聚酰亚胺初生纤维的形态结构

以聚酰亚胺浓溶液为纺丝浆液 ,以乙醇及其与水的混合物为凝固浴 ,采用干湿法纺丝工艺路线纺制聚酰亚胺纤维。用扫描电子显微镜研究了初生纤维形态结构 ,发现聚酰亚胺初生纤维的内部孔洞较小 ,而且受凝固浴配比的影响也较小。同时发现聚酰亚胺干湿法成形过程中存在轻微的原纤化现象     

聚酰亚胺纤维的制备及其结构研究

将均苯四甲酸二酐(PMDA)和4,4’-二氨基二苯醚(ODA)在N-甲基吡咯烷酮(NMP)中进行溶液聚合得到聚酰胺酸(PAA)溶液,并用该溶液进行干湿法纺丝得到PAA纤维,分别用化学酰亚胺化法和热酰亚胺化法得到聚酰亚胺(PI)纤维。研究了凝固浴组成和工艺条件对PAA形态结构和纤维性能的影响,以及不同酰亚胺化方法对PI纤维形态结构和性能的影响。结果表明:以甲醇为凝固浴制备的PAA初生纤维,无孔致密,最高拉伸强度和初始模量分别为2．21 cN/dtex和40．73 cN/dtex;采用化学酰亚胺化法制得的PI纤维中存在少许孔洞缺陷,其强度较低,热酰亚胺化法制得的PI纤维无孔致密,其强度和模量分别达到2．83 cN/ dtex和43．4 cN/dtex。     

离子液体/二甲基亚砜复合溶剂干喷湿纺制备再生纤维素纤维凝固工艺研究

以棉浆粕为原料,使用离子液体/二甲基亚砜复合溶剂配制纺丝溶液,采用干喷湿法纺丝工艺制备纤维素纤维。探索了气隙长度、喷头牵伸比、凝固浴浓度、凝固浴温度对纤维结构与性能的影响。结果表明当采用气隙长度2.5 cm、喷头牵伸比1.9、凝固浴浓度30%、凝固浴温度35℃时可获得力学性能最佳、取向度最高、结晶较为完善的纤维素纤维。     

PI/NMP/H_2O三元体系相行为与纤维成形研究

介绍了湿法纺丝中凝固剂/溶剂/聚合物三元体系热力学理论及三元相图双节线和旋节线的计算方法;在聚酰亚胺/N-甲基-2-吡咯烷酮/水(PI/NMP/H2O)三元体系中,采用黏度法计算了PI-NMP相互作用参数(χ23),平衡溶胀法测得PI-H2O相互作用参数(χ13),结合NMP-H2O相互作用参数,并根据FloryHuggins溶液理论绘制出不同温度下PI/NMP/H2O三元体系的理论相图,并研究了不同凝固浴温度下PI纤维纺制中的相分离及成形过程。结果表明:在25,40,60℃时,χ23分别为0.489 6,0.480 1,0.473 4,χ13分别为1.52,1.47,1.30;随着凝固浴温度升高至60℃时,纤维表面逐渐变得致密光滑,断面形态由肾形变为规则的圆形;凝固浴温度升高时,相图中亚稳态区域扩大,纤维成形过程更加缓和,有利于制备结构致密的PI纤维。     

干喷湿纺中凝固牵伸对碳纤维前驱体PAN初生纤维的影响

为了研究PAN纤维干喷湿纺中凝固浴牵伸的作用机理。采用DMso水溶液作为凝固浴,利用纤维强伸度仪、分析天平、X射线衍射仪、电子探针等手段,研究了干喷湿纺中凝固牵伸对PAN初生纤维及最终原丝结构及性能的影响。结果表明,干喷瀑纺中,在凝固浴浓度（65％）、温度（20℃）、空气层厚度（2mm）等条件下,随凝固浴牵伸的增加,初生纤维及PAN原丝的孔隙率逐步降低,结晶度逐渐增大,初生纤维表现出较高的断裂强度,纵表面更加光洁,横截面更加致密;适当调整凝固浴牵伸,得到了纤度1．01dtex,强度7．52cN,dtcx的聚丙烯腈原丝。     

三元共聚聚酰亚胺初生纤维结构与性能的研究

以BTDA-TDI/MDI(P84)三元共聚聚酰亚胺(PI)粉末为原料,采用湿法纺丝技术制备BTDA-TDI/MDI三元共聚PI初生纤维,并对其结构和性能进行表征。实验结果表明:三元共聚PI初生纤维的最高抗断裂强度为0.65 cN/dtex;纺丝浆液PI质量分数19%时所得初生纤维表面较光滑;凝固浴溶液NMP质量分数70%时初生纤维结晶度分别比质量分数60%和80%时结晶度大;不同NMP质量分数凝固浴溶液所得初生纤维的热稳定性相差不大。     

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。     

凝固条件对PAN初生纤维微结构的影响

通过湿法纺丝工艺制备聚丙烯腈(PAN)初生纤维,借助于X射线衍射仪、声速仪、扫描电子显微镜、小角X光散射仪等,研究了凝固浴温度、凝固浴浓度、喷丝头拉伸等凝固条件对初生纤维晶态结构、取向结构、形态结构的影响。结果表明:PAN纤维的凝聚态结构和形态结构在初生纤维形成时已基本形成;PAN初生纤维的结晶度达40%以上,其结晶度和结晶尺寸受凝固浴温度和浓度的影响;PAN初生纤维和原丝的晶区取向和全取向随着喷丝头拉伸的增大而增大;PAN初生纤维具有沿纤维轴向高度取向的沟槽,通过改变成形条件,可以获得沟槽浅且规整性完美的纤维表面;提高凝固浴浓度,可以形成结构均质、致密的PAN初生纤维,避免皮芯结构及芯部出现较多孔洞。     

热拉伸条件对聚酰亚胺纤维结构和性能的影响

研究了热拉伸温度以及拉伸倍率对3,3',4,4'-联苯四甲酸酐(BPDA)、对苯二胺(PDA)以及2-(4-氨基苯基)-5-氨基苯并咪唑(BIA)三元共聚聚酰亚胺纤维聚集态结构和性能的影响。结果表明:提高热拉伸温度,可促进聚合物分子链运动,形成更规整的聚集态结构;合适的拉伸倍率使纤维获得充分拉伸;在460℃、热拉伸倍率为2.5时,所制备的共聚聚酰亚胺纤维的拉伸强度和弹性模量分别为3.31 GPa和137 GPa,表现出最优的力学性能。     

高浓度纤维素纺丝液湿法纺丝工艺研究

以棉纤维为原料,采用离子液体-二甲基亚砜复合溶剂配制固含量17%的纺丝液,通过湿法纺丝制备纤维素纤维,探讨了凝固牵伸比、水洗牵伸比及水洗温度对纤维结构和性能的影响。研究结果表明:采用凝固正牵伸,可以有效提高纤维力学性能与结晶性能。当凝固牵伸比为1.05、水洗牵伸比为1.3、水洗牵伸温度为60℃时,得到的再生纤维素纤维性能较好,断裂强度为2.11cN/dtex,断裂伸长率为10.29%;纤维素纤维取向度较高,结晶比较完善。     

PMDA-6FHP-DR1／SiO2杂化纳米材料的结构设计和合成

以含氟的二胺5，5′—(六氟异丙基)—二—(2—氨基苯酚)及均苯四甲酸酐(PMDA)为单体，首先合成了经酰胺化的主链上带有活性羟基的含氟聚酰亚胺，再通过Mitsunobu反应将活性生色分子分散红1(DR1)共价链接到聚酰亚胺的侧链骨架上，合成了含氟聚酰亚胺．采用溶胶—凝胶(SOl—Gel)技术，并利用偶联剂γ—氨丙基三乙氧基硅烷(AFTES)制备带有发色团的和含有硅氧烷端分子的聚酰胺酸，其中的Si(OR)3基经水解、缩合后，与正硅酸乙酯(TEOS)在催化剂作用下反应，经杂化、凝胶后，得到光学透明且热稳定性高的有机／无机杂化材料．将制得的含氟聚酰亚胺／SiO2杂化材料，采用红外光谱(FT—IR)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、示差扫描量热法(DSC)，对材料的结构、表面形貌、热性能进行了表征．     

The influence of hoop shear field on the structure and performances of glass fiber reinforced three-layer polypropylene random copolymer pipe

Three-layer pipe has many advantages over single layer one, especially for the pipe of glass fiber (GF) reinforced materials. But the hoop strength of the pipe produced via convention extrusion is poor because GFs orient along axial direction. In this work, a self-designed rotation extrusion system was adopted to extrude GF reinforced three-layer polypropylene random copolymer (PPR) pipe, in which a hoop shear field was applied to the polymer matrix and fibers in the middle layer. The structure and performance of pipes were investigated via scanning electronic microscope (SEM) and synchrotron two-dimensional wide-angel X-ray diffraction (2D-WAXD). Due to the hoop shear field, the orientation of GFs in middle layer deviated from axial direction. As a result, PPR pipes with enhanced hoop tensile strength were obtained. Because of the three-layer structure and the production process, the molecular chains of middle layer did not emerge distinct orientation after rotation shear, as shown in 2D-WAXD and SEM experimental results. This three-layer pipe rotation extrusion system offers a novel method for the modification of pipes in manufacture industry. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46985.     

Preparation and characterization of polyimide/kaolinite nanocomposite films based on functionalized kaolinite

The polyimide/kaolinite nanocomposite films based on the functionalized kaolinite were prepared and studied systematically. The natural kaolinite was modified by the indirect coupling to obtain the reactive kaolinite, which could be dispersed uniformly in the polymer matrix. It was found that the reactive kaolinite had effect on the crystal structure and increased the molecular weight of the polyimide. The significant improvement in the water resistance, thermal stability and mechanical property of polyimide/kaolinite nanocomposite was achieved with the addition of the reactive kaolinite. The tensile strength of polyimide/kaolinite nanocomposite increased by 40.6% compared to pure polyimide, Young's modulus of polyimide/kaolinite nanocomposite was increased to 1.95 GPa from 1.56 GPa. Finally, the mechanism to prepare the polyimide/kaolinite nanocomposite was proposed. POLYM. ENG. SCI., 59:E380–E386, 2019. © 2019 Society of Plastics Engineers     

Polyimide nanocomposites: Comparison of their properties with precursor polymer nanocomposites

A precursor poly(amic acid) was obtained by solution polymerization of pyromellitic dianhydride and benzidine in N, N‐dimethylacetamide. Poly(amic acid)/Organoclay hybrids were prepared by the solution intercalation method with dodecylamine‐montmorillonite. A polyimide hybrid was obtained from poly(amic acid) hybrid by heat treatment at various temperatures. The film type polyimide hybrids showed better thermal properties than poly(amic acid) hybrids. Also, the thermal stability of the two polymer hybrids were enhanced linearly with increasing clay content from 0 to 8 wt%. Tensile properties and gas barriers of the hybrids, however, were enhanced remarkably compared to pristine polymers. Intercalations of the polymer chains in clar were examined through wide angle X‐ray diffraction (XRD) and electron microscopy (SEM and TEM). Transmission electron microscopy revealed that a partially exfoliated structure had been obtained from polyimide/organo‐clay hybrids.     

Morphology evolution including formation of cylindrulite in isotactic polypropylene derived from periodical shear field

It has been well established that periodical shear stress can improve the mechanical performance of isotactic polypropylene during injection molding. In the current study, Polarized Light Microscopy (PLM), two-dimensional Wide-Angle X-ray Diffraction (2D-WAXD), Scanning Electron Microscopy (SEM) were employed to investigate the morphology evolution of vibration sample. Compared with static sample, the morphology of vibration one, which is derived from periodical shear field, exhibits different hierarchy structure: there is an additional fiber layer containing cylindrulites between the shear layer and the core layer, and the orientation is enhanced obviously. Through etching technique, it is found that there exists non-crystalline component in the fibril (core) of cylindrulite, and it may induce the growth of β crystals directly regardless of its non-crystalline nature. Based on the investigated results, a model of formation of cylindrulite is proposed.     

Influence of alkali fiber treatment and fiber processing on the mechanical properties of hemp/epoxy composites

Industrial hemp fibers were treated with a 5 wt % NaOH, 2 wt % Na₂SO₃ solution at 120°C for 60 min to remove noncellulosic fiber components. Analysis of fibers by lignin analysis, scanning electron microscopy (SEM), zeta potential, Fourier transform infrared (FTIR) spectroscopy, wide angle X‐ray diffraction (WAXRD) and differential thermal/thermogravimetric analysis (DTA/TGA), supported that alkali treatment had (i) removed lignin, (ii) separated fibers from their fiber bundles, (iii) exposed cellulose hydroxyl groups, (iv) made the fiber surface cleaner, and (v) enhanced thermal stability of the fibers by increasing cellulose crystallinity through better packing of cellulose chains. Untreated and alkali treated short (random and aligned) and long (aligned) hemp fiber/epoxy composites were produced with fiber contents between 40 and 65 wt %. Although alkali treatment generally improved composite strength, better strength at high fiber contents for long fiber composites was achieved with untreated fiber, which appeared to be due to less fiber/fiber contact between alkali treated fibers. Composites with 65 wt % untreated, long aligned fiber were the strongest with a tensile strength (TS) of 165 MPa, Young's modulus (YM) of 17 GPa, flexural strength of 180 MPa, flexural modulus of 9 GPa, impact energy (IE) of 14.5 kJ/m², and fracture toughness (K_Ic) of 5 MPa m^1/2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and properties of novel PMDA/ODA/PABZ polyimide fibers

A series of random copolyamic acid were synthesized from various ratios of two diamines 4, 4′‐oxydianiline (ODA) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (PABZ) by polycondensation with pyromellitic dianhydride (PMDA) in N‐methyl‐2‐pyrrolidone (NMP). Their inherent viscosities were in the range of 1.89–2.91 dl/g. The polyamic acid (PAA) solution drops were spun into fibers by the wet spinning process. The polyimide (PI) fibers were obtained from PAA fibers after drawn and treated in heating tube. The fibers were characterized by fourier transform infrared (FTIR), wide X‐ray diffraction (WAXD), scanning electron microscope (SEM), thermal gravimetry analysis (TGA), dynamic mechanical analysis (DMA), and tensile testing. WAXD showed these PI fibers were basically amorphous. The tensile strength and initial modulus of the PI fiber reached 1.53 and 220.5 GPa when diamine ratio of PABZ/ODA was 7/3, which were almost three times and 30 times over that of the PMDA/ODA PI fibers. TGA showed that the PI fibers were thermally stable with 10% weight losses recorded in the range of 492–564°C under nitrogen atmosphere, and their glass transition temperature (T_g) were found to be 410–440°C by DMA with increasing PABZ content from 30 to 70%. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

改性竹纤维增强聚丙烯复合材料的性能研究

以聚丙烯为基体材料,不同处理工艺改性的竹纤维为增强材料,采用密炼-注塑工艺制备聚丙烯/竹纤维复合材料。通过红外光谱仪(FTIR)、扫描电子显微镜(SEM)、热重分析仪(TGA)、万能试验机等对复合材料的化学结构、表面形态、热性能、力学性能等进行表征和测试。结果表明:偶联剂与碱处理均可改变竹纤维的表面特性,改善复合材料的界面相容性,其力学性能、热性能均随处理工艺有所改善。当偶联剂KH-550含量为2%时,复合材料有较好的力学性能,其断裂伸长率为14.5%,拉伸强度为30.48 MPa,冲击强度为22.4 kJ/m2。     

聚酰胺酸纤维热酰亚胺化的研究

采用聚酰胺酸纤维热酰亚胺化处理方法制备聚酰亚胺纤维,研究了不同热处理条件对聚酰亚胺纤维性能的影响。结果表明,采用定长处理和持续升温方式,真空氛围,热处理温度420℃,得到的聚酰亚胺纤维性能较好,其断裂强度达5.06 cN/dtex。     

Polyimide Fibers Obtained by Spinning Lyotropic Solutions of Rigid‐Rod Aromatic Poly(amic ethyl ester)s

Summary: Fibers were spun from a lyotropic solution of a high‐molecular‐weight (η = 5.89 g · dL^?1), rigid‐rod, fully aromatic polyimide precursor polymer in a dry‐jet, wet‐spinning process in NMP. Acetone was identified as the coagulant of choice since fibers could be drawn extensively in this solvent, resulting in improved mechanical properties (tensile modulus: E = 17 GPa, strength at break: σ_break = 400 MPa, elongation at break: ε_break = 5.3%) and orientation, which was shown by WAXS patterns. SEM images showed a layered, skin‐core morphology without any visible fibrillation. Additional processing of these fibers by step‐wise hot‐drawing up to 400 °C under tension rendered oriented polyimide fibers with excellent mechanical properties. (E = 68 GPa, σ_break = 700 MPa, ε_break = 1%). An analysis of the WAXS diffraction patterns showed an improved orientation of the fibers in the axial and lateral directions; however, probably due to the CF₃ side groups, the lateral distance was still too large for crystallization. SEM images of these imidized fibers showed, for the first time, a fibrillar morphology in addition to the typical, skin‐core, sheet‐like morphology.

SEM image of the hot‐drawn fiber PI 4 (12). The image shows a skin‐core morphology which was delaminating into ribbons during preparation.