The non-uniform phase structure in blend fiber. II. The migration phenomenon in melt spinning

The migration phenomenon was investigated in polypropylene/polystyrene (PP/PS) blend fiber and low density polyethylene/polyamide 6 (LDPE/PA6) blend fiber. The migration of fibrils in melt spinning was evaluated by the variation of fibrils’ area ratio over the cross section of blend fiber. In PP/PS blend fiber, the dispersed PS deformed into many highly oriented fibrils in the PP matrix, and PS fibrils migrated towards the surface of the take-up fiber in the fiber spinning process. On the contrary, PA6 fibrils migrated into the core of the take-up fiber, while the dispersed PA6 deformed into many highly oriented fibrils in the LDPE matrix for LDPE/PA6 blend fiber. Otherwise, no migration phenomenon was observed in the special fiber that was prepared without any drawing, neither in PP/PS nor in LDPE/PA6. Therefore, in the fiber spinning process, the migration phenomenon actually occurred mainly in the drawing process, which is the non-isothermal uniaxial extensional flow. Comparing with migration mechanisms in the shear flow, the migration phenomenon in melt spinning was probably due to the radial non-uniform extensional stress, the extensional viscosity.     

The variation of fibrils’ number in the sea-island fiber -low density polyethylene/polyamide 6-

In melt spinning of low density polyethylene/polyamide6 (LDPE/PA6), fibrils’ number in LDPE/PA6 blend fiber is calculated at different take-up velocity. Firstly, PA6 fibrils are dispersed in the LDPE matrix in LDPE/PA6 blend fiber (55:45, weight ratio). The number of PA6 fibrils increases with an increase of the take-up velocity. Because the shorter processing time suppresses the coalescence at the high take-up velocity, it causes an increase of PA6 fibrils. Besides, the irregular shape of PA6 fibrils’ cross section also confirms fibrils’ coalescence. Secondly, LDPE fibrils are dispersed in the PA6 matrix in LDPE/PA6 blend fiber (6:94, weight ratio). However, the number of LDPE fibrils doesn’t change no matter how the takeup velocity is. In case of LDPE/PA6 (6:94) blend fiber, the low weight ratio of the dispersed LDPE causes the absence of fibrils’ coalescence, so fibrils’ number does not change. In conclusion, the variation of fibrils’ number implies the existence of the coalescence phenomenon in the fiber spinning process. The variation of fibrils’ number in the sea-island fiber is of practical importance for manufacturing the micro-fine fiber, and is a method to investigate the coalescence behavior in the extensional flow.     

Deformation of dispersed polystyrene droplets in immiscible polypropylene/polystyrene blend fibers under uniaxial elongational flow

The deformation of dispersed polystyrene (PS) droplets in immiscible polypropylene (PP) matrices during melt spinning of blend fibers were simulated by adopting the droplet deformation criteria. The ratios of number-average length to diameter were measured through morphology analysis, and compared with the simulated values. It was found that the adopted deformation models described the deformation behavior of the dispersed droplets during melt spinning very well. Dispersed droplets in the center of the fiber tend to be stretched longer than those of near to the surface, due to the radial temperature gradient during fiber formation. Moreover, combining with the rheological studies of raw materials, a theoretical relation between temperature and deformation was established and used to determine the radial temperature differences along the spinning line. It was found that the radial temperature gradients vary from 0.22 to 0.35 °C/μm at 40 cm beneath to the spinneret at the discussed take-up velocities.     

Studies on melt spinning of sea-island fibers. I. morphology evolution of polypropylene/polystyrene blend fibers

Isotactic polypropylene/atactic polystyrene (iPP/aPS) immiscible polymer blends are prepared and are melt-spun to prepare blend fibers with matrix-fibril morphologies. The running fibers are captured at different positions of the spinning line, and the morphologies including dispersions of aPS droplets in iPP matrix fibers, droplets diameter and their distributions, as well as the radial gradients on counts and diameter of droplets are analyzed. The effect of take-up velocity on the morphology of take-up fibers is discussed by comparing with that of extrudate fibers. At low take-up velocities, the enhanced radial gradients are attributed to shrinking of matrix fibers on the elongation of spinning stress. While the effects of non-uniform deformation, coalescence and migration of droplets play a role to resist the effects of shrinking of matrix fibers at high take-up velocities. Based on morphology analysis, the mechanisms of compression from the shrinking of matrix fibers, non-uniform deformation, coalescence and migration of droplets are presented to explain why and how the radial gradients form.     

Study on the matrix-fibril morphologies of polypropylene/polystyrene blends under non-isothermal uniaxial elongational flow

Polypropylene/polystyrene blends with different viscosity ratios, p, ranging from 1.6×10^?2 to 10.8, were prepared by using textile-grade isotactic polypropylene (iPP) and five kinds of atactic polystyrene (aPS), named PS1, PS2, PS3, PS31 and PS46 with different molecular weight, and then melt-spun into composite fibers with matrix-fibril morphology at different take-up velocities, v _L , ranging from 125 to 1000 m/min. The effects of p on the diameters and quantities of dispersed droplets in extrudate fibers, and the effects of p and v _L on the size and quantities of fibrils in take-up fibers were discussed, respectively. Based on a quantitatively characterization for the coalescence and deformation of droplets during melt spinning, a theoretical analysis based on Newtonian fluids simplification and the deformation theory was presented to predict the deformation and breakup of droplets during melt spinning. It is found that there is a good fit between theoretical and observed experimental results at most discussed take-up velocities. Furthermore, the uncertainties of Newtonian fluids simplification and a hypothesis of local energy dissipation from migration and coalescence were noted to explain the deviations between predicted and experimental data.     

Matrix-fibril morphology development of polypropylene/poly(butylenes terephthalate) blend fibers at different zones of melt spinning process and its relation to mechanical properties

Different shapes of dispersed phase such as sphere, laminar and fibrillar can form in the matrix phase of polymer blends. Production of blend fibers in melt spinning process can result more effective in fibrillar phase morphology formation than in other processes. In this research, the matrix-fibril morphology development during the melt spinning of polypropylene/poly(butylenes terephthalate) was studied. The shapes of blend dispersed phase collected from different zones of the melt spinning line were evaluated by scanning electron micrographs (SEM) and rheological mechanical spectra (RMS). The results showed that fibrillar shape could not be created in the PP/PBT blend fiber samples exited from the spinneret orifice (gravity spun fibers) at low contents (5 percent) of the PBT dispersed phase. However, a complete fibrillar structure was formed in all the as-spun PP/PBT blend fiber samples (melt drawn). The rheological evaluations confirmed a network structure resulting from fibril formation for the samples with high contents (20–40 %) of the PBT dispersed phase and the formation of spherical shape with low contents (5–10 %) of the PBT dispersed phase in matrix of the blend fibers. It was observed that the flow fields of processing zones and blend ratio, in producing the blend fibers, have intensive effects on morphological variations; besides there was a strong relation between the mechanical and morphological properties.     

Optimizing the morphology,mechanical and crystal properties of in-situ polypropylene/polystyrene blends by reactive extrusion

In this study, in-situ polypropylene/polystyrene (PP/PS) blends were prepared via a reactive extrusion technique. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the generation of polypropylene-grafted-polystyrene (PP-g-PS) copolymer in the reactive process. The morphology of the in-situ PP/PS blend tended to form a homogeneous structure, as observed by scanning electron microscopy (SEM). Owing to the introduction of PP-g-PS in the reactive extrusion, a remarkable enhancement of mechanical properties was achieved for the in-situ PP/PS blend. The elongation at break of the in-situ PP/PS blend with 15 wt% PS can reach 500 %, over 10 times higher than that of the normal PP/PS blend. Differential scanning calorimetry (DSC) showed an increased crystallization temperature of PP, which can be attributed to the heterogeneous nucleation effect of the PS and grafted PS. The analysis of wide angle X-ray diffraction (WAXD) indicated the development of beta crystals in the in-situ PP/PS blend.     

Effect of chemical softening of coconut fibres on structure and properties of its blended yarn with jute

Coconut fibres were subjected to chemical treatment to obtain softer and finer fibres, suitable to blend with other finer fibre like jute. The chemical softening recipe was optimized using Box-Behnken design of experiments as 40 % Na₂S, 10 % NaOH and 6 % Na₂CO₃, which notably reduced the fineness (33 %) and flexural rigidity (74 %) and improved tensile property of coconut fibre. Effect of softening of coconut fibre on its process performance was studied in high speed mechanized spinning system at different blend ratios with jute. Blending with jute assists in spinning of coconut fibre to produce yarn of 520 tex at production rate of 5-6 kg/h, as compared to 15 kg/day for hand spun 5300 tex raw coconut fibre yarn in manual system. Analysis of blended yarn structure in terms of packing density, radial distribution of fiber components (SEM) and mass irregularity were investigated. SEM shows yarns made from softened coconut fibre -jute blends are more compact than raw coconut fibre -jute blend yarns. Coconut fibres were preferentially migrated to core of the yarn. Major yarn properties viz., tensile strength, and flexural rigidity of raw and chemically softened blended yarns were compared against their finest possible 100 % coconut fibre yarn properties. Yarn made up to 50:50 chemically softened coconut fibre-jute blend showed much better spinning performance, and having superior property in terms of reduced diameter, higher compactness, strength, initial modulus and less flexural rigidity than 100 % raw, 100 % chemically softened coconut fibre rope, and raw coconut fibre-jute blend yarns.     

Air-gap spinning of cellulose/ionic liquid solution and its characterization

In order to study the effects of the spinning conditions on the structure and the properties of the regenerated fiber, cellulose was dissolved in ionic liquid and then spun into fiber using an air-gap spinning process. The solution concentration, the take-up speed and the fixation of the fiber ends during coagulation improved the crystallinity and the tensile strength at the same time. The fiber surface became smooth by addition of DMF (dimethylformamide). However, it decreased the crystallinity and the tensile strength of the fibers. We revealed that the developed structure during coagulation determined the morphology and the properties of the fibers. The co-solvent resulted in smooth surface of the fiber and also changed the mechanical properties.     

Investigating the effect of various blend ratios of prepared masterbatch containing Ag/TiO2 nanocomposite on the properties of bioactive continuous filament yarns

In this research, possibility of producing and processing antibacterial organic/inorganic nanocomposite polypropylene filament yarns for permanent antimicrobial efficiency has been investigated. First PP powder and inorganic nanocomposite filler were mixed in a twin screw extruder and modified masterbatch was produced. Continuous filament yarn was made by a pilot plant melt spinning machine from the blend of PP granule and various blending contents of the prepared masterbatch. Pure PP and all other combined samples showed acceptable spinnability at the spinning temperature of 240 °C and take-up speed of 2000 m/min. After producing as-spun filament yarns, samples were drawn, textured and finally weft knitted. Physical and structural properties of as-spun and drawn yarns with constant and variable draw ratios were investigated and also tensile and crimp properties of textured yarns were evaluated. Moreover, the DSC, SEM, FTIR techniques have been used for characterization of samples. Finally antibacterial efficiency of knitted samples was evaluated. The experimental results indicated that the maximum crystallinity reduction of modified drawn yarns has reached to 5 %. The observed improvement in the tensile properties of modified as-spun yarns compared to the pure PP was significant. Drawing process improved generally the tensile properties of as-spun yarns. Tensile properties of modified textured and drawn yarns were higher than the pure PP. An optimum of antibacterial activity has been observed in the sample containing 0.75 wt% of nano-filler. It is interesting that the optimum of tensile properties has been also obtained for the sample with maximum bioactivity.     

Structure and properties of syndiotactic polystyrene fibers prepared in high-speed melt spinning process

High-speed melt spinning of syndiotactic polystyrene was carried out using high and low molecular weight polymers, HMs-PS and LMs-PS, at the throughput rates of 3 and 6 g/min. The effect of take-up velocity on the structure and properties of as-spun fibers was investigated. Wide angle X-ray diffraction (WAXD) patterns of the as-spun fibers revealed that the orientation-induced crystallization started to occur at the take-up velocities of 2–3 km/min. The crystal modification wasα-form. Birefringence of as-spun fibers showed negative value, and the absolute value of birefringence increased with an increase in the take-up velocity. The cold crystallization temperature analyzed through the differential scanning calorimetry (DSC) decreased with an increase in the take-up velocity in the low speed region, whereas as the melting temperature increased after the on-set of orientation-induced crystallization. It was found that the fiber structure development proceeded from lower take-up velocities when the spinning conditions of higher molecular weight and lower throughput rate were adopted. The highest tensile modulus of 6.5 GPa was obtained for the fibers prepared at the spinning conditions of LMs-PS, 6 g/min and 5 km/min, whereas the highest tensile strength of 160 MPa was obtained for the HMs-PS fibers at the take-up velocity of 2 km/min. Elongation at break of as-spun fibers showed an abrupt increase, which was regarded as the brittle-ductile transition, in the low speed region, and subsequently decreased with an increase in the take-up velocity. There was a universal relation between the thermal and mechanical properties of as-spun fibers and the birefringence of as-spun fibers when the fibers were still amorphous. The orientation-induced crystallization was found to start when the birefringence reached — 0.02. After the starting of the orientation-induced crystallization, thermal and mechanical properties of as-spun fibers with similar level of birefringence varied significantly depending on the processing conditions.     

Comparison of the structure-property relationships for PTT and PET fibers spun at various take-up speeds

A comparison of poly(trimethylene terephthalate)(PTT) and poly(ethlene terephthalate)(PET) fibers spun at various take-up speeds was presented. Fiber characterization included tensile and thermal properties, optical birefringence, density, sonic modulus, boil-off shrinkage, and wide-angle X-ray diffraction. The phenomenon of stress-induced crystallization was inferred from the X-ray diffraction diagrams for fibers spun with take-up speeds over 4000 m/min. The tenacity and elongation of PTT and PET fiber showed typical results, but the initial modulus of PTT fiber was nearly unchanged over the entire take-up speed range (2000–7000 m/min), whereas that of PET, as expected, increased monotonically with increasing take-up speed. This divergent behavior could be explained by the different molecular deformations in the c-axis as determined from X-ray diffraction patterns. The fiber crystallinity, density, and heat of fusion of both polymers increased with take-up speed. The boil-off shrinkage decreased with increasing take-up speed. The optical birefringence of the two fiber types showed a maximum level at a take-up speed of ca. 5000 m/min. The melting temperature behavior of PTT fiber was different from that of PET fibers. It was found that PTT is less sensitive to stress induced changes at high spinning speeds than is PET.     

Characterization of PET/PP blend fiber and it’s application to wig

As PET (Polyester) fiber has better heat resistance than PVC fiber or modacryl fiber, it has been used as wig fiber for human hair alternatives. However, PET is heavier and has higher specific gravity than human hair, and therefore the authors attempted to make lighter wig fiber by blending PP (polypropylene) into PET by mixing the PET/PP blend with a compatibilizer, a ethylene-acrylic ester-GMA(EAG) component grafted material, to overcome poor compatibilities of PET and PP. The thermal properties of the PET/PP blend mixed with EAG were measured using DSC, and the results showed that EAG affected melting point and crystallization temperature of the blend polymer. As blend ratio of PP increased, specific gravity of blend fiber reduced and thermal shrinkage rate increased. Blend ratio of PP was greater for shorter lengths of initial curl, although curl loosening increased as time elapsed.     

Fabrication of long and discontinuous natural fiber reinforced polypropylene biocomposites and their mechanical properties

Natural fiber reinforced polypropylene (PP) biocomposites were fabricated by blending long-and-discontinuous (LD) natural fibers (NF) with LD PP fibers. Firstly, random fiber mats were prepared by mixing NFs and PP fibers using a carding process. Then, heat and pressure were applied to the mats, such that the PP fibers dispersed in the mats melted and flowed out, resulting in the formation of consolidated sheets upon subsequent cooling. The effect of the fiber volume fraction on the mechanical properties of the bio-composites was scrutinized by carrying out tensile and flexural tests and observing the interface between the fiber and matrix. It was observed that the natural LD fiber content needs to be maintained at less than the nominal fiber fraction of 40 % by weight for the composites fabricated using the current method, which is quite low compared to that of continuous or short fiber reinforced composites. The limited fiber fraction can be explained by the void content in the biocomposites, which may be caused by the non-uniform packing or the deficiency of the matrix PP fibers.     

Interfacial localization of multiwalled carbon nanotubes in immiscible blend of poly(ethylene terephthalate)/polyamide 6

In this study, multiwalled carbon nanotubes (MWCNTs) were confined or localized in an immiscible blend of poly(ethylene terephthalate)/polyamide 6 (PET/PA6). A co-rotating twin-screw extruder and melt-compounding were used to prepare nanocomposites of PET/PA6 (60/40, w/w) and MWCNTs with various MWCNT contents in the range 0.001–2 phr. The raw, unfunctionalized MWCNTs were used as fillers. A remarkable change in the morphology of the blend happened on the basis of the amount of MWCNTs added to the blend: the PET phase converted into the PA6 phase at a certain MWCNT content. Although the PA6 phase was formed as a domain phase in the PET matrix in blends containing less than 0.01 phr of MWCNTs, the PET phase suddenly became discontinuous because of phase conversion in the PA6 matrix in blends containing 0.01 and 0.05 phr of MWCNTs. In the blends containing more than 0.1 phr of MWCNTs, the initial morphology was recovered, that is, the PET phase became the matrix phase again. Moreover, in the recovered state, the of the PA6 domain was much larger in the blends containing more than 0.1 phr of MWCNTs than it was in the composites that did not contain any MWCNTs and in those that contained 0.001 phr of MWCNTs. The MWCNTs, on the other hand, selectively located at the interface of the PET and PA6 phases. The rheological, electrical, and crystallization behaviors of the blends were also investigated to study the effects of the concentration of MWCNTs on the structure of the prepared composites.     

Effect of polystyrene mixing on mechanical properties and structural changes in melt spinning

To increase the spinning speed of poly(trimethylene terephthalate) (PTT) fibers, polystyrene (PS) was selected as an additive polymer in the PTT matrix. Mixing of the immiscible PS with PTT led to an increase in spinning speed up to 5,500 m/min. PS was employed to improve the extensibility of the matrix PTT in the spinning process as it can prevent PTT molecular orientation. Experimental results show that the mixing of PS achieved this. The elongation at break of spun fibers increased with the amount of PS. PS addition prevented fiber orientation, especially amorphous orientation, and improved drawability, and as such, increased spinning speed up to 5,500 m/min.     

Modification and properties of polypropylene fibers using aluminosiloxane

Siloxylated polypropylene fibers composed of polypropylene (PP) and aluminosiloxane (AS) were prepared by melt blending followed by spinning. The effects of blend compositions on the thermal behaviors, surface and tensile properties of PP/AS blend fibers were investigated by DSC, WAXD, SEM, static honestometer, etc. The heat of fusion of PP/AS blends decreased with increasing AS contents. In addition, the peak intensity of PP/AS blends in X-ray diffraction patterns decreased with increasing AS contents. It was observed that the silicone molecules exist and well distribute on the surface of siloxylated polypropylene fibers. From the results of the half-life period measurements, the anti-static properties of PP fibers siloxylated with AS was found to be significantly modified.     

Spinnability in pre-gelled gel spinning of polyacrylonitrile precursor fibers

The spinnability in pre-gelled gel spinning of polyacrylonitrile (PAN) precursor fibers was investigated. The spinning solutions were aged at 25 °C for different times prior to fiber spinning. The pre-gelled spinning solution aged for 2.5 h was much more strain hardening than the ungelled one, which can increase the spinnability of the solution. The maximum take-up velocity of the first winding roller V _1m, which reflects the spinnability of the spinning solutions, was found to be largest when the aging time was 1.5 h. The spinnability increased with the increase of the air gap length and the lengthdiameter ratio L/D of the spinnerette. Once the L/D increased beyond 15, the spinnability hardly changed. The fibers spun from the spinning solution aged for 1.5 h had the best mechanical properties and favorable structure, showing that good spinnability favors the performance increase of resultant PAN precursor fibers.     

Investigation on the physical and structural properties of melt-spun multifilament yarns,drawn yarns and textured yarns produced from blend of PP and oxidized PP

In the present study, effect of OPP (oxidized PP) fraction on the mechanical and structural properties of produced fibers is investigated. Polypropylene powder without antioxidant materials was oxidized at the suitable thermal condition. The various fractions of OPP were blended with PP in the chips shape, and employed as starting material in a melt spinning machine for production of filament yarn. Then as-spun filaments were drawn and finally textured. Structural properties including density, birefringence and FTIR and physical properties consisting of shrinkage, tensile properties and crimp properties were measured. Results show that blending of OPP with virgin PP reduces tacticity and crystallinity, but it hasn’t any effect on orientation. Physical properties of drawn yarns and textured yarns were reduced with increasing of OPP fraction. Moreover, increasing of OPP fraction in blend, reduce crimp properties of textured yarn.