Crystalline Morphology Of Poly Research Articles

Polymorphic crystalline structure and diversified crystalline morphology of poly(butylene adipate) blended with low‐molecular‐mass liquid crystals

Polymorphic crystalline structure and diversified crystalline morphology of poly(butylene adipate) blended with low‐molecular‐mass liquid crystals

Isothermal Crystallization Kinetics and Crystalline Morphologies of Poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) Copolymers

In this study, the isothermal crystallization kinetics and crystalline morphology of poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) (PBAC), which refers to a copolyester containing a non-planar ring structure, were investigated by differential scanning calorimetry and polarized optical microscopy, and compared with those of neat poly(butylene 1,4-cyclohexanedicarboxylate) (PBC). The results indicate that the introduction of butylene adipate (BA) unit into PBAC did not change the intrinsical crystallization mechanism. But, the crystallization rate and ability, and equilibrium melting temperature of PBAC copolymers were reduced. All PBC and PBAC copolymers could only form high density of nucleation from melt at given supercooling, while no Maltese cross or ring-banded spherulites could be observed. PBAC copolymers with a high amount of BA unit became amorphous after quenching with liquid nitrogen from melt, while PBC and PBAC copolymers with a low amount of BA unit could still form a large amount of nuclei under the same treatment.

Synthesis, thermal properties and crystalline morphology of poly(trimethylene terephthalate)/ZnO nanocomposites prepared by dual in situ polymerization

Synthesis, thermal properties and crystalline morphology of poly(trimethylene terephthalate)/ZnO nanocomposites prepared by dual <i>in situ</i> polymerization

Effects of Preexisting Poly(butylene succinate-co-24 mol % hexamethylene succinate) Crystals on the Crystallization Behavior and Crystalline Morphology of Poly(butylene adipate) in Their Melt-Miscible Polymer Blend

The effects of preexisting poly(butylene succinate-co-24 mol % hexamethylene succinate) (PBHS) crystals on the crystallization behavior and crystalline morphology of poly(butylene adipate) (PBA) were studied in their fully biodegradable melt-miscible crystalline/crystalline blend. Regardless of crystallization conditions, PBHS crystallized first, and PBA must crystallize in the presence of preexisting PBHS crystals. The preexisting PBHS crystals may not only enhance the nonisothermal melt crystallization behavior but also favor the nucleation and growth of only α-form crystals of PBA, providing an easy method of controlling the polymorphic crystals of PBA through polymer blending; moreover, the preexisting PBHS crystals could accelerate the overall isothermal melt crystallization process of PBA in the blend. PBA must crystallize as tiny crystals at the same orientation as the crystallites of the host PBHS spherulites in the blend, unlike the spherulitic morphology in its neat state. Both components crysta...

Confined Nucleation and Growth of Poly(ethylene oxide) on the Different Crystalline Morphology of Poly(butylene succinate) From a Miscible Blend

The confined and fractional crystallization behavior of poly(ethylene oxide)(PEO) in miscible poly(butylene succinate)(PBS)/PEO blends has been investigated. Both nucleation and growth of PEO cryst...

Effects of amorphous poly(vinyl acetate) on crystalline morphology of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)

The amorphous and crystalline phase behavior, spherulite morphology, and interactions between amorphous poly(vinyl acetate) (PVAc) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) were examined using differential scanning calorimetry, polarized-light optical and scanning electron, atomic-force microscopy (DSC, POM, SEM, AFM), and small-angle X-ray scattering (SAXS). The PHBV/PVAc blend was found to be miscible with an almost linear Tg-composition relationship, indicating perfect homogeneity. Interaction parameter by melting point depression is a negative value of χ = −0.32, suggesting quite favorable interaction strength. With the intimate interaction between the amorphous PVAc and crystalline PHBV polymers, effects of PVAc on the spherulitic morphology of PHBV are quite significant. Owing to the higher Tg of PVAc (than that of PHBV), the spherulite growth rate of PHBV was depressed by increasing PVAc content in blends. Neat PHBV exhibits ring-banded spherulites when crystallized at \( {T_{\rm{c}}} = {6}0\sim {11}0^\circ {\hbox{C}} \); however, with increasing PVAc content in the blends, the temperature range at which the PHBV/PVAc blends exhibit ring-banded spherulites remains similar but the regularity increases, and the inter-ring spacing significantly decreases. In addition, the spherulite size and ring-band patterns therein are strongly dependent on Tmax (190 vs. 220 °C, respectively, for erasing prior nuclei), from which the blends were quenched to a Tc (60–110 °C) for crystallization. For PHBV/PVAc blends crystallized at the same Tc from different Tmax, higher Tmax tends to erase nuclei, leading to larger spherulites. However, such larger spherulites owing to higher Tmax are not necessarily packed with thicker lamellae.

Crystallization kinetics and crystalline morphology of poly(ε‐caprolactone) in blends with grafted rubber particles

AbstractThe crystallization behavior of pure PCL and PCL in blends with crosslinked rubber particles was studied under (non)isothermal crystallization conditions, where the rubber particles were grafted with PCL chains via hydrogen abstraction of the aliphatic moieties in PCL. The crystal growth and the organization of crystals into spherulitic superstructures are significantly influenced by the presence of the grafted rubber particles, which act as an excellent nucleating agent for PCL. The nucleating efficiency shows an exponential dependency on the PCL grafting density and, according to an Avrami analysis, an increased PCL grafting density increases the overall crystallization rate of the PCL matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1438–1448, 2010

Shear-induced crystallization of poly(phenylene sulfide)

The crystalline morphology of poly(phenylene sulfide) (PPS) isothermally crystallized from the melt under shear has been observed by polarized optical microscope (POM) equipped with a CSS450 hot-stage. The shish–kebab-like fibrillar crystal structure is formed at a higher shear rate or for a longer shear time, which is ascribed to the tight aggregation of numerous oriented nuclei in the direction of shear. The crystallization induction time of PPS decreases with the shear time, indicating that the shear accelerates the formation of stable crystal nuclei. Under shear, the increase of spherulite growth rate results from highly oriented chains. The melting behavior of shear-induced crystallized PPS performed by differential scanning calorimetry (DSC) shows multiple melting peaks. The lower melting peak corresponds to melting of imperfect crystal, and the degree of crystal perfection decreases as the shear rate increases. The higher melting peak is related to the orientation of molecular chains. These oriented molecular chains form the orientation nuclei which have higher thermal stability than the kebab-like lamellae that are developed later. A new model based on the above observation has been proposed to explain the mechanism of shish–kebab-like fibrillar crystal formation under shear flow.

Row nucleation phenomenon of Poly(phenylene sulfide) under shear condition

The crystalline morphology of Poly(phenylene sulfide) (PPS) isothermally crystallized from the melt under shear conditions has been investigated by polarized optical microscope (POM) equipped with a CSS450 hot stage. The crystalline morphology of PPS is mainly spherulite and greatly influenced by shear flow field. That is, the shear can cause these spherulite orientations, and the row nucleation structure occurs under shear flow conditions. We ascribe it to the tight aggregation of numerous nuclei in the direction of shear.

Various Crystalline Morphology of Poly(butylene Succinate-co-butylene Adipate) in Its Miscible Blends with Poly(vinylidene Fluoride)

Poly(vinylidene fluoride) (PVDF) and poly(butylene succinate-co-butylene adipate) (PBSA) are crystalline/crystalline polymer blends with PVDF being the high-T(m) component and PBSA being the low-T(m) component, respectively. PVDF/PBSA blends are miscible as shown by the decrease of crystallization peak temperature and melting point temperature of each component with increasing the other component content and the homogeneous melt. The low-T(m) component PBSA presents various confined crystalline morphologies due to the presence of the high-T(m) component PVDF crystals by changing blend composition and crystallization conditions in the blends. There are mainly three different types of crystalline morphologies for PBSA in its miscible blends with PVDF. First, crystallization of PBSA commenced in the interspherulitic regions of the PVDF spherulites and continued to develop inside them in the case of PVDF-rich blends under two-step crystallization conditions. Second, PBSA spherulites appeared first in the left space after the complete crystallization of PVDF, contacted and penetrated the PVDF spherulites by forming interpenetrated spherulites in the case of PVDF-poor blends under two-step crystallization condition. Third, PBSA spherulites nucleated and continued to grow inside the PVDF spherulites that had already filled the whole space during the quenching process in the case of PBSA-rich blends under one-step crystallization condition. The conditions of forming the various crystalline morphologies were discussed.

Light scattering studies on the crystalline morphology of stretched poly(ethylene 2,6-naphthalate) film

The crystalline morphology of poly(ethylene 2,6-naphthalate) (PEN) film obtained by uniaxial stretching at 145°C (Tg+25°C) was investigated by use of a light scattering photometer equipped with a CCD camera system. The Hv scattering showed a symmetric, circular pattern at a low stretch ratio of λ<3. The intensity profile became sharper with an increase in λ, suggesting that anisotropic crystal rods are randomly assembled and that the length of the rods increases with λ. At a high stretch ratio of λ≥3, a double-cross-type pattern consisting of a broad rod-like pattern and sharp cross streaks was observed. The rod-like pattern became smaller and the streaks became sharper with an increase in λ. By the model calculation of the scattering pattern, the double-cross-type pattern is explained by the stacking of anisotropic crystal rods oriented in the stretch direction. As λ increases, the thickness of the rods and the number per stack increase, and the stacks and rods are slightly oriented in the stretch direction. The change in the wide angle X-ray diffraction pattern suggested that the ordering of the molecular chain in the crystal rods increases with increasing λ.

Characterization of poly(3-hydroxybutyrate) produced by Cupriavidus necator in solid-state fermentation

Solid-state fermentation (SSF) has recently been proposed as an alternative to submerged fermentation for the production of poly(hydroxyalkanoates). In the present work, X-ray diffraction, differential scanning calorimetry, nuclear magnetic resonance and infrared spectroscopy were employed to investigate the chemical structure, as well as the thermal properties and the crystalline morphology of poly(3-hydroxybutyrate) samples produced by SSF, using as raw material either soy cake or soy cake supplemented with 2.5% (m/m) sugarcane molasses. The results obtained showed that the biopolymer obtained by SSF presented the same properties as commercial PHB, except for the higher molar mass and the lower degree of crystallinity that were observed. Thus, the present data indicate that solid-state fermentation is an interesting alternative for the production of PHB, allowing the production of biopolymers with adequate properties from low-cost, renewable resources.

Crystalline morphology of poly(dimethylsiloxane)

The crystalline morphology of poly(dimethylsiloxane) was studied using a scanning electron microscope equipped with a cold stage. Samples of two different molecular weights were used. In both cases, spherulitic morphology is seen, from −70°C, with spherulites of about 100μ in size. Small single crystals of about a micron in size are also seen, and these are attributed to the presence of cyclics.

The effect of crystalline morphology of poly (butylene terephthalate) phases on toughening of poly(butylene terephthalate)/epoxy blends

In an effort to investigate the effect of the crystalline morphology of a poly(butylene terephthalate) (PBT) phase on the toughening of PBT/epoxy blends, the blends, having different degrees of perfectness of the PBT crystalline phase, were prepared by blending PBT and epoxy at various temperatures ranging from 200 to 240 °C. As the blending temperature decreases, the degree of perfectness of the PBT crystalline phase increases as a result of the increase of crystal growth rate. For PBT/epoxy blends, the change in crystalline morphology induced by processing may be the most important cause for the dependency of the fracture energy on blending temperatures. It has been found that PBT phases with a well-developed Maltese cross are most effective for epoxy toughening. This dependency reveals the occurrence of a phase transformation toughening mechanism. Also, the higher relative enhancement of fracture energy of a higher molecular weight epoxy system is further indirect evidence for a phase transformation toughening mechanism. Some other toughening mechanisms observed from the fracture surfaces, such as crack bifurcation, crack bridging, and ductile fracture of PBT phases, have been found to also be affected by the blending temperatures.

The competition between crystallization and phase separation in polymer blends: 2. Small-angle X-ray scattering studies on the crystalline morphology of poly(ε-caprolactone) in its blends with polystyrene

The courses of crystallization and of demixing or mixing, respectively, can interfere and compete in polymer blends with a miscibility gap. Crystallization dominates at lower temperatures, possibly inhibiting rejection of the non-crystallizing component into the remaining melt and enhancing its concentration in the amorphous regions between the crystalline domains. Time-resolved small-angle X-ray scattering measurements on poly(ε-caprolactone)/polystyrene (PCL/PS) blends, this system exhibiting an upper critical solution temperature, reveal that the amorphous regions between the lamellae within the PCL spherulites nearly do not phase separate when passing the binodal composition. Instead, supersaturation of composition occurs. The initially bent lamellae flatten with time, and the supersaturated spherulite amophous phase post-crystallizes according to the insertion crystallization scheme on a timescale that is comparable to the overall crystallization rate.

The relationship between the equilibrium melting temperature and the supermolecular structure of several polyoxetanes and polyethylene oxide

AbstractThe relationships between equilibrium melting temperatures (Tm*) and crystalline morphology of poly[3,3bis(ethoxymethyl)oxetane], (polyBEMO), poly[3,3‐bis (azidomethyl)oxetane], (polyBAMO), and poly(ethylene oxide), (PEO), were characterized. The Hoffman‐Weeks extrapolation procedure led to Tm* values of 92, 102, and 69°C for these three polymers, respectively. The gross morphologies of polyBEMO, polyBAMO, and PEO were studied as a function of melt‐liquid temperature (Ti) and isothermal crystallization temperature (Tc) by visible light microscopy. Spherulitic morphologies were observed for polyBEMO, polyBAMO, and PEO when Ti was above Tm*, while nonspherulitic (hedritic) morphologies were observed at Tls below Tm*. Mixed morphologies were observed when Tl was approximately equal to Tm*.