Impact of the wet spinning parameters on the alpaca-based polyacrylonitrile composite fibers: Morphology and enhanced mechanical properties study

The study examined the effect of different wet spinning parameters (e.g., total solid content, coagulation bath concentration, drawing, and stretching) on the morphology and mechanical properties of the wet spun alpaca/polyacrylonitrile (PAN) composite fibers. The alpaca/PAN composite fibers were wet spun using 10, 20, and 30% of alpaca particles along with the PAN polymer. The shear-thinning or non-Newtonian flow behavior was observed among the dope solutions with different solid content. The cross-sectional fiber morphology showed the bean-shaped characteristic for the control PAN fibers, whereas the alpaca/PAN composite fibers exhibited almost circular shape. “Cavity healing” was observed, where noticeable voids and porous areas were demolished in the cross section of the composite fibers, by changing the total solid content and coagulation bath concentration. Although the control PAN fibers exhibited the highest tenacity with lower fiber diameter, the alpaca/PAN composite fibers showed a gradual deterioration in tenacity while adding alpaca particles into the PAN polymeric matrix. Nevertheless, due to the increment in the total solid content, higher draw ratio, and stretching of the fibers, the tenacity, molecular orientation, and the crystallinity of the composite fibers were increased.     

PAN原丝成形过程中孔隙结构的形成和演变

采用干湿法纺丝在梯级凝固成形条件和后续工艺下得到聚丙烯腈(PAN)原丝,利用扫描电镜、氮气吸附等方法测试研究了PAN原丝中孔隙的形成和演变。结果表明:在凝固成形阶段,PAN原丝内孔隙的形成是溶剂和非溶剂双扩散及PAN相分离双重作用的结果;PAN原丝经过沸水拉伸、干燥致密化、饱和蒸汽拉伸和热定型等处理,其纤维密度、结晶度增大,力学性能提高,其孔隙平均孔径、孔隙体积和孔隙含量均逐渐减小;PAN原丝内闭合孔隙经过拉伸后会形成新的开放孔隙,开放孔隙在干燥致密化后闭合和消失。     

Factors influencing the small‐scale melt spinning of poly(ε‐caprolactone) monofilament fibres

Some of the main factors affecting the small‐scale melt spinning of poly(ε‐caprolactone), PCL, monofilament fibres have been studied. These factors included spinning temperature, extrusion rate, take‐up rate and draw ratio. The underlying influence of the polymer's own characteristic properties, in particular its chemical structure, transition temperatures (T_g, T_m) and crystallizability, were also interpreted within the context of the melt spinning process. Physically, the as‐spun fibres obtained were uniform in diameter and smooth in surface appearance. They were also semi‐crystalline (>50%) in morphology. Mechanically, however, they were still very weak and highly extensible. Subsequent off‐line cold‐drawing at room temperature introduced the required degree of molecular orientation to reinforce the fibres, yielding tensile strengths of approaching 300 MPa. PCL fibres of precisely controlled physical dimensions and matrix morphology are attracting increasing interest for use in biomedical applications. This paper describes how this control can be achieved through the processing operation. Copyright © 2003 Society of Chemical Industry     

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     

Effects of zinc oxide nanoparticles on the physical properties of polyacrylonitrile

Polyacrylonitrile (PAN)/zinc oxide (ZnO) nanocomposites were prepared by solution mixing in dimethylacetamide, followed by film casting, and their physical properties were investigated. The heating scan of differential scanning calorimetry displayed only a single crystallization peak (T_c) without a melting peak, regardless of the presence of ZnO. The incorporation of ZnO nanoparticles decreased T_c by 13°C, and increased the heat of crystallization by 18%. Further, it greatly improved the thermal stability of PAN, even at the ZnO content as low as 0.1 wt %. The nanocomposites showed the UV transmittance peak at 365 nm, whose intensity was increased as ZnO content was increased. The presence of ZnO did not produce new peak nor shift the peaks with respect to PAN in wide angle X‐ray diffraction pattern. Introduction of a small amount of ZnO nanoparticles did not have notable effect on the tensile properties. However, 5 wt % loading of the nanoparticles increased the tensile modulus of PAN by 14.5% and decreased elongation at break dramatically. PAN nanocomposites with 5 wt % ZnO did not show any plateau region in stress–strain curve. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1854–1858, 2006     

Preparation of polysulfone hollow fiber affinity membrane modified with mercapto and its recovery properties. I. Synthesis and preparation of hollow fiber matrix membrane

Several kinds of chloromethyl polysulfones (CMPSF) with different chlorinity and reactive groups were synthesized by Friedel‐Crafts reaction, which could be utilized as reactively matrix membrane materials. The CMPSF hollow matrix membranes were prepared with phase inversion by utilization of the CMPSF/additive/DMAC casting solution and CMPSF as membrane materials. The rheological behavior of CMPSF/additives/DMAC spinning casting solution was studied. The experimental results showed that the spinning casting solution was a pseudoplastic fluid, the apparent viscosity of the spinning casting solution decreased with the increase of shearing rate, and the viscous flow activity energy of the spinning casting solution was inclined to unchange at high shearing rate. The effects of composition of spinning casting solution and process parameters of dry–wet spinning on the structure of CMPSF hollow fiber matrix membrane were investigated. The pore size, porosity, and water flux of membrane decreased with the increase of additive content, bore liquid, and dry spinning distance. With the increase of extrusion volume outflow, the external diameter, wall thickness, and porosity of the hollow fiber matrix membrane increased, but the pore size and water flux of the membrane decreased. It was also found that the effects of internal coagulant composition and external coagulant composition on the structure of CMPSF hollow fiber matrix membrane were different. The experimental results showed that thermal drawing could increase the mechanical properties of CMPSF hollow fiber matrix membrane and decrease the pore size, porosity, and water flux of the CMPSF hollow fiber matrix membrane, and the thermal treatment could increase the homogeneity and stability of the structure of the CMPSF hollow fiber matrix membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 758–771, 2006     

PAN/PMMA共混制备纳米碳纤维的结构与性能

以N,N-二甲基甲酰胺(DMF)为溶剂,以聚丙烯腈(PAN)为碳前驱体,聚甲基丙烯酸甲酯(PMMA)为热裂解聚合物,制备PAN/PMMA溶液共混体系,经湿法纺丝及碳化工艺制备了纳米碳纤维(CNFs);讨论了影响CNFs形态、尺寸的主要因素,通过傅里叶变换红外光谱、X射线衍射、拉曼光谱和电导率测试等对CNFs进行了表征。结果表明:相对分子质量为8.0×10~4的PAN与PMMA以质量比30/70进行共混纺丝和碳化,可以得到CNFs;增加原丝的拉伸倍数有利于减小CNFs的直径,当拉伸倍数提高到6时,CNFs直径为50～150nm;碳化温度为800℃时,CNFs出现石墨相结构;提高碳化温度有利于CNFs石墨化结构的形成与电导率的提高。     

Preparation and characterization of ultrafine electrospun polyacrylonitrile fibers and their subsequent pyrolysis to carbon fibers

The present contribution reports the fabrication and characterization of ultrafine polyacrylonitrile (PAN) fibers by electrospinning and further development of the as‐spun PAN fibers into ultrafine carbon fibers. The effects of solution conditions (i.e., solution concentration, viscosity, conductivity, and surface tension) and process parameters (i.e., applied electrostatic field strength, emitting electrode polarity, nozzle diameter, and take‐up speed of a rotating‐drum collector) on morphological appearance and average diameter of the as‐spun PAN fibers were investigated by optical scanning (OS) and scanning electron microscopy (SEM). The concentration, and hence the viscosity, of the spinning solutions significantly affected the morphology and diameters of the as‐spun PAN fibers. The applied electrostatic field strength and nozzle diameter slightly affected the diameters of the as‐spun fibers, while the emitting electrode polarity did not show any influence over the morphology and size of the as‐spun fibers. Utilization of the rotating‐drum collector enhanced the alignment of the as‐spun fibers. Within the investigated concentration range, the average diameter of the fibers ranged between 80 and 725 nm. Finally, heat treatment of the as‐spun fibers with their average diameter of about 450 nm was carried out at 230 and 1000 °C, respectively. Various characterization techniques revealed successful conversion into carbon fibers with an average diameter of about 250 nm. Copyright © 2006 Society of Chemical Industry     

Wet‐spinning of biomedical polymers: from single‐fibre production to additive manufacturing of three‐dimensional scaffolds

Wet‐spinning of polymeric materials has been widely investigated for various biomedical applications, such as extracorporeal blood treatment, controlled drug release and tissue engineering. This review is aimed at summarizing and assessing current advances in wet‐spinning of biomedical polymers to manufacture single fibres and three‐dimensional scaffolds, as well as their functionalization through loading with bioactive agents. The theoretical principles and the main technological aspects of fibre production by wet‐spinning on either a laboratory or an industrial scale are outlined. The non‐solvent‐induced phase inversion determining polymer coagulation during the wet‐spinning process is discussed by highlighting its influence on the resulting fibre morphology and how it can be exploited to induce a nano/microporosity in the solidified polymeric matrix. The versatility of wet‐spinning in material selection, bioactive agent loading and fibre morphology tuning is underlined through an overview of significant literature reporting on the processing of various naturally derived and synthetic polymers. A special focus is given to cutting‐edge advancements in the application of additive manufacturing principles to wet‐spinning for enhanced control and reproducibility of three‐dimensional polymeric scaffold morphology at different scale levels (i.e. macrostructural to micro/nanostructural features). © 2017 Society of Chemical Industry     

Morphology,mechanical property,and modeling evaluation of P(3HB‐co‐4HB)/nano‐ZnO composites

Poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P(3HB‐co‐4HB)) and nanometer zinc oxide (nano‐ZnO) modified by solid titanate coupling agent (TMC980) were selected to prepare P(3HB‐co‐4HB)/nano‐ZnO composites via melt blending. Scanning electron microscope (SEM), capillary rheometer, polarized optical microscopy (POM), and universal testing machine were used to characterize the fracture morphology, rheological property, spherulitic morphology, and mechanical properties of P(3HB‐co‐4HB)/nano‐ZnO composites. Halpin‐Tsai equation was used to quantitatively evaluate the dispersion and enhancement effects of modified nano‐ZnO on P(3HB‐co‐4HB). The results demonstrated that modified nano‐ZnO at 0.2%∼0.3% of volume fraction could significantly improve the tensile strength, elastic modulus and toughness, increase the melt viscosity, refine the spherulitic size, and rough the fracture morphology of P(3HB‐co‐4HB)/nano‐ZnO composites. Based on the effective aspect ratio (ξ) from Halpin‐Tsai model evaluation, the optimal dosage of nano‐ZnO for P(3HB‐co‐4HB)/nano‐ZnO composites was also at 0.2%∼0.3% of volume fraction. The Halpin‐Tsai equation was found to predict the experimental data most accurately for the P(3HB‐co‐4HB)/nano‐ZnO composites. POLYM. COMPOS., 37:3113–3121, 2016. © 2015 Society of Plastics Engineers     

聚丙烯腈原丝的凝固成形与相分离研究进展

以热力学相图为工具,探讨了聚丙烯睛(PAN)原丝凝固成形过程。从相图中原丝凝固成形的不同途径和相应的织态结构可以知道,原液体系以旋节方式分相是最佳的热力学路径。原丝凝固成形可以看作是浓度致变相分离(CIPS)和热致变相分离(TIPS)两种相分离形式的组合,通过后者得到高性能原丝要容易实现得多。可以根据相图来优化纺丝工艺条件,通过调节凝固浴浓度、纺丝液浓度、初始纺丝温度以及淬火深度.削弱CIPS过程在凝固成形中的作用,使凝固成彤尽可能多的以TIPS方式通过旋节线和双节线的交界处进行,以得到具有理想结构的优质的PAN原丝。     

Toughened electrospun nanofibers from crosslinked elastomer‐thermoplastic blends

A crosslink‐able elastomeric polyester urethane (PEU) was blended with a thermoplastic, polyacrylonitrile (PAN), and electrospun into nanofibers. The effects of the PEU/PAN ratio and the crosslinking reaction on the morphology and the tensile properties of the as‐spun fiber mats were investigated. With the same overall polymer concentration (9 wt %), the nanofiber containing higher composition of PEU shows a slight decrease in the average fiber diameter, but the tensile strength, the elongation at break and tensile modulus of the nanofiber mats are all improved. These tensile properties are further enhanced by slight crosslinking of the PEU component within the nanofibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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     

In situ hybridization and characterization of fibrous hydroxyapatite/chitosan nanocomposite

Nano‐fibrous hydroxyapatite/chitosan (HA/CS) composites with HA contents of 0–70 wt % were prepared by in situ hybridization with a preprepared chitosan film as semipermeable membrane to slow down the hybridization process. The phase composition, microstructure, and morphology of the composites were characterized by means of Fourier transform infrared spectroscopy, X‐ray diffraction, and high‐resolution transmission electron microscopy. It was found that the in situ prepared inorganic phase was hydroxyapatite nano‐fibers that were uniformly dispersed in the chitosan matrix. The average diameter of the fibers were about 3 nm, while the length of the fibers increases from 20 to 60 nm when the hydroxyapatite content increased from 10 to 70 wt %. The compressive strength and Young's modulus of these nano‐fibrous HA/CS composites increased with the increasing HA content and reached the highest values of 170 and 1.7 GPa, respectively, at the HA content of 50–70 wt %, which were much higher than the values of samples prepared by coprecipitation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of poly(styrene butylacrylate) latex/nano‐ZnO nanocomposites

Poly(styrene butylacrylate) latex/nano‐ZnO composites were prepared by blending poly(styrene butylacrylate) latex with a water slurry of nano‐ZnO particles, and the effects of certain parameters, such as particle size, dispersant type, dispersing time and others, on the dispersibility, mechanical properties, ultraviolet (UV) shielding and near infrared (NIR) shielding were investigated with transmission electron microscopy (TEM), an Instron testing machine, dynamic mechanical analysis and ultraviolet‐visible‐near infrared (UV‐VIS‐NIR) spectrophotometry. TEM observation showed that dispersants with long chains are better than those with short chains at enhancing the dispersibility of nano‐ZnO particles in a matrix; extending dispersing time also improves the dispersibility of nano‐ZnO particles in a matrix. Instron tests showed that the nanocomposite polymers embedded with nano‐ZnO particles had much higher tensile strength than the corresponding composite polymers with micro‐ZnO particles. As the nano‐ZnO content increased, the temperature of glass transition (T_g) of the nanocomposite polymer embedded with 60 nm ZnO particles first increased then decreased, but 100 nm ZnO and micro‐ZnO particles seemed to have no influence on the T_g of the composite polymers. The better dispersibility of nano‐ZnO particles resulted in higher T_g values. Increasing nano‐ZnO content or dispersibility could enhance the UV shielding properties of the nanocomposite polymers, and 60 nm ZnO particles could more effectively shield UV rays than 100 nm ZnO particles. Micro‐ZnO particles basically had no effect on the UV absorbance of the composite polymers. A blue‐shift phenomenon was observed at 365 nm when nano‐ZnO particles were present in the nanocomposite polymers. NIR analysis indicated that as nano‐ZnO content increased, the NIR shielding of the nanocomposite polymers increased, but the NIR shielding properties seemed to be more influenced by particle size than by the nano‐effect. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1923–1931, 2003     

Mechanical and antibacterial properties of modified nano‐ZnO/high‐density polyethylene composite films with a low doped content of nano‐ZnO

Nano‐ZnO/high‐density polyethylene (HDPE) composite films were prepared via melt blending and a hot compression‐molding process. The properties, including ultraviolet absorption, mechanical and antibacterial properties of the films, and plasticizing behavior of the composites, were investigated. The results show that the absorbance in the ultraviolet region of the HDPE films was enhanced after the addition of modified nano‐ZnO to the HDPE matrix. Also, we found that improvement in the HDPE films of the tensile strength and elongation at break was achieved by the incorporation of modified ZnO nanoparticles up to 0.5 wt % in contrast with the original nano‐ZnO/HDPE composite films. Antibacterial testing was carried out via plate counting, and the results indicate that the HDPE films doped with modified ZnO nanoparticles showed favorable antibacterial activity, especially for Staphylococcus aureus. However, the low doped content of modified nano‐ZnO in the HDPE matrix made the balance torque of the composites increase slightly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology,reversible phase crystallization,and thermal sensitive shape memory effect of cellulose whisker/SMPU nano‐composites

To investigate the morphology, crystallization properties of reversible phase and thermal sensitive shape memory properties of CW/SMPU (Cellulose Whisker/Shape Memory Polyurethane) nano‐composite, the CW/SMPU nano‐composite having CW contents of 0.1–3.8 wt % were prepared. SEM investigation showed the evolution of reversible phase morphology from spherolite crystallization structure to uniform matrix with tiny CW aggregates with the addition of CW into the SMPU matrix. DSC and isothermal crystallization kinetic method revealed the effect of CW on crystallization properties of reversible phase and fixed phase, suggesting that the effect of CW on the crystallization of hard segment phase is not comparable with thermal history; the more CW causes the higher crystallization rate of reversible phase; the crystallization mechanism of reversible phase in nano‐composite gradually evolves to heterogeneous nucleation and crystal growth in two dimensions with the increase of CW content; the excellent nucleation effect of CW for the reversible phase leads to the drop of activity energy from 134.1 kJ/mol (N‐0), to 95.1 kJ/mol (N‐4). Cyclic tensile tests illustrate the addition of CW content can engender rapid shape fixity ability after a relative short cooling time; the shape fixity ratio of nano‐composite and the control sample after sufficient cooling all can be identically high. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of nano‐silica filler on the rheological and morphological properties of polypropylene/liquid‐crystalline polymer blends

A fumed hydrophilic nano‐silica‐filled polypropylene (PP) composite was blended with a liquid‐crystalline polymer (LCP; Rodrun LC5000). The preblended polymer blend was extruded through a capillary die; this was followed by a series of rheological and morphological characterizations. The viscosity of the PP matrix increased with the addition of the hydrophilic nano‐silica. At shear rates between 50 and 200 s^?1, the composite displays marked shear‐thinning characteristics. However, the incorporation of LC5000 in the PP composite eliminated the shear‐thinning characteristic, which suggests that LC5000 destroyed the agglomerated nano‐silica network in the PP matrix. Although the viscosity ratio of LCP/PP was reduced after the addition of nano‐silica fillers, the LCP phases existed as droplets and ellipsoids. The nano‐silicas were concentrated in the LC5000 phase, which hindered the formation of LCP fibers when processed at high shear deformation. We carried out surface modification of the hydrophilic nano‐silica to investigate the effect of modified nano‐silica (M‐silica) on the morphology of the PP/LC5000 blend system. Ethanol was successfully grafted onto the nano‐silica surface with a controlled grafting ratio. The viscosity was reduced for PP filled with ethanol‐M‐silica when compared to the system filled with untreated hydrophilic nano‐silica. The LC5000 in the (PP/M‐silica)/LC5000 blend existed mainly in the form of fibrils. At high shear rates (e.g., 3000 s^?1), the LC5000 fibril network was formed at the skin region of the extrudates. The exclusion of nano‐silica in the LC5000 phase and the increased viscosity of the matrix were responsible for the morphological changes of the LCP phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1484–1492, 2003     

成形条件对PAN原丝微孔结构及热性能的影响

将不同浓度的聚丙烯腈(PAN)原液在不同凝固浴温度下进行湿法纺丝,制得PAN原丝,再将PAN原丝在沸水浴中进行5倍拉伸。探讨了成形条件以及拉伸对PAN原丝微孔结构及热性能的影响。结果表明:当PAN纺丝原液质量分数为22%,凝固浴温度为10℃时,可以得到结构均匀致密的PAN原丝。PAN原丝经5倍拉伸后热分解温度降低,残留量减小。     

PAN原丝沸水收缩率影响因素的探讨

采用溶液聚合和湿法纺丝制备碳纤维用聚丙烯腈(PAN)原丝,探讨了共聚组成、凝固浴温度、凝固浴浓度、拉伸介质和热定型温度对PAN纤维沸水收缩率的影响。结果表明,采用二元共聚物丙烯腈/甲叉丁二酸的质量比为99/1,凝固浴温度为30℃、凝固剂中二甲基亚砜质量分数为70%,热定型温度为160℃,拉伸介质为加压饱和蒸汽时,制备的PAN原丝沸水收缩率最低。