The fine structure of bicomponent polyester fibers

The application of alkaline hydrolysis to study the change in the fine structure of bicomponent polyester fibers as their surface is removed progressively was explored. The samples were prepared with a poly(butylene terephthalate) (PBT) sheath and a poly(ethylene terephthalate) (PET) core. The reagent used to hydrolyze the PBT was 1M NaOH in 75/25 methanol to water since it appeared to react topochemically with the fiber. The solution reacted more rapidly with PET than with PBT. Thus, when necessary to retard the weight loss of the bicomponent fibers, after a 2‐h hydrolysis with this reagent to remove PBT, it was replaced with aqueous 1M NaOH solution containing 0.1% cetrimmonium bromide. Unlike homofil PET or PBT fibers, where alkaline attack appeared to be confined to the surface and left the residue relatively smooth, the bicomponent fiber was attacked unevenly, and penetration to the PET core occurred before all the PBT at the surface was removed. Nevertheless, most of the reaction was confined initially to the PBT sheath. The tenacity and extension at break of the PBT–PET fiber passed through a maximum as hydrolysis progressed. The fall in tenacity at high weight losses is ascribed to increasing surface defects in the fiber surface. After removal of the PBT by the hydrolysis, the birefringence of the residue became progressively higher. The synergistic effect of the PBT sheath on the properties of the PET core and the possible causes of the nonuniform hydrolysis at the PBT surface are discussed. An equation is proposed that includes an interaction parameter, which can be utilized to determine which property is affected most by the hydrolysis of a bicomponent fiber. In this instance, it appears from the parameters that the order is strength > extension at break ≈ birefringence. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1163–1173, 1999     

PET/EVA共混物的制备及其流变性能研究

以PTE和EVA为原料 ,用带有静态混合器的螺杆挤出机制备了PET/EVA共混物 ,并对其流变性进行研究。结果表明 :在所研究的温度和剪切速率范围内 ,PET/EVA流体属于假塑性流体 ,且随着EVA含量的增加 ,共混物流体的黏度增大     

Preparation and anisotropic mechanical behavior of highly‐oriented electrospun poly(butylene terephthalate) fibers

This work describes the effect of the speed of drum‐type rotating collector in an electrospinning process on the orientation of electrospun poly(butylene terephthalate) fiber mats, and its effect on the tensile properties. The degree of orientation increased with the increase in the drum speed (surface velocity) up to a critical level, and thereafter, wavy fibers were observed. The average diameter reduced and its distribution became narrower with increase in the velocity. The mechanical properties in a parallel direction improved about three times with increase in the surface velocity. The anisotropic mechanical behavior could be predicted with a simple classical equation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2017–2021, 2006     

Spinning speed–throughput rate relationships for polyester,nylon, and polypropylene fibers

The relationship between spinning speed and throughput rate has been investigated for fibers having the same fiber denier in the drawn state when produced by melt spinning of poly(ethylene terephthalate), nylon 6, and polypropylene polymers over a range of take-up speed (750–3000 m min^-1) and throughput rate. To understand the structural origin of the relationship, a limited amount of characterization of structure and properties of the as-spun and drawn fibers was also done. A comparison of the results for the three polymers shows that while the increase in productivity with increase in spinning speed is relatively less for polyester and nylon 6, it is quite high for polypropylene. The birefringence data show that while molecular orientation increases rapidly with increasing wind-up speed in polyester and nylon 6, the rate of increase is relatively less in the case of polypropylene. The possible reasons for the observed differences in behavior are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1773–1788, 1997     

Influence of ethylene vinyl acetate on the spinnability and mechanical properties of poly(propylene)/zeolite‐Ag blend fibers

The spinnability and mechanical properties of poly(propylene) (PP)/zeolite‐supported Ag⁺ (zeolite‐Ag)/ethylene vinyl acetate (EVA) ternary blend fibers were studied. It was found that the spinning temperature of the ternary blend fibers was decreased in the presence of EVA. The addition of 2 wt % EVA substantially improved the spinnability of the blend system by enhancing its flowability. It was also found that the ternary fiber with EVA₂₈ (28 wt % vinyl acetate content) showed balanced improvement of mechanical properties by a concomitant increase in modulus and tensile strength. The improvements of spinnability and mechanical properties suggested that a core–shell structure of zeolite‐Ag/EVA₂₈ particles, with zeolite‐Ag as the core and EVA₂₈ as the shell, was formed and remained during the melt‐mixing process of the blended chips and during the course of fiber processing. EVA probably enhanced the binding between the zeolite‐Ag and the PP matrix, as made evident in SEM microphotographs. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1460–1466, 2005     

Rheological properties of UHMWPE/HDPE blend gels and morphology and mechanical properties of gel-spun fibers

To produce polyethylene (PE) fibers with relatively high tensile strength but low cost, ultra-high-molecular-weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) (UH) blend gels were prepared from paraffin oil and further fabricated into UH blend fibers by gel spinning. This research focused on the rheological properties of UH blend gels with high solid contents (SCs) ranging from 25 to 100 g/L, as well as morphology and mechanical properties of resultant gel-spun UH blend fibers. The rheological measurements indicated that the apparent viscosity, shear storage, and loss moduli of the UH blend gels were not markedly increased compared with those of the UHMWPE gel with much less SC. No obvious solid–liquid phase separation occurred in UH blend gels at a temperature above the sol–gel transition temperature. UH blend fibers were prepared by drawing as-spun fibers (draw ratio [λ] = 3) at 110°C to λ = 15, 45, 60, and 80, respectively. The orientation degree of fibril structure in UH blend fibers increased with increasing λ but the length of fibrils (L_fibril) showed a complex change. The L_fibril of UH blend fibers became larger due to chain arrangement in company with the transformation of the kebab structure to the extended shish structure when the λ was less than 45 but decreased during further elongation (λ = 60 and 80) because of fibril breakage and recrystallization. The change in morphological behavior led to the corresponding change in mechanical properties of resultant gel-spun UH blend fibers. The tensile strength of gel-spun UH55-45 blend fiber (UHMWPE/HDPE = 5/5 and λ = 45) reached 15.6 cN/dtex, which could fulfill the requirement of mechanical properties in common application.     

Morphology and thermal behavior of PP/EHDPET blend fibers by alkaline hydrolysis treatment

Polypropylene superfine fibers or cell porous fibers were prepared from the Bi‐component blend fibers of polypropylene/easy hydrolytic degradation polyester (PP/EHDPET) by alkaline hydrolysis process. EHDPET is a kind of copolyester that can be rapidly hydro‐degraded in the hot alkaline solution. This article discusses the kinetics of alkaline hydrolysis of EHDPET, and the effect of catalyst, bulk ratio, and the content of PP‐grafted maleic anhydride on the alkaline hydrolysis process. Meanwhile, the morphological change of the outer surface of blend fibers during this process was also investigated by the technology of scanning electron microscope. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3010–3014, 2000     

Rheological and thermal properties of blends of modified poly(ethylene terephthalate) with p‐acetoxybenzoic acid and poly(butylene terephthalate)

Blending of thermotropic liquid crystalline polyesters (LCPs) with conventional polymers could result in materials that can be used as an alternative for short fiber‐reinforced thermoplastic composites, because of their low melt viscosity as well as their inherent high stiffness and strength, high use temperature, and excellent chemical resistance and low coefficient of expansion. In most of the blends was used LCP of 40 mol % of poly(ethylene terephthalate) (PET) and 60 mol % of p‐acetoxybenzoic acid (PABA). In this work, blends of several copolyesters having various PABA compositions from 10 to 70 mol % and poly(butylene terephthalate) (PBT) were prepared and their rheological and thermal properties were investigated. For convenience, the copolyesters were designated as PETA‐x, where x is the mol % of PABA. It was found that PET‐60 and PET‐70 copolyesters decreased the melt viscosity of PBT in the blends and those PBT/PETA‐60 and PBT/PETA‐70 blends showed different melt viscosity behaviors with the change in shear rate, while blends of PBT and PET‐x having less than 50 mol % of PABA exhibited totally different rheological behaviors. The blends of PBT with PETA‐50, PETA‐60, and PETA‐70 showed the morphology of multiple layers of fibers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1797–1806, 1999     

聚对苯二甲酸乙二酯/聚丙烯不相容共混体系的结构流变学

通过熔融共混制备了不相容的聚对苯二甲酸乙二醇酯（PET）/聚丙烯（PP）复合体系,研究了复合体系的结构流变学。结果表明,PET/PP共混体系的不相容相形态显著影响其稳态和动态流变行为。当PP组分为分散相时,复合体系表现出动态形状松弛;当两组分呈多种相形态共存时,复合体系表现出强烈的低频区弹性响应;而当PET组分为分散相时,复合体系的剪切敏感性则相对较小。在较高剪切应力作用下,分散相液滴的凝聚是影响体系流变行为的控制因素,而在较低的剪切应力作用下,液滴的破碎则成为控制因素。     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

Structure and property relationship of thermotropic liquid crystal polymer and polyester composite fibers

Poly(ethylene 2,6‐naphthalate) (PEN) and poly(ethylene terephthalate) (PET) composite fibers reinforced with a thermotropic liquid crystal polymer (TLCP) were prepared by the melt blending and spinning process to achieve high performance fibers with improved processability. Polymer composite fibers consisting of cheap polyester and small quantity of expensive TLCP are of interest from an economic point of view and from an industrial perspective. The increase in the birefringence and density of the TLCP/PEN/PET composite fibers with the spinning speed was attributable to the enhancement of the molecular orientation and effective packing between chains in the TLCP/PEN/PET composite fibers. Annealing process resulted in the formation of more ordered and perfect crystalline structure and higher crystallinity, improving the mechanical properties of the TLCP/PEN/PET composite fibers. The increase in the crystallite size and the degree of chain extension with increasing spinning speed resulted in the gradual increment of the long period for the TLCP/PEN/PET composite fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006.     

Characterization of the physical and molecular structure of thermally elongating poly(ethylene terephthalate) fibers

The mechanism of thermally induced elongation in poly(ethylene terephthalate) fiber spun at 3500 m min⁻¹ has been examined. This partially oriented fiber has a crystalline content of about 25% and a high degree of orientation. The effect of time and tension during heat treatment was examined, and it was found that yarns that were allowed to relax during an initial brief heat treatment at 130°C subsequently elongated by up to 5% during a long heat treatment at the same temperature. Yarns that were not allowed to relax during the brief heat treatment did not elongate on subsequent heating. The morphological and mechanical changes associated with these processes have been studied using differential scanning calorimetry, X-ray diffraction (XRD), birefringence measurement, microscopy, and tensile testing. A large increase in crystallinity was observed during the brief heat treatment, but a much smaller increase took place during the long heat treatment. XRD indicated that substantial crystal reorganization occurred during both heat treatments, but c-axis growth was most significant in those materials that elongated during long heat treatment. It is proposed that it is this c-axis growth, in conjunction with conversion of disordered amorphous material into oriented crystalline material, that is responsible for the observed elongation. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 989–995, 1997     

Dye–fiber interactions in PET fibers: Hydrogen bonding studied by IR‐spectroscopy

Dye–fiber interactions are studied in poly (ethylene terephthalate) fibers by FT‐IR spectroscopy. It is shown for the first time that DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) serves as an easy applicable and accurate technique for the study of fibrous structures. This article focuses on the possible hydrogen bond interactions in the dye–fiber system, where the PET fibers are dyed with anthraquinone‐based disperse dyes. The dyes and related anthraquinone structures are studied in both the dilute solution state, the solid state, and as present in the PET fibers. It is proven that 1‐amino anthraquinones show strong “chelate‐type” intramolecular hydrogen bonding in all three states. In the fibers an important supplementary intermolecular hydrogen bonding with the C?O groups in the PET fiber is observed. The extend of hydrogen bonding seems to be prone to dye concentration variations. Further analysis by modulated differential scanning calorimetry links the hydrogen bonding to an intrinsic plasticizing effect of the dyes affecting the dye diffusion process. This thus offers a tool for the fundamental understanding of the dyeing process and possible observed differences in dyeing behavior in dye–fiber systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Properties of uncompatibilized and compatibilized poly(butylene terephthalate)–LLDPE blends

In this work, blends of poly(butylene terephthalate) (PBT) and linear low‐density polyethylene (LLDPE) were prepared. LLDPE was used as an impact modifier. Since the system was found to be incompatible, compatibilization was sought for by the addition of the following two types of functionalized polyethylene: ethylene vinylacetate copolymer (EVA) and maleic anhydride‐grafted EVA copolymer (EVA‐g‐MAH). The effects of the compatibilizers on the rheological and mechanical properties of the blends have been also quantitatively investigated. The impact strength of the PBT–LLDPE binary blends slightly increased at a lower concentration of LLDPE but increased remarkably above a concentration of 60 wt % of LLDPE. The morphology of the blends showed that the LLDPE particles had dispersed in the PBT matrix below 40 wt % of LLDPE, while, at 60 wt % of LLDPE, a co‐continuous morphology was obtained, which could explain the increase of the impact strength of the blend. Generally, the mechanical strength was decreased by adding LLDPE to PBT. Addition of EVA or EVA‐g‐MAH as a compatibilizer to PBT–LLDPE (70/30) blend considerably improved the impact strength of the blend without significantly sacrificing the tensile and the flexural strength. More improvement in those mechanical properties was observed in the case of the EVA‐g‐MAH system than for the EVA system. A larger viscosity increase was also observed in the case of the EVA‐g‐MAH than EVA. This may be due to interaction of the EVA‐g‐MAH with PBT. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 989–997, 1999     

聚乙烯醇／水滑石共混纤维的制备及其性能研究

采用凝胶纺丝法制备聚乙烯醇／水滑石（PVA／HT）共混纤维。通过扫描电镜（SEM）观察水滑石在PVA／HT共混纤维中的分散状况和共混纤维的表面形态。从傅里叶变换红外光谱（FT-IR）可以看出HT和PVA之间存在明显的氢键作用;热重分析（TG）测试表明水滑石的加入可以有效提高PVA的热性能;加入适量的HT可以提高PVA纤维的断裂强度;随着HT含量的增加,PVA／HT共混纤维的最大拉伸倍数下降且表面易产生缺陷。     

Solvent‐induced modifications in polyester yarns. II. Structural and thermal behavior

The structural and thermal behaviors of polyester yarns treated with trichloroacetic acid–chloroform (TCAC) mixture were investigated by differential scanning calorimetric analysis (DSC), wide‐angle X‐ray scattering (WAXS), infrared spectroscopy (IR), and scanning electron microscopy (SEM). The effects of TCAC treatment on original fine filament (FFP) and microdenier (MDP) polyester yarns and on heat‐set polyester yarns were studied. It was found that the glass transition temperature of TCAC‐treated polyester yarns decreases with an increase in treatment concentration due to the plasticization effect, which is remarkable even at lower treatment concentration. The TCAC treatment on polyester yarns resulted in the formation of new crystallites in the extended noncrystalline domains of PET as well as growth and perfection of these new crystallites and the preexisting crystals. Further, the DSC thermograms revealed that TCAC treatment with 3% concentration could be able to overcome the structural changes in PET produced by heat setting at 180°C. The substantial changes in noncrystalline and crystalline domains observed were related to the mechanical properties of yarns. From the WAXS studies, an increase in crystal size and lateral order of TCAC‐treated polyester yarns was noted. The most distinct changes brought about by TCAC treatment include overall orientation determined by the trans–gauche ratio from IR measurements. The removal of oligomers and smoothening out of the fiber surface by TCAC treatment were observed from SEM studies. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1555–1566, 2003     

Modification of polyester fibers by grafting with poly(acrylic acid)

The grafting of acrylic acid on PET using benzoyl peroxide has been investigated. The influence of the main parameters of grafting, the effect of additives on the degree of grafting, and the amount of homopolymer formed during the process have been determined. Futhermore, the values of apparent activation energy have been calculated. Also, the influence of the degree of grafting on the moisture sorption and swelling of modified fibers have been determined. By an additional treatment of the grafted fibers with antibiotics it is possible to provide the fibers with antibacterial properties. Liberation of antibiotics from fibers into solutions has been examined and mathematically described. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:967–977, 1997     

Liquid-liquid phase separation and crystallization behavior of poly(ethylene terephthalate)/poly(ether imide) blend

The liquid-liquid (L-L) phase separation and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blend were investigated with optical microscopy, light scattering, and small angle X-ray scattering (SAXS). The thermal analysis showed that the concentration fluctuation between separated phases was controllable by changing the time spent for demixing before crystallization. The L-L phase-separated specimens at 130 °C for various time periods were subjected to a temperature-jump of 180 °C for the isothermal crystallization and then effects of L-L phase separation on crystallization were investigated. The crystal growth rate decreased with increasing L-L phase-separated time (t_s). The slow crystallization for a long t_s implied that the growth path of crystals was highly distorted by the rearrangement of the spinodal domains associated with coarsening. The characteristic morphological parameters at the lamellar level were determined by the correlation function analysis on the SAXS data. The blend had a larger amorphous layer thickness than the pure PET, indicating that PEI molecules in the PET-rich phase were incorporated into the interlamellar regions during crystallization.     

Rheological and mechanical behavior of non-spherical poly(lactic acid) particles embedded poly(butylene adipate-co-terephthalate) blend

In this study, the poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate)(PBAT) blend is investigated to improve rheological and mechanical performances of PBAT based on rheological, mechanical, and thermal behavior analyses. The multi-step mixing method is developed to fabricate the blend with non-spherical morphology. In the multi-step mixing method, blends with a wide composition range (25/75–75/25) are mixed with additional PBAT at a mixing temperature between the melting temperatures of PBAT and PLA to produce the PBAT blend embedded with non-spherical PLA particles (10 wt%). The embedding of non-spherical PLA particles in PBAT increases the resistance against deformation, resulting in strain hardening behavior and an increase in the yield strength as well as the tear resistance of the PBAT. The presence of stiff PLA particles enhances the crystallization behavior of PBAT, meaning that polymer chains may interpenetrate. The findings of this study suggest that the multi-step mixing method is beneficial for embedding non-spherical PLA particles into a PBAT matrix, which in turn facilitates the maintenance of good interfacial adhesion to increase the melt strength, yield strength, and tear resistance.     

Solvent‐induced modifications in polyester yarns. I. Mechanical properties

The mechanical properties of polyester (PET) yarns, fine filament, and microdenier (original and heat‐set), treated with a trichloroacetic acid–chloroform (TCAC) mixture were investigated. The treatments were carried out in an unstrained state with various concentrations of the TCAC reagent at room temperature. The TCAC treatment on PET yarns resulted in notable changes in the tensile behavior. The TCAC‐treated yarns exhibited higher extensibility and work of rupture without much loss in strength. The improvement in elongation was less in the case of heat‐set polyester yarns due to solvent treatment. The depression of the glass transition temperature (T_g) of TCAC‐treated PET yarns, even at the minimum concentration, showed its effectiveness to plasticize the fibers and the closeness of the solubility parameter of TCAC and PET. The T_g depression favors molecular relaxation, which has resulted in a higher shrinkage percentage of TCAC‐treated PET yarns and the effective shrinkage was reached more easily for the original fine‐filament polyester (FFP) and microdenier polyester (MDP) yarns at the lowest concentration. The effects of the concentration of TCAC on the strength, elongation, yield behavior, and work of rupture on PET were also investigated. A significant plastic flow was observed in the TCAC‐treated yarns. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1500–1510, 2003