High-Speed Melt Spinning of Polylactide/Poly(Butyleneterephthalate) Bicomponent Fibers: Mechanism of Fiber Structure Development and Dyeing Behavior

Bicomponent fibers consisting of polylactide (PLA) as the sheath and poly(butylene terephthalate) (PBT) as the core were produced by high-speed spinning to obtain materials suitable for medical clothing. The higher-order structure of the PLA fiber component appeared to exhibit simple, alternately stacked, uniaxially oriented amorphous and crystalline regions. Therefore, fairly large tanδ peaks were observed for single-component PLA fibers, even when the orientation-induced crystallization was achieved by high-speed spinning. By conjugating PLA with PBT, although limited mutual interference with the crystallization of each component occurred, both the PLA (Mw?=?170,000, L-lactide content?=?98.7%) and PBT (intrinsic viscosity?=?0.835-0.865 dL/g) could crystallize on a high-speed spinning line, and the proposed formation of a shish-kebab-like structure in the PBT component enhanced the thermal stability of the bicomponent fibers, particularly resulting in shrink-proof properties. The bicomponent fibers developed herein could be deeply dyed at 98?°C, with results comparable to those of industrial polyester, and peeling of the PLA skin layer was rarely observed, even when the dyed fibers were flattened by a rubbing force.     

Development of Stereocomplex Crystal of Polylactide in High-Speed Melt Spinning and Subsequent Drawing and Annealing Processes

High-speed melt spinning of racemate polylactide (r-PLA), which is a blend of equal amounts of poly(l-lactide) and poly(d-lactide) molecules, was performed up to the take-up velocity of 7.5 km/min. In the fiber structure analysis, particular attention was paid to the formation of stereocomplex crystals, because this crystal form has a melting temperature about 60° higher than the homocrystals. It was found that highly oriented and highly crystallized fibers containing the α-form and stereocomplex crystals were obtained when the take-up velocity exceeded about 4 km/min. The amount of stereocomplex crystal was higher under the spinning conditions of higher take-up velocity, lower throughput rate, and lower extrusion temperature. Under these conditions, higher tensile stress can be applied to the spinning line, and therefore, the orientation-induced crystallization is promoted. Annealing of the fibers obtained at high-take-up velocities, such as 6 km/min, which already have the crystalline structure with a certain amount of stereocomplex crystal, at a temperature between the melting temperatures of α-form and stereocomplex crystals, yielded the fiber structure mainly consisting of highly oriented stereocomplex crystal. The annealed fibers showed fairly high mechanical properties and good thermal stability.     

Melting behavior of the oriented β-phase polypropylene texture crystallized by the temperature slope method

Isotactic polypropylene consisting of uniaxially oriented P-phase lamellae was crystallized in a temperature gradient. The β → α transition was investigated by simultaneous measurements with differential scanning calorimetry (DSC) and X-ray diffraction using synchrotron radiation (SR). To compare the transition mechanism, the β-phase sample was deformed by rolling it along the direction of the crystallization. During rolling, the β-crystal is deformed by interlamellar and interchain slip, which induces c-axis-oriented molecules along the rolling direction. The melting behavior is changed by the rolling deformation. For the as-grown β-crystal, the DSC thermogram has three peaks: the β-melting endotherm at 150°C, an exotherm by recrystallization into the °-form, and the endotherm at 167°C caused by melting of the recrystallized α-form. After the rolling deformation, the β-endotherm is extinguished by the successive exotherm. Simultaneous X-ray measurements reveal that the β → α transition is shifted to a lower temperature and that the recrystallized α-form has a c-axis-orientation caused by the rolling deformation. In the process of the β→ α transition, higher-order lamellar structure is developed earlier than formation of the crystalline structure. In this study, the heating phenomena, such as the β α transition and thickening of the β- and α-lamellae, are consistently explained by a mechanism involving melting and subsequent recrystallization.     

Causes for the variable superconducting transition temperature in uranium metal

The variable superconducting transition temperature of uranium metal appears to depend upon the variability of a low-temperature martensitic transformation. Local structural fluctuations and phase instabilities are suggested as resulting when the transformation is incomplete. The thermodynamic stability of a two-phase modulated structure involving domain formation is discussed along with possible consequences of a domain configuration. Factors affecting T_c are used to explain the anamalous thermal property behavior of α-phase uranium.     

Synthesis and Properties of Thermotropic Poly(oxybenzoate-co-oxynaphthoate) Copolyester Modified by a Third AB Type Monomer

Abstract

The synthesis and modification of high performance thermotropic liquid crystal polyesters (TLCP) are still being investigated due to their excellent properties. In this study modification of poly(oxybenzoate-co-oxynaphthoate) (P-HBA/HNA), a random copolymer of 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), by 5?mol% of one of three AB type monomers (AB type monomers are those who have hydroxy and carboxylic end groups), vanillic acid (VA), 4-hydroxyphenylacetic acid (HPA) and 4-hydroxycinnamic acid (HCA), was conducted. The influence of the AB type third monomer on the liquid crystal properties, melting behavior, thermal stability, microstructure and fiber morphology of the resulting modified terpolyesters was comparatively studied relative to the parent copolymer. When 5?mol% of the HBA units were replaced, the resulting terpolyesters had much lower melting temperatures and could be easily melt processed, while the modified terpolyesters exhibited higher melting and glass transition temperatures when 5?mol% of the HNA units were replaced. Weaker melting peaks and larger melting ranges were observed for the modified terpolyesters, attributed to the existence of nonperiodic layer crystallites caused by the modifiers. The obtained terpolyesters showed good thermal stability and could be melt processed in a broad nematic phase temperature region. The molecular chain packing of the modified terpolyesters was almost destroyed by the third AB type reactants. Fibers prepared from the resulting terpolyesters exhibited well developed fibrillar structure and higher orientation factors, indicating that modification of the P-HBA/HNA by using the AB type monomers to improve its properties would be useful.     

Anisotropy of mechanical and thermal properties of perovskite LaYbO3: first-principles calculations

LaYbO₃ ceramic material with a perovskite structure has the advantages of a high melting point, sintering resistance and high-temperature phase stability. It is a promising candidate for a structurally and functionally integrated material. However, the anisotropy of physical properties of LaYbO₃ has rarely been studied. Herein, the anisotropy of the mechanical and thermal properties of LaYbO₃ was studied by first-principles calculations. The elastic coefficients, Young’s modulus, Poisson’s ratio and minimum thermal conductivity of LaYbO₃ were found to exhibit anisotropic characteristics. In particular, the sound velocity of the longitudinal wave was nearly twice that of the transverse wave. Especially, the minimum thermal conductivity of LaYbO₃ at high temperature was found to be as low as 0.88?W/m?K, indicating that the compound has potential for use in thermal insulation applications.     

Substructure and orientation of Pd-Cu solid solution thin films

The phase and elemental composition, substructure, orientation, and relief of Pd-Cu thin films produced by magnetron sputtering have been investigated using the techniques of TEM, HEED, and AFM. Three-orientation epitaxial β-phase structures (CsCl-type lattice) have been obtained by plasma-ion sputtering a Pd-Cu target on (001) fluorphlogopite (F) cleavages in the substrate temperature range of 550–800 K. The β-phase crystallites in the two-phase epitaxial solid solution films were oriented, with respect to the α-phase, according to Nishiyama—Wassermann and Kurdyumov—Sachs relations. Single-crystal films of α-and β-phase solid solutions have been grown on fluorphlogopite. The effect of the second component appeared as the formation of (001)[110] β_CuAu ∥ (001)[100]_F-type orientations.     

Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

Effect of Temperature and Comonomer Content on Thermal Behavior and Crystallization Property of the Propylene–Ethylene Random Copolymers

The effects of ethylene units content and crystallization temperature on the conformations, and the thermal and crystallization behavior were investigated by a combination of Fourier transform infrared (FTIR) spectroscopy, wide angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). The characterization of FTIR spectroscopy proves that the longer helical conformation sequences of the propylene–ethylene random (PER) samples decrease, whereas the shorter helical conformation sequences increase with the increase in ethylene units content. The increase of the shorter helical conformation sequences is favorable for the formation of the γ-phase in the crystals. A group of broad endothermic peaks can be seen clearly in the DSC curves of PER copolymers, which may be associated with the melting of mixtures of the α- and γ-forms in the crystals. The melting point, crystallization temperature, and crystallinity degree of the PER copolymers decrease with the increase in ethylene units contents. Three typical melting peaks of the PER copolymers crystallized isothermally between 80°C and 130°C were observed. The two higher melting peaks result from melting of the α- and γ-phase in the crystals, whereas the materials crystallized on quenching give the lowest peak. The WAXD results confirm that the PER copolymers crystallize from the melt, as mixtures of α and γ forms, in a wide temperature range. The critical number ζ_lim of the crystallizable units for the α-form increases with the increase in crystallization temperature for PER copolymers, which is favorable for the formation of the γ phases. The amount of γ-form increases with the increase in crystallization temperature at the expense of its α component, then reaches a maximum value at the crystallization temperature of 115°C, and finally decreases with further increase in the crystallization temperature.     

Electronic and crystal structure of α- and β-CeIr2Si2

We present the results of XRD, magnetization, resistivity and specific heat measurements of CeIr₂Si₂ single crystals for both, the low-temperature α-phase and the high-temperature β-phase, respectively. The α-phase adopts the tetragonal ThCr₂Si₂-type whereas the β-phase forms in the CaBe₂Ge₂-type structure. Both the phases remain paramagnetic down to low temperatures, nevertheless both, the magnetization and resistivity exhibit pronounced anisotropy in the whole temperature range of measurements (2-300 K). Results of fitting the temperature dependence of the susceptibility within the interconfiguration-fluctuation model point to the Ce valence fluctuating between 3+ and 4+. The α-phase behaves as a Fermi-liquid (FL) at low temperatures whereas the β-phase exhibits non-Fermi-liquid (NFL) features. The results are discussed in context of other similar polymorphic compounds.     

The effects of thermal activation on the complex conductivity of Ag2HgI4 in the microwave region

The complex conductivity of polycrystalline Ag₂HgI₄, a superionic conductor, has been measured as a function of temperature at 10, 24 and 70 GHz. Both conductivity and permittivity exhibited sharp changes at the β?α phase transition. The microwave conductivity of the β-phase was found to be insensitive to temperature changes and that of the α-phase has thermal activation energies lower than that of dc. The observed monotonic increasing conductivity, decreasing permittivity, together with thermal activation effects are indicative of hopping ionic transport.     

Size effect in the melting and freezing behaviors of Al/Ti core-shell nanoparticles using molecular dynamics simulations

The thermal stability of Ti@Al core/shell nanoparticles with different sizes and components during continuous heating and cooling processes is examined by a molecular dynamics simulation with embedded atom method. The thermodynamic properties and structure evolution during continuous heating and cooling processes are investigated through the characterization of the potential energy, specific heat distribution, and radial distribution function(RDF). Our study shows that, for fixed Ti core size, the melting temperature decreases with Al shell thickness, while the crystallizing temperature and glass formation temperature increase with Al shell thickness. Diverse melting mechanisms have been discovered for different Ti core sized with fixed Al shell thickness nanoparticles. The melting temperature increases with the Ti core radius. The trend agrees well with the theoretical phase diagram of bimetallic nanoparticles. In addition, the glass phase formation of Al–Ti nanoparticles for the fast cooling rate of 12 K/ps, and the crystal phase formation for the low cooling rate of 0.15 K/ps. The icosahedron structure is formed in the frozen 4366 Al–Ti atoms for the low cooling rate.     

On the decomposition of the transition rhombohedral phase in the Al-30 wt.% Zn alloy

The decomposition of the transition rhombohedral α′_R-phase at the temperatures between 85 and 250 °C was investigated by transmission electron microscopy and by X-ray diffraction on single crystals. Below 161 °C the direct decomposition of α′_R-phase into the equilibrium hexagonal β-phase without the formation of the transition cubic α′-phase was found. Both transformation sequences α′_R → β and α/′_R→α′ → β were observed in the temperature range from 161 to 180 °C whereas only the previously known sequence α′_R → α′ → β was detected on ageing the alloy between 180 and 250 °C. The precipitation process at the temperatures from 161 to 180 °C is characterized by the decomposition of α′_R-phase into the equilibrium β-phase prior to the formation of the transition α′-phase and by the increased rate of decomposition of α′-precipitate. The observed transformation processes are related to the variation of strains at the partially coherent interface between α′_R-phase and α-matrix with the temperature in correlation with the metastable α′_R-phase boundary. These considerations allowed to estimate the relative stabilities of precipitated phases and their activation energies of formation and thus to discuss the decomposition mechanism of α′_R-phase at various temperatures.     

Rheological,thermal, and mechanical properties of poly(ethylene naphthalate)/poly(ethylene terephthalate) blends

Structural, Theological, thermal, and mechanical properties of blends of poly(ethylene naphthalate) (PEN) and poly(ethylene terephthalate) (PET) obtained by melt blending were investigated using capillary rheometry, differential scanning calorimetry (DSC), scanning electron microscopic (SEM) observation, tensile testing. X-ray diffraction, and ¹H nuclear magnetic resonance (NMR) measurements. The melt Theological behavior of the PEN/PET blends was very similar to that of the two parent polymers. The melt viscosity of the blends was between that of PEN and that of PET. Thermal properties and NMR measurement of the blends revealed that PEN is partially miscible with PET in the as molded blends, indicating that an interchange reaction occurs to some extent on melt processing. The blend of 50/50 PEN/PET was more difficult to crystallize compared with blends of other PEN/PET ratios. The blends, once melted during DSC measurements, almost never showed cold crystallization and subsequent melting and definitely exhibited a single glass transition temperature between those of PEN and PET during a reheating run. Improvement of the miscibility between PEN and PET with melting is mostly due to an increase in transesterification. The tensile modulus of the PEN/PET blend strands had a low value, reflecting amorphous structures of the blends, while tensile strength at the yield point increased linearly with increasing PEN content.     

63Cu NMR analysis of microstructure evolution in Al–Cu–Mg alloys

⁶³Cu NMR spectroscopy has been used to detect metastable Guinier–Preston–Bagaryatsky (GPB) zones and nanoscale precipitates of equilibrium S-phase (Al₂CuMg) in dilute alloys of aluminium containing copper and magnesium with compositions which lie in the α?+?S phase field. The GPB zones are observed to form rapidly at room temperature with a time development closely related to the Vickers hardness. The final development of S-phase in the alloy has been confirmed by the observation of a line shape in the alloy identical to that observed in a specimen prepared from stoichiometric Al₂CuMg. Analysis of the hyperfine structure of the ⁶³Cu line shape observed for S-phase shows clearly that two Cu sites are present with approximately equal population. This result suggests that possibly two crystallographically distinct Al₂CuMg phases are present. The addition of small amounts of silver to Al–Cu–Mg alloys in the α?+?θ phase field is known to induce the formation of Ω-phase: a slight distortion of tetragonal θ-phase Al₂Cu. A hyperfine-structured ⁶³Cu line shape assigned to Ω-phase, indicating one distinct Cu site, has been observed in two separate Al–1.7?at.%?Cu–0.33?at.%?Mg alloys containing 0.1 and 0.18?at.%?Ag, but not in the same Al–Cu–Mg alloy without Ag.     

Critical point wetting in NbH0.31

The local α-α' phase distribution in a thin Nb single crystal loaded with the critical H-concentration was investigated with X-rays. The sample used in the experiment showed a macroscopic hydrogen density mode, leading to a curvature of the whole crystal plate with the α-phase on the concave side and the α'-phase on the convex side. In addition an α-phase wetting layer was found on top of the α'-phase separated from the bulk α'-phase by a mixed α-α' phase region. In a simple model their thickness were determined to about $\text{\$}\text{?}$1.0 and 7?0μm, resp. This thin wetting layer leads to a new interpretation of the phase transition of H and Nb, involving the familiar long-range elastic interaction as well as a short-range surface free energy contribution.     

Optical vortices in anisotropic optical fibers with torsional stress

Analytical expressions for the higher-order modes with the azimuthal number equal to unity and for corresponding propagation constants of optical fibers with linear anisotropy of the fiber material and a circular anisotropy induced by torsional mechanical stress been obtained at practically important relationships between fiber parameters. The possibility of stable propagation of optical vortices in these fibers and the dependence of characteristics of sustained optical vortices on the fiber parameters are demonstrated.     

Investigation on (EC/DMC)(70−x)wt% to LiBETI(x)wt% impact on PVdF-co-HFP/octadecylamine-MMT(montmorillonite) nano clay composite electrolytes

The composition dependence of plasticizer (ethylenecarbonate(EC)/dimethyl carbonate(DMC))_(70?x)wt% to Lithium bis(perfluoroethanesulfonyl)imide(LIBETI)_(x)wt% salt (where x?=?1.5, 3.0, 4.5, 6.0 wt%) on PVdF-co-HFP (25 wt%)/surface modified octadecylamine containing montmorrillonite (ODA-MMT) nano clay (5 wt%) matrix has been investigated by AC impedance, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dielectric and cyclic voltammetry studies. The enhanced conductivity 2.1?×?10^?5 Scm^?1 is noted in salt rich phase (EC/DMC)_(70–6)wt% /LiBETI_(x=6)wt% (VK4). In XRD, 2θ at 20.9° confirms β-phase. In FTIR studies, vibrational bands 838, 522 and 611 cm^?1 confirm β-phase of PVdF due to clay intercalation. In DSC studies, the melting of α-phase crystallites is noted between 140–150 °C. In SEM studies, one of the membranes presents fern leaf texture confirming swelling of clay. The increase in dielectric constant and dielectric loss with decrease in frequency is attributed to high contribution of charge accumulation at the electrode–electrolyte interface. In cyclic voltammetry studies, salt-rich phase membrane (VK4) shows good cyclability than other membranes.     

Transition of β to α phase in isotactic polypropylene

In samples of isotactic polypropylene, the influence of the nucleation agent chinacridine permanent red E3B on the crystallization rate and content of α and β modifications and on the rate and mechanism of the β → α transition was investigated using x-ray diffraction, DSC microcalorimetry, and electron microscopy. It was found that, though E3B increases the content of the β phase, it is also a very efficient nucleation agent for the α-phase crystallization. The β → α transition occurring above 140°C could be characterized by a gradual melting and annealing of the β phase, accompanied by a surface crystallization of the α phase on lateral faces of β lamellae by a mechanism similar to cross-branching of α lamellae.     

Kinetics of α-γ Phase Transition of Fe-12Cr-4Ni Alloy Aged between 500–650 °C

Using Mössbauer spectroscopy and X-ray diffraction as analytical tools, an "anomalous" α-γ phase transformation observed previously in steels was studied. It was shown in this work that this phase transformation is a feature of the Fe-12Cr-4Ni ternary alloy, and the ageing-time dependence of the γ-phase formation follows Avrami kinetics representing a diffusion controlled process. The activation energy of the process was also determined. The equilibrium composition of the samples could be interpreted in terms of calculated phase diagrams of the Fe-Cr-Ni system. On the basis of the hyperfine-field distributions derived from the spectra it was shown that two processes take place in the ferromagnetic α-phase during the ageing at different rates in which the slower one is in accordance with a decrease of the chromium concentration in the α-phase owing to the γ-phase formation.