Poly(thiodiethylene adipate): Melting behavior,crystallization kinetics,morphology, and crystal structure

The melting behavior and crystallization kinetics of poly(thiodiethylene adipate) (PSDEA) were investigated with differential scanning calorimetry and hot‐stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature (T_c) and ascribed to melting and recrystallization processes. Linear and nonlinear treatments were applied to estimate the equilibrium melting temperature for PSDEA with the corrected values of the melting temperature. The nonlinear estimation yielded a higher value by about 9 °C. Isothermal crystallization kinetics were analyzed according to Avrami's treatment. Values of Avrami's exponent close to 3 were obtained, independently of T_c, in agreement with a crystallization process originating from predetermined nuclei and characterized by three‐dimensional spherulitic growth. As a matter of fact, space‐filling spherulites were observed by optical microscopy at all T_c's. The rate of crystallization became lower as T_c increased, as usual at a low undercooling, the crystallization process being controlled by nucleation. Moreover, the crystal structure of PSDEA was determined from powder X‐ray diffraction data by full profile fitting. A triclinic unit cell containing two polymer chains arranged parallel to the c axis was found. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 553–566, 2004     

Crystallization and thermal properties of PLLA comb polymer

Poly(L ‐lactide) (PLLA) on poly(2‐hydroxyethyl methacrylate) (PHEMA) backbone was prepared by a combination of atom transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP). The structure of the comb polymer was analyzed by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering (SAXS), and differential scanning calorimetry (DSC). WAXD result indicates that the comb polymer has α crystalline modification with a 10₃ helical conformation. Lamellar parameters of the crystalline structure were obtained by one‐dimension correlation function (1DCF) calculated from SAXS results. The calculations show that the thickness of crystalline layer is controlled by annealing temperature and comb structure. DSC was applied to study kinetics of the crystallization and melting behavior. Two melting peaks on melting curves of the comb polymer at different crystallization temperature were detected, and the peak at higher temperature is attributed to the melt‐recrystallization. The equilibrium melting temperature is found to be influenced by the comb structure. In this article the effects of the comb structure on Avrami exponent, equilibrium melting point and melting peak of the comb polymer were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 589–598, 2008     

Poly(vinylidene fluoride)/clay nanocomposites prepared by melt intercalation: Crystallization and dynamic mechanical behavior studies

The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X‐ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. The tan δ peak signifying the glass‐transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002     

Morphological changes during heating in poly(L‐lactic acid)/poly(butylene succinate) blend systems as studied by synchrotron X‐ray scattering

Blends of poly(L ‐lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared in various compositions via melt mixing, and the morphological changes were investigated with differential scanning calorimetry and synchrotron wide‐angle and small‐angle X‐ray scattering techniques at a heating rate of 10 °C/min. Differential scanning calorimetry thermograms of PLA/PBS blends showed two distinct melting peaks over the entire composition range. The exothermal peak for PLA shifted significantly to a lower temperature and overlapped with that of PBS around 100 °C. A depression of the melting point of the PLA component via blending was observed. The synchrotron wide‐angle X‐ray scattering during heating revealed that there was no cocrystallization or crystal modification via blending. The synchrotron small‐angle X‐ray scattering data showed that well‐defined double‐scattering peaks (or peaks with a clear scattering shoulder) appeared during crystallization, indicating that this system possessed dual lamellar stacks. These peaks were deconvoluted into two components with a peak separation computer program, and then the morphological parameters of each component were obtained by means of the correlation function. The long period and average lamellar thickness of the two components before melting decreased with an increasing content of the other polymer component. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1931–1939, 2002     

Miscibility,crystallization kinetics,and morphology of poly(β‐hydroxybutyrate) and poly(methyl acrylate) blends

The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(β‐hydroxybutyrate) (PHB) and poly(methyl acrylate) (PMA) were studied with differential scanning calorimetry, optical microscopy, and small‐angle X‐ray scattering (SAXS). As the PMA content increases in the blends, the glass‐transition temperature and cold‐crystallization temperature increase, but the melting point decreases. The interaction parameter between PHB and PMA, obtained from an analysis of the equilibrium‐melting‐point depression, is −0.074. The presence of an amorphous PMA component results in a reduction in the rate of spherulite growth of PHB. The radial growth rates of spherulites were analyzed with the Lauritzen–Hoffman model. The spherulites of PHB were volume‐filled, indicating the inclusion of PMA within the spherulites. The long period obtained from SAXS increases with increased PMA content, implying that the amorphous PMA is entrapped in the interlamellar region of PHB during the crystallization process of PHB. All the results presented show that PHB and PMA are miscible in the melt. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1860–1867, 2000     

Analysis of the complex thermal behavior of poly(L‐lactic acid) film. I. Samples crystallized from the glassy state

The melting behavior of poly(L ‐lactic acid) film crystallized from the glassy state, either isothermally or nonisothermally, was studied by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering (SAXS), differential scanning calorimetry (DSC), and temperature‐modulated differential scanning calorimetry (TMDSC). Up to three crystallization and two melting peaks were observed. It was concluded that these effects could largely be accounted for on the basis of a “melt‐recrystallization” mechanism. When molecular weight is low, two melting endotherms are readily observed. But, without TMDSC, the double melting phenomena of high molecular weight PLLA is often masked by an exotherm just prior to the final melting, as metastable crystals undergo melt‐recrystallization during heating in the DSC. The appearance of a double cold‐crystallization peak during the DSC heating scan of amorphous PLLA film is the net effect of cold crystallization and melt‐recrystallization of metastable crystals formed during the initial cold crystallization. Samples cold‐crystallized at 80 and 90 °C did not exhibit a long period, although substantial crystallinity developed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3200–3214, 2006     

The double melting behavior of a liquid crystalline polyimide derived from PMDA and 1,3‐bis[4‐(4′‐aminophenoxyl) cumyl] benzene

The double melting behavior of a thermotropic liquid crystalline polyimide was studied by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS). This liquid crystalline polyimide exhibited a normal melting peak around 278 °C and transformed into a smectic A phase. The smectic A phase changed to nematic phase upon heating to 298 °C, then became isotropic melt around 345 °C. The samples annealed or isothermally crystallized at lower temperature showed double melting endotherms during heating scan. The annealing‐induced melting endotherm was highly dependent on annealing conditions, whereas the normal melting endotherm was almost not influenced by annealing when the annealing temperature was low. Various possibilities for the lower melting endotherm are discussed. The equilibrium melting points of both melting peaks were extrapolated to be 283.2 °C. Combined analytical results showed that the double melting peaks were from the melting of the two types of crystallites generated from two crystallization processes: a slow and a fast one. Fast crystallization may start from the well‐aligned liquid crystal domains, whereas the slow one may be from the fringed or amorphous regions. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3018–3031, 2000     

Multiple melting behavior of poly(lactic acid) filled with modified carbon black

Two melting peaks are generally observed in a heating scan for isothermally crystallized poly(lactic acid) (PLA)/carbon black (CB) and PLA/modified carbon black (MCB) composites. To investigate the origin of the above double melting behavior, the melting behavior after isothermal crystallization was analyzed with differential scanning calorimetry, wide‐angle X‐ray diffraction, and small angel X‐ray scattering techniques. The double melting of the crystallized samples can be explained by the model of two populations of lamellae, the double peaks of low and high temperatures are contributed to the melting of the small lamellae produced by secondary crystallization and that of the major crystals formed in the primary crystallization process, respectively. Spherulitic growth rates of the neat PLA and PLA/MCB composite were analyzed and the occurrence of a regime transition was demonstrated. For the PLA, a clear regime transition was observed at around 125 °C. For the PLA/MCB, it occurred at 130 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1971–1980, 2009     

Nonisothermal crystallization behavior of syndiotactic polystyrene/montmorillonite nanocomposites

X‐ray diffraction methods and differential scanning calorimetry were used to investigate the crystalline structure and crystallization kinetics of syndiotactic polystyrene (sPS)/clay nanocomposites. X‐ray diffraction data showed the presence of polymorphism in sPS/montmorillonite (MMT) nanocomposites, which was strongly dependent on the processing conditions (premelting temperature and cooling rate) of the sPS/MMT nanocomposites and on the content of MMT in the sPS/MMT nanocomposites. The α‐crystalline form could be transformed into β‐crystalline forms at higher premelting temperatures. The nonisothermal melt‐crystallization kinetics and melting behavior of the sPS/MMT nanocomposites were also studied at various cooling rates. The correlation of the crystallization kinetics, melting behavior, and crystalline structure of the sPS/MMT nanocomposites was examined. The results indicated that the addition of a small amount of MMT to sPS caused a change in the mechanism of nucleation and the crystal growth of the sPS crystallite. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 560–570, 2003     

Lamellar morphology and equilibrium melting temperature of syndiotactic polystyrene in β‐crystalline form

Lamellar morphology and thickness of syndiotactic polystyrene (sPS) samples melt‐crystallized at various temperatures were probed using transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS). In addition, the melting temperature and enthalpy of the crystallized samples were characterized with differential scanning calorimetry. Under appropriate thermal treatments, all the samples investigated in this study were crystallized into β′ crystal modification, as revealed by wide‐angle X‐ray diffraction. From the SAXS intensity profiles, a scattering peak (or shoulder) associated with lamellar features as well as the presence of anomalous scattering at the zero‐scattering vector were evidently observed. The peculiar zero‐angle scattering was successfully described by the Debye–Bueche model, and subtraction of its contribution from the raw intensity profiles was carried out to deduce the intensity profile merely associated with the lamellar feature. The lamellar thickness obtained from Lorentz‐corrected intensity profiles in this manner agrees with that measured from the TEM images, provided that the two‐phase model is applied. On the basis of the Gibbs–Thomson equation, the modest estimations of equilibrium melting temperature and the surface free energy of the fold lamellar surface are 292.7 ± 2.7 °C and 20.2 ± 2.6 erg/cm², respectively, when lamellar thicknesses measured by TEM are applied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1626–1636, 2002     

Isothermal and nonisothermal crystallization kinetics of nylon‐46

Isothermal and nonisothermal crystallization kinetics of nylon‐46 were investigated with differential scanning calorimetry. The equilibrium melting enthalpy and the equilibrium melting temperature of nylon‐46 were determined to be 155.58 J/g and 307.10 °C, respectively. The isothermal crystallization process was described by the Avrami equation. The lateral surface free energy and the end surface free energy of nylon‐46 were calculated to be 8.28 and 138.54 erg/cm², respectively. The work of chain folding was determined to be 7.12 kcal/mol. The activation energies were determined to be 568.25 and 337.80 kJ/mol for isothermal and nonisothermal crystallization, respectively. A convenient method was applied to describe the nonisothermal crystallization kinetics of nylon‐46 by a combination of the Avrami and Ozawa equations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1784–1793, 2002     

Crystallization,melting behavior,and morphology of PP/Novolac blends

The crystallization, melting behavior, and morphology of Polypropylene (PP) and PP/Novolac blends were studied by scanning electron microscopy, wide angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscope. The results showed that the crystallization of PP in PP/Novolac blends was strongly influenced by crystallization temperature, particles size of Novolac, crosslinking, and compatibilizer maleic anhydride‐grafted PP. The Novolac resin could not only affect the crystal structure, but also acted as effective nucleating agents, accelerating the crystallization of PP in the PP/Novolac blends. And the smaller the Novolac particles were, the more effective were the nucleating agent for PP crystallization. Avrami equation was used to analyze the isothermal crystallization kinetics of PP and PP/Novolac blends. The influences of curing and compatibilizer on the crystallization behavior of PP were rather complicated. The crystallization thermodynamics were estimated using the Hoffman theory. The incorporation of cured Novolac and compatibilizer evidently decreased the chain folding energy of PP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3288–3303, 2006     

Polymer crystalline structure and morphology changes in nylon‐6/ZnO nanocomposites

The influence of ZnO nanoparticles on the crystalline structures of nylon‐6 under different crystallization conditions (annealing at different temperatures from the amorphous solid, isothermal crystallization from the melt at different temperatures, and crystallization from the solution) has been examined with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared. ZnO nanoparticles can induce the γ‐crystalline form in nylon‐6 when it is cooled from the melted state and annealed from the amorphous solid. This effect of ZnO nanoparticles increases with decreasing particle size and changes under different crystallization conditions. The effects of ZnO nanoparticles on the crystallization kinetics of nylon‐6 have also been studied with DSC. The results show that ZnO nanoparticles have two competing effects on the crystallization of nylon‐6: inducing the nucleation but retarding the mobility of polymer chains. Finally, the melting behavior of the composites has been investigated with DSC, and the multiple melting peaks of composites containing ZnO nanoparticles and pure nylon‐6 are ascribed to the reorganization of imperfect crystals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1033–1050, 2003     

Structure development and physical properties achieved in the drawing and/or annealing of PEN fibers

As‐spun poly(ethylene‐2,6‐naphthalate) (PEN) fibers (i.e., precursors) prepared from high molecular weight polymer were drawn and/or annealed under various conditions. Structure and property variations taking place during the treatment process were followed via wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering, differential scanning calorimetry (DSC), and mechanical testing. Both the WAXS and DSC measurements of the cold‐drawn samples stretched from a low‐speed‐spun amorphous fiber indicate that strain‐induced crystallization can occur at a temperature below the glass‐transition temperature and that the resultant crystal is in the α‐form modification. In contrast, when the same precursor was subjected to constrained annealing, its amorphous characteristics remained unchanged even though the annealing was performed at 200 °C. These results may imply that the application of stretching stress is more important than elevated temperatures in producing α‐form crystallization. The crystalline structure of the hot‐drawn samples depends significantly on the morphology of the precursor fibers. When the precursor was wound at a very low speed and in a predominantly amorphous state, hot drawing induced the formation of crystals that were apparently pure α‐form modification. For the β‐form crystallized precursors wound at higher speeds, a partial crystalline transition from the β form to the α form was observed during the hot drawing. In contrast with the mechanical properties of the as‐spun fibers, those of the hot‐drawn products are not improved remarkably because the draw ratio is extremely limited for most as‐spun fibers in which an oriented crystalline structure has already formed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1424–1435, 2000     

Crystallization in PHB/DGEBA blends

Real‐time experiments using small‐angle X‐ray scattering and differential scanning calorimetry on blends of the semicrystalline polyester poly(3‐hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) were performed. Differences in the processes of melting and re‐crystallization were observed in blends relative to pure PHB. The results obtained in this study indicated that re‐crystallization is more important in blends with 50% DGEBA than in pure PHB. Moreover, segregation toward the interfibrillar region would facilitate re‐crystallization. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 882–886     

Structure development in multistage stretching of PTFE films

The structure of expanded poly(tetrafluoroethylene) (ePTFE) films that were produced by uniaxial or biaxial stretching of a calendared sheet were studied by wide angle X‐ray diffraction (WAXD), small angle X‐ray scattering, differential scanning calorimetry (DSC), and scanning electron microscopy. The molecular orientation of the stretched films was analyzed by WAXD flat films and pole figures. Biaxial orientation factors were computed to interpret the level of orientation quantitatively. DSC scans showed that oriented samples exhibited two melting peaks, one at the commonly observed temperature in the range 340–345 °C and one around 380 °C. The possible causes of this high‐temperature melting peak and its relation to previously described processes is discussed. The microporous nature of the ePTFE films is also briefly discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Analysis of the complex thermal behavior of poly(L‐lactic acid) film. II. Samples crystallized from the melt

The complex thermal behavior of poly(l ‐lactic acid) films crystallized from the melt, either isothermally or nonisothermally, was studied by differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and small angle X‐ray scattering. The variation of the thermal behavior with crystallization temperature, time, and cooling rate was documented and analyzed. After nonisothermal crystallization at low cooling rates that develop high crystallinity, an obvious double melting peak appears at modest heating rates (e.g., 10 °C/min). At higher heating rates, these samples exhibit only single melting. However, an unusual form of double melting occurs under the majority of the conditions studied under either isothermal or nonisothermal conditions. In this case, double melting is marked by the appearance of a recrystallization exotherm just prior to the final melting that obscures the observation of the melting of the crystals formed during the initial crystallization process. The occurrence of double melting in melt‐crystallized samples was concluded to be the result of a melt‐recrystallization process occurring during the subsequent DSC heating scan; it is a function of crystalline perfection, not the initial crystallinity, nor whether or not the crystallization reached completion at the crystallization temperature. Many other very interesting observations are also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3378–3391, 2006     

Real‐time SAXS and WAXS study of the multiple melting behavior of poly(ε‐caprolactone)

The multiple melting behavior of poly(ε‐caprolactone) (PCL) was investigated by real‐time small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) measurements coupling with differential scanning calorimetry (DSC). Semicrystalline specimens prepared by a continuous cooling process showed lengthening of the Bragg period during the progress of double melting. A model of variable thickness of lamella was proposed to fit to the SAXS patterns and revealed that both the crystalline lamella and the amorphous layer contributed to the increase in Bragg period while the later dominated the contribution. The model of variable thickness although satisfied the SAXS data was unable to compromise the data from other probing tools. A modification of the model proposed that each lamella piling up to construct the stacks in the crystallites was itself nonuniform in thickness. The modification with the parallel occurrence of the mechanism of surface melting and crystallization successfully compromised the observations from SAXS, DSC, and optical microscopy and provided a new perspective for the explanation to lengthening of the Bragg period related to multiple melting behavior. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1777–1785, 2010     

Crystallization behavior and morphology of poly(propylene terephthalate) copolymers containing neopenthyl glycol moieties

The melting behavior and the crystallization kinetics of random poly(propylene/neopenthyl terephthalate) copolymers (PPT‐PNT) were investigated by means of differential scanning calorimetry and hot‐stage optical microscopy. Multiple endotherms were evidenced in the PPT‐PNT samples, due to melting and recrystallization processes, similarly to PPT. By applying the Hoffman‐Weeks' method, the T_m° of the copolymers was derived. Baur's equation described well the T_m‐composition data. The isothermal crystallization kinetics was analyzed according to the Avrami's treatment. The introduction of NT units decreased the crystallization rate in comparison to pure PPT. Values of the Avrami's exponent close to three were obtained in all cases, regardless of T_c, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three dimensional spherulitic growth. As a matter of fact, space‐filling spherulites were observed by optical microscopy at all T_cs. Banded spherulites were found for PPT‐PNT5 and PPT‐PNT10, the band spacing being affected by both T_c and composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 818–830, 2008     

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

A 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 & Sons, Inc. J Polym Sci B: Polym Phys 39: 881–894, 2001