Force field in coagulation bath at low temperature induced microfibril evolution within PAN nascent fiber and precursor fiber

The coagulation process was vital for the microfibril evolution and mechanical properties of polyacrylonitrile (PAN) fibers. The PAN nascent fibers and precursor fibers were prepared by controlling drawing ratio of coagulation bath at low temperature during the dry-jet wet spinning process. The microfibril morphological changes induced by force fields in coagulation bath were investigated by scanning electron microscopy and high-resolution transmission electron microscopy. During the coagulation process, the spinning solution evolved into an interconnected network composed of random microfibrils and tie joints as a building block of the network. At low drawing ratio, the random interconnected network existed in nascent fibers. Increasing drawing ratio, the fiber filaments underwent shrinkage and the network was transformed into the transverse lamellae. Furthermore, the lamellar thickness also decreased. After the treatment of post-spinning, similar transverse lamellae were formed in all of precursor fibers, and random microfibrillar network was stretched and oriented to develop into the aligned microfibrils in precursor fibers. The transverse fold-chain crystal layers were densely stacked in the microfibrils. Increasing drawing ratio, the lamellae and microfibrils in precursor fibers were packed more densely and orderly. Consequently, the order and homogeneity of microfibrils in nascent fibers and precursor fibers were improved by increasing drawing ratio, which were benefit to increase fiber tensile strength and modulus.     

Wet-spinning assembly of continuous and macroscopic graphene oxide/polyacrylonitrile reinforced composite fibers with enhanced mechanical properties and thermal stability

Polyacrylonitrile (PAN) composite microfibers with different contents of graphene oxide (GO) were fabricated via wet-spinning route in this work. Based on nonsolvent-induced phase separation theory, N,N-dimethyl formamide/water mixture system was employed as coagulation bath, nonsolvent (water) diffused into PAN spinning solution and led to a quick PAN fiber solidification. Nematic liquid crystal state of GO dispersions and GO/PAN spinning solutions were determined via polarized optical microscopy images, and the morphology and structure of the composite fibers were characterized via scanning electron microscope, Transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. 1 wt % GO/PAN composite fibers exhibited outstanding mechanical properties, 40% enhancement in tensile strength and 34% enhancement in Young's modulus compared with pure PAN fiber. The results of dynamic mechanical analysis indicated that the composite fiber with 1 wt % GO performed the best thermal mechanical property with 5.5 GPa and 0.139 in storage modulus and loss tangent, respectively. In addition, thermogravimetric analysis showed that thermal stability of the composite fibers enhanced with the increasing GO contents. GO/PAN composite fibers can be as the candidate of carbon fiber precursor, high performance fibers, and textiles applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46950.     

Processing,structure, and properties of gel spun PAN and PAN/CNT fibers and gel spun PAN based carbon fibers

Polyacrylonitrile (PAN) and PAN/carbon nanotube (PAN/CNT) fibers were manufactured through dry‐jet wet spinning and gel spinning. Fiber coagulation occurred in a solvent‐free or solvent/nonsolvent coagulation bath mixture with temperatures ranging from ?50 to 25°C. The effect of fiber processing conditions was studied to understand their effect on the as‐spun fiber cross‐sectional shape, as well as the as‐spun fiber morphology. Increased coagulation bath temperature and a higher concentration of solvent in the coagulation bath medium resulted in more circular fibers and smoother fiber surface. as‐spun fibers were then drawn to investigate the relationship between as‐spun fiber processing conditions and the drawn precursor fiber structure and mechanical properties. PAN precursor fiber tows were then stabilized and carbonized in a continuous process for the manufacture of PAN based carbon fibers. Carbon fibers with tensile strengths as high as 5.8 GPa and tensile modulus as high as 375 GPa were produced. The highest strength PAN based carbon fibers were manufactured from as‐spun fibers with an irregular cross‐sectional shape produced using a ?50°C methanol coagulation bath, and exhibited a 61% increase in carbon fiber tensile strength as compared to the carbon fibers manufactured with a circular cross‐section. POLYM. ENG. SCI., 55:2603–2614, 2015. © 2015 Society of Plastics Engineers     

Analysis of the tensile modulus of poly(p‐hydroxybenzoate)/poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) ternary polyester composite fibers

Liquid crystalline polymer reinforced plastics were prepared by compounding (PHB/PEN/PET) blends. A fibrillar PHB structure was formed in situ in the PEN/PET matrix under a high elongational flow field during melt‐spinning of the composite fibers. The formation of PHB microfibrils in the composite fiber with different PHB contents and winding speeds was observed. The PHB microfibril reinforced PEN/PET composite fibers exhibited an unexpectedly low tensile modulus. We have evaluated the tensile modulus of the fibers using the non‐modified 22 and a modified 23 Halpin–Tsai model. From the analysis of both models, large differences were found between the theoretical and experimental values of the tensile modulus, and the low value of the tensile modulus of the composite fiber could not adequately be explained by either model. Thus, we analyzed the observed modulus values using the Takayanagi model, 24 which describes the concept of mechanical discontinuities in semi‐crystalline polymers. Using the Takayanagi model, the effective fraction of continuous or discontinuous microfibrils was evaluated. Consequently, we could successfully explain the very low modulus of the PHB/PEN/PET composite fiber, having a large number of PHB microfibrils, using the Takayanagi model. Copyright © 2003 Society of Chemical Industry     

Preparation of carbon fibers from linear low density polyethylene

Carbon fibers were produced from linear low density polyethylene (LLDPE) instead of commonly used precursors, such as viscose rayon, mesophase pitch and polyacrylonitrile (PAN). Cross-linked fibers were produced at various temperatures, times and stress conditions during a sulfuric acid treatment using LLDPE fibers obtained from dry-wet spinning. The effects of cross-linking were analyzed using a range of characterization techniques, such as differential scanning calorimetry, color change, fourier transform infrared spectroscopy, elemental analysis, density, scanning electron microscopy, and single filament mechanical properties. The carbonization process of cross-linked fibers was carried out at 950 °C for 5 min in a nitrogen atmosphere. The carbon fibers with the best mechanical properties were obtained from the cross-linked fiber with the highest tensile modulus. In particular, the carbon fibers with the best mechanical properties (tensile strength and tensile modulus of 1.65 GPa and 110 GPa, respectively), similar to commercial-grade carbon fiber, were obtained from the cross-linked fiber that had undergone a carbonization process with a stress of 0.25 MPa after an acid treatment for 150 min at 140 °C and a stress of 0.26 MPa.     

凝胶染色过程中腈纶沿纺程的结构性能变化的研究

采用湿法纺丝工艺制备腈纶(即聚丙烯腈(PAN)纤维),研究了凝胶染色过程中PAN纤维在不同工序段的结构和物理性能.结果表明:沿着纺程,PAN纤维的直径逐渐减小,纤维的玻璃化转变温度和结晶度逐渐提高;在水洗后PAN纤维表面有明显的微观结构缺陷、且无定形区占比高;经过热拉伸和干燥致密化之后,纤维致密化,结晶度大大增加,凝胶...     

Effect of spinning conditions on the mechanical properties of polyacrylonitrile fibers modified with carbon nanotubes

Carbon nanotubes (CNTs) were used to modify polyacrylonitrile (PAN) polymer. The PAN/CNT composite fibers were spun from dimethylformamide solutions containing different types of CNTs. The effect of nanotube addition to the fiber precursor on the resulting mechanical properties is discussed. In this study, we examined the relationship of the rheological properties of PAN spinning solutions containing various types of CNTs and the tensile strength of the resulting PAN fibers. The presence of CNTs in the PAN spinning solution enhanced its deformability during the drawing stage. This effect resulted in a higher tensile strength in the fibers containing nanotubes, as compared to the pure fibers. The use of a three‐stage drawing process resulted in a significant increase in the tensile strength of PAN fibers modified with multiwalled nanotubes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study of flame‐resistant acrylic fibers reinforced by poly(vinyl alcohol)

Acrylic fibers [polyacrylonitrile (PAN) fibers] have excellent flame‐retardant properties after they are modified by hydrazine hydrate and metal ions; however, their widespread applications are restricted because of poor mechanical properties. To improve the mechanical properties of these modified PAN fibers, poly(vinyl alcohol) (PVA) was added to the spinning solution of PAN as an effective reinforcing agent. The structure of the fibers before and after modification was studied by Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive spectroscopy, and wide‐angle X‐ray diffraction. The mechanical properties and flame resistance of the fibers after treatment were also tested by a single‐fiber tensile tester and a limiting oxygen index (LOI) analyzer, respectively. We found that the LOI of the modified fibers was reduced from 54.7 to 29.1 after the introduction of 50 wt % PVA; however, the tensile strength was dramatically improved from about 1.50 cN/dtex to more than 4.00 cN/dtex. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43006.     

Effect of the drawing process on the wet spinning of polyacrylonitrile fibers in a system of dimethyl sulfoxide and water

The effect of the drawing process on the structural characteristics and mechanical properties of polyacrylonitrile (PAN) fibers was comparatively studied. The protofibers extruded from the spinneret were the initial phase of stretching, which involved the deformation of the primitive fiber with the concurrent orientation of the fibrils. Wet‐spun PAN fibers observed by scanning electron microscopy exhibited different cross‐sectional shapes as the draw ratio was varied. X‐ray diffraction results revealed that the crystalline orientation of PAN fibers increased with increasing draw ratio; these differences in the orientation behaviors were attributed to the various drawing mechanisms involved. The crystalline and amorphous orientations of the PAN fibers showed different features; at the same time, the tensile properties were strongly dependent on the draw ratio. However, the stream stretch ratio had most influence on the tensile strength and the orientation of PAN fibers for the selected process parameters. Electron spin resonance proved that the local morphology and segmental dynamics of the protofibers were due to a more heterogeneous environment caused by the sequence structure. Differential scanning calorimetry indicated that the size and shape of the exotherm and exoenergic reaction were strongly dependent on the morphology and physical changes occurring during fiber formation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1026–1037, 2007     

Stabilization and carbonization of gel spun polyacrylonitrile/single wall carbon nanotube composite fibers

Gel spun polyacrylonitrile (PAN) and PAN/single wall carbon nanotube (SWNT) composite fibers have been stabilized in air and subsequently carbonized in argon at 1100 °C. Differential scanning calorimetry (DSC) and infrared spectroscopy suggests that the presence of single wall carbon nanotube affects PAN stabilization. Carbonized PAN/SWNT fibers exhibited 10-30 nm diameter fibrils embedded in brittle carbon matrix, while the control PAN carbonized under the same conditions exhibited brittle fracture with no fibrils. High resolution transmission electron microscopy and Raman spectroscopy suggest the existence of well developed graphitic regions in carbonized PAN/SWNT and mostly disordered carbon in carbonized PAN. Tensile modulus and strength of the carbonized fibers were as high as 250 N/tex and 1.8 N/tex for the composite fibers and 168 N/tex and 1.1 N/tex for the control PAN based carbon fibers, respectively. The addition of 1 wt% carbon nanotubes enhanced the carbon fiber modulus by 49% and strength by 64%.     

KMnO4对改性聚丙烯腈纤维物理与化学结构的影响

通过X射线衍射、傅里叶变换红外光谱、扫描电子显微镜和拉伸仪研究了KMnO_4对改性聚丙烯腈(PAN)纤维化学结构、物理结构和力学性能的影响。实验结果表明,在KMnO_4改性PAN纤维过程中使PAN纤维不仅发生了氰基环化反应,还伴随氰基的水解;随改性温度的升高PAN纤维晶粒尺寸与结晶度呈现下降趋势;同时改性PAN纤维的断裂伸长率逐渐升高、杨氏模量与拉伸强度逐渐降低。     

超高相对分子质量PPTA树脂及其高模量芳纶的研究

对高相对分子质量聚对苯二甲酰对苯二胺(PPTA)树脂进行了表征,开展了添加超高相对分子质量PPTA树脂与普通相对分子质量PPTA树脂共混进行液晶纺丝得到高强度和高模量芳纶的结构表征与性能试验,同时对芳纶的力学性能与其PPTA树脂相对分子质量的关系进行了研究。结果表明,芳纶的力学性能与其PPTA聚合体的相对分子质量紧密相关,如果PPTA树脂的相对分子质量不够高,加上液晶纺丝和高模量热处理过程分子链的进一步降解,高模量芳纶的制备就无法实现。在系统研究PPTA聚合反应规律,特别是聚合诱导相互转变规律及其影响因素研究基础上,通过调控连续聚合的反应条件,在1 000 t/a连续聚合生产线上制备出比浓对数粘度高达9.2 dl/g的超高相对分子质量PPTA树脂;用超高相对分子质量PPTA树脂与通用级PPTA树脂(比浓对数粘度6.8 dl/g)混合进行纺丝,制备出高强度的芳纶,并进一步热处理得到高强度和高模量的芳纶。     

Process–structure–property relationship of melt spun poly(lactic acid) fibers produced in the spunbond process

We report on the process–structure–property relationships for Poly(lactic acid) (PLA) filaments produced through the spunbond process. The influence of spinning speed, polymer throughput, and draw ratio on crystallinity and birefringence of fibers were evaluated. We established that increasing spinning speed increases crystallinity and birefringence of fibers. We also investigate the role of fiber structures on fiber tensile properties—breaking tensile strength, strain at break, initial modulus, and natural draw ratio. An increase in spinning speed leads to a higher breaking tensile strength, higher initial modulus and lower strain at break. We have shown an almost linear relationship between breaking tensile strength of PLA fibers and birefringence. This indicates that improved tensile properties at high spinning speeds can be attributed to enhanced molecular orientation. The dependency of fiber breaking tensile strength and strain at break on spun orientation were explained with natural draw ratio, as a measure of spun orientation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44225.     

Fiber preparation and mechanical properties of recycled polypropylene for reinforcing concrete

Polypropylene (PP) fibers have been widely used to reinforce concrete footpaths as an alternative to steel mesh. The reinforcing effect of the PP fiber is directly proportional to its tensile strength and Young modulus. This research explored the feasibility of using an improved melt spinning and hot drawing process to produce virgin and recycled PP fibers of high mechanical properties in an industrial scale. Commercial grade granules of virgin PP, recycled PP and HPDE were mixed in different proportions in preparing five different types of fibers. All the fibers obtained high tensile strength and Young modulus. A relationship between the structural parameters and mechanical properties was then established. It was observed that the melt spinning and hot drawing process formed both α‐form and β‐form crystals in the PP fibers, and significantly improved crystallinity from about 50% to 80%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41866.     

Effects of processing conditions on the mechanical performance of maleic anhydride compatibilized in-situ composites of polypropylene with liquid crystalline polymer

Maleic anhydride compatibilized blends of isotactic polypropylene (PP) and thermotropic liquid crystaline polymer (LCP) were prepared either by the direct injection molding (one-step process), or by twin-screw extrusion blending, after which specimens were injection molded (two-step process). The morphology and mechanical properties of these injection molded in situ LCP composites were studied by means of scanning electron microscopy (SEM), Izod impact testing, static tensile, and dynamic mechanical measurements. SEM observations showed that fine and elongated LCP fibrils are formed in the maleic anhydride compatibilized in situ composites fabricated by means of the one-step process. The tensile strength and modulus of these composites were considerably close to those predicted from the rule of mixtures. Furthermore, the impact behavior of LCP fibril reinforced composites was similar to that of the glass fiber reinforced polymer composites. On the other hand, the maleic anhydride compatibilized blends prepared from the two-step process showed lower mechanical performance, which was attributed to the poorer processing behavior leading to the degradation of PP. The effects of the processing steps, temperatures, and compatibilizer addition on the mechanical properties of the PP/LCP blends are discussed.     

高模量碳纤维的现状及发展(3)

主要介绍了国内外聚丙烯腈基和沥青基高模量碳纤维的研究现状及发展趋势。⑴高模量碳纤维的发展方向:1980年代,两大高模量碳纤维都朝着高强高模方向发展,以满足飞机主承力结构件高强高模并重的需要,因而促使高模量碳纤维的性能从单一高模化向高强高模化方向迈进,如东丽公司的M50J和M60J的抗拉伸强度(σ)分别为4.12 GPa和3.92 GPa,抗拉伸模量(E)分别为475 GPa和588 GPa,与M50(σ:2.45 GPa,E:490 GPa)相比均大幅度提高;1990年代率先研制出XN-70(σ:3.3 GPa,E:690 GPa)和FT-700(σ:3.3 GPa,E:700 GPa)沥青基高强高模碳纤维产品不久,美国AMOCO公司也生产出Thorne K-1000(σ:3.1 GPa,E:956 GPa)商品,满足了工业界的需求。⑵原丝的品质是提升高强高模碳纤维性能的关键:人们特别关注聚合物单体、溶剂、环境等的净化,以及聚合纺丝工艺参数的选择和调整,目的是如何能生产出低灰份杂质,细直径,高碳收率,高取向度和结晶度,毛丝少,柔韧性好,均匀稳定的优质原纤维。优质原纤维是制备高强高模的物质基础。⑶热处理制备工序、设备选型及工艺参数的调控也是提高高强高模碳纤维性能不可或缺的条件:人们在热处理过程用DSC-TG(热分析仪)、EA(元素分析仪)、FE-SEM(场发射扫描电镜)、HRTEM(高分辨透射电镜)、XES(X-射线能谱仪)、XRD(X-射线衍射仪)、Raman(拉曼光谱)、NMR(核磁共振仪)、STM(原子力显微镜)和AAS(原子吸收光谱)等先进的测试分析方法以及万能材料试验机等,研究各工序的工艺参数对产品性能和结构的影响,并详细的用图表阐述之。前人研究的成果加速了世界高强高模碳纤维性能的提升。进而提出了提高我国高强高模碳纤维的关键技术(例如研制非硅系新油剂,加强各工序的净化度和设备加工精度,强化工艺参数调控精度和加强灵活可变性,分析测试的准确度和测试方法的统一性等)。同时简介了高模量碳纤维的应用领域和前景。     

The index of dry‐jet wet spinning for polyacrylonitrile precursor fibers

A new spinning index for a PAN precursor fiber is proposed that includes the viscosity of a spinning dope, the thermodynamic affinity, and the draw ratio during the spinning process. Through dry‐jet wet spinning, six types of PAN precursor fibers with different spinning parameters, including solid content, solvent content in a bath, and draw ratio, were fabricated and analyzed with tensile tests, SEM, and XRD. The results show that the spinning index can reflect the mechanical properties of the fibers but is less indicative of crystallinity. Hence, the current spinning index is recommended for use as an indicator for the mechanical properties of PAN precursor fibers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41265.     

Structural and thermal property changes of plasticized spinning polyacrylonitrile fibers under different spinning speeds

The effect of the spinning speed on structural and thermal properties of polyacrylonitrile (PAN) fibers prepared by plasticized spinning was investigated. The PAN fibers were characterized by scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. We found that the surface morphology of the fibers was relatively smooth. The presence of a small amount of surface defects was caused by the instability of spinning process. The final fibers may have had two tensile fracture modes, that is, cluster breaking and axial split fracture. The structure of the as‐spun fibers was destroyed when the spinning speed was up to 500 m/min; this led to chain scission in the amorphous region. The final fibers exhibited mechanical properties that were roughly comparable to those of commercial PAN fibers. The changing trend in the cyclization temperature of the final fibers was consistent with that of crystallinity, which first increased and then decreased. The decomposition temperature in the amorphous region increased with increasing spinning speed. The decomposition temperature in the crystalline region increased with increasing crystallinity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45267.     

Oriented and exfoliated single wall carbon nanotubes in polyacrylonitrile

Polyacrylonitrile (PAN)/single wall carbon nanotubes (SWNT) fibers were gel spun at 0, 0.5, and 1 wt% SWNT content to a draw ratio of 51. Structure, morphology, and mechanical and dynamic mechanical properties of these fibers have been studied. PAN/SWNT composite exhibited much higher electron beam radiation resistance than PAN. As a result, PAN lattice images could be easily observed in the composite fiber by high resolution transmission electron microscopy. The PAN/SWNT composite fiber also exhibited higher solvent resistance than the control PAN fiber. UV-vis spectroscopy of highly drawn fiber exhibited van Hove transitions, suggesting SWNT exfoliation upon drawing. SWNT exfoliation was also confirmed by high resolution transmission electron microscopy (HRTEM). At 1 wt% SWNT loading, fiber storage modulus (at 1 Hz) increased by 13.9, 6.6, and 0.2 GPa at −75, 25, and 150 °C, respectively. This suggests that the load transfer ability and hence interfacial strength is increasing with decreasing temperature, even below the polymer's γ transition temperature.     

高模量碳纤维的现状及发展(2)

主要介绍了国内外聚丙烯腈基和沥青基高模量碳纤维的研究现状及发展趋势。⑴高模量碳纤维的发展方向:1980年代,两大高模量碳纤维都朝着高强高模方向发展,以满足飞机主承力结构件高强高模并重的需要,因而促使高模量碳纤维的性能从单一高模化向高强高模化方向迈进,如东丽公司的M50J和M60J的抗拉伸强度(σ)分别为4.12 GPa和3.92 GPa,抗拉伸模量(E)分别为475 GPa和588 GPa,与M50(σ:2.45 GPa,E:490 GPa)相比均大幅度提高;1990年代率先研制出XN-70(σ:3.3 GPa,E:690 GPa)和FT-700(σ:3.3 GPa,E:700 GPa)沥青基高强高模碳纤维产品不久,美国AMOCO公司也生产出Thorne K-1000(σ:3.1 GPa,E:956 GPa)商品,满足了工业界的需求。⑵原丝的品质是提升高强高模碳纤维性能的关键:人们特别关注聚合物单体、溶剂、环境等的净化,以及聚合纺丝工艺参数的选择和调整,目的是如何能生产出低灰份杂质,细直径,高碳收率,高取向度和结晶度,毛丝少,柔韧性好,均匀稳定的优质原纤维。优质原纤维是制备高强高模的物质基础。⑶热处理制备工序、设备选型及工艺参数的调控也是提高高强高模碳纤维性能不可或缺的条件:人们在热处理过程用DSC-TG(热分析仪)、EA(元素分析仪)、FE-SEM(场发射扫描电镜)、HRTEM(高分辨透射电镜)、XES(X-射线能谱仪)、XRD(X-射线衍射仪)、Raman(拉曼光谱)、NMR(核磁共振仪)、STM(原子力显微镜)和AAS(原子吸收光谱)等先进的测试分析方法以及万能材料试验机等,研究各工序的工艺参数对产品性能和结构的影响,并详细的用图表阐述之。前人研究的成果加速了世界高强高模碳纤维性能的提升。进而提出了提高我国高强高模碳纤维的关键技术(例如研制非硅系新油剂,加强各工序的净化度和设备加工精度,强化工艺参数调控精度和加强灵活可变性,分析测试的准确度和测试方法的统一性等)。同时简介了高模量碳纤维的应用领域和前景。