Kinetics of Isothermal and Nonisothermal Crystallization of Poly(ethylene oxide) (PEO) in PEO/Fatty Acid Blends

In this work, isothermal and nonisothermal crystallization kinetics of poly(ethylene oxide) (PEO) and PEO in PEO/fatty acid (lauric and stearic acid) blends, that are used as thermal energy storage materials, was studied using differential scanning calorimetry (DSC) data. The Avrami equation was adopted to describe isothermal crystallization of PEO and nonisothermal crystallization was analyzed using both the modified Avrami approach and Ozawa method. Avrami exponent (n) for PEO crystallization was in the range 1.08–1.32 (10–90% relative crystallinity), despite of spherulites formation, while for PEO in PEO/fatty acid blends n was between 1.61 and 2.13. Hoffman and Lauritzen theory was applied to calculate the activation energy of nucleation (K_g) – the lowest value of K_g was observed for pure PEO, despite of heterogeneous nucleation of fatty acid crystals in PEO/fatty acid blends. For nonisothermal crystallization of PEO in PEO/lauric acid (1:1 w/w) and PEO/stearic acid (1:3 w/w) blends, secondary crystallization occurred and values of the Avrami exponent were 2.8 and 2.0, respectively. The crystallization activation energies of PEO were determined to be ?260 kJ/mol for pure PEO, ?538 kJ/mol for PEO/lauric acid blend, and ?387 kJ/mol for PEO/stearic acid blend for isothermal crystallization and ?135,6 kJ/mol, ?114,5 kJ/mol, and ?92,8 kJ/mol, respectively, for nonisothermal crystallization.     

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.     

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.     

Crystalline Morphology and Nonisothermal Crystallization Behaviors of iPP/PcBR Blends

Isotactic polypropylene/poly(cis‐butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. The influence of PcBR content on crystalline morphology and nonisothermal crystallization behaviors of iPP was investigated by polarized optical microscopy (POM), small angle light scattering (SALS), and differential scanning calorimetry (DSC). The POM showed that an increase of PcBR ranging from 10 vol% to 40 vol% led to less perfection of spherulites, vaguer boundaries between spherulites, and smaller spherulite size, which was quantitatively validated by SALS. The presence of PcBR also remarkably affected the nonisothermal crystallization behaviors of iPP. An addition of PcBR caused higher crystallization peak temperature and a faster crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak temperature moved to lower temperature and the crystallization rate increased as the cooling rate increased. The Ozawa and combined Avrami and Ozawa equations were used to describe the nonisothermal crystallization process of iPP and blends. The combined Avrami and Ozawa equation was more appropriate for the crystallization of the blends. Crystallization activation energy of iPP and blends was calculated by the Kissinger equation; the result showed that crystallization activation energy decreased as the content of PcBR increased from 30 vol% to 40 vol%.     

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.     

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.     

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.     

Miscibility Determination in Poly(ε-caprolactone)/Poly(Vinyl Formal) Blend by Equilibrium Melting Temperature and Spherulite Morphology

Miscibility of poly(ε-caprolactone), (PCL), containing 1, 5, and 10 wt.% poly(vinyl formal) (PVF) blends was investigated by polarized optical microscopy (POM), atomic force microscopy (AFM), and differential scanning calorimetry (DSC) for spherulitic morphology and equilibrium melting temperature (T°_m, via Hoffman-Weeks plot). The T°_m of PCL in the blends was similar to that of pure PCL, indicating immiscibility. Isothermally, melt crystallized virgin PCL between 30°C and 50°C showed spherulitic morphology with negative birefringence, Maltese cross, and without extinction rings. The nucleation and growth rates of PCL spherulites were found to be dramatically reduced with the addition of PVF. Extinction rings and a change in the sign of the birefringence of the PCL spherulites were observed and were found to be dependent on blend composition and crystallization temperature. The presence of a ring pattern in spherulites was an indication of miscibility between the two polymers that had failed to be detected by thermal methods. The formation of a ring pattern is discussed in terms of lamella twisting originating from a change in the crystallization mechanism.     

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.     

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.     

Nonisothermal Crystallization Nucleation of In‐Situ Fibrillar and Spherical Inclusions in Poly (Phenylene Sulfide)/Isotactic Polypropylene Blends

Nonisothermal crystallization nucleation and its kinetics of in‐situ fibrillar and spherical dispersed phases in poly (phenylene sulfide) (PPS)/isotactic polypropylene (iPP) blends are discussed. The PPS/iPP in‐situ microfibrillar reinforced blend (MRB) was obtained via a slit‐die extrusion, hot stretching, and quenching process, while PPS/iPP common blend with spherical PPS particles was prepared by extrusion without hot stretching. Morphological observation indicated that the well‐defined PPS microfibrils were in situ generated. The diameter of most microfibrils was surprisingly larger than or equal to the spherical particles in the common blend (15/85 PPS/iPP by weight). The nonisothermal crystallization kinetics of three samples (microfibrillar, common blends, and neat iPP) were investigated with differential scanning calorimetry (DSC). The PPS microfibrils and spherical particles could both act as heterogeneous nucleating agents during the nonisothermal crystallization, thus increasing the onset and maximum crystallization temperature of iPP, but the effect of PPS spherical particles was more evident. For the same material, crystallization peaks became wider and shifted to lower temperature when the cooling rate increased. Applying the theories proposed by Ozawa and Jeziorny to analyze the crystallization kinetics of neat iPP, and microfibrillar and common PPS/iPP blends, both of them could agree with the experimental results.     

Study on the Nonisothermal Crystallization Kinetics of Poly(Vinylidene Fluoride)/Tributyl Citrate Blends Via Thermally Induced Phase Separation

The nonisothermal crystallization kinetics of poly (vinylidene fluoride) (PVDF) in PVDF/tributyl citrate (TBC) blends having undergone thermally induced phase separation were investigated through differential scanning calorimetry measurements. Ozawa theory, Mo's method and Kissinger model were used to analyze the kinetics of the nonisothermal crystallization process. The Ozawa theory failed to describe the crystallization behavior of PVDF in the PVDF/TBC blends, whereas the Mo model was able to describe the nonisothermal crystallization process fairly well. The crystallization activation energy was determined by the Kissinger method, and was in the range of 90–165 kJ/mol.     

Study of the Nonisothermal Crystallization Kinetics and Melting Behaviors of Polypropylene Reinforced with Single-Walled Carbon Nanotubes Nanocomposite

Nonisothermal crystallization kinetics of polypropylene (PP) nanocomposite reinforced with 0.5 wt. % single-walled carbon nanotubes (SWNT) was characterized by differential scanning calorimetry at five different cooling and heating rates. The Avrami, Ozawa, and Seo-Kim kinetic models were used to describe the nonisothermal crystallization of the polymer and its nanocomposite. The addition of nano-filler, in general, improved the crystallization rate and increased the peak crystallization temperature of the nanocomposite as compared to PP. The results show that the Avrami and Seo-Kim models are suitable under different cooling rate conditions but that the Ozawa model is inappropriate for the nanocomposite. Equilibrium melting temperatures, derived from the linear Hoffman-Weeks equation, were shown to decrease in the nanocomposite. Additional analysis was performed based on the Thomson-Gibbs, Lauritzen-Hoffman, and Dobreva-Gutzowa theories, which were applied to take into account the lamellar thickness, nucleating agent, and nucleating activity of the nanocomposite in the nonisothermal melt crystallization process.     

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.     

Nonisothermal Crystallization Kinetics of Poly(lactic acid) Nucleated with a Multiamide Nucleating Agent

Addition of a commercial available multiamide compound (N,N′,N′′-tricyclohexyl-1,3,5- benzenetricarboxylamide, defined here as TMC) into ecofriendly poly(lactic acid) (PLA) can accelerate the crystallization rate of the material remarkably and broaden its applications. In this paper, the nonisothermal crystallization behavior of biodegradable PLA nucleated by 0.3 wt.% of TMC was investigated by differential scanning calorimetry (DSC). The modified Avrami, Tobin, Ozawa, and Mo models were applied to describe the kinetics of the crystallization process. Various parameters of nonisothermal crystallization, such as the crystallization half-time and crystallization rate constant, reflected that TMC significantly accelerated the crystallization process. The activation energy values of the neat PLA and PLA/TMC blend, determined by the Kissinger method, increased with the addition of TMC. The study should be helpful for understanding the relationship between processing and properties of this material.     

同步扫描光谱方法研究聚合物结晶动力学过程

固体表面反射光与其折射指数之间存在余弦函数关系,而折射指数的均方起伏又和固体表面的密度和浓度起伏有关。因此从反射光的变化可以反映材料内部结构的一些变化。基于此理论指导,本文利用同步扫描光谱(SSS)方法,即荧光光谱仪的同步扫描模式进行反射光的检测,成功地监测了聚己内酯(PCL)薄膜在铜片上的熔融和非等温结晶过程。PCL薄膜的SSS谱图出现了两个明显的荧光光谱仪的光源峰(467和473 nm),利用这两个峰的信息可以表征聚合物的熔融和结晶过程中分子链结构的变化。采用SSS方法表征分析得到了PCL的热动力学和结晶动力学参数,其结晶Avrami exponent n为2.8～3.2,平均值为3.1,表明PCL的非等温结晶遵循异相成核、三维球晶生长机理。这些与差示扫描量热仪(DSC)得到的参数一致。研究结果表明SSS方法是一种简单、有效的原位测试聚合物熔融和结晶动态过程的方法。此外,SSS方法是一种基于荧光光谱仪的具有普适性的光谱方法,对发光和不发光固态聚合物均可以检测研究。     

Mechanical Property,Crystal Morphology,and Nonisothermal Crystallization Kinetics of Poly(Trimethylene Terephthalate)/Maleinized Acrylonitrile-Butadiene-Styrene Blends

The mechanical properties, morphology, crystallization, and melting behaviors and nonisothermal crystallization kinetics of poly (trimethylene terephthalate)(PTT)/maleinized acrylonitrile-butadiene-styrene (ABS-g-MAH) blends were investigated by an impact tester, polarized optical microscopy, and differential scanning calorimetry (DSC). The results suggested that the ABS-g-MAH component served as both a nucleating agent for increasing the crystallization rate and as a toughening agent for improving the impact strength of PTT. When the ABS-g-MAH content was 5wt.%, the blend had the best toughness and a high crystallization rate. The blends showed different crystallization rates and subsequent melting behaviors due to their different ABS-g-MAH contents. The Ozawa theory and the method developed by Mo and coworkers were used to study the nonisothermal crystallization kinetics of the blends. The kinetic crystallization rate parameters suggested that the proper contents of ABS-g-MAH can highly accelerate the crystallization rate of PTT, but this effect nearly reaches saturation for ABS-g-MAH contents over 5%. The Ozawa exponents calculated from the DSC data suggested that the PTT crystals in the blends have similar growth dimensions as those in neat PTT, although they are smaller and/or imperfect. The effective activation energy calculated by the method developed by Kissinger also indicates that the blends with higher ABS-g-MAH content were easier to crystallize.     

Isothermal Melt Crystallization Kinetics for Poly(Trimethylene Terephthalate)/Poly(Butylene Terephthalate) Blends

The kinetics of isothermal melt crystallization of poly(trimethylene terephthalate) (PTT)/poly(butylene terephthalate) (PBT) blends were investigated using differential scanning calorimetry (DSC) over the crystallization temperature range of 184–192°C. Analysis of the data was carried out based on the Avrami equation. The values of the exponent found for all samples were between 2.0 and 3.0. The results indicated that the crystallization process tends to be two‐dimensional growth, which was consistent with the result of polarizing light microscopy (PLM). The activation energies were also determined by the Arrhenius equation for isothermal crystallization. The values of ΔE of PTT/PBT blends were greater than those for PTT and PBT. Lastly, using values of transport parameters common to many polymers (U*=6280 J/mol, T _∞=T _g – 30), together with experimentally determined values of T _m ⁰ and T _g, the nucleation parameter, K _g, for PTT, PBT, and PTT/PBT blends was estimated based on the Lauritzen–Hoffman theory.     

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.     

Peroxide-based route assisted with inverse microemulsion process to well-dispersed Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> nanocrystals

Well-dispersed bismuth titanate (BIT) nanocrystals with an average size ranged from 3 to 60 nm were synthesized via a peroxide-based route assisted with an inverse microemulsion process. The crystallite size and lattice parameter of BIT upon variable-temperature were determined by X-ray diffraction (XRD). The particle size was confirmed by transmission electron microscopy (TEM). Thermal decomposition behaviour of Ti-peroxy and BIT gel and crystallization kinetics of BIT nanocrystals were investigated by differential scanning calorimetry/thermogravimetry (DSC/TG) and Fourier-Transform infrared spectroscopy (FTIR). Analysis of nonisothermal DSC data yielded a value of 220.84 ± 2.73 KJ/mol and 2.25 ± 0.26 for the activation energy of crystallization (E _a) and the Avrami exponent (n), respectively.