Isothermal and nonisothermal crystallization kinetics of irradiated nylon 1212

The crystallization behavior of nylon 1212, irradiated at ⁶⁰Co γ‐rays (50 kGy), was studied by a rheometer, polarized optical microscopy (POM), and differential scanning calorimeter (DSC). The results showed that irradiated nylon 1212 samples exhibited abnormal crystallization behavior during the crystallization process: The Avrami exponent n was calculated and was found to be in the range from 2.06–2.41 for isothermal crystallization, and from 2.67–4.91 for nonisothermal crystallization; the spherulite morphology also changed largely by polarized optical microscopy (POM); the crystallization activation energy ΔE for isothermal and nonisothermal crystallization process of irradiated nylon 1212 are determined to be 57.4 kJ/mol and 78.65 kJ/mol, respectively, which are lower than that of nonirradiated nylon 1212. At the same time, a new method by a combination of the Avrami and Ozawa equations was successfully applied to analyze the noncrystallization process of irradiated nylon 1212. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2326–2333, 2005     

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     

Investigation on nonisothermal crystallization kinetics of the high‐flow nylon 6 by differential scanning calorimetry

The crystallization kinetics of the high‐flow nylon 6 containing polyamidoamine (PAMAM) dendrimers units in nylon 6 matrix was investigated by differential scanning calorimetry. The Ozawa and Mo equations were used to describe the crystallization kinetics under nonisothermal condition. The values of Avrami exponent m and the cooling crystallization function F(T) were determined from the Ozawa plots, which showed bad linearity, and were divided into three sections depending on different cooling rates. The plots of the m and log F(T) values versus crystallization temperatures were obtained, which indicated that the actual crystallization mechanisms might change with the crystallization temperatures. The high‐flow nylon 6 has higher values of m and log F(T) than those of pure nylon 6, which implied that the high‐flow nylon 6 had more complicated crystallization mechanisms and slower crystallization rate than those of pure nylon 6. The good linearity of the Mo plots verified the success of this combined approach. The activation energies of the high‐flow nylon 6 ranged from 157 to 174 kJ/mol, which were determined by the Kissinger method. The ΔE values were lower than those of pure nylon 6, and the ΔE values were affected by both the generation and the content of PAMAM units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2201–2211, 2008     

Characterization,crystallization kinetics,and melting behavior of poly(ethylene succinate) copolyester containing 10 mol % butylene succinate

Copolyester was synthesized and characterized as having 89.9 mol % ethylene succinate units and 10.1 mol % butylene succinate units in a random sequence, as revealed by NMR. Isothermal crystallization kinetics was studied in the temperature range (T_c) from 30 to 73 °C using differential scanning calorimetry (DSC). The melting behavior after isothermal crystallization was investigated using DSC by varying the T_c, the heating rate and the crystallization time. DSC curves showed triple melting peaks. The melting behavior indicates that the upper melting peaks are associated primarily with the melting of lamellar crystals with various stabilities. As the T_c increases, the contribution of recrystallization slowly decreases and finally disappears. A Hoffman‐Weeks linear plot gives an equilibrium melting temperature of 107.0 °C. The spherulite growth of this copolyester from 80 to 20 °C at a cooling rate of 2 or 4 °C/min was monitored and recorded using an optical microscope equipped with a CCD camera. Continuous growth rates between melting and glass transition temperatures can be obtained after curve‐fitting procedures. These data fit well with those data points measured in the isothermal experiments. These data were analyzed with the Hoffman and Lauritzen theory. A regime II → III transition was detected at around 52 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2431–2442, 2008     

Temperature‐modulated differential scanning calorimetry studies on the origin of double melting peaks in isothermally melt‐crystallized poly(L‐lactic acid)

In this work, the melting behaviors of nonisothermally and isothermally melt‐crystallized poly(L ‐lactic acid) (PLLA) from the melt were investigated with differential scanning calorimetry (DSC) and temperature‐modulated differential scanning calorimetry (TMDSC). The isothermal melt crystallizations of PLLA at a temperature in the range of 100–110 °C for 120 min or at 110 °C for a time in the range of 10–180 min appeared to exhibit double melting peaks in the DSC heating curves of 10 °C/min. TMDSC analysis revealed that the melting–recrystallization mechanism dominated the formation of the double melting peaks in PLLA samples following melt crystallizations at 110 °C for a shorter time (≤30 min) or at a lower temperature (100, 103, or 105 °C) for 120 min, whereas the double lamellar thickness model dominated the formation of the double melting peaks in those PLLA samples crystallized at a higher temperature (108 or 110 °C) for 120 min or at 110 °C for a longer time (≥45 min). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 466–474, 2007     

Nonisothermal crystallization kinetics of in situ nylon 6/graphene composites by differential scanning calorimetry

The nonisothermal crystallization kinetics was investigated by differential scanning calorimetry for the nylon 6/graphene composites prepared by in situ polymerization. The Avrami theory modified by Jeziorny, Ozawa equation, and Mo equation was used to describe the nonisothermal crystallization kinetics. The analysis based on the Avrami theory modified by Jeziorny shows that, at lower cooling rates (at 5, 10, and 20 K/min), the nylon 6/graphene composites have lower crystallization rate than pure nylon 6. However, at higher cooling rates (at 40 K/min), the nylon 6/graphene composites have higher crystallization rate than pure nylon 6. The values of Avrami exponent m and the cooling crystallization function F(T) from Ozawa plots indicate that the mode of the nucleation and growth at initial stage of the nonisothermal crystallization may be as follows: two‐dimensional (2D), then one‐dimensional (1D) for all samples at 5–10 °C/min; three‐dimensional (3D) or complicated than 3D, then 2D and 1D at 10–20 and 20–40 °C/min. The good linearity of the Mo plots indicated that the combined approach could successfully describe the crystallization processes of the nylon 6 and nylon 6/graphene composites. The activation energies (ΔE) of the nylon 6/graphene composites, determined by Kissinger method, were lower than those of pure nylon 6. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1381–1388, 2011     

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     

The effect of proton irradiation on the melting and isothermal crystallization of poly(ether‐ether‐ketone)

Amorphous poly(ether‐ether‐ketone) (PEEK) progressively crosslinks on irradiation with 11.0 MeV protons, and this has a marked effect on the extent of crystallinity that subsequently develops and on the kinetics of the high temperature isothermal crystallization. The extent of crystallinity with time was analyzed using the Avrami equation, and the temperature dependence of the rate constants was analyzed in terms of nucleation theory. While irradiation inhibits the overall rates of crystallization by the reduction in the mobility of the chain segments as observed by the progressive increase in the glass transition temperature, it also alters the fold surface free energy. The observed melting points were consistent with depression of the equilibrium melting point by the crosslinks produced by irradiation. These two effects alone are sufficient to account for the inhibition of crystallization on irradiation of PEEK by protons. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1094–1103, 2008     

The effect of molecular weight on the crystallization kinetics of polycaprolactone

The crystallization kinetics and degree of crystallinity of polycaprolactone (PCL) were studied using the technique of differential scanning calorimetry (DSC). The crystallization exotherms measured using DSC were analyzed using a modified Avrami equation. The modification limited the analysis of the data to the primary crystallization process, where the Avrami equation is applicable. Both the degree of crystallinity and primary composite rate constant were found to decrease with increasing molecular weight. The observations have been explained in terms of the unified reptation‐nucleation theory. Copyright © 2006 John Wiley & Sons, Ltd.     

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

In 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     

Two crystal populations with different melting/reorganization kinetics of isothermally crystallized polyamide 6

Differential scanning calorimetry and fast scanning chip calorimetry heating experiments were carried out in a wide range of rates of temperature change from 0.2 to 60,000 K s^?1 for isothermally crystallized polyamide 6. Multiple melting peaks were observed. With increasing heating rate, the highest‐temperature endotherm shifts toward lower temperatures and finally disappears due to suppression of the reorganization. The critical heating rate to suppress reorganization was 15–50 times higher than the critical cooling rate to cause complete vitrification. On heating at rates higher than the critical heating rate to suppress reorganization, there were observed two melting processes of different kinetics. Four possible assignments were considered regarding the two crystal populations. These are (i) crystals grown during primary and secondary crystallization, (ii) crystals grown in the bulk and nucleated at the surface/substrate, (iii) crystals, which are subjected to different local stress originating from heterogeneities in interlamellar regions, and (iv) the crystal/mesophase polymorphism. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2126–2138     

The effect of molecular weight on the crystallization kinetics and equilibrium melting temperature of poly(tetramethylene ether glycol)

Isothermal crystallization of poly(tetramethylene ether glycol) (PTMEG) with relatively low molecular weight (M_n = 991, 2004 and 2864, respectively) was investigated by differential scanning calorimetry, and the equilibrium melting temperature (T) determined using the Hoffman–Weeks analysis. The crystallization kinetics of PTMEG were characterized using an Avrami analysis. Mechanistic n values ranged from 2.2 to 2.9 for the primary crystallization process for three molecular weight grades, indicating heterogeneous nucleation of spherulites. Polarized light microscopy confirmed that PTMEG crystallized by the growth of spherulites from heterogeneous nuclei. The half–life for crystallization (t_1/2) and the composite rate constant were found to be dependent on the degree of supercooling (ΔT) and the molecular weight. Copyright © 2006 John Wiley & Sons, Ltd.     

Flash DSC crystallization study of blown film grade bimodal high density polyethylene (HDPE) resins. Part 2. Non‐isothermal kinetics

Non‐isothermal ultra‐fast cooling crystallization tests were conducted on three blown film grade bimodal high density polyethylene (HDPE) resins using a fast differential scanning calorimeter, the Flash DSC. Non‐isothermal tests were performed at cooling rates between 50 and 4000°K/s, and the data were analyzed using the modified Avrami model by Jeziorny (Polymer, 1978 , 19, 1142). Non‐isothermal data were used to propose a new method named crystallization–time–temperature–superposition, and the two activation energies were obtained for each of the resins. This is very useful for obtaining theoretical crystallization kinetics data at different cooling rates, allowing its use in ultra‐fast cooling polymer processes such as blown film. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1822–1827     

Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h^?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.     

Isothermal and nonisothermal crystallization kinetics of poly(propylene terephthalate)

The kinetics of crystallization of poly(propylene terephthalate) (PPT) samples of different molecular weights were studied under both isothermal and nonisothermal conditions. The Avrami and Lauritzen–Hoffmann treatments were applied to evaluate kinetic parameters of PPT isothermal crystallization. It was found that crystallization is faster for low‐molecular‐weight samples. The modified Avrami equation, and the combined Avrami–Ozawa method were found to successfully describe the nonisothermal crystallization process. Also, the analysis of Lauritzen–Hoffmmann was tested and it resulted in values close to those obtained with isothermal crystallization data. The nonisothermal kinetic data were corrected for the effect of the temperature lag and shifted alone with the isothermal kinetic data to obtain a single master curve, according to the method of Chan and Isayev, testifying to the consistency between the isothermal and corrected nonisothermal data. A new method for ranking of polymers, referring to the crystallization rates, was also introduced. This involved a new index that combines the maximum crystallization rate observed during cooling with the average crystallization rates over the temperature range of the crystallization peak. Furthermore, the effective energy barrier of the dynamic process was evaluated with the isoconversional methods of Flynn and Friedmann. It was found that the energy barrier is lower for the low‐molecular‐weight PPT. The effect of the catalyst remnants on the crystallization kinetics was also investigated and it was found that this is significant only for low‐molecular‐weight samples. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3775–3796, 2004     

Nonisothermal crystallization and melting behavior of a luminescent conjugated polymer,poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene)

The nonisothermal crystallization kinetics of a luminescent conjugated polymer, poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene) (PF6OC10) with three different molecular weights was investigated by differential scanning calorimetry under different cooling rates from the melt. With increasing molecular weight of PF6OC10, the temperature range of crystallization peak steadily became narrower and shifted to higher temperature region and the crystallization rate increased. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of PF6OC10. Although the Avrami method did not effectively describe the nonisothermal crystallization kinetics of PF6OC10 for overall process, it was valid for describing the early stage of crystallization with an Avrami exponent n of about 3. The combined method proposed in our previous report was able to satisfactorily describe the nonisothermal crystallization behavior of PF6OC10. The crystallization activation energies determined by Kissinger, Takhor, and Augis‐Bennett models were comparable. The melting temperature of PF6OC10 increased with increasing molecular weight. For low‐molecular‐weight sample, PF6OC10 showed the characteristic of double melting phenomenon. The interval between the two melting peaks decreased with increasing molecular weight, and only one melting peak was observed for the high‐molecular‐weight sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 976–987, 2007     

Competition between supernucleation and plasticization in the crystallization and rheological behavior of PCL/CNT‐based nanocomposites and nanohybrids

PCL was blended with pristine multiwalled carbon nanotubes (MWCNT) and with a nanohybrid obtained from the same MWCNT but grafted with low molecular weight PCL, employing concentrations of 0.25 to 5 wt % of MWCNT and MWCNT‐g‐PCL. Excellent CNT dispersion was found in all samples leading to supernucleation of both nanofiller types. Nanohybrids with 1 wt % or less MWCNTs crystallize faster than nanocomposites (due to supernucleation), while the trend eventually reverses at higher nanotubes content (because of plasticization). Rheological results show that yield‐like behavior develops in both nanocomposites, even for the minimum content of carbon nanotubes. In addition, the MWCNT‐g‐PCL family, when compared with the neat polymer, exhibits lower values of viscosity and modulus in oscillatory shear, and higher compliance in creep. These rheological differences are discussed in terms of the plasticization effect caused by the existence of low molecular weight free and grafted PCL chains in the nanohybrids. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1310–1325     

Multiple melting behavior of poly(butylene succinate). II. Thermal analysis of isothermal crystallization and melting process

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights (MWs) of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were isothermally crystallized at various crystallization temperatures (T_c) ranging from 70 to 97.5 °C. The T_c dependence of crystallization half‐time (τ) was obtained. DSC melting curves for the isothermally crystallized samples were obtained at a heating rate of 10 K min⁻¹. Three endothermic peaks, an annealing peak, a low‐temperature peak L, and a high‐temperature peak H, and an exothermic peak located between peaks L and H clearly appeared in the DSC curve. In addition, an endothermic small peak S appeared at a lower temperature of peak H. Peak L increased with increasing T_c, whereas peak H decreased. The T_c dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of T_c. T_m(L), T_re, and ΔH increased almost linearly with T_c, whereas T_m(H) was almost constant. The maximum rate of recrystallization occurred immediately after the melting. The mechanism of the multiple melting behavior is explained by the melt‐recrystallization model. The high MW samples showed similar T_c dependence of τ, and τ for the lowest MW sample was longer than that for the others. Peak L increased with MW, whereas peak H decreased. In spite of the difference of MW, T_m(L), T_m(H), and T_re almost coincided with each other at the same T_c. The ΔH values, that is crystallinity, for the highest MW sample were smaller than those for the other samples at the same T_c. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2039–2047, 2005     

Isothermal crystallization kinetics of poly(butylene terephthalate)/attapulgite nanocomposites

Poly(butylene terephthalate) (PBT)/organo‐attapulgite (ATT) nanocomposites containing 2.5 and 5 wt % nanoparticles loadings were fabricated via a simple melt‐compounding approach. The crystal structure and isothermal crystallization behaviors of PBT composites were studied by wide‐angle X‐ray diffraction and differential scanning calorimetry, respectively. The X‐ray diffraction results indicated that the addition of ATT did not alter the crystal structure of PBT and the crystallites in all the samples were triclinic α‐crystals. During the isothermal crystallization, the PBT nanocomposites exhibited higher crystallization rates than the neat PBT and the varied Avrami exponents when compared with the neat PBT. At the same time, the regime II/III transition was also observed in all the samples on the basis of Hoffman‐Laurizten theory, but the transition temperature increased with increasing ATT loadings. The fold surface free energy (σ_e) of polymer chains in the nanocomposites was lower than that in the neat PBT. It should be reasonable to treat ATT as a good nucleating agent for the crystallization of PBT, which plays a determinant effect on the reduction in σ_e during the isothermal crystallization of the nanocomposites, even if the existence of ATT could restrict the segmental motion of PBT. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2112–2121, 2006     

Nonisothermal crystallization behavior and crystalline structure of poly(3‐hydroxybutyrate)/layered double hydroxide nanocomposites

X‐ray diffraction method and differential scanning calorimetry analysis have been used to investigate the nonisothermal crystallization of poly(3‐hydroxybutyrate) (PHB)/poly(ethylene glycol) phosphonates (PEOPAs)‐modified layered double hydroxide (PMLDH) nanocomposites. Effects of cooling rates and PMLDH contents on the nonisothermal crystallization behavior of PHB were explored. These results show that the addition of 2 wt % PMLDH into PHB caused heterogeneous nucleation increasing the crystallization rate and reducing the activation energy. By adding PMLDH into the PHB probably hinder the transport ability of the molecule chains and result in a decreasing crystallity of PHB, thus increasing the activation energy. The correlation among melting behavior, apparent crystallite size, and paracrystalline distortion of PHB/PMLDH nanocomposites has been also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 995–1002, 2007