Improvement of interfacial adhesion and nondestructive damage evaluation for plasma-treated PBO and Kevlar fibers/epoxy composites using micromechanical techniques and surface wettability

Comparison of interfacial properties and microfailure mechanisms of oxygen-plasma treated poly(p-phenylene-2,6-benzobisoxazole (PBO, Zylon) and poly(p-phenylene terephthalamide) (PPTA, Kevlar) fibers/epoxy composites were investigated using a micromechanical technique and nondestructive acoustic emission (AE). The interfacial shear strength (IFSS) and work of adhesion, Wa, of PBO or Kevlar fiber/epoxy composites increased with oxygen-plasma treatment, due to induced hydrogen and covalent bondings at their interface. Plasma-treated Kevlar fiber showed the maximum critical surface tension and polar term, whereas the untreated PBO fiber showed the minimum values. The work of adhesion and the polar term were proportional to the IFSS directly for both PBO and Kevlar fibers. The microfibril fracture pattern of two plasma-treated fibers appeared obviously. Unlike in slow cooling, in rapid cooling, case kink band and kicking in PBO fiber appeared, whereas buckling in the Kevlar fiber was observed mainly due to compressive and residual stresses. Based on the propagation of microfibril failure toward the core region, the number of AE events for plasma-treated PBO and Kevlar fibers increased significantly compared to the untreated case. The results of nondestructive AE were consistent with microfailure modes.     

Interfacial Properties of Two-Carbon Fiber Reinforced Polycarbonate Composites Using Two-Synthesized Graft Copolymers as Coupling Agents

Two model coupling agents, water-dispersible (WDGP) and tetrahydrofuran (THF)-soluble graft copolymers (TSGP), were synthesized for carbon fiber/polycarbonate (PC) composites. WDGP contains a long polyacrylamide (PAAm) chain grafted on a PC backbone, whereas TSGP contains a short grafted PAAm chain. Measurements of the interfacial shear strength (IFSS) and other interfacial properties were evaluated using a fragmentation test for two-fiber composites (TFC) to provide the same loading state. Optimal conditions for the treatment was established as a function of treatment time, temperature, initial concentration, and melting procedure. The amount adsorbed on the carbon fiber was higher for TSGP then for WDGP; the maximum improvements in IFSS for WDGP and TSGP were 54% and 74%, respectively. Mechanisms of energy adsorption for WDGP and intermolecular interaction for TSGP can be considered to contribute differently to IFSS improvement. The improvement in IFSS for both coupling agents may be due to chemical and hydrogen bonding in the interface between functional groups in the carbon fiber and PAAm in the coupling agents and to interdiffusion in the interface between PC in coupling agents and matrix PC. Copyright 2000 Academic Press.     

Study of the carbon fiber–poly(ether–ether–ketone) (PEEK) interfaces, 2: relationship between interfacial shear strength and adhesion energy

In the second part of this general study, the carbon fiber–PEEK interfacial shear strength is measured by means of a fragmentation test on single-fiber composites. Different thermal treatments (continuous cooling from the melt, isothermal treatments and long melting temperature time) are applied to these model composites prior to testing. The results are systematically compared with the previously determined reversible work of adhesion between carbon fiber and PEEK. It is shown that physical interactions at the interface determine, to a large extent, the magnitude of the interfacial shear strength between both materials. However, it appears that the magnitude of the stress transfer from the matrix to the fiber is affected either by the existence of an interfacial layer or by a preferential orientation of the polymer chains near the fiber surface. The results obtained on systems that have been subjected to isothermal treatments (isothermal crystallization of PEEK) seem to confirm the existence of a transcrystalline interphase, the properties of which are dependent upon the crystallization rate of the matrix and the interfacial adhesion energy.     

Transcrystallization of PTFE fiber/PP composites. II. Effect of transcrystallinity on the interfacial strength

It has been found that transcrystallinity of polypropylene (PP) develops easily on the polytetrafluoroethylene (PTFE) fiber surface in spite of the low surface energy of the fiber. Effect of the transcrystallinity on the interfacial strength has been extensively investigated using a single-fiber pull-out test. By controlling the crystallization temperature, range 25–130°C, the thickness of the transcrystalline layer varied from 0 to 175 μm for thick specimens, ca. 1 mm thick. Measurements of the adhesive fracture energy, the interfacial shear strength and the frictional stress were carried out for specimens with different embedded fiber lengths. Results show that interfacial strength and fracture energy are independent of the transcrystalline thickness. The calculated value of interfacial shear strength is 3.6 MPa, and the fracture energy for debonding is 2.1 J/m². The presence of transcrystallinity does not promote the level of adhesion in PTFE/PP composites. However, the frictional stresses at the debonded fiber/matrix interface increase with transcrystalline thickness. It is attributed to the residual stresses which arise from shrinkage when specimens are cooled from crystallization temperature to room temperature. © 1996 John Wiley & Sons, Inc.     

表面复合纳米SiO_2和碳纳米管玻璃纤维增强尼龙6的结构与性能

利用静电相互作用在玻璃纤维(GF)表面分别复合纳米二氧化硅(SiO2)和多壁碳纳米管(MWNTs),制备了GF-SiO2、GF-MWNTs复合增强体,并通过转矩流变仪制备了尼龙6(PA6)/GF-SiO2和尼龙6(PA6)/GF-MWNTs复合材料.利用扫描电子显微镜(SEM),示差扫描量热仪(DSC),热机械分析仪(DMA)等手段研究了复合材料的微观结构、热学及力学性能.结果表明,静电复合的方法可以使纳米二氧化硅(nano-SiO2)、多壁碳纳米管(MWNTs)在GF表面达到均匀吸附,复合增强体能加快尼龙6的结晶速度,并使材料的玻璃化温度、动态模量、拉伸强度、结晶温度等明显提高,其中GF-MWNTs对复合材料性能的提高最明显,拉伸强度提升了21%,模量提高了28%.     

Influence of coupling agent chain lengths on interfacial performances of carbon fiber and polyarylacetylene resin composites

The influence of chain lengths on interfacial performances of carbon fiber/polyarylacetylene composites was studied. For this purpose, four coupling agents, methyltrimethoxysilane, propyltrimethoxysilane, octyltrimethoxysilane and dodecyltrimethoxysilane, were grafted onto fiber surface to obtain different chain lengths. The resulting carbon fiber surface was characterized by XPS and dynamic contact angle test. Interfacial adhesion in the resulting fiber reinforced polyarylacetylene resin composites was also evaluated by fracture morphology analysis and interfacial shear strength test. It was found that the interfacial adhesion in composites greatly increased with chain lengths on fiber surface. The improvement of interfacial adhesion was attributed to the interaction between the chain of coupling agents on fiber surface and that of polyarylacetylene resin at the interface. Copyright © 2009 John Wiley & Sons, Ltd.     

Interfacial studies on the ozone and air‐oxidation‐modified carbon fiber reinforced PEEK composites

In this work, ozone modification method and air‐oxidationwere used for the surface treatment of polyacrylonitrile(PAN)‐based carbon fiber. The surface characteristics of carbon fibers were characterized by XPS. The interfacial properties of carbon fiber‐reinforced (polyetheretherketone) PEEK (CF/PEEK) composites were investigated by means of the single fiber pull‐out tests. As a result, it was found that IFSS (interfacial shear strength) values of the composites with ozone‐treated carbon fiber are increased by 60% compared to that without treatment. XPS results show that ozone treatment increases the amount of carboxyl groups on carbon fiber surface, thus the interfacial adhesion between carbon fiber and PEEK matrix is effectively promoted. The effect of surface treatment of carbon fibers on the tribological properties of CF/PEEKcomposites was comparativelyinvestigated. Experimental results revealed that surface treatment can effectively improve the interfacial adhesion between carbon fiber and PEEK matrix. Thus the wear resistance was significantly improved. Copyright © 2009 John Wiley & Sons, Ltd.     

芳纶纤维/SMPU-SiO2复合材料的界面性能研究

选用形状记忆聚氨酯(SMPU)和正硅酸乙酯(TEOS)为前驱体,固体酸对甲基苯磺酸(PTSA)为催化剂,利用空气中的水分为水解水源,通过溶胶-凝胶法原位制备了形状记忆聚氨酯与二氧化硅( SMPU-SiO2)杂化材料,并将杂化材料应用于芳纶纤维增强的柔性复合材料中,以期改善芳纶纤维与基体的界面性能.同时,针对芳纶纤维表面...     

The effect of post cure temperature on fiber/matrix adhesion of T650/Cycom 5320-1 using the micro-droplet technique

The interfacial shear strength (IFSS) of a specific carbon fiber/epoxy composite (T650/Cycom 5320-1) was investigated to determine how changes in post cure temperature affects the fiber/matrix adhesion. The degree of cure of the Cycom resin cured with the same post cure temperatures was also determined using a DSC technique. The mechanical and viscoelastic properties of the samples made from Cycom 5320-1 resin were also measured and related to the degree of cure. It was shown that the mechanical and viscoelastic properties changed as the curing temperature, and hence the degree of cure, increased. The results of the micro-droplet tests showed the interfacial adhesion increased with increasing the post cure temperature. This was attributed to the higher degree of cure and change in mechanical and viscoelastic properties of the resin, as well as the residual stresses as the post cure temperature increased.     

The interfacial feature of thermoplastic polystyrene composite filled with nitric acid oxidized carbon fiber

The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibers and the composition of the matrix. The composition of polystyrene was modified by the addition of maleic anhydride (MAH) grafted polystyrene. The surface properties of the various matrix formulations were characterized by contact angle. Carbon fibers were modified by oxidation in nitric acid. The surface composition of the carbon fibers was characterized. The interaction between modified polystyrene and the carbon fibers was studied by single fiber pull‐out tests. The best adhesion behavior was achieved between polystyrene containing grafted MAH and nitric acid oxidation carbon fibers. The addition of MAH‐grafted polystyrene to the unmodified polystyrene caused the interfacial shear strength (IFSS) to increase. The IFSS of this fiber‐matrix combination allowed for the full utilization of the tensile strength of polystyrene. Copyright © 2009 John Wiley & Sons, Ltd.     

连续纤维增强含二氮杂萘酮联苯结构聚芳醚砜酮树脂基复合材料的界面

利用射频感性耦合冷等离子体(ICP)处理技术改性连续纤维表面,分别采用X射线光电子能谱(XPS)、原子力显微镜(AFM)及动态接触角分析(DCA)系统研究了等离子体处理时间、放电气压、放电功率等工艺参数对连续碳纤维、芳纶纤维和对亚苯基苯并二噁唑(PBO)纤维的表面化学成分、表面形貌、表面粗糙度及表面自由能的影响.研究结...     

Interfacial Aspects of Electrodeposited Conductive Fibers/Epoxy Composites using Electro-Micromechanical Technique and Nondestructive Evaluation

Interfacial adhesion and nondestructive behavior of the electrodeposited (ED) carbon fiber reinforced composites were evaluated using the electro-micromechanical technique and acoustic emission (AE). Interfacial shear strength (IFSS) of the ED carbon fiber/epoxy composites was higher than that of the untreated case. This might be expected because of the possible chemical and hydrogen bonding based on an electrically adsorbed polymeric interlayer. Logarithmic electrical resistivity of the untreated single-carbon fiber composite increased suddenly to infinity when the fiber fracture occurred, whereas that of the ED composite increased relatively broadly up to infinity. This may be due to the retarded fracture time as a result of the enhanced IFSS. In single- and 10-carbon fiber composites, the number of AE signals coming from the interlayer failure of the ED carbon fiber composite was much larger than that of the untreated composite. As the number of each first fiber fracture increased in the 10-carbon fiber composite, the electrical resistivity increased stepwise, and the slope of logarithmic electrical resistance increased. In the three-graphite filament composite with a narrow 1 time inter-filament distance, the total numbers of the filament fracture and the IFSS were smaller than those of the wider 5 times case. This might be because the interacting fracture energy caused by a filament break could affect the adjacent filaments. Copyright 2001 Academic Press.     

Comparison of interfacial properties of electrodeposited single carbon fiber/epoxy composites using tensile and compressive fragmentation tests and acoustic emission

Interfacial and microfailure properties of carbon fiber/epoxy composites were evaluated using both tensile fragmentation and compressive Broutman tests with an aid of acoustic emission (AE). A monomeric and two polymeric coupling agents were applied via the electrodeposition (ED) and the dipping applications. A monomeric and a polymeric coupling agent showed significant and comparable improvements in interfacial shear strength (IFSS) compared to the untreated case under both tensile and compressive tests. Typical microfailure modes including cone-shaped fiber break, matrix cracking, and partial interlayer failure were observed under tension, whereas the diagonal slipped failure at both ends of the fractured fiber exhibited under compression. Adsorption and shear displacement mechanisms at the interface were described in terms of electrical attraction and primary and secondary bonding forces. For both the untreated and the treated cases AE distributions were separated well in tension, whereas AE distributions were rather closely overlapped in compression. It might be because of the difference in molecular failure energies and failure mechanisms between tension and compression. The maximum AE voltage for the waveform of either carbon or large-diameter basalt fiber breakages in tension exhibited much larger than that in compression. AE could provide more likely the quantitative information on the interfacial adhesion and microfailure.     

邻苯二酚-四乙烯五胺改性超高分子量聚乙烯纤维

应用Cat-TEPA改性超高分子量聚乙烯(UHMWPE)纤维,在难黏附的纤维表面形成均匀涂层.采用透射电子显微镜(TEM)、红外光谱(FTIR)、X射线光电子能谱(XPS)、X射线衍射(XRD)、示差扫描量热(DSC)、热重分析(TGA)和静态接触角测试等手段对其结构和性能进行了表征,并通过单丝拔出实验研究改性前后纤维与环氧树脂之间的界面剪切强度(IFSS),探索了反应物配比、反应时间对表面性能的影响,并确定最佳改性条件.结果表明Cat-TEPA共沉积改性未影响纤维的结晶和热稳定性,改性后纤维表面浸润性得到改善,且适当增加反应时间和TEPA含量能够提高纤维和树脂之间的IFSS,当Cat-TEPA摩尔比为1:4,反应时间为24 h时效果最佳,与未改性纤维相比,界面剪切强度提升约44%.     

Surface modification of PBO fibers with 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane in supercritical carbon dioxide for enhancing interfacial strength

PBO fiber is one of the most promising reinforcements in resin matrix composite because of its excellent mechanical properties. However, the inert and smooth surfaces make it the poor interface adhesion with resin matrix, which seriously limits the application in composites. In this article, we report a method to modify the surface of PBO fibers with 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane（BisAPAF）in supercritical CO₂ to enhance interfacial properties. Chemical structures, surface elemental composition and functional groups, and surface morphology were characterized by FT-IR spectrometer, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), respectively. The mechanical properties of the samples were tested by a tensile tester. Static contact angle and microdebonding tests were used to characterize the wetting ability and interfacial shear strength (IFSS) of the fiber and epoxy resin. The results showed that the BisAPAF could be solved in scCO₂ and introduced more groups, –NH₂, –OH, and –CF₃ on the fiber surface, resulting in the mechanical properties and the wettability of PBO fiber slightly improved. Moreover, the fiber surface roughness was also increased obviously. The IFSS between the modified PBO fiber and epoxy resin increased from 8.18 MPa to 31.4 MPa when the treating pressure was 14 MPa. In general, the method to modify PBO fibers surface using BisAPAF in scCO₂ can effectively improve their interfacial properties.     

Influence of maleic anhydride-grafted EPDM and flame retardant on interfacial interaction of glass fiber reinforced PA-66

In this paper, the effects of melamine polyphosphate flame retardant (MPP-FR) and maleic anhydride-grafted EPDM (MA-EPDM) on the interfacial interaction of PA66/GF were investigated by means of scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), rheological behavior and mechanical properties. The experimental results demonstrate that MPP-FR and MA-EPDM could effectively improve interfacial interactions between the PA66 and GF. Based on SEM, good interfacial adhesion between PA66 and GF in PA66/GF/FR and PA66/GF/FR/MA-EPDM composites was observed, however, MPP-FR destroyed the PA66 matrix. DMA results show that MPP-FR increased glass transition temperature (T_g) and storage modulus, and lower tan δ, while MA-EPDM showed a little effect on them in PA66/GF/FR/MA-EPDM composite compared with PA66/GF/FR. MPP-FR made PA66 crystallization temperature and the activation energy of the macromolecular segments transport increase clearly, and enhanced crystallization degree of PA66 according to DSC results. These results demonstrate MPP-FR presented the nucleate effect for the crystallization of PA66. At the low shear rate, MPP-FR and MA-EPDM obviously enhanced apparent viscosities of the composites. This is attributed that MPP-FR improved the interfacial interaction of the composites, and MA-EPDM promoted the formation of high molecular weight structures by the reactions between MA and amine groups. All results in this paper were consistent, and showed the good interaction among PA66, GF, MPP and MA-EPDM, which were proved by the mechanical properties of the composites.     

The addition of clay on the mechanical properties of surface‐treated CF‐filled PA66 composites

Polyamide 66 (PA66) composites filled with clay and carbon fiber (CF) were prepared by twin‐screw extruder in order to study the influence of nanoparticle reinforcing effect on the mechanical behavior of the PA66 composites (CF/PA66). The mechanical property tests of the composites with and without clay were performed, and the fracture surface morphology was analyzed. The results show that the fracture surface area of the clay‐filled CF/PA66 composite was far smoother than that of the CF/PA66 composite, and there formed a tense interface on the CF surface after the addition of clay. The tensile and flexural strength of CF/PA66 composites with clay was improved. The impact strength decreased because of the high interfacial adhesion. In conclusion, the addition of clay favored the improvement of the higher interface strength and so had good effect on improving the tensile and flexural properties of the composites. Copyright © 2017 John Wiley & Sons, Ltd.     

Interfacial adhesion and microfailure modes of electrodeposited carbon fiber/epoxy-PEI composites by microdroplet and surface wettability tests

Interfacial properties and microfailure modes of electrodeposition (ED)-treated carbon fiber-reinforced polyetherimide (PEI) toughened epoxy composite were investigated using microdroplet test and the measurement of surface wettability. ED was performed to improve the interfacial shear strength (IFSS). As PEI content increased, IFSS increased due to enhanced toughness and plastic deformation of PEI. In the untreated case, IFSS increased with adding PEI content, and the IFSS of the pure PEI matrix showed the highest. On the other hand, for the ED-treated case IFSS increased with PEI content with rather low improvement rate. In the untreated case, neat epoxy resin appeared brittle microfailure mode, whereas the pure PEI matrix exhibited a more likely ductile microfailure mode. In the ED-treated case, neat epoxy exhibited a more ductile fracture than that of the untreated case. Critical surface tension and polar surface free energy of ED-treated carbon fiber was higher than those of the untreated fiber. The work of adhesion between fiber and matrix was not directly proportional to IFSS for both the untreated and ED-treated cases. The matrix toughness might contribute to IFSS more likely than the surface wettability. Interfacial properties of the epoxy-PEI composite can be affected efficiently by both the control of matrix toughness and ED treatment.     

Study of the carbon fiber–Poly(Ether–Ether–Ketone) (PEEK) interfaces, 3: influence and properties of interphases

The aim of this third part is to analyze the structure and properties of the interfacial region between carbon fibers and PEEK as a function of different thermal conditioning treatments. First, it is shown by means of optical microscopy that the interfacial zone is not different from the bulk matrix when standard cooling conditions are used. On the contrary, a transcrystalline interphase is formed near the carbon fiber surface in systems that have been subjected to isothermal treatments. By comparison with previous results concerning the mechanical properties of the fiber–matrix interface, it appears that the interfacial shear strength decreases in the presence of a transcrystalline interphase or when the crystallization rate of PEEK increases. Moreover, it seems that the “constraint state” of the amorphous phase of PEEK near the fiber surface could also play a role in the interfacial shear strength. Secondly, a method is proposed in order to estimate the elastic modulus of crystalline interphases. It seems that this modulus is strongly dependent on the crystallization rate of the polymer. Finally, the determination of the stress-free temperature, defined as the temperature at which a longitudinal compressive stress just appears on the carbon fiber during the processing of the composites, is performed by recording the acoustic events corresponding to the fragmentation process in single-fiber composites. The results confirm that the crystallization rate and the “constraint state” of the amorphous phase of the matrix play an important role in the mechanical behavior of carbon fiber–PEEK interfaces.     

The interfacial enhancement of LLDPE/whisker composites via interfacial crystallization

Interfacial interaction plays a key role in the preparation of high performance polymer composites. In this work, in order to explore the possibility to enhance the interfacial interaction via interfacial crystallization of polymer matrix onto the filler surface, interfacial crystallization structure and mechanical properties of linear low density polyethylene (LLDPE)/whisker composites were investigated. The composites were firstly prepared by melt compounding, followed by processing in both traditional and dynamic injection molding. DSC, WAXD, SEM were used to characterize the interfacial crystallization structure. And the mechanical properties were measured by tensile testing. An imperfect shish‐calabash structure, with whisker served as shish, and irregular LLDPE spherulite as imperfect calabash, was formed during common injection molding processing. Such a structure was considered as the main reason for the strong interfacial adhesion and the obviously improved tensile strength and modulus. Furthermore, introducing shear could cause the formation of relatively perfect shish‐calabash structure, leading to the stronger interfacial adhesion. Copyright © 2011 John Wiley & Sons, Ltd.