Oxygen‐barrier properties of cold‐drawn polyesters

The improvement of oxygen‐barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET‐BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass‐transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold‐drawn polyester could be regarded as a one‐phase densified glass. This allowed an analysis of oxygen solubility in accordance with free‐volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess‐hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero‐solubility) condition. Cold drawing most effectively reduced the free volume of PET‐BB55. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 862–877, 2002     

Oxygen‐barrier properties of oriented and heat‐set poly(ethylene terephthalate)

The improvement in the oxygen‐barrier properties of poly(ethylene terephthalate) (PET) by orientation and heat setting was examined. Orientation was carried out at 65 °C by constrained uniaxial stretching to a draw ratio of about 4. Heat setting was performed at temperatures from 90 to 160 °C with the specimen taut. Orientation decreased the permeability of PET to almost one‐third that of the unoriented, amorphous polymer because of decreases in both the diffusion coefficient and the solubility coefficient. The proposed two‐phase model for oriented PET consisted of a permeable isotropic amorphous phase (density = 1.335 g/cm³) with ethylene linkages predominately in the gauche conformation and an impermeable oriented phase (density = 1.38 g/cm³) with ethylene linkages that had transformed from the gauche conformation to the trans conformation during stretching. Chain segments in the trans conformation did not possess crystalline order; instead, they were viewed as forming an ordered amorphous phase. Crystallization by heat setting above the glass‐transition temperature did not dramatically affect the permeability. However, a decrease in the diffusion coefficient, offset by an increase in the solubility coefficient, indicated that crystallization affected the barrier properties of the permeable amorphous phase. Analysis of the barrier data, assuming a two‐phase model with variable density for both the permeable and impermeable phases, revealed that the impermeable phase density increased during crystallization, approaching a value of 1.476 g/cm³. This value is consistent with previous measurements of the density of the defective crystalline phase in PET. The density of the permeable amorphous phase decreased concurrently to about 1.325 g/cm³, indicating the appearance of additional free volume. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1679–1686, 2000     

X‐ray absorption,particle orientation,and rheological behavior of talc–calcite mixed‐particle compounds in a polystyrene matrix

This article presents experimental studies of (a) X‐ray absorption, (b) particle orientation, and (c) the shear viscosity of ternary talc–calcite–polystyrene compounds. A quantitative investigation of X‐ray absorption using a wide‐angle X‐ray diffraction (WAXD) intensity method for binary mixture (PS/talc, PS/calcite) systems and ternary mixtures (PS/talc/calcite) systems is reported. The Alexander–Klug equation was used to interpret the data. X‐ray diffraction pole figures indicate that talc particles orient in shear flows perpendicular to the direction of shear with their surfaces parallel to die/mold walls. There was a general tendency in mixed particle systems for the talc particles to decrease in orientation with increasing calcite content. The shear viscosity of the compounds was measured and found to increase with increasing particle loading and vary with particle composition. The talc, calcite, and talc/calcite‐filled thermoplastic melts at higher loadings were found by creep measurements to exhibit yield values, i.e., stresses below which there is no flow. We found a viscosity–shear stress plateau at low shear stress. The true yield values are much lower than yield values measured by extrapolation of higher shear stress data. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1787–1802, 1999     

Diffusion of oxygen and carbon dioxide in thermally crystallized syndiotactic polystyrene

The diffusion, solubility, and permeability behavior of oxygen and carbon dioxide were studied in amorphous and semicrystalline syndiotactic polystyrene (s‐PS). The crystallinity was induced in s‐PS by crystallization from the melt and cold crystallization. Crystalline s‐PS exhibited very different gas permeation behavior depending on the crystallization conditions. The behavior was attributed to the formation of different isomorphic crystalline forms in the solid‐state structure of this polymer. The β crystalline form was virtually impermeable for the transport of oxygen and carbon dioxide. In contrast, the α crystalline form was highly permeable for the transport of oxygen and carbon dioxide. High gas permeability of the α crystals was attributed to the loose crystalline structure of this crystalline form containing nanochannels oriented parallel to the polymer chain direction. A model describing the diffusion and permeability of gas molecules in the composite permeation medium, consisting of the amorphous matrix and the dispersed crystalline phase with nanochannels, was proposed. Cold crystallization of s‐PS led to the formation of a complex ordered phase and resulted in complex permeation behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2519–2538, 2001     

Crystallization and melting behavior of liquid crystalline copolyesters based on poly(ethylene terephthalate)

A series of copolyesters were prepared by the incorporation of p‐hydroxybenzoic acid (HBA), hydroquinone (HQ), and terephthalic acid (TA) into poly(ethylene terephthalate) (PET). On the basis of viscosity measurements, high molar mass copolyesters were obtained in the syntheses, and ¹H‐NMR analyses indicated the total insertion of comonomers. They exhibit nematic phase above melting temperature, as observed by polarized light microscope (PLM). Their crystallization and melting behaviors were also studied by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). It was found that these copolyesters are more crystalline than copolyesters prepared from PET and HBA. Introduction of HQ/TA disrupts longer rigid‐rod sequences formed by HBA, and thus enhances molecular motion and increases crystallization rate and crystallinity. Isothermal crystallization at solid phase polymerization conditions (up to 24 h at 200°C) resulted in increased copolymer randomness (by NMR) and higher melting point, the latter attributed to structural annealing. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 369–377, 1999     

Isothermal crystallization kinetics and melting behavior of poly(ethylene terephthalate)/barite nanocomposites

Poly(ethylene terephthalate) (PET)/Barite nanocomposites were prepared by direct melt compounding. The effects of PET‐Barite interfacial interaction on the dynamic mechanical properties and crystallization were investigated by DMA and DSC. The results showed that Barite can act as a nucleating agent and the nucleation activity can be increased when the Barite was surface‐modified (SABarite). SABarite nanoparticles induced preferential lamellae orientation because of the strong interfacial interaction between PET chains and SABarite nanoparticles, which was not the case in Barite filled PET as determined by WAXD. For PET/Barite nanocomposites, the Avrami exponent n increased with increasing crystallization temperature. Although at the same crystallization temperature, the n value will decrease with increasing SABarite content, indicating of the enhancement of the nucleation activity. Avrami analyses suggest that the nucleation mechanism is different. The activation energy determined from Arrhenius equation reduced dramatically for PET/SABarite nanocomposite, confirming the strong interfacial interaction between PET chains and SABarite nanoparticles can reduce the crystallization free energy barrier for nucleus formation. In the DSC scan after isothermal crystallization process, double melting behavior was found. And the double endotherms could be attributed to the melting of recrystallized less perfect crystallites or the secondary lamellae produced during different crystallization processes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 655–668, 2009     

Structure and mechanical properties of talc‐filled blends of polypropylene and styrenic block copolymers

The structure–property relationships of isotactic polypropylene (iPP)/styrenic block copolymer blends filled with talc were examined by optical and scanning electron microscopy, wide‐angle X‐ray diffraction, and tensile‐ and impact strength measurements. The composites were analyzed as a function of the poly(styrene‐b‐ethylene‐co‐propylene) diblock copolymer (SEP) and the poly(styrene‐b‐butadiene‐b‐styrene) triblock copolymer (SBS) content in the range from 0 to 20 vol % as elastomeric components and with 12 vol % of aminosilane surface‐treated talc as a filler. Talc crystals incorporated in the iPP matrix accommodated mostly plane‐parallel to the surface of the samples and strongly affected the crystallization process of the iPP matrix. The SBS block copolymer disoriented plane‐parallel talc crystals more significantly than the SEP block copolymer. The mechanical properties depended on the final phase morphology of the investigated iPP blends and composites and supermolecular structure of the iPP matrix because of the interactivity between their components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1255–1264, 2004     

Comparison of statistical and blocky copolymers of ethylene terephthalate and ethylene 4,4′‐bibenzoate based on thermal behavior and oxygen transport properties

Poly(ethylene terephthalate) (PET) was blended with a frustrated liquid‐crystalline polymer, poly(ethylene terephthalate‐co‐4,4′‐bibenzoate) (PETBB55), in the weight ratio 70:30. Under the melt conditions used for blending, NMR analysis showed that some transesterification had occurred. Accordingly, the blended product resembled a blocky copolymer more closely than it did a physical blend. A random copolymer with the same composition was synthesized for comparison. The study examined the effect of the comonomer distribution (blocky vs random) on the thermal behavior and oxygen transport properties of the glassy and cold‐drawn polymers. The glass‐transition temperatures and the crystallization behavior suggested that the PETBB55 blocks phase‐separated as very small domains. Higher levels of orientation, as indicated by higher densities and higher trans glycol fractions, were achieved by the cold drawing of the blocky copolymer. It was speculated that the cold drawing of the blocky copolymer at temperatures up to the glass‐transition temperature of the PETBB55 blocks produced highly oriented PETBB55 domains. Constraints imposed by connections between PET and the PETBB55 blocks prevented the relaxation of the continuous PET phase, even at temperatures well above the glass‐transition temperature of the PET blocks. In this sense, the blocky copolymer embodied the concept of a self‐reinforcing polymer. As a result, an improved oxygen barrier was obtained over a wider range of cold‐draw temperatures with the blocky copolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 289–307, 2003     

Phase separation in semicrystalline blends of poly(phenylene sulfide) and poly(ethylene terephthalate). II. Effect of poly(phenylene sulfide) homopolymer solubilization of PPS‐graft‐PET copolymer on morphology and crystallization behavior

The morphology and crystallization behavior of poly(phenylene sulfide) (PPS) and poly(ethylene terephthalate) (PET) blends compatibilized with graft copolymers were investigated. PPS‐blend‐PET compositions were prepared in which the viscosity of the PPS phase was varied to assess the morphological implications. The dispersed‐phase particle size was influenced by the combined effects of the ratio of dispersed‐phase viscosity to continuous‐phase viscosity and reduced interfacial tension due to the addition of PPS‐graft‐PET copolymers to the blends. In the absence of graft copolymer, the finest dispersion of PET in a continuous phase of PPS was achieved when the viscosity ratio between blend components was nearly equal. As expected, PET particle sizes increased as the viscosity ratio diverged from unity. When graft copolymers were added to the blends, fine dispersions of PET were achieved despite large differences in the viscosities of PPS and PET homopolymers. The interfacial activity of the PPS‐graft‐PET copolymer appeared to be related to the molecular weight ratio of the PPS homopolymer to the PPS segment of the graft copolymer (M_H/M_A). With increasing solubilization of the PPS graft copolymer segment by the PPS homopolymer, the particle size of the PET dispersed phase decreased. In crystallization studies, the presence of the PPS phase increased the crystallization temperature of PET. The magnitude of the increase in the PET crystallization temperature coincided with the viscosity ratio and extent of the PPS homopolymer solubilization in the graft copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 599–610, 2000     

Effect of water sorption on oxygen‐barrier properties of aromatic polyamides

Aromatic polyamides based on poly(m‐xylylene adipamide) (MXD‐based polyamides) and poly(hexamethylene isophthalamide) (HMD‐based polyamides) were examined. Insight into the excellent gas‐barrier properties was obtained by the characterization of the effect of water sorption on the thermal transitions, density, refractive index, free‐volume hole size, and oxygen‐transport properties. Reversing the carbonyl position with respect to the amide nitrogen substantially lowered the oxygen permeability of MXD‐based polyamides in comparison with that of HMD‐based polyamides by facilitating hydrogen‐bond formation. The resulting restriction of conformational changes and segmental motions reduced diffusivity. The primary effect of water sorption was a decrease in the glass‐transition temperature (T_g) attributed to plasticization by bound water. No evidence was found to support the idea that sorbed water filled holes of free volume. When the polymer was in the glassy state, the drop in T_g accounted for hydration‐dependent changes in the density, refractive index, and free‐volume hole size. The correlation of the oxygen solubility with T_g and density confirmed the concept of oxygen sorption as filling holes of excess free volume. In some cases, water sorption produced a glass‐to‐rubber transition. The onset of rubbery behavior was associated with a minimum in the oxygen permeability. The glass‐to‐rubber transition also facilitated the crystallization of MXD‐based polymers, which complicated the interpretation of oxygen‐transport behavior at higher relative humidity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1365–1381, 2005     

Morphology and nonisothermal crystallization of in situ microfibrillar poly(ethylene terephthalate)/polypropylene blend fabricated through slit‐extrusion,hot‐stretch quenching

This study describes the morphology and nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) in situ micro‐fiber‐reinforced blends (MRB) obtained via slit‐extrusion, hot‐stretching quenching. For comparison purposes, neat PP and PET/PP common blends are also included. Morphological observation indicated that the well‐defined microfibers are in situ generated by the slit‐extrusion, hot‐stretching quenching process. Neat iPP and PET/iPP common blends showed the normal spherulite morphology, whereas the PET/iPP microfibrillar blend had typical transcrystallites at 1 wt % PET concentration. The nonisothermal crystallization kinetics of three samples were investigated with differential scanning calorimetry (DSC). Applying the theories proposed by Jeziorny, Ozawa, and Liu to analyze the crystallization kinetics of neat PP and PET/PP common and microfibrillar blends, agreement was found between our experimental results and Liu's prediction. The increases of crystallization temperature and crystallization rate during the nonisothermal crystallization process indicated that PET in situ microfibers have significant nucleation ability for the crystallization of a PP matrix phase. The crystallization peaks in the DSC curves of the three materials examined widened and shifted to lower temperature when the cooling rate was increased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 374–385, 2004     

Isothermal crystallization kinetics of chain‐extended PET

The crystallization behavior of a commercial chain‐extended PET (foam grade) was evaluated and compared to that of bottle‐grade PET. Cold and melt isothermal crystallization were analyzed by using the Avrami' model. The foam grade PET showed a slower crystallization kinetic compared to the bottle‐grade PET. The Hoffman‐Lauritzen analysis showed that the energetic barriers to nucleation and molecular mobility were higher for the chain‐extended PET. This resulted in a lower nucleation rate in both cold and melt crystallization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1966–1972, 2005     

Phase behavior and structure development in extruded poly(ethylene terephthalate)/poly(ethylene‐2,6‐naphthalate) blend

Liquid–liquid phase separation and subsequent homogenization during annealing in an extruded poly(ethylene terephthalate) (PET)/poly(ethylene‐2,6‐naphthalate) (PEN) blend were investigated with time‐resolved light scattering and optical microscopy. In the initial stage, the domain structure was developed by demixing via spinodal decomposition. In the later stage, the blend was homogenized by transesterification between the two polyesters. The crystallization rate depended on the sequence distribution of polymer chains, which was determined by the level of transesterification rather than the composition change of separated phases. When the crystallization of PEN preceded that of PET, PEN showed a higher melting point. However, when the crystallization rate of PEN was slower than that of PET, the previously formed PET crystals suppressed the crystallization of PEN, causing the coarse crystalline structure of PEN to have a lower melting point. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2625–2633, 2000     

Solvent‐induced crystallization in poly(ethylene terephthalate) during mass transport

Solvent transport in poly(ethylene terephthalate) (PET) and related phase transformation were investigated. The data of mass sorption were analyzed according to Harmon's model for Case I (Fickian), Case II (swelling), and anomalous transport. This transport process in PET is accompanied by the induced crystallization of the original amorphous state. The transformation was examined by wide‐angle X‐ray scattering, small‐angle X‐ray scattering, differential scanning calorimetry, and Fourier transform infrared spectroscopy. During this process, the matrix is under a strain state that causes different kinetic paths of crystallization as compared with that by thermal annealing. This state of strain assists the development of the solvent‐induced crystallization. The model regarding crystallization was proposed in terms of the study of long period L, the crystal thickness l_c, and the thickness of amorphous layer l_a obtained from the one‐dimensional correlation function and interface distribution function. Different kinetic paths were discovered for different crystallization processes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1444–1453, 2002     

Effect of crystallization on oxygen‐barrier properties of copolyesters based on ethylene terephthalate

The effect of crystallization from the glassy state (cold crystallization) on the oxygen‐barrier properties of copolyesters based on ethylene terephthalate with up to 10 mol % isophthalate, phthalate, or naphthalate was examined. Generally, crystallization affected diffusivity D more than solubility S; thus, the reduction in permeability P reflected primarily a reduction in D. Systematic changes in crystallinity made it possible to test free‐volume concepts in which permeation of a small gas molecule through a semicrystalline polymer is viewed as proceeding through the amorphous regions with an increased pathway (tortuosity) imposed by plateletlike crystallites. Of the copolymers studied, those with the highest isophthalate or phthalate content (10 mol %) conformed to the simple two‐phase model with constant densities of an impermeable crystalline phase and a permeable amorphous phase. Within the two‐phase model, solubility S correlated linearly with the volume fraction of the amorphous phase, and diffusivity D depended on crystallinity in accordance with the Nielsen model for randomly dispersed platelets with an aspect ratio of 4. The reduction in permeability of the other examined copolyesters could not be described only by the filler effect of crystallites. Data on solubility demonstrated a decrease in amorphous‐phase density upon cold crystallization (de‐densification) like that previously reported for polyethylene terephthalate. Increasing the isophthalate or phthalate content reduced the de‐densification effect, and 10 mol % of these comonomers was sufficient to eliminate the effect altogether. In contrast, 10 mol % naphthalate did not prevent de‐densification. This was attributed to different effects of kinked and linear comonomers on chain packing in the amorphous phase. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1911–1919, 2001     

Free volume and oxygen transport in cold‐drawn polyesters

Poly(ethylene terephthalate) (PET), poly(ethylene terephthalate‐co‐4,4′‐bibenzoate) (PETBB55), and poly(ethylene 2,6‐naphthalate) (PEN) were cold‐drawn to achieve uniform extension without crystallization or stress whitening, and oxygen transport properties were studied at temperatures from 10 to 40 °C. Correlation of oxygen solubility and polymer specific volume made it possible to consider the oriented polyester as a one‐phase densified glass. Orientation was viewed as decreasing the amount of excess‐hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium condition. Between 10 and 40 °C, the amount of excess‐hole free volume in PET decreased as the polymer approached the glass transition temperature. In contrast, temperature changes in this range had little effect on the excess‐hole free volume in PETBB55 and PEN, which were well below their glass transition temperature. Gas diffusion was viewed as discrete jumps of the oxygen molecule between holes of excess‐free volume. The jump length was extracted from the activation energy for diffusion according to a channel‐formation model. The result agreed well with the hole spacing estimated from a simple lattice model using the hole density reported in the literature. Extending the lattice model to estimate the mean excess‐free volume hole radius from the fractional free volume resulted in good correlation with the hole radius obtained from positron annihilation lifetime spectroscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 493–504, 2004     

Isothermal crystallization kinetics of PEO in poly(ethylene terephthalate)–poly(ethylene oxide) segmented copolymers. I. Effect of the soft‐block length

The isothermal crystallization kinetics of poly(ethylene oxide) (PEO) block in two poly(ethylene terephthalate) (PET)–PEO segmented copolymers was studied with differential scanning calorimetry. The Avrami equation failed to describe the overall crystallization process, but a modified Avrami equation, the Q equation, did. The crystallizability of the PET block and the different lengths of the PEO block exerted strong influences on the crystallization process, the crystallinity, and the final morphology of the PEO block. The mechanism of nucleation and the growth dimension of the PEO block were different because of the crystallizability of the PET block and the compositional heterogeneity. The crystallization of the PEO block was physically constrained by the microstructure of the PET crystalline phase, which resulted in a lower crystallization rate. However, this influence became weak with the increase in the soft‐block length. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3230–3238, 2000     

Impact of coated calcium carbonate nanofillers and annealing treatments on the microstructure and gas barrier properties of poly(lactide) based nanocomposite films

Amorphous poly(lactide) (PLA) and nanocomposite films were prepared from melt‐blending with precipitated calcium carbonate nanofillers (PCC). Nanocomposites based on uncoated PCC (PCC‐UT), stearic acid coated PCC (PCC‐S), and poly(ε‐caprolactone) coated PCC (PCC‐P) were investigated for an inorganic content fixed to 8 wt %. Using coated nanofillers allowed preserving both PLA average molar mass and thermal stability while enhancing the nanofiller dispersion state. Poly(ε‐caprolactone) was identified as the best coating for optimized morphology and thermal properties. Maxwell law accurately described the increase in oxygen barrier properties observed for the nanocomposites based on PCC‐S. A modified Maxwell law was proposed to take account of the additional increase in barrier properties evidenced for the PLA/PCC‐P nanocomposites and assigned to the particularly strong compatibility between PCL and PLA. Different annealing conditions were investigated to respectively study the impact of physical ageing and PLA crystallization on gas permeability. Different extents of physical ageing did not significantly modify the oxygen transport properties. However, a high permeability decrease was observed for the semicrystalline nanocomposites with respect to the amorphous reference PLA film. Finally, the gain in barrier properties was shown to result from both contribution of the nanofillers and the crystalline phase. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 649–658     

A new thermoplastic vulcanizate (TPV)/organoclay nanocomposite: Preparation,characterization, and properties

The preparation, characterization, and properties of the new thermoplastic vulcanizate (TPV)/organoclay nanocomposites are reported in this article. The nanocomposites were prepared by the melt intercalation method. The organoclay was first treated with glycidyl methacrylate, which acts as a swelling agent for organoclays, as well as a grafting agent for TPV (in the presence of dicumyl peroxide) during the melt mixing. The nanocomposite was intercalated, as evidenced by X‐ray diffraction. The tensile modulus of the 5% TPV/organoclay nanocomposite was higher than that of the 20% talc‐filled microcomposite. The storage modulus of the nanocomposite was higher than that of the pristine TPV. The most important observation is obtained from dynamic mechanical analysis, which reveals that the glass‐transition temperature of the polypropylene phase of the nanocomposite increases (as compared to virgin TPV), whereas the ethylene–propylene–diene monomer phase remains almost the same. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2900–2908, 2004