Multiple Melting Behavior Research Articles

Multiple Melting Behavior of Poly(thiodiethylene terephthalate): Further Investigations by Means of X‐ray and Thermal Techniques

AbstractSummary: The complex multiple melting behavior of poly(thiodiethylene terephthalate) (PSDET) was investigated by means of differential scanning calorimetry, X‐ray diffraction and hot‐stage optical microscopy. The phenomenon was ascribed to the existence of two different crystal structures (α and β), each of them being able to melt and recrystallize under the experimental conditions adopted. Linear and nonlinear treatments were applied in order to estimate the equilibrium melting temperature for α PSDET, by using the corrected values of Tm. The nonlinear estimation led to a higher value by about 25 °C. Isothermal crystallization kinetics of each crystalline form were analyzed according to Avrami's treatment. In both cases, values of Avrami's exponent, n, close to 3 were obtained, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three dimensional spherulitic growth. The rate of crystallization of each crystalline structure was found to become lower as the crystallization temperature is increased, as usual at low undercooling, where the crystallization process is controlled by nucleation.XRD patterns of PSDET samples isothermally crystallized at the indicated Tcs.imageXRD patterns of PSDET samples isothermally crystallized at the indicated Tcs.

Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

AbstractNylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L100 and L010 of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003

Multiple melting behavior of isotactic polypropylene and poly(propylene-co-ethylene) after stepwise isothermal crystallization

The multiple melting behavior of several commercial resins of isotactic polypropylene (iPP) and random copolymer, poly(propylene-co-ethylene) (PPE), after stepwise isothermal crystallization (SIC) were studied by differential scanning calorimeter and wide-angle X-ray diffraction (WAXD). For iPP samples, three typical melting endotherms appeared after SIC process when heating rate was lower than 10 °C/min. The WAXD experiments proved that only α-form crystal was formed during SIC process and no transition from α1- to α2-form occurred during heating process. Heating rate dependence for each endotherm was discussed and it was concluded that there were only two major crystals with different thermal stability. For the PPE sample, more melting endotherms appeared after stepwise isothermal crystallization. The introduction of ethylene comonomer in isotactic propylene backbone further decreased the regularity of molecular chain, and the short isotactic propylene sequences could crystallize into γ-form crystal having a low melting temperature whereas the long sequences crystallized into α-form crystal having high melting temperature.

Effects of several lanthanide trichloride hydrates on the melting behavior and spherulitic superstructure of poly(ethylene oxide)

AbstractBinary mixtures of poly(ethylene oxide) (PEO) with the trichloride hydrates of lanthanum, cerium, europium, terbium, and ytterbium have been studied with calorimetry, polarized optical microscopy, and infrared spectroscopy. Melting‐point depression of the PEO‐rich phase occurs in all cases. At sufficiently high concentrations of the low molecular weight lanthanide complex, crystallization of the polymer is absent. The lighter lanthanides with larger ionic radii, such as lanthanum and cerium, are more effective in suppressing PEO crystallization from solution or the molten state because they are more oxophilic. The spherulitic superstructure of PEO disappears at rather low concentrations of the lanthanide salts, between 2 and 8 mol % Ln3+. Lanthanum and terbium are most efficient at disrupting the formation of PEO spherulites, and europium is least efficient. Infrared spectroscopy identifies twisting and wagging vibrational absorptions of CH2 groups in the polymer that are sensitive to the morphologies of these mixtures. Modifications of the PEO infrared absorbances in the presence of these five lanthanide salts correlate more closely with the presence or absence of major PEO melting, not the formation of a spherulitic superstructure. The phase behavior is rather simple, with no evidence of eutectic solidification upon cooling from the molten state. Multiple melting endotherms are observed in the differential scanning calorimetry heating traces of binary mixtures containing 8 mol % Yb3+ and between 10 and 20 mol % Eu3+, but the concentration dependence of these first‐order endothermic transitions is not characteristic of eutectic phase behavior. The presence of trivalent cations, such as Eu3+ or Yb3+, in these complexes perturbs the crystallization kinetics of PEO upon cooling from the molten state, as well as the melting behavior upon heating. Ion–dipole or electrostatic interactions between the lanthanide cation and the ether oxygen of PEO might alter the surface free energy at the periphery of the crystalline lamellae and perturb the chain‐folding characteristics of PEO. Consequently, coupling between the amorphous matrix and the PEO crystallites is strengthened, and this provides stability for the existence of multiple‐chain‐folded crystals composed of rather thin lamellae that could be responsible for multiple melting behavior. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2200–2213, 2003

In Situ FTIR Studies on the Cold-Crystallization Process and Multiple Melting Behavior of Isotactic Polystyrene

The structure evolution of iPS during isothermal cold-crystallization and subsequent melting processes is studied by in situ monitoring its FTIR spectra. Through following the intensity changes of the characteristic bands associated with its crystalline status and 31 helix conformation chains, the multiple melting behavior of iPS cold-crystallized at different temperatures has been discussed in detail. It is concluded that (i) the lowest-temperature annealing peak can be ascribed either to the relaxing of locally ordered long 31 helix chains in the amorphous phase or to the melting of some microcrystallites formed upon long-time annealing; (ii) the double melting behavior of iPS cold-crystallized at temperatures lower than 180 °C is mainly attributed to the model of melting, recrystallization, and remelting of the iPS crystals; and (iii) for the sample cold-crystallized at a temperature of 200 °C, the in situ IR experiments give strong evidence to support the existence of different kinds of crystals which...

Crystalline structure and thermal behavior of nylon‐10,14

AbstractThe structure and morphology of a novel polyamide, nylon‐10,14, and its lamellar crystals from dilute solution were examined by transmission electron microscopy and wide‐angle X‐ray diffraction (WAXD). Both the electron‐diffraction pattern and WAXD data demonstrated that nylon‐10,14 adopts the structure of a triclinic lattice similar to that of the traditional nylon‐66 but with a corresponding increase of the c parameter to 3.23 nm. In addition, the thermal behavior of melt‐crystallized nylon‐10,14 was investigated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The glass‐transition temperature of nylon‐10,14 determined by the DMA data was 46.6°C. DSC indicated that the multiple melting behavior of isothermally crystallized nylon‐10,14 probably results from the melt and recrystallization mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1422–1427, 2003

Melting behaviour of poly(butylene succinate) in miscible blends with poly(ethylene oxide)

The melting behavior of poly(butylene succinate) (PBSU) in miscible blends with poly(ethylene oxide) (PEO), which is a newly found polymer blends of two crystalline polymers by our group, has been investigated by conventional differential scanning calorimetry (DSC). It was found that PBSU showed double melting behavior after isothermal crystallization from the melt under certain crystallization conditions, which was explained by the model of melting, recrystallization and remelting. The influence of the blend composition, crystallization temperature and scanning rate on the melting behavior of PBSU has been studied extensively. With increasing any of the PEO composition, crystallization temperature and scanning rate, the recrystallization of PBSU was inhibited. Furthermore, temperature modulated differential scanning calorimetry (TMDSC) was also employed in this work to investigate the melting behavior of PBSU in PBSU/PEO blends due to its advantage in the separation of exotherms (including crystallization and recrystallization) from reversible meltings (including the melting of the crystals originally existed prior to the DSC scan and the melting of the crystals formed through the recrystallization during the DSC scan). The TMDSC experiments gave a direct evidence of this melting, recrystallization and remelting model to explain the multiple melting behavior of PBSU in PBSU/PEO blends.

Crystallization kinetics and melting behavior of nylon 10,10 in nylon 10,10–montmorillonite nanocomposites

AbstractThe crystallization kinetics and melting behavior of nylon 10,10 in neat nylon 10,10 and in nylon 10,10–montmorillonite (MMT) nanocomposites were systematically investigated by differential scanning calorimetry. The crystallization kinetics results show that the addition of MMT facilitated the crystallization of nylon 10,10 as a heterophase nucleating agent; however, when the content of MMT was high, the physical hindrance of MMT layers to the motion of nylon 10,10 chains retarded the crystallization of nylon 10,10, which was also confirmed by polarized optical microscopy. However, both nylon 10,10 and nylon 10,10–MMT nanocomposites exhibited multiple melting behavior under isothermal and nonisothermal crystallization conditions. The temperature of the lower melting peak (peak I) was independent of MMT content and almost remained constant; however, the temperature of the highest melting peak (peak II) decreased with increasing MMT content due to the physical hindrance of MMT layers to the motion of nylon 10,10 chains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2181–2188, 2003

Multiple melting behavior of nucleated polypropylene

Journal of Applied Polymer ScienceVolume 88, Issue 6 p. 1608-1611 Note Multiple melting behavior of nucleated polypropylene Kancheng Mai, Corresponding Author Kancheng Mai [email protected] Materials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of ChinaMaterials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of China===Search for more papers by this authorKefeng Wang, Kefeng Wang Materials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of ChinaSearch for more papers by this authorHanmin Zeng, Hanmin Zeng Materials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of ChinaSearch for more papers by this author Kancheng Mai, Corresponding Author Kancheng Mai [email protected] Materials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of ChinaMaterials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of China===Search for more papers by this authorKefeng Wang, Kefeng Wang Materials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of ChinaSearch for more papers by this authorHanmin Zeng, Hanmin Zeng Materials Science Institute, Key Laboratory for Polymeric Composites and Functional Materials of the Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, People's Republic of ChinaSearch for more papers by this author First published: 21 February 2003 https://doi.org/10.1002/app.11652Citations: 13Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume88, Issue69 May 2003Pages 1608-1611 RelatedInformation

On the nature of multiple melting in poly(ethylene terephthalate) (PET) and its copolymers with cyclohexylene dimethylene terephthalate (PET/CT)

The multiple melting behavior of poly(ethylene terephthalate) (PET) homopolymers of different molecular weights and its cyclohexylene dimethylene (PET/CT) copolymers was studied by time-resolved simultaneous small-angle X-ray scattering/wide-angle X-ray scattering diffraction and differential scanning calorimetry techniques using a heating rate of 2°C/min after isothermal crystallization at 200°C for 30min. The copolymer containing random incorporation of 1,4-cyclohexylene dimethylene terephthalate monomer cannot be cocrystallized with the ethylene terephthalate moiety. Isothermally crystallized samples were found to possess primary and secondary crystals. The statistical distribution of the primary crystals was found to be broad compared to that of the secondary crystals. During heating, the following mechanisms were assumed to explain the multiple melting behavior. The first endotherm is related to the non-reversing melting of very thin and defective secondary crystals formed during the late stages of crystallization. The second endotherm is associated with the melting of secondary crystals and partial melting of less stable primary crystals. The third endotherm is associated with the melting of the remaining stable primary crystals and the recrystallized crystals. Due to their large statistical distribution, the primary crystals melt in a broad temperature range, which includes both second and third melting endotherms. The amounts of secondary, primary and recrystallized crystals, being molten in each endotherm, are different in various PET samples, depending on variables such as isothermal crystallization temperature, time, molecular weight and co-monomer content.

Multiple melting behavior of poly(butylene succinate). I. Thermal analysis of melt‐crystallized samples

AbstractThe multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights of 1.1 × 105, 1.8 × 105, and 2.5 × 105, were cooled from the melt (150 °C) at various cooling rates (CRs) ranging from 0.2 to 50 K min−1. The peak crystallization temperature (Tc) of the DSC curve in the cooling process decreased almost linearly with the logarithm of the CR. DSC melting curves for the melt‐crystallized samples were obtained at 10 K min−1. Double endothermic peaks, a high‐temperature peak H and a low‐temperature peak L, and an exothermic peak located between them appeared. Peak L decreased with increasing CR, whereas peak H increased. An endothermic shoulder peak appeared at the lower temperature of peak H. The CR dependence of the peak melting temperatures [Tm(L) and Tm(H)], recrystallization temperature (Tre), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of log(CR). Tm(L), Tre, and ΔH decreased almost linearly with log(CR), whereas Tm(H) was almost constant. Peak H decreased with the molecular weight, whereas peak L increased. It was suggested that the rate of the recrystallization decreased with the molecular weight. Tm(L), Tm(H), Tre, and Tc for the lowest molecular weight sample were lower than those for the others. In contrast, ΔH for the highest molecular weight sample was lower than that for the others. If the molecular weight dependence of the melting temperature for PBSu is similar to that for polyethylene, the results for the molecular weight dependence of PBSu can be explained. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2411–2420, 2002

Comparative differential scanning calorimetric analysis of vegetable oils: I. Effects of heating rate variation.

The melting curves of 11 vegetable oils have been characterised. Vegetable oil samples that were cooled at a constant rate (5 degrees C/min) from the melt showed between one and seven melting endotherms upon heating at four different heating rates (1, 5, 10 and 20 degrees C/min) in a differential scanning calorimeter (DSC). Triacylglycerol (TAG) profiles and iodine value analyses were used to complement the DSC data. Generally, the melting transition temperature shifted to higher values with increased rates of heating. The breadth of the melting endotherm and the area under the melting peak also increased with increasing heating rate. Although the number of endothermic peaks was dependent on heating rate, the melting curves of the oil samples were not straightforward in that there was no correlation between the number of endothermic peaks and heating rates. Multiple melting behaviour in DSC experiments with different heating rates could be explained by: (1) the melting of TAG populations with different melting points; and (2) TAG crystal reorganisation effects. On the basis of the corollary results obtained, vegetable oils and fats may be distinguished from their offset-temperature (Toff) values in the DSC melting curves. The results showed that Toff values of all oil samples were significantly (p < 0.01) different in the melting curves scanned at four different scanning rates. These calorimetric results indicate that DSC is a valuable technique for studying vegetable oils.

Polydispersity of ethylene sequence length in metallocene ethylene/α‐olefin copolymers. II. Influence on crystallization and melting behavior

AbstractIn this work, crystallization and melting behavior of metallocene ethylene/α‐olefin copolymers were investigated by differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The results indicated that the crystallization and melting temperatures for all the samples were directly related to the long ethylene sequences instead of the average sequence length (ASL), whereas the crystallization enthalpy and crystallinity were directly related to ASL, that is, both parameters decreased with a decreasing ASL. Multiple melting peaks were analyzed by thermal analysis. Three phenomena contributed to the multiple melting behaviors after isothermal crystallization, that is, the melting of crystals formed during quenching, the melting‐recrystallization process, and the coexistence of different crystal morphologies. Two types of crystal morphologies could coexist in samples having a high comonomer content after isothermal crystallization. They were the chain‐folded lamellae formed by long ethylene sequences and the bundlelike crystals formed by short ethylene sequences. The coexistence phenomenon was further proved by the AFM morphological observation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 822–830, 2002

Melting behavior of poly(trimethylene terephthalate)

AbstractIn this study, the melting behavior of isothermally crystallized polytri‐ methylene terephthalate (PTT) was investigated. Multiple melting behaviors in DSC heating trace were found because two populations of lamellar stacks were formed during primary crystallization and the recrystallization at heating process, respectively. This fact could be also confirmed from the result of optical microscopy observation. The Hoffman–Weeks equation was applied to obtain equilibrium melting temperature (T). The T value of PTT is about 525 K, which is 10 K higher than that reported. Combining the enthalpy of fusion from the DSC result and the degree of crystallinity from WAXD result, the value of the equilibrium‐melting enthalpy ΔH was deduced to be approximately 28.8 kJ mol−1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2426–2433, 2002

Effect of molecular weight and branch structure on the crystallization and rheological properties of poly(butylene adipate)

AbstractHigh molecular weight linear and branched poly(butylene adipate)s (PBAs) were prepared, and crystallization behavior and rheological properties were investigated. PBAs showed multiple melting behavior. Increasing molecular weight retarded the crystallization rate and increased the induction time for crystallization. Introducing branches to the polymer led to similar results. The Avrami exponent (n) for the linear and branched PBAs were 3.79–4.39 and 2.09–3.64, respectively. The Mark‐Houwink exponent of the PBAs was 0.554. Unlike general‐purpose polyesters, high molecular weight PBAs did not exhibit a Newtonian flow region. High molecular weight PBAs exhibited gel‐like rheological properties, producing high elasticity. The slopes of a log‐log plot of storage modulus (G′) vs. loss modulus (G″) ranged from 1.75 to 1.17, and the slope decreased with increasing molecular weight. For comparable molecular weights, the branched PBAs had higher viscosity and G′ than the linear polymers.

Multiple melting endotherms in melt‐crystallized nylon 10,12

AbstractThe melting behaviour of melt‐crystallized nylon 10,12 was investigated by differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). The results show that all nylon 10,12 crystals obtained under various conditions, including isothermal, non‐isothermal and stepwise crystallization, and also after partial melting or annealing, show multiple melting behaviour. It was found that each melting endotherm has a different origin. The highest melting peak corresponds to melting of the recrystallized material while the other melting endotherms are related to melting of lamellae with different thicknesses developing under different crystallization conditions. The equilibrium melting point of nylon 10,12 was also firstly estimated to be about 206 °C.© 2001 Society of Chemical Industry

Multiple melting behavior in isothermally cold-crystallized isotactic polystyrene

The multiple melting behavior and lamellar morphologies of isotactic polystyrene (iPS) isothermally crystallized from the glassy state have been investigated by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The influences of different experimental variables (such as crystallization temperature and time, heating rate) on the melting behavior of iPS are studied. The combination of thermal analysis and morphological results indicates that: (1) the ‘annealing peak’ is not associated with the melting of subsidiary crystals formed by secondary crystallization as often suggested in the literature; (2) two lamellar populations with different degrees of perfection within a single lamella are responsible for the so-called double melting behavior in iPS. The partial melting and repairing (via recrystallization) of iPS crystals are observed on lamellar level by TEM observations. From the obtained calorimetric and morphological results, the applicability of several crystallization and (subsequent) melting models is discussed.

Probing multiple melting behaviors in poly(ethylene naphthalene 2,6‐dicarboxylate) with different thermal histories by simultaneous wide‐angle and small‐angle X‐ray scattering

AbstractA simultaneous wide‐angle and small‐angle X‐ray scattering study of two poly(ethylene naphthalene 2,6‐dicarboxylate) samples crystallized from the glassy state at different annealing temperatures for different annealing times was carried out with synchrotron radiation. Either single or dual melting was induced in the samples, as confirmed by differential scanning calorimetry (DSC). The correlation function and interface distribution function were calculated to evaluate microstructural parameters such as the long spacing, the thickness of the amorphous and crystalline phases, and the width of the size distributions. The sample with dual melting behavior exhibited an abrupt increase of all microstructural parameters at temperatures above the melting of the lowest endotherm, whereas the sample revealing a single melting endotherm did not show such a sudden change. This finding agrees with the concept that the appearance of two melting peaks in DSC traces can be explained by the dual lamellar stacking model. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci B: Polym Phys 39: 881–894, 2001

Heat treatment‐induced multiple melting behavior of carbon black‐filled polymer blends in relation to the conductive performance stabilization

AbstractPolymer blend‐based electrical conductive composites are provided with more possibilities for tailoring the performance in comparison with single polymer systems. To find an optimum heat treatment temperature of the composites, which is critical to practical applications, detailed thermal analyses of the related materials were carried out as a function of different annealing conditions. Based on the discussion of the morphological variation during treatment in terms of multiple melting behavior, it was found that an annealing temperature of 75°C is able to stabilize the resistivity of the composites within a reasonable period of time, as only solid‐state crystallization of LDPE and uniformization of EVA crystalline size are involved. In contrast to treatment at a temperature higher than 75°C, the ultimate equilibrium resistivity resulting from the above annealing procedure approaches the resistivity of the composites as‐manufactured. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 80: 1267–1273, 2001

Multiple melting behavior of poly(butylene-2,6-naphthalate)

Multiple melting behaviors of poly(butylene-2,6-naphthalate) (PBN) prepared by various crystallization conditions were studied by differential scanning calorimetry at a heating rate of 10°C/min. It is found that the crystallization rate of PBN is so rapid that the glass transition temperature cannot be detected by simply heating the quenched sample. Two melting peaks are generally perceptible in a heating scan for isothermally crystallized samples that can be properly explained by the model proposed by Zhou and Clough (Polym Engng Sci 28 (1988) 65). The low-temperature melting peak can be ascribed to the melting of primary and secondary crystals generated during the crystallization or annealing process, while the high-temperature melting peak comes from the significant contribution of the melting of recrystallized species formed during heating. The step-crystallization was performed to clarify the relationship between the melting behavior and crystal modifications of PBN. In this study, it is found that the melting behavior of PBN is independent of the crystal forms and dominated by the crystal lamellar thickness and the perfection of crystals, which are dependent upon the thermal history. Finally, an equilibrium melting temperature of 276°C is obtained for the neat PBN, which is lower than that published in the literature.