Effect of graphene nanoplatelets presence on the morphology,structure, and thermal properties of polypropylene in fiber melt‐spinning process

Melt spinning of graphene nanoplatelets (GnPs)‐polypropylene (PP) nanocomposite fibers are reported for the first time. PP/GnPs fibers were spun with a pilot‐plant spinning machine with varying concentration of GnPs by mixing PP/GnPs masterbatch with PP. The effect of inclusion of GnPs on the morphology and crystalline structure of PP fibers was investigated. The thermal stability of the fibers was also evaluated by thermogravimetric analysis. The light microscopy images showed that the GnPs are uniformly distributed over the PP matrix. The differential scanning calorimetry (DSC) results revealed that presence of GnPs affects both the melting and crystallization behaviors. The melting peaks of PP/GnPs nanocomposite fibers were broader than that of neat PP fibers, indicating a broader crystal size distribution in PP/GnPs nanocomposite fibers as compared to the neat PP fibers. Besides, an obvious increment in the crystallization peak temperature was observed in GnPs‐PP nanocomposite fibers. The wide‐angle X‐ray diffraction spectra (WAXD) results showed that the crystal type of nanocomposite fibers did not change and was still the α‐monoclinic crystal form. Moreover, the morphology of spherulites demonstrated that GnPs increased the nucleation sites in the nanocomposite fibers which in turn restricted the crystal growth of PP chains. This finding supported the DSC and WAXD results. Activation energies were calculated by Horowitz and Metzger's method as 77.87 and 105.41 kJ/mol for neat PP and PP/0.2 wt% GnPs fibers, respectively, suggesting an increase in the thermal stability of GnPs‐PP nanocomposite fibers. POLYM. COMPOS., 36:367–375, 2015. © 2014 Society of Plastics Engineers     

Spinning the supercooled PET to obtain highly oriented and crystallized PET fibers at low speeds

An attempt has been made to investigate the feasibility for a novel concept of supercooled spinning to obtain orientation‐induced crystallization at speeds lower than that for the high‐speed spinning technology. This is achieved by setting the nozzle temperature lower than the melting point for PET, making the polymer a supercooled fluidic liquid, and then spinning the supercooled. The experimental results show that high orientation and high crystallinity can be achieved at a spinning speed of 2500 m/min, which is in good comparison with a speed of 5000–6000 m/min to obtain similar degree of orientation and crystallinity in the high‐speed spinning. The properties of the as‐spun fibers obtained by supercooled spinning were analyzed, and a rational theoretical account for the supercooled spinning is explored. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3078–3082, 2006     

聚苯硫醚纤维与聚醚砜纤维的结构与性能

分别以聚苯硫醚(PPS)、聚醚砜(PES)切片为原料,在一位4头的熔融纺丝实验机上,制备了PPS及PES纤维,并对两者结构与性能的差异进行比较。结果表明:PPS和PES的初生纤维都具有光滑的表面,PES的流动性能比PPS差,表观黏度也比PPS要大;PPS纤维的玻璃化转变温度为90¹00℃,结晶温度为130.09℃,熔融温度为279.56℃,初始热分解温度为500℃,半寿温度为625℃;PES纤维的玻璃化转变温度为225℃,初始热分解温度为460℃,半寿温度为600℃,没有结晶温度和熔融温度;PPS纤维为半结晶聚合物,结晶速率为0.045 s-1,而PES纤维属于无定形或极低结晶度材料;PES纤维和PPS纤维都具有优异的热稳定性和阻燃性,都非常适合应用在阻燃及耐高温场合。     

聚丙烯/聚苯乙烯/膨润土共混纤维研究

研究了聚丙烯(PP)纤维可染改性添加剂聚苯乙烯/膨润土(PS/Garamite)杂化复合粒子的原位悬浮聚合及PP/PS/Garamite共混纤维的熔纺成形。对聚合产物中膨润土的层间距、PP/PS/Garamite共混体系中PP的结晶形态、共混纤维的热性能及染色性能进行了表征。结果表明:聚合过程中膨润土的层间距几乎没有变化,添加剂的加入使共混纤维的熔点降低,结晶温度从115℃升高到117℃,结晶度从44.2%降低至40.2%,无定形区域增加。采用分散染料染色,共混改性纤维具有较好的染色深度。     

Melt‐spinning process of a tetrafluoroethylene– hexafluoropropylene copolymer

An industrial melt‐spinning process of tetrafluoroethylene– hexafluoropropylene copolymer (FEP) using an extruder was studied. The novel “spinneret,” having both a large‐diameter spinning nozzle and a high‐temperature vessel, was used to solve the problem of filament breakage on the spinning line caused by high melting viscosity of FEP. The extruder, with its long feed zone, was newly designed to function with a geared pump. The strength of fibers increased with drawing of as‐spun fiber. FEP fibers up to six denier were continuously produced through long‐run production. According to this new process, FEP fibers can be supplied for textile or industrial application. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2366–2371, 2002     

Fiber and film developments from immiscible blends of cellulose acetate propionate and poly(butylene terephthalate)

Binary blends of cellulose acetate propionate (CAP) and poly(butylene terephthalate) (PBT) in the composition range of 5–15 wt % for CAP were prepared in the form of films and fibers by compression molding and spinning, respectively. The presence of two invariant glass‐transition temperatures corresponding to the CAP and PBT components and viscosities lower than those of the neat PBT of the CAP–PBT blends implied that the CAP–PBT blends were immiscible. Moreover, the crystallinity of the PBT component was higher in the spun fibers than in the films; this was possibly due to the different cooling methods or the chain orientation in the spinning process. In the meantime, the CAP component could not undergo crystallization because of its rigid structure and alkyl substituents. For the CAP–PBT films, the amorphous CAP was present as dispersed particles in the PBT matrix; but it became rods in the spun fibers. In addition, the presence of the amorphous CAP resulted in a decrease in the tensile strength and an increase in the elongation at break for the CAP–PBT fibers. The CAP–PBT films and fibers could be applied in a wide range of applications requiring renewable properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45013.     

Study on parameters influencing shape change of melt spun cross-shaped polypropylene and poly (lactic acid) fibers

Melt spinning of cross-shaped polypropylene (PP) and poly (lactic acid) (PLA) fibers was conducted to investigate influences of polymer properties and processing conditions on cross-sectional shape change in fibers. PP fibers possessed cross-shaped profile, resembling that of the original spinneret orifice, with dull edges due to die swell. Their shape factor (SF) values (1.4–1.6) were close to that of the spinneret orifice (1.7), indicating that the complex shape of the orifice could be maintained. High melt viscosity of PP, as well as its rapid crystallization, helped preventing shape change induced by surface tension. PLA fibers, on the other hand, exhibited shape change from cross to square and to round shape when spinning temperature was increased from 200 to 220 and 240 °C, respectively. Their SF values (1.1–1.2) were close to unity, indicating shape change towards circular shape. Shape deviation towards circular shape in PLA fibers was mainly driven by surface tension. Slow crystallization in PLA allowed great influence of surface tension in determining shape change of the extrudate. Increasing fiber take up speed tended to decrease SF value. Such effect was small compared to that of spinning temperature.     

Effect of solid‐state shearing of poly(ethylene terephtalate) on isothermal crystallization and fiber structure formation

Solid‐state shearing was applied on recycled poly(ethylene terephtalate) (PET) using twin‐screw extruder. The shearing effect on isothermal crystallization was investigated by DSC. Structure formation in melt spinning was also studied by characterizing the spun fibers. It was found that the solid‐state shearing imposes a great influence on its crystallization behavior. Crystallization peak temperature of the sheared PET (199°C) was much higher than that of the PET without shearing (188°C). Overall isothermal crystallization rate was found to be accelerated to more than 50 times by the shearing. The shearing effect remained even after fiber spinning (melt processing). Differences in crystallization behavior, fiber structure formation, and tensile properties of the fibers were found. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 787–791, 2007     

低熔点聚酰胺的结晶和熔融行为

采用差示扫描量热法和X射线衍射法对低熔点聚酰胺的结晶和熔融行为进行研究,考察了共聚单体、等温结晶温度和时间对样品结晶和熔融行为的影响。结果表明:经等温结晶后的样品再次升温时,均出现了双熔融峰,且随等温结晶温度的升高或时间的延长,低温熔融峰向高温方向移动,而高温熔融峰则基本不变。等温结晶温度80℃时,两种样品的熔融焓值均较大,并且随结晶时间的延长会变大。X射线衍射结果表明:随着结晶温度的升高或时间的延长,衍射峰变得尖锐,样品的结晶度增大。添加了十二烷基二胺的切片B比添加癸二胺的切片A具有更好的结晶能力,比较适合纺丝加工。     

Electrically conductive poly(3,4‐ethylenedioxythiophene)–polystyrene sulfonic acid/polyacrylonitrile composite fibers prepared by wet spinning

Composite conductive fibers based on poly(3,4‐ethylenedioxythiophene) (PEDOT)–polystyrene sulfonic acid (PSS) blended with polyacrylonitrile (PAN) were prepared via a conventional wet‐spinning process. The influences of the PEDOT–PSS content on the electrical conductivity, thermal stability, and mechanical properties of the composite fibers were investigated. The fibers with 1.83 wt % PEDOT–PSS showed a conductivity of 5.0 S/cm. The breaking strength of the fibers was in the range 0.36–0.60 cN/dtex. The thermal stability of the PEDOT–PSS/PAN composite fibers was similar to but slightly lower than that of the pure PAN. The X‐ray diffraction results revealed that both the pure PAN and PEDOT–PSS/PAN composite fibers were amorphous in phase, and the crystallization of the latter was lower than that of the former. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of the addition of lubricant on the properties of poly(ether ether ketone) fibers

A high‐temperature lubricant genioplast pellets (GPPS) was used in order to improve the processing behavior of poly(ether ether ketone) (PEEK) resin and high‐performance PEEK fibers were produced by melt‐spinning. The rheological properties of spinning material, morphology, mechanical, and thermal properties of PEEK fibers were characterized by using a polymer capillary rheometer, scanning electron microscopy, single fiber electronic tensile strength tester, wide‐angle X‐ray diffraction and thermal gravimetric analyzer, respectively. The results indicated that the introduction of lubricant GPPS decreased the melting viscosity of PEEK resin and improved spinnability of PEEK resin without sacrificing its thermal properties. The filaments are cylindrical with smooth surface and uniform diameter. The optimized content of GPPS was determined to be 1.0 wt% by balancing the decreased torque and changes of the mechanical properties. The strength and modulus of PEEK fibers were 420 MPa and 3.6 GPa, respectively. This should be due to the improvement in spinnability, followed by the enhancements in the orientation and crystallization of PEEK fibers in the process of drawing and annealing. POLYM. ENG. SCI., 53:2254–2260, 2013. © 2013 Society of Plastics Engineers     

PET/PBT反应性共混纺丝初生纤维的结构性能研究

通过反应性共混纺丝的方法制备了一系列PET /PBT初生纤维,并对其结构和性能进行了研究。DSC结果表明:随着共混物在螺杆中停留时间的增加,冷结晶温度增加而熔融结晶温度和熔点下降,结晶行为的差异可能与嵌段的序列长度随酯交换进行而不断减小有关。 WAXD及SEM的分析还表明:PET /PBT体系在无定形区是相容的,在晶区却是晶相分离的,而非共晶结构。并在实验基础上,对PET/PBT共混体系的可纺性进行了初步探讨。     

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

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

DSC Study of Syndiotactic Polypropylene/Organoclay Nanocomposite Fibers: Crystallization and Melting Behavior

The effect of anisotropic particles of organophilic layered silicate on the crystallization and melting behavior of prepared nanocomposite systems was studied. The matrix was syndiotactic polypropylene (sPP). Organophilic layered silicate M-QDA filler was prepared by modification of hectorite SOMASIF ME 100 with octadecyl amine. The compatibilizer was isotactic polypropylene (iPP) grafted with maleic anhydride (iPP-g-MA). The silicate was exfoliated in situ within the sPP during the melting process to produce anisotropic nanoparticles. The sPP/M-ODA nanocomposite was spun at different drawing ratios. The resulting fibers were examined by differential scanning calorimetry. It was found that neither the spinning process nor the presence of nanofiller affected the crystallinity of the sPP matrix of the nanocomposite in comparison with the neat sPP. At a raised drawing ratio of the fibers slightly increased crystallinity of matrix was observed; however, it was still lower than the neat sPP fibers prepared at the same drawing ratio. The presence of M/ODA nanofiller in sPP matrix increased the melting temperature of the fibers.     

Morphology–property relationship in oriented PET films: Microstructural reorganization during heat treatment

Morphology–property relationships for simultaneously biaxially stretched films and heatset with fixed dimensions in the temperature range of 100–240°C have been studied. The observed transition in various properties at 180°C can be explained on the basis of microstructural changes caused by competition among several processes, such as crystallization, solid-state thickening, melting, and molecular relaxation as well as by melting and recrystallization. The resulting structures and, thereby, the properties are different in temperature Regime-II (T_g to T_max) and Regime-III (T_max to T_m). In Regime-II, the high rate of crystallization compared to the rate of molecular relaxation develops a constrained amorphous phase, whereas the predominant melting and recrystallization process in Regime-III generates the relaxed amorphous phase. The structural reorganization during heat treatment is almost the same for uniaxially oriented film, fibers, and biaxially oriented films prepared under similar processing conditions. © 1994 John Wiley & Sons, Inc.     

Fiber structure formation in ultra-high-speed melt spinning of poly(ethylene 2,6-naphthalene dicarboxylate)

The high-speed melt spinning of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) was performed up to the take-up velocity of the ultra-high-speed region, 9 km/min. From the investigations of the structure and physical properties of the as-spun fibers, the high-speed spinning of PEN was divided into three regions in terms of the mechanism of fiber structure formation. The first region is the take-up velocity of up to 2.5 km/min and the birefringence of up to 0.08 where only a slight increase in molecular orientation was attained. At the take-up velocity of 2.5–4.5 km/min and the birefringence of 0.08–0.25, although some experimental evidences indicated that the orientation-induced crystallization did not occur, there was an increase in the fiber density which suggested the formation of some ordered structure. At the take-up velocity > 4.5 km/min and birefringence > 0.25, the orientation-induced crystallization occurred. The fibers obtained in this region were characterized by the formation of the crystalline structure dominated by the β form. The presence of the necklike deformation in the spinning line was also confirmed. The solidification temperature of the spinning line analyzed from the diameter profile suggested that the formation of β modification crystals occurred at relatively low crystallization temperatures in comparison with that in an isotropic state. Therefore it was indicated that the presence of elongational stress in the spinning line promoted the formation of the β modification crystals. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1415–1427, 1997     

Effect of metallic wire inserted in nozzle in high-speed melt spinning of poly(ethylene terephthalate)

High-speed melt spinning of poly(ethylene terephthalate) was performed using a spinning nozzle with an inserted metallic wire of various lengths (0, 8, 30, and 45 mm). The molecular orientation of as-spun fibers increased with the increase in the wire length at all the take-up velocities examined. Along with the enhanced molecular orientation, the longer wire length led to the starting of orientation-induced crystallization at lower take-up velocities. The structure of crystallized fibers obtained at low speeds can be characterized by high crystallinity and relatively low molecular orientation. From the on-line measurement of the diameter and temperature profiles of the spin line with the 30-mm metallic wire, it was revealed that the spin-line had a maximum diameter of about 6 mm at the wire end. The spin-line temperature at this position was about 190°C. The solidification of the spin-line occurred at positions much closer to the spinneret in comparison with ordinary high-speed spinning. These results show that high-speed spinning with a wire inserted in the nozzle corresponds to a spinning process operated at extremely low extrusion temperature using a nozzle with an extremely large diameter. From the starting of orientation-induced crystallization at lower levels of birefringence in comparison with ordinary high-speed spinning, the alteration of the inherent fiber structure that cannot be represented by birefringence was also suggested. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 665–674, 1998     

Enhancing mechanical properties of aromatic polyamide fibers containing benzimidazole units via temporarily suppressing hydrogen bonding and crystallization

The copolymerization modified poly(p‐phenylene terephthalamide) containing 2‐(4‐aminophenyl)?5‐aminobenzimidazole (PABZ) units in the main chain was synthesized and the corresponding poly‐p‐phenylene‐benzimidazole‐terephthalamide (PBIA) fibers were prepared by wet spinning. The HCl, the by‐product released during polymerization, can complex with PABZ units to prevent the formation of hydrogen bonding between PABZ units, resulting in amorphous PBIA fibers and a lower glass transition temperature (T_g). Therefore, for the purpose of gaining strong hydrogen bonding and high orientation degree at the same time in PBIA fibers, two‐step drawing–annealing processing was adopted. The as‐spun PBIA/HCl complex fibers were drawn first at 280°C, higher than the T_g of the PBIA/HCl complex fibers and lower than the decomplexed temperature of HCl, which temporarily suppresses the formation of hydrogen bonding and crystallization. Subsequently, the fibers were annealed to reform hydrogen bonding between PABZ units and crystallization via decomplexation of HCl at 400°C. However, when the drawing is above the decomplexed temperature of HCl, the decomplexation of HCl begins to occur which leads to the reform of hydrogen bonding and crystallization, and the tensile strength of the drawn‐annealed PBIA/HCl complex fibers decreases with a decrease in the HCl content of fibers. The tensile strength of two‐step drawn‐annealed fibers increased by approximately 15% compared to that of one‐step drawn PBIA/HCl complex fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42482.     

Mechanical,thermal properties and isothermal crystallization kinetics of biodegradable poly(butylene succinate-<Emphasis Type="Italic">co</Emphasis>-terephthalate) (PBST) fibers

Biodegradable copolymer poly(butylene succinate-co-terephthalate) (PBST), with 70 mol% butylene terephthalate (BT), was melt-spun into fibers with take-up velocity of 2 km/min. The mechanical and thermal properties of the as-spun fibers were investigated through tensile test, DSC and TGA. Compared to poly(butylene terephthalate) (PBT) fibers, PBST fibers exhibited lower initial tensile modulus and higher tensile elongation at break which indicated their better flexibility. DSC results showed high melting temperature (ca.180.7 °C) of PBST fibers helpful to the textile processing compared to other biodegradable polyesters. Furthermore, isothermal crystallization behaviors of PBST fibers at low and high supercoolings were investigated by DSC and DLI, respectively. The measurement of crystallization kinetics at low supercoolings indicated that Avrami exponent n for PBST fibers was at a range of 2.9 to 3.3, corresponding to the heterogeneous nucleation and a 3-dimensional spherulitic growth. Similar results were given for isothermal crystallization behavior at high supercoolings investigated by DLI technique. Additionally, the equilibrium melting temperature of PBST fibers was obtained for 206.5 °C by Hoffman-Weeks method. Further investigation through DLI measurement provided the temperature at maximum crystallization rate for PBST fibers located at about 90 °C, which was very useful to polymer processing.     

The thermal effects on electrospinning of polylactic acid melts

We demonstrate that melt electrospinning can be a feasible way to produce sub-micron scale polylactic acid (PLA) fibers in this paper. This solvent-free approach to produce sub-micron scale fibers is more environmentally benign than common solution electrospinning processes, and has a potential to increase the production rate significantly. Our experimental results show that temperatures at the spinneret and in the spinning region are critical to produce sub-micron sized fibers: a high-speed photographic investigation reveals that when spinning temperature is below glass transition temperature, whipping of the jet is suppressed by fast solidification in the spinning region, leading to a larger jet diameter. Both thermal and mechanical degradations of PLA in melt electrospinning can be significant but no change in chemical composition is found. Due to rapid solidification, melt electrospun PLA fibers are mostly amorphous, and the small presence of β crystals is noted in the sub-micron scale PLA fibers by XRD studies. The highly oriented structure of PLA fibers gives rise to cold crystallization at around 95 °C, and the degree of crystallinity of fibers increases with increasing the degree of annealing. Finally, PLA nanofibers have directly been electrospun onto cellulose filter media, and a drastic enhancement in collection efficiency of sub-micron sized dust particles is presented. Melt electrospun PLA nanofiber mats with no residual solvent may serve as better filter media and tissue scaffolds than those obtained from solution electrospinning processes.