Spherulitic Morphology Of Poly Research Articles

Effect of a Self-Assembled Nucleating Agent on the Crystallization Behavior and Spherulitic Morphology of Poly(lactic acid).

Herein, decanedioic acid dibenzoylhydrazide (DDBH) was used as a nucleating agent to improve the crystallization of poly(lactic acid) (PLA). The formation of DDBH assemblies in PLA melts at different concentrations was systematically investigated. The DDBH (0.5-0.9 wt %) recrystallized as dendrite-like structures during the isothermal crystallization process, and the crystal morphology of PLA underwent a morphological change from spherical form to a similar dendritic crystal form. Differential scanning calorimetry and in situ wide-angle X-ray diffraction analysis results showed that crystallizability and overall crystallization rate of PLA were enhanced by the addition of DDBH. The half-crystallization time at 120 °C reduced to 0.28 min compared to pure PLA (6.12 min), after adding 0.9 wt % DDBH. Moreover, the crystallinity and lamellar thickness of crystalline PLA increased, while the size of the microcrystal of PLA decreased with an increase in DDBH content. The heat deflection temperatures of PLA/DDBH blends increased and hence heat resistance improved.

Crystallization behavior and morphology of novel aliphatic poly(monothiocarbonate)s

Aliphatic poly(monothiocarbonate)s synthesized by alternating copolymerization of carbonyl sulfide (COS) and epoxides are a new type of crystalline polymers. In this work, the isothermal crystallization behavior and spherulite morphology of poly(trimethylene monothiocarbonate) (PTMMTC) and poly(ethylene monothiocarbonate) (PEMTC) are studied. PTMMTC tends to form banded spherulites, especially at low crystallization temperatures, while PEMTC forms non-banded spherulites. The overall crystallization rate and spherulitic growth rate of PTMMTC are larger than those of PEMTC at the same degree of supercooling. PTMMTC with longer alkane segment in the main chain has a higher equilibrium melting temperature (Tm0) than PEMTC. Both polymers exhibit double melting peaks, but the formation mechanisms are different for PTMMTC and PEMTC. Small-angle X-ray scattering (SAXS) result reveals that more amorphous phases are located in interlamellae of PTMMTC, leading to a larger long period (L) and a thicker amorphous layers (la), which can account for the stronger tendency of PTMMTC to form banded spherulites. The melting enthalpies of PTMMTC and PETMC crystals with 100% crystallinity (ΔHm0) are obtained by extrapolating the melting enthalpies of the samples with different crystallinities. The free energy of the folding surface (σe) of PTMMTC is larger than that of PETMC, indicating that the PTMMTC chain is stiffer. The higher Tm0 and larger ΔHm0 and σe of PTMMTC can be attributed to its stronger interchain interaction.

Isothermal crystallization and spherulite morphology of poly(ethylene terephthalate)/Na+-MMT nanocomposites prepared through solid-state mechanochemical method

Differential scanning calorimetry (DSC) and polarized optical microscopy were used to comparatively investigate the multiple melting behavior and isothermal crystallization kinetic of pure PET and PET/Na+-MMT nanocomposites prepared through solid-state mechanochemical method and conventional method. The results showed that both pure PET and Na+-MMT-filled PET system isothermally treated at different crystallization temperature exhibited three melting endotherms, including peak I, II and III in the DSC heating process. The increases in both crystallization temperature and Na+-MMT loading and the mechanochemical pan-milling prove to be beneficial to the formation of crystals related to endotherm II in the primary crystallization process. The mechanochemical pan-milling effect and the increase in the Na+-MMT loading also decrease the size of the formed spherulite. The investigation of isothermal crystallization kinetics indicated that the calculated Avrami exponent n of the milled sample (PETSNx) shows the higher value than that of both pure PET and the conventional unmilled sample (PETCNx) and also increases with increasing the Na+-MMT content. In addition, the calculated crystallization activation energy of PETSNx is found to be lower than that of pure PET as well as PETCNx.

Polymorphism and spherulite morphology of poly(1,4‐butylene adipate)/organically‐modified layered double hydroxide nanocomposites

ABSTRACTA novel biodegradable poly(1,4‐butylene adipate)/organically‐modified layered double hydroxide (PBA/m‐LDH) nanocomposites are synthesized using the solution mixing process. The m‐LDH is originally prepared with magnesium nitrate hexahydrote (Mg(NO3)2 6H2O), aluminum nitrate‐9‐hydrate (Al(NO3)3 9H2O), oleic acid, and sorbitol by a novel one‐step co‐precipitation method to intercalate the organo‐modifier of oleic acid and sorbitol into the interlayer of LDH. The structure and morphology of the PBA/m‐LDH nanocomposites are characterized using X‐ray diffraction and transmission electron microscopy (TEM). It has been shown that the m‐LDH is exfoliated and well distributed in PBA matrix. The effect of m‐LDH on the polymorphic crystal and morphology of PBA at various crystallization temperatures (Tcs) would be investigated using WAXD and POM. Both data indicate that the addition of m‐LDH can change the starting formation temperature of α‐form crystals. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42526.

Effects of Glycine‐Based Ionic Liquid on Spherulite Morphology of Poly(l‐Lactide)

Crystalline morphology, lamellar assembly, spherulitic growth rate, and physical properties of poly(l‐lactide acid) (PLLA) modified by a room‐temperature ionic liquid (IL), N‐alkyl‐substituted‐glycine ester [N,N‐dimethyl‐N‐propyl glycine ethyl ester (DMPGlyET)+] bis(fluoromethanesufonyl)imide [TFSI−], are investigated by using polarized optical microscopy, optical microscopy, differential scanning calorimetric, and atomic‐force microscopy. Thermal analyses and in situ microscopy characterization reveal the PLLA/IL mixture with upper‐critical‐solution‐temperature behavior. Crystalline morphology of PLLA is significantly changed by the addition of IL to display massive diversification of spherulites morphology which has never been reported before in neat PLLA or PLLA blends with polymers. The morphological change and diversifications in PLLA/IL mixture are associated with strong interactions between PLLA and IL, which impede the melt crystallization of PLLA and tend to form PLLA nuclei of various geometry shapes. In addition, neat PLLA is generally brittle with extensive crack formation during postcrystallization cooling process; however, with the addition of IL, cracks are reduced or diminished entirely, potentially to enhance the performance and properties of PLLA. image

Non-isothermal crystallization behaviors and spherulitic morphology of poly(lactic acid) nucleated by a novel nucleating agent

The effect of cadmium phenylmalonate (PMA- Cd) as a novel nucleating agent on the crystallization be- haviors and spherulitic morphology of poly(lactic acid) (PLA) as well as non-isothermal crystallization kinetics of the nucleated PLA were studied by means of differential scanning calorimetry and polarized light microscopy. The results showed that PMA-Cd served as an effective nu- cleating agent to accelerate the crystallization rate of PLA. The presence of PMA-Cd significantly increased the number and decreased the size of the spherulites. The non- isothermal crystallization kinetics of the nucleated PLA was well described by Mo's model. The activation energies (DE) of non-isothermal crystallization were calculated by Kissinger's method. The crystallization rate of PLA/0.5 % PMA-Cd sample was faster than that of PLA/0.2 % PMA- Cd sample, while the DE of the former was greater than that of the latter. The nucleation mechanism between PMA-Cd and PLA was satisfactorily explained by dimen- sional lattice-matching criterion.

Non‐isothermal crystallization kinetics and spherulitic morphology of nucleated poly(lactic acid): effect of dilithium cis‐4‐cyclohexene‐1,2‐dicarboxylate as a novel and efficient nucleating agent

The effect of dilithium cis‐4‐cyclohexene‐1,2‐dicarboxylate (CHDA‐Li) as a novel and efficient nucleating agent on the crystallization behaviors and spherulitic morphology of poly(lactic acid) (PLA) as well as non‐isothermal crystallization kinetics of the nucleated PLA was studied by means of differential scanning calorimetry and polarized light microscopy. The results show that CHDA‐Li serves as a good nucleating agent to accelerate the crystallization rate of PLA. The nucleation ability of CHDA‐Li is superior to octamethylenedicarboxylic dibenzoylhydrazide. With the incorporation of CHDA‐Li, the number of the spherulites increases, and the size decreases significantly. The non‐isothermal crystallization kinetics of the nucleated PLA can be well described by Jeziorny's and Mo's models. The activation energies (ΔE) of non‐isothermal crystallization were calculated by Kissinger's and Friedman's methods. The crystallization rate of PLA/0.5 wt% CHDA‐Li sample is faster than that of PLA/0.2 wt% CHDA‐Li sample, while the ΔE of the former is lower than that of the latter. Copyright © 2015 John Wiley & Sons, Ltd.

Crystallization behavior and spherulitic morphology of poly(lactic acid) films induced by casting process

A novel way using a polarized optical microscopy and statistical image analysis techniques for direct investigation of the crystallization kinetics and spherulitic morphology of poly (lactic acid) induced by casting process has been proposed. DSC analyses were carried out to explore the effect of drawing in thermal properties of PLA. We found that the rate of cold crystallization was sharply increased with draw ratio. Isothermal calorimetric results reveal that thin films crystallize slowly compared to sheets. Moreover, thin films don't fit the Avrami model demonstrating that more stretching may modify the crystallization kinetics of films. A comparison was made between pure PLA and stretched materials using Hoffman theory and giving a compiled view on the details of crystallization behavior with relation to stretch effect. At draw ratio 167, the growth rate reach its maximum and the crystallization rate go up exponentially. POM experiments showed the existence of two different spherulitic populations in thin films and two nucleation mechanisms was identified. Accordingly, the growth rate was found to be not linear with time. Furthermore, the X-ray diffraction analyses showed the presence of α and α' crystal form in thin films contrarily to sheets with α form. POLYM. ENG. SCI., 55:1881–1888, 2015. © 2014 Society of Plastics Engineers

Non-isothermal crystallization kinetics and spherulitic morphology of nucleated poly(lactic acid): Effect of dilithium hexahydrophthalate as a novel nucleating agent

The effect of dilithium hexahydrophthalate (HHPA-Li) as a novel and efficient nucleating agent on the non-isothermal crystallization behaviors and spherulitic morphology of poly(lactic acid) (PLA) was studied. Jeziorny’s, Ozawa’s and Mo’s models were employed to describe the non-isothermal crystallization kinetics of the nucleated PLA samples. The activation energies (ΔE) of non-isothermal crystallization were calculated by Friedman formula. The results showed that Jeziorny’s and Mo’s methods well described the non-isothermal crystallization kinetics of the nucleated PLA samples, while Ozawa’s model failed. The crystallization rate of PLA/0.5wt% HHPA-Li sample was faster than that of PLA/0.2wt% HHPA-Li sample, while ΔE of the former was lower than that of the latter. It was also found that the presence of HHPA-Li significantly increased the number and decreased the size of spherulites.

Enhanced Nucleation and Crystallization of Poly(l-lactic acid) by Immiscible Blending with Poly(vinylidene fluoride)

Effects of poly(vinylidene fluoride) (PVDF) on the non-isothermal and isothermal crystallization kinetics, crystalline structure, and spherulitic morphology of poly(l-lactic acid) (PLLA) in their immiscible blends were investigated. Both the cold and melt crystallizations of PLLA are accelerated after blending with PVDF. The crystallization rate of PLLA further increases as the PVDF content increases. PLLA does not crystallize upon cooling (10 °C/min) from the melt, while it can almost crystallize sufficiently under the same conditions after blending with 10% PVDF. PLLA crystallizes after the crystallization of PVDF in the melt crystallization process. The isothermal crystallization kinetics of PLLA in the blends was analyzed by the Avrami model. Crystallization half-time decreases and crystallization rate constant of PLLA increases after blending with PVDF. With the presence of PVDF, the spherulitic size of PLLA decreases and spherulitic number increases. Nucleation density of PLLA increases by 2–3 orders of magnitude by blending with 10 or 25% PVDF. It is found that PLLA spherulites can epitaxially grow on the PVDF crystalline domains, forming a transcrystalline structure in the PLLA/PVDF interface. It is proposed that the PVDF-promoted crystallization of PLLA in their immiscible blends is ascribed to the heterogeneously epitaxial and interface-assisted nucleation mechanism.

Crystallization Regimes and Spherulitic Morphology of Poly(trimethylene terephthalate/isophthalate) Random Copolyesters

The crystallization regimes and spherulitic morphology of poly (trimethylene terephthalate/isophthalate) (TI) random copolyesters were studied in this work. A hot stage polarizing microscope was used to observe morphology and measure growth rate of the spherulite of TI copolyesters. Lauritzen-Hoffman secondary nucleation theory was applied to investigate crystallization kinetics and regimes of TI copolyesters. Results show that the spherulitic growth rate decreased with an increase in isophthalic acid content of the copolyesters. The analysis of Lauritzen-Hoffman secondary nucleation theory shows that regime I, II, and III were observed in TI11 and TI21. Regime III was observed in TI29. The spherulitic morphology of TI11, TI21, and TI29 changed from elliptical-shaped spherulite to irregular spherulite and then to normal spherulite at the regime transitions.

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 Tc, 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 Tc. 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.

Rheological Properties and Spherulite Morphology of Poly(trimethylene terephthalate)/Rubber Blends

Poly(trimethylene terephthalate) (PTT), and three different rubbers(maleated styrene-butylene-co-ethylene-styrene copolymer (SEBS-g-MA), ethylene-propylene-diene copolymer grafted with maleic anhydride (EPDM-g-MA) and maleic anhydride grafted poly (ethylene-octene) (POE-g-MA)) were mixed in the melt state. Their rheological properties and spherulite morphology were investigated. Rheological properties shows torque decreases with the time increasing for all blends. PTT/SEBS-g-MA blend have better processability than PTT/EPDM-g-MA and PTT/ POE-g-MA blend. Polarizing optical microscopy (POM) experiments showed that the introduction of rubber chain greatly affects the size of the PTT spherulites. Small-sized PTT spherulites were formed when rubber added to PTT.

Crystallization behaviors and morphology of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Crystallization behaviors and spherulitic morphology of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with different 4-hydroxybutyrate (4HB) molar fraction were investigated by differential scanning calorimetry and polarized optical microscopy. Crystallization behaviors of P(3HB-co-4HB) are significantly affected by 4HB molar fraction. The melting temperature (Tm), glass transition temperature (Tg), and crystallinity (Xc) decrease with the increase of 4HB molar fraction. Banded spherulites are observed in poly (3-hydroxybutyrate) (PHB) and P(3HB-co-4HB) copolymers. The band spacing decreases with the increase of 4HB molar fraction. The morphology and growth rate of the spherulites strongly depend on 4HB molar fraction and the crystallization temperatures. The introduction of 4HB unit can inhibit the emergence of cracks in PHB spherulites.

Fractionated crystallization, polymorphic crystalline structure, and spherulite morphology of poly(butylene adipate) in its miscible blend with poly(butylene succinate)

It has been investigated the effects of poly(butylene succinate) (PBS) component on the fractionated crystallization, crystalline structure, and spherulite morphology of polymorphic poly(butylene adipate) (PBA) with melting temperature lower than that of PBS in their miscible binary blends. Fractionated crystallization of the PBA component occurs upon blending with PBS depending on the content and crystallization temperature of the PBS component. It is probably related to the distribution of PBA in the PBS matrix. The PBS component suppresses the crystallization of PBA, due to the physical confinement effect of PBS on the PBA component. PBS is favorable for the formation of the PBA α-crystal in the PBS/PBA blends with C PBS ≤ 70%, suggesting that the polymorphism of PBA can be regulated by PBS. The morphology observation reveals that the spherulite growth direction of PBA is controlled by that of PBS. Furthermore, the morphology of PBA is also manipulated by that of PBS rather than the crystallization temperature. The possible mechanism of morphology generation of PBA controlled by PBS has been proposed. The PBS/PBA blend system is an ideal system to study not only on the polymorphism regulation but also on morphology control of biodegradable polymorphic material by polymer blending without losing the biodegradability.

Isothermal crystallization kinetics and spherulitic morphology of poly(4‐hydroxybutyric acid‐alt‐glycolic acid)

AbstractIsothermal crystallization behavior of a new regular polyester constituted by glycolic acid and 4‐hydroxybutyric acid units is studied by means of differential scanning calorimetry and hot‐stage optical microscopy. A wide range of crystallization conditions were experimentally accessible, allowing various morphological features to be observed and accurate estimates made of characteristic growth parameters, including radial growth and nucleation rates. Three‐dimensional spherulitic growth from heterogeneous nuclei is deduced from the Avrami analysis, whereas optical micrographs reveal two different spherulitic textures that agree with the existence of two crystallization regimes. These can be well distinguished from the breaks observed in the Lauritzen and Hoffman plots when the linear crystal growth rate or the overall crystallization rate is considered. Ringed and nonringed spherulites with negative and positive birefringence, respectively, can be obtained depending on crystallization conditions and regimes. The studied polyester shows rather complex melting behavior which is interpreted in terms of a recrystallization process involving the two different kinds of spherulites. This study allows polymorphism to be discounted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2640–2653, 2007

Effect of small amount of poly(ethylene naphthalate) on isothermal crystallization and spherulitic morphology of poly(trimethylene terephthalate)

The effect of a small amount of poly(ethylene naphthalate) (PEN) in its blends with poly(trimethylene terephthalate) (PTT) on isothermal melt-crystallization kinetics and spherulitic morphology of the blends was thoroughly investigated. The maximum PEN content in the blends was 9 wt%. Due to the single composition-dependent glass transition temperature ( T g) that was observed for each blend, these blends appeared to be miscible in the amorphous state. After isothermal crystallization from the melt state, the neat PTT and its blends with PEN exhibited either double or triple melting endotherms. The triple endothermic peaks were observed in both the neat PTT and the blends when being crystallized at crystallization temperatures ( T c) of less than or equal to ∼195 °C. The equilibrium melting temperature ( T m 0 ) for the neat PTT was determined based on the linear Hoffman–Weeks extrapolative method to be ∼248 °C. Such values for the blends were found to decrease with the addition and increasing amount of PEN. Both the neat PTT and the blends were isothermally crystallized over the T c range of 190–205 °C. At a given T c, the 97PTT/3PEN blend exhibited a half-time of crystallization ( t 0.5) value that was lower, while it exhibited reciprocal half-time ( t 0.5 - 1 ), Avrami rate constant ( K A), and spherulitic growth rate ( G) values that were greater, than those of the neat PTT. With further increase in the PEN content, the t 0.5 value increased, while the t 0.5 - 1 , K A, and G values decreased. Analysis of the G values based on the Lauritzen–Hoffman's (LH) secondary nucleation theory showed that the neat PTT and the 91PTT/9PEN blend exhibited a regime II→III transition at ∼194 °C (∼467.2 K), while no regime transition was observed for the other two blends. The lateral and the fold surface free energies ( σ and σ e) and the work of chain folding ( q) for the neat PTT and the blends were 19.4, 30.2–46.3 erg cm −2, and 2.4–3.6 kcal mol −1, respectively. Lastly, the effect of both the T c and the PEN content on morphology and texture of the PTT spherulites was also investigated and the results showed that the texture of the spherulites became coarser with increasing T c and PEN content.

Crystallisation and morphology of poly( p ‐dioxanone)

The crystallisation and spherulitic morphology of poly(p-dioxanone) (PPDX), a thermoplastic polyester-ether used for medical applications have been studied. Polarised Optical Microscopy (PM) revealed that isothermally crystallised PPDX exhibits large double banded spherulites with a mean banding spacing that increases as the crystallisation temperature increases. The lack of resolution of optical microscopy prevents the double banding from being clearly observed at crystallisation temperatures below 75°C. The spherulitic morphology changed somewhat as a function of crystallisation temperature from well developed structures with a very clear Maltese cross to spherulites with a more granular texture. A Regime III to Regime II transition in growth was detected according to the Lauritzen and Hoffman analysis of spherulitic growth rate data even though there were no apparent major morphological changes in spherulitic structure as crystallisation temperature was varied apart from that described above. The equilibrium melting point was determined using the Hoffman-Weeks extrapolation procedure and found to be 127°C. Avrami theory was applied to caloriometric overall crystalline conversion data and good fits were obtained with exponents ranging from 3 to 4 as isothermal crystallisation temperature was increased from 50 to 100°C indicating a change from instantaneous to sporadic spherulitic nucleation that was consistent with PM observations. PPDX exhibited a marked tendency to undergo partial fusion and recrystallisation during DSC heating scans. Self-nucleation results evidenced the existence of the usual three self-nucleation domains depending on the self-nucleation temperature (T s ) employed. Additionally, the complex behaviour upon cooling from T s and subsequent melting was studied in detail.

Investigation on the spherulitic morphology of poly(ether‐ether‐ketone)

AbstractThe spherulitic morphology of poly(ether‐ether‐ketone)Systematic name: poly(oxy‐1, 4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene). (PEEK) has been studied by using polarizing light microscopy, IR and differential scanning calorimetry. It has been found that in distinct cases the spherulites of PEEK show radiated or banded morphology, which can change from one to another upon thermal treatment. The process was found to be reversible and also affected by the film thickness.