Correlation between interlamellar amorphous structure and gas permeability in poly(lactic acid) films

We have investigated the relationship between amorphous structure and its gas permeability of poly(lactic acid) (PLA) using differential scanning calorimetry, wide‐angle X‐ray scattering, and small‐angle X‐ray scattering measurements. We focused on the hierarchical interlamellar amorphous structure of various gas‐permeable PLA films. The films crystallized just above T_g did not have any long‐spacing period peaks at the room temperature even with the existence of crystals; conversely, peaks could be observed from long spacing periods with heating. Therefore, the interlamellar amorphous density became as high as crystalline region one at the room temperature. These high‐density amorphous regions, the so‐called rigid‐amorphous phase, reduced the gas diffusion and permeation. In the case of samples crystallized above 90°C, the long spacing period peaks could be observed even at the room temperature. The amorphous region did not develop the rigid‐amorphous phase, and the gas permeability depended only on crystallinity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40626.     

Structure and characterization of poly[(vinylidene fluoride)‐co‐hexafluoropropene]–(dibutyl phthalate) blends

Blends of poly[(vinylidene fluoride)‐co‐hexafluoropropene] with dibutyl phthalate were examined by wide‐ and small‐angle X‐ray scattering, differential scanning calorimetry and dynamic mechanical spectroscopy, in order to study the influence of amount of plasticizer and the crystallization rate on the crystallinity and lamellar morphology of the copolymer. The dibutyl phthalate seems, at least for the cooling and heating rates used, simply to dilute the crystalline phase without affecting the amount of polymer that is able to crystallize. Furthermore, the small‐angle X‐ray scattering technique points out that the plasticizer mostly enters the amorphous phase either outside or inside the lamellar stacks. © 2001 Society of Chemical Industry     

Creep deformation and its correspondence to the microstructure of different polyester industrial yarns at room temperature

The room temperature creep behaviors and related microstructural changes of a high‐tenacity (HT) poly(ethylene terephthalate) (PET) industrial yarn and a super‐low‐shrinkage (SLS) PET industrial yarn were investigated and compared by using wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering (SAXS), birefringence measurements and Fourier transform infrared spectroscopy (FTIR) in order to identify their respective underlying creep mechanisms. The crystal structure including crystalline orientation and crystallinity of fibers did not show obvious changes after the creep process, while the amorphous structures varied with creep stress. The HT yarn creep deformation was mainly elastic, and its creep recovery ratio was high. The amorphous orientation, amorphous layer thickness and degree of conformation change from gauche to trans conformers showed a slight increase. The mechanism of this slight change is that the coiled molecular chains are oriented under tensile loading and most of the extended chains are disoriented under offloading in the small amorphous region. By contrast, the SLS yarn underwent plastic creep deformation with a low recovery ratio. After the creep test, the amorphous orientation and lamellar thickness both increased but the crystallinity remained unchanged. The creep mechanism for the SLS yarn is that the molecular chains in the large amorphous domain are easily extended and oriented subjected to tensile loading, while conformation transition from gauche to trans conformers and the formation of irreversible mesophase take place. © 2018 Society of Chemical Industry     

High modulus polypropylene fibers. II. Influence of fiber preparation upon structure and morphology

The influence of drawing on the limiting draw ratio upon formation of the morphological structure of fibers spun from binary polypropylene (PP) blends was studied. Fibers were spun from a fiber‐grade CR‐polymer and from the blends of a fiber‐grade CR‐polymer with a molding‐grade polymer in the composition range of 10–50 wt % added. As‐spun fibers were immediately moderately and additionally highly drawn at the temperature of 145°C. The structure and morphology of these fibers were investigated by small‐angle X‐ray scattering, wide‐angle X‐ray scattering, differential scanning calorimetry, scanning electron microscopy, density, birefringence, and sound velocity measurements. It was shown that continuously moderately drawn fibers are suitable precursors for the production of high tenacity PP fibers of very high modulus, because of so called oriented “smectic” structure present in these fibers. With drawing at elevated temperature, the initial metastable structure of low crystallinity was disrupted and a c‐axis orientation of monoclinic crystalline modification was developed. Hot drawing increased the size of crystallites and crystallinity degree, the orientation of crystalline domains, and average orientation of the macromolecular chains and resulted in extensive fibrillation and void formation. It was found that the blend composition has some influence on the structure of discontinuously highly drawn fibers. With increasing the content of the molding‐grade polymer in the blend, the size of crystalline and amorphous domains, density and crystallinity, as well as amorphous orientation decreased. Relationship has been established between the mechanical properties, crystallinity, and orientation of PP fibers. It was confirmed that by blending the fiber‐grade CR‐polymer by a small percentage of the molding‐grade polymer, maximization of elastic modulus is achieved, mainly because of higher orientation of amorphous domains. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1067–1082, 2006     

Insights into process–structure–property relationships of poly(ethylene terephthalate) industrial yarns by synchrotron radiation WAXD and SAXS

Synchrotron radiation wide angle X‐ray diffraction (WAXD) and small angle X‐ray scattering (SAXS) were performed to study the structures of four typical types of poly(ethylene terephthalate) (PET) industrial yarns. Three‐dimensional structural models of the yarns and comprehensive insights into the process–structure–property relationships were gained. High spinning speed, low draw ratio, and high heat‐setting temperatures lead to HMLS yarns with high crystallinity, high amorphous orientation, densely packed lamellar stacks, and a small tilting angle of crystalline lamellae. High draw ratio tends to result in PET industrial yarns with large long period and a large tilting angle of lamellae. Heat‐setting process has a significant influence on the amorphous orientation and crystalline structures, such as crystallinity, crystallite size, as well as crystal grain number. Compared with other structure characteristics, amorphous orientation plays a more important role in determining the tenacity, initial modulus, part load elongation, ultimate elongation, as well as shrinkage of PET industrial yarns. The crystal grain number seems to have an effect on the initial modulus, while the long period influences the elongation of the yarns to some extent. In addition, the small tilting angle of crystalline lamellae may relate to the dimensional stability of PET yarns. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42512.     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. IV. Morphological investigations using X‐ray photoelectron spectroscopy

Morphological investigations of poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA)‐g‐polystyrene sulfonic acid membranes prepared by radiation‐induced graft copolymerization of styrene onto PFA films followed by sulfonation were performed by X‐ray photoelectron spectroscopy. The analyzed materials included grafted film and sulfonated membrane samples having various degrees of grafting. Original PFA film was used as a reference material. The results of the X‐ray photoelectron spectral analysis show that PFA film undergoes changes in terms of chemical compositions and binding energies of its basic elemental components under the influence of membrane preparation procedure, i.e., grafting and sulfonation. The chemical compositions of the surfaces of the membranes were found to be dependent on the degree of grafting unlike the binding energies of their elemental components (C, F, O, and S), which were found to be independent of the degree of grafting. The atomic ratio of F/C was found to decrease drastically with the increase in the degree of grafting and the membranes were found to have almost pure hydrocarbon structure at the layers close to their surfaces where degradation is suggested to be concentrated. The results of these investigations suggest that the morphology of the membranes plays an important role in the chemical degradation of the membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2455–2463, 2000     

Dependence of alcohol vapor‐induced crystallization on gas and vapor permeabilities of poly(lactic acid) films

The effects of methanol and ethanol vapor‐induced crystallization on vapor and gas permeabilities and on the structure of poly(lactic acid) (PLA) films were systematically investigated. At high temperature conditions, the vapor permeability of PLA films decreased with increasing exposure time. The PLA films that were exposed to alcohol vapor became slightly cloudy, and no changes in chemical structure were observed. Alcohol vapor‐induced crystallization formed α‐crystal structure. The vapor permeability decreased with increasing crystallinity. However, nitrogen permeability slightly increased after vapor‐induced crystallization. The dependence of crystallinity on vapor and gas permeabilities was different from each penetrant. Total crystalline structures, including continuous crystal structures, remaining amorphous regions, and their interface depend on vapor and gas permeabilities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40140.     

Crystallization behavior of poly(ethylene terephthalate‐co‐neopentyl terephthalate‐co‐ethylene isophthalate‐co‐neopentyl isophthalate) copolyester and its application in laminated tin‐free steel

A low crystallinity, the copolyester poly(ethylene terephthalate‐co‐neopentyl terephthalate‐co‐ethylene isophthalate‐co‐neopentyl isophthalate) (PENIT) was synthesized and applied for laminated tin‐free steel. The structures and thermal properties of the copolyester were characterized by ¹H‐NMR, thermogravimetry analysis, differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscopy. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and polarized optical microscopy results show that the crystallization ability of the copolyester decreased obviously. Meanwhile, the peel strength, crystallinity, and water‐vapor permeability of the copolyester film were also measured at varied lamination temperatures. The result confirm that an improvement in the lamination temperature led to an increased ratio of amorphous PENIT to crystalline PENIT and decreased structural orientation, and the decrease in the structural orientation sped up the increase in the rate of water‐vapor permeability. On the basis of the purpose of reducing a detrimental effect on the corrosion resistance caused by water permeation, a reasonable lamination temperature was selected. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42308.     

Spherulitic structures of poly [tetrafluoroethylene‐co‐(perfluoroalkyl vinyl ether)]

Spherulitic textures of poly[tetrafluoroethylene‐co‐(perfluoropropyl vinyl ether)] (PFA) were examined in detail using polarized optical microscopy. The PFA consisting of random comonomer units among the tetrafluoroethylene units crystallizes as spherulites composed of lamellae, although polytetrafluoroethylene usually forms extended‐chain crystals because of the rigid nature of 13/6 helices. The spherulites obtained exhibit positive birefringence since the polymer crystal has a larger refractive index in the direction normal to the chain than that along it. These fluorocopolymers exhibit a thicker long period of at least 30 nm in small‐angle X‐ray scattering profiles than is generally the case for hydrogenated crystalline polymers. In these copolymers, we consider the formation of a switchboard‐type lamellae model according to P. J. Flory's suggestion. In addition, we find the overlooked reflections near 2θ = 8.5° based on the superlattice in wide‐angle X‐ray diffraction profiles of fluorocopolymers with high reproducibility. From this result, it was found that the lattice constant that was previously proposed is required to be refined to twice the value on the a‐ and b‐axes of the reciprocal lattice to assign all the reflection indices. Copyright © 2007 Society of Chemical Industry     

Structural investigations of poly(ethylene terephthalate)‐graft‐polystyrene copolymer films

Structural investigations of poly(ethylene terephthalate)‐graft‐polystyrene (PET‐g‐PS) films prepared by radiation‐induced grafting of styrene onto commercial poly(ethylene terephthalate) (PET) films were carried out by FTIR, X‐ray diffraction (XRD), and differential scanning calorimetry (DSC). The variation in the degree of crystallinity and the thermal characteristics of PET films was correlated with the amount of polystyrene grafted therein (i.e., the degree of grafting). The heat of melting was found to be a function of PET crystalline fraction in the grafted films. The grafting is found to take place by incorporation of amorphous polystyrene grafts in the entire noncrystalline (amorphous) region of the PET films and at the surface of the crystallites. This results in a decrease in the degree of crystallinity with the increase in the degree of grafting, attributed to the dilution of PET crystalline structure with the amorphous polystyrene, without almost any disruption in the inherent crystallinity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1949–1955, 2002; DOI 10.1002/app.10515     

Small‐angle X‐ray scattering investigation of the deformation processes in the amorphous phase of high density polyethylene

In situ small‐angle X‐ray scattering of high density polyethylene under uni‐axial tensile test was used for investigating the deformation at the scale of the periodic crystalline–amorphous nano‐structure. The more or less uniform elastic straining of the rubbery amorphous layers is discussed in terms of mechanically active intercrystalline tie chains. Correlation is made with the long‐term use properties. It is concluded that this approach is a powerful means to assess the mechanical efficiency of tie molecules. Copyright © 2004 Society of Chemical Industry     

Structure and properties of oriented polyethylene films

Cast films of a metallocene Linear Low Density Polyethylene (mLLDPE) have been cold‐drawn in the machine direction in two sequential steps to form ultra‐oriented films. The initial films were cast under low shear conditions to form essentially isotropic films, as shown by very low orientation birefringence. The first draw yields moderately oriented films, which display block‐shear type chevron morphology. Under controlled conditions, void formation occurs during the second draw and the ultradrawn films whiten (become opaque), and display a fine crystalline morphology. Surprisingly, the films do not become more permeable; rather, they become high barrier films. In their ultra‐oriented state, the water vapor transmission of the films is equivalent to that of poly(vinylidene chloride) (PVDC). The transport behavior of the films to various gases was studied using transient permeation methods. The decrease in permeability with orientation is attributed to an increase in the degree of crystallinity and increase in tortuosity due to the blocky crystalline morphology. A decrease in the permeability of the amorphous phase due to an increase in the amorphous phase density is also suggested by the data.     

Permeability of oxygen and nitrogen gases in ethyl cellulose solid films retaining cholesteric liquid crystalline order

Ethyl cellulose (EC) films that retain lyotropic and thermotropic cholesteric liquid crystalline order, and an amorphous EC film were prepared. The liquid crystalline order was identified by optical measurements. The comparative permeability of oxygen and nitrogen gases for three kinds of EC film was determined, and the applicability of the EC films that retained cholesteric liquid crystalline order to oxygen enrichment are discussed. The permeability of oxygen or nitrogen gas for the liquid crystalline films was lower than that for the amorphous ones. The activation energy for the permeability coefficient of oxygen gas was ca. 3.5 kcal/mol. The ratio of permeability coefficient for oxygen gas to that for nitrogen gas was less than 4. Interestingly, the permselectivity of oxygen and nitrogen gases for the liquid crystalline films was greater than that for the amorphous ones. © 1996 John Wiley & Sons, Inc.     

Thermal and wide angle X‐ray analysis of chemically and radiation‐crosslinked low and high density polyethylenes

Low and high density polyethylenes (PE) were crosslinked by two methods, namely, chemically by use of different amounts of tert‐butyl cumyl peroxide (BCUP) and by irradiation with different doses of electron beam. A comparison between the effects of these two types of crosslinking on crystalline structure, crystallinity, crystallization, and melting behaviors of PE was made by wide angle X‐ray diffraction and DSC techniques. Analysis of the DSC first heating cycle revealed that the chemically induced crosslinking, which took place at melt state, hindered the crystallization process and decreased the degree of crystallinity, as well as the size of crystals. Although the radiation‐induced crosslinking, which took place at solid state, had no significant influence on crystalline region, rather, it only increased the melting temperature to some extent. However, during DSC cooling cycle, the crystallization temperature showed a prominent decrease with increasing irradiation dose. The wide angle X‐ray scattering analysis supported these findings. The crystallinity and crystallite size of chemically crosslinked PE decreased with increasing peroxide content, whereas the irradiation‐crosslinked PE did not show any change in these parameters. As compared with HDPE, LDPE was more prone to crosslinking (more gel content) owing to the presence of tertiary carbon atoms and branching as well as owing to its being more amorphous in nature. HDPE, with its higher crystalline content, showed relatively less tendency toward crosslinking especially by way of irradiation at solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3264–3271, 2006     

Microstructure and mechanical properties of a polyethylene/polydimethylsiloxane composite prepared using supercritical carbon dioxide

A polymer composite of polyethylene (PE) and polydimethylsiloxane (PDMS) was prepared using supercritical carbon dioxide despite the two polymers usually being immiscible and possessing a phase‐separated morphology. This article reports in detail the preparation, microstructure, crystallinity, and mechanical properties of the resulting PE/PDMS composite. The formation mechanism of the PE/PDMS composite consisted of supercritical impregnation of an octamethylcyclotetrasiloxane (D4) monomer and an initiator into a PE substrate followed by in situ polymerization within the substrate. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering measurements showed that PE and PDMS were blended at the nanometer level. The PDMS generated in the amorphous region of PE did not affect its crystallinity. Dynamic viscoelastic analyses and tensile tests were used to measure the mechanical properties of the composites including storage and Young's modulus, fracture stress, and strain. These properties were found to depend on the composition of the composite. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Determination of the physicochemical characteristics and electrical performance of postsulfonated and grafted sulfonated derivatives of poly(para‐phenylene) as new proton‐conducting membranes for direct methanol fuel cell

Poly(para‐phenylene)s (PPPs) are an interesting class of rigid‐rod polymers that have excellent thermal and mechanical properties. Because of their high degree of crystallinity and lower permeability to methanol, PPPs are insoluble and infusible. A number of methods have been developed to synthesize substituted sulfonated PPPs bearing lateral chains to improve their solubility. In this work, a comparison of the physicochemical properties of three PPP‐based polymers is made with respect to Nafion membranes. One of these polymers was prepared with the postsulfonation method, and the other two were made with a new method of grafting developed in the Commissariat à l'Energie Atomique laboratory (a grafted sulfonated PPP polymer and a grafted perfluorinated sulfonated polymer). The sulfonated PPP polymers were examined for their mechanical properties, small‐angle X‐ray scattering, water absorption, proton conductivity, and methanol permeability. Relations between structures and properties were also investigated. Performances in fuel‐cell tests were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 944–952, 2006     

Phase behavior of side‐chain liquid‐crystalline elastomers and their precursors containing para‐nitro azobenzene

Side‐chain liquid‐crystalline copolymethacrylates (PMm's), containing para‐nitro azobenzene as the mesogenic group and 2‐hydroxylethyl methacrylate (HEMA) as a comonomer, were synthesized by radical polymerization, and their corresponding liquid‐crystalline elastomers (LCEm's) were prepared through chemical crosslinking. All of the polymers (PMm's) and the elastomers studied showed enantiotropic smectic A phases; the clearing temperature (T_i) of the PMm polymers decreased with increasing amount of HEMA, and the T_i of the corresponding LCEm's decreased compared to that of their precursors. Small‐angle X‐ray scattering studies on the copolymers quenched from their liquid‐crystalline phases indicated that the characteristic distance increased with increasing amorphous component content and thus, the amorphous components were in between the smectic layers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2275–2279, 2003     

Pebax membrane for CO2/CH4 separation: Effects of various solvents on morphology and performance

In this study, the effects of different solvents on the morphology and permeation of poly(ether‐block‐amide) (Pebax‐1657) membranes were investigated. Pebax membranes were fabricated via a solution casting method with five different solvents, that is, N,N‐dimethyl formamide (DMF), N,N‐dimethyl acetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), formic acid, and a mixture of ethanol (EtOH) with water (H₂O). Cross‐sectional scanning electron microscopy analysis of the membranes was performed to investigate the morphology of the prepared membranes. X‐ray diffraction and Fourier transform infrared analysis were also carried out to characterize the membranes. The interactions of the polymer and various solvents were evaluated with Hansen solubility parameters. Permeation experiments for CO₂ and CH₄ gases were performed to study the effects of the solvents on the permeation properties of the membranes. The solvent properties, such as the molar volume, boiling point, and solubility parameters, were investigated as were the membranes characteristics, such as the crystallinity, d‐spacing, and fractional free volume. The results obtained from the experiments show that the CO₂ permeability for the membranes prepared with different solvents followed this order: NMP > DMF > Formic acid > DMAc > H₂O/EtOH mixture. With increasing molar volume, the gas permeability increased for all of the membranes, except for DMAc, which showed a lower permeability because of its highly crystalline structure. DMF showed a higher CO₂/CH₄ ideal selectivity compared to the other membranes and, consequently, could be introduced as the best solvent from all aspects for the Pebax‐1657 membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44531.     

Mechanical investigation of confined amorphous phase in semicrystalline polymers: Case of PET and PLA

The effect of confinement onto the mechanical properties of the amorphous phase of Polyethylene terephthalate (PET) and poly(lactic acid) (PLA) was investigated. These polymers have the advantage of being in bulk amorphous or in semicrystalline state allowing mechanical and physical investigation of the amorphous phase on bulk and confined configuration. Based on small angle X‐ray scattering (SAXS), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) experiments, the micro‐structural arrangement of the amorphous and crystalline phase, the rigid amorphous fraction, and the visco‐elastic mechanical properties of the different semicrystalline samples were investigated. DSC results help quantifying the rigid amorphous fraction dependence on the crystallinity. DMA measurements lead to quantify the viscoelastic properties of the free and confined amorphous phases for PET and PLA polymers. Indeed, based on the DMA tests, where the maximum of tan(δ) peak is usually related to the glass transition temperature, shifts upon crystallization, the mechanical properties of the restricted and mobile amorphous phase were determined. This result was correlated along with the amorphous phase thickness distribution determined by SAXS results. This observation was bolstered based on literature results about geometrical confinement configurations and their effect on the glass transition temperature of polymeric materials. POLYM. ENG. SCI., 55:397–405, 2015. © 2014 Society of Plastics Engineers     

Preparation and characterization of EVA/clay Nanocomposites with improved barrier performance

Poly (ethylene‐co‐vinyl acetate) (EVA)/clay nanocomposites containing two different organoclays with different clay loadings were prepared. The transport of gases (oxygen and nitrogen) through the composite membranes was investigated and the results were compared. These studies revealed that the incorporation of nanoclays in the polymer increased the efficiency of the membranes toward barrier properties. It was also found that the barrier properties of the membranes decreased with clay loadings. This is mainly due to the aggregation of clay at higher loadings. The morphology of the nanocomposites was studied by scanning electron microscopy, transmission electron microscopy and X‐ray scattering. Small angle X‐ray scattering results showed significant intercalation of the polymer chains between the organo‐modified silicate layers in all cases. Better dispersed silicate layer stacking and more homogeneous membranes were obtained for Cloisite® 25A based nanocomposites compared with Cloisite® 20A samples. Microscopic observations (SEM and TEM) were coherent with those results. The dispersion of clay platelets seemed to be maximized for 3 wt % of clay and agglomeration increased with higher clay loading. Wide angle X‐ray scattering results showed no significant modifications in the crystalline structure of the EVA matrix because of the presence of the clays. The effect of free volume on the transport behavior was studied using positron annihilation spectroscopy. The permeability results have been correlated with various permeation models. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012