Isothermal Crystallization Of Poly Research Articles

Isothermal crystallization of poly(vinylidene fluoride) blended with the ionic liquid [Emim]2[Co(SCN)4]: Simultaneous analysis of crystalline phases by infrared spectroscopy and differential scanning calorimetry

The combination of poly (vinylidene fluoride) (PVDF) with ionic liquids (ILs) is increasingly being studied for the development of smart materials. Together with the functional response provided by the IL, its incorporation into PVDF allows to nucleate specific electroactive phases of the polymer, depending on the processing conditions. Thus, the isothermal crystallization of PVDF incorporating different contents of the magnetic ionic liquid bis(1-ethyl-3-methylimidazolium) tetrathiocyanatocobaltate ([Emim]2 [Co(SCN)4]) is reported in this work.Morphological properties of the films were obtained by field emission scanning electronic microscopy (FESEM), and particularly, for the higher contents of IL, segregation was observed through artifacts present on the film surface. This fact has been further confirmed by energy-dispersive x-ray spectroscopy (EDX).The growth of the crystalline phases of PVDF during isothermal crystallization at different temperatures has been analyzed by Fourier transform infrared (FTIR) spectroscopy. Although α, β and γ crystalline phases were present in all samples, their relative percentages varied greatly with the amount of IL present, demonstrating that [Emim]2 [Co(SCN)4] is a strong inductor of the electroactive (EA) phases of PVDF.By evaluating both FTIR and DSC data, this effect has been ascribed to the higher melting temperatures of the EA structures whose formation is favored at higher crystallization temperatures. The melting temperature (Tm) of the β phase is higher than that of the α phase, whereas Tm for the γ phase is higher than for α and β phases.Thus, together with the specific functional properties provided by the IL, such as magnetic response and ionic conductivity, the addition of [Emim]2 [Co(SCN)4] strongly influences PVDF's crystallization kinetics, proving to be a simple and very effective way to nucleate specific phases of PVDF, according also to the specific processing conditions.

The effect melt processing temperature on the isothermal crystallization of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

The effect melt processing temperature on the isothermal crystallization of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Crystallization Behavior of Semicrystalline Polymers Characterized by an In Situ Fluorescence Technique and its Sensing Mechanism

AbstractIn this study, fluorescence spectroscopy is used to study the bulk nonisothermal and isothermal crystallization of poly(L‐lactic acid) (PLLA) by monitoring in situ, the temperature (T)‐ and time (t)‐dependent fluorescence intensity of the fluorophores incorporated into the PLLA matrix, respectively. The crystallization behavior characterized by fluorescence resembles those measured by conventional differential scanning calorimetry, confirming the validity of this fluorescence technique for sensing crystallization. Combined in situ fluorescence results and ex situ X‐ray diffraction characterizations demonstrate that this fluorescence technique shows great sensitivity not only to the degree of crystallinity but also to the crystalline microstructures formed during crystallization (e.g., α vs α' form PLLA crystals). Moreover, complementary fluorescence microscopy helps reveal the fluorescence's intrinsic crystallization sensing mechanism: As crystals form during crystallization, the bulky fluorescent probes excluded from the crystalline regions reside in the rigid/mobile amorphous (i.e., non‐crystalline) regions of the resulting semicrystalline matrix, and their intramolecular motions are restricted by the neighboring crystalline domains; and thus, their fluorescence intensity is greatly enhanced upon crystallization. Owing to its high sensitivity, fluorescence is powerful for studying the crystallization behavior of ultrathin polymer films (e.g., 75 nm) and elucidating confinement and interfacial effects through future studies.

Isothermal crystallization of poly[3-hydroxybutyrate-co-4-hydroxybutyrate] mixtures

Isothermal crystallization of poly[3-hydroxybutyrate-co-4-hydroxybutyrate] mixtures

Isothermal Crystallization of Poly(ε–Caprolactone) PCL in Three‐Armed Copolymers

AbstractBranched copolymers are a special class of polymeric materials in which are reflected the combined effects of polymer segments and architectural constraints of the branched architecture. In this work, three‐armed graft copolymers, poly (hydroxyethyl methacrylate‐graft‐poly(caprolactone), [P(HEMA‐g‐PCL)]3, are synthesized by combination of reversible addition‐fragmentation chain‐transfer (RAFT) and ring opening polymerization (ROP) mechanisms in a one‐pot/one‐step protocol. The resulting macromolecules are characterized by 1H Nuclear Magnetic Resonance (NMR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The preliminary results indicate the success of the methodology and are in agreement with literature reports. In addition, DSC isothermal crystallization are performed, and Avrami's theory is employed in order to obtain kinetics parameters of interest, such as the half‐life for the crystallization process (t1/2), the bulk crystallization constant (k), and the Avrami's exponent (n). Thermal analysis evidences a noticeable reduction in the melting temperature compared with linear PCL homopolymer. However, the presence of branches does not modify the values of the maximum degradation temperatures significantly. Finally, the synthesized copolymers adopt a two‐dimensional crystallization type (disk and cylindrical).

Modeling of polymorphic composition development during isothermal crystallization of poly(l-lactide acid)

Development of polymorphic composition during isothermal crystallization of unstressed amorphous PLLA is considered in the introduced model. The model analysis of the overall crystallization half-time indicates involvement of both α′ and α polymorphs in the crystallization kinetics at substantial impact of the α′ form strongly dependent on temperature. Above 120 °C effective creation of α form takes place at much slower amorphous-to-α transformation and proceeds via α′-to-α transformation which occurs through orders of magnitude faster direct solid-to-solid transition mechanism. The model allows to predict development of individual α′ and α phases during isothermal crystallization of PLLA basing only on the overall temperature-dependent crystallization half-time, t1/2. The predictions are in good agreement with the experimental data reported by different authors in the literature. The model indicates that the transformation degrees to the individual α′ and α polymorphs vs. crystallization temperature, as well as the overall transformation degree are independent of the nuclei concentration in terms of the multiples of the crystallization half-time, because the concentration of nuclei is directly involved in t1/2.

Modeling the crystallization kinetics of polymers displaying high levels of secondary crystallization

The isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was evaluated using a range of models, namely, Avrami, simplified Hillier, Tobin, Malkin, Urbanovici–Segal, Velisaris–Seferis, and Hay. Two methods of model evaluation were used: determination of the parameters through traditional double log plots and curve fitting via nonlinear, multivariable regression. Visual inspection of the cumulative crystallization curves, calculation of the R2 value and standard error of the regression, and evaluation of the returned parameters were used to assess which model best describes the experimental data. The Hay model was found to generate the best fit, closely followed by the Velisaris–Seferis parallel model, suggesting that primary and secondary crystallization occur concurrently. The Avrami, Malkin, and Tobin models were found to perform well when the data is restricted to the region where primary crystallization dominates; however, they could not be used to successfully model the entire crystallization process. This work highlights the importance of selecting the most appropriate model for analyzing kinetics, especially when high levels of lamellar thickening and infilling occur during crystallization.

In-Situ Isothermal Crystallization of Poly(l-lactide)

The isothermal crystallization of poly(l-lactide) (PLLA) has been investigated by in-situ wide angle X-ray diffraction (WAXD) and polarized optical microscopes (POM) equipped with a hot-stage accessory. Results showed that the spherulites of PLLA were formed at high temperature, whereas irregular morphology was observed under a low temperature. This can be attributed to the varying rates of crystallization of PLLA at different temperatures. At low temperatures, the nucleation rate is fast and hence the chains diffuse very slow, resulting in the formation of imperfect crystals. On the other hand, at high temperatures, the nucleation rate is slow and the chains diffuse fast, leading to the formation of perfect crystals. The change in the value of the Avrami exponent with temperature further verifies the varying trend in the morphological feature of the crystals.

Isothermal crystallization of poly(ether ether ketone) with different molecular weights over a wide temperature range

Isothermal crystallization of poly(ether ether ketone) with different molecular weights over a wide temperature range

Isothermal crystallization of poly(glycolic acid) studied by terahertz and infrared spectroscopy and SAXS/WAXD simultaneous measurements

Isothermal crystallization of poly(glycolic acid) (PGA) has been studied using terahertz (THz) and infrared (IR) spectroscopy and simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements. Changes in the intermolecular interactions in PGA during the isothermal crystallization were monitored using THz spectroscopy, which is an efficient technique for analyzing the higher-order structure of polymers. In the THz spectra, the temporal difference in the intensity observed in the isothermal crystallization is due to the difference in the vibrational origins of two bands at 192 and 65 cm−1. The band at 192 cm−1 primarily originates from the intramolecular vibrational mode (twisting of the local structure of the PGA molecular chain). Furthermore, the band at 65 cm−1 exists due to the intermolecular vibration mode (C = O···H-C hydrogen bonds between polymer chains). In addition, these THz bands appeared after the appearance of the SAXS and WAXD peaks. When a lamellar structure is formed and the molecular chains are oriented, the THz band originating from the intermolecular vibration is observed. It is highly possible that the intermolecular vibration appearing in the THz spectra requires the molecular chains to be oriented. Isothermal crystallization of poly(glycolic acid) (PGA) was carried out using terahertz (THz) and infrared (IR) spectroscopy and simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements. The intensity of the absorption peak at 192 cm−1 increased before the increase in intensity of the peak at 65 cm−1 during the isothermal melt-crystallization process at 185 °C. This is due to a difference in the vibrational origins of these two bands. In addition, these THz bands appeared after the appearance of the SAXS and WAXD peaks

A study on the isothermal crystallization of poly(3-methylbutene-1)

Poly(3-methylbutene-1) (P3MB1) is a polyolefin with a high melting temperature Tm (≈ 305 °C). We investigated the structural evolution of P3MB1 during isothermal crystallization from the melt by synchrotron radiation X-ray scattering and polarizing optical microscopy. At crystallization temperatures (Tc) of 297 and 290 °C or shallow quench conditions (ΔT = Tm0-Tc = 26 and 33 °C), needle-like crystals comprising lamellae were formed and flowed during their growth in the molten portion. To clarify the origin of the wide temperature region of the needle-like crystals in P3MB1, we estimated the critical lamellar width λ*, which is a parameter characterizing the suppression of lamellar branching, of P3MB1 and polyethylene (PE). The λ* of P3MB1 was larger than that of PE at the same ΔT, owing to the low viscosity of P3MB1. However, the range of λ* in the temperature region of the needle-like crystals of P3MB1 was 0.41 < λ* < 7.4 μm; PE formed spherulites in this range. Thus, suppression is not only the origin of the needle-like crystals in P3MB1, but may also be responsible for the flow of the needle-like crystals in melts.

Influence of Chain Topology (Cyclic versus Linear) on the Nucleation and Isothermal Crystallization of Poly(l-lactide) and Poly(d-lactide)

Ring closure click chemistry methods have been used to produce cyclic c-PLLA and c-PDLA of a number-average molecular weight close to 10 kg/mol. The effects of stereochemistry of the polymer chains and their topology on their structure, nucleation, and crystallization were studied in detail employing wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), polarized light optical microscopy (PLOM), and standard and advanced differential scanning calorimetry (DSC). The crystal structures of linear and cyclic PLAs are identical to each other, and no differences in superstructural morphology could be detected. Cyclic PLA chains are able to nucleate much faster and to produce a higher number of nuclei in comparison to linear analogues, either upon cooling from the melt or upon heating from the glassy state. In the samples prepared in this work, a small fraction of linear or higher molecular weight cycles were detected (according to SEC analyses). The presence of such “impurities” retards spher...

Investigation on shear induced isothermal crystallization of poly (lactic acid) nanocomposite based on graphene

ABSTRACTIn this study, the isothermal crystallization of poly (lactic acid) (PLA) and its graphene-based nanocomposites (containing 0.5, 1, 2, and 3 wt% of graphene nanoplatelets – GNp) was studied at 135°C under quiescent and different presheared conditions (0.1, 0.3, 0.5, 1.1, and 1.8 s for 60s). Induction time of crystallization was determined from the plot of storage modulus versus time in time sweep test. Results showed that increase in GNp content decreased the induction time significantly. The preshear flow did not significantly affect the induction time of PLA containing 0.5 wt% of GNp and neat PLA. However, an increase in the intensity of preshear for graphene-based nanocomposites containing 1, 2, and 3 wt% of GNp first decreased the induction time and then increased it. The induction time also decreased with increase in the duration of shear flow.

Mesophase-Mediated Crystallization of Poly(l-lactide): Deterministic Pathways to Nanostructured Morphology and Superstructure Control

The effect of the CO2-induced mesophase on the isothermal crystallization of poly(l-lactide) (PLLA) was investigated by infrared (IR) spectroscopy and microscopy. It was found that the crystallization rate of PLLA was significantly enhanced by the CO2-induced mesophase, showing that the crystallization was completed even in a short period of 100–101 s. Compared with the directly crystallized samples that showed typical spherulites with lamellae, the crystallization via CO2-induced mesophase led to nonspherulitic (granular or featureless) morphologies consisting of nanorods, whereas the polymorphic behavior remained unaffected by the initial state, resulting in crystallized PLLA containing identical polymorphs of uniquely different nanostrutured morphologies and superstructures. The IR imaging results indicated that the formation of the equilibrium crystal was preceded by the formation of various metastable intermediate phases, including mesomorphic phase, preordering, and metastable crystal, all of which ...

The isothermal crystallization of poly(ether ether ketone) by two‐dimensional differential scanning calorimetry correlation mapping

ABSTRACTThis article reports the first application of the two‐dimensional differential scanning calorimetry correlation mapping, two‐dimensional‐DSC‐CM to analyze DSC rate–time data of PEEK. This provided evidence that the isothermal crystallization reduced rate–time curves exhibited fractional n values when analyzed by the Avrami equation. These fractional n values, which increased with temperature, were consistent with the presence of two processes, primary and secondary crystallization, with an increasing contribution of the secondary crystallization to the overall crystallinity. In contrast to the known literatures, secondary crystallization was observed to proceed at early stage of primary crystallization. The study of the effect of proton irradiation, up to a dose of 9.9 MGy, showed that the fractional n value was below 3.0, and does not appear to be temperature dependent. DSC analysis of the crystallization kinetics, combined with two‐dimensional correlation mapping proved a powerful tool for investigating irradiation damage of PEEK. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44378.

Effect of wood flour as nucleating agent on the isothermal crystallization of poly(lactic acid)

The effect of wood flour (WF) as an efficient nucleating agent on the isothermal melt crystallization and isothermal cold crystallization behavior of poly(lactic acid) (PLA) was investigated by differential scanning calorimeter and polarized optical microscopy. It was found that the incorporation of 4 wt% WF promoted the crystallization of PLA about 4.2%. Polarized optical microscopy results showed the Maltese cross of the samples. The presence of the 4 wt% WF may increase the nucleation density, leading to the increase of the spherulites; however, the size of the spherulites decreased, and the structure became incomplete. The Avrami model was applied to analyze the isothermal crystallization kinetics. It is concluded that the addition of WF modified the crystallization process of PLA (the value of Avrami exponent changed). Various parameters, such as the crystallization half time and crystallization rate constant, reflect that 4 wt% WF significantly improves the crystallization process. The observations in this article indicate that WF is an efficient nucleating agent of PLA. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of functionalized graphenes on the isothermal crystallization of poly(L-lactide) nanocomposites

The effects of graphene oxide (GO) with polar groups and functionalized GO (fGO) with nonpolar groups on the isothermal crystallization of poly(L-lactide) (PLLA) were compared. Functionalized GO was obtained by grafting octadecylamine and characterized by FTIR, WAXD and TGA. Isothermal crystallization kinetics of PLLA/GO and PLLA/fGO nanocomposites were investigated by combining DSC data and Avrami equation. The results showed that fGO could improve PLLA crystallization rate more obviously than GO. By analyzing the morphology obtained from POM, SEM and TEM, it was found fGO with large layer space dispersed better in PLLA and supplied more nucleation sites than GO. Therefore, for the multilayer graphene, increasing the layer spaces is important to improve its dispersion in polymers, which will cause the crystal kinetics changing of polymers.

Miscibility and isothermal crystallization of poly(L-lactide) and poly(trimethylene carbonate) blends

Miscibility, isothermal crystallization kinetics, and morphology of poly(L-lactide)/poly(trimethylene carbonate) (PLLA/PTMC) crystalline/amorphous blends were studied by differential scanning calorimetry (DSC) and optical microscopy (OM). The heterogeneity of OM images and an unchanged glass transition temperature showed that PLLA was immiscible with PTMC. During isothermal crystallization, the crystallization rate of PLLA improved when the PTMC content was low (≤ 20%). However, when the PTMC content was high (≥ 30%), the crystallization rate decreased significantly. The reason of these nonlinear changes in crystal kinetics was analyzed according to the nucleation and growth process by virtue of a microscope heating stage. The isothermal crystallization morphologies of the blends were also studied by polarized optical microscopy and the results confirmed the conclusions obtained from crystallization kinetics.

Morphology and crystallization behavior of poly(l‐lactide)/poly(butylene oxalate) blends

ABSTRACTThe isothermal crystallization of poly(l‐lactide) (PLLA) in blends with poly(butylene oxalate) (PBOX) is investigated by time‐resolved small‐angle X‐ray scattering, differential scanning calorimetry, and optical microscopy. We focus on the temperatures at which only PLLA crystallizes while PBOX is amorphous. It is obtained that the addition of PBOX causes a reduction of the melting temperature of PLLA. The lamellar thickness of PLLA crystals decreases whereas the amorphous layer thickness increases with blend composition, suggesting the occurrence of the interlamellar incorporation upon the addition of PBOX. The crystal growth rate and morphology of PLLA/PBOX blends are analyzed by polarized optical microscopy. The spherulite growth rate of PLLA is found to increase with the addition of PBOX. Analysis of the isothermal crystallization in terms of the Lauritzen and Hoffman equation give the reduction of the fold surface free energy upon the addition of PBOX in PLLA, indicating that the mobility of the PLLA chains is significantly improved due to the presence of PBOX. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 192–202

Molecular Weight and Crystallization Temperature Effects on Poly(ethylene terephthalate) (PET) Homopolymers, an Isothermal Crystallization Analysis

The isothermal crystallization of poly(ethylene terephthalate) (PET) homopolymers with different molecular weight was studied in a wide temperature range (140–230 °C) using different experimental techniques. Three different morphological regions, labeled r1, r2 and r3, were distinguished as a function of crystallization temperature (Tc). In r1 (low Tc) crystallized samples were characterized by a low crystalline degree with a small spherulite texture containing thin crystals. In r2 (intermediate Tc) samples showed medium size spherulites composed of two distinct crystalline families (thin and thick crystals). In this temperature range, the crystallization exhibited a maximum value and it was associated with a high content of secondary crystals. In r3 (high Tc), samples presented considerable amorphous zones and regions consisting of oversized spherulites containing only thick crystals. Time-resolved wide-angle X-ray diffraction measurements, using synchrotron radiation, indicated a rapid evolution of the crystalline degree within the second region, in contrast with the quite slow evolution observed in the third region. On the other hand, by small-angle X-ray scattering (SAXS) and time-resolved SAXS experiment, it was found that the long period (L) as well as the lamellar thickness (lc) increase as a function of Tc, corroborating the formation of the thickest crystals in the third region. From all these observations, a morphological model was proposed for each region.