纤维粘结性的研究

以氦气为载气,氧气为反应气体,对高强度聚乙烯和Twaron 1000芳纶两种高性能纤维进行常压等离子体处理,来改善纤维的粘结性能;采用单纤维抽拔实验测定等离子体处理前后纤维与环氧树脂之间的界面剪切力;利用原子力显微镜和X射线光电子能谱仪分析等离子体处理前后纤维表面形态和化学成分的变化。结果表明:高强度聚乙烯纤维和芳纶经常压等离子体处理后,纤维表面粗糙度增加,纤维表面碳元素含量下降,羟基、羧基等含氧或氮的极性基团增加,纤维粘结性能得到提高,但其强度无明显变化。     

Tantalum and chromium adhesion to polyimide. Part 2. Peel and locus of failure analyses

Ta and Cr adhesion to 3,3'-4,4'-biphenyl tetracarboxylic acid dianhydride-p-phenylenediamine derived (BPDA-PDA) polyimide (PI) surfaces has been studied before treatment, and after CF₄ reactive ion etching (RIE), and Ar sputtering. The initial peel adhesion results for both metals on the BPDA-PDA surfaces are comparable and show increased peel adhesion as a function of the surface treatment in the following order: virgin (no treatment) < Ar sputter < CF₄ RIE ~ CF₄ RIE followed by Ar sputter. The surface roughness effect on metal/PI adhesion has also been investigated. The data suggest that the surface roughness does not primarily affect peel adhesion. In this case, it is the removal of the weak boundary layer and the cracking of the residual PI on the metal peel interface surface during the peeling process which cause the increase in the peel strength. It is also proposed that the changes observed in the peel strength as a function of the surface treatment are due to differences in the fracture toughness of the modified PI layers rather than differences in the surface roughness.     

Surface properties of glass plates activated by air,oxygen, nitrogen and argon plasma

Glass surface properties were investigated after air, nitrogen, oxygen and argon plasmas treatment. The samples were treated by low pressure plasma for 30 s with the gas flow 22 sccm. After modification kinetics of water spreading was measured. Surface topography was determined using optical profilometry, scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that using all types of gases plasma treatment leads to decrease of the surface roughness. The kinetics of water spreading depends on gases type used for glass plates modification. Analyzing the photoelectron spectra the increase of oxygen amount on the surface was observed. For the increase of wettability and adhesive properties of plasma treated glass, the introduction of new polar functional groups on the surface has greater influence than changing the surface roughness.     

Effect of plasma treatment and electron beam radiations on the strength of nanofilled adhesive‐bonded joints

This investigation highlights the adhesion performance of carbon fiber‐ and glass fiber‐reinforced polyphenylene sulfide when joined by high‐performance neat epoxy adhesive and nanofilled epoxy adhesive. A significant increase in the surface energy of these materials is observed after the surface modification with atmospheric plasma treatment. An increase in surface roughness is observed after exposing the surface to plasma. Lap shear testing of untreated and plasma‐treated joints is carried out to correlate the improvement in adhesion properties with the joint strength. A considerable increase in joint strength is observed when the surfaces of these materials are modified by atmospheric pressure plasma. There is a further increase in joint strength when the composites are joined by nanofilled epoxy adhesive, and subsequent exposure to electron beam radiations results in minor increase in the joint strength. Finally, the fractured surfaces of the joints are examined and the analysis is performed. POLYM. ENG. SCI., 50:1505–1511, 2010. © 2010 Society of Plastics Engineers     

Investigation of optimal surface treatments for carbon/epoxy composite adhesive joints

Although an adhesive joint can distribute the load over a larger area than a mechanical joint, requires no holes, adds very little weight to the structure and has superior fatigue resistance, but it not only requires a careful surface preparation of the adherends but also is affected by service environments. In this paper, suitable conditions for surface treatments such as plasma surface treatment, mechanical abrasion, and sandblast treatment were investigated to enhance the mechanical load capabilities of carbon/epoxy composite adhesive joints. A capacitively coupled radiofrequency plasma system was used for the plasma surface treatment of carbon/epoxy composites and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the surface free energies of treated specimens. The optimal mechanical abrasion conditions with sandpapers were investigated with respect to the mesh number of sandpaper, and optimal sandblast conditions were investigated with respect to sandblast pressure and particle size by observing geometric shape changes of adherends during sandblast process. Also the failure modes of composite adhesive joints were investigated with respect to surface treatment. From the peel tests on plasma treated composite adhesive joints, it was found that all composite adhesive joints failed cohesively in the adhesive layer when the surface free energy was higher than about 40 mJ/m², because of high adhesion strength between the plasma treated surface and the adhesive. From the peel tests on mechanically abraded composite adhesive joints, it was also found that the optimal surface roughness and adhesive thickness increased as the failure load increased.     

Interfacial adhesion and water resistance of stainless steel–polyolefin improved by functionalized silane

The adhesion strength and water resistance of stainless steel and adhesive resin composites determine the long‐term performance of wires and cables; however, adhesion at stainless steel interfaces is difficult. Herein, we prepared ethylene acrylic acid/linear low‐density polyethylene (EAA/LLDPE) blends with good mechanical and adhesive properties. Silane was anchored to the surface of stainless steel. The effects of silane functionalization on the adhesion surface were investigated by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The reaction mechanism between the stainless steel, silane, and EAA/LLDPE revealed adhesion was optimized when a 3:7 volume ratio of 3‐methacryloxypropyltrimethoxysilane (MEMO): 3‐aminopropyltrimethoxysilane (A‐1110) was used to modify the stainless steel substrate. SEM images of EAA/LLDPE film peel surfaces found the silane‐treated stainless steel substrates produced rough surfaces with a uniform void indicating the silane treatment enhanced the stainless steel and EAA/LLDPE film interaction. The stainless steel and EAA/LLDPE film adhesion and water resistance improved and the peel strength after water resistance testing at 68°C for 168 h increased from 3.18 N/cm to 9.37 N/cm compared to untreated stainless steel. Silane‐modified stainless steel and EAA/LLDPE blend film composite materials demonstrate potential for application in wires and cables used in environmental corrosion‐resistant applications. POLYM. ENG. SCI., 59:1866–1873, 2019. © 2019 Society of Plastics Engineers     

Adhesion Improvement of Glass-Fibre-Reinforced Polyester Composites by Gliding Arc Discharge Treatment

A gliding arc is a plasma that can be operated at atmospheric pressure and applied for plasma surface treatment for adhesion improvement. In the present work, glass-fibre-reinforced polyester plates were treated using an atmospheric pressure gliding arc discharge with an air flow to improve adhesion with a vinylester adhesive. The treatment improved wettability and increased the polar component of the surface energy and the density of oxygen-containing polar functional groups at the surfaces. Double cantilever beam specimens were prepared for fracture mechanics characterisation (fracture resistance as a function of nominal mode mixity) of the laminate adhesive interface. It was found that gliding arc treatment significantly increases the interfacial fracture energy and fracture resistance in comparison with a standard peel ply treatment, although the mixed mode fracture energy of the gliding arc treated specimen was not as high as that of the laminate itself.     

Surface modification of aramid fibers via ammonia‐plasma treatment

In this article, aramid fibers III were surface modified using an ammonia‐plasma treatment to improve the adhesive performance and surface wettability. The surface properties of fibers before and after plasma treatment were investigated by X‐ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and water contact angle measurements. The interfacial shear strength of each aramid fibers III‐reinforced epoxy composites was studied by micro‐debonding test. The ammonia‐plasma treatment caused the significant chemical changes of aramid fibers III, introducing nitrogen‐containing polar functional groups, such as ? C? N? and ? CONH? , and improving their surface roughness, which contributed to the improvement of adhesive performance and surface wettability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40250.     

Ion‐plasma modification of polyvinylchloride microfiltration membranes

Here we present how the surface and some filtration properties of PVC microfiltration membranes are affected by controlled and well‐defined modification by ion‐plasma treatment in the kinetic region of the high voltage (HVGD) or normal glow discharge (NGD) in air. The surface energy and work of adhesion of the samples were calculated from the contact angle with both polar (H₂O) and nonpolar (CH₂I₂) liquid measurement data. The surface morphology was observed by SEM and the surface chemical composition was analyzed by ESCA. The trans‐membrane water flux, the average pore size, and the pore‐size distribution as well as the “bubble point” were used to control the effect of the ion‐plasma treatment on the filtration properties of the PVC microfiltration membranes. Two characteristic regions of the ion‐plasma treatment in air were found in our experiments where the surface properties and filtration characteristics of the membranes are extremely changed: at a pressure of 10–15 Pa in the region of the HVGD and at a pressure of 100–120 Pa in the region of the NGD. It was shown that the ion‐plasma treatment in air is an effective technological method for regulation of some important surface and filtration properties of PVC microfiltration membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2433–2440, 2003     

Influence of Processing Additives on Adhesive Properties of Surface‐Modified Low‐Density Polyethylene

Summary: The paper deals with the surface and adhesive properties of low‐density polyethylene modified by corona discharge, which appear during the long‐term hydrophobic recovery of the modified polymer. The study was aimed at the change in polarity during aging of low‐density polyethylene modified by corona discharge reducing the surface free energy, its polar component and the mechanical work of adhesion. During the long‐term hydrophobization of low‐density polyethylene the main decrease of the surface properties appeared within the first 30 d after modification. In the course of further aging the hydrophobic recovery of the polymer proceeded more slowly. It has been found that the value of the surface and adhesive properties of low‐density polyethylene after modification with corona discharge as well as the dynamics of their decrease during the aging is to a great extent dependent on the presence of the processing additives in the polymer.

Mechanical work of adhesion of LDPE modified by corona discharge to poly(vinyl acetate) during hydrophobic recovery: a) additive‐free LDPE, b) LDPE with additives.     

Argon low‐temperature plasma modification of chopped aramid fiber and its effect on paper performance of aramid sheets

Chopped aramid fiber was modified by an argon low‐temperature plasma treatment to enhance the interfacial strength of aramid paper. The water contact angle of the aramid fiber and the tensile strength, tearing strength, and evenness of the aramid sheets were investigated under different conditions, and the parameters of the argon low‐temperature plasma modification, like gas pressure, discharge power, and discharge time, were optimized. The chemical structure and surface morphology of the fiber after plasma modification were characterized by X‐ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy. The strengthening mechanism of aramid paper by low‐temperature plasma modification was also studied. It was found that the argon low‐temperature plasma treatment introduced some new polar groups onto the fiber surface and increased the fiber surface wettability and roughness. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45215.     

Surface modifications of EVA copolymers induced by low pressure RF plasmas from different gases and their relation to adhesion properties

Two ethylene vinyl acetate (EVA) copolymers (12 and 20 wt% of vinyl acetate,VA, content) have been treated with low pressure RF plasmas from non-oxidizing gases (Ar, N₂) and oxidizing gases (air, a mixture of 4N₂: 6O₂ (v/v), O₂ and CO₂). The formation of polar moieties on both EVAs was more noticeable by treatment with plasmas from non-oxidizing gases than from oxidizing ones (the higher the reactivity, the lower the difference with respect to untreated EVA surfaces). The surface etching with the non-oxidizing plasmas, giving rise to a high roughness, depends on the wt% of VA in the composition of the copolymer because of the different resistances of VA (low) and PE (high) to the non-oxidizing plasma particles bombardment. The adhesion properties obtained using a polyurethane adhesive (PU) showed high T-peel strength values and adhesion failure in EVAs treated with plasmas from oxidizing gases, due to roughness produced causing mechanical interlocking of the adhesive. Lower T-peel strength values were obtained with non-oxidizing plasmas: the values for EVA12 being, in general, lower than those obtained for EVA20. The durability of the treated EVAs/PU adhesive joints after ageing in humidity and temperature was quite good.     

碱性电池隔膜用丙纶非织造布的等离子体改性

利用低温等离子体技术对碱性电池隔膜用丙纶非织造布进行表面改性处理,探讨了影响电池隔膜性能的因素,利用红外光谱、扫描电镜对材料表面性能进行了表征分析。结果表明,不同气体的等离子体对丙纶非织造布进行表面处理的最佳工作参数放电气体、放电功率、放电时间、工作压强分别为:氩气,70 W,3 min,15 Pa;氧气,120 W,3 min,30 Pa;空气,100 W,3 min,50 Pa。通过等离子体表面活化处理,在丙纶表面引入了亲水性基团,同时产生了刻蚀,丙纶非织造布的吸碱速率可提高至每10 min 8 cm左右,吸碱率提高至250%,面电阻大幅降低至8 Ω/cm2左右。     

Surface modification of a polyurethane film by low pressure glow discharge oxygen plasma treatment

Low pressure oxygen plasma has been used to improve the surface wettability of a polyurethane film. The modifications induced by the plasma treatment in the material were analyzed using contact angle measurements. X‐ray photoelectron spectroscopy technique was used for surface characterization of the plasma‐treated films. Atomic force microscopy and scanning electron microscopy were used to analyze topography changes due to the plasma‐etching mechanism. The results show a much better surface wettability of the film even for short exposure times, with a considerable increase in the surface energy values. As expected, functionalization with oxygen plasma is mainly because of surface oxidation with species like (C? O, C?O, OH, etc). An aging process with regard to polar groups rearrangement has been observed, thus promoting a partial hydrophobic recovery. Besides functionalization, the surface wettability of the material improves as a consequence of a slight increase in surface roughness because of the etching effect of oxygen plasma. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007