DMSO湿法PAN纤维截面形状形成条件的研究

对DMSO(二甲基亚砜)湿法制备PAN(聚丙烯腈)纤维的截面形状的形成因素进行了研究。随着凝固浴浓度的增大和温度的升高,纤维截面形状由椭圆形或肾形逐渐变为圆形。当凝固浴浓度在一定范围(55％-70％)时,不同凝固浴浓度对应一个凝固浴温度下限值,在该下限温度以上都可得到圆形截面纤维,且凝固浴浓度越低,此下限温度越高。纤维离开凝固浴后,截面形状基本形成并固定,水洗、拉伸、喷丝速度和干燥对纤维截面形状的形成影响都很小。     

湿纺凝固条件对PAN初生纤维形态结构的影响

分析了凝固浴温度、浓度、表观负拉伸等凝固条件对聚丙烯睛初生纤维形态结构的影响规律及作用机理,得出最佳的凝固工艺参数。结果表明:在其他凝固参数不变时,凝固浴温度、浓度及表观负拉伸均存在各自的临界值,低于或超过此临界值,初生纤维及原丝的性能均下降;采用凝固浴温度60℃、凝固浴质量分数为65％的最佳凝固工艺参数,可获得截面圆形且结构致密的初生纤维,并制得力学性能优异的原丝。     

干湿法PAN纤维截面成形条件的研究

对干湿法纺丝中PAN纤维的截面形状影响因素进行了研究。研究发现,凝固浴浓度和温度是影响纤维截面的主要因素,随着凝固浴浓度的增大和温度的升高,纤维截面逐渐由扁平形变为圆形,纤维截面的异形度逐渐减小;干湿法比湿法纺丝更有利于得到圆形截面的纤维;随着空气层高度的增大,纤维截面的异形度减小,但当空气层高度超过10mm时,纤维截面形状不再变化;在一定条件下,喷丝头拉伸比对纤维的截面形状有一定影响,后拉伸过程和干燥对纤维截而形状基本上没影响。     

凝固浴条件对对位芳纶成形的影响

将聚对苯二酰对苯二胺(PPTA)浆液浸入凝固浴来模拟纺丝过程中纤维的凝固过程。通过偏光显微镜分析了不同凝固浴条件下非溶剂在PPTA浆液中的扩散速率;用XRD分析了不同凝固浴条件下PPTA膜的结晶情况;用SEM分析了不同凝固浴条件下PPTA膜的表面形貌。结果表明,随着凝固浴温度和硫酸质量分数的升高,PPTA膜的致密程度不断下降,且由于边缘和中心区域相分离模式的不同其致密程度也不同。验证了PPTA纤维在凝固浴中形成皮芯层结构的结论。     

聚砜酰胺原液凝固性能研究

研究了凝固浴浓度、原液温度、聚合物相对分子质量、凝固浴中的盐分、共聚物分布序列和第三单体物质的量对聚砜酰胺原液的凝固值和临界浓度的影响。结果表明：凝固浴浓度越高,凝固值越高,而临界浓度基本不变;随着原液温度的提高,凝固值略有提高,临界浓度略有下降;凝固浴中盐分含量越大,凝固值越高,临界浓度越低;聚合物相对分子质量越大,凝固值越低,临界浓度越高;共聚物大分子链越规整,第三单体含量越少,则凝固值越低,临界浓度越高。     

凝固浴组成和温度对PVDF疏水微孔膜结构与性能的影响

利用非溶剂相转化法(NIPS),以聚偏氟乙烯(PVDF)/磷酸三乙酯(TEP)-N,N-二甲基乙酰胺(DMAc)为铸膜液体系,乙醇水溶液为凝固浴制备高性能的PVDF疏水微孔膜。考察了凝固浴中乙醇(EtOH)含量及凝固浴温度对PVDF成膜分相速率、膜结构和膜疏水性的影响。实验结果表明,在20℃的凝固浴温度下,凝固浴中乙醇含量的升高减慢了铸膜液体系的分相速率,提高了PVDF膜的孔隙率;在凝固浴中添加60%(wt)的乙醇,可形成表面荷叶状结构和截面对称的海绵状结构,膜表面的接触角为130.3°,呈很强的疏水性,并具有较优的膜强度。     

超声波对聚砜酰胺结晶性能影响研究

首先通过将制备好的聚砜酰胺样品超声处理不同的时间,在这个基础上通过偏光显微镜观察晶体形貌发现超声波可以明显提高聚砜酰胺溶液的成核率,并出现明显的晶体细化现象。同时通过作图发现聚砜酰胺的球晶尺寸与时间呈线性关系,并且超声处理能提高晶体的生长速率。最后通过对聚砜酰胺薄膜进行XRO、IR和力学性能测试发现超声处理能增加聚砜酰胺的结晶度同时增强了聚砜酰胺薄膜的力学性能。     

凝固浴工艺对聚对苯二甲酰对苯二胺膜性能的影响

将聚对苯二甲酰对苯二胺(PPTA)树脂和浓硫酸进行高温溶解,经过脱泡处理,得到PPTA-H_2SO_4溶液,在凝固浴中凝固制备PPTA膜,研究了凝固浴种类及工艺对PPTA膜的结构与性能的影响。结果表明:在质量分数为7%的H_2SO_4、质量分数为4%的Na OH、H_2O 3种凝固浴中,H_2SO_4凝固浴适合PPTA树脂成膜;PPTA膜最佳凝固浴工艺条件为凝固浴H_2SO_4质量分数7%,凝固浴温度3℃,凝固时间3.0 min,在此条件下PPTA膜具有均匀致密的结构,出现明显的彩色条纹状的液晶现象,热稳定性能最好,其拉伸强度约68MPa,900℃时质量保持率达59.81%。     

一步法聚酰亚胺纤维的制备及其性能研究

利用实验室自制的聚酰亚胺(P)I溶液,通过干湿法纺丝制得PI初生纤维。在以水和N-甲基吡咯烷酮(NMP)混合溶液(体积比8∶2)作为凝固浴,凝固浴温度为5～15℃的条件下,所得初生纤维结构均匀密实,纤维截面呈圆形或腰圆形。在对初生纤维进行热处理时,随着热处理温度升高和时间增加,PI纤维的力学性能增强。当热处理温度为300～320℃、时间为30 min时,PI纤维的力学性能最优,其断裂强度和初始模量达到2.474 cN/dtex和50.066 cN/dtex;当热处理温度高于320℃,时间超过1 h,纤维力学性能又缓慢下降。纤维的热稳定性较好,在500℃左右仍具有较好的热稳定性。     

高性能聚砜中空纤维纳滤膜基膜的研制

采用干-湿法工艺制备聚砜基膜,研究了聚砜铸膜液中聚砜含量、添加剂种类、溶剂组成及含量和凝固浴温度对膜性能的影响。研究结果表明,铸膜液中聚砜含量和添加剂含量对膜性能影响较大;使用混合溶剂可有效改善膜的孔结构和提高聚砜基膜的性能;控制凝胶浴温度可以得到较高性能的基膜。通过选择最佳铸膜液组成及工艺条件,可以制备较高性能的基膜。     

Effect of nonsolvent coagulant on the morphology and radionuclide detection efficiency of CAYS‐impregnated polysulfone films

Single‐ or double‐layered porous films consisting of polysulfone (PSF) and cerium‐activated yttrium silicate (CAYS) were prepared through the phase inversion of polymeric solutions. For a single‐layered structure, a casting solution including n‐methylpyrrolidone (NMP) as a solvent was cast on a glass substrate and solidified by immersing into a nonsolvent bath. In a double‐layered structure, the bottom layer is a dense PSF film, prepared by vacuum coagulation of a methylene chloride/PSF solution. The top layer was formulated by coagulating the NMP solution, cast over the dense film, in a nonsolvent bath. The morphology and the radionuclide detection efficiency of the prepared films were significantly affected by the nonsolvent coagulants used. The water‐coagulated, double‐layered film showed a relatively clear‐cut interface between the two layers, indicating the rapid coagulation of the second layer. On the contrary, the film coagulated by isopropanol retained well‐developed sponge structures highly intertwined in the interface, associated with the delayed precipitation of the second layer. When spotted on the prepared films, radionuclides stayed mainly on the top surface of the isopropanol‐coagulated film, but went deep into the substructure of the film coagulated with water. In comparison with the mono‐layered films, the double‐layered ones improved the detection capacity of the spotted radionuclides, owing to the dense support layer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1903–1909, 2006     

间位芳纶溶解及凝固性能研究

以二甲基乙酰胺(DMAc)、二甲基甲酰胺(DMF)、二甲基亚砜(DMSO)、1-甲基-2-吡咯烷酮(NMP)为溶剂,分别加入LiCl和CaCl_2制备溶解体系,研究了间位芳纶在这几种溶解体系中的溶解性能。再以H_2O-DMAc、H_2O-DMF、H_2O-DMSO、H_2O-NMP为凝固浴,研究了溶剂种类、芳纶溶液质量分数、离子浓度等对间位芳纶溶液的凝固性能的影响。结果显示:Li Cl-DMAc溶解体系具有更强的溶解性能;凝固值随凝固浴中凝固剂H_2O的含量的增加不断减小,而临界浓度几乎没有变化;随着凝固浴温度的增加,凝固值增大,临界浓度减小;凝固值随凝固浴中离子浓度的升高而增大,但临界质量分数则不断降低。另外,间位芳纶溶液的扩散系数随着凝固浴中H_2O的含量的减少不断减小,随着芳纶浓度的增加不断减小。     

混凝试验中效果评判的新方法

通过对两类不同的水源进行混凝试验,发现用混凝后水的浊度来评判混凝效果的方法,对一般水质的水源是有效的,但对某些特殊水质的水源如低温低浊水,或对混凝处理后水质要求较高的场合如反渗透进水,就无法准确找出最佳的混凝剂和混凝条件.因此,提出了用测量矾花(絮凝体)大小及生长速度和泥渣虚度的指标来评判混凝试验效果的新方法,与常用的以混凝后水的浊度来评判混凝效果相比,用此方法更能准确地评判混凝试验效果的优劣.     

含杂环芳香族聚酰胺浆液凝固热力学条件研究

采用浊点滴定法对含杂环的均缩聚芳香族聚酰胺(简称缩聚物)浆液凝固过程的热力学条件进行了研究。结果表明:采用浊点滴定法研究重现性好,在滴定温度30℃,滴定质量分数为0.1%～0.5%的缩聚物N,N-二甲基乙酰胺(DMAc)溶液,滴定剂为质量分数30%的DMAc水溶液,滴定相对平均偏差小于3%;和其他非溶剂相比,水的凝固值(25 mL滴定液)最小,为16.35 mL,是一种强的凝固剂,同时聚合物在DMAc中溶解性比在N-甲基吡咯烷酮(NMP)中好;随着滴定剂浓度的增大,凝固值增大,临界凝固浓度基本不变;随着滴定温度的升高和滴定液中无机盐含量的增大,凝固值降低,临界凝固浓度增大,缩聚溶解性变好。     

Processing of polymer latex emulsion: Batch coagulation

A small-scale batch experiment has been developed to establish processing conditions for latex coagulation in an extruder environment—characterized by the prevailing flow field, temperature, and pressure. Our experiments have shown that the most effective processing means to control the particle size distribution and also the particle morphology is the coagulation temperature. The changes in hydrodynamics, introduced by variations in the channel depth and rotor speed, affect the average particle size to a lesser degree. The morphology of the coagulated particles and their size distribution have been found to play an important role in the latex dewatering process. By coagulating well above the glass transition temperature(s) of the polymer, an order of magnitude drop in the specific surface area of the coagulated particles has been observed.     

Direct coagulation casting of yttria-stabilized zirconia using magnesium citrate and glycerol diacetate

Direct coagulation casting via controlled release of high valance counter ions (DCC-HVCI) has been reported in recent years. In this paper, concentrated yttria-stabilized zirconia (YSZ) suspensions were coagulated using DCC-HVCI method with magnesium citrate as coagulating agent assisted by pH shift in the presence of glycerol diacetate. The effect of ammonium polyacrylate (PAA-NH₄) on the dispersibility of YSZ powder was investigated. The influence of concentrations of glycerol diacetate and magnesium citrate on pH and viscosities of YSZ suspensions was studied. The results indicate that concentrated YSZ suspensions can be coagulated by adding 2 vol% glycerol diacetate and magnesium citrate above 0.5 wt% at room temperature for 2–5 h. The compressive strength of coagulated wet samples is above 2.0 MPa. YSZ ceramics sintered at 1450 °C show homogeneous microstructures with relative densities of 98.9–99.2%. Flexural strength of YSZ ceramics is 869±84 MPa.     

The Coagulation of Finely-Divided Ion Exchange Resins and the Use of the Coagulated Material for Rapid Ion Removal

Abstract

Finely-ground ion exchange resin particles remove ions from solution much more rapidly than the conventional-size beads. Such finely-divided solids form suspensions when added to aqueous solutions. A method was required for rapidly removing such suspensions once ion adsorption had occurred, and to this end it is shown that the particles (-400 mesh) can be completely coagulated within a few minutes by the addition of suspensions of oppositely-charged solids. Thus anion exchange resins are coagulated by cation exchange resins (200 to 400), montmorillonite (200), kaolin (30), charcoal (10), silica (10), and glass (5), the figures representing arbitrarily defined relative coagulating abilities. Coagulating power is shown to increase markedly with decreasing particle size. Most suitable for ion removal is a mixed finely-divided resin formed by coagulation of anionic and cationic resins from pure water. The mixed resin, when added to 1 liter of 3 × 10^?4 M sodium phosphate solution removes all the phosphorus within 2 min, and when added to 1 liter of 2.5 × 10^?4 M calcium chloride, removes over 90% of the calcium within 3 min.     

Microfocus small‐angle X‐ray scattering investigation of the skin–core microstructure of lyocell cellulose fibers

Skin–core microstructures in hydrated lyocell cellulose fibers were investigated using microfocus small‐angle X‐ray scattering (SAXS). Both single fibers and fiber cross sections were observed. In all the fibers studied, a thin skin layer was observed in which the voids were smaller in cross section and better oriented than those in the core. The division between skin and core may not be sharp. A draw ratio of 0.80 gave fibers with voids that were shorter, larger in cross section, and more misoriented than the fibers produced with a draw ratio of 1.68. In contrast, there was little difference in void structure between samples coagulated in water and in 25% amine oxide aqueous solution. The results are explained in the context of the spinodal decomposition, which is thought to occur during coagulation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2799–2816, 2002; DOI 10.1002/app.10256     

凝固浴组成对SMA/CPVC共混超滤膜的结构与性能影响

通过非溶剂致相分离（NIPS）法制备了苯乙烯-马来酸酐共聚物（SMA）/氯化聚氯乙烯（CPVC）共混超滤膜,探讨了凝固浴中不同溶剂（DMAc）含量对其超滤膜表面酸酐基团偏析程度、微观结构、亲水性、水通量、截留率和抗污染的影响。结果表明：凝固浴中溶剂含量的增加抑制了酸酐基团向膜表面的偏析,导致亲水性减弱;同时,铸膜液中溶剂与水分子之间扩散速率的变小引起延迟分相,使得膜表面孔径变小和分布变窄。当溶剂质量分数为3%时,超滤膜对牛血清白蛋白（BSA）截留率提升至98.10%、通量恢复率为96.82%,且不可逆污染率降为3.77%,表明凝固浴中适量的溶剂可进一步提高超滤膜抗污染性能。     

制备工艺对NR性能的影响

采用新鲜天然胶乳分别制备乙酸凝固NR(NR-1)、微生物凝固NR(NR-2)、乙醇胺混合微生物凝固NR(NR-3)和蛋白酶混合自然凝固NR(NR-4),研究制备工艺对NR性能的影响。结果表明:NR-1和NR-2生胶的耐热老化性能和热稳定性好于NR-3和NR-4生胶;NR-4胶料的MH最大,t90最短,NR-3胶料的MH较小,t90最长;NR-4硫化胶的定伸应力和拉伸强度较大,拉断伸长率较小,NR-1硫化胶的定伸应力和拉伸强度较小;NR-4生胶、混炼胶和硫化胶的弹性转矩(S′)和剪切储能模量(G′)最大,损耗因子(tanδ)最小,NR-1生胶、混炼胶和硫化胶的S′和G′最小,tanδ值最大。