Improving Mechanical Properties of Carbon/Epoxy Composite by Incorporating Functionalized Electrospun Polyacrylonitrile Nanofibers

Electrospun functionalized polyacrylonitrile grafted glycidyl methacrylate (PAN‐g‐GMA) nanofibers are incorporated between the plies of a conventional carbon fiber/epoxy composite to improve the composite's mechanical performance. Glycidyl methacrylate (GMA) is successfully grafted onto polyacrylonitrile (PAN) polymer powder via a free radical mechanism. Characterization of the electrospun PAN and PAN‐g‐GMA nanofibers indicates that the grafting of GMA does not significantly alter the tensile properties of the PAN nanofibers but results in an increase in the diameter of nanofibers. Statistical analysis of the mechanical characterization studies on PAN‐carbon/epoxy hybrid composites conclusively shows that the composite reinforced with functionalized PAN nanofibers has greater mechanical properties than that of both the neat PAN nanofiber enriched hybrid composite and control composite (without nanofibers). The improved performance is attributed to the grafted glycidyl groups on PAN, leading to stronger interactions between the nanofibers and the epoxy matrix. PAN‐g‐GMA nanofiber reinforced composite outperforms their neat PAN counterparts in tensile strength, short beam shear strength, flexural strength, and Izod impact energy absorption by 8%, 9%, 6%, and 8%, respectively. Compared to the control composite, the improvements resulting from the PAN‐g‐GMA nanofiber incorporation are even more pronounced at 28%, 41%, 32%, and 21% in the corresponding tests, respectively.

     

静电纺再生丝素纳米纤维的结构与性能

静电纺丝获得的丝素纳米级纤维可作为细胞培养支架,用于纺丝工艺及后处理能改变丝素微细结构,影响其水溶性和力学性能。本文采用XRD、FTIR、固态13CNMR和DSC研究了不同工艺下丝素纳米纤维及经甲醇处理后的微细结构,比较了不同微细结构下的水溶性和力学性能。结果表明,电纺丝的微细结构受纺丝工艺影响,高电压、纺丝液中丝素质量分数大时纺得的电纺丝结晶度高,经甲醇处理后,β化程度提高;w(丝素)=11%、15%时制备的电纺丝断裂强度分别为8.5、11.9 cN/mm;w(丝素)=11%、19%,水溶性由51.2%下降到43.3%;w(丝素)=19%、电压32 kV制得的电纺丝甲醇处理前后水溶性从43.3%下降到6.6%,说明丝素纳米纤维结晶度提高,强度增加、水溶性下降,满足了细胞支架的要求。     

聚氨酯弹性体力学性能的研究进展

从聚氨酯弹性体的原料、合成方法、合成工艺、原料配比等方面介绍了聚氨酯弹性体力学性能的研究进展。     

聚醚型聚氨酯弹性体力学性能的研究

研究了以不同相对分子质量的聚醚多元醇、二异氰酸酯和扩链剂为原料制备PU弹性体的力学性能。结果表明：PU弹性体的力学性能随-NCO基含量的增加而提高;提高聚醚的相对分子质量,PU的定伸强度、拉伸强度和撕裂强度下降,断裂伸长率提高;后熟化时间及R值对PU弹性体性能有显著的影响;聚醚相对分子质量相同时,MDI—PU的力学性能优于TDI—PU。     

电纺纳米纤维的研究及应用

静电纺丝(电纺)技术是一种制备直径为数10 nm到数100nm纳米纤维的有效方法.本文介绍了静电纺丝中原料聚合物的类型、纺丝条件和纺丝技术等方面的研究成果,电纺纳米纤维和产品的特性及其应用.     

静电纺纳米纤维束的制备与表征

利用静电纺丝法,采用尖角圆盘实现了具有定向排列纤维束的收集,应用SEM、XRD、DSC等方法对纤维束进行了理化性能表征。将多锭经拉伸、加捻、热定型等处理后的纤维束编织成线,研究了纤维束的锭数对编织线力学性能的影响。结果表明:圆盘的收集时间对纤维束力学性能影响并不明显,编织线相对单根纤维束的力学性能大幅提高,8锭不加芯的编织结构表现的力学性能最好。     

Tunable Mechanical and Electrical Properties of Coaxial Electrospun Composite Nanofibers of P(VDF-TrFE) and P(VDF-TrFE-CTFE)

The coaxial core/shell composite electrospun nanofibers consisting of relaxor ferroelectric P(VDF-TrFE-CTFE) and ferroelectric P(VDF-TrFE) polymers are successfully tailored towards superior structural, mechanical, and electrical properties over the individual polymers. The core/shell-TrFE/CTFE membrane discloses a more prominent mechanical anisotropy between the revolving direction (RD) and cross direction (CD) associated with a higher tensile modulus of 26.9 MPa and good strength-ductility balance, beneficial from a better degree of nanofiber alignment, the increased density, and C-F bonding. The interfacial coupling between the terpolymer P(VDF-TrFE-CTFE) and copolymer P(VDF-TrFE) is responsible for comparable full-frequency dielectric responses between the core/shell-TrFE/CTFE and pristine terpolymer. Moreover, an impressive piezoelectric coefficient up to 50.5 pm/V is achieved in the core/shell-TrFE/CTFE composite structure. Our findings corroborate the promising approach of coaxial electrospinning in efficiently tuning mechanical and electrical performances of the electrospun core/shell composite nanofiber membranes-based electroactive polymers (EAPs) actuators as artificial muscle implants.     

静电纺丝聚合物纳米纤维研究进展

将静电纺丝技术应用到高分子材料研究中,可以制备聚合物纳米纤维,在众多领域有广阔的应用前景。从静电纺丝聚合物纳米纤维原理、有序性、应用的角度,简述其研究进展,并指出一些仍待解决的问题,同时对电纺聚合物纳米纤维未来发展进行了展望。     

Effect of Drying Temperature on Mechanical Properties of Dried Corn

The effect of drying air temperature on the mechanical properties of corn kernels was investigated. Corn was dried at drying temperatures of 40, 50, 60 and 70°C and air flow rate of 1.8 kg/min in a convective dryer. The kernels were then loaded uniaxially in a material testing machine at a loading rate of 3 mm/min, up to the rupture point. An increase in drying temperature from 40 to 70°C increased kernel deformation at the rupture point by an average of 12%. Moreover, values of force, stress, toughness, and modulus of elasticity of corn decreased on average by 21, 26, 36, and 38%, respectively.     

温度对聚氨酯固化材料力学性能的影响

为探究不同温度下聚氨酯固化道床的适应性,研究了温度对聚氨酯固化材料拉伸性能、黏结性能和动态力学性能的影响。结果表明,在-60~70 ℃内,随着环境温度的降低,聚氨酯固化材料的拉伸模量、拉伸强度和黏结强度均逐渐增加,变形性能先增加后降低,且固化材料的黏结强度破坏均为内聚破坏;在-50 ℃左右,聚氨酯固化材料发生了玻璃化转变,当温度接近玻璃化转变温度时,固化材料的损耗因子较高,变形性能较好;随着聚醚多元醇相对分子质量的增加,聚氨酯固化材料的玻璃化转变温度降低,低温下聚氨酯固化材料的拉伸性能变化率越小;聚氨酯固化材料的性能能够满足不同温度下的使用需求,当在低温环境下服役的聚氨酯应优先选用相对分子质量较高的聚醚多元醇。     

烧结温度对氧化锆陶瓷相组成及力学性能的影响

本文以经900 ℃、1000 ℃和1100 ℃三种不同温度煅烧处理的3mol%的氧化钇稳定氧化锆粉体为原料,在1450 ℃、1500 ℃和1550 ℃三个温度下烧结致密块体陶瓷.并测定了烧结体的相组成、密度、硬度和断裂韧性等性能.结果表明:经高温煅烧的粉体的烧结致密度随烧结温度的上升而提高;材料的硬度随密度的增加而相应提高;烧结氧化锆的断裂韧性指标主要与材料中亚稳四方相含量有关.     

Production of Continuous Electrospun Mats with Improved Mechanical Properties

A new concept of top‐down electrospinning is described. A dedicated apparatus was designed including the adaptation of a movable needle system in combination with a thin conveyor belt made of an insulation material on the top of the grounded collector plate. The new design, termed ‘needle printing’, permits to electrospin mats with increased size, homogeneous and controllable thicknesses. Due to the increase of bending instability and to the ‘needle printing’, the produced fibres are more regular in shape, longer and are deposited more stretched. In contrast to traditional electrospinning, the fibre population is the same in all regions of the mats imparting the same morphological and mechanical properties to each point of the produced structures.

     

重组蛛丝蛋白/聚氨酯共混电纺丝膜的力学性能

重组蛛丝蛋白(recombinant spider silk protein)是一种新颖的材料,有广泛的应用前景,静电纺丝技术是目前制备纳米纤维最重要的基本方法.文章中,以六氟异丙醇(HFIP)作为蛛丝蛋白/聚氨酯的共溶剂,采用电纺丝工艺制备纳米纤维以供应用,扫描电镜照片可以看到纤维表面均匀,没有显著的相分离.将所得纤维膜在乙醇/水溶液中后处理后,纤维膜的力学性能、拉伸强度、断裂伸长率得到很大改善.     

Fabrication and Thermal Dissipation Properties of Carbon Nanofibers Derived from Electrospun Poly(Amic Acid) Carboxylate Salt Nanofibers

Polyimides (PIs) possess excellent mechanical properties, thermal stability, and chemical resistance and can be converted to carbon materials by thermal carbonization. The preparation of carbon nanomaterials by carbonizing PI‐based nanomaterials, however, has been less studied. In this work, the fabrication of PI nanofibers is investigated using electrospinning and their transformation to carbon nanofibers. Poly(amic acid) carboxylate salts (PAASs) solutions are first electrospun to form PAAS nanofibers. After the imidization and carbonization processes, PI and carbon nanofibers can then be obtained, respectively. The Raman spectra reveal that the carbon nanofibers are partially graphitized by the carbonization process. The diameters of the PI nanofibers are observed to be smaller than those of the PAAS nanofibers because of the formation of the more densely packed structures after the imidization processes; the diameters of the carbon nanofibers remain similar to those of the PI nanofibers after the carbonization process. The thermal dissipation behaviors of the PI and carbon nanofibers are also examined. The infrared images indicate that the transfer rates of thermal energy for the carbon nanofibers are higher than those for the PI nanofibers, due to the better thermal conductivity of carbon caused by the covalent sp² bonding between carbon atoms.     

Growth of Nanograins in Electrospun ZnO Nanofibers

ZnO nanofibers were synthesized using an electrospinning method with polyvinyl alcohol and zinc acetate as precursor materials. The effects of the processing parameters on the microstructure of the synthesized ZnO nanofibers were investigated. X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy showed that the ZnO nanofibers were distributed uniformly over the Si substrates and had a polycrystalline nature. Individual nanofibers consisted of nanograins. Interestingly, the nanograins coalesced and grew under higher calcination temperatures and longer calcination times. The activation energy for grain-growth was estimated to be 13.126 kJ/mol, and the dominant growth mechanism was most likely to be related to lattice diffusion in pore control mode.     

养护温度对UHPC水化及力学性能影响研究

热养护能够提高超高性能混凝土(UHPC)的早期力学性能,促使UHPC水化,但对UHPC长期性能的发展尚未有系统深入的研究.通过力学性能测试、SEM和XRD研究了五种养护温度(20℃标养、90℃蒸汽养护、120℃干热养护、200℃干热养护和250℃干热养护)对UHPC长期力学性能发展以及水化的影响.结果表明,热养护能够促...     

GAP型PU/PMMA聚合物互穿网络的力学性能研究

利用互穿聚合物网络技术 (IPN)对GAP粘合剂进行了力学性能改性 ,研究了组分比、引发剂用量、催化剂用量、固化参数、交联剂用量对以GAP为基体材料的PU/PMMA型IPN力学性能的影响 ;同时用动态力学谱 (DMA)分析了不同组分比下IPN的相容性     

接枝聚醚对聚氨酯泡沫塑料性能的影响

采用加入接枝聚醚的方法来改善聚氨酯泡沫塑料的性能,研究了接枝聚醚用量对泡沫硬度的影响,并对比了与其他填料对聚氨酯泡沫塑料性能的影响,结果表明,接枝聚醚添加量为15%～25%(质量分数)时,可以大大提高聚氨酯泡沫塑料的压缩强度及拉伸强度,并能降低成本,提高生产的安全性.     

芳纶纳米纤维对溶聚丁苯橡胶性能的影响

制备芳纶纳米纤维(ANFs)预分散体,研究ANFs用量对溶聚丁苯橡胶(SSBR)胶料性能的影响。结果表明：随着ANFs用量的增大,SSBR混炼胶的t₁₀和t₉₀无明显变化,F_L、储能模量和损耗模量增大,Payne效应增强;SSBR硫化胶的邵尔A型硬度、100%定伸应力和撕裂强度增大,拉伸强度先减小后增大,损耗因子(tanδ)最大值减小。ANFs用量为4份的SSBR硫化胶0℃时的tanδ最大,抗湿滑性能最好。     

Structuring and Molding of Electrospun Nanofibers: Effect of Electrical and Topographical Local Properties of Micro‐Patterned Collectors

The controlled deposition of electrospun nanofibers at the micro‐scale is studied. Several collectors with microscopic patterns are prepared using photolithography. Nanofiber deposition is influenced by the geometry, the size, and the distance between micro‐patterns. Within certain conditions, membranes with multiple “micro spider‐webs” or perpendicularly interconnected microgrids are obtained. Dielectric micro‐holes having a conductive bottom can be filled by the nanofiber. This kind of micro‐molding is rationalized using simulations that show the influence of the collector relative permittivity on the electric field at the pattern vicinity. “Micro‐woven” membranes of PCL with good mechanical properties can be produced, allowing their use for biomedical applications in tissue engineering.