Carrier effect on structure and properties of heat-treated poly(ethylene terephthalate) fibers. II. Dyeing behavior

The changes in the morphology of heat-setted poly (ethylene terephthalate) (PET) fibers (as spun and 2.8×) submitted to benzoic acid action at different concentrations and times were analyzed by wide-angle x-ray scattering and dynamic and mechanical thermal analysis. Also, dyeings in the presence of two different Disperse dyes were performed. Therefore, the calculated diffusivities as well as the dye absorption percentage at equilibrium were related to the morphological changes of the fibers, due to the benzoic acid action. The plasticization effect of the benzoic acid over the as-spun fiber occurs in the first 30 min of exposition and in 24 h for the drawn one. This plasticizing action of the benzoic acid seems to be the commanding factor over the dyeing behavior of the fibers, as demonstrated by an increase of the diffusion coefficient with the increase of benzoic acid concentration. However, the morphological changes due to exposition for long periods of time at increased benzoic acid concentrations are one of the major responsible factors by the observed maxima in the figures of percentage of dye on the fibers at equilibrium versus benzoic acid concentration. Also, changes in the angular coefficient (B) calculated from the free volume theory equation are indicative that factors such as the size of the dye molecules as well as their solubilities in water in addition to the morphological changes may be playing a role in the dyeing behavior. © 1996 John Wiley & Sons, Inc.     

Improved mechanical properties of poly(ethylene terephthalate) nanocomposite fibers

Improvements in Young's modulus and strength (tenacity) of poly(ethylene terephthalate) (PET) fibers were obtained by drawing unoriented nanocomposite filaments containing low concentrations (<3 wt%) of various organically modified montmorillonites (MMTs) in a second step at temperatures above the glass transition. Prior to melt spinning, solid‐state polymerization was used to rebuild lost molecular weight, due to MMT‐induced degradation, to a level suitable for producing high strength fibers. Greater improvements in mechanical properties occurred when the MMT stacks were intercalated with PET. A nominal 1 wt% loading of dimethyl‐dehydrogenated tallow quaternary ammonium surface modified MMT in drawn PET fiber showed a 28% and 63% increase in Young's modulus and strength, respectively. Relative to an unfilled PET fiber, these results surpassed the upper bound of the rule of mixtures estimate and suggested that both the type of surface modification and concentration of MMT affect the degree of PET orientation and crystallinity. Furthermore, drawability above T_g and elongation at break increased upon the addition of organically modified MMT to unoriented PET fibers, which was a key distinction of this work from others examining similar systems. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Lamellar structure and properties in poly(ethylene terephthalate) fibers

The fibrillar and the lamellar structures in a range of poly(ethylene terephthalate) fibers were studied by small-angle X-ray scattering. The intensity maxima in the lamellar peaks lie on a curve that can be described as an ellipse. Therefore, the two-dimensional images were analyzed in elliptical coordinates. The dimensions of the coherently diffracting lamellar stack, the dimensions of the fibrils, the interfibrillar spacing, and the orientation of the lamellar surfaces were measured in addition to the lamellar spacing. The orientation of the lamellar planes and the size of the lamellar stacks had a better correlation with mechanical properties of the fibers than did the lamellar spacing. In particular, longer and wider lamellar stacks reduced fiber shrinkage, as did the closer alignment of the lamellar normal to the fiber axis. These structural features were also associated with lower tenacity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2527–2538, 1998     

Structure‐mechanical properties relationship of poly(ethylene terephthalate) fibers

The correlation between the fiber structure and mechanical properties of two different poly(ethylene terephthalate) fiber types, that is, wool and cotton types produced by three producers, was studied. Fiber structure was determined using different analytical methods. Significant differences in the suprastructure of both types of conventional textile fibers were observed, although some slight variations in the structure existed between those fibers of the same type provided by different producers. A better‐developed crystalline structure composed of bigger, more perfect, and more axially oriented crystallites was characterized for the cotton types of PET fibers. Crystallinity is higher, long periods are longer, and amorphous domains inside the long period cover bigger parts in this fiber type in comparison with the wool types of fibers. In addition, amorphous and average molecular orientation is higher. The better mechanical properties of cotton PET fiber types, as demonstrated by a higher breaking tenacity and modulus accompanied by a lower breaking elongation, are due to the observed structural characteristics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3383–3389, 2003     

The effect of heat setting on the structure and mechanical properties of poly(ethylene terephthalate) fiber. I. Structural changes

We report structural changes in commercial multifilament poly(ethylene terephthalate) (PET) yarn when it is heat set in silicone oil over a range of temperatures between 100 and 220°C for times ranging from 1 min to 1 hr, while the yarn was (1) free to relax, and (2) held taut at constant length. In one case, viz., a sample heat treated for 1 hr, the cooling time was also varied to study the effect of rate of cooling. The free-annealed and taut-annealed samples showed considerable differences. The predominant role of the temperature of heat setting on structure is discussed in detail. There are considerable changes in the amount and orientation of the amorphous phase, and these will be shown to have important influence on mechanical properties in subsequent reports.     

Fine structure and physical properties of polyethylene/poly(ethylene terephthalate) bicomponent fibers in high‐speed spinning. I. Polyethylene sheath/poly(ethylene terephthalate) core fibers

The high‐speed melt spinning of sheath/core type bicomponent fibers was performed and the change of fiber structure with increasing take‐up velocity was investigated. Two kinds of polyethylene, high density and linear low density (HDPE, LLDPE) with melt flow rates (MFR) of 11 and 50, [HDPE(11), LLDPE(50)], and poly(ethylene terephthalate) (PET) were selected and two sets of sheath/core combinations [HDPE(11)/PET and LLDPE(50)/PET bicomponent fibers] were studied. The fiber structure formation and physical property effects on the take‐up velocities were investigated with birefringence, wide‐angle X‐ray diffraction, thermal analysis, tensile tests, and so forth. In the fiber structure formation of PE/PET, the PET component was developed but the PE components were suppressed in high‐speed spinning. The different kinds of PE had little affect on the fine structure formation of bicomponent fibers. The difference in the mechanical properties of the bicomponent fiber with the MFR was very small. The instability of the interface was shown above a take‐up velocity of 4 km/min, where the orientation‐induced crystallization of PET started. LLDPE(50)/PET has a larger difference in intrinsic viscosity and a higher stability of the interface compared to the HDPE(11)/PET bicomponent fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2254–2266, 2000     

Influence of branching on the properties of poly(ethylene terephthalate) fibers

A series of branched poly(ethylene terephthalate) samples was prepared by employing 0.07–0.42 mol % trimethylolpropane (TMP) for melt polycondensation. These polymers were characterized with respect to molar mass, intrinsic viscosity, and melt viscosity. Spinning into fibers took place at spinning speeds ranging from 2500 to 4500 m/min. The molecular orientation of the fibers as measured by birefringence and polarized fluorescence decreases with growing amounts of TMP, as does crystallinity. Thus with slightly branched polymers, higher spinning speeds than with a linear polymer can be used to achieve a certain property profile. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 728–734, 1999     

Thermal and mechanical properties of poly(ethylene terephthalate)/lamellar zirconium phosphate nanocomposites

The preparation of nanocomposites of poly (ethylene terephthalate) (PET) and lamellar zirconium phosphorous compounds by melt extrusion was investigated. Two types of zirconium phosphorous compounds were synthesized by the direct precipitation reaction method: α‐zirconium bis(monohydrogen orthophosphate) monohydrate (ZrP) and organic–inorganic hybrid layered zirconium phenylphosphonate (ZrPP). Composites containing 2 and 5 wt % ZrP and ZrPP were prepared in a twin‐screw extruder and specimens were obtained by injection molding. The extent of dispersion of the layered filler in the composite matrix was investigated by X‐ray diffraction and transmission electron microscopy (TEM). The crystallization and thermal properties were analyzed by differential scanning calorimetry and thermogravimetry, and the mechanical properties were evaluated by tensile tests. Whereas ZrP‐containing composites showe characteristic diffraction peaks at 2θ 11.7° (d = 7.54 Å), indicative of no delamination, ZrPP showed practically no low‐angle diffraction peak at 2θ 5.5° (d = 15.24 Å), indicating loss of the layered order. TEM images of ZrPP particles indicated the formation of an intercalated/partially delaminated nanocomposite. The behavior was attributed to the higher affinity of the polyester with phenyl groups on the platelet surface of ZrPP. In both cases, the addition of the fillers increased the crystallization rate and the modulus. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3868–3876, 2006     

Structure and mechanical properties of compatibilized poly(ethylene terephthalate)/poly(ethylene octene) blends

Poly(ethylene terephthalate) (PET) based blends were obtained by melt blending PET with up to 30 wt% poly(ethylene‐octene) either modified with maleic anhydride (mLLDPE) or not (LLDPE). Both PET/LLDPE and PET/mLLDPE blends were immiscible. The dispersed phase particle size was large in LLDPE blends, but upon mLLDPE addition, it decreased to a small (submicron) and rather constant value with composition. This indicated compatibilization, and was attributed to specific interactions between the ester and maleic groups of PET and mLLDPE, respectively, rather than grafting reactions between components. Linear decreases in Young's modulus and yield stress, and ductility increases were observed in blends with mLLDPE. Super‐toughness was achieved in blends with mLLDPE, which took place when the critical interparticle distance (ID_c) was below 0.17 μm and with only half the cross section of the specimens broken. The ID_c of these blends and those of other blends from bibliography were compared with the adhesion levels estimated from the expected main interactions between the components of the blends. This comparison strongly indicated that, at least through an adhesion range, ID_c depends on the adhesion level, and that ID_c decreases as the adhesion level increases. POLYM. ENG. SCI. 46:172–180, 2006. © 2005 Society of Plastics Engineers     

Morphology and mechanical properties of injection molded poly(ethylene terephthalate)

This work reports on the relationships between processing, the morphology and the mechanical properties of an injection molded poly(ethylene terephthalate), PET. Specimens were injection molded with different mold temperatures of 30°C, 50°C, 80°C, 100°C, 120°C, 150°C, while maintaining constant the other operative processing parameters. The thermomechanical environment imposed during processing was estimated by computer simulations of the mold‐filling phase, which allow the calculation of two thermomechanical indices indicative of morphological development (degree of crystallinity and level of molecular orientation). The morphology of the moldings was characterized by differential scanning calorimetry (DSC) and by hot recoverable strain tests. The mechanical behavior was assessed in tensile testing at 5 mm/min and 23°C. A strong thermal and mechanical coupling is evidenced in the injection molding process, significantly influencing morphology development. An increase in the mold temperature induces a decrease of the level of molecular orientation (decrement in the hot recoverable strain) and an increment in the initial crystallinity of the moldings (decrement in the enthalpy of cold crystallization), also reflected in the variations of the computed thermomechanical indices. The initial modulus is mainly dependent upon the level of molecular orientation. The yield stress is influenced by both the degree of crystallinity and the level of molecular orientation of the moldings, but more significantly by the former. The strain at break was not satisfactorily linked directly to the initial morphological state because of the expected morphology changes occurring during deformation. Polym. Eng. Sci. 44:2174–2184, 2004. © 2004 Society of Plastics Engineers.     

The effect of heat setting on the structure and mechanical properties of poly(ethylene terephthalate) fiber. III. Anelastic properties and their dependence on structure

Viscoelastic parameters for poly(ethylene terephthalate) (PET) fibers heat set under different conditions were determined at 110 Hz between room temperature and about 200°C. The correlation of dynamic mechanical properties with structure and their dependence on the temperature of the measurement are discussed. It was found that in addition to the structural parameters such as degree of crystallinity, crystallite and amorphous orientation, etc., morphological factors such as size and distribution of crystallites also influence the dynamic mechanical properties. The activation energy of the α-transition is reported, and the effect of the distribution of relaxation times on the activation energy is discussed.     

Thermal deformations of oriented noncrystalline poly (ethylene terephthalate) fibers in the presence of mesophase structure

Thermally induced dimensional changes, thermal shrinkage and elongation, in oriented noncrystalline PET fibers were investigated. The fibers exhibited two very distinct thermal responses depending on the fiber orientation. The local structure of the oriented noncrystalline PET chains as studied by the X-ray diffraction and FTIR spectroscopy revealed the mesophase structure with the well extended chain conformation in some fibers of high orientation. It was suggested that the oriented noncrystalline structure of PET consists of partially oriented noncrystalline phase and chain-extended noncrystalline phase. Our results demonstrated that the evolution of mesophase structure, i.e. chain-extended noncrystalline phase in the spin line not only led the drastic increase of packing density but also had a strong effect on thermal deformations upon post heat treatment. The amount of thermal shrinkage or the elongation reduced drastically in the fibers containing the mesophase. The high population of trans conformer and the strong inter-chain interactions of the extended chains provided the dimensional stability of the fibers during the thermal treatment.     

Influence of different functionalized multiwall carbon nanotubes on the mechanical properties of poly(ethylene terephthalate) fibers

Master batches with four different kinds of functionalized multiwall carbon nanotubes (MWCTs) were prepared through the mixing of MWCTs with poly(ethylene terephthalate) (PET) (0.01 : 0.99 w/w) in trifluoroacetic acid/dichloromethane mixed solvents (0.7 : 0.3 v/v) followed by the removal of the solvents in the mixture by flocculation. The results of scanning electron microscopy showed that a good dispersion of MWCTs in PET was achieved. The reinforced fibers were fabricated by the melt spinning of PET chips with small amounts of the master batch and then further postdrawing. The optimal spinning conditions for the reinforcement of fibers were a 0.6-mm spinneret hole and a 250 m/min wind-up speed. Among the four master batches, the fibers obtained from PET/master batch B made by acid-treatment had the highest enhancement of mechanical properties. For a 0.02 wt % loading of acid-treated MWCT, the breaking strength of the PET/master batch B composite fibers increased by 36.9% (from 4.45 to 6.09 cN/dtex), and the initial modulus increased by 41.2% (from 80.7 to 113.9 cN/dtex). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface nanostructures and dynamic contact angles of functionalized poly(ethylene terephthalate) fibers

An approach (a combination of techniques) to studying poly(ethylene terephthalate) (PET) fibers metal-coated by the sputtering of copper is reported. The effects of copper coatings on the surface morphology, surface chemistry, and surface energy were investigated with atomic force microscopy (AFM), energy-dispersive X-ray (EDX) analysis, and dynamic contact angle measurements. Functional nanostructures formed by sputter coating on the fiber surface were revealed with AFM. The introduction of copper onto the fiber surface was also detected by EDX analysis. The fibers functionalized by the sputter coating resulted in changes in the surface energy measured with the advancing and receding contact angles. Both the advancing and receding contact angles were reduced after sputter coating by copper, but the contact angle hysteresis was significantly increased as the coating was applied. The surface resistivity measurements revealed that sputter coating by copper considerably improved the surface conductivity of the PET fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The effect of processing conditions on structure evolution in melt spun poly(ethylene terephthalate) fibers

An investigation has been made into the structural evolution in poly(ethylene terephthalate) fibers as a function of wind-up speed (WUS) and quench air temperature (QAT). Analysis of the mechanics and mechanisms of cold drawing reveals that the fiber structure is heterogeneous. Evidence from differential scanning calorimetry (DSC) and density measurements indicates the presence of crystallites which are imperfect according to wide-angle diffraction (WAXD). Increased thread-line stress (higher WUS and higher QAT) appears to induce larger and more oriented crystallites in a progressively oriented matrix. A radially layered structure is disclosed from high resolution scanning electron microscopy (SEM) micrographs.     

Thermal analysis of heat set poly(ethylene terephthalate) fibres

Differential thermal analysis (d.t.a.) has been used for characterization of the thermal history of poly(ethylene terephthalate) (PET) fibres. The latter were treated under a variety of temperatures and times in a manner similar to conditions employed in conventional textile processing. The d.t.a. revealed an endotherm at temperatures below the main melting peak of the fibre polymer, related directly to temperature and time of thermal treatment, even with yarns that were heat set for less than 0.2 sec (e.g. false twisting process). The maximum of this low temperature endotherm is a direct measure of the effective temperature (T_eff) that has been acquired by the PET fibres during the thermal processing. In practice, several thermal treatments are often involved in textile processing. Results of this work imply that PET fibres subjected to a second heat treatment will show an additional low temperature endotherm on d.t.a. scanning, provided that the structural characteristics formed in the first thermal process are not neutralized in the second thermal process and recrystallizable material is still present in the fibre polymer.     

Dynamic mechanical analysis of poly(trimethylene terephthalate)—A comparison with poly(ethylene terephthalate) and poly(ethylene naphthalate)

The fiber properties of PTT have been the subject of several reports, although very few reports describe the properties of molded specimens. In this work, the dynamic mechanical relaxation behavior of compression‐molded PTT films has been investigated. The added flexibility of the PTT was found to lower the temperature of the β‐ and α‐transitions relative to the PET and PEN. The results suggest that the β‐transition is at least two relaxations for PET and PTT due to the increase in the breadth of the relaxation. The results seem to support the hypothesized mechanism of others, in that the β‐transition involves the relaxation of the carbonyl entity and the aromatic C1–C4 ring flips for PTT and PET, and the relaxation of the carbonyl for PEN. The β*‐ and α‐transitions for all three polymers seem to be cooperative in nature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2791–2796, 2004     

Polyester nanocomposite fibers: comparison of their properties with poly(ethylene terephthalate) and poly(trimethylene terephthalate) (II)

Summary Two polyester nanocomposites were synthesized, one with poly(ethylene terephthalate) (PET) and the other with poly(trimethylene terephthalate) (PTT), by using organoclay. The in-situ interlayer polymerization method was used to disperse the organoclay in polyesters at different organoclay contents and at different draw ratios to produce monofilaments. The thermal stability and tensile mechanical properties increased with increasing organoclay content at a DR=1 . However, the values of the tensile mechanical properties of the hybrid fibers decreased with increasing DR. The reinforcing effects of the organoclay of the PET hybrid fibers were higher than those of the PTT hybrid fibers.     

The effect of a liquid isothermal bath in the threadline on the structure and properties of poly(ethylene terephthalate) fibers

The process of melt-spinning poly(ethylene terephthalate) (PET) filament at high speeds was modified through the inclusion of a liquid isothermal bath (LIB) in the spinline. A wide range of positions, temperatures, and depths associated with the operation of the LIB were utilized in this study. The structural characteristics and mechanical properties of the as-spun fibers were characterized by birefringence, wide-angle X-ray diffraction (WAXD), infrared spectroscopy, and tensile testing. Experimental results showed that the structure and mechanical properties of the as-spun fibers were significantly influenced by the LIB operating conditions. The as-spun fibers prepared under optimum LIB conditions exhibit high birefringence and excellent mechanical properties. Results suggest the development of a critical value of threadline stress that is determined primarily by LIB depth and take-up velocity. Below this critical value, raising of LIB temperature, LIB depth, and take-up velocity resulted in increases of the apparent crystallite size, sample crystallinity, and both the crystalline and amorphous orientation. As would be expected, the mechanical properties of the fiber samples were improved in a corresponding manner. Above this critical stress value, molecular chains in the amorphous phase are stretched tautly, but the crystal growth process is restricted, resulting in a decrease in crystallite size and crystallinity, as well as a continued increase in mechanical properties. The fiber properties were also found to be very responsive to the relative location of the LIB. A unique structure, believed never before obtained in a one-step high-speed PET melt-spinning process, has been achieved that combines high amorphous orientation, low crystallinity, and high tenacity. © 1995 John Wiley & Sons, Inc.