Non-Isothermal Crystallization Kinetics of Poly(Butylene Terephthalate)/Silica Nanocomposites

Poly(butylene terephthalate)/silica nanocomposites were prepared by in situ polymerization of terephthalic acid, 1,4-butanediol and silica. Transmission electron microscopy (TEM) was used to examine the quality of the dispersion of silica in the PBT matrix. The non-isothermal crystallization behavior of pure PBT and its nanocomposites was studied by differential scanning calorimetry (DSC). The results show that the crystallization peak temperatures of PBT/silica nanocomposites are higher than that of pure PBT at a given cooling rate. The values of halftime of crystallization indicate that silica could act as a heterogeneous nucleating agent in PBT crystallization and lead to an acceleration of crystallization. The non-isothermal crystallization data were analyzed with the Avrami, Ozawa, and Mo et al. models. The non-isothermal crystallization process of pure PBT and PBT/silica nanocomposites can be best described by the model developed by Mo et al. According to the Kissinger equation, the activation energies were found to be ?217.1, ?226.4, ?259.2, and ?260.2 kJ/mol for pure PBT and PBT/silica nanocomposites with silica weight content of 1, 3 and 5 wt%, respectively.     

Study on the Non-isothermal Melt Crystallization Kinetics of PTT/PBT Blends

Macro-kinetic models, namely the modified Avrami, Ozawa, Mo, and Kissinger models, were applied to investigate the non-isothermal melt crystallization process of PTT/PBT blends by DSC measurements. It was found that the modified Avrami model can describe the non-isothermal melt crystallization processes of PTT/PBT blends fairly well. When the cooling rates range from 5 to 20°C/min, the Ozawa model could be used to satisfactorily describe the early stage of crystallization. However, the Ozawa model didn't fit the polymer blends in the late stage of crystallization, because it ignored the influence of secondary crystallization. Under the conditions of the non-isothermal melt crystallization, it was found that the cooling rates and the blend composition affect the crystallization for blends according to Kissinger crystallization kinetics parameters. The crystallization kinetics constant K_a increases with increasing cooling rate, indicating the crystallization rates of PTT, PBT, and PTT/PBT blends were improved. The crystallization kinetic activation energy parameters are good agreement with the results from isothermal crystallization processes of the polymer blends. The crystallization activation energy of PTT/PBT blends is higher than the activation energy of PTT and PBT.     

Synthesis of Poly(butylene terephthalate)/Attapulgite Nanocomposites by In-Situ Polymerization and Its Crystallization Behavior

Poly(butylene terephthalate) (PBT)/attapulgite (AT) nanocomposites were prepared via in-situ polymerization without pre-modification of AT. By this method, PBT chains were successfully grafted onto the surface of AT, which was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. Scanning electron microscope examination indicated the uniform dispersion of AT nanoparticles in PBT matrix. The crystallization behavior of PBT/AT nanocomposites was investigated by X-ray diffraction patterns, differential scanning calorimetry, and step-scan differential scanning calorimetry. The non-isothermal crystallization processes were analyzed with the Avrami, Ozawa, and Mo methods. Crystallization activation energies of the samples were also determined by the Kissinger method. The results indicated that AT could act as a heterogeneous nucleating agent in PBT crystallization and lead to an acceleration of crystallization, while AT also acted as a physical hindrance to retard the transport of polymer chains to the growing crystals.     

Isothermal and non-isothermal crystallization kinetics of PVA + ionic liquid [BDMIM][BF4]-based polymeric films

The effect of ionic liquid (IL), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM][BF₄], on crystallization behavior of poly(vinyl alcohol) (PVA) has been studied by isothermal and non-isothermal differential scanning calorimetry techniques. The PVA + IL based polymer electrolyte films have been prepared using solution casting technique. To describe the isothermal and non-isothermal crystallization kinetics, several kinetic equations have been employed on PVA + IL based films. There is strong dependence of the peak crystallization temperature (T_c), relative degree of crystallity (X_t), half-time of crystallization (t_1/2), crystallization rate constants (Avrami K_t and Tobin A_T), and Avrami (n) and Tobin (n_T) exponents on the cooling rate and IL loading.     

Nonisothermal Crystallization of Recycled Poly(Ethylene Terephthalate)/Poly(Ethylene Octene) Blends

Recycled poly(ethylene terephthalate) (r-PET) was blended with poly(ethylene octene) (POE) and glycidyl methacrylate grafted poly(ethylene octene) (mPOE). The nonisothermal crystallization behavior of r-PET, r-PET/POE, and r-PET/mPOE blends was investigated using differential scanning calorimetry (DSC). The crystallization peak temperatures (T _p ) of the r-PET/POE and r-PET/mPOE blends were higher than that of r-PET at various cooling rates. Furthermore, the half-time for crystallization (t _1/2 ) decreased in the r-PET/POE and r-PET/mPOE blends, implying the nucleating role of POE and mPOE. The mPOE had lower nucleation activity than POE because the in situ formed copolymer PET-g-POE in the PET/mPOE blend restricted the movement of PET chains. Non-isothermal crystallization kinetics analysis was carried out based on the modified Avrami equation, the Ozawa equation, and the Mo method. It was found that the Mo method provided a better fit for the experimental data for all samples. The effective energy barriers for nonisothermal crystallization of r-PET and its blends were determined by the Kissinger method.     

Nonisothermal Crystallization Behavior of Polypropylene-C60 Nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C₆₀) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (T_c), half-time for the crystallization (t_1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C₆₀ accelerates the crystallization of PP, implying a nucleating role of C₆₀. Furthermore, due to the reduced viscosity of PP by adding 5% C₆₀, the parameters of crystallization kinetics for the PP-5%C₆₀ nanocomposites changed remarkably relative to that of neat PP and when lower contents of C₆₀ were added to PP.     

ZnO nanoparticles favours heterogeneous nucleation in PET–ZnO nanocomposites

The structural and chemical properties with non-isothermal crystallization kinetics of PET–ZnO nanocomposites have been reported in this article. ZnO nanoparticles have been synthesized via chemical route with average diameter 19 nm which made confirm by transmission electron microscopy and X-ray diffractometer (XRD) techniques. PET–ZnO nanocomposites have been prepared by solution casting method. The structural and chemical changes occurred in poly (ethylene terephthalate) after inclusion of ZnO nanoparticles have been studied with the help of XRD and Fourier transform infrared spectroscopy, respectively. It was observed from differential scanning calorimeter that ZnO nanoparticles work as nucleating agent for heterogeneous nucleation in PET matrix under non-isothermal crystallization process. The combined Avrami and Ozawa models have been proved adequate to explain non-isothermal crystallization kinetics of PET–ZnO nanocomposites, and also, ZnO nanoparticles have been caused to reduce crystallization activation energy in pristine PET as per the applied Kissinger model.     

Nonisothermal Crystallization Kinetics of Miscible Blends of Polycaprolactone and Crosslinked Carboxylated Polyester Resin

The nonisothermal crystallization process of polycaprolactone (PCL)/crosslinked carboxylated polyester resin (CPER) blends has been investigated for different blend concentrations by differential scanning calorimetry (DSC). The DSC measurements were carried out under different cooling rates namely: 1, 3, 5, 10, and 20°C/min. Thermally induced crosslinking of CPER in the blends was accomplished using triglycidyl isocyanurate as a crosslinking agent at 200°C for 10 min. The cured PCL/CPER blends were transparent above the melting temperature of PCL and only one glass transition temperature, T_g, located in the temperature range between the two T_gs of the pure polymer components, was observed, indicating that PCL and crosslinked CPER are miscible over the entire range of concentration. The nonisothermal crystallization kinetics was analyzed based on different theoretical approaches, including modified Avrami, Ozawa, and combined Avrami–Ozawa methods. All of the different theoretical approaches successfully described the kinetic behavior of the nonisothermal crystallization process of PCL in the blends. In addition, the spherulitic growth rate was evaluated nonisothermally from the spherulitic morphologies at different temperatures using polarized optical microscope during cooling the molten sample. Only one master curve of temperature dependence of crystal growth rate could be constructed for PCL/CPER blends, regardless of different blend concentrations. Furthermore, the activation energy of nonisothermal crystallization process (ΔE_a) was calculated as a function of blend concentration based on the Kissinger equation. The value of ΔE_a was found to be concentration dependent, i.e., increasing from 83 kJ/mol for pure PCL to 115 and 119 kJ/mol for 75 and 50 wt% PCL, respectively. This finding suggested that CPER could significantly restrict the dynamics of the PCL chain segments, thereby inhibit the crystallization process and consequently elevate the ΔE_a.     

Cold crystallization from chiral smectic phase

Cold crystallization of liquid crystalline (S)-4’-(1-methylheptyloxycarbonyl) biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-2-fluorobenzoate (3F7HPhF) was studied in isothermal as well as non-isothermal conditions. For isothermal conditions at temperatures between 233 and 250?K X-ray diffraction and differential scanning calorimetry were used. The crystallization kinetics was described by the Avrami–Avramov model, and the values of Avrami exponent, characteristic time and activation energy were determined. The kinetics of the cold crystallization in non-isothermal conditions for chosen heating rates up to 0.5?K/s was studied by differential scanning calorimetry and analyzed using Ozawa, Mo and Augis–Bennett models. Cold crystallization was found to be three-dimensional and controlled by diffusion both in the isothermal and non-isothermal process, however the activation energy determined in the non-isothermal process is about two times smaller than in the isothermal one.     

Effect of Organoclay Platelets on Crystallization of PTT/EPDM-g-MA Blends: Nonisothermal Melt Crystallization Kinetics

PTT/EPDM-g-MA (80/20 w/w) nanocomposites were prepared by melt mixing of poly(trimethylene terephthalate) (PTT), ethylene-propylene-diene copolymer grafted with maleic anhydride (EPDM-g-MA), and organoclay. The blend nanocomposites show typical sea-island morphologies. The nonisothermal crystallization kinetics of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay were extensively studied by differential scanning calorimetry (DSC). The Avrami, Ozawa, and Mo methods were used to describe the nonisothermal crystallization process of pure PTT and 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay. Avrami analysis results show that the crystallization rates of 80/20 (w/w) PTT/EPDM-g-MA blends with the clay were faster than those of pure PTT or PTT/EPDM-g-MA blends without clay, which indicates that the clay particles promote crystallization effectively, in agreement with the Mo analysis results. Ozawa analysis can describe the nonisothermal crystallization of pure PTT very well but was rather inapplicable to the 80/20 (w/w) PTT/EPDM-g-MA blends with various amounts of the clay.     

Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride) in a Poly(Vinylidene Fluoride)/Poly(Methyl Methacrylate)/Dipropylene Glycol Dibenzoate System via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/polymethyl methacrylate (PMMA)/dipropylene glycol dibenzoate (DPGDB) blends, where DPGDB served as a diluent, via solid–liquid (S-L) phase separation during a thermally induced phase separation process was investigated through differential scanning calorimetry (DSC) measurements. It was found that the Ozawa model could only describe the nonisothermal crystallization behavior of PVDF/PMMA/DPGDB system to some extent. The influence of the cooling rate and PMMA/PVDF weight ratio in the PVDF/PMMA/DPGDB system on the crystallization mechanism was also examined based on the Avrami–Jeziorny method and Mo method. Primary crystallization and secondary crystallization were observed in the Avrami–Jeziorny analysis. The analysis by the Avrami–Jeziorny and Mo models indicated that the increase of PMMA/PVDF weight ratio decreased the crystallization rate during the primary crystallization stage. The results showed that the Mo method could well explain the kinetics of the primary PVDF crystallization. The Avrami–Jeziorny method, however, could not well describe the nonisothermal crystallization process of PVDF in the primary crystallization stage. The activation energy, determined by the Kissinger method, was not suitable to reflect the PVDF crystallization process in the PVDF/PMMA/DPGDB system.     

Thermorheology and Crystallization Behaviors of Polyethylenes: Effect of Molecular Attributes

Correlations between polyethylenes of different compositions and branching architectures and the temperature dependence of their viscoelastic behavior as well as the dependence of the nonisothermal crystallization behaviors on the cooling rate were described. To analyze the thermorheological behavior of the various classical polyethylenes, a method proposed by van Gurp and Palmen was utilized and the classical high-pressure low-density polyethylene (LDPE) was found to be thermorheologically complex, while for high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE), thermorheological simplicity was observed. The Avrami and Mo methods were applied to describe the nonisothermal crystallization kinetics of the different PEs for various cooling rate. The values of the kinetic parameter F(T), kinetic crystallization rate constant (Z_c), and half-time of crystallization (t_1/2) indicated that long-chain branching (LCB) had the role of being a heterogeneous nucleating agent and accelerated the crystallization of polyethylene. Moreover, an HDPE sample of both high molecular weight (M_w) and molecular weight distribution (MWD) had a different crystallization rate dependence from the other samples at various corresponding cooling rates. The crystallization activation energy for nonisothermal crystallization of different PEs was determined using the Kissinger method and showed that the presence of LCB as well as high M_w can increase the crystallization activation energy of polyethylene.     

Nonisothermal Crystallization Kinetics of Poly(ϵ-caprolactone)/Zinc Oxide Nanocomposites with High Zinc Oxide Content

Poly(?-caprolactone) (PCL)/zinc oxide (ZnO) nanocomposites (PCLZs) with high ZnO contents were prepared by using ZnO to initiate ring-opening polymerization of ?-caprolactone (?-CL). The Ozawa and Mo equations were chosen to analyze the nonisothermal crystallization kinetics of PCLZs. The results showed that the Ozawa equation was not successful while the Mo equation was successful in describing the nonisothermal crystallization kinetics of PCLZs. When the ZnO content in PCLZs was high, the effect of ZnO content on crystallization behaviors was small and the crystallization rates of PCLZs only increased slightly with the increase of ZnO content. Crystallization activation energies (E_c s) of PCLZs were estimated by Kissinger's method. The results showed that the E_c s of PCLZs with three different ZnO contents were nearly identical within the tolerance, which further demonstrated that the effect of ZnO content on crystallization behaviors was small when the ZnO content in PCLZs was high.     

Crystallization Kinetics of Nucleated Polypropylene with Organic Phosphates

The crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with two organic phosphates, sodium salt (NA7) and triglyceride ester (NA8) of 2,2'-methylene-bis(4,6-di-tert-butylphenyl) phosphoric acid, were investigated by means of a differential scanning calorimeter under isothermal and nonisothermal conditions. During isothermal crystallization, a modified Avrami equation was used to describe the crystallization kinetics. Moreover, kinetics parameters, such as the Avrami exponent, n, the crystallization rate constant, k, and the half-time of crystallization, τ_1/2, are compared. The results showed that a dramatic decrease of the half-time of crystallization, as well as a significant increase of the overall crystallization rate, were observed in the presence of the organic phosphates. During nonisothermal crystallization, the primary crystallization was analyzed using the Ozawa model, leading to similar Avrami exponents for iPP and iPP/NA7, which means simultaneous nucleation with three-dimensional spherulitic growth. However, for iPP/NA8, the Avrami exponent in nonisothermal crystallization is evidently different from that in isothermal crystallization, which would indicate a different mechanism of crystal growth. Adding the nucleating agent to iPP makes the overall crystallization activation energy increase.     

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T _m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.     

Diffusion Control of Homogeneous Crystallization in Nanoconfined Domains of Block Copolymers

Abstract

Confined crystallization in a poly(oxyethylene)‐b‐poly(oxybutylene)/poly(oxybutylene) blend (E₁₁₅B₁₀₃/B₂₈, φ_E = 0.14) with bcc morphology and in a polystyrene‐b‐poly (oxyethylene)‐b‐polystyrene (S‐E‐S) triblock copolymer (S₄₀E₁₃₆S₄₀, φ_E = 0.407) with lamellar morphology was studied using differential scanning calorimetry (DSC). Two types of confined crystallization with different characteristic Avrami exponents were identified in both systems. At higher crystallization temperature (T _c), the Avrami exponent is 1.0 and the overall crystallization rate is controlled by the homogeneous nucleation rate. At lower T _c, the Avrami exponent is 0.5, which is attributed to diffusion‐controlled confined crystallization. This shows that diffusion has a great influence on the overall crystallization rate when chain mobility is reduced, which can be caused either by lower T _c or by constrained microstructure.     

Synthesis and Non-isothermal Crystallization Behavior of PET/Surface-treated TiO 2 Nanocomposites

Poly(ethylene terephthalate) (PET)/TiO ₂ nanocomposites were prepared by melt-blending PET and surface-treated TiO ₂ . The crystallization behavior and the non-isothermal crystallization kinetics of these composites were investigated by differential scanning calorimetry (DSC). Jeziorny and Mo's methods were applied to describe the kinetics of the non-isothermal crystallization process. It was found that the PET matrix with incorporated surface-treated TiO ₂ particles has lower crystallization temperature and melting point than that with incorporated pure nano-TiO ₂ particles. Unlike plain TiO ₂ , surface-treated TiO ₂ particles showed less effect on the degree of crystallization of the PET matrix.     

Crystallization kinetics and Avrami index of Sb-doped Se–Te–Sn chalcogenide glasses

Bulk amorphous samples of Sb-substituted Se_78?xTe₂₀Sn₂Sb_x (0 < x < 6) have been prepared using melt quench technique. The structure of Se_78?xTe₂₀Sn₂Sb_x (x = 0, 2, 4, 6) glassy alloys has been investigated using X-ray diffraction technique. Calorimetric studies of the prepared samples have been performed under non-isothermal conditions using differential scanning calorimetry (DSC) and glass transition temperature as well as crystallization temperature has been evaluated using DSC scans. The activation energy of crystallization kinetics (E_c) has been determined using model-free approaches such as Kissinger, Ozawa, Tang and Starink methods. The Avrami index (n) and frequency factor (K_o) have been calculated by Matusita and Augis–Benett method.     

Nonisothermal Crystallization Kinetics of Poly(lactic acid)/Nanosilica Composites

Poly(lactic acid) (PLA)/nanosilica composites were prepared by blending the PLA and nanosilica in chloroform and then evaporating the solvent to form the composite films in a dish. The Ozawa and Mo equations were used to characterize the nonisothermal cold crystallization kinetics of the PLA/nanosilica composites. The results indicated that the Ozawa equation was not successful while the Mo equation was successful to describe the nonisothermal crystallization kinetics of PLA/nanosilica composites. The values of crystallization activation energy (E _c) of the samples were calculated by the Kissinger method. Although the sample crystallization rates were enhanced with the increase of nanosilica content, the samples exhibited increased E _c in the presence of nanosilica. The results showed that nanosilica had an effect on both the nucleation and the crystal growth of PLA, promoting the nucleation but interfering with the molecular motion of PLA in the crystallization process.     

Study on the Nonisothermal Melt Crystallization Kinetics of DBS/PBT Blends

The modified Avrami, Mo, and Kissinger models were applied to investigate the nonisothermal melt crystallization process of dibenzylidene sorbitol (DBS)/poly(butylene terephthalate) (PBT) blends by differential scanning colorimetry (DSC) measurements. The modified Avrami model can describe the nonisothermal melt crystallization processes of DBS/PBT blends fairly well. The cooling rates and the blend composition affect the crystallization of the blends according to Mo crystallization kinetics parameters. The Mo model shows that F(T) increases with increasing crystallinity, indicating that the needed cooling rate when it reached a certain crystallinity increased in unit time, the crystallization rate of DBS/PBT blends is faster than the crystallization rate of pure PBT, and the crystallization rate of the DBS/PBT blends with 0.5% DBS is fastest. The Kissinger model showed that the crystallization activation energy of DBS/PBT blends is lower than the activation energy of pure PBT; the crystallization activation energy of the DBS/PBT blends with 0.5% DBS is the lowest.