Effect of spinning conditions on the mechanical properties of PA6/MWNTs nanofiber filaments

Carbon nanotube (CNT ) reinforced composite materials is a hot research issue now , but CNT/polymer composite nano-scale fibers still cannot be obtained readily, not mention to successfully prepare continuous CNTs/polymer composite nano-scale fiber filaments manufactured by electrospinning. In this paper, continuous filaments constructed of nano-scale PA6/MWNTs fibers in single-axis orientation were obtained by an improved wet-electrospinning technique. The effects of the concentrations of MWNTs, spinning speed and post-drawing on the mechanical properties of PA6/MWNTs nanofiber filaments were studied. The results show that when the concentrations of MWNTs is below 0.8 wt%, the increase of MWNTs content enhances the Young’s modules and breaking stress but reduces the breaking strain, while the breaking stress decreases when the MWNTs concentration exceeds 0.8 wt%. The Young’s modules and breaking stress increased as the spinning speed raised at the range of 1.8–9.0 m/min, but declined when the speed exceeded 9.0 m/min. The mechanical properties of the as-spun filaments can be improved by either dry or wet post-drawing, and the breaking stress of the wet post-drawn filaments was improved 2.64 times while that of the dry post-drawn filaments 2.28 times.     

TEMPO-oxidized cellulose nanofibril/poly(vinyl alcohol) composite drawn fibers

PVA/TOCN composite fiber with a weight ratio of 100:1 was prepared from a mixture of aqueous poly(vinyl alcohol) (PVA) solution and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-oxidized cellulose nanofibril (TOCN) dispersion using spinning, drawing, and drying processes. The as-spun PVA/TOCN composite fiber was further drawn, up to a draw ratio of 20 by heating at up to 230 °C. The maximum tensile modulus of the PVA/TOCN composite drawn fiber reached 57 GPa, remarkably higher than that of commercial PVA drawn fibers. Moreover, the PVA/TOCN composite drawn fiber had storage modulus higher than that of the PVA drawn fiber at each temperature in the range from 28 to 239 °C. Structural analyses showed that amorphous PVA regions in the composite drawn fiber were more oriented than those in neat PVA fiber after the addition of the small amount of TOCN used. These results indicate that TOCN elements were individually dispersed in the PVA matrix without aggregation and formed hydrogen bonds with amorphous PVA molecules in the composite drawn fiber.     

Physical modification of polypropylene. III. Novel morphology of polypropylene and poly(ethylene-co-vinyl alcohol) with epoxy blend fibers

In this study, the novel morphology of polypropylene (PP) and poly(ethylene-co-vinyl alcohol) (EVOH) blend fibers is described. More precisely, the blend fibers of PP–EVOH containing a small amount of EVOH (1, 3, 5, 7, and 9% by weight), with and without epoxy (1 wt %), have been melt-spun at a constant spinning velocity (500 m/min). For the as-spun fiber, both the initial modulus and the tenacity increased with the increase in the EVOH content. The blend fibers with three draw ratios (2, 3, and 4) drawn at room temperature. The scanning electron microscopic study showed that a draw ratio of 2 reveals little about the morphological changes, whereas a draw ratio of 4 showed a streak structure perpendicular to the fiber axis for PP–EVOH (91/9 wt %) blend fibers. In addition, epoxy (1 wt %) containing PP–EVOH (91/9 wt %) blend fiber showed latitudinal streaks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1049–1057, 1999     

Effect of spinning temperature and blend ratios on electrospun chitosan/poly(acrylamide) blends fibers

We report the formation of non-woven fibers without bead defects by electrospinning blend solutions of chitosan and polyacrylamide (PAAm) with blend ratios varying from 75 wt% to 90 wt% chitosan using a modified electrospinning unit wherein polymer solutions can be spun at temperatures greater than ambient up to 100 °C. Electrospinning at elevated temperature leads to further expansion of the processing window, by producing fibers with fewer defects at higher chitosan weight percentage in the blends. Effects of varying blend ratios, spinning temperatures, and molecular weights on fiber formation were studied and optimum conditions for formation of uniform non-woven fiber mats with potential applications for air and water filtration were obtained. Uniform bead-less fiber mats with fiber diameter as low as 307 ± 67 nm were formed by spinning 90% chitosan in blend solutions at 70 °C.     

Morphology and rheology of immiscible polymer blends filled with silica nanoparticles

The effect of silica nanoparticles on the morphology and the rheological properties of an immiscible polymer blend (polypropylene/polystyrene, PP/PS 70/30) was investigated. Two types of pyrogenic nanosilica were used: a hydrophilic silica with a specific surface area of 200 m²/g and a hydrophobic silica having a specific surface area of 150 m²/g. First, a significant reduction in the PS droplet volume radius, from 3.25 to nearly 1 μm for filled blends with 3 wt% silica, was observed. More interestingly, image analysis of the micrographs proved that the hydrophilic silica tends to confine in the PS phase whereas hydrophobic one was located in the PP phase and at the PP/PS interface (interphase thickness ≈ 100-200 nm). Furthermore, a migration of hydrophilic silica from PP phase toward PS domains was observed.An analysis of the rheological experimental data was based on the framework of the Palierne model, extended to filled immiscible blends. Due to the partition of silica particles in the two phases and its influence on the viscosity ratio, limited cases have been investigated. The rheological data obtained with the hydrophobic silica were more difficult to model since the existence of a thick interphase cannot be taken into account by the model. Finally, the hypothesis that hydrophilic silica is homogeneously dispersed in PS droplets and that hydrophobic silica is dispersed in PP matrix was much closer to the actual situation. It can be then concluded that stabilization mechanism of PP/PS blend by hydrophilic silica is the reduction in the interfacial tension whereas hydrophobic silica acts as a rigid layer preventing the coalescence of PS droplets.     

Effect of blend ratio on bulk properties and matrix-fibril morphology of polypropylene/nylon 6 polyblend fibers

Ternary blends of polypropylene (PP), nylon 6 (N6) and polypropylene grafted with maleic anhydride (PP/N6/PP-g-MAH) as compatibilizer with up to 50 wt% of N6 were investigated. PP-g-MAH content was varied from 2.5 to 10%. Blends of the two polymers PP/N6 (80/20) without the compatibilizer were also prepared using an internal batch mixer and studied. The ternary blends showed different rheological properties at low and high shear rates. The difference depended on the amount of N6 dispersed phase. Co-continuous morphology was observed for the blend containing 50% N6. This blend also exhibited higher viscosity at low shear rate and lower viscosity at high shear rates than the value calculated by the simple rule of mixture. At higher shear rates, viscosity was lower than that given by the rule of mixture for all blend ratios. An increase in viscosity was observed in the 80/20 PP/N6 blend after the concentration of the interfacial agent (PP-g-MAH) was increased. Polyblends containing up to 30% N6 could be successfully melt spun into fibers. DSC results showed that dispersed and matrix phases in the fiber maintained crystallinity comparable to or better than the corresponding values found in the neat fibers. The dispersed phase was found to contain fibrils. By using SEM and LSCM analyses we were able to show that the N6 droplets coalesced during melt spinning which led to the development of fibrillar morphology.     

Drawing behavior of polyblend fibers from polypropylene and liquid crystal polymers

Polyblend fibers were made from mixtures of polypropylene (PP) and thermotropic liquid crystal polymers (LCPs). The as-spun fibers were drawn to produce the oriented structure for the PP matrix. The LCPs were found to exist in thin and long fibrils in the as-spun fibers; after drawing, they were split into short fragments. From a simplified model whereby a single LCP fibril is embedded in a PP matrix fiber, it was calculated out that the length of the LCP fibril in the drawn fiber is directly proportional to the fibril diameter and tenacity, and is reversely proportional to the compressional stress on the fibril and the friction coefficient between the fibril and the surrounding matrix. With regard to the drawing conditions, it was found that a long length of the LCP fibrils can be preserved by increasing the drawing temperature, or by reducing the draw rate. The effect of two-stage drawing on the LCP phase morphology was also studied in the present work. © 1994 John Wiley & Sons, Inc.     

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.     

Fibers from polypropylene/nano carbon fiber composites

Fibers from polypropylene and polypropylene/vapor grown nano carbon fiber composite have been spun using conventional melt spinning equipment. At 5 wt% nano carbon fiber loading, modulus and compressive strength of polypropylene increased by 50 and 100%, respectively, and the nano carbon fibers exhibited good dispersion in the polypropylene matrix as observed by scanning electron microscopy.     

Orientation of multiwalled carbon nanotubes in composites with polycarbonate by melt spinning

A conductive polycarbonate (PC) composite containing 2 wt% multiwalled carbon nanotubes (MWNT) and pure PC were melt spun using a piston type spinning device. Different take-up velocities up to 800 m/min and throughputs leading to draw down ratios up to 250 were used. The composite material of PC with MWNT was prepared by diluting a PC based masterbatch consisting of 15 wt% MWNT by melt mixing in an extruder. The alignment of the nanotubes within melt spun fibers with draw down ratios up to 126 was investigated by TEM and Raman spectroscopy. The nanotubes align in their length axis along the fiber axis increasingly with the draw down ratio, however, the curved shape of the nanotubes still exist in the melt spun fibers. At higher draw down ratios, the MWNT started to align by reducing their curvature. Polarized Raman spectroscopy indicated that the D/D and G/G ratios parallel/perpendicular to the fiber axis increase for both MWNT bands in a similar manner with the draw down ratio. Interestingly, with increasing alignment electrical conductivity of the fibers is lost. Mechanical investigations revealed that at low spinning speeds elongation at break and tensile strength of the composite are lower than those of the pure PC. However, at the highest take-up velocity of 800 m/min the elongation at break is higher and true stress at break of the composite fiber is comparable to the pure PC fiber.     

国产Z30S聚丙烯纺制细旦丙纶复丝的研究

研究了国产Ｚ３０Ｓ聚丙烯及其改性切片的分子量（ＭＷ）和分子量分布（ＭＷＤ）以及纺丝工艺对纺制细旦丙纶复丝可纺性和卷绕丝结构性质的影响。研究表明，采用Ｚ３０Ｓ切片即使纺丝温度高达２８０℃时，卷绕丝仍是α晶型结构，若添加少量降温母粒共纺或经改性后纺丝，卷绕丝可获得准晶型或混晶型结构，有较好的可纺性和后拉伸性；纺丝工艺条件，诸如纺丝温度、冷却条件、泵供量和纺丝速度等对卷绕丝的结构和性质虽起重要的影响，但ＰＰ的ＭＷ和ＭＷＤ则起首要的影响。     

Effect of organoclay on the morphology, phase stability and mechanical properties of polypropylene/polystyrene blends

The effect of organically modified clay on the morphology, phase stability and mechanical properties of polypropylene (PP) and polystyrene (PS) blends was studied using three molecular weight grades of PP. Maleated polypropylene was used, at a PP-g-MA/organoclay ratio of 1, to preferentially promote dispersion of the organoclay in the PP matrix. The MMT content was fixed at 3 wt% based on the PP/PP-g-MA/MMT phase and the PS content was varied from 0-100 wt% in the blend. All blends were processed using a twin screw extruder. The organoclay resides in the PP phase and at the PP/PS interface. The dispersed PS particle size is significantly reduced by the presence of MMT, with maximum decrease observed for the low viscosity PP compared to its blend without MMT. The blends with MMT did not show any change in onset of co-continuity, though MMT shifts the phase inversion composition toward lower PS contents. The phase stability of the blend was significantly improved by the presence of MMT; for blends annealed at 210 °C for 2 h the dispersed phase particle size increased by as much as 10x without MMT with little change was noted with MMT present in the blend. The tensile modulus of blends improved with the addition of MMT at low PS contents. Blends based on the highest molecular weight grade PP showed increase in the tensile yield stress up to 40 wt% PS in the absence of MMT. The tensile strength at break for blend increased slightly with MMT while elongation at break and impact strength decreased in the presence of MMT. Surface energy analysis model was used to predict the orientation and equilibrium position of the clay platelet at the interface based on the surface energies.     

β晶相聚丙烯纤维的纺制及其性能的研究

本文研究了纺丝冷却条件对β晶相聚丙烯初生纤维中β晶相含量的影响和拉伸工艺条件与制得纤维的结构及其性质的关系。研定表明,纺丝冷却速率是纺制含β晶相聚丙烯纤维的关键工艺因素,初生纤维中的K值、拉伸温度和拉伸倍数是纺制含微孔聚丙烯纤维的主要参数。用密度法、压汞法证实制得纤维具有微孔结构,其平衡吸湿率比普通浆丙烯纤维有明显的提高。     

The morphology and mechanical properties of dynamic packing injection molded PP/PS blends

As a part of long-term project aimed at super polyolefin blends, in this work, we report the mechanical reinforcement and phase morphology of the immiscible blends of polypropylene (PP) and polystyrene (PS) achieved by dynamic packing injection molding (DPIM). The shear stress (achieved by DPIM) and interfacial interaction (obtained by using styrene-butadiene-styrene (SBS) as a compatibilizer) have a great effect on phase morphology thus mechanical properties. The shear-induced morphology with core in the center and oriented zone surrounding the core was observed in the cross-section areas of the samples. The phase inversion was also found to shift towards lower PS content under shear stress, at 70 wt% in the core and 30 wt% in the oriented zone, compared with 80 wt% for static samples (without shear). The tensile strength, tensile modules and impact strength were found largely increase by means of either shear stress or compatibilizer. The PS particle size is greatly reduced with adding of SBS, and the reduced particle size results in greater resistance to deformation, which causes the co-continuous structure at oriented zone change into droplet morphology. The morphology resulting from blending and processing was discussed based on effect of interfacial tension, shear rate, phase viscosity ratio and composition. The observed change of mechanical properties was explained based on the combined effect of phase morphology (droplet-matrix or co-continuous phase) and molecular orientation under shear stress.     

Radial crystallization difference of melt-spun polypropylene fiber along spinning line

The radial crystallization difference of polypropylene (PP) fiber along spinning line was investigated via synchrotron radiation microbeam X-ray diffraction (μ-XRD) analysis for the first time. Running fibers were collected at different spinning line positions to study its radial crystallization difference. The distribution of crystallinity, crystal form, and crystal size of PP fiber were obtained based on peak deconvolution. The relation between radial crystallization difference and processing condition was also investigated. The results indicate that the crystallinity of PP in the center region is found higher than the surface due to the radial temperature gradient during melt spinning, and the structure of fiber is highly sensitive to the radial temperature gradient. The crystallinity increased along spinning line and reaches a steady rate after 50 cm of spinning line position. The crystallite size increased before 50 cm of spinning line position and has a slight decrease after 50 cm due to the growth and splitting of crystal. These results display a 2D view of crystallization development of fiber during the melt spinning and give us a basic knowledge about the relation between structure evolution and processing conditions both in axis and radial directions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47175.     

Rheological behavior of polyester blend and mechanical properties of the polypropylene–polyester blend fibers

The article deals with method of preparation, rheological properties, phase structure, and morphology of binary blend of poly(ethylene terephthalate) (PET)/poly(butylene terephthalate) (PBT) and ternary blends of polypropylene (PP)/(PET/PBT). The ternary blend of PET/PBT (PES) containing 30 wt % of PP is used as a final polymer additive (FPA) for blending with PP and subsequent spinning. In addition commercial montane (polyester) wax Licowax E (LiE) was used as a compatibilizer for spinning process enhancement. The PP/PES blend fibers containing 8 wt % of polyester as dispersed phase were prepared in a two‐step procedure: preparation of FPA using laboratory twin‐screw extruder and spinning of the PP/PES blend fibers after blending PP and FPA, using a laboratory spinning equipment. DSC analysis was used for investigation of the phase structure of the PES components and selected blends. Finally, the mechanical properties of the blend fibers were analyzed. It has been found that viscosity of the PET/PBT blends is strongly influenced by the presence of the major component. In addition, the major component suppresses crystallinity of the minor component phase up to a concentration of 30 wt %. PBT as major component in dispersed PES phase increases viscosity of the PET/PBT blend melts and increases the tensile strength of the PP/PES blend fibers. The impact of the compatibilizer on the uniformity of phase dispersion of PP/PES blend fibers was demonstrated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4222–4227, 2006     

A comparative study of in-situ composite fibers reinforced with different rigid liquid crystalline polymers

Poly(ethylene terephthalate) (PET) and 2 thermotropic liquid crystalline polymers (LCPs) with different chain rigidity were blended to make in-situ composite fibers on a conventional melt spinning equipment. The addition of the LCP-1 (60PHB–PET) with a less rigid chain has been found to lower the orientation of the as-spun fibers while the LCP-2 (VectraA900) with whole aromatic rigid chain has a reverse effect, as evidenced from the birefringence results. Both kinds of composite fibers with 5 wt % LCP have a good drawability. There is a diffraction peak characteristic of intermolecular packing of LCP on the wide-angle X-ray diffraction curve for the as-spun fibers containing LCP-2 but not the case for LCP-1. The morphology formed during elongational flow is highly dependent on the composition and rigidity of LCP. For the dispersed phases of LCP-1, it is relatively difficult to be elongated, whereas LCP-2 dispersed phases will be easily deformed into fibrils during melt spinning. The mechanical properties of the blend fibers containing the LCP-1 component are inferior to those containing the LCP-2 component. For the fibers with discontinuous fibril morphology, a Halpin–Tsai equation could well be used to describe the elastic modulus of in-situ composite fiber with LCP-2. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1035–1045, 1998     

Fabrication of high strength PVA/SWCNT composite fibers by gel spinning

High-strength composite fibers were prepared from polyvinyl alcohol (PVA) (Degree of polymerization: 1500) reinforced by single-walled carbon nanotubes (SWCNTs) containing few defects. The SWCNTs were dispersed in a 10 wt.% PVA/dimethylsulfoxide solution using a mechanical homogenizer that reduced the size of SWCNT aggregations to smaller bundles. The macroscopically homogeneous dispersion was extruded into cold methanol to form fibers by gel spinning followed by a hot-drawing. The tensile strength of the well-oriented composite fibers with 0.3 wt.% SWCNTs was 2.2 GPa which is extremely high value among PVA composite fibers ever reported using a commercial grade PVA. The strength of neat PVA fibers prepared by the same procedure was 1.7 GPa. Structural analysis showed that the PVA component in the composite fibers possessed almost the same structure as that of neat PVA fibers. Hence a small amount of SWCNTs straightforward enhanced by 0.5 GPa the tensile strength of PVA fibers. The results of mechanical properties and Raman spectra for the SWCNT composites suggest the relatively good interfacial adhesion of the nanotubes and PVA that improves the load transfer from the polymer matrix to the reinforcing phase.     

Crystallization and orientation studies in polypropylene/single wall carbon nanotube composite

Crystallization behavior of melt-blended polypropylene (PP)/single wall carbon nanotube (SWNT) composites has been studied using optical microscopy and differential scanning calorimetry. Polypropylene containing 0.8 wt% SWNT exhibits faster crystallization rate as compared to pure polypropylene. PP/SWNT fibers have been spun using typical polypropylene melt spinning conditions. The PP crystallite orientation and the SWNT alignment in the fibers have been studied using X-ray diffraction and polarized Raman spectroscopy, respectively.     

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10 wt%) and failed doing so for those of which the dispersed contents were high (30 wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30 wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palierne model. A methodology was developed to use Palierne emulsion model upon taking into account the effects of the EE structure on the viscosity of the continuous phase and the effective volume fraction of the dispersed phase.