Oxygen plasma processing and improved interfacial adhesion in PBO fiber reinforced epoxy composites

The effects of oxygen plasma processing on the improved interfacial adhesion properties of poly(1,4-phenylene-cis-benzobisoxazole) (PBO) fiber reinforced epoxy composites have been investigated in this paper. Both As-spun (AS) and high-modulus (HM) PBO fiber systems were studied. The characterization techniques included microscopy, surface analysis, and composite interfacial adhesion tests. The results showed that the high-modulus fiber surface free energy could be increased significantly by 42.2% from 46.2 to 65.7 mJ/m², while the tensile strength was only slightly decreased by 3.4% from 5.87 to 5.67 GPa. In addition, the interfacial adhesion strength of PBO fiber reinforced epoxy composite was improved by 37.5% from 32.5 to 44.7 MPa for the HM fiber system. The improvement has been attributed to the enhanced cohesive failure that dissipated more fracture energy.     

Effect of air plasma treatment on mechanical and tribological properties of PBO fabric composites

Friction and wear behavior of one-step or two-step air plasma treated and untreated PBO fabric composites has been evaluated in a pin-on-disc friction and wear tester. Tensile property of impregnated fabric and bond property between fabric and metallic substrate have also been studied. A comparison has been made between untreated and plasma treated fibers by using XPS, FTIR, FESEM and SEM. The results indicated that, air plasma treatment could increase the friction coefficient but decrease the wear rate of the PBO fabric composites. The most suitable condition of plasma treatment was 50 W and 15 min. After two-step plasma treatment, the tensile strength of the PBO fabric was decreased by 40%. While the antiwear property and bonding strength of the PBO fabric composites could be improved by 40–67% and 64%, respectively, which was due to the improvement of the bond property among the fiber, the adhesive and substrate.     

Mechanical strength of cold plasma treated PET fibers

In this work, the effects of cold plasma treatment on the mechanical strength of polyethyleneterephthalate (PET) fibers has been verified. Single fibers were treated with oxygen and a mixture of oxygen and tetrafluoroethylene in a cold plasma reactor for 30, 100 and 200 s. The single fibers were then tested in tensile mode and the mechanical strength was analyzed by using the Weibull distribution function.     

Properties of CuS thin films treated in air plasma

Copper sulfide thin films were grown by chemical deposition and post treated in air plasma during 20 min. Air plasma was generated by alternating current discharge at a pressure of 4 × 10² Pa. The power discharge was maintained at an output of 220 V and a current of 0.2 A. Thermal annealing at 300 °C was performed for comparison. X-ray diffraction shows that plasma treatment results in phase transformation of Cu₃₉S₂₈ (as grown) to CuS (treated by plasma). The copper lost is confirmed by X-ray fluorescence. No significant change in the optical band gap was observed due to plasma action. In addition, the electrical conductivity increases in one order of magnitude. On the other hand, the samples under plasma condition show a parallel growth to the substrate and an increase in the surface uniformity. The plasma etching removes copper due to its affinity with oxygen to form CuO, as is corroborated by optical emission spectroscopy.     

Effect of oxygen plasma treatment of PPTA and PBO fibers on the interfacial properties of single fiber/epoxy composites studied by Raman spectroscopy

The interfacial micromechanics of single poly(p-phenylene terephthalamide (PPTA) and poly(p-phenylene benzobisoxazole (PBO) fibers embedded in an epoxy resin has been investigated by determining the interfacial shear stress distributions along the fiber length. The effects of an oxygen plasma treatment on the interfacial shear stress of the fiber-epoxy systems are analyzed. Raman spectroscopy was used to map the stress distributions along the fiber when the composite is subjected to a small axial tensile strain (3.5% for PPTA and 2.5% for PBO). The quality of the interface or adhesion was improved after the surface treatment, supporting the ability of plasma oxidation to enhance the adhesion of high-performance fibers to epoxy resins. The tensile behavior of fiber-reinforced systems was different in each case. PPTA reinforcements underwent fragmentation, likely by fiber microfailure, whereas debonding or bridging is the most probable fragmentation mechanism in the case of PBO.     

羟基基团对PBO纤维表面性能及界面粘结性能的影响

以2,5-二羟基对苯二甲酸(DHTA)为改性单体,采用化学共聚改性的方法,合成了大分子链上含有羟基基团的聚对苯撑苯并二噁唑(PBO)与DHTA 的共聚物(DHPBO),并通过液晶纺丝技术得到了DHPBO 纤维。利用FTIR、接触角等分析手段对其化学结构和纤维表面性能进行了表征,并通过微脱粘实验和SEM评价了DHPBO纤维与环氧树脂基体的界面剪切强度。结果表明：50 mol%DHTA的加入使水在PBO纤维表面的接触角由71.4° 减小到50.7°,乙醇在PBO纤维表面的接触角由37.2° 减小到27.4°;当DHTA含量为20 mol%时,DHPBO纤维的表面自由能增加到43.96 mJ/m2,比PBO纤维提高了23.83%。当 DHTA含量为10 mol%时,DHPBO纤维与环氧树脂的界面剪切强度为18. 87 MPa,比PBO纤维与环氧树脂的界面剪切强度提高了92.55%。     

液晶高分子PBO纤维的性能、合成与纺制

液晶高分子PBO(聚对苯撑苯并双噁唑)纤维是一种高强度、高模量、耐腐蚀的高分子材料,是新一代超高性能纤维。对PBO纤维性能、合成、纺制的研究作了较详细的概述。特别阐述了4,6-二氨基-1,3-苯二酚盐酸盐和PBO纤维的合成方法,并对各种方法进行了比较。     

Wettability of glass fibres with different sizings and their adhesion to unsaturated polyester matrices

The wetting characteristics of unsaturated polyester resins on glass fibres with different sizings have been studied by contact angle determination periods. The styrene content of the matrix and the nature of the coatings result to be determinant in the wettability of glass fibres by the polyester matrices. Highest styrene content and styrene-soluble-coatings determine better wetting characteristics. Mechanical properties of the cured specimens and scanning electron microscopy on the fracture surfaces were also performed. Interesting correlations between the nature of the sizing agent and cohesive energy density with mechanical properties and fibre/matrix adhesion were found.[/p]     

Al doping effect on microstructure, electrical properties, dielectric characteristics, and aging behaviors of ZPCCY-based varistors

The Al doping effect on the microstructure, electrical properties, dielectric characteristics, and aging behaviors of ZPCCY-based varistors was investigated in the range of 0.0–0.1 mol%. The breakdown electric field in the E-J characteristics decreased in a wide range from 4,921 to 475 V/cm with increasing amounts of Al₂O₃. The nonlinear properties were improved by increasing amounts of Al₂O₃ up to 0.005 mol%, whereas the further additions caused it to decrease. The highest nonlinear coefficient (α = 45.2) was obtained when Al₂O₃ concentration is 0.005 mol%. The Al₂O₃ acted as a donor due to the increase of electron concentration in the small range of 0.0–0.1 mol%. On the other hand, an appropriate addition of Al₂O₃ in the range of 0.001–0.005 mol% was found to significantly improve the electrical stability against DC accelerated aging stress.     

The fragmentation test applied to adhesion measurements and microstructural characterization in plasma pre‐treated metallized plastic webs

A theoretical and experimental approach based on cracking analysis of stressed films (fragmentation test) has been applied to the study of interface dominant properties of metallized plastic flexible films. The test was found to be accurate for quantitative aluminium adhesion measurements and was used for an evaluation of the effect of different plasma pre‐treatments on the final properties of the metallized poly(ethylene) films. The test proved to be a powerful method for better understanding both the adhesion and the mechanical and microstructural properties of thin metal films. A clear improvement of aluminium adhesion was demonstrated for increasing plasma pre‐treatment times up to 0.8 s, and microstructural features were deduced from the test data. Copyright © 2009 John Wiley & Sons, Ltd     

微交联聚乙烯应力-光氧老化开裂行为的研究

为了提高桥梁缆索护套耐老化性能,通过制备微交联的聚乙烯材料研究不同交联度聚乙烯材料的应力-光氧老化开裂行为.采用剥离一段缆索护套并测定收缩率来计算聚乙烯护套在实际中的内应力,利用表面形貌观察、形变量测定、红外光谱分析、差式量热扫描法、凝胶含量测定等表征手段研究样品老化过程中的老化开裂行为.研究表明：随着交联度的增加,聚乙烯材料发生断裂的时间先增加后减少,表面裂纹发展的速度先增加后减小,裂纹发展速度及抗老化开裂性能最佳的交联度约为10%;聚乙烯材料的氧化速率与断裂时间呈正相关;表面裂纹出现后,材料被完全氧化;老化过程中,聚乙烯凝胶含量和结晶度均不断上升.     

Mechanical properties of basalt fibers and their adhesion to polypropylene matrices

This work is aimed to study the mechanical properties of basalt fibers, and their adhesion to polypropylene (PP) matrices. Single filament tensile tests were used to calculate the strength of different types of fibers, characterized by different providers and surface treatment. Single fiber fragmentation tests (SFFT) were used to calculate the critical length of the fibers, in a homopolymer PP matrix and in a maleic anhydride modified PP matrix. It was shown that the tensile strength of the fibers is not significantly influenced by the origin or the surface treatment. Only fibers without any sizing show very reduced mechanical properties. On the other hand, the tensile strength was shown to be severely dependent on the filament length. Weibull theory was used in order to calculate the fitting parameters σ₀ and β, which were necessary in order to extrapolate the tensile strength to the critical length determined by SFFT. This allowed calculating the adhesion properties of the basalt fibers. It was shown that fiber–matrix adhesion is dependent on both the presence of sizing on the fiber surface, as well as on the modification of the matrix.     

Relationship between surface properties and adhesion for etched ultra-high-molecular-weight polyethylene fibers

Chemical etching is an established and popular method of increasing the adhesion to such materials as polyethylene. Ultra-high-molecular-weight polyethylene (UHMWPE) fibers are exceptional candidates for composite materials except for their poor adhesion. In this research, the bulk, surface and adhesive properties of as-received and chromic acid etched UHMWPE fibers have been examined. The fiber tensile properties, surface chemistry and wettability have been characterized. The adhesion of epoxy has been characterized by the interfacial shear strength of a droplet microbond. The more than six-fold increase in interfacial shear strength observed in this work is related to the etching process. The removal of an oxygen-rich weak boundary layer, surface roughening and oxidation of the UHMWPE contribute to the enhanced adhesion.     

韧皮纤维的层级结构及其力学行为研究进展

韧皮纤维是一种重要的非木质植物纤维,具有较好的力学性能和环境友好性,被广泛用于增强复合材料。在韧皮纤维细胞壁中,螺旋结构的纤维素被半纤维素、果胶、木质素等无定形基质聚合物包裹。随着纤维素微纤丝角度变化,形成了多薄层/壁层的细胞壁结构。这种不同层级细胞壁的组装构筑,对于韧皮纤维力学性能的产生与力学行为的表现均具有重要影响。本文总结了以麻为代表的韧皮纤维在组织层级、细胞层级、细胞壁层级及分子层级的结构特点;重点分析了不同微观尺度的构造特征对单轴拉伸过程中纤维力学行为的影响;最后对韧皮纤维层级结构与力学行为研究存在的问题及未来发展方向提出了建议和展望,以期为韧皮纤维的利用及多尺度仿生结构的构建提供新思路。     

Multi-scale study of the adhesion between flax fibers and biobased thermoset matrices

The environmental impact of composite materials made with a thermoset matrix can be reduced in two ways. First, glass fibers can be replaced by natural fibers. Second, petrochemical components from the matrix can be replaced by biobased renewable equivalents. The quality of the interface between the matrix and the fibers has a strong influence on the composite mechanical properties. In this study, tensile performances of flax fibers and commercially partly biobased epoxy and polyester matrices have been investigated and corresponding unidirectional composites were elaborated. Their mechanical performances are in accordance with fiber and matrices properties, taking into account fiber dispersion. Then, at the microscopic scale, the debonding test was used; a great adhesion between flax fiber and thermoset matrices was highlighted. Finally, tensile tests on ±45° laminates were carried out to create an in-plane shear at the macroscopic scale. Interestingly, the results obtained at the macroscopic scale are well correlated to the ones given by the debonding test at the microscopic scale.     

Effect of cooling rate on electrical properties, impulse surge and dc-accelerated aging behaviors of ZPCCD-based varistors

The effect of cooling rate on nonlinear electrical properties, and stability against impulse surge and dc-accelerated aging stress of ZPCCD-based varistors was investigated. The cooling rate relatively slightly affects the microstructure, whereas it did not significantly modify the densification process. The nonlinear coefficient increased with the increase of cooling rate up to 240 °C/h, whereas the further fast cooling rate caused it to decrease. The samples cooled at 240 °C/h exhibited the highest nonlinearity, in which the nonlinear coefficient is 61.6 and the leakage current density is 6.8 μA/cm². The aging was not significantly affected by the specified impulse surge stress, whereas it was greatly affected by dc-accelerated aging stress. The samples cooled at 120 °C/h exhibited the highest stability, in which the variation rate of breakdown field is −5.5% and the variation rate of nonlinear coefficient is −29.1% under continuous stress composed of the specified impulse surge and dc-accelerated aging stress of 0.95 E _B/150 °C/24 h.     

Carbon,polyethylene and PBO hybrid fibre composites for structural lightweight armour

The properties of hybrid composite materials (based on carbon and organic fibres) have been investigated, with a view to using these materials in polymer composites lightweight structural armour. Laminates were manufactured and their specific ballistic properties and specific compressive strength after impact were determined. The introduction of organic fibres in order to improve ballistic properties has been successful. The associated reduction of specific compressive strength can be more than compensated for by an increase of specific ballistic properties. To achieve this, fractions of each fibre type and their distribution must be optimised and matrices must be optimised to the function of the respective fibre.