The oriented crystallization of poly[(R)-3-hydroxybutyrate] (PHB) in the miscible blends with poly(vinylidene fluoride) (PVDF) was investigated with various compositions. The PVDF/PHB blend films were prepared by solution casting and subsequent melt-quenching in ice water. Oriented films of the blends were prepared by uniaxially stretching the melt-quenched film at 0 °C in ice water using a hand-operated stretching apparatus. The oriented blend films were heat-treated at a fixed length in order to crystallize PHB in the oriented state. The crystal orientation and the lamellar textures of the obtained samples were studied with wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS), respectively. The SAXS measurements showed that a considerable amount of molecular chains of PHB are excluded from the lamellar stacks of PVDF and exist in the interfibrillar regions in the oriented films of the blends. The cold crystallization of PHB in the interfibrillar region results in the orientation of PHB crystals, and the type of crystal orientation depends upon the composition of the blends. For the PVDF/PHB=4/6-7/3 blends, the crystal a-axis of PHB is highly oriented parallel to the drawing direction and the crystal c-axis (molecular chain axis) in PHB crystals is perpendicular to the drawing direction, i.e. orthogonal to the chain axis of the crystals of PVDF. It is considered that the a-axis orientation is induced by the confinement of crystal growth in the interfibrillar nano-domains. For the PVDF/PHB=2/8-3/7 blends, however, the crystal c-axis of PHB is primarily oriented in the drawing direction, suggesting that the stressed molecular chains of PHB are crystallized with the molecular orientation retained. 相似文献
Studies have been done on strain-induced microstructure development in syndiotactic polystyrene (s-PS) and its blends with poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) in 70/30 and 50/50 compositions of stretched annealed samples. Wide-angle X-ray showed that crystal orientation is less in annealed blend samples compared to annealed pure s-PS for a higher draw ratio. It increases with annealing, and relaxation occurs after a certain annealing temperature at above 180° for both s-PS and s-PS/PPO 70/30 blends. No crystal orientation was observed in the blend of s-PS/PPO 50/50 stretched samples. Small angle X-ray scattering (SAXS) shows the inclusion of amorphous PPO chains in between s-PS crystals lamella. Fourier transform infrared (FTIR) spectroscopy shows that the s-PS molecular chain packing band at 905 cm?1 is enhanced due to annealing in oriented samples and saturates to around 0.63. The crystal chain relaxation is lower than amorphous chains of s-PS. The molecular chains of amorphous PPO are less oriented into the blend matrix, whereas its relaxation is enhanced during heat treatment and reaches an optimum value after full relaxation. The different behaviors of orientation and relaxation of s-PS and PPO chains into the blend matrix produce superstructures. 相似文献
Oriented films of nylon 11/poly(vinylidene fluoride) (PVDF) blend were prepared by uniaxially stretching the melt-mixed blends. The drawn films of fixed length were heat-treated at 170 °C for 5 min to melt the PVDF component, followed by quenching in ice water or isothermal crystallization at various temperatures. The crystal forms and orientation textures of the obtained samples were studied using wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). It was found that PVDF can crystallize into both and β forms in the nylon 11/PVDF blends, and that the content of the β form increases with increasing crystallization temperature above 120 °C. The orientation behavior of the -form PVDF was observed to be dependent on the crystallization conditions: c-axis orientation to the stretching direction was produced for the sample crystallized below 50 °C; the a-axis of crystals was tilted from the stretching direction when PVDF was crystallized at about 75 °C; the parallel orientation of the a-axis to the stretching direction becomes dominant at higher crystallization temperatures (above 100 °C). In contrast, the β crystalline form maintains the c-axis orientation irrespective of crystallization temperature. It was shown by the confocal laser scanning microscopy that cylindrical domains of PVDF were dispersed in the oriented matrix of nylon 11. The mechanism for the formation of the unique orientation textures is discussed in detail. It was proposed that the a-axis orientation is a result of the trans-crystallization of PVDF in the cylindrical domains confined by the oriented matrix of nylon 11. The crystallization kinetics, WAXD analysis, and morphology studies preferred the trans-crystallization mechanism. The mechanical properties of the as-drawn and heat-treated samples were measured not only in the stretching direction but also in the direction perpendicular to it. It was found that the heat-treated samples show slightly lower tensile strength, but more elongation at the break in the two directions than the as-drawn samples. 相似文献
Amorphous oriented poly(l-lactide) (PLLA)/poly(vinyl acetate) (PVAc) 50/50 films were prepared by uniaxial drawing of melt-mixed blends at 65 °C. The morphology development and crystal organization of the blends during heat treatment under strain were investigated using small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). Equatorial scattering maxima in the SAXS patterns for samples annealed at 75 °C were observed before the appearance of crystal reflections. Further annealing of the samples at higher temperature induced two further discrete meridian scattering maxima. The observations indicated that homogenous oriented PLLA/PVAc film undergoes micro-phase separation first, followed by crystallization of PLLA in the PLLA-rich phase. The micro-phase separated PVAc nanodomains are aligned parallel to the stretching direction, whereas the crystallized PLLA lamellae are oriented perpendicular to the stretching direction (crystal c-axis along the stretching direction). Micro-phase separation was not observed when films were annealed at 120 °C, at which temperature the high crystallization rate of PLLA overwhelmed the micro-phase separation process. 相似文献
In this work we report the effects of single stage zone drawing on the properties of NEW-TPI thermoplastic polyimide homopolymer, and its blends with Amoco's Xydar liquid crystalline polymer. Zone drawing was performed first on homopolymer NEW-TPI films to determine the effect of load weight, heater speed, and drawing temperature on the attainable draw ratio. Degree of crystallinity and chain orientation increase as the draw ratio increases for NEW-TPI. Blends of NEW-TPI/Xydar compositions 90/10 and 70/30 were studied next. In blends, the Xydar component is not molecularly dispersed, and is initially preferentially oriented along the machine direction during the film processing stage. Xydar acts as a nucleation site and lowers the temperature for crystallization of the NEW-TPI from the rubbery amorphous state. Zone drawing was performed either parallel or perpendicular to Xydar's initial preferred orientation direction. Blends with lower Xydar fraction could be zone-drawn to higher ratios. Zone drawing perpendicular to Xydar's initial orientation direction also resulted in increased draw ratio. Dynamic mechanical properties of the zone drawn materials were studied. In homopolymer NEW-TPI, dynamic modulus increased by a factor of two to 4.0 GPa in zone drawn films, largely as a result of the formation of oriented crystallites. In the blends, the modulus parallel to Xydar's initial orientation direction was greater than that in the transverse direction. Depending upon composition and test direction, zone drawing increased the dynamic moduli of the blends from 1.5 up to 2.7 times, in the temperature range from 150°C to 300°C. 相似文献
Rheo-optical Fourier-transform infrared (FTIR) spectroscopy is based on the simultaneous acquisition of stress-strain data and FTIR spectra on-line to the mechanical treatment of polymers and is frequently applied for the characterization of transient structural changes during deformation and stress-relaxation. In the present communication, this technique has been employed in order to investigate the distribution of molecular orientation and its relaxation in uniaxially drawn solution-cast films of semicrystalline partial miscible blends of poly(butylene terephthalate) (PBT) with polycarbonate (PC) containing 10, 30 and 50 wt% PC. The uniaxial deformation of these blend films having a PBT-crystallinity degree ranging from 31 to 12%, in unstretched blends, leads to a appreciable high segmental orientation for the crystalline PBT due to a structural transformation from lamellae to microfibrils. The formation of this fibrillar structure is attributed to non-reversibility of an extended phase with all-trans conformational sequence of the aliphatic segments of PBT, occurring during elongation. The rate of relaxation of this conformational transition, however, increases with increasing amorphous content in the blends. Also it is observed that even with increasing amorphous content in the PBT/PC blends the crystalline PBT shows significant orientation. In such cases, apart from the few lamellae which transform to microfibrils, it is suggested that a stress induced transformation of PBT chains in amorphous PBT-component to irreversible all-trans extended crystalline form also contributes to PBT crystalline orientation. In contrast with this high crystalline orientation, the amorphous PBT located in the interlamellar regions inside the PBT-spherulites show a lower orientation in blends as compared in pure PBT.On the other hand, an overall segmental orientation of PC chains in blends is of lower order which is attributed mainly to low stretching temperature compared to Tg of pure PC. The results are discussed in terms of the resulting spherulitic morphology and the temporary network formed by the elongated PBT and PC chains inside the interlamellar regions, in blends. 相似文献
Four kinds of polypropylene (PP) cast films with different die draw ratios (DDR) were prepared. The impact of different DDR on the crystalline and oriented properties of PP cast films and annealed films was explored herein. Wide angle X-ray diffraction (WAXD) and fourier transform infrared (FTIR) methods were adopted to examine the orientation degree of crystalline and amorphous phases. Long period distance (Lp) of the crystalline structure was tested by small angle X-ray scattering (SAXS). Crystallization was determined by differential scanning calorimeter (DSC). The oriented and crystalline behaviors of the samples were carried out by the elastic recovery (ER) testing. Then, samples after being annealed were examined by the same methods. The influence of annealing process on the films’ structures and properties was explored. Besides, the final stretched microporous membranes manufactured via stretching the annealed films along machine direction were examined by scanning electronic microscope (SEM). No matter for cast films or for annealed films, it is found that the films’ orientation degree of crystalline and amorphous phases, as well as Lp and crystallinity are larger at higher DDR and relatively lower at lower DDR. When the DDR is overly high (DDR?=?170), both the oriented and crystalline properties will decline. Elastic recovery testing indicates that a film with better orientation of the crystalline and the amorphous phases as well as with higher crystallinity can be obtained at an appropriate DDR. SEM images show that stretched membranes with better microporous structure can be obtained when the precursor film is prepared at a proper DDR. 相似文献
Development of supermolecular structure in drawn polypropylene (PP)/polybutene-1 (PB-1) blends was studied. PP (matrix)/PB-1 (70/30) blend films were drawn and heat-treated at fixed length or free ends at temperatures above the melting point of PB-1. It was found that a long axis of the PB-1 lamella is aligned perpendicular to the draw direction, and the c-axis of the PB-1 crystal is oriented perpendicular both to the draw direction and the plane of the surface of the blend film. Drawn, then heat-treated PP/PB-1 blend films gave a SAX pattern having a cross type scattering maximum on the meridian. It was confirmed that vertical scattering originates from the PB-1 crystal developed during melt recrystallization. It was proposed that the structural development of PB-1 in drawn PP/PB-1 film can be explained on the basis of transcrystallization of PB-1 in the confined 2-dimensional space in the PP matrix. The kinetics of isothermal crystallization of PB-1 was examined by use of a DSC technique. The result supports the conclusion that the heterogeneous nucleation of PB-1 followed by 2-dimensional crystal growth prevailed in oriented PP/PB-1 blend film. 相似文献
Summary: Miscibility in amorphous phase and behavior in a crystalline phase of blends of two semicrystalline and isomeric polymers, isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), was probed. Optical and scanning electron microscopy results indicate no discernible heterogeneity in iPS/sPS blends in either melt state or rapidly quenched amorphous super‐cooled state, while the Tg behavior of the quenched amorphous blends shows an intimately mixed state of two polymer chains. The crystal forms of the blends were further analyzed to provide additional evidence of miscibility in the amorphous domain. The sPS in the iPS/sPS blends upon melt crystallization was found to predominantly exist as the more stable β‐form (rather than mixed β‐form and α‐form in neat sPS), which also suggests evidence of miscibility in the iPS/sPS blends. The melting behavior of semicrystalline sPS in the iPS/sPS mixtures was analyzed using the Flory‐Huggins approach for estimation of interactions. By measuring the equilibrium melting point of the higher‐melting sPS species in the sPS/iPS blends, a small negative value, for the interaction parameter (χ ≈ ?0.11) was found. Further, by introducing a third polymer, poly(2,6‐dimethyl‐p‐phenylene oxide) (PPO), a ternary iPS/sPS/PPO blend system was also proven miscible, which constituted a further test for stable phase miscibility in the iPS/sPS blend. General nature of miscibility in blends composed of two crystalline isomeric polymers is discussed. Issues in dealing with blends of polymers of the same chemical repeat unit but different tacticities were addressed.
X‐ray diffractograms for neat sPS and iPS/sPS blends, each having been isothermally crystallized at 245 °C for 4 h. 相似文献
The miscibility for melt-mixed poly(vinylidene fluoride) (PVDF)/acrylic rubber (ACM) blends and the crystal morphology of PVDF in the blends were investigated over the whole composition ranges by dynamic mechanical analysis (DMA), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). DMA measurements revealed that PVDF is miscible with ACM in ACM-rich system, and partially miscible in PVDF-rich system. Two kinds of PVDF lamellar structures with different long periods were detected by SAXS and TEM for the partially miscible blends. In the miscible system, only one kind of crystal lamellae with enlarged long period is found. The two kinds of lamellar structures in the blend show different orientation behavior during the uniaxial stretching to result in a biaxial orientation. The lamellae with short long period are oriented vertical to the stretching direction, while those with large long period were found to be oriented parallel to the stretching direction. 相似文献
The development of crystalline structure and orientation during uniaxial stretching of cast amorphous linear and branched lactic acid films were investigated in the rubbery temperature ranges that spans between glass transition temperature and cold crystallization temperature. This material exhibited almost ideal stress‐strain behavior in the temperature range 65–80°C. Because of its strain crystallizability, films with uniform thickness can be obtained at high deformation levels as a result of self‐leveling. Branching was found to retard this self‐leveling through its slightly detrimental effect on the strain hardening. Upon stretching the material undergoes rapid orientation in the amorphous state and beyond a critical level very sharp and highly oriented β crystalline form chains with ?3/1 helix. If the temperature is at or below Tg, with additional stretching, the films were found to revert to a highly oriented amorphous state through the destruction of the crystalline domains. At higher temperatures, further stretching results in continuation of improvement in crystalline order. 相似文献
Biaxially oriented polypropylene (BOPP) films were produced by simultaneous and sequential biaxial stretching to various balanced and unbalanced draw ratios. The BOPP films were characterized in terms of density, crystallinity, refractive index, oxygen permeability and dynamic mechanical relaxation behavior. It was found that the density and crystallinity of BOPP films decreased as the area draw ratio increased. Sequential stretching led to a slightly lower density than simultaneous stretching to the same draw ratio. Moreover, sequential stretching produced lower orientation in the first stretch direction and higher orientation in the second stretch direction compared to simultaneous stretching. The study confirmed the generality of a one-to-one correlation between the oxygen permeability of BOPP films and the mobility of amorphous tie chains as measured by the intensity of the dynamic mechanical β-relaxation. Moreover, the study established the correlation for commercially important sequentially drawn BOPP films with an unbalanced draw ratio. Finally, the chain mobility in the stretch direction was found to depend on the final stress during stretching. 相似文献
Structural evolution during constrained annealing of PLA films biaxially stretched in simultaneous and sequential biaxial stretching was compared. Annealing of simultaneous biaxially stretched films yields films with in-plane isotropy with (100) crystallographic planes parallel to the surface. The first stage of sequential stretching where the films are stretched in Uniaxial constrained mode was found to yield films exhibiting transverse isotropy. The transverse stretching of these films lead to formation of a distinct second population of chains primarily oriented in transverse direction, generating bimodal orientation texture. When the extent of stretching in two directions are balanced, constrained annealed samples were found to exhibit uniplanar axial (100)[001] texture with the primary chain axial direction now switched to transverse direction. Two new superstructures, along [110] and [100] respectively were discovered in annealed PLA films. 相似文献
The orientation of poly(ε-caprolactone) crystals in miscible poly(ε-caprolactone)/poly(vinyl chloride) (PCL/PVC) blends, melt crystallized under strain, has been studied by wide angle X-ray diffraction (WAXD). At low draw ratios or low PVC contents, all the observable (hk0) crystal reflections orient towards the meridional direction in WAXD patterns, indicating the presence of ring-fibre orientation. With the increase of draw ratio or PVC content, additional crystal orientation with the crystal a-axis parallel to the stretching direction is found to superimpose on the WAXD pattern of ring-fibre orientation. Both the ring-fibre orientation, which dominates the WAXD pattern, and the a-axis orientation are characterized by the perpendicular orientation of the crystal c-axis to the stretching direction. The unusual PCL orientation is a consequence of the combined effects of both the stretching and the presence of PVC in the PCL/PVC blends. 相似文献