Thermal behavior and morphological characteristics of cationic dyeable poly(ethylene terephthalate) (CD‐PET)/metallocene isotactic polypropylene (m‐iPP) conjugated fibers

Cationic dyeable poly(ethylene terephthalate) (CD‐PET) and metallocene isotactic polypropylene (m‐iPP) polymers were extruded (in the proportions of 75/25, 50/50, 25/75) from two melt twin‐screw extruders to prepare CD‐PET/m‐iPP (and m‐iPP/CD‐PET)‐conjugated fibers of the island‐in‐sea type. This study investigated the thermal behavior and mechanical and morphological characteristics of the conjugated fibers using DSC, TGA, WAXD, melting viscosity rheometer, density indicator, tenacity measurement, and a polarizing microscope. Melting behavior of CD‐PET/m‐iPP polyblended polymers exhibited negative‐deviation blends (NDB) and the 50/50 blend showed a minimum value of the melt viscosity. Experimental results of the DSC indicated CD‐PET and m‐iPP molecules formed a partial miscible system. The tenacity of CD‐PET/m‐iPP‐conjugated fibers decreased initially and then increased as the m‐iPP content increased. Crystallinities and densities of CD‐PET/m‐iPP‐conjugated fibers presented a linear relation with the blend ratio. On the morphological observation, it was revealed that the blends were in a dispersed phase structure. In this study, the CD‐PET microfibers were successfully produced with enhanced diameters (from 2.2 to 2.5 μm). Additionally, m‐iPP colored fibers (m‐iPP fibers covered with CD‐PET polymer) were also successfully prepared. Meanwhile, the presence of PP‐graft‐MA compatibilizer improved the tenacity considerably. Blends with 10 wt % compatibilizer exhibited maximum improvement in the tenacity for m‐iPP colored fibers. The dye exhaustions of various fabrics followed the order: m‐iPP colored fibers > conventional CD‐PET fibers > CD‐PET microfibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5396–5405, 2006     

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.     

Crystalline morphology of isotactic polypropylene (iPP) in injection molded poly(ethylene terephthalate) (PET)/iPP microfibrillar blends

The poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) in situ microfibrillar blends have been prepared through a “slit die extrusion-hot stretch-quenching” process, in which PET assumes microfibrils with 0.5-15 μm in diameter depending on the hot stretching ratios (HSR, the area of the transverse section of the die to the area of the transverse section of the extrudate). The injection molded specimens of virgin iPP and the PET/iPP blends were prepared by conventional injection molding (CIM) and by shear controlled orientation injection molding (SCORIM), respectively. The effect of shear stress and PET phase with different shape on superstructures and their distribution of injection molded microfibrillar samples were investigated by means of small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). The shear (or elongational) flow during CIM and SCORIM can induce oriented lamellae (i.e. kebabs induced by shish). The shish-kebab structure appears not only in the skin and intermediated layers of CIM samples, but also in the whole region of SCORIM samples. For the neat iPP samples, a more “stretched” shish-kebab structure with higher orientation degree can be obtained in the interior region (intermediate and core layers) by the SCORIM method; moreover, the SCORIM can result in the growth of β-form crystal both in intermediate layer and in core layer, which only appears in intermediate layer of the neat iPP samples obtained by CIM. For the PET/iPP blends, interestingly, the addition of microfibrils as well as their aspect ratios can affect the orientation degree of kebabs only in the intermediate layers, and the addition of microfibrils with a low aspect ratio can bring out a considerable increase in the orientation degree of kebabs along the flow direction. However, for the SCORIM, the addition of microfibrils seems to be a minor effect on the orientation degree of kebabs, and it tends to hamper the formation of a more “stretched” shish-kebab structure and suppresses the growth of β-form crystal distinctly. Furthermore, It appears from experiment that γ-form crystals can grow successfully in this oriented iPP melt with the synergistic effect of shear and pressure only when the growth of β crystals can be restrained by some factors, such as the PET dispersed phase and thermal conditions (cooling rate).     

Shear amplification and re-crystallization of isotactic polypropylene from an oriented melt in presence of oriented clay platelets

In this study, we first prepared isotactic Polypropylene (iPP)/organoclay nanocomposite specimens via twin-screw extruder and by adding compatibilizer (maleic anhybride grafted PP). Then PP and the composites were subjected to dynamic packing injection molding, in which the melt was firstly injected into the mold then forced to move repeatedly in a chamber by two pistons that moved reversibly with the same frequency as the solidification progressively occurred from the mold wall to the molding core part. The dispersion and orientation of layered organoclay in the nanocomposite were estimated by transmission electron microscopy (TEM) and 2d-wide angle X-ray scattering (2d-WAXS). A much higher degree of orientation of PP was found in the composites compared with the pure PP. This was explained by so called shear amplification in that a great enhancement of local stress occurred in the small interparticles region of two adjacent layered tactoids with different velocities. Furthermore, re-crystallization of isotactic polypropylene (iPP) by melting the dynamic packing injection molded samples has been investigated by polarizing light microscopy (PLM). A highly oriented threadlike crystallites was observed for the first time when crystallization occurs by melting the dynamic packing injection molded samples at 180 °C. However, spherulitic morphology is always obtained once PP crystallizes from an isotropic melt by melting the samples at 200 °C. The shear amplification mechanism and the formation mechanism of oriented threadlike crystallites have been discussed in detail.     

Crystallization of poly(ethylene terephthalate) (PET) from the oriented mesomorphic form

Yarns of different inherent viscosities, in the range 0.6–1.1 dL/g, spun in industrial plants, and drawn at room temperature to obtain mesomorphic samples, have been characterized. The evolution from the mesomorphic form toward the triclinic crystalline form has also been studied by combined differential scanning calorimetry (DSC), dynamic mechanical analyses (DMA), and accurate wide angle X-ray diffraction experiments. The DMA analysis of the mesomorphic samples allows better resolution of the glass transition and crystallization phenomena, which are superimposed in the DSC scans. The degree of molecular orientation in the mesomorphic samples, and the temperature of crystallization from the mesomorphic form (60–80°C), are essentially independent of the polymer molar mass. © 1994 John Wiley & Sons, Inc.     

Microstructure of amorphous and crystalline poly(ethylene terephthalate)

The microstructures of amorphous and crystalline poly(ethylene terephthalate) (PET) homopolymers have been determined in terms of their trans and gauche conformational isomer contents by using a combination of infrared and density characterization techniques. The effects of isothermal crystallization (from the glassy state between 105–150°C), as well as the effects of different monomer units in the polymerization process, have been investigated. Results indicate that samples, polymerized from different monomer and catalyst systems, show different microstructures in terms of trans and gauche isomers.These variations result in significant differences in PET optical properties. Further investigations find that these dissimilar behaviors accompany conformational isomer variations in the amorphous phase, suggesting different transformation mechanisms of trans and gauche isomers at early stages of crystallization. These unlike microstructural transformation processes give rise to further changes, which are evident in terms of the intensity of Vv light scattering, haze values, thermal properties, and FTIR spectral results. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1965–1976, 1998     

Morphology and mechanical behavior of isotactic polypropylene (iPP)/syndiotactic polypropylene (sPP) blends and fibers

The crystallization morphologies and mechanical behaviors of iPP/sPP blends and the corresponding fibers were investigated in the present work. For all the investigated iPP/sPP blends, the starting crystallization temperature of sPP during cooling process was significantly increased with increasing iPP content. The iPP/sPP blends are strongly immiscible at the conventional melt processing temperatures, in consistence with the literature results. As isothermally crystallized at 130 °C, sPP still keeps melt state, while iPP component is able to crystallize and the spherulites become imperfect accompanied by decreasing of the crystallite size as sPP content increases. The addition of sPP decreases the crystallinity of iPP/sPP blends and fibers. The storage modulus, E′, of the iPP/sPP blends is higher than that of sPP homopolymer in the temperature range from −90 to 100 °C. The iPP/sPP fibers can be prepared favorably by melt-spinning. As sPP content exceeds 70%, the elastic recovery of the iPP/sPP fibers is approximately equal to that of sPP homopolymer fiber. The drawability of the as-spun fiber of iPP/sPP (50/50) is better than that of sPP fiber, which improves the fiber processing performance and enhances the mechanical properties of the final product. The drawn fiber of sPP presents good elastic behavior within the range of 50% deformation, whereas the elastic property of the iPP/sPP (50/50) fiber slightly decreases, but still much better than that of iPP fiber.     

Non-isothermal Crystallization of Poly(ethylene terephthalate) with Poly(oxybenzoate-p-trimethylene terephthalate) Copolymer

The influence of a poly(oxybenzoate-p-trimethylene terephthalate) copolymer, designated T64, on the non-isothermal crystallization process of poly(ethylene terephthalate) (PET) was investigated. All samples were prepared by solution blending in a 60/40 by weight phenol/tetrachloroethane solvent at 50°C. The solidification process strongly depended on cooling rate and composition of system. The crystallization rate of blends was estimated by crystallization rate parameter (CRP) and crystallization rate coefficient (CRC). From these results of CRP and CRC, it was predicted that the overall non-isothermal crystallization rate of PET would be accelerated by blending with 1–15 wt% of T64. The acceleration of PET crystallization rate was most pronounced in the PET/T64 blends with 5 wt% T64. The observed changes in crystallization behavior are explained by the effect of the physical state of the copolyester during PET crystallization as well as the amount of copolymer in the blends. An Ozawa plot was used to analyze the data of non-isothermal crystallization. The obvious curvature in the plot indicated that the Ozawa model could not fit the PET/T64 blend system well, and there was an abrupt change in the slope of the Ozawa plot at a critical cooling rate.     

Study of poly(ethylene terephthalate)/polypropylene microfibrillar composites. I. Morphological development in melt extrusion

Poly(ethylene terephthalate)/polypropylene (PET/PP) blends of different compositions were extruded through a 2‐mm capillary die using a corotating twin‐screw extruder. The extrudates were cryogenically fractured and examined using scanning electron microscopy. The viscosity ratio of the constituent polymers alone was found to be unsuitable for explaining the polymer blend morphology. At a PET concentration of 20%, the extrudate consists of three regions. The skin layer, which is about 10 μm thick, has a lower concentration of the dispersed PET phase than the overall concentration. The intermediate region, which is about 400 μm thick, has profuse PET fibers and some small PET particles. The central region, which is approximately 800 μm in diameter, mainly contains PET particles that are generally bigger. A low barrel temperature, low die temperature, and fast cooling rate helped to retain the fibers near the extrudate skin. Meanwhile, the variation of the barrel temperature, die temperature, and cooling media did not produce a significant affect on the PET particle size distribution in the central region of the extrudate. A high screw speed and a high postextrusion drawing speed were very effective in producing fibers in the extrudates through elongation of particles. At a PET concentration of 30%, coalescence of the PET phase was prevalent, leading to the formation of PET platelets near the extrudate skin and irregular PET networks in the central region of the extrudate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1743–1752, 2003     

Dynamic rheology of branched poly(ethylene terephthalate)

Branched poly(ethylene terephthalate)s (BPET) of varying molar mass have been synthesized with glycerol and pentaerythritol as branching comonomers, and their rheological behaviour has been measured. In this study, we describe the use of dynamic and steady shear measurements to examine the influence of the proportion and type of branching comonomers on the melt viscosity of BPET. Steady shear rheology has been used to measure the shear rate dependence on the apparent viscosity. Dynamic (oscillatory) measurements have been used to obtain the complex viscosity η* (ω) and the storage modulus G′ (ω) as a function of frequency. G′ (ω) represents the elastic component of the viscoelastic melt; this variable was measured as a function of frequency at various temperatures in the linear viscoelastic domain. Linear poly(ethylene terephthalate) (LPET) exhibited nearly Newtonian behaviour, while BPET became shear thinning at relatively low shear rates. The viscosity and elasticity increased with increase in molar mass and specific branching composition. This was attributed to increasing chain entanglements at higher molar mass and to increasing branching of the BPET. At higher shear rates or frequencies, the BPET show much greater shear thinning character than LPET and this is more pronounced with higher branching proportions. © 2000 Society of Chemical Industry     

Raman spectroscopy of stressed samples of oriented poly(ethylene terephthalate)

Measurements of the shift and change of shape of the 1616 cm⁻¹ Raman scattering peak of two moderately oriented samples of poly(ethylene terephthalate) (PET) under tensile loads of up to 0.2 GPa are reported, together with the corresponding strains. To obtain reproducible results load cycling procedures were adopted similar to those established for the study of viscoelastic behaviour. The Raman scattering was observed with polarized incident and scattered light, with the polarization directions either both parallel or both perpendicular to the draw direction in the samples. The results showed that for both samples the Raman shift was linearly related to the applied stress below the yield point. Up to the yield point very little change of line width was observed but above the yield point the width increased significantly. Differences in both widths and shifts were observed for the two polarization directions at the same stress level. The results are discussed in terms of the usual assumptions that the shift of the line gives a measure of the average stress in those chains which predominantly contribute to the peak and that the width and shape of the line give information about the spread of stresses. It is concluded that the technique can give useful information about the molecular stress distribution in thick samples of moderately oriented PET under load, including information about the different stress distributions on chains at different angles to the draw direction.     

Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Isothermal crystallization

Poly(ethylene‐octene) (POE), maleic anhydride grafted poly(ethylene‐octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE, PBT/mPOE, and PBT/mPOE/POE blends by a twin‐screw extruder. Observation by scanning electron microscopy revealed improved compatibility between PBT and POE in the presence of maleic anhydride groups. The melting behavior and isothermal crystallization kinetics of the blends were studied by wide‐angle X‐ray diffraction and differential scanning calorimeter; the kinetics data was delineated by kinetic models. The addition of POE or mPOE did not affect the melting behavior of PBT in samples quenched in water after blending in an extrude. Subsequent DSC scans of isothermally crystallized PBT and PBT blends exhibited two melting endotherms (T_mI and T_mII). T_mI was the fusion of the crystals grown by normal primary crystallization and T_mII was the melting peak of the most perfect crystals after reorganization. The dispersed second phase hindered the crystallization; on the other hand, the well dispersed phases with smaller size enhanced crystallization because of higher nucleation density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization kinetics of oriented poly (ethylene terephthalate) from the glassy state

Crystallization kinetics of oriented poly(ethylene terephthalate) have been studied in a temperature range close to T_g. It has been shown that orientation of the amorphous phase promotes a substantial increase in crystallization rate. This effect, in turn, depends on the crystallization temperature: the higher the temperature, the stronger is the effect of orientation. From experimental results it was possible to make an estimation of parameters describing quantitatively the crystallization kinetics in the oriented state.     

Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Nonisothermal crystallization

Poly(ethylene octene) (POE), maleic anhydride grafted poly(ethylene octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE (20 wt % POE), PBT/mPOE (20 wt % mPOE), and PBT/mPOE/POE (10 wt % mPOE and 10 wt % POE) blends with an extruder. The melting behavior of neat PBT and its blends nonisothermally crystallized from the melt was investigated with differential scanning calorimetry (DSC). Subsequent DSC scans exhibited two melting endotherms (T_mI and T_mII). T_mI was attributed to the melting of the crystals grown by normal primary crystallization, and T_mII was due to the melting of the more perfect crystals after reorganization during the DSC heating scan. The better dispersed second phases and higher cooling rate made the crystals that grew in normal primary crystallization less perfect and relatively prone to be organized during the DSC scan. The effects of POE and mPOE on the nonisothermal crystallization process were delineated by kinetic models. The dispersed phase hindered the crystallization; however, the well‐ dispersed phases of an even smaller size enhanced crystallization because of the higher nucleation density. The nucleation parameter, estimated from the modified Lauritzen–Hoffman equation, showed the same results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization kinetics of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) blends

The crystallization kinetics of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) (PET/PEN) blends were investigated by DSC as functions of crystallization temperature, blend composition, and PET and PEN source. Isothermal crystallization kinetics were evaluated in terms of the Avrami equation. The Avrami exponent (n) is different for PET, PEN, and the blends, indicating different crystallization mechanisms occurring in blends than those in pure PET and PEN. Activation energies of crystallization were calculated from the rate constants, using an Arrhenius‐type expression. Regime theory was used to elucidate the crystallization course of PET/PEN blends as well as that of unblended PET and PEN. The transition from regime II to regime III was clearly observed for each blend sample as the crystallization temperature was decreased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 23–37, 2001     

Characterization of optical anisotropy in oriented poly(ethylene terephthalate) films using reflectance difference spectroscopy

We present a new method for the characterization of molecular orientation in polymer materials based on the determination of the optical anisotropy by reflectance difference spectroscopy (RDS). Data interpretation is quite straightforward even in the case of thin transparent films, as shown for the example of biaxially oriented poly(ethylene terephthalate) (PET). A comparison with birefringence data obtained by spectroscopic ellipsometry (SE) demonstrates the superior measurement precision and robustness of RDS. Using azimuth dependent RDS, the position of the optical eigenaxes in the film plane can be established, which are found to coincide with the crystalline orientation determined by wide-angle X-ray scattering.     

Roll-drawing and die-drawing of toughened poly(ethylene terephthalate). Part 2. Fracture behaviour

Orientation of polymers in the solid-state has been used for a long time in enhancing the properties of the products and the die-drawing process at Leeds University (UK) and the roll-drawing process at IMI (Canada) have been used to produce oriented polymer products in a wide variety of shape and sizes. In this work, we explore the fracture behaviour of isotropic and oriented toughened poly(ethylene terephthalate) (PET) in order to improve the toughness of the oriented products in a direction other than the principal draw direction.The fracture behaviour of isotropic and oriented PET homopolymer and the two PET blends (containing 10% polyethylene elastomer and 10% compatibilized elastomer) was studied using the multi-specimen J-integral approach. In the isotropic case, the compatibilized blend had higher toughness than the homopolymer and the non-compatibilized blend. The oriented sheets from the die-drawing and roll-drawing process, drawn to a draw ratio of 3.2 at 170 °C were tested with the initial notch both parallel and perpendicular to the draw direction. For the former case, the compatibilized blend was tougher and in the other direction the drawn homopolymer was tougher than the blends. At similar draw ratios, the fracture behaviour and the toughness of the oriented sheets from the die-drawing and roll-drawing processes were identical.     

Crystallization behavior and morphology of double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers

Double crystalline poly(trimethylene terephthalate)/poly(ethylene oxide terephthalate) copolymers (PTT/PEOT), with PTT content ranging from 16.5 to 65.5 wt%, were synthesized by melt copolycondensation. The morphological transformation of samples from microphase separation to macrophase separation was investigated by gel permeation chromatography and transmission electron microscopy. Differential scanning calorimetry and in situ wide‐angle X‐ray diffraction suggested that all copolycondensation samples displayed double crystalline behavior. The melt‐crystallization peak temperatures (T_{m, c} values) of PTT chains monotonously increased with increasing PTT content and were higher than that of homo‐PTT when the content of PTT was above 30.6 wt%. Interestingly, T_{m, c} values of PEOT chains were also increased with increasing PTT content. Polarized optical microscopy revealed that all copolycondensation samples studied could form ring‐banded spherulites and band spacing increased with increasing T_c values. In addition, band spacing decreased with increasing PTT content at a given T_c. Strangely, although PEOT was the main component in all copolycondensation samples, spherulitic morphology formed by the advance crystallization of PTT did not change after PEOT crystallization. Only a subtle change of quadrant tones was detected. © 2012 Society of Chemical Industry     

Glycolysis of poly(ethylene terephthalate) wastes in xylene

To reclaim the monomers or prepare intermediates suitable for other polymers zinc acetate catalayzed glycolysis of waste poly(ethylene terephthalate) (PET) was carried out with ethylene or propylene glycol, with PET/glycol molar ratios of1 : 0.5–1 : 3, in xylene at 170–245°C. During the multiphase reaction, depolymerization products transferred to the xylene medium from the dispersed PET/glycol droplets, shifting the equilibrium to glycolysis. Best results were obtained from the ethylene glycol (EG) reaction at 220°C, which yielded 80 mol % bis-2-hydroxyethyl terephthalate monomer and 20 mol % dimer fractions in quite pure crystalline form. Other advantages of employment of xylene in glycolysis of PET were improvement of mixing at high PET/EG ratios and recycling possibility of excess glycol, which separates from the xylene phase at low temperatures. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2311–2319, 1998     

Rubber-Toughened polymer blends of polycarbonate (PC) and poly (ethylene terephthalate (PET)

The intrinsically impact brittle nature of the PC/PET blends can be effectively toughened by incorporating butylacrylate core-shell rubber. The rubber-modified PC/PET blend possess both excellent low temperature impact properties and reduced notch sensitivity. The ductile-brittle transition temperature of the blend decreases with the increase of rubber content. The presence of rubber in the PC/PET blend does not relieve the strain rate induced yield stress increase. Two separate modes, localized shear yielding and mass hear yielding, work simultaneously in the rubber toughening mechanism. The plane-strain localized shear yielding dominates the toughening mechanism at lower temperature and results in brittle failure. At higher temperature, the planestress mass shear yielding dominates the toughening mechanism and results in ductile failure. The critical plastic zone volume can be used to interpret the observed phenomenon.