Effect of coagulation temperature on structures and properties of poly(<Emphasis Type="Italic">p</Emphasis>-phenylene benzobisoxazole) (DHPBO) fibers during dry-jet wet-spinning process

The effect of coagulation temperature on the morphology, microstructures and mechanical properties of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) fibers was investigated during dry-jet wet-spinning process, in which the coagulation bath concentration and drawn ratio were kept as 10 wt% of PPA in water and 1.7, respectively. The structures and mechanical properties of the as-spun DHPBO fibers were characterized by FTIR, XRD, SEM, and single fiber tensile testing. The results indicated that in PPA/H₂O coagulation system, when the coagulation temperature was 25°C, highly crystallized DHPBO as-spun fibers possessing fine crystallites, circular and smooth morphology, and excellent mechanical properties could be achieved. Supported by the National Natural Science Foundation of China (Grant No. 50673017), Shanghai Leading Academic Discipline Project (Grant No. B603) and the Program of Introducing Taleuts of Discipline to University of People’s Republic of China (“111” Program) (Grant No. 111-2-04)     

凝固浴对蓄热调温聚丙烯腈纤维性能的影响

以聚酰胺石蜡相变微胶囊(MEPCM)为相变材料,硫氰酸钠(NaSCN)水溶液为溶剂,通过湿法纺丝工艺制备MEPCM质量分数为16.7%的蓄热调温聚丙烯腈纤维,考察了凝固浴中NaSCN质量分数对纤维性能的影响。随着NaSCN质量分数的增大,纤维的线密度增大,断裂强度、热收缩率和沸水收缩率下降,断裂伸长率和钩接强度先增大后减小。通过实验分析确定最佳NaSCN质量分数为10%,在此条件下制备的蓄热调温聚丙烯腈纤维强度为1.35cN/dtex,热焓值为26.0J/g,MEPCM在纤维中的热效率达到78.4%,具有良好的物理机械性能和较好的蓄热调温性能。     

The coagulation process of nascent fibers in PAN wet-spinning

The evolvement of microstructure and properties of nascent fibers during coagulation process in the polyacrylonitrile (PAN) wet-spinning and the effect of coagulation bath conditions on the structure and properties of the nascent fibers were investigated by the means of X-ray diffraction (XRD), scanning electron microscope (SEM), fiber fineness machine, fiber tensile strength machine, etc. The experimental results indicate that the nascent fibers become denser and have fewer inner defects, the diameter of nascent fibers shrink and the crystallization degree of nascent fibers gradually increases with the increasing of coagulation time. Too large spinning tension leads to grooves occurring on surface of fibers. To obtain circular cross-section of nascent fibers the optimal coagulation conditions are 50 °C, 65% (concentration) and 0.9 (draw ratio).     

The Coagulation Process of Nascent Fibers in PAN Wet-spinning

The evolvement of microstructure and properties of nascent fibers during coagulation process in the polyacrylonitrile (PAN) wet-spinning and the effect of coagulation bath conditions on the structure and properties of the nascent fibers were investigated by the means of X-ray diffraction (XRD), scanning electron microscope (SEM), fiber fineness machine, fiber tensile strength machine, etc. The experimental results indicate that the nascent fibers become denser and have fewer inner defects, the diameter of n...     

紫外辐射对聚酯纤维表面形态结构的影响

研究了紫外辐射对聚酯纤维的机械性能、表面形态结构的影响.结果表明,紫外辐射后的聚酯纤维强伸度大幅度下降,表面形态发生了很大的变化.本文通过研究聚酯纤维表面形态结构的变化来探讨聚酯纤维的断裂过程.     

苎麻/聚碳酸亚丙酯复合材料力学性能的研究

采用苎麻纤维和聚碳酸亚丙酯制备了可降解复合材料。讨论了碱处理、苎麻纤维长度对苎麻／聚碳酸亚丙酯复合材料机械性能的影响，并借助扫描电子显微镜对复合材料的冲击断口形貌进行了观察。结果表明：苎麻经碱液处理后，苎麻／聚碳酸亚丙酯复合材料的拉伸强度和冲击强度有了明显提高，分别由23．90MPa、30．04kl／m^2增加到25．39MPa、36，40kl／m^2。     

玄武岩纤维超高性能混凝土力学性能试验

为了降低超高性能混凝土中水泥的用量,制备绿色超高性能混凝土,研究了玄武岩纤维对超高性能混凝土力学性能的影响,提出了力学性能最优的低水泥用量超高性能混凝土配合比和玄武岩纤维的最佳掺量.采用粉煤灰和硅灰以不同比例组合作为水泥的替代材料制备超高性能混凝土,分析了添加纤维和不添加纤维试件的和易性、力学性能和微观结构.结果表明,当粉煤灰和硅灰混杂替代水泥比例达50%时,其力学性能与原试件强度相当;掺加0.1%玄武岩纤维的试件其力学性能高于掺加0.2%和0.3%纤维和没有掺加纤维试件的力学性能.     

凝固浴中加入碳纳米管对ＰＡＮ碳纤维原丝结构性能的影响

在凝固浴中加入经酸处理的多壁碳纳米管（MWNTs）,制得多壁碳纳米管-聚丙烯腈纤维,并对其进行了表征．结果表明：在凝固浴中加入酸处理MWNTs,对填补PAN碳纤维原丝内部的微孔有明显的作用;对PAN原丝的结晶结构几乎没有影响;降低了原丝的晶区取向;提高了原丝的断裂强度、断裂伸长率及拉伸韧度．     

Fiber-reinforced Mechanism and Mechanical Performance of Composite Fibers Reinforced Concrete

To understand the enhancing effect and fiber-reinforced mechanism of composite fibers reinforced cement concrete, the influences of composite fibers on micro-cracks and the distribution of composite fibers were evaluated by optical electron micrometer(OEM) and scanning electron microscope(SEM). Three kinds of fiber, such as polyacrylonitrile-based carbon fiber, basalt fiber, and glass fiber, were used in the composite fibers reinforced cement concrete. The composite fibers could form a stable structure in concrete after the liquid-phase coupling treatment, gas-liquid double-effect treatment, and inert atmosphere drying. The mechanical properties of composite fibers reinforced concrete(CFRC) were studied by universal test machine(UTM). Moreover, the effect of composite fibers on concrete was analyzed based on the toughness index and residual strength index. The results demonstrated that the composite fibers could improve the mechanical properties of concrete, while the excessive amount of composite fibers had an adverse effect on the mechanical properties of concrete. The composite fibers could significantly improve the toughness index of CFRC, and the increment rate is more than 30%. The composite fibers could form a mesh structure, which could promote the stability of concrete and guarantee the excellent mechanical properties.     

Morphological,Mechanical and Thermal Properties of Poly(lactic acid)(PLA)/Cellulose Nanofibrils(CNF) Composites Nanofiber for Tissue Engineering

Composite nanofiber membranes based on biodegradable poly(lactic acid)(PLA) and cellulose nanofibrils(CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mechanical properties of PLA/CNF composite nanofiber membranes were characterized by field scanning electron microscopy(FE-SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), and dynamic mechanical analysis(DMA), respectively. The results show that the PLA/CNF composite nanofibers with smooth, free-bead surface can be successfully fabricated with various CNF contents. The introduction of CNF is an effective approach to improve the crystalline ability, thermal stability and mechanical properties for PLA/CNF composite fibers. The Young's moduli and tensile strength of the PLA/CNF composite nanofiber reach 106.6 MPa and 2.7 MPa when the CNF content is 3%, respectively, which are one times higher and 1.5 times than those of pure PLA nanofiber. Additionally, the water contact angle of PLA/CNF composite nanofiber membranes decreases with the increase of the CNF loading, resulting in the enhancement of their hydrophilicity.     

Spalling and mechanical properties of fiber reinforced high-performance concrete subjected to fire

Spalling and mechanical properties of FRHPC subjected to fire were tested on notched beams. The results confirm that the internal vapor pressure is the leading reason for spalling of high-performance concrete （HPC）. At the same time, the temperature-increasing velocity and constrained conditions of concrete element also play significant roles in spalling. Steel fibers cannot reduce the risk of spalling, although they have obvious beneficial effects on the mechanical properties of concrete before and after exposure to fire. Polypropylene （PP） fibers are very useful in preventing HPC from spalling, however, they have negative effects on the strengths. By using hybrid fibers （steel fibers＋PP fibers）, both good anti-spalling performance and improved mechanical properties come true, which may provide necessary safe guarantee for the rescue work and structure repair after fire disaster.     

Mechanical Properties of Layered Hybrid Fiber Reinforced Concrete

1　IntroductionManyexpertsandscholarshavebeentryingtoim provethepropertiesofconcrete (mainlyimprovetensilestrengthandtoughness)foralongtime .Fiberreinforcedconcrete,akindofcompositematerialmadeofconcreteandreinforcingmaterials ,bymetalfibers ,inorganicfi bers ,organicfibersetc ,hasbeenstudiedandappliedlargelyasaneffectivewaytostrengthenconcrete .General lyspeaking ,highmodulusfiber (suchassteelfiber)cannotablyimprovethestrengthandtoughnessofconcrete ,butitscostishigh ;whilelowmodulusfiber (suc…     

Mechanical Properties of Mo Fiber-reinforced Resin Mineral Composites with Different Mass Ratio of Resin and Hardener

Mo fibers were added to RMC with different mass ratios of resin and hardener to improve its mechanical properties. The influences of fiber surface state and hardener content on interface bonding strength and mechanical properties of RMC were studied, respectively. Furthermore, strain values of typical measuring points on samples of Mo fiber reinforced RMC(MFRRMC) under different loads were obtained by experiments and finite element analysis. The experimental results prove that scrap Mo fibers can improve interface bonding strength and mechanical properties of RMC better than new smooth Mo fibers because of the discharge pits randomly distributed on the surface of scrap fibers. With the decrease of hardener content, not only interface bonding strength between fiber and matrix, but also compression and flexural strength of MFRRMC increase firstly and then decrease. The properties are best while the mass ratio of resin and hardener reaches 4:1. It is indicated that finite element calculation data basically agree with experimental data by comparison of strain values on typical measuring points, which can provide an important intuitive reference for successive study on other mechanical properties of MFRRMC, validating the correctness of simulation method as well.     

Dynamic mechanical and thermal properties of cross-linked polystyrene/glass fiber composites

Cross-linked polystyrene/glass fiber composites were fabricated using cross-linked polystyrene (CLPS) as matrix and E-glass fiber as the reinforcement. Surfaces of E-glass fibers were modified by vinyl triethoxysilane (VTES), vinyl trimethoxysilane (VTMS) and γ-methacryloylpropyl trimethoxysilane (MPS). The treated glass fibers were analyzed by fourier transform infrared spectroscopy (FTIR). Dynamic mechanical thermal analysis (DMTA) and thermo-gravimetric analysis (TGA) were employed to investigate the effect of glass fibers surface modification on viscoelastic behavior and thermal properties. The morphology of fracture surfaces of various composites was observed by scanning electron microscopy (SEM). The results revealed that these coupling agents were connected to the surfaces of the fibers by chemical bonding. Dynamic mechanical properties as well as thermal stability of the composites were improved considerablely, but to varying degrees depending on the fiber modification. The diversities of improvement of properties were attributed to the different interfacial adhesion between CLPS matrix and the glass fibers.     

In situ construction of BiVO4(-)cellulose fibers@CDs(-)polyvinyl alcohol composites for tetracycline photocatalytic degradation

Non-biodegradable and toxic photocatalysts pose as secondary threats to the environmental security. In this work, non-toxic biocomposites were prepared using natural bamboo cellulose fibers(CF), polyvinyl alcohols(PVAs), BiVO_4, and carbon dots(CDs) from biomaterials. Thereafter, their optical properties, chemical characterizations, and photocatalytic performances were evaluated. The novel BiVO_4(-)CF@CDs(-)PVA composites were prepared via the combined implementation of in situ and impregnation methods. The optical properties revealed that the CDs and fibers increased the range and intensity of light absorption. The PVAs were used as the shield and dispersant to enhance stability because they have numerous chemical groups.In view of the various possible paths of electron migration, the enhanced photocatalytic activity of BiVO_4(-)CF@CDs(-)PVA composites for tetracycline degradation was observed under visible light illumination. The origins of the structure, morphology,and optical mechanism in the enhancement of the photocatalytic ability of BiVO_4(-)CF@CDs(-)PVA composites were discussed and demonstrated.     

Technora纤维的处理条件对其性能影响的探讨

研究了不同环境下的热处理、湿处理以及等离子处理对Technora纤维力学性能以及表面形态的影响,并初步探讨了其影响规律和机理.研究表明:在本实验测试范围内,经热处理后,Technora纤维的力学性能有一定程度的下降;湿处理时间对纤维的力学性能没有显著影响,随着湿处理温度的升高,纤维的断裂强度有所下降,而断裂伸长有小幅度的提高;等离子处理后,纤维表面有刻蚀,纤维的断裂强度和断裂伸长下降.     

PVA/EVOH纤维力学性能研究

通过凝胶纺丝获得PVA／EVOH纤维，当纺丝原液浓度为16％而PVA／EVOH配比低于93／7时即会形成凝胶。为了获得可纺性较好的原液和避免凝胶的产生，配制了不同比例的PVA／EVOH(100／0，98／2，97／3和95／5)的纺丝原液。通过凝胶纺丝获得PVA／EVOH初生纤维经过拉伸后，可获得不同机械性能的纤维。另外，在PVA中加入少量的EVOH可以提高拉伸倍数，适当的PVA／EVOH配比及适当的拉伸倍数可获得机械性能较好的纤维。     

Influences of Mo Fibers on Mechanical Properties of Resin Mineral Composites

The influences of new,scrap,and five modified Mo fibers on interface bonding strength of fiber-matrix and mechanical strength of RMC were studied.Typical specimens with different fibers and mass ratio of resin and hardener were prepared to verify the above assumptions.Theoretical analysis and experimental results prove that,compared with ordinary new Mo fibers,scrap Mo fibers can perform better in improving interface bonding strength and mechanical properties of RMC because many discharge pits randomly distribute on the surface of scrap fibers.For five modified Mo fibers,interface bonding strength and the reinforcing effect on RMC have been improved obviously.Wherein,comprehensive mechanical properties of RMC are optimal with the addition of M6 fibers which have undergone combined surface treatment including acidification,gas-phase oxidation and coupling treatment.And interface bonding strength between M6 fiber and matrix is the maximum.     

凝胶质量分数对超高分子质量聚乙烯纤维加工及结构性能的影响

采用凝胶纺丝工艺制备了具有不同质量分数的超高分子质量聚乙烯凝胶纤维,并对其进行了萃取干燥和后拉伸等处理.利用SEM、WAXD和INSTRON力学试验机研究了凝胶质量分数对未拉伸纤维的网络结构、结晶性能、最大可拉伸性能和力学性能的影响.研究结果表明,随着凝胶质量分数的提高,未拉伸纤维网络结构致密程度提高,纤维最大拉伸倍数减小,拉伸后纤维结晶度提高,结晶完善程度下降,垂直于纤维轴向的裂纹数量增加,最终导致纤维强度、模量等力学指标变差.     

熔融法纺制聚苯砜纤维的探索研究

对不同流动性的聚苯砜树脂的热性能、流变性进行研究;在不同温度及卷绕速度下模拟纺丝,对其可纺性进行探索;对初生丝进行适当牵伸和热定型等后处理,将所得纤维进行机械性能、热性能的测试.结果表明：聚苯砜具备熔融纺丝的潜力,可以制得到热稳定性好、尺寸稳定性突出,具有一定机械强度的纤维.