Influence of moisture regain of aramid fibers on effects of atmospheric pressure plasma treatment on improving adhesion with epoxy

One difference between a low‐pressure plasma treatment and an atmospheric pressure plasma treatment is that in the atmosphere, the substrate material may contain significant quantities of moisture, which could potentially influence the effects of the plasma treatment. To investigate how the existence of moisture affects atmospheric pressure plasma treatment, aramid fibers (Twaron 1000) with three different moisture regains (0.5, 4.5, and 5.5%) were treated by an atmospheric pressure plasma jet for 3 s at a gas flow rate of 8 L/min, a treatment head temperature of 100°C, and a power of 10 W. The scanning electron microscopy analysis showed no observable surface morphology change for the plasma treated samples. X‐ray photoelectron spectroscopy analysis showed the oxygen contents of the 0.5 and 4.5% moisture regain groups increased from that of the control, although the opposite was true for the 5.5% moisture regain group. The advancing contact angles of the treated fibers decreased about 8°–16° whereas their receding contact angles decreased about 17°–27°. The interfacial shear strengths of the treated fibers as measured using microbond pull‐out tests were more than doubled when the moisture regain was 4.5 or 5.5%, whereas it increased by 58% when the moisture regain was 0.5%. In addition, no significant difference in single fiber tensile strength was observed among the plasma treated samples and the control sample. Therefore, we concluded that moisture regain promoted the plasma treatment effect in the improvement of the adhesion property of aramid fibers to epoxy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 242–247, 2006     

常压等离子体改善合成纤维吸湿性的研究

用氦气作为等离子体的气体源、对涤纶、锦纶6、高强度聚乙烯纤维,Twaron 1000芳纶4种合成纤维进行常压等离子体处理,改善纤维的吸湿性能。结果表明:常压等离子体处理,对涤纶和锦纶6的表面有一定的刻蚀作用,但对高强度聚乙烯纤维、Twaron 1000芳纶的表面没有明显影响;经常压等离子体处理后,合成纤维表面氧、氮有所增加,吸湿性能得到提高,强度没有显著变化。     

RETRACTED ARTICLE: Surface modification of aramid fibers with novel chemical approach

Friedel–Crafts Reaction as a simple and convenient approach to the surface modification of aramid fiber was introduced in this paper. Epoxy chloropropane was chosen as the treatment reagent to modify aramid fibers surface via Graft reaction. After the modification, the interfacial properties of aramid/epoxy composites were investigated by the single fiber pull-out test (SFP), and the mechanical properties of aramid fibers were investigated by the tensile strength test. The results showed that the interfacial shear strength (IFSS) value of aramid/epoxy composites was enhanced by about 50%, and the tensile strength of aramid fibers had no obvious damage. The crystalline state of aramid fibers was determined by X-ray diffraction instrument (XRD), and the results showed that there were not any distinct crystal type varieties. The surface elements of aramid fibers were determined by X-ray photoelectron spectroscopy (XPS), the analysis of which showed that the oxygen/carbon ratio of aramid fiber surface increased obviously. The possible changes of the chemical structure of aramid fibers were investigated via Fourier transform infrared spectrum (FTIR), and the analysis of which showed that the epoxy functional groups were grafted into the molecule structure of aramid fibers. The surface morphology of aramid fibers was analyzed by Scanning electron microscope (SEM), and the SEM results showed that the physical structure of aramid fibers was not etched or damaged obviously. The surface energy of aramid fibers was investigated via the dynamic capillary method, and the results showed that the surface energy was enhanced by 31.5%, and then the wettability degree of aramid fiber surface was enhanced obviously too. All of the results indicated that this novel chemical modification approach not only can improve the interfacial bonding strength of aramid/epoxy composites remarkably, but also have no negative influence on the intrinsic tensile strength of aramid fibers.     

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     

Surface modification of aramid fibers with γ‐ray radiation for improving interfacial bonding strength with epoxy resin

Co⁶⁰ γ‐ray radiation as a simple and convenient method for surface modification of Armos aramid fibers was introduced in this article. Two kinds of gas mediums, N₂ and air, were chosen to modify aramid fiber surface by γ‐ray irradiation. After fiber surface treatment, the interlaminar shear strength values of aramid/epoxy composites were enhanced by about 17.7 and 15.8%, respectively. Surface elements of aramid fibers were determined by XPS, the analysis of which showed that the ratio of oxygen/carbon was increased. The crystalline state of aramid fibers was determined by X‐ray diffraction instrument. The surface topography of fibers was analyzed by atomic force microscopy and scanning electron microscope. The degree of surface roughness and the wettability of fiber surface were both enhanced by γ‐ray radiation. The results indicated that γ‐ray irradiation technique, which is a suitable way of batch process for industrialization, can significantly improve the surface properties of aramid fibers reinforced epoxy resin matrix composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of Atmospheric Plasma Treatment on Carbon Fiber/Epoxy Interfacial Adhesion

In this work the effect of atmospheric plasma treatment on carbon fiber has been studied. The carbon fibers were treated for 1, 3 and 5 min with a He/O₂ dielectric barrier discharge atmospheric pressure plasma. The fiber surface morphology, surface chemical composition and interfacial shear strength between the carbon fiber and epoxy resin were investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and the single fiber composite fragmentation test. Compared to untreated carbon fibers, the plasma treated fiber surfaces exhibited surface morphological and surface composition changes. The fiber surfaces were found to be roughened, the oxygen content on the fiber surfaces increased, and the interfacial shear strength (IFSS) improved after the atmospheric pressure plasma treatment. The fiber strength showed no significant changes after the plasma treatment.     

Surface ammonification of the mutual‐irradiated aramid fibers in 1,4‐dichlorobutane for improving interfacial properties with epoxy resin

The mutual irradiated aramid fibers in 1,4‐dichlorobutane was ammoniated by ammonia/alcohol solution, in an attempt to improve the interfacial properties between aramid fibers and epoxy matrix. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), dynamic contact angle analysis (DCA), interfacial shear strength (IFSS), and single fiber tensile testing were carried out to investigate the functionalization process of aramid fibers and the interfacial properties of the composites. Experimental results showed that the fiber surface elements content changed obviously as well as the roughness through the radiation and chemical reaction. The surface energy and IFSS of aramid fibers increased distinctly after the ammonification, respectively. The amino groups generated by ammonification enhanced the interfacial adhesion of composites effectively by participating in the epoxy resin curing. Moreover, benefited by the appropriate radiation, the tensile strength of aramid fibers was not affected at all. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44924.     

Surface modification of ultra high modulus polyethylene fibers by an atmospheric pressure plasma jet

To improve their adhesion properties, ultra high modulus polyethylene (UHMPE) fibers were treated by an atmospheric pressure helium plasma jet (APPJ), which was operated at radio frequency (13.56 MHz). The surface properties of the fibers were investigated by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurement. The surface dyeability improvement after plasma treatments was investigated using laser scanning confocal microscopy (LSCM). The adhesion strengths of the fibers with epoxy were evaluated by microbond tests. In addition, the influence of operational parameters of the plasma treatment including power input and treatment temperature was studied. XPS analysis showed a significant increase in the surface oxygen content. LSCM results showed that the plasma treatments greatly increased fluorescence dye concentrations on the surface and higher diffusion rate to the fiber center. The tensile strength of UHMPE fiber either remained unchanged or decreased by 10–13.6% after plasma treatment. The contact angle exhibited a characteristic increase in wettability, due to the polar groups introduced by plasma treatment. The microbond test showed that the interfacial shear strengths (IFSS) increase significantly (57–139%) after plasma treatment for all groups and the optimum activation is obtained at 100°C and 5 W power input. SEM analysis showed roughened surfaces after the plasma treatments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

低温氨气等离子体对芳纶表面的改性

采用氨气等离子体对芳纶表面进行改性,用X-射线光电子能谱、场发射扫描电子显微镜、力学性能测试等手段对改性前后纤维表面的元素组成、形貌及其拉伸强度进行表征,并进一步通过微脱黏方法分析了等离子体处理条件对芳纶/环氧树脂复合材料界面黏结强度的影响。结果表明:芳纶经表面改性后,其表面极性官能团、表面粗糙度均有所增加,同时与环氧树脂基体的界面黏结强度明显增加。     

Application of the microbond technique. IV. Improved fiber–matrix adhesion by RF plasma treatment of organic fibers

The microbond technique is a modification of the single-fiber pullout test for measuring interfacial shear strength. Briefly, a cured microdroplet of material is debonded in shear from a single fiber. Ultra-high modulus polyethylene (Spectra) fibers and aramid fibers (Kevlar) were treated using a radio frequency plasma in order to increase the interfacial bond between the fibers and an epoxy resin. The treated fiber surface was subsequently analyzed by X-ray photoelectron spectroscopy (XPS). Plasma treatment resulted in an increased concentration of oxygen containing functionalities on the fiber surface. The interfacial shear strength as determined by the microbond test increased by 118% for the Spectra fibers and by 45% for the Kevlar fibers with the same epoxy resin. Scanning electron microscopy indicated little change of the surface topography of either fiber following plasma treatment. Effects of friction and surface composition of the plasma-treated fibers is discussed. © 1993 John Wiley & Sons, Inc.     

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。     

Wetting and adhesion behavior of armos fibers after dielectric barrier discharge plasma treatment

To investigate the influence of atmospheric plasma treatment on aramid fiber wetting and adhesion behavior, an air dielectric barrier discharge (DBD) was applied to the Armos aramid fiber surface at different discharge power densities. Dynamic contact angle analysis indicated that the total surface free energy was increased from 49.6 to 68.3 mJ/m 2 , an increment of 37.7%, whereas the single-fiber tensile strength testing showed that the mechanical properties of the Armos fibers were almost unaffected. With the enhancement of fiber surface wettability, the interlaminar shear strength, which was used to determine the interfacial adhesion in Armos-fiber-reinforced thermoplastic poly(phthalazinone ether sulfone ketone) composites, increased by 17.2% to 71.4 MPa. Scanning electron microscopy photos showed that the predominant failure mode of the composites changed from interface failure to matrix and/or fiber failure after the plasma treatment. Taken together, these results suggest that the air DBD plasma was an effective technique for improving the surface and interfacial performance of the Armos fibers without damaging their bulk properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

高能辐照对国产芳纶纤维/环氧复合材料界面性能影响

芳纶纤维因其表面惰性、光滑使其与树脂浸润性差,界面结合强度低。以环氧氯丙烷为介质1,采用60Coγ-射线辐照方法对国产芳纶纤维进行表面改性,以界面剪切强度（IFSS）和层间剪切强度（ILSS）表征芳纶/环氧复合材料界面结合性能。结果表明在400kGy辐照剂量下改性效果最好;经高能辐照处理的芳纶纤维表面能升高,并失去了原有的光滑表面,且纤维表面氧含量有大幅度提高,使得纤维表面活性增大。     

Effect of ultrasound on wettability between aramid fibers and epoxy resin

Good wetting of reinforced fiber by resin was a main factor in the improvement of the interface adhesion of their composites. Ultrasound with a frequency of 20 kHz was used to improve the wettability between aramid fibers and epoxy resin during the winding process of the composites. The effects of ultrasound on the viscosity and surface tension of epoxy resin and on the surface characteristics of aramid fibers were investigated. The wettability of aramid fibers and treated epoxy resin under different conditions and of aramid fibers and epoxy resin under ultrasonic online treatment were compared. The results indicated that the main action of ultrasound was to force epoxy resin to impregnate aramid fibers, in addition to the influence of ultrasound on the properties of epoxy resin and aramid fibers. The results of microdebond testing showed that the interfacial shear strength (IFSS) of aramid/epoxy composites could be 26% higher than that of untreated composites because of the improved wettability between aramid fibers and epoxy resin subjected to ultrasonic online treatment. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

The effect of atmospheric pressure helium plasma treatment on the surface and mechanical properties of ultrahigh-modulus polyethylene fibers

Ultrahigh-modulus polyethylene fibers were treated with atmospheric pressure He plasma on a capacitively coupled device at a frequency of 7.5 kHz and a He partial vapor pressure of 3.43 × 10³ Pa. The fibers were treated for 0, 1, and 2 min. Microscopic analysis showed that the surfaces of the fibers treated with He plasma were etched and that the 2-min He plasma-treated group had rougher surfaces than the 1-min He plasma-treated group. XPS analysis showed a 200% increase in the oxygen content and a 200% increase in the concentration of C—O bonds (from 11.4% to 31%) and the appearance of C=O bonds (from 0% to 7.6%) on the surface of plasma-treated fibers for the 2-min He plasma-treated group. In the microbond test, the 2-min He plasma-treated group had a 100% increase of interfacial shear strength over that of the control group, while the 1-min He plasma-treated group did not show a significant difference from the control group. The 2-min He plasma-treated group also showed a 14% higher single-fiber tensile strength than the control group.     

芳纶纤维/AFR树脂复合材料界面粘结性能的研究

为了改善芳纶纤维复合材料的界面粘结性能,合成了一种新型树脂(AFR)作为基体,以未经任何表面处理的芳纶纤维作增强材料,制备了芳纶纤维/AFR复合材料。采用测定表面能、接触角、层间剪切强度、横向拉伸性能和扫描电镜观察形貌等方法,从宏观和微观等方面研究了芳纶纤维/AFR复合材料的界面粘结性能。结果表明,AFR树脂与芳纶纤维有相近的表面能,AFR树脂溶液与芳纶纤维的接触角为42.8°,而环氧树脂(EP)与芳纶纤维的接触角为68°,说明AFR树脂对芳纶纤维的润湿性优于EP树脂;芳纶/AFR复合材料的层间剪切强度、横向拉伸强度和纵向拉伸强度分别为74.64MPa、25.34MPa和2256MPa,比芳纶/EP复合材料的相应强度分别提高了28.7%、32.5%和13.4%,其复合材料破坏面的形貌也说明芳纶纤维与AFR树脂之间的界面粘结性能较好。     

芳纶纤维等离子体接枝改性处理研究

采用等离子体接枝对芳纶纤维表面进行改性处理,采用XPS、浸润性、界面剪切强度对等离子体接枝处理前后的表面组成、复合材料界面粘接性能等进行了研究,结果表明:等离子体接枝处理可以有效地提高芳纶纤维表面的极性官能团,增加与基体树脂-环氧树脂的浸润性,进而提高芳纶/环氧复合材料的界面粘接强度.     

Influence of Moisture on Effectiveness of Plasma Treatments of Polymer Surfaces

Abstract

In atmospheric pressure plasma treatments water molecules in the substrate material may disrupt the molecular arrangement in the substrate and thus greatly influence the outcome of the plasma treatment. This paper summarizes the results of our recent studies on how moisture influences the etching, surface chemical modification, crystallinity and aging of aramid, ultrahigh molecular weight polyethylene (UHMWPE), polyamide fibers, and poly(vinyl alcohol) (PVA) films. Overall, a higher moisture regain often results in a greatly enhanced etch rate, less surface chemical composition change, increased near-surface crystallinity, which could lead to a higher surface wettability, higher interfacial shear strength between the fibers and resin, decreased water solubility for PVA films, and delayed hydrophobic recovery of plasma treated fibers. Therefore, it is important to control the moisture contained in the substrate in atmospheric pressure plasma treatments.     

左旋多巴胺处理对芳纶表面结构与性能的影响

利用L-3,4-二羟基苯丙氨酸(L-DOPA)的氧化自聚合,在杂环芳纶表面修饰聚L-3,4-二羟基苯丙氨酸(PDOPA)活性涂层来提高芳纶的表面活性及耐紫外辐照性能。结果表明:改性后芳纶表面粗糙度显著提高,同时,PDOPA涂层上大量的羧基、羟基等活性单元均有利于增强与环氧树脂的机械锁合力,改性后芳纶/环氧树脂复合材料的界面剪切强度提高了32.0%。此外,上述改性过程对杂环芳纶本身力学性能影响较小,纤维的拉伸强度保持率可以达到100%,基本实现了无损改性。同时,由于PDOPA的保护作用,改性后芳纶的耐紫外辐射性能显著提高;经过168 h紫外线辐照处理后,其拉伸强度保持率可达到92.5%,显著提升了杂环芳纶的耐紫外线辐照特性。     

Experimental investigation into the effect of adhesion properties of PEEK modified by atmospheric pressure plasma and low pressure plasma

High performance polymer, Polyether Ether Ketone (PEEK) (service temperature ?250°C to +300°C, tensile strength: 120 MPa) is gaining significant interest in aerospace and automotive industries. In this investigation, attention is given to understand adhesion properties of PEEK, when surface of the PEEK is modified by two different plasma processes (i) atmospheric pressure plasma and (ii) low pressure plasma under DC Glow Discharge. The PEEK sheets are fabricated by ultra high temperature resistant epoxy adhesive (DURALCO 4703, service temperature ?260°C to +350°C). The surface of the PEEK is modified through atmospheric pressure plasma with 30 and 60 s of exposure and low pressure plasma with 30, 60, 120, 240, and 480 s of exposure. It is observed that polar component of surface energy leading to total surface energy of the polymer increases significantly when exposed to atmospheric pressure plasma. In the case of low pressure plasma, polar component of surface energy leading to total surface energy of the polymer increases with time of exposure up to 120 s and thereafter, it deteriorates with increasing time of exposure. The fractured surface of the adhesively bonded PEEK is examined under SEM. It is observed that unmodified PEEK fails essentially from the adhesive to PEEK interface resulting in low adhesive bond strength. In the case of surface modified PEEK under atmospheric pressure plasma, the failure is entirely from the PEEK and essentially tensile failure at the end of the overlap resulting in significant increase in adhesive bond strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010