Effects of the coagulation temperature on the properties of wet‐spun poly(vinyl alcohol)–graphene oxide fibers

Graphene oxide (GO) as a positive reinforcement filler was dispersed into a poly(vinyl alcohol) (PVA) dope and wet‐spun into composite fibers. The effects of two EtOH coagulation baths maintained at ?5 and 25 °C, respectively, on the morphology, structure, and mechanical properties of the composite fibers were investigated. The results show that gel spinning at ?5 °C led to a relatively large shrinkage ratio, thin diameter, and low porosity of the as‐spun fibers. Simultaneously, the low coagulation temperature also greatly contributed to the formation and preservation of the liquid‐crystalline phase of the GO sheets and interrupted the crystalline zone of PVA less. As a result, either the tenacity or the elongation at break of the fibers spun at ?5 °C was higher than those of the fibers spun through a coagulation bath at 25 °C. In particular, 1 wt % GO showed the highest reinforcement effects among all of the wet‐spun composite fibers. Hence, controlling the gelling–demixing process at a low temperature will provide more instructive insights for tailoring functional industrial textiles with excellent mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45463.     

Simultaneously improving tensile strength and toughness of melt‐spun β‐nucleated isotactic polypropylene fibers

Polymer processing methods generally play a crucial role in determining the development of microstructure in the fabricated product. In this study, isotactic polypropylene (iPP) melt containing 0.05 wt % β‐nucleating agent (β‐NA) was extruded via a melt flow rate indicator. The molten extrudate was stretched into a fiber upon various take‐up velocities (TVs). The microstructures of the fiber were investigated by differential scanning calorimeter, two‐dimensional wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering. Also, its tensile properties (including tensile strength, modulus, elongation at break, and toughness) were measured by tensile test. Interestingly, the tensile strength (135.0 MPa) of a melt‐spun β‐nucleated iPP fiber fabricated at 400 cm/min was enhanced by 115.2%, compared with that (62.7 MPa) prepared at 100 cm/min, with a considerable increment in toughness (from 661 to 853 MJ/m³). The enhancement mechanism for tensile properties was discussed based on the microstructures. This work offers a simple approach to prepare β‐nucleated iPP fibers with excellent strength and toughness. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43454.     

Effect of process parameters on properties of wet‐spun poly(L,D‐lactide) copolymer multifilament fibers

Poly(L,D ‐lactide) [P(L,D )LA], LL/D ratio 96/4, and poly(L,DL ‐lactide) [P(L,DL )LA], L/DL ratio 70/30, multifilament fibers were prepared by wet‐spinning and the effects of the spin draw ratio and the coagulant on the morphological, thermal, and mechanical properties of the filaments were studied. The hydrolytic degradation of filaments was studied in vitro. The filament diameter and the mechanical properties of filaments were highly dependent on the spin draw ratio, whereas the coagulant had no or minor effect. The filament diameters were in the range of 11–36 μm and the maximum tenacity of 150 MPa was obtained at the spin draw ratio of 7.0 for both copolymers. The copolymer had the main importance on the crystallinity of filaments, but it was also affected by the duration of the coagulation process. The crystallinities of P(L,D )LA 96/4 filaments were in the range of 5–16%, whereas P(L,DL )LA 70/30 filaments were totally amorphous. The degree of crystallinity had effect on the hydrolytic degradation of filaments. The tenacity loss of P(L,D )LA 96/4 filaments was about 10% and that of P(L,DL )LA 70/30 filaments was as high as 50% after 24 weeks in vitro. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of hot drawing on properties of wet‐spun poly(L,D‐lactide) copolymer multifilament fibers

Polylactide stereocopolymer multifilament fibers were prepared by wet spinning and subsequent hot drawing. The stereocopolymers were poly‐(L,D ‐lactide) [P(L,D )LA], L/D ratio 96/4, and poly‐(L,DL ‐lactide) [P(L,DL )LA], L/DL ratio 70/30. They were dissolved in dichloromethane and coagulated in a spin bath containing ethanol. The hot‐drawing temperature was 65°C. The draw ratios (DR) were upto 4.5 to the P(L,D )LA 96/4 filaments and upto 3 to the P(L,DL )LA 70/30 filaments. Wet spinning decreased crystallinities of both copolymers. Hot drawing increased the crystallinity of the P(L,D )LA 96/4 filament but not to the level of the original copolymer, whereas the as‐spun and the hot‐drawn P(L,DL )LA 70/30 filaments were amorphous. The filament diameter, tenacity, Young's modulus, and elongation at break were dependent on the DR. The maximum tenacity (285 MPa) and Young's modulus (2.0 GPa) were achieved with the P(L,D )LA 96/4 filament at the DR of 4.5. Respectively, the maximum tenacity of the hot‐drawn P(L,DL )LA 70/30 filament was 175 MPa and Young's modulus 1.3 GPa at the DR of 3. Hot drawing slowed down in vitro degradation rate of both stereocopolymer filaments. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of high‐performance poly(ether ether ketone) fibers with improved spinnability based on thermotropic liquid crystalline poly(aryl ether ketone) copolymer

High‐performance poly(ether ether ketone) (PEEK) fibers were prepared by melt‐spinning in the presence of thermotropic liquid crystalline poly(aryl ether ketone) copolymer (FPAEKLCP). The rheological and mechanical properties, birefringence, orientation, and crystallization of the resulting PEEK/FPAEKLCP fibers were characterized by using a melt flow indexer, capillary rheometer, single fiber electronic tensile strength tester, polarized light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD), respectively. The results indicate that the melt viscosity of PEEK significantly reduced by introducing FPAEKLCP, followed by the improvements in the spinnability and the quality of as‐spun fibers. The tensile properties of PEEK/FPAEKLCP fibers mainly depend on the content of FPAEKLCP, drawing temperature, drawing ratio, and annealing processes. Moreover, the tensile strength and modulus of PEEK/FPAEKLCP fibers are obviously higher than those of neat PEEK fibers under the same processing conditions. This should be attributed to an enhancement in the orientation and crystallization of PEEK compounded with FPAEKLCP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1406‐1414, 2013     

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.     

Chitin nanocrystal reinforced wet‐spun chitosan fibers

Chitosan (CS) has been extensively studied and found wide applications in the field of biomedicine because of its favorable biological properties. Normal CS fibers are manufactured either by wet‐spinning or by dry‐jet wet‐spinning. However, the poor tensile strength of CS fibers raises much concern. The present study uses chitin nanocrystal (ChiNC), a stiff rod‐like nanofiller, to enhance the mechanical properties of wet‐spun CS fibers. Owing to the good compatibility between CS and ChiNC, the nanoparticles are well distributed in the CS matrix. When the ChiNCs loading is 5 wt %, the optimal mechanical properties of CS fibers are obtained, and the peak stress is 2.2 cN/dtex and modulus is 145.6 cN/dtex, which are increased by 57% and 84.5%, respectively, compared to that of nonfilled CS fibers under the same processing condition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40852.     

Carbon fibers derived from wet‐spinning of equi‐component lignin/polyacrylonitrile blends

Equi‐component blends of polyacrylonitrile (PAN) and lignin, i.e., with a lignin content as large as 50 wt %, were successfully used as precursors to produce carbon fibers. Rheological measurements demonstrated that increasing lignin content in spinning solution reduced shear viscosity and normal stress, indicating a decrease of viscoelastic behavior. This was confirmed by Fourier transform infrared results that show no discernable chemical reaction or crosslinking between PAN and lignin in the solution. However, the resulting carbon fibers display a large I_D/I_G ratio (by Raman spectroscopy) indicating a larger disordered as compared to that from pure PAN. The macro‐voids in the lignin/PAN blend fibers typically generated during wet‐spinning were eliminated by adding lignin in the coagulant bath to counter‐balance the out‐diffusion of lignin. Carbon fibers resulting from lignin/PAN blends with 50 wt % lignin content displayed a tensile strength and modulus of 1.2 ± 0.1 and 130 ± 3 GPa, respectively, establishing that the equi‐component wet‐spun L/P‐based carbon fibers possessed tensile strength and modulus higher than 1 and 100 GPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45903.     

Preparation and properties of novel thermally stable pyridine‐based poly(amide imide amide)s

The 2,6‐bis(4‐nitrobenzamido)pyridine was prepared via reaction of 2,6‐diaminopyridine with two moles of 4‐nitrobenzoyl chloride in the presence of propylene oxide. Catalytic reduction of nitro groups of 2,6‐bis(4‐nitrobenzamido)pyridine with hydrazine yielded 2,6‐bis(4‐aminobenzamido)pyridine. Reaction of this diamine with two moles of trimellitic anhydride afforded a diacid with preformed amide and imide structures. Poly(amide imide amide)s were prepared by direct polycondensation reactions of the diacid with different diamines in the presence of triphenyl phosphite. All the precursors and polymers were fully characterized using common spectroscopic methods and elemental analysis and physical properties of the polymers including solution viscosity, thermal stability, thermal behavior, and solubility were studied. According to the obtained results the polymers showed high thermal stability and enhanced solubility. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Carbon fibers derived from UV‐assisted stabilization of wet‐spun polyacrylonitrile fibers

A rapid, dual‐stabilization route for the production of carbon fibers from polyacrylonitrile (PAN) precursor fibers is reported. A photoinitiator, 4,4′‐bis(diethylamino)benzophenone, was added to PAN solution before the fiber wet‐spinning step. After a short UV treatment that induced cyclization and crosslinking at a lower temperature, precursor fibers could be rapidly thermo‐oxidatively stabilized and successfully carbonized. Scanning electron microscopy micrographs show no deterioration of the microstructure or hollow‐core formation in the fibers due to UV treatment or presence of photoinitiator. Fast‐thermally stabilized pure PAN‐based carbon fibers show hollow‐core fiber defects due to inadequate thermal stabilization, but such defects were not observed in carbon fibers derived from fast‐thermally stabilized fibers that contained photoinitiator and were UV treated. Tensile testing results confirm that fibers containing 1 wt % photoinitiator and UV treated for 5 min display higher tensile modulus than all other sets of thermally stabilized and carbonized fibers. Wide‐angle X‐ray diffraction results show a higher development of the aromatic structure and molecular orientation in thermally stabilized fibers. No significant increase in interplanar spacing or decrease in crystals size were observed within the UV‐stabilized carbon fibers containing photoinitiator, but such fibers retain a higher extent of molecular orientation when compared with control fibers. These results establish for the first time, the positive effect of the external addition of photoinitiator and UV treatment on the properties of the PAN‐based fibers, and may be used to reduce the precursor stabilization time for faster carbon fiber production rate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40623.     

Polyimide fibers prepared by a dry‐spinning process: Enhanced mechanical properties of fibers containing biphenyl units

Polyimide (PI) fibers with enhanced mechanical properties and high thermal and dimensional stability were prepared via a two‐step dry‐spinning process through the introduction of 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride (BPDA) containing biphenyl units into rigid homopolyimide of pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline. The attenuated total reflectance–Fourier transform infrared spectra results imply that the incorporated BPDA moieties accelerate the imidization process and increase the imidization degree (ID) of the precursor fibers; this was attributed to the increased molecular mobility of the polymer chains. Two‐dimensional wide‐angle X‐ray diffraction spectra indicated that the prepared PI fibers possessed a well‐defined crystal structure and polymer chains in the crystalline region were highly oriented along the fiber axis. The PI fiber, with the molar ratio of PMDA/BPDA being 7/3, showed optimum tensile strength and modulus values of 8.55 and 73.21 cN/dtex, respectively; these were attributed to the high IDs and molecular weights. Meanwhile, the PI fibers showed better dimensional stability than the commercial P84 fiber, and this is beneficial for its security applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43727.     

Determination of the minimum sample size for a reliable strength measurement of talc‐filled polypropylene fibers

Accurate determination of mechanical properties plays an important role to comment on improvement in the mechanical properties of particle‐filled PP fibers. However, the existing standards are not totally suitable for reliable strength determination of particle‐filled PP fibers. In the framework of this study, microsized talc particle‐filled PP fibers were produced with different talc ratio and tensile strength measurements were performed with various gage lengths. Statistical Akaike Information Criterion analysis shows that strength distribution of talc‐filled PP fibers is best characterized by Weibull distribution function. It is reported that, the gage length has almost no influence of Weibull parameters of pure PP fibers while strong effects on Weibull parameters of talc‐filled PP fibers. It is shown that if the tensile strength of talc‐filled PP fibers is to be measured, at least 50 samples, which is more than value suggested by existing standard, should be used for a reliable determination of Weibull parameters. Therefore, the main aim of this study is to question the feasibility of minimum sample size suggested by the existing ASTM D3822 standard for reliable strength measurement of talc filled PP fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44083.     

Enhanced toughness and strength of poly (d‐lactide) by stereocomplexation with 5‐arm poly (l‐lactide)

The enhancement of mechanical properties were achieved by solution blending of poly(d ‐lactide) (PDLA) and 5‐arm poly(l ‐lactide) (5‐arm PLLA). Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) results indicated almost complete stereocomplex could be obtained when 5‐arm PLLA exceeded 30wt %. Tensile test results showed that the addition of 5‐arm PLLA in linear PDLA gave dramatically improvement both on tensile strength and elongation at break, which generally could not be increased simultaneously. Furthermore, this work transformed PDLA from brittle polymer into tough and flexible materials. The mechanism was proposed based on the TEM results: the stereocomplex crystallites formed during solvent evaporation on the blends were small enough (100–200 nm), which played the role of physical crosslinking points and increased the interaction strength between PDLA and 5‐arm PLLA molecules, giving the blends high tensile strength and elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42857.     

Influences of pre‐ordered melt structures on the crystallization behavior and polymorphic composition of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

As part of continuous efforts to understand the surprising synergetic effect between β‐nucleating agent and pre‐ordered structures of isotactic polypropylene (iPP) in significant enhancement of β‐crystallization (Ordered Structure Effect, OSE), two β‐nucleated iPP with different uniformities of stereo‐defect distribution (WPP‐A and WPP‐B) were prepared, their crystallization behaviors with variation of melt structures were studied in detail. The results revealed that β‐phase can hardly form in WPP‐A (whose stereo‐defect distribution is less uniform) because of its strong tendency of α‐nucleation caused by its less uniform stereo‐defect distribution, while WPP‐B is more favorable for β‐crystallization; As fusion temperature decreases, similar variation trends of crystallization temperature and β‐phase proportion can be observed from WPP‐A and WPP‐B, indicating the occurrence of OSE behavior, which provides unsurpassed β‐nucleation efficiency and induces β‐crystallization even in WPP‐A which is less favorable for β‐crystallization; moreover, the upper and lower limiting temperatures of Region II of WPP‐A and WPP‐B are identical, suggesting the uniformity of stereo‐defect distribution has little influence on temperature window for OSE (denoted as Region II). To explore the physical nature of Region II, self‐nucleation behavior and equilibrium melting temperature of PP‐A and PP‐B were studied. The lower limiting temperatures of exclusive self‐nucleation domain of both PP‐A and PP‐B are identical with the lower limiting temperatures of Region II in OSE (168°C); moreover, the T_m⁰ of both PP‐A and PP‐B are close to their upper limiting temperatures of Region II in OSE behavior (189°C). The possible explanation was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42632.     

Effect of protein‐loading on properties of wet‐spun poly(L,D‐lactide) multifilament fibers

Protein‐loaded multifilament fibers were fabricated by the wet‐spinning method. The polymers which were tested included poly(L,D ‐lactide) [P(L,D )LA], L/D ratio 96/4 and poly(L,DL ‐lactide) [P(L,DL )LA], L /DL ratio 70/30. The polymers were dissolved in dichloromethane and bovine serum albumin (BSA) was dissolved in water, respectively. The solutions were mixed together using a probe sonicator to form a polymer‐protein emulsion. This emulsion was extruded to an ethanol spin bath. The fibers possessed a distinct sheath‐core structure, where the inner core was porous and the outer sheath was smooth. The diameters of the filaments were in the range of 46 and 70 μm. The tenacity values of the filaments were between 7 and 17 MPa. In vitro drug release rate of the P(L,DL )LA 70/30 filament was faster than that of the P(L,D )LA 96/4 filament. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of acrylonitrile–butadiene–styrene (ABS) morphology and poly(styrene‐co‐acrylonitrile) (SAN) content on fracture behavior of ABS/SAN blends

This study attempted to correlate morphological changes and physical properties for a high rubber content acrylonitrile–butadiene–styrene (ABS) and its diluted blends with a poly(styrene‐co‐acrylonitrile) (SAN) copolymer. The results showed a close relationship between rubber content and fracture toughness for the blends. The change of morphology in ABS/SAN blends explains in part some deviations in fracture behavior observed in ductile–brittle transition temperature shifts. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2606–2611, 2004     

Shape‐memory behavior of high‐strength amorphous thermoplastic poly(para‐phenylene)

The purpose of this study was to investigate the shape‐memory behavior of poly(para‐phenylene) (PPP) under varying programming temperatures, relaxation times, and recovery conditions. PPP is an inherently stiff and strong aromatic thermoplastic, not previously investigated for use as a shape‐memory material. Initial characterization of PPP focused on the storage and relaxation moduli for PPP at various frequencies and temperatures, which were used to develop continuous master curves for PPP using time–temperature superposition (TTS). Shape‐memory testing involved programming PPP samples to 50% tensile strain at temperatures ranging from 155°C to 205°C, with varying relaxation holds times before cooling and storage. Shape‐recovery behavior ranged from nearly complete deformation recovery to poor recovery, depending heavily on the thermal and temporal conditions during programming. Straining for extended relaxation times and elevated temperatures significantly decreased the recoverable deformation in PPP during shape‐memory recovery. However, PPP was shown to have nearly identical full recovery profiles when programmed with decreased and equivalent relaxation times, illustrating the application of TTS in programming of the shape‐memory effect in PPP. The decreased shape recovery at extended relaxation times was attributed to time‐dependent visco‐plastic effects in the polymer becoming significant at longer time‐scales associated with the melt/flow regime of the master curve. Under constrained‐recovery, recoverable deformation in PPP was observed to have an exponentially decreasing relationship to the bias stress. This study demonstrated the effective use of PPP as a shape‐memory polymer (SMP) both in mechanical behavior as well as in application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42903.     

Preparation of a poly(vinyl chloride) ultrafiltration membrane through the combination of thermally induced phase separation and non‐solvent‐induced phase separation

To regulate the polymer–diluent interaction and control the viscosity of the casting solution, diphenyl ketone (DPK) and a N,N‐dimethylacetamide/N,N‐dimethylformamide mixture were selected as a combined diluent. Poly(vinyl chloride) (PVC) utlrafiltration membranes, which had sufficient mechanical properties for their practical applications because of their bicontinuous spongy structure, were prepared by a combined process of thermally induced phase separation and non‐solvent‐induced phase separation. The phase‐separation mechanism was analyzed. In an air bath, the cast nascent solution immediately transformed into a transparent gel, and liquid–liquid phase separation was induced by a sudden drop in the temperature before crystallization. An ice–water bath was used to coagulate the membrane. The effects of the DPK and PVC concentrations on the membrane structures and performances were mainly investigated. The results show that an increase in the DPK content made the membrane pores change from fingerlike to spongy. Fully spongy pores formed, and the pores size decreased with increasing PVC concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42953.     

Tailoring the crystalline morphologies and mechanical properties of high‐density polyethylene parts by a change in the fluid flow pattern under gas‐assisted injection molding

In this study, an increase in the cooling rate of high‐density polyethylene parts was carried out via a change in the fluid flow pattern to introduce gas cooling under a gas‐assisted injection‐molding process; this was conducive to the retention of orientation chains shaped during the injection stage and further developed into much more oriented crystals. Morphological observation showed that the parts without gas cooling (WOGC) were composed of oriented crystals except the gas channel zone, whereas the parts with gas cooling (WGC) were full of oriented crystals, especially much more interlocking shish‐kebab structures in the subskin zone. The WGC parts had a higher degree of orientation than the corresponding zone of the WOGC parts. Although the lower crystallinity, the wider orientation regions, and much more interlocking shish‐kebab structures led to considerable increases from 32 and 990 MPa in the WOGC parts to 36 and 1150 MPa in the WGC parts for the yield strength and elastic modulus, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40349.     

Enhancing particle erosion resistance of glass‐reinforced polymeric composites using carbon nanofiber‐based nanopaper coatings

Sand erosion may cause severe damage of blades in wind turbine and helicopter blades as well as many surface components of airplanes. In this study, thin nanopapers made of carbon nanofibers (CNFs) are used to enhance the resistance of solid particle erosion of glass fiber (GF)/wind epoxy composites. Finite element computer simulations are used to elucidate the underlying mechanisms. The much higher particle erosion resistance of nanopapers compared to GF‐reinforced epoxy composites is attributed to the high strength of CNFs and their nanoscale structure. The excellent performance in particle erosion resistance makes the CNF‐based nanopaper a prospective protective coating material for the turbine blades in the wind energy industry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013