Interfacial properties and impact toughness of methylphenylsilicone resin composites by chemically grafting POSS and tetraethylenepentamine onto carbon fibers

Octaglycidyl polyhedral oligomeric silsesquioxane (gly-POSS) was successfully grafted on carbon fibers (CFs) surface to enhance interfacial properties and impact toughness of CFs reinforced methylphenylsilicone resin (MPSR) composites. After gly-POSS modification, POSS grafted CF (CF-POSS) with many epoxy functional groups was modified with tetraethylenepentamine (TEPA) to further enhance the interfacial strength. Atomic force microscopy (AFM) images showed that POSS and TEPA were grafted onto CFs surface uniformly and the surface roughness enhanced obviously. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirmed the chemical bonding nature between CFs and POSS, as well as between POSS and TEPA. POSS and TEPA modification could increase the fiber polarity, wettability and surface energy significantly. The interlaminar shear strength (ILSS) and impact toughness of composites showed a dramatic improvement, especially for grafting with POSS and further with TEPA (CF-POSS-TEPA). Additionally, the reinforcing and toughening mechanisms were also analyzed. Meanwhile, single fiber tensile strength (TS) had no decrease after modification.     

Effect of a multiscale reinforcement by carbon fiber surface treatment with graphene oxide/carbon nanotubes on the mechanical properties of reinforced carbon/carbon composites

An effective carbon fiber/graphene oxide/carbon nanotubes (CF-GO-CNTs) multiscale reinforcement was prepared by co-grafting carbon nanotubes (CNTs) and graphene oxide (GO) onto the carbon fiber surface. The effects of surface modification on the properties of carbon fiber (CF) and the resulting composites was investigated systematically. The GO and CNTs were chemically grafted on the carbon fiber surface as a uniform coating, which could significantly increase the polar functional groups and surface energy of carbon fiber. In addition, the GO and CNTs co-grafted on the carbon fiber surface could improve interlaminar shear strength of the resulting composites by 48.12% and the interfacial shear strength of the resulting composites by 83.39%. The presence of GO and CNTs could significantly enhance both the area and wettability of fiber surface, leading to great increase in the mechanical properties of GO/CNTs/carbon fiber reinforced composites.     

甲基丙烯酰氧基倍半硅氧烷改性碳纤维/聚芳基乙炔复合材料界面性能

利用微脱粘法、三点弯曲法、扫描电镜（SEM）、力调制模式原子力显微镜（AFM）和动态力学热分析（DMTA）研究了甲基丙烯酰氧基倍半硅氧烷（Methacryl-POSS）涂层改性前后的碳纤维增强的聚芳基乙炔（PAA）复合材料的界面性能。用Wilhelmy法研究了处理前后的碳纤维与PAA树脂的浸润性。结果表明: POSS涂层处理后的碳纤维表面粗糙度增大,与PAA树脂的浸润性提高;复合材料的界面剪切强度提高了36%,层间剪切强度提高了50%。DMTA图谱表明, POSS涂层改性后,复合材料的玻璃化转变温度提高了12℃,损耗因子降低了53%,表明复合材料的界面粘接性能得到大幅度的改善。      

Interfacial microstructure and mechanical properties of carbon fiber composites by fiber surface modification with poly(amidoamine)/polyhedral oligomeric silsesquioxane

Polyhedral oligomeric silsesquioxane (POSS) was grafted onto carbon fiber surface using poly(amidoamine) (PAMAM) as a novel coupling agent at mild reaction conditions. Firstly, the reinforcement was designed with propagation of PAMAM on the fiber surface by in situ polymerization to improve the surface activities of carbon fiber. Secondly, the POSS further grafted on the fiber could significantly enhance fiber surface energy and wettability, which would greatly increase the interfacial strength of fiber-matrix. The microstructure and mechanical properties of carbon fiber and the resulting composites were investigated. The results indicated that PAMAM and POSS, which could significantly increase the surface roughness and wettability of carbon fiber, were successfully grafted on the fiber surface. Compared with the desized fiber composites, the interlaminar shear strength and the interfacial shear strength of the modified carbon fiber composites increased by 48% and 89%, respectively.     

电泳沉积氧化石墨烯的碳纤维表面改性及其增强环氧树脂复合材料界面性能

采用超声辅助电泳沉积法,以异丙醇作为溶剂,在连续碳纤维(CF)表面沉积一层氧化石墨烯(GO),对CF表面进行改性。再经200℃高温处理来增强(GO)与CF之间的黏合性,从而增加CF/环氧树脂(EP)复合材料的界面结合强度。利用SEM和AFM对改性前后CF的表面形貌及微观结构变化进行了表征,通过XPS对改性前后CF表面官能团的变化进行了检测。结果表明,在CF表面沉积GO并经200℃处理后,有效地部分还原了GO(RGO),填补或桥联了CF表面缺陷,使改性后CF的拉伸强度提高了34.58%。同时,高温处理使RGO与CF之间生成牢固的化学键,从而提高了RGO与CF之间的结合强度,最终使RGO-CF/EP复合材料的界面剪切强度(IFSS)提高了69.9%。      

氧化石墨烯改性不同表面性质的碳纤维/环氧树脂复合材料的微观形貌与动态热力学性能

通过模压成型，采用氧化石墨烯(GO)对四种碳纤维(CCF300、T700、CCF800、CCM40J)织物/环氧树脂(CF/EP)复合材料进行改性，通过复合材料的微观形貌、动态热力学性能等研究了GO对四种不同表面性质的CF/EP复合材料的改性效果。研究表明，添加GO后，GO/EP对四种CF的浸润性均比EP明显提高，纤维与GO/EP间的界面黏接比与EP基体间的黏接明显改善；CF/EP复合材料的破坏主要发生在CF与EP的界面，而GO的存在使GO-CF/EP复合材料的破坏由CF与EP基体的界面向GO/EP区域过渡。CF表面的氧碳比和沟槽均显著影响复合材料的玻璃化转变温度(T_g)，具有最高表面氧碳比的GO-CCF300/EP复合材料表现出最高的T_g，但沟槽更丰富的CCM40J和CCF300碳纤维对CF/EP复合材料的T_g表现出更好的GO改性效果。      

Effects of thermal histories on interfacial properties of carbon fiber/polyamide 6 composites: Thickness,modulus, adhesion and shear strength

Interface thickness and modulus of carbon fiber (CF) reinforced polyamide 6 (PA 6) composites with different thermal histories are characterized as 331–394 nm and 0.24–0.30 times to fiber modulus, respectively. Transverse fiber bundle (TFB) test is firstly employed for evaluating semi-crystalline PA 6 interfacial adhesion. TFB Failure mechanisms are schematically given. Besides enhanced molecular entangling on fiber surface, increased matrix toughness is also found to have a great effect on improved TFB results. Droplet micro-debonding results show that decreasing cooling rate and increasing annealing temperature both decrease interfacial shear strength (IFSS) though residual PA 6 on carbon fiber surface increases. In the end, the above data are normalized together with some previous measured parameters. It shows that quenching of the CF/PA 6 composites and subsequent annealing are shown to give similar results as slow cooling. Relationships between each other are also discussed.     

One-pot strategy for covalent construction of POSS-modified silane layer on carbon fiber to enhance interfacial properties and anti-hydrothermal aging behaviors of PPBES composites

In this study, we describe a novel strategy to design and construct POSS-modified silane layer on carbon fiber (CF) to strengthen the interfacial adhesion and anti-hydrothermal aging behaviors of CF-reinforced copoly(phthalazinone ether sulfone)s (PPBES). POSS was first modified by 3-aminopropyltriethoxysilane (APS) to improve chemical reactivity. Without separation and purification, APS-c-POSS was used to functionalize CF to improve reactivity and ensure the covalent linkages between CF and POSS-modified silane layer. CF coated with POSS-modified silane layer was obtained by in situ hydrolysis of APS-c-POSS. FTIR and XPS confirmed the chemical bonds between CF and POSS-modified silane layer. Dynamic contact angle, dynamic wetting test and AFM tests demonstrated that POSS-modified silane coating can increase the wettability and roughness, which could improve interlaminar shear strength and flexural strength of CF/PPBES composites by 17.5 and 30.0% with slight enhancement on tensile strength of CF. The failure mechanisms of CF/PPBES composites with and without POSS-modified silane layer were both investigated by SEM in detail. Moreover, this layer was helpful to dynamic mechanical property and hydrothermal resistance of CF/PPBES composites. This study provides alternate strategy to modify CF with POSS, which will significantly broaden the application field of POSS in advanced composites.     

Interfacial evaluation of carbon fiber/epoxy composites using electrical resistance measurements at room and a cryogenic temperature

Interfacial properties between fiber and matrix were evaluated using an electrical resistance (ER) fragmentation method. The single carbon fiber (CF) tensile test was performed in conjunction with electrical resistance measurements. The relationship between tensile properties of single carbon fiber specimens and the electrical resistance ratio (ERR) was investigated. The data showed a linear relationship between these properties. Fragmentation specimens were tested under tensile loading, and it was observed that, due to stress transfer from the matrix to the reinforcing fiber, the single carbon fiber broke first. The stress distribution along the carbon fiber was monitored via electrical resistance changes. ER fragmentation measurements were performed to predict CF fractured strength embedded in epoxy by an empirical formula of CF tensile results. These interfacial properties of CF epoxy composites were measured at room and a cryogenic temperature. Work of adhesion between the carbon fiber and the matrix was measured to verify the results of the ER fragmentation method, and the two procedures yielded consistent results and conclusions.     

Preparation of carbon nanotube/copper/carbon fiber hierarchical composites by electrophoretic deposition for enhanced thermal conductivity and interfacial properties

A facile electrophoretic deposition method was proposed to deposit copper (Cu) and carbon nanotubes (CNTs) on the surface of carbon fiber (CF) to improve the thermal conductivity and interfacial properties of carbon fiber-reinforced polymer (CFRP) composites. Surface morphologies, crystallographic properties, thermal conductivity, interlaminar shear strength (ILSS) and element distribution of the composites were characterized by scanning electron microscopy (SEM), X-ray diffraction, thermal constant analysis, short-beam bending tests and SEM energy-dispersive X-ray diffractometer (SEM–EDX), respectively. The results indicate that the presence of Cu and CNTs generated networks and bridges with each other, which produced continuous heat conduction pathways and significantly enhanced both the specific surface area and roughness of the fiber surface. These pathways obviously promoted an improvement in the thermal and interfacial properties. The thermal conductivity and ILSS of the CNTs–Cu–CF/epoxy composites increased by 292 and 39.5%, respectively, compared with CF/epoxy composites. Therefore, this method is anticipated to be utilized in the future fabrication of multifunctional CFRP composites.     

Effects of maleated polypropylene on the morphology,thermal and mechanical properties of short carbon fiber reinforced polypropylene composites

The aim of this study was to determine the effect of the maleic anhydride grafted polypropylene (PP-g-MAH) on the properties of short carbon fiber (CF) reinforced polypropylene (PP) composites. The composites were prepared by melt blending and injection molding techniques at different percentages of CF. Tensile tests, hardness, differential scanning calorimeter (DSC) and scanning electron microscopy (SEM) were performed to characterize the physical and morphological properties of the prepared composites. It was observed from SEM photographs that modification with PP-g-MAH improved the interfacial adhesion between the carbon fibers and PP matrix. The ultimate tensile strength, hardness and modulus values of modified PP composites were higher compared to the values of CF reinforced PP composites. Melting temperature of all composites was not changed significantly with increasing CF content; however degree of crystallinity values were decreased with the increasing CF content level.     

Improved interfacial properties of carbon fiber/epoxy composites through grafting polyhedral oligomeric silsesquioxane on carbon fiber surface

Carbon fibers were grafted with a layer of uniform octaglycidyldimethylsilyl POSS in an attempt to improve the interfacial properties between carbon fibers and epoxy matrix. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and dynamic contact angle analysis were performed to characterize the carbon fibers. AFM results show that the grafting of POSS significantly increased the carbon fiber surface roughness. XPS indicates that oxygen-containing functional groups obviously increased after modification. Dynamic contact angle analysis shows that the surface energy of modified carbon fibers is much higher than that of the untreated ones. Results of the mechanical property tests show that interlaminar shear strength (ILSS) increased from 68.8 to 90.5 MPa and impact toughness simultaneously increased from 2.62 to 3.59 J.     

An effective surface modification of carbon fiber for improving the interfacial adhesion of polypropylene composites

A simple and effective modification for carbon fiber (CF) was presented in our work. CF was coated with ethylene–methyl acrylate–glycidyl methacrylate (E–MA–GMA) terpolymer through solution dipping. A uniform layer of 2.0 wt.% E–MA–GMA was confirmed on CF by IR, TGA and SEM. XPS showed that surface oxygen-containing functional groups were obviously increased after modification, which were advantageous to promote the reactivity of CFs. The treatment turned out to be helpful in enhancing the interfacial adhesion by micro-droplet experiment and the interfacial shear strength was 157% higher. The physical properties of PP/mCF composites were improved by static and dynamic mechanical analysis and the improvement was more noteworthy when maleic anhydride grafted PP (MAPP) was added to the matrix, which was consistent with the fracture morphology. The ultimate flexural strength, impact energy and tensile strength were increased by 139.3%, 233.9% and 126.1%. Besides, the mechanical performance of PP composites with 0–30 wt.% CFs were all significantly enhanced by CF surface treatment in combination with MAPP modification. We believed that the excellent performance was not caused by fiber length or crystallinity, it was mainly due to the superior interfacial interaction by intermolecular chain entanglement, as well as chemical reaction between E–MA–GMA and MAPP.     

Interfacial resistive heating and mechanical properties of graphene oxide assisted CuO nanoparticles in woven carbon fiber/polyester composite

Woven carbon fiber (WCF)-based polyester composites were developed via a vacuum-assisted resin transfer molding (VARTM) process in combination with CuO and graphene oxide (GO). The interlaminar resistive heating behavior and allied mechanical properties of the composites were investigated. The CuO nanoparticles were synthesized from copper nitrate and hexamethylenetetramine precursors using traditional microwave green synthesis, while the GO was synthesized by slight modification of Hummer’s method. The nanoparticle shapes and sizes were assessed via scanning electron microscopy, and the nanoparticle distributions in the composites and their chemical interactions were examined using X-ray diffraction and Fourier transform infrared spectroscopy. It was found that the composite strengths and moduli were enhanced by up to 61.2% and 57.5%, whereas the interfacial shear strength was enhanced by 89.9%. A composite filled with 120-mM CuO and 1.2-phr GO exhibited maximum performance as regards mechanical and resistive heating. Impact resistance measurements were conducted at 3-J penetration energy, and a 154.2% increase in nanofiller content was achieved. The addition of CuO nanoparticles increased the interlaminar resistive heating of the composite and, at 120-mM concentration, a 78.9% increment in the average temperature was attained. The presence of nanoparticles in the interlaminar region also decelerated the cooling process.     

Mechanical properties of injection-molded carbon fiber/polypropylene composites hybridized with nanofillers

Short-carbon-fiber/polypropylene composites (CF/PP composites) have high processability and recyclability but low strength. To improve the strength, various nanofillers were hybridized to form fiber-reinforced composites. Adding nanofillers improves not only the strength but also the elastic modulus, with the exception of clay nanofillers. To understand the strengthening mechanism resulting from the addition of nanofillers, the residual fiber length and interfacial shear strength were measured. For CF/PP composites, the addition of alumina, silica, and CNT improves the interfacial shear strength, and thereby, the mechanical properties. On the basis of this result, proper choice of nanofiller type and content for improving the mechanical properties of PP/CF composites is discussed.     

Application of continuously-monitored single fiber fragmentation tests to carbon nanotube/carbon microfiber hybrid composites

To assess the effect of carbon nanotube (CNT) grafting on interfacial stress transfer in fiber composites, CNTs were grown upon individual carbon T-300 fibers by chemical vapor deposition. Continuously-monitored single fiber composite (SFC) fragmentation tests were performed on both pristine and CNT-decorated fibers embedded in epoxy. The critical fragment length, fiber tensile strength at critical length, and interfacial shear strength were evaluated. Despite the fiber strength degradation resulting from the harsh CNT growth conditions, the CNT-modified fibers lead to a twofold increase in interfacial shear strength which correlates with the nearly threefold increase in apparent fiber diameter resulting from CNT grafting. These observations corroborate recently published studies with other CNT-grafted fibers. An analysis of the relative contributions to the interfacial strength of the fiber diameter and strength due to surface treatment is presented. It is concluded that the common view whereby an experimentally observed shorter average fragment length leads to a stronger interfacial adhesion is not necessarily correct, if the treatment has changed the fiber tensile strength or its diameter.     

Highly dispersed graphene oxide electrodeposited carbon fiber reinforced cement-based materials with enhanced mechanical properties

Mechanical behavior of carbon fiber (CF) reinforced cement-based materials greatly depends on the dispersion of CF and interfacial properties between the CF and cement matrix. In this study, graphene oxide (GO) was utilized to modify the surface properties of CF, including the roughness, wettability and chemical reactivity, and the graphene oxide/carbon fiber (GO/CF) hybrid fibers were fabricated by a newly designed electrophoretic depositing method. The scanning electron microscopy and contact angle measurement results indicated that GO/CF hybrid fibers not only had a rougher surface which was expected to improve the physical friction when CF was pulled out from cement matrix, but also had a higher wettability surface that made it easier to contact with cement hydrates as nucleation sites. In addition, GO/CF hybrid fibers were capable of high chemical reactivity due to the introduction of GO with many functional groups, which ensured them more likely to interact with cement hydrates due to the hydrogen bonding at interface and therefore benefited to strengthen the bonding between the CF and cement matrix. In terms of mechanical behavior, three-point bending test showed that compared with the CF reinforced cement paste, flexural strength of the GO/CF hybrid fibers reinforced cement paste was enhanced by 14.58%, and could be further improved by 10.53% when the GO/CF hybrid fibers were pre-dispersed in the GO solution and then mixed with cement powders. The larger electrostatic repulsion and steric stabilization led to the better dispersion of GO/CF hybrid fibers in GO solution, which were responsible for the further mechanical enhancement of cement paste. In conclusion, the research outcomes provided a novel way for utilizing GO as both of dispersant and surface modifier to improve the dispersion of CF in cement and strengthen its bonding with cement hydrates, consequently achieving a significant enhancement in the mechanical properties of cement paste.     

氧化石墨烯改性碳纤维/环氧树脂复合材料的湿热性能及微观形貌

采用湿法预浸技术和模压工艺制备了氧化石墨烯(GO)改性碳纤维/环氧树脂(CF/EP)复合材料,研究了 GO在室温干态及湿热处理后对CF/EP复合材料动态热力学性能和层间剪切性能的影响,并通过微观形貌分析了复合材料的改性机制.结果表明,当GO添加量分别为0.5％和0.8％时,GO-CF/EP复合材料的玻璃化转变温度(Tg...     

Enhancement of ablative and interfacial bonding properties of EPDM composites by incorporating epoxy phenolic resin

Effects of epoxy phenolic resin (EPR) on ablative and interfacial bonding properties of EPDM composites were evaluated. Ablative properties of EPDM composites were enhanced by two folds with incorporating 10 phr EPR. This significant enhancement was attributed to positive effect of EPR on thermal stability and thermal insulating properties of EPDM composites as well as formation of compact char layer onto composites. Furthermore, interfacial shear strength of EPDM composites with carbon fiber/epoxy (CF/EP) composites was increased by 55.6% with incorporating 10 phr EPR, due to interfacial chemical reaction of epoxide groups of EPR molecule from EPDM composites with amine group of hardener from CF/EP composites.     

MWCNTs对环氧树脂及多尺度MWCNTs-碳纤维/环氧树脂复合材料力学性能的影响

通过对胺基化多壁碳纳米管（MWCNTs-NH₂）进行改性,得到改性MWCNTs悬浮液（MWCNTs-NH₂（M））。分别将羧基化MWCNTs （MWCNTs-COOH）和MWCNTs-NH₂（M）分散在环氧树脂（EP）中,采用热熔法制备了多尺度MWCNTs-碳纤维（CF）/EP复合材料。研究了MWCNTs对EP模量、韧性及EP与CF之间界面黏结强度的影响,并分析了MWCNTs与CF上浆剂的作用,评价了多尺度MWCNTs-CF/EP复合材料的力学性能。结果表明：官能团化的MWCNTs可对EP的模量和韧性起到更好的增强作用。MWCNTs接枝的-COOH或-NH₂可与CF上浆剂中的环氧基团发生化学反应,提高EP与CF之间的界面剪切强度。MWCNTs-NH₂（M）对多尺度MWCNTs-CF/EP复合材料力学性能的增强效果优于MWCNTs-COOH,当MWCNTs-NH₂（M）的含量为1wt%时,多尺度复合材料的0°压缩强度、90°压缩强度、弯曲强度、弯曲模量、冲击后压缩强度（CAI）分别提高了16.7%、16.3%、40.9%、30.3%、20.6%。