Time-dependent effect of spherulite size on the tensile behavior of polypropylene

The mechanical behavior of isotactic polypropylene following primary crystallization is known to be dependent on the aging time (e.g., at room temperature). This aging time effect is believed to be related to a form of additional crystallization (sometimes called secondary crystallization). We show in the present work that the aging characteristics depend on spherulite size and that indeed the spherulite size effects reported by others very likely reflect chain rearrangements upon aging, rather than some property associated with the as-crystallized material.     

The distribution of lamellar lengths within a spherulite

One of the problems to be considered in the application of the Halpin-Kardos theory to crystalline polymers is the relation of the crystal length to the only related and measurable parameter, spherulite size. The number average crystal length has been computed for various two and three dimensional models for the crystallization process assuming heterogeneous nucleation. It was found that high values of crystallinity are consistent only with lamellae that are stacked in a parallel fashion. For these systems the number average lamellar length is 0.55 of the spherulite radius. Lower crystallinity polymers have an average lamellar length 0.3 to 0.5 of the spherulite radius, the actual value being determined by the radius. For spherulites of radius 1μm or greater, the size of the primary nucleus has no noticeable influence on the average lamellar length.     

Penetration of PBSU spherulite into P(VDC-VC) spherulite observed with microbeam- and macrobeam-SAXS/WAXS measurements

PBSU/P(VDC-VC) is a crystalline/crystalline miscible polymer blend, which has characteristics that (1) the melting temperature difference is small (ΔT=33 °C), (2) the spherulite of both components can be observed with polarized optical microscope (POM), and (3) the interpenetrated spherulite is formed under specific condition: Interpenetrated spherulite means a structure formed by the penetration of PBSU spherulite growing into P(VDC-VC) spherulite. In order to clarify the nano-structure of penetrated P(VDC-VC) spherulite and penetrating PBSU lamella, we have performed the microbeam (beam size: about 10×10 μm²) SAXS/WAXS simultaneous measurements as well as macrobeam SAXS/WAXS during formation of the interpenetrated spherulite. From our experimental results, we have concluded that P(VDC-VC) lamellae hardly stack and isolate from each other, and that PBSU penetrates into the inter-fibril region of P(VDC-VC) spherulite. Further, it is found that PBSU lamella penetrating into P(VDC-VC) spherulite excludes amorphous P(VDC-VC) from PBSU inter-lamella region.     

Controlling the deformation behavior of thermoplastic slips with ultrasound

The effect of ultrasound on the deformation properties of thermoplastic slips was investigated. It was shown that in treatment with ultrasound, the change in the plastic strength of beryllium oxide — thermoplastic binder casting system in the process temperature range (40–55°C) was due to cavitation and dissipative heat release effects and can be characterized with the equation for a thermal activation process.     

Deformation behavior of banded spherulite during drawing investigated by simultaneous microbeam SAXS-WAXS and POM measurement

The local deformation behavior inside a poly(ε caprolacton) (PCL)/polyvinylbutyral (PVB) banded spherulite during drawing was observed by in-situ microbeam small-angle X-ray scattering (SAXS) - wide-angle X-ray scattering (WAXS) - polarized optical microscopy (POM) simultaneous measurements. From experimental results, we found that the local deformation of a PCL/PVB banded spherulite can be divided into four stages. In stage I, disordering of the crystalline structure occurs. In stage II, the disordering of the crystalline structure ceases and disordering of the stacking and coarse slippage of the lamellae occur. In stage III, after the breakdown of the twisted lamella structure, the reconstruction of a long period structure occurs. In stage IV, further lamella slippage occurs. Our results show no evidence of fine slippage at a local region during the drastic decrease in the long period. This strongly indicates that the melting and recrystallization mechanism occurs during the lamella reconstruction of PCL/PVB.     

Determination of lamellar twisting manner in a banded spherulite with scanning microbeam X-ray scattering

We investigated lamellar twisting manner in a banded spherulite, the blend of poly-(?-caprolactone) and poly-(vinyl butyral), with scanning microbeam X-ray diffraction. We obtained the diffraction contour intensity map with a scanning pitch of 1 μm by employing a rotation of a spherulite around its radial direction along which the microbeam scans. The results confirm that the twisting manner depends on the crystallization temperature and that it changes from continuous twisting to step-wise twisting with the increase of crystallization temperature. Moreover, we observed that the phase of long-period lamellar twisting advanced by about 15° compared to that of short-period lamella. In addition, it was confirmed that c-axis of packing structure was normal to lamella, which was represented by dominant short-period lamella.     

Studying deformation of fine grain zirconia green products during sintering

Conclusions Deformation during the sintering of specimens of finely grained zirconia, prestabilized with calcium oxide, and its mixtures with monoclinic modifications can exceed the deformation of prestabilized zirconia; furthermore the composition containing 30% monoclinic phase will deform to a greater extent at 1300–1400°C.The deformation of specimens with an addition of CeO₂ and especially of Y₂O₃ is less than with an addition of CaO even during partial stabilization of the zirconia, although in the temperature range studied the open porosity is reduced to zero.We investigated the effect of the content of active zirconium dioxide in mixtures with industrial zirconia on the nonsteady rate of deformation of specimens in the range 1100–1500°C with a staged heating cycle.The method of preparing the products from finely grained bodies, in which we combine stabilization by additives of CaO, Y₂O₃ and CeO₂ with sintering, does not increase deformation compared with the method of preparing the articles from prestabilized (completely or partially) material.Translated from Ogneupory, No. 6, pp. 46–51, June, 1969.     

The rise and deformation of a single bubble in ionic liquids

Ionic liquids constitute a new class of substances that are considered as potential substitutes for many traditional organic solvents in reaction and separation systems. But there is still a lack of transfer data due to the deficiency of research on the flow behavior. In this work, the motion and deformation of single bubbles rising in quiescent ionic liquids were investigated by injecting bubbles into three different ionic liquids ([bmim]BF₄, [omim]BF₄ and [bmim]PF₆) through orifices with different inner diameters at various temperatures. Bubble size, aspect ratio and velocity were measured by processing images taken by high-speed camera, operated at 1000 frames per second with a resolution of 1280×512 pixels. The measured drag coefficient and aspect ratio were compared with correlations available in literature. The comparison showed that these correlations do not give fully satisfactory results in predicting the drag coefficient and aspect ratio of bubbles rising in ionic liquids, showing a big relative error. As a result, two new empirical correlations were proposed to correlate the drag coefficient as a function of Reynolds number and the aspect ratio as a function of a new dimensionless parameter IL which could group experimental data for gas bubble in ionic liquids. It was found that the values predicted by new empirical correlations are generally in good agreement with the experiment results.     

Large deformation behavior of some thermoplastics

In this experimental study the deformation behavior of two thermoplastics under uniaxial and biaxial loadings has been investigated. The experiments were conducted on thin walled tubular specimens of nylon-6, a semicrystalline polymer, and polymethyimethacrylate (PMMA),:an amorphous polymer. These specimens were subjected to tension, torsion and combined tension-torsion loadings until very large deformations were produced or specimen failure took place. The results are presented in the form of generalized stress-generalized strain curves which are applicable to all types of loadings, provided the generalized stress is monotonically increasing. In addition, the results show that the generalized stress-generalized strain relationship for nylon-6 is parabolic in nature, whereas that for PMM A can be represented by a bilinear curve. This characterization of the response of the thermoplastics under a biaxial stress field can be used to obtain a more realistic stress interaction between fiber and matrix in composite materials, since until now all theoretical studies on this aspect have assumed an elastic or elastic-perfectly plastic behavior of the matrix.     

Mechanical behavior of a single polymer chain in a non-solvent

Mechanical properties of a single polystyrene chain in mixtures of dioxane and methanol were measured with AFM. The effect of the solubility of the surrounding liquid on mechanical behavior of a polymer chain was examined. In good and Θ solvents, the force-extension curves exhibit a freely jointed chain (FJC)-like trend with good reproducibility. In a non-solvent, the profile of force-extension curve was dependent on the extension speed: an FJC-like nature emerged at the lower speed of 200 nm/s while saw-toothed curves were obtained at the higher speed of 2000 nm/s. The shape of saw-toothed curves varied from measurement to measurement. A force relaxation was also observed in the non-solvent under a fixed extension distance after 2000 nm/s extension. The mechanical behavior in non-solvents suggests that inhomogeneous deformation of a PS chain occurs due to reduction of the chain mobility.     

Features of the deformation behavior of granular media under a load

The piecewise linear character of the load–strain dependences of a granular medium consisting of fragile particles was experimentally established and theoretically substantiated. A model for grinding a granular medium in a conic or roller inertia mill was developed taking into consideration the features of its deformation behavior.     

Crystallization behavior and spherulite growth rate of isotactic polypropylene in isotactic polypropylene/natural rubber based thermoplastic elastomers

The melting and crystallization behavior of isotactic polypropylene/natural rubber (PP/NR) based thermoplastic elastomers (TPEs) were investigated using differential scanning calorimetry. The samples were scanned at a heating rate of 10°C/min under nitrogen atmosphere. The effects of blend ratio on the melting and crystallization characteristics of the blends were analyzed. Normalized crystallinity is unchanged by the addition of small amount of NR, but as the amount of rubber increases crystallinity increased for the 30/70 NR/PP and lowered for the 50/50 NR/PP blend system. Morphology of the blend was analyzed using scanning electron microscopy (SEM). Blend ratio showed a pronounced influence on the phase morphology of the NR/PP TPEs. As the amount of NR increases more than 50 wt % the system changes from dispersed to cocontinuous structure. Hot‐stage polarizing optical microscopy (POM) was used to study the radial growth of spherulite as a function of blend ratio, cooling rate, and crystallization temperature. Spherulite growth rate is marginally influenced by the rubber inclusions. The spherulite morphology observed under polarized optical microscopy is influenced by the blend morphology. It was found that for the cocontinuous 50/50 blend system, spherulites are much different from the usual appearance under polarized light. Attempts have been made to correlate the crystallization behavior with the morphology of the blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

An in-situ infrared cell and its application in study of sulfidation of a model Co/Mo catalyst

A flow cell was constructed to measure infrared spectra of catalyst samples with controlled heating at 673 K. We monitored sulfidation of an unsupported Co-Mo catalyst by thiophene. Correlation was found between the intensity changes and frequency shifts of the metal-oxygen IR bands and the appearance of oxythiomolybdate bands and the simultaneous increase of thiophene conversion. These results point to short-living cobalt-oxythiomolybdates which may have highest HDS activity.     

Study on high thermal conductivity of mesogenic epoxy resin with spherulite structure

The microstructure of a mesogen-containing epoxy resin that exhibits high thermal conductivity (0.33 W/m K) was investigated by observations of the scanning electron microscope (SEM) and the polarized optical microscope (POM). It was found that there are many spherulite structures formed in the resin. We supposed that the reason for the high heat-conductivity obtained in the resin is ascribed to the existence of the spherulite morphology where highly ordered lamellar structures aggregated. The argument was strongly supported by preparing the resin films with size-changed spherulites which are induced by changing the initial curing temperature. The result revealed that the thermal conductivity increased with the increase in spherulite size. On the other hand, we have developed the spherulite size in the resin from 10 to 80 μm in diameter that resulted in a greatly improved thermal conductivity of up to 1.16 W/m K in the highest value. This study may provide a useful method to improve the thermal conductivities of mesogenic resins themselves by producing spherulite structures.     

Phase behavior,polymorphism and spherulite morphology in Poly(1,4-butylene adipate) interacting with two structurally similar acrylic polymers

Polymorphism and spherulite morphology of poly(1,4-butylene adipate) (PBA) influenced by two structurally similar acrylic polymers: poly(benzyl methacrylate) (PBzMA) and poly(phenyl methacrylate) (PPhMA) were investigated by differential scanning calorimeter (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). Characterization first proves that PBA is similarly miscible with PBzMA and PPhMA, respectively, but effects of these two polymers on polymorphism and spherulite morphology of PBA differ dramatically. The depression of PBA growth rate in blends retards the formation of kinetically stable β-form crystal and favors the formation of α-form crystal of PBA. In PBA/PBzMA blend, the spherulite morphology remains all ringless after addition of PBzMA at any T_c, regardless of polymorphism or not. By contrast, the spherulite morphology in PBA/PPhMA blend can change from ringless, ring-banded, to dendritic with respect to T_c. In general, the formation of ring-banded spherulites in either of blends has no relation with the polymorphic crystal cells. Effects of amorphous PBzMA or PPhMA polymers on the polymorphic and ring-banded patterns on PBA differ and were likely controlled by the interaction strength between the two constituents of the blends.     

一段炉转化催化剂的还原性能研究

用定温还原迎头色谱法和程序升温还原法对加与不加稀土氧化物的两种转化催化剂的还原性能进行了研究、测定了两种催化剂的还原动力学参数。结果表明，温度对催化剂还原性能有明显影响；讨论了稀土促进镍催化剂还原的原因和还原进行的方式．认为低温时遵从速率控制成核作用机理．高温时按瞬间成核收缩球模型机理。     

Hydrodynamic behavior of single particles in a draft-tube bubble column

Velocities of single particles (magnetic tracer particles) were measured in the draft tube region and annular region of a draft-tube bubble columns by use of the magnet-detector coil technique. The relative particle to liquid velocity was also obtained. The observed distribution of particle velocity was broader than that of liquid velocity. The relative particle to liquid velocity depended significantly on superficial gas velocity. Those for the draft tube region had minimums with increasing gas velocity, while those for the annular region decreased monotonously. The effective drag coefficients for the particles were correlated with particle Reynolds number and gas holdup.