Improvement of interfacial shear strengths of polybenzobisoxazole fiber/epoxy resin composite by n‐TiO2 coating

Smooth polybenzobisoxazole (PBO) fiber has limited interfacial interaction with resin matrix. In this article, nano‐TiO₂ coating on PBO fiber is applied to improve the interfacial adhesion between PBO fiber and epoxy resin. The test results suggest that the PBO fiber had good interaction with epoxy resin matrix after its treatment with n‐TiO₂ sol. Nano TiO₂ particle embedded onto PBO fiber surface, acting as a chock, which made fiber implanted into the resin better. This greatly improved the shear strengths (IFSS) of PBO fiber/epoxy resin composite. It has been found that a 56% increase in interfacial IFSS has achieved without sacrificing mechanical properties of fiber. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improvement of the interfacial shear strength of poly(p‐phenylene benzobisoxazole) fiber/epoxy resin composite via a novel surface coating agent

Poly(p‐phenylene benzobisoxazole) (PBO) fiber with a smooth surface exhibits limited interfacial interaction with resin matrix. One of the effective strategies to improve the adhesion between the fiber and resin matrix is through surface modification of the fiber. In this study, we have proposed a novel surface treatment agent based on phosphoester cross‐linked castor oil (PCCO) for effective surface treatment of PBO fibers. The surface treatment agent was prepared by a simple cross‐linking reaction between hydroxy phosphorylated castor oil (PCO) and epoxy resin, with alcohol as the solvent at 65°C. Once the PBO fiber was treated with this agent, the interfacial adhesion between the PBO fiber and the epoxy resin could then be improved. Systematic analyses suggest that the surface treatment with (PCO + epoxy)/alcohol solution improves the interaction of the PBO fiber with the epoxy resin matrix. The PCCO coated onto the surface of PBO fiber acts as a coupling agent, improving the interfacial shear strength (IFSS) of the PBO fiber/epoxy resin composite. Results indicate a 156% increase in IFSS without compromising the mechanical properties of the fiber. POLYM. COMPOS., 37:1198–1205, 2016. © 2014 Society of Plastics Engineers     

氧气低温等离子体对PBO纤维的表面改性

采用氧气低温等离子体对聚对苯撑苯并双噁唑(PBO)纤维进行表面改性,讨论了处理时间、处理功率及气压对PBO纤维单丝强度、与环氧树脂基体的界面剪切强度(π_(IFSS))、形态结构、表面元素组成和亲水性的影响。结果表明:在处理时间为2.5 min,处理功率为30 W,处理气压为50 Pa的最佳工艺条件下,经氧气等离子处理后的PBO纤维与环氧树脂的π_(IFSS)比原丝提高60%,达9.38 MPa,与水的接触角也从105°下降到72°。     

Improvement of interfacial adhesion between PBO fibers and cyanate ester matrix

Poly(p‐phenylene benzobisoxazole) (PBO) fibers were activated by the horseradish peroxidases (HRP) and then treated by 3‐Glycidoxypropyltrimethoxysilane (KH‐560) to improve the wettability and the interfacial adhesion between PBO fibers and cyanate ester matrix. The chemical compositions of PBO fibers were characterized and analyzed by FTIR and XPS. Surface morphologies of PBO fibers were examined by SEM. The wettability of PBO fibers was evaluated by the dynamic contact angle analysis test. The mechanical properties were evaluated by tensile strength and interfacial shear strength, respectively. The results demonstrated that hydroxyl groups and epoxy groups were introduced onto the surface of PBO fibers during the treatments. These treatments can effectively improve the wettability and adhesion of PBO fibers. The surface free energy of PBO fibers was increased from 31.1 mN/m to 55.2 mN/m, and the interfacial adhesion between PBO fiber and cyanate ester resin was improved to 10.77 MPa. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40204.     

EP/PBO复合材料的制备工艺研究

采用自制的专用处理剂处理聚对苯撑苯并双恶唑(PBO)纤维,研究了PBO纤维增强环氧树脂(EP)(EP/PBO)复合材料的配方体系与制备工艺参数.研究表明,采用EP与4,4-二胺基二苯甲烷(DDS)混合制备的复合材料的剪切强度最高.控制预浸胶带的含胶量为35%～37%,在适宜的缠绕工艺参数与固化条件下,制备的EP/PBO复合材料的NOL环剪切强度达26.28～29.32 MPa.     

Poly(p‐phenylene benzoxazole) fiber chemically modified by the incorporation of sulfonate groups

Two kinds of modified poly(p‐phenylene benzoxazole) (PBO), the copolymer of TPA (SPBO) and p‐SPBO, containing ionic groups in the macromolecular chains were obtained by copolymerization from 1,3‐diamino‐4,6‐dihydroxybenzene dihydrochloride (DAR) and terephthalic acid (TPA), with the addition of selected amounts (1.5–5.0% molar ratio over DAR) of 5‐sulfoisophthalic acid monosodium salt or sulfoterephthalic acid monopotassium salt in place of the TPA, respectively, in poly(phosphoric acid) (PPA). The resultant PBO/PPA, SPBO/PPA, and p‐SPBO/PPA lyotropic liquid‐crystalline solutions were spun into fibers by a dry‐jet wet‐spinning technique. Chemically modified PBO fibers with sulfonate salt pendants in the polymer chains were obtained for the first time. The surface wetting behavior and interfacial shear strength between the fiber and epoxy resin were investigated. The interference of sulfonate salt pendants on the crystalline morphology was measured. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Promoting the adhesion of high‐performance polymer fibers using functional plasma polymer coatings

Plasma‐copolymerized functional coatings of acrylic acid and 1,7‐octadiene were deposited onto high strength, high modulus, poly‐p‐phenylene benzobisoxazole (PBO) fibers. X‐ray photoelectron spectroscopy (XPS) with trifluoroethanol derivatization confirmed that the PBO fibers were covered completely with the plasma copolymer and that the coating contained a quantitative concentration of carboxylic acid groups. Microdebond single filament adhesion and interlaminar shear strength (ILSS) tests were used to evaluate the interfacial strength of epoxy resin composites containing these functionalized PBO fibers. Both the interfacial shear strength (IFSS) obtained from single filament tests, and the ILSS of high volume fraction composites were a function of the surface functionality of the fibers so that there was a good correlation between ILSS and IFSS data. The tensile strengths of single fibers with or without coating were comparable, demonstrating that the fiber surface was not damaged in the plasma‐coating procedure. Indeed, the statistical analysis showed that Weibull modulus was increased. Therefore, plasma‐polymerized coatings can be used to control the interfacial bond between PBO fibers and matrix resins and act as a protective size for preserving the mechanical properties of the fibers. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

用于辐照改性的PBO纤维复合材料的树脂体系配方设计及其性能研究

结合γ-射线辐照改性PBO纤维表面技术,将辐照介质(接枝体化合物)作为树脂基体的一个成分设计出环氧树脂基体配方.通过浸润试验、树脂浇铸体力学试验、纤维湿法缠绕工艺试验和Microbond界面剪切试验等方法研究了树脂基体的各项性能.结果表明,与另外几种常用的树脂基体相比,本文设计的树脂基体与表面改性PBO纤维的浸润性能和界面粘接性能有明显的提高.树脂浇铸体力学性能满足高性能纤维复合材料的要求.     

PBO纤维表面改性与热处理研究

运用扫描电镜对自制的聚对苯撑苯并二噁唑(PBO)纤维表面进行观察,发现未经烘干的PBO纤维表面有许多的裂纹和沟槽,而烘干的纤维表面则较光滑。通过单丝拔出实验研究了偶联剂对不同表面形态纤维的表面处理情况,结果表明:用偶联剂表面处理后,纤维与树脂间的界面剪切强度得到提高,偶联剂对未经烘干纤维表面处理比对烘干纤维处理的效果要好,与原丝相比,提高率可达69.4%。对自制的PBO纤维进行了热处理,发现未烘干的PBO纤维比经烘干而干燥致密化的纤维的热处理效果要好,模量有很大提高,强度也有一定的增加。     

Effects of Basic Chemical Surface Treatment on PBO and PBO Fiber Reinforced Epoxy Composites

The effects of chemical surface treatment on PBO fiber and its composite materials were investigated using a basic sodium hydroxide solution. We evaluated several important treatment parameters quantitatively, including treatment concentration, treatment temperature and treatment time. Both as-spun (AS) and high-modulus (HM) PBO fibers were studied. The results showed that PBO fibers exhibited minimum or negligible reduction in their tensile strengths after the proposed treatment processes. The fibers’ contact angles with several liquid media were greatly reduced and the surface free energy could be increased to 58 mJ/m² or by 17%. The interfacial shear strength between PBO fiber and the epoxy matrix was improved to 38 MPa or by 11% with the same treatment process. The composite’s failure mode also shifted from fiber/matrix interface adhesive failure to partly cohesive failure.     

Surface modification of PBO fibers by argon plasma and argon plasma combined with coupling agents

The methods of argon plasma and argon plasma combined with coupling agents were employed to modify the poly[1,4‐phenylene‐cis‐benzobisoxazole] (PBO) fiber surface. The interfacial shearing strength (IFSS) of PBO fibers/epoxy resin was measured by the single fiber pull‐out test. The surface chemical structure and surface composition of PBO fibers were determined by FTIR and X‐ray photoelectron spectroscopy respectively. The morphology of the fiber surface was investigated by scanning electron microscopy and the specific surface area of the fibers was calculated by B.E.T. equation. Furthermore, the wettability of PBO fibers was confirmed by the droplet profile analysis method. The results showed that the elemental composition ratio of the fiber surface changed after the modification. The IFSS increased by 42 and 78% when the fibers were treated by argon plasma and argon plasma combined with the coupling agents, respectively. Meanwhile, the specific surface areas of the treated fibers were improved. In addition, compared with the modification of argon plasma, the modification of argon plasma combined with the coupling agents inhibited the attenuation phenomena of the IFSS and the wettability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1428–1435, 2006     

Characterization of interfacial toughness in carbon fiber/epoxy resin composite subjected to water aging using single‐fiber fragmentation method in an energy‐based model

The toughness of the interphase between carbon fibers and epoxy resin was characterized by the interfacial fracture energy, which was derived from the modified Wagner‐Nairn‐Detassis (WND) model, considering the moisture swelling stress. The characterization was used to evaluate the changes of interphase bonding before and after water aging, including boiling water and 70°C water immersion. The effects of the water aging on the parameters in WND model were analyzed. The mechanism of interphase degradation under water aging was interpreted considering the change of interphase thickness, which was measured using the dynamic nanomechanical mapping method. It is shown that the single‐fiber fragmentation test with the proposed energy‐based model can quantify the degradation of interphase toughness after water aging. For the studied system, the interphase thickness has a close relationship with the interfacial fracture energy, indicating that the swelling of the resin matrix and interphase results in an increase in interphase thickness and a decrease in interphase bonding property. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Influence of fiber modification on interfacial adhesion and mechanical properties of pineapple leaf fiber‐epoxy composites

Three kinds of surface treatment, that is, the alkalization (5% w/v NaOH aqueous solution), the deposition of diglycidyl ether of bisphenol A (DGEBA) from toluene solution (1% w/v DGEBA), and the alkalization combined with the deposition of DGEBA (5% w/v NaOH/1% w/v DGEBA) were applied to modify interfacial bonding and to enhance mechanical properties of pineapple leaf fiber (PALF) reinforced epoxy composites. The fiber strength and strain were measured by single fiber test and the fiber strength variation was assessed using Weibull modulus. Furthermore, a fragmentation test was used to quantify the interfacial adhesion of PALF‐epoxy composite. It was verified that the interfacial shear strength of modified PALFs was substantially higher than that of untreated PALF by almost 2–2.7 times because of the greater interaction between the PALFs and epoxy resin matrix. The strongest interfacial adhesion was obtained from the fibers that had been received the alkalization combined with DGEBA deposition. Moreover, the flexural and impact properties of unidirectional PALF‐epoxy composites were greatly enhanced when reinforced with the modified PALFs due to an improvement in interfacial adhesion, particularly in the synergetic use of 5% NaOH and 5% NaOH/1% DGEBA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Temperature effect on interfacial bonding property of single‐carbon fiber/epoxy resin composite

The changes in interfacial fracture energy of three kinds of commercially sized carbon fiber (CF)/epoxy resin composites in the range from ambient temperature to 130°C were investigated using the single‐fiber fragmentation test to evaluate the heat resistance of the interphase. The effects of CF sizing on the interfacial bonding property were studied using desized CF/epoxy resin composites. Thermogravimetric analysis and differential scanning calorimetry of the combination of sizing and matrix were employed to investigate the role of sizing on the variations in the fiber/matrix interfacial property under elevated temperature. The interfacial fracture energy values of all the studied CF composites were found to decrease quickly during the initial stage of temperature rise and drop gradually at higher temperature. At elevated temperature, the desized CF composites had higher heat resistance than the corresponding sized fiber composites. The differences in the interfacial heat resistance among the three kinds of CF composites and the difference in the interfacial thermal stability between the sized and the desized fiber composites were related to different glass transition temperatures of the interphases. The interaction between sizing and the matrix and the chain motion of the crosslink structure of the interphase has been suggested to determine the interfacial heat resistance. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Toughening of epoxy resin by functional‐terminated polyurethanes and/or semicrystalline polymer powders

Hydroxyl‐, amine‐, and anhydride‐terminated polyurethane (PU) prepolymers, which were synthesized from polyether [poly(tetramethylene glycol)] diol, 4,4′‐diphenylmethane diisocyanate, and a coupling agent, bisphenol‐A (Bis‐A), 4,4′‐diaminodiphenyl sulphone (DDS), or benzophenonetetracarboxylic dianhydride, were used to modify the toughness of Bis‐A diglycidyl ether epoxy resin cured with DDS. Besides the crystalline polymers, poly(butylene terephthalate) (PBT) and poly(hexamethylene adipamide) (nylon 6,6), with particle sizes under 40 μm were employed to further enhance the toughness of PU‐modified epoxy at a low particle content. As shown by the experimental results, the modified resin displayed a significant improvement in fracture energy and also its interfacial shear strength with polyaramid fiber. The hydroxyl‐terminated PU was the most effective among the three prepolymers. The toughening mechanism is discussed based on the morphological and the dynamic mechanical behavior of the modified epoxy resin. Fractography of the specimen observed by the scanning electron microscopy revealed that the modified resin had a two‐phase structure. The fracture properties of PBT‐particle‐filled epoxy were better than those of nylon 6,6‐particle‐filled epoxy. Nevertheless, the toughening effect of these crystalline polymer particles was much less efficient than that of PU modification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2903–2912, 2001     

Effect of silane coupling agents on basalt fiber–epoxidized vegetable oil matrix composite materials analyzed by the single fiber fragmentation technique

The fiber–matrix interfacial shear strength (IFSS) of biobased epoxy composites reinforced with basalt fiber was investigated by the fragmentation method. Basalt fibers were modified with four different silanes, (3‐aminopropyl)trimethoxysilane, [3‐(2‐aminoethylamino)propyl]‐trimethoxysilane, trimethoxy[2‐(7‐oxabicyclo[4.1.0]hept‐3‐yl)ethyl]silane and (3‐glycidyloxypropyl)trimethoxysilane to improve the adhesion between the basalt fiber and the resin. The analysis of the fiber tensile strength results was performed in terms of statistical parameters. The tensile strength of silane‐treated basalt fiber is higher than the tensile strength of the untreated basalt fiber; this behavior may be due to flaw healing effect on the defected fiber surfaces. The IFSS results on the composites confirm that the interaction between the fiber modified with coupling agents and the bio‐based epoxy resin was much stronger than that with the untreated basalt fiber. POLYM. COMPOS., 36:1205–1212, 2015. © 2014 Society of Plastics Engineers     

Surface modification of UHSPE fibers through allylamine plasma deposition. II. Effect on fiber and fiber/epoxy interface

The surface of ultra-high strength polyethylene (UHSPE) fibers was modified using allylamine plasma deposition to improve their adhesion to epoxy resins. Allylamine plasma polymerization was investigated at different power inputs and polymerization times. The adhesion of treated fibers to epoxy resin was studied by single-fiber, pull-out tests. A special silicon rubber mold was developed to embed the single fiber in epoxy resin. The results show that the interfacial shear strength (IFSS) increased by a factor of 2 to 3 after allylamine plasma treatments. The greatest improvement, by a factor of 3.25, was obtained at 30 W for 10 min. Scanning electron microscopy (SEM) was also used to study the surface topography of fibers pulled from the epoxy resin. In most cases, it was observed that pull-out failure occurred at the interface, as evidenced from clean fiber surfaces. In a few cases, however, fibrils were peeled from fibers. The fiber strength decreased, but initial modulus increased after the plasma treatments. The decrease in fiber strength was insignificant for treatments at a lower power input, but was significant at higher power inputs. Treatment time, however, had no significant effect on fiber strength.     

Improvement of the interfacial adhesion between PBO fibers and PPESK matrices using plasma‐induced coating

This work deals with the plasma‐induced coating process on the surface of PBO fibers to obtain a strong interfacial adhesion between the poly(p‐phenylene benzobisoxazole) (PBO) fibers and the poly(phthalazinone ether sulfone ketone) (PPESK) matrices. The process consisted of four steps: (a) plasma preactivation of PBO fibers; (b) immersion in an epoxy resin solution; (c) drying and then soaking with the PPESK solution; (d) shaped by compression molding technique. The orthogonal experiments used in this study enable the determination of the significant experimental parameters that influence efficiency of the process by comparing the values of ILSS. The order of their influences was the concentration > power > treating time > treating pressure. The results of the interlaminar shear strength (ILSS) and water absorption showed that the ILSS of the composite increased by 56.5% after coating, meanwhile the water absorption declined to 0.32%. The changes of the surface chemical composition, the surface morphology, and the surface free energy of fibers were studied by FTIR spectroscopy, atomic force microscope (AFM), and dynamic contact angle analysis (DCAA), respectively. Fracture mechanism of the composite was examined by scanning electron microscope (SEM). The results indicated that plasma‐induced coating process was an efficient method to enhance the interfacial adhesion of PBO fibers and PPESK matrices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical,thermal, and burning properties of viscose fabric composites: Influence of epoxy resin modification

The influence of epoxy resin modification by 3‐aminopropyltriethoxysilane (APTES) on various properties of warp knitted viscose fabric is reported in this study. Dynamic mechanical, impact resistance, flexural, thermal properties, and burning behavior of the epoxy/viscose fabric composites are studied with respect to varying content of silane coupling agent. The results obtained for APTES‐modified epoxy resin based composites reinforced with unmodified viscose fabric composites are compared to unmodified epoxy resin based composites reinforced with APTES‐modified viscose fabric. The dynamic mechanical behavior of the APTES‐modified resin based composites indicates improved interfacial adhesion. The composites prepared from modified epoxy resin exhibited a twofold increase in impact resistance. The improved adhesion between the fiber and modified resin was also visible from the scanning electron microscope analysis of the impact fracture surface. There was less influence of resin modification on the flexural properties of the composites. The 5% APTES modification induced early degradation of composites compared to all other composites. The burning rate of all the composites under study is rated to be satisfactory for use in automotive interior applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46673.     

环氧树脂/石英纤维透波复合材料制备

为改善环氧树脂的介电性能及提升石英纤维的界面性能,使用缩水甘油醚基笼型倍半硅氧烷(G–POSS)和γ–氨丙基三乙氧基硅烷(KH–550)分别对环氧树脂和石英纤维进行改性。利用差示扫描量热法研究改性后环氧树脂的固化过程,并通过外推法确定了其固化工艺,根据固化工艺制备环氧树脂/石英纤维复合材料,分别对该复合材料的热稳定性、介电性能和弯曲性能进行表征,结果表明,使用G–POSS和KH–550改性后的环氧树脂/石英纤维复合材料热稳定性、介电性能和弯曲性能达到最佳,初始分解温度达到369.59℃,常温下在12~18 GHz的介电常数稳定在3.2~3.5之间,介电损耗角正切值在0.005~0.02之间,弯曲强度达到376.4 MPa,弯曲弹性模量为21.7 GPa。