Nonisothermal crystallization kinetics of high‐density polyethylene/barium sulfate nanocomposites

The high‐density polyethylene (HDPE)/barium sulfate (BaSO₄) nanocomposites had been successfully prepared by melt‐blending. Nonisothermal melt‐crystallization kinetics of neat HDPE and HDPE/BaSO₄ nanocomposites was investigated with differential scanning calorimetry under different cooling rates. The nonisothermal crystallization behavior was analyzed by Ozawa, Avrami, and combined Ozawa–Avrami methods. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of neat HDPE and HDPE/BaSO₄ nanocomposites. The modified Avrami method by Jeziorny was only valid for describing the middle stage of crystallization but was not able to describe the later stage of neat HDPE and HDPE/BaSO₄ nanocomposites crystallization. The value of Avrami exponent n for neat HDPE ranged from 3.3 to 5.7 and for HDPE/BaSO₄ nanocomposites ranged from 1.8 to 2.5. It is postulated that the values of n close to 3 are caused by spherulitic crystal growth with heterogeneous nucleation, whereas simultaneous occurrence of spherulitic and lamellar crystal growth with heterogeneous nucleation account for lower values of n. The combined Ozawa–Avrami method by Mo and coworkers (Polym. Eng. Sci., 37(3) , 568 (1997)) was able to satisfactorily describe the crystallization behavior of neat HDPE and HDPE/BaSO₄ nanocomposites. In addition, the activation energy of nonisothermal crystallization was determined using the Kissinger (J. Res. Natl. Bur. Stand., 57(4) , 217 (1956)) method, showing that the crystallization activation energy of HDPE/BaSO₄ nanocomposites was lower than that of neat HDPE. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Crystallization kinetics of poly (L‐lactic acid)/montmorillonite nanocomposites under isothermal crystallization condition

Poly(L ‐lactic acid)/o‐MMT nanocomposites, incorporating various amounts of organically modified montmorillonite (o‐MMT; 0–10 wt %), were prepared by solution intercalation. The montmorillonite (MMT) was organically modified with dilauryl dimethyl ammonium bromide (DDAB) by ion exchange. Transmission electron microscopy (TEM) and X‐ray diffraction (XRD) reveal that the o‐MMT was exfoliated in a poly(L ‐lactic acid), (PLLA) matrix. A series of the test specimens were prepared and subjected to isothermal crystallization at various temperatures (T₁–T₅). The DSC plots revealed that the PLLA/o‐MMT nanocomposites that were prepared under nonisothermal conditions exhibited an obvious crystallization peak and recrystallization, but neat PLLA exhibited neither. The PLLA/o‐MMT nanocomposites (2–10 wt %) yielded two endothermic peaks only under isothermal conditions at low temperature (T₁), and the intensity of Tm₂ (the higher melting point) was proportional to the o‐MMT content (at around 171°C). The melting point of the test samples increased with the isothermal crystallization temperature. In the Avrami equation, the constant of the crystallization rate (k) was inversely proportional to the isothermal crystallization temperature and increased with the o‐MMT content, especially at low temperature (T₁). The Avrami exponent (n) of the PLLA/o‐MMT nanocomposites (4–10 wt %) was 2.61–3.56 higher than that of neat PLLA, 2.10–2.56, revealing that crystallization occurred in three dimensions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Pre‐melting temperature effect on the isothermal melt crystallization and multiple melting behavior of syndiotactic polystyrene

This work examined how pre‐melting temperature (T_max) affects the isothermal melt crystallization kinetics, the resulting melting behavior and crystal structure of syndiotactic polystyrene (sPS) by using differential scanning calorimetry (DSC), polarized light microscopy (PLM) and the wide angle X‐ray diffraction (WAXD) technique. Experimental results indicated that raising T_max decreased the nucleation rate and the crystal growth rate of sPS. The Avrami equation was also used to analyze the overall crystallization kinetics. The Avrami exponent n and rate constant K were determined for different T_max specimens at various crystallization temperatures (T_c's). Our results indicated that the nucleation type of sPS is T_max and T_c dependent as well. Evaluation of the activation energy for the isothermal crystallization processes revealed that it increases from 375 kJmol^?1 to 485 kjmol ^?1 with an increase of T_max. From the melting behavior study, we believe that the T_max and T_c‐dependent multiple melting peaks are associated with different polymorphs as well as recrystallized crystals formed during heating scans. Moreover, the percentage content of α form in the crystals formed under different crystallization conditions was estimated through WAXD experiments.     

Isothermal crystallization of high density polyethylene and nanoscale calcium carbonate composites

High density polyethylene (HDPE) and calcium carbonate (CaCO₃) nanocomposites with maleic anhydride grafted HDPE (manPE) as a compatibilizer were prepared via compounding in a twin‐screw extruder. The CaCO₃ are well dispersed in the HDPE matrix from the observation of transmission electron microscope. The isothermal crystallization kinetics was studied by differential scanning calorimetry and simulated by Avrami and Tobin models. The nucleation constants and fold surface free energy were estimated from Lauritzen–Hoffman relation. The results indicate that both manPE and well‐dispersed CaCO₃ particles would act as nuclei to induce heterogeneous nucleation and enhance crystallization rate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization kinetics and melting behaviour of microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

Isothermal and non‐isothermal crystallization kinetics of microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐3HHx)] was investigated by differential scanning calorimetry (DSC) and ¹³C solid‐state nuclear magnetic resonance (NMR). Avrami analysis was performed to obtain the kinetic parameters of primary crystallization. The results showed that the Avrami equation was suitable for describing the isothermal and non‐isothermal crystallization processes of P(3HB‐3HHx). The equilibrium melting temperature of P(3HB‐3HHx) and its nucleation constant of crystal growth kinetics, which were obtained by using the Hoffman–Weeks equation and the Lauritzen–Hoffmann model, were, respectively, 121.8 °C and 2.87 × 10⁵ K² when using the empirical ‘universal’ values of U* = 1500 cal mol^?1. During the heating process, the melting behaviour of P(3HB‐3HHx) for both isothermal and non‐isothermal crystallization showed multiple melting peaks, which was the result of melting recrystallization. The lower melting peak resulted from the melting of crystals formed during the corresponding crystallization process, while the higher melting peak resulted from the recrystallization that took place during the heating process. Copyright © 2005 Society of Chemical Industry     

Isothermal and nonisothermal crystallization kinetics of syndiotactic polystyrene/clay nanocomposites

Differential scanning calorimeter (DSC) and X‐ray diffraction methods were used to investigate the isothermal and nonisothermal crystallization behavior and crystalline structure of syndiotactic polystyrene (sPS)/clay nanocomposites. The sPS/clay nanocomposites were prepared by mixing the sPS polymer solution with the organically modified montmorillonite. DSC isothermal results revealed that introducing 5 wt% of clay into the sPS structure causes strongly heterogeneous nucleation, inducing a change of the crystal growth process from mixed three‐dimensional and two‐dimensional crystal growth to two‐dimensional spherulitic growth. The activation energy of sPS drastically decreases with the presence of 0.5 wt% clay and then increases with increasing clay content. The result indicates that the addition of clay into sPS induces the heterogeneous nucleation (a lower ΔE) at lower clay content and then reduces the transportation ability of polymer chains during crystallization processes at higher clay content (a higher ΔE). We studied the non‐isothermal melt‐crystallization kinetics and melting behavior of sPS/clay nanocomposites at various cooling rates. The correlation among crystallization kinetics, melting behavior and crystalline structure of sPS/clay nanocomposites is discussed. Polym. Eng. Sci. 44:2288–2297, 2004. © 2004 Society of Plastics Engineers.     

Isothermal crystallization of HDPE/octamethyl polyhedral oligomeric silsesquioxane nanocomposites: Role of POSS as a nanofiller

The isothermal crystallization of HDPE/POSS (polyhedral oligomeric silsesquioxane) nanocomposites (POSS content varying from 0.25 to 10 wt %) was studied using differential scanning calorimetry (DSC) technique. The Avrami model could successfully describe the isothermal crystallization behavior of the nanocomposites. The value of Avrami exponent (n) varies between 2 and 2.5 for all the compositions studied. For a given composition, the values vary with crystallization temperature and in general increased with POSS content up to 1 wt % POSS content and decreased thereafter. The presence of POSS was found to increase the rate of crystallization, which manifested itself in the increased value of the Avrami rate constant (K) and reduced value of crystallization half‐time (t_1/2). The rate of crystallization peaked at 1 wt % POSS content and was almost constant at higher POSS loadings. X‐ray diffraction studies revealed that POSS exists as nanocrystals in HDPE matrix while some POSS gets dispersed at molecular level too. It is observed that only the POSS dispersed at molecular level acts as a nucleating agent while the POSS nanocrystals do not affect the crystallization process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Isothermal crystallization kinetics of poly(phenylene sulfide)/TLCP composites

The isothermal crystallization kinetics, the morphology, and the melting behavior of melt‐processed composites of poly(phenylene sulfide) (PPS) with a thermotropic liquid crystalline copolyester, Vectra A950, (TLCP) were studied by differential scanning calorimetry (DSC) and optical microscopy. The crystallization behavior of PPS in PPS/TLCP composites is observed to be highly sensitive to T_c and immiscible TLCP content in the composites. The spherulite growth rate, the overall crystallization rate, and the activation energy of PPS in PPS/TLCP composites are markedly depressed by the presence of TLCP. The analysis of the Avrami kinetic parameters (n and k) indicates that blending of TLCP with PPS causes heterogeneous growth process and nucleation mechanisms. At low T_cs, the PPS crystallization rate is faster than that neat PPS with ≤30 wt% TLCP loading whereas at high T_cs it remains almost unchanged. The analysis of the melting behavior of these composites indicates that the stability of PPS crystals and their reorganization is influenced both by the T_cs and the composite compositions. The sizes and the number of spherulites change a great extent with composite composition with a drop of spherulite rapid growth rate, at constant T_c, with increasing content of TLCP in composites. The analysis based on the Lauritzen‐Hoffmann secondary nucleation theory, using present DSC data, indicates that present data predominantly follow a linear growth trend over a present range of T_cs and PPS crystallization in composites still occurs according to regime II kinetics, whereby multiple surface nuclei form on the substrate with multiple nucleation acts commencing before initially formed growth layer is completed. The fold surface free energy of PPS chains in composites is found higher than that of neat PPS, leading to an average higher work of chain folding and is ascribed to a general development of the PPS chain mobility in the composite melt. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Study on the Phase Behavior of High Density Polyethylene – Ethylene Octene Copolymer Blends

The processes of melting and crystallization of blends based on HDPE and EOC were investigated. DSC thermograms showed that a separate crystallization and co‐crystallization occurred in the blends studied. Avrami approach was used to analyze the kinetics of crystallization in the blends. It is shown that the Avrami exponent depends on the EOC concentration of the samples studied. The difference in the Avrami parameters for HDPE, EOC and the blends indicated that the nucleation mechanism and dimension of the spherulite growth of the blends were different from that of HDPE to some extent. The crystal growth was examined in the context of the Lauritzen‐Hoffman theory. DSC traces obtained at different cooling rates were used for analyzing the non‐isothermal crystallization. It was found that the Ozawa model was rather inapplicable for the materials studied. In contrast, the Avrami equation modified by Jeziorny can be used more efficiently to describe the non‐isothermal crystallization behavior of HDPE‐EOC blends.

     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

Thermophysical properties of bacterial poly(3‐hydroxybutyrate): Characterized by TMA,DSC, and TMDSC

The melting, isothermal and nonisothermal crystallization behaviors of poly(3‐hydroxybutyrate) (PHB) have been studied by means of temperature modulated differential scanning calorimetry (TMDSC) and conventional DSC. Various experimental conditions including isothermal/annealing temperatures (80, 90, 100, 105, 110, 120, 130, and 140°C), cooling rates (2, 5, 10, 20, and 50°C/min) and heating rates (5, 10, 20, 30, 40, and 50°C/min) have been investigated. The lower endothermic peak (T_m1) representing the original crystals prior to DSC scan, while the higher one (T_m2) is attributed to the melting of the crystals formed by recrystallization. Thermomechanical analysis (TMA) was used to evaluate the original melting temperature (T_melt) and glass transition temperature (T_g) as comparison to DSC analysis. The multiple melting phenomenon was ascribed to the melting‐recrystallization‐remelting mechanism of the crystallites with lower thermal stability showing at T_m1. Different models (Avrami, Jeziorny‐modified‐Avrami, Liu and Mo, and Ozawa model) were utilized to describe the crystallization kinetics. It was found that Liu and Mo's analysis and Jeziorny‐modified‐Avrami model were successful to explain the nonisothermal crystallization kinetic of PHB. The activation energies were estimated in both isothermal and nonisothermal crystallization process, which were 102 and 116 kJ/mol in respective condition. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42412.     

Effects of dodecyl amine functionalized graphene oxide on the crystallization behavior of isotactic polypropylene

Dodecyl amine functionalized graphene oxide (DA‐GO)/isotactic polypropylene (iPP) nanocomposites were prepared via solution mixing method. Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and X‐ray photoelectron spectroscopy (XPS) verified that the DA was successfully grafted onto the surface of graphene oxide. The crystallization behavior of iPP/DA‐GO nanocomposites was investigated by differential scanning calorimetry (DSC) and polarized optical microscope (POM). The DSC results of both isothermal and non‐isothermal crystallization process indicated that the addition of DA‐GO can decrease the half‐time crystallization (t_1/2) and elevate crystallization peak temperature (T_p) of iPP. The results of isothermal crystallization kinetics showed that the overall crystallization rates of iPP/DA‐GO nanocomposites, especially with higher DA‐GO content, were much faster than that of neat iPP. During the non‐isothermal crystallization process, the nucleation ability (Φ) of nanocomposites containing 0.05, and 0.5 wt % DA‐GO were 0.83 and 0.69, respectively. And the crystallization activation energy of iPP decreased from 348.7 (neat iPP) to 309.2 and 283.1 kJ/m 2 by addition of 0.05 and 0.5 wt % DA‐GO, respectively. The decrease of Φ and indicated DA‐GO has strong heterogeneous nucleation effect and can promote the crystallization of iPP significantly. Additionally, POM micrographs showed the DA‐GO in iPP matrix can form more nucleation sites for the spherulite growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40000.     

Crystallization and melting behavior of polyester/clay nanocomposites

Polyester/clay nanocomposites were prepared by melt compounding with different clay loadings. Comparing against neat polyester resins, the crystallization and multiple melting behavior of the nanocomposites was investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). Nanoclay filler is an effective heterogeneous nucleating agent, as evidenced by a decrease and an increase in the crystallization temperature for both cold and melt crystallization of polyesters, respectively. The degree of crystallinity was found to increase with increasing clay content, due to heterogeneous nucleation effects by the addition of a nanofiller. For the annealed samples, multiple melting peaks were always observed for both neat polyester and its nanocomposites. The origins of the multiple melting behavior are discussed, based on the DSC and XRD results. Interestingly, an ‘abnormal’ high‐temperature endothermic peak (T_{m, 3}) at about 260 °C was observed when the nanocomposite samples were annealed at higher temperatures (eg ≥240 °C). The constrained polyester crystals formed within intercalated clay platelets due to confinement effects were probably responsible for this melting event at these higher temperatures. Copyright © 2004 Society of Chemical Industry     

Isothermal crystallization kinetics and melting behavior of polyamide 11/silica nanocomposites prepared by in situ melt polymerization

Polyamide 11 (PA 11)/silica nanocomposites were prepared via in situ melt polymerization by the dispersion of hydrophobic silica in 11‐aminoundecanoic acid monomer. Their isothermal crystallization process and melting behaviors were analyzed by differential scanning calorimetry. The isothermal crystallization kinetics was analyzed by the Avrami equation. The obtained data showed that the model of nucleation and growth of PA 11 was not affected after the incorporation of silica and was a mixture with two‐dimensional, circular, three‐dimensional growth with thermal nucleation. Double and single melting peaks were observed depending on the crystallization temperature. The equilibrium melting point of samples was evaluated, and the spherulites growth kinetics parameters and fold surface free energy were further calculated according to the classical theories. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal crystallization and melting behavior of polypropylene with lanthanum complex of cyclodextrin derivative as a β‐nucleating agent

A novel highly active β‐nucleating agent, β‐cyclodextrin complex with lanthanum (β‐CD‐MAH‐La), was introduced to isotactic polypropylene (iPP). Its influence on isothermal crystallization and melting behavior of iPP was investigated by differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized light microscopy (PLM). WAXD results demonstrated that β‐CD‐MAH‐La was an effective β‐nucleating agent, with β‐crystal content of iPP being strongly influenced by the content of β‐CD‐MAH‐La and the isothermal crystallization temperature. The isothermal crystallization kinetics of pure iPP and iPP/β‐CD‐MAH‐La was described appropriately by Avrami equation, and results revealed that β‐CD‐MAH‐La promoted heterogeneous nucleation and accelerated the crystallization of iPP. In addition, the equilibrium melting temperature (T) of samples was determined using linear and nonlinear Hoffman‐Weeks procedure. Finally, the Lauritzen‐Hoffman secondary nucleation theory was applied to calculate the nucleation parameter (K_g) and the fold surface energy (σ_e), the value of which verify that the addition of β‐CD‐MAH‐La reduced the creation of new surface for β‐crystal and then led to faster crystallization rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crystal morphology,melting behaviors and isothermal crystallization kinetics of SCF/PTT composites

Isothermal crystallization kinetics, subsequent melting behavior, and the crystal morphology of short carbon fiber and poly(trimethylene terephthalate) composites (SCF/PTT) were investigated by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The crystal morphology of the composites isothermally crystallized at T_c = 205°C is predominantly banded spherulites observed under polarizing micrographs, while the pattern of banded spherulites changed from ring to serration as the SCF content added into the PTT. Moreover, nonbanded spherulites formed at T_c = 180°C. The commonly used Avrami equation was used to fit the primary stage of the isothermal crystallization. The Avrami exponents n are evaluated to be 1.6–2.0 for the neat PTT and 2.7–3.0 for SCF/PTT composites, and the SCF acting as nucleation agents in composites accelerates the crystallization rate with decreasing the half‐time of crystallization and the sample with SCF component of 2% has the fastest crystallization rate. The crystallization activation energy calculated from the Arrhenius formula suggests that the adding SCF component improved the crystallization ability of the PTT matrix greatly, and the sample with of 2% SCF component has the most crystallization ability. Subsequent melting scans of the isothermally crystallized composites all exhibited triple melting endotherms, in which the more the component of SCF, the lower temperature of the melting peak, indicating the less perfect crystallites formed in those composites. Furthermore, the melting peaks of the same sample are shifted to higher temperature with increasing T_c, suggesting the more perfect crystallites formed at higher T_c. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Melting behavior,isothermal and nonisothermal crystallization kinetics of nylon 1111

The isothermal and nonisothermal crystallization kinetics of nylon 1111 was extensively studied using differential scanning calorimetry (DSC). The equilibrium melting temperature of nylon 1111 was determined to be 188°C. In this article, the Avrami equation was used to describe the isothermal crystallization behavior of nylon 1111. On the basis of the DSC results, the Avrami exponent, n, was determined to be around 3 during the isothermal crystallization process. Nonisothermal crystallization was analyzed using both the Avrami equation as modified by Jeziorny and an equation suggested by Mo. The larger value of the Avrami exponent, n, during the nonisothermal crystallization process indicates that the development of nucleation and crystal growth are more complicated during the nonisothermal crystallization for nylon 1111, and that the nucleation mode might simultaneously include both homogeneous and heterogeneous nucleations. The isothermal and nonisothermal crystallization activation energies of nylon 1111 were determined to be ?132 kJ/mol and ?121 kJ/mol using the Arrhenius equation and the Kissinger method, respectively. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Crystallization and melting behavior of HDPE in HDPE/teak wood flour composites and their correlation with mechanical properties

The nonisothermal crystallization behavior and melting characteristics of high‐density polyethylene (HDPE) in HDPE/teak wood flour (TWF) composites have been studied by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) methods. Composite formulations of HDPE/TWF were prepared by varying the volume fraction (?_f) of TWF (filler) from 0 to 0.32. Various crystallization parameters evaluated from the DSC exotherms were used to study the nonisothermal crystallization behavior. The melting temperature (T_m) and crystallization temperature (T_p) of the composites were slightly higher than those of the neat HDPE. The enthalpy of melting and crystallization (%) decrease with increase in the filler content. Because the nonpolar polymer HDPE and polar TWF are incompatible, to enhance the phase interaction maleic anhydride grafted HDPE (HDPE‐g‐MAH) was used as a coupling agent. A shift in the crystallization and melting peak temperatures toward the higher temperature side and broadening of the crystallization peak (increased crystallite size distribution) were observed whereas crystallinity of HDPE declines with increase in ?_f in both DSC and WAXD. Linear correlations were obtained between crystallization parameters and tensile and impact strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystal morphology and crystallization kinetics of polyamide‐11/clay nanocomposites

Polyamide‐11 (PA11)/clay nanocomposites were prepared by in situ intercalative polymerization. The crystal morphology and crystallization kinetics of these nanocomposites were investigated via polarized light microscopy (PLM), small‐angle laser scattering (SALS) and differential scanning calorimetry (DSC). PA‐11 can crystallize into well‐formed spherulites, while only very tiny crystallites were observed by PLM and SALS for the nanocomposites. Both isothermal and non‐isothermal crystallization methods were employed to investigate the crystallization kinetics by DSC. Both techniques showed an increased crystallization rate with the addition of clay. However, the Avrami exponent decreased with the addition of clay in isothermal crystallization but showed a wide range of values depending on the cooling rate in the non‐isothermal crystallization. The changes in crystal morphology and crystallization kinetics can be understood as being due to the ‘supernucleating’ effect of the nanodispersed clay layers. Copyright © 2004 Society of Chemical Industry