THE CHARACTERISTIC STRUCTURE AND ITS FORMATION MECHANISM OF GEL-SPUN UHMW-PE FIBERS

Ultra-high strength and modulus polyethylene fibers can be produced from UHMW-PE(ul-tra-high molecular weight polyethylene) by gel spinning and ultra-high drawing method.The spe-cial supermolecular structure of″shish-kebabs″ is the intrinsic course for the fiber having highperformance.In this paper,the formation mechanism of the characteristic structure of PE fibershas been investigated by means of SEM,DSC,WAXD,SAXS and TEM,The experimental resultsshow that the extended-chain structure of PE fibers is formed originally from the bridged mole-cules in amorphous region and increased gradually during further drawing porcess.The″shish-kebab″ structure is formed by the combination of extended-chalnS and originalfolded-chains.

EFFECTS OF PROCESS CONDITIONS ON THE STRUCTURE AND PROPERTIES OF GEL-SPUN PVA FIBERS

Some noticeable effects of process conditions, such as coagulation bath, solvent extraction, drying shrinkage and ultra-drawing, on the structure and properties of gel-spun PVA fibers are studied and discussed. High strength and high modulus PVA fibers with tensile strength of 11.3 cN / dtex and initial modulus of 430 cN / dtex have been obtained.

Preparation of Crack-free 3Y-TZP/Al_2O_3 Composite Ceramic Fiber by Electrolysis-sol-gel Method

Polycrystalline 3Y-TZP/Al2O3 tetragonal zirconia fiber was obtained by the pyrolysis of gel fibers using zirconium oxychloride octahydrate（ZOC） as the raw material. The spinnable zirconia sol was prepared by electrolyzing the zirco-nium oxychloride octahydrate（ZOC） solution in the presence of acetic acid and sugar（ sucrose, glucrose or fructose） , in which the molar ratios of CH3 COOH/ZOC and sugar/ZOC were 1.0-4.0 and 0.2-0.4, respectively. The pre- pared tetragonal zireonia fibers sintered at different temperatures showed smooth and crack-free surfaces with diame, ters of 5-10 μm. The addition of Al2O3 enhanced the sintering process and prevented the crystals from growing. Thermogravimetric analysis（TG）, X-ray diffraction （ XRD ）, Fourier transform infrared spectroscopy（FTIR）, and scanning electron microscope（SEM） techniques were used to characterize the prepared fibers.

Evaluation of diffusion in gel entrapment cell culture within hollow fibers

AIM: To investigate diffusion in mammalian cell culture by gel entrapment within hollow fibers.METHODS: Freshly isolated rat hepatocytes or human oral epidermoid carcinoma (KB) cells were entrapped in type Ⅰ collagen solutions and statically cultured inside microporous and ultrafiltration hollow fibers. During the culture time collagen gel contraction, cell viability and specific function were assessed. Effective diffusion coefficients of glucose in cell-matrix gels were determined by lag time analysis in a diffusion cell.R ESULTS: Significant gel contractions occurred in the collagen gels by entrapment of either viable hepatocytes or KB cells. And the gel contraction caused a significant reduction on effective diffusion coefficient of glucose. The cell viability assay of both hepatocytes and KB cells statically cultured in hollow fibers by collagen entrapment further confirmed the existence of the inhibited mass transfer by diffusion. Urea was secreted about 50% more by hepatocytes entrapped in hollow fibers with pore size of 0.1 pm than that in hollow fibers with MWCO of 100 ku.CONCLUSION: Cell-matrix gel and membrane pore size are the two factors relevant to the limited mass transfer by diffusion in such gel entrapment of mammalian cell culture.

Preparation of long alumina fibers by sol-gel method using tartaric acid

Long alumina fibers were prepared by sol-gel method.The spinning sol was obtained by mixing aluminum nitrate,tartaric acid,and polyvinylpyrrolidone with a mass ratio of 10∶3∶1.5.Thermogravimetry-differential scanning calorimetry （TG-DSC）,Fourier transform infrared （FT-IR） spectra,X-ray diffraction （XRD）,and scanning electron microscopy （SEM） were used to characterize the properties of the gel and ceramic fibers.A little of α-Al2O3 phase is observed in the alumina precursor gel fibers sintered at 1273 K.The fibers with a uniform diameter can be obtained when sintered at 1473 K,and its main phase is also indentified as α-Al2O3.

THE EFFECTS OF ULTRA DRAWING ON THE CRYSTAL STRUCTURE OF GEL SPUN POLYETHYLENE FIBERS

It is believed that gel spun polyethylene(PE)fibers have a somewhat extended chain crystalstructure,because of the disentangling of the chains which takes place in semi-dilute solutionand the ultra high draw ratio used.Ten years ago,PE shish-kebabs grown from dilute solutionwere proved to have extended chain backbone which causes the raising of its melting point.These crystals were found to have a triclinic crystal phase,This study shows a different result forgel spun ultra high drawn PE fiber.The unit cell remains orthorhombic even if the draw ratioreaches 50;as the draw ratio increases,the length in a and b axes are shortened while that in c ax-is changes quite insignificantly.When the draw ratio is over 10,two endothermic melting peakscan be seen in the DSC curves with corresponding peak temperature of 136.7-145.3℃.The lat-ter peak is attributed to the amount of extended chain crystal.

Preparation of ferromagnetic binary alloy fine fibers by organic gel-thermal reduction process

Ferromagnetic metal fibers with a high aspect ratio (length/diameter) are attractive for use as high performance electromagnetic interference shielding materials. Ferromagnetic binary alloy fine fibers of iron-nickel, iron-cobalt and cobalt-nickel were prepared by the organic gel-thermal reduction process from the raw materials of critic acid and metal salts. These alloy fibers synthesized were featured with a diameter of about 1 μm and a length as long as 1 m. The structure, thermal decomposition process and morphologies of the gel precursors and fibers derived from thermal reduction of the gel precursors were characterized by FTIR, XRD, TG/DSC and SEM. The gel spinnability largely depends on the molecular structure of metal- carboxylates formed during the gel formation. The gel consisting of linear-type structural molecules shows good spinnability.

Preparation and Characterization of M-Type Barium Ferrite Fibers via Aqueous Sol-Gel Process

BaFe12O19 fibers was prepared via an aqueous sol-gel process using Fe(OH)(HCOO)2 synthesized in laboratory and Ba(CH3COO)2 as the original materials and citrate as the chelate. The rheological behaviour of spinnable sol was characterized on rheometer, and the development of gel fibers to barium ferrite fibers was studied by IR, TG and XRD. Morphology observation of the fibers was given on SEM, and the diameter of the obtained fibers was between 5 and 10 μm corresponding to different additives. The additives affected the surface tension of the precursor sol which had close relation to the microstructure of fibers. Sucrose and hydroxyethylic cellulose could improve the surface tension while diethanolamine and hexadecylamine reduce that of the precursor sol. And using diethanolamine or hexadecylamine as an additive, well-structured BaFe12O19 fibers could be obtained.

Metal Fe,Ni and Fe-Ni Fine Fibers Derived from the Organic Gel-Thermal Reduction Process

The organic gel-thermal reduction process was successfully used for the preparation of magnetic metal Ni, Fe, Fe-Ni fine fibers from raw materials of citric acid or lactic acid and metal salts. Ni, Fe and Fe-Ni fine fibers synthesized were featured with diameters of around 1 μm and lengths of as long as 2 m for Ni fibers, 0.5 m for iron fibers, 1 m for Fe-Ni fibers. The structure, thermal decomposition process and morphologies of the gel precursors and fibers derived from thermal reduction of these gel precursors were characterized by FTIR, XRD,TG/DSC and SEM, respectively. The gel spinnability largely depends on molecular structures of metal-carboxylate complexes formed in the gel. It is reasoned that these gels consist of linear-type structural molecules [（C6H6O7）Ni]n or [（C6H5O7）2Ni3] for the nickel citrate gel, [（C3H5O3）3Fe] for the ferric lactate gel, [（C6H5O7）5（NiFe）3] for the iron-nickel citrate gel respectively and the gels obtain showed a good spinning performance.

Preparation of ferromagnetic metal fine fibers by organic gel-thermal reduction process

The organic gel-thermal reduction process was used for the preparation of ferromagnetic metal Ni, Co and Fe fine fibers from the raw materials of citric acid, lactic acid and metal salts. The structure, thermal decomposition process and morphologies of the gel precursors and fibers derived from thermal reduction of these gel precursors were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermo-gravimetric/differential scanning calorimetry and scanning electron microscopy. The results show that spinnability of gel largely depends on molecular structure of metal-carboxylate complex that is a linear-type structure formed in the gel. As a result, the gels exhibit a good spinnability. Metal Ni, Co and Fe fine fibers are featured with diameters of around 1 μm and a high aspect ratio up to 1×106.

Structures and magnetic properties of nanocomposite CoFe_2O_4-BaTiO_3 fibers by organic gel-thermal decomposition process

The nanocomposite xCoFe2O4-(1-x)BaTiO3(x=0.2,0.3,0.4,0.5,molar fraction) fibers with fine diameters and high aspect ratios(length to diameter ratios) were prepared by the organic gel-thermal decomposition process from citric acid and metal salts.The structures and morphologies of gel precursors and fibers derived from thermal decomposition of the gel precursors were characterized by Fourier transform infrared spectroscopy,X-ray diffractometry and scanning electron microscopy.The magnetic properties of the nanocomposite fibers were measured by vibrating sample magnetometer.The nanocomposite fibers consisting of ferrite(CoFe2O4) and perovskite(BaTiO3) are formed at the calcination temperature of 900 ℃ for 2 h.The average grain sizes of CoFe2O4 and BaTiO3 in the nanocomposite fibers increase from 25 to 65 nm with the calcination temperature from 900 to 1 180 ℃.The single fiber constructed from these nanograins of CoFe2O4 and BaTiO3 has a necklace-like morphology.The saturation magnetization of the nanocomposite 0.4CoFe2O4-0.6BaTiO3 fibers increases with the increase of CoFe2O4 grain size,while the coercivity reaches a maximum value when the average grain size of CoFe2O4 is around the critical single-domain size of 45 nm obtained at 1 000 ℃.The saturation magnetization and remanence of the nanocomposite xCoFe2O4-(1-x)BaTiO3(x=0.2,0.3,0.4,0.5) fibers almost exhibit a linear relationship with the molar fraction of CoFe2O4 in the nanocomposites.

Formation of Ultrafine Apatite Fibers by Sol-gel/Electrospinning

Ultrafine apatite fibers were prepared by electrospinning of sol-gel precursor/poly（ vinyl pyrrolidone） （PVP） solutions followed by subsequent calcination. The as-electrospun and calcinated fibers were observed under a scanning electron microscope and an optical polarizing microscope. Results show that the morphology and the diameter of as-electrospun fibers strongly depend on the viscosity and the surface tension of sol-gel precursor/PVP solutions. After calcination, the smooth as-electrospun fibers shrink and the fiber diameter decreases because of the removal of the polymer. The chemical evolution upon the transformation of the precursor from a gel to the final apatite fibers was investigated by thermogravimetric-differenfial thermal analysis, X-ray diffraction, and Fourier transform infrared spectroscopy. It is thus suggested that the crystalline structure of the calcined fibers is largely influenced by the calcination temperature. After being calcined at 600 ℃, the apatite fibers with a diameter of about 280 nm containing β-tricalcium phosphate were obtained.

A Chemiluminescence Optical Fiber Glucose Biosensor Based on Co-immobilizing Glucose Oxidase and Horseradish Peroxidase in a Sol-gel Film

An optical fiber bienzyme sensor based on the luminol chemiluminescent reaction was developed and demonstrated to be sensitive to glucose. Glucose oxidase(GOD) and horseradish peroxidase(HRP) were co-immobilized by microencapsulation in a sol-gel film derived from tetraethyl orthosilicate(TEOS). The calibration plots for glucose were established by the optical fiber glucose sensor fabricated by attaching the bienzyme silica gel onto the glass window of the fiber bundle. The linear range was 0 2-2 mmol/L and the detection limit was approximately 0 12 mmol/L. The relative standard deviation was 5.3% ( n =6). The proposed biosensor was applied to glucose assay in ofloxacin injection successfully.

Preparation and Properties of Modified Sol-Gel Sensing Membrane for Fiber Optic Oxygen Sensor

Modified sensing membranes based on fluorescence quenching were prepared by the sol-gel method,using formamide as the drying control chemical additive,tetraethoxysilane as the main material,Ru(phen) 3Cl 2 as the indicator.The membrane with the optimum thickness of 20-50μm is uniform and crack-free,in which the indicator has a very small leaking rate.The membrane is immersed in water for 50h,the membrane sensing parameter M decreases by less than 5%.The fiber optic oxygen sensor with the sensing membrane has a detection limit of 5×10 -6M(ppm),a response time of less than 30s,excellent reproducibility and stability.

Sol-Gel法制备新型多晶钇-铝石榴石纤维

采用溶胶－凝胶法,以硝酸钇、铝片和水为原料,在酸的催化作用下经过一系列复杂的水解、缩聚反应制备出一种钇氧铝溶胶,向该溶胶中加入适当的水溶性高分子聚合物,经浓缩、纺丝及９００℃高温后处理可得到直径均匀的新型多晶钇－铝石榴石纤维．

TiO_2/ACF复合材料的Sol-Gel法制备及其对苯的去除性能

以钛酸四丁酯为钛源,采用改进溶胶-凝胶法合成TiO2前驱体;采用浸渍-提拉法将TiO2前驱体负载在活性炭纤维(ACF)表面制得TiO2/ACF复合材料.采用X射线衍射(XRD)、扫描电镜(SEM)、低温液氮吸附等对TiO2/ACF复合材料晶相结构、表面结构等进行了表征.在静态自制光催化反应装置中紫外光照射条件下,以高浓度(2926.5mg/m3)气态苯考察TiO2/ACF对气相有机污染物的去除性能,以气相色谱-质谱(GC-MS)检测中间产物种类与分布.结果表明:TiO2于ACF表面形成完整薄层,随负载次数增加,TiO2/ACF比表面积下降;TiO2薄层变厚、开裂,甚至脱落.400℃煅烧时TiO2已完全转变为锐钛矿相,随煅烧温度升高,锐钛矿型TiO2晶粒尺寸变大,至700℃时开始有金红石相生成.负载2次,400℃煅烧TiO2/ACF复合材料TiO2/ACF-400-2表现出最高活性.TiO2/ACF对苯的去除过程中未检测到毒性较大的酚、醌类中间产物.

玄武岩纤维-Ag^(+)/TiO_(2)光催化剂的制备及其光催化性能研究

以钛酸四丁酯为钛源、硝酸银为银源、玄武岩纤维为载体,采用溶胶-凝胶法成功制备了玄武岩纤维-Ag^(+)/TiO_(2)光催化剂。XRD测试结果表明,TiO_(2)以锐钛矿型成功负载到玄武岩纤维表面。催化剂性能评价表明,在钛酸四丁酯加入量为5 mL、硝酸银加入量为0.01 g的条件下制备的催化剂加入量为90 mg,反应时间为90min的反应条件下,催化剂对罗丹明B废水可以达到最高99%的降解率,并且催化剂在经过4次重复使用后仍可达84%的降解率。研究结果表明,玄武岩纤维-Ag^(+)/TiO_(2)光催化剂可以作为一种潜在的低成本绿色光催化剂。

陶瓷纤维制备技术的研究进展

综述了石英纤维、碳化硅纤维、氮化硅纤维、氮化硼纤维、氧化铝纤维、莫来石纤维、硅酸铝纤维等不同种类陶瓷纤维的制备技术研究现状和技术难点。石英纤维主要采用溶胶-凝胶法制备,需要纤维表面引入氮化硼涂层改善其界面析晶行为;碳化硅纤维主要采用前驱体转化法和活性炭转化法制备,需进行表面涂层增强其性能;氮化硅纤维主要采用溶胶-凝胶法和碳热还原氮化法制备;氮化硼纤维主要采用无机转化法和有机前驱体法制备;溶胶-凝胶法是氧化铝、莫来石和硅酸铝纤维的主要制备方法。未来国内陶瓷纤维研究应进一步提高纤维性能、开发新品种、提高制备技术水平、加强应用研究和拓展应用领域。

氧化铝连续纤维用前驱体溶胶的制备和可纺性研究

以铝(Al)粉和六水合氯化铝(AlCl_(3)·6H_(2)O)为Al源、中性硅溶胶(SiO_(2))为Si源,通过溶胶-凝胶法制备Al溶胶,再经浓缩、老化制得可纺性前驱体Al溶胶,研究物料配比、反应时间、浓缩温度及时间对制备Al溶胶的影响,以及浓缩、老化和稀盐酸(HCl)加入量对前驱体Al溶胶可纺性的影响,并测试了可纺性前驱体Al溶胶的流变性能。结果表明:在80℃水浴、电动搅拌转速为1000 r/min的条件下合成固含量为20%的Al溶胶,较佳的物料配比为Al粉/AlCl_(3)·6H_(2)O质量比11,较佳的反应时间为3 h;将固含量为20%、动力黏度(μ)为20 mPa·s的Al溶胶在80℃下浓缩5.0 h,再在28℃下老化40 h,可得到μ约60000 mPa·s且具有良好可纺性的前驱体Al溶胶;在可纺性前驱体Al溶胶的制备中添加稀HCl可有效抑制溶胶凝胶化,25 g Al溶胶中加入稀HCl 1.5 g较为合适;可纺性前驱体Al溶胶表现为切力变稀的假塑性流体,在温度为25~35℃、剪切速率为0~1000 s^(-1)时,溶胶的μ为50000~70000 mPa·s,具有良好的可纺性。

溶胶-凝胶(Sol-Gel)技术在氧化物纤维中的应用

溶胶-凝胶(Sol-Gel)技术是一种很有发展前途的固体材料制备方法,已引起众多领域重视.简述了溶胶-凝胶技术的发展历史,总结了溶胶-凝胶技术的分类、原料以及无机盐和金属醇盐的水解反应机理,并概括了该技术的优点及存在的问题,着重介绍了溶胶-凝胶技术在耐烧蚀陶瓷纤维、高温超导纤维、铁电压电纤维、磁性纤维等氧化物纤维制备方面的应用现状,并对溶胶-凝胶技术的未来发展进行了展望.