Nonisothermal crystallization kinetics of linear bimodal–polyethylene (LBPE) and LBPE/low‐density polyethylene blends

Nonisothermal crystallization kinetics of linear bimodal–polyethylene (LBPE) and the blends of LBPE/low‐density polyethylene (LDPE) were studied using DSC at various scanning rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of LBPE and LBPE/LDPE blends. The theory of Ozawa was also used to analyze the LBPE DSC data. Kinetic parameters such as, for example, the Avrami exponent (n), the kinetic crystallization rate constant (Z_c), the crystallization peak temperature (T_p), and the half‐time of crystallization (t_1/2) were determined at various scanning rates. The appearance of double melting peaks and double crystallization peaks in the heating and cooling DSC curves of LBPE/LDPE blends indicated that LBPE and LDPE could crystallize, respectively. As a result of these studies, the Z_c of LBPE increases with the increase of cooling rates and the T_p of LBPE for LBPE/LDPE blends first increases with increasing LBPE content in the blends and reaches its maximum, then decreases as the LBPE content further increases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2431–2437, 2003     

Melting behavior and isothermal crystallization kinetics of PP/mLLDPE blends

The melting/crystallization behavior and isothermal crystallization kinetics of polypropylene (PP)/metallocene-catalyzed linear low density polyethylene (mLLDPE) blends were studied with differential scanning calorimetry (DSC). The results showed that PP and mLLDPE are partially miscible and interactions mainly exist between the mLLDPE chains and the PE segments in PP molecules. The isothermal crystallization kinetics of the blends was described with the Avrami equation. Values of the Avrami exponent indicated that crystallization nucleation of the blends is heterogeneous, the growth of spherulites is almost three-dimensional, and the crystallization mechanism of PP is not affected much by mLLDPE. The Avrami exponents of the blends are higher than that of pure PP, showing that the mLLDPE helps PP to form perfect spherulites. The crystallization rates of PP are decreased by mLLDPE because the crystallization temperature of PP was decreased by addition of mLLDPE and consequently the supercooling of the PP was correspondingly lower. The crystallization activation energy was estimated by the Friedman equation, and the result showed that the activation energy increased by a small degree by addition of mLLDPE, but changed little with increasing content of mLLDPE in the blends. The nucleation constant (K _g) was determined by the Hoffman–Lauritzen theory. Supported by the Science Foundation of Hebei University (2006Q13).     

Melting behavior,isothermal and nonisothermal crystallization kinetics of PP/mLLDPE blends

Melting behavior, nonisothermal crystallization and isothermal crystallization kinetics of polypropylene (PP) with metallocene‐catalyzed linear low density polyethylene (mLLDPE) were studied by differential scanning calorimetry (DSC). The results show that PP and mLLDPE were partially miscible. The Avrami analysis was applied to analyze the nonisothermal and isothermal crystallization kinetics of the blends, the Mo Z.S. method was used to take a comparison in nonisothermal kinetics. Values of Avrami exponent indicate the crystallization nucleations of both pure PP and PP in the blends were heterogeneous, the growth of spherulites is tridimensional and the spherulites in the blends were more perfect than that in pure PP. The crystallization activation energy was estimated by Kissinger method and Arrhenius equation and the two methods draw similar results. The mLLDPE increased the crystallization rate of PP in nonisothermal crystallization process and decreased it in isothermal process. The results from nonisothermal crystallization and isothermal crystallization kinetics were not consistent because the two processes were completely different. Addition of minor mLLDPE phase favors to increase the overall crystallinity of PP, showing the mLLDPE entered the PP crystals. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nonisothermal crystallization,melting behavior,and morphology of PP/EPPE blends

Nonisothermal crystallization, melting behavior, and morphology of polypropylene (PP)/Easy processing polyethylene (EPPE) blends were studied by differential scanning alorimetry (DSC) and scanning electron microscope (SEM). The results showed that PP and EPPE are miscible, and there is no obvious phase separation in microphotographs of the blends. The modified Avrami analysis, Ozawa equation, and also Mo Z.S. method were used to analyze the nonisothermal crystallization kinetics of the blends. Values of Avrami exponent indicated the crystallization nucleation of the blends is homogeneous, the growth of spherulites is tridimensional, and crystallization mechanism of PP is not affected much by EPPE. The crystallization activation energy was estimated by Kissinger method. The result obtained from modified Avrami analysis, Mo Z.S. method, and Kissinger methods were well agreed. The addition of minor EPPE phase favored to decrease the overall crystallization rate of PP, showing some dilution effect of EPPE on PP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study on the nonisothermal crystallization process of mLLDPE/EVA blends using FTIR micro‐spectroscopy

The nonisothermal crystallization process has been investigated by Fourier transform infrared (FTIR) micro‐spectroscopy for the 40/60 wt % blends of metallocene linear low density polyethylene (m‐LLDPE) and ethylene/vinyl acetate copolymer (EVA) at the molecular level. In the cooling process, thermal spectra of mLLDPE/EVA blends were collected between 150°C and 67°C at 1°C interval. According to the van't Hoff equation at constant pressure, the changes of absorbance ratio corresponding to high and low vibrational states were calculated; hereby, apparent enthalpy differences of vibration energy states transformation (?H_v) of characteristic groups could be obtained. Combining with DSC analysis, two exothermal peaks were examined in the crystallization process, corresponding to mLLDPE‐rich and EVA‐rich domains, respectively; while in comparison of the ?H_v values of various characteristic groups corresponding to the two exothermal peaks, the bending vibrational mode of methylene groups has been found to make a prominent contribution to the movement and regular arrangement of mLLDPE and EVA chain segments towards each rich domain in the crystallizing process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 261–267, 2005     

Nonisothermal crystallization kinetics of poly(ethylene terephthalate) and poly(methyl methacrylate) blends

The nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA) blends were studied. Four compositions of the blends [PET 25/PMMA 75, PET 50/PMMA 50, PET 75/PMMA 25, and PET 90/PMMA 10 (w/w)] were melt‐blended for 1 h in a batch reactor at 275°C. Crystallization peaks of virgin PET and the four blends were obtained at cooling rates of 1°C, 2.5°C, 5°C, 10°C, 20°C, and 30°C/min, using a differential scanning calorimeter (DSC). A modified Avrami equation was used to analyze the nonisothermal data obtained. The Avrami parameters n, which denotes the nature of the crystal growth, and Z_t, which represents the rate of crystallization, were evaluated for the four blends. The crystallization half‐life (t_½) and maximum crystallization (t_max) times also were evaluated. The four blends and virgin polymers were characterized using a thermogravimetric analyzer (TGA), a wide‐angle X‐ray diffraction unit (WAXD), and a scanning electron microscope (SEM). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3565–3571, 2006     

Effects of size and shape of dispersed poly(butylene terephthalate) on isothermal crystallization kinetics and morphology of poly(lactic acid) blends

The isothermal crystallization kinetics and morphology of the poly(lactic acid) (PLA) blends containing three different sizes of both spherical and fibrous poly(butylene terephthalate) (PBT) domains have been comparatively investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The dynamic DSC measurement reveals that PBT domains significantly increase the degree of crystallinity of the PLA. Furthermore, the Avrami model is employed to evaluate the crystallization kinetics under isothermal conditions and it is found that PBT acts as nucleating agent, leading to a high overall crystallization rate constant k and shortened crystallization half time t_1/2. Furthermore, the crystallization rate of PLA is promoted with the incorporation of PBT with a large specific surface area. The average Avrami index n of all samples lies within the range of 3.3 ? 4.0, suggesting that morphologies of PBT do not affect the nucleation mechanism; however, the depression of equilibrium melting temperature in the blends ascribes the reductions of perfectness and size of the PLA crystallites. Besides, the nucleation of PLA crystallites around PBT fibers is probably faster than those around PBT spheres because the PBT chains oriented at the fiber surface as a result of flow‐induced crystallization during melt stretching may serve as the primary nuclei for PLA chains to drastically crystallize at the fiber surface. POLYM. ENG. SCI., 56:258–268, 2016. © 2015 Society of Plastics Engineers     

Isothermal crystallization kinetics and melting behavior of in situ compatibilized polyamide 6/Polyethylene-octene blends

We developed in situ compatibilization technology to improve the compatibility between polyamide 6 (PA 6) and polyethylene-octene (POE). In the present work, we investigated the isothermal crystallization and melting behavior of PA 6/POE blends using differential scanning calorimetry (DSC). All specimens exhibited double melting peaks at lower temperature and single melting peaks at higher temperature. The Avrami exponent and equilibrium melting temperature were obtained by analysis of DSC experimental data using the Avrami equation and Hoffman-Weeks theory, respectively. It has demonstrated that the crystallization model of PA 6 for all specimens might be a mixture with two-dimensional, circular, three-dimensional growth with thermal nucleation. We further calculated the nucleation parameter (K _g ) from the obtained crystallization kinetics data using Lauritzen-Hoffmann equation. It was found that the K _g values of the compatibilized PA 6 were lower than that of pure PA 6 whereas increased with the increase of POE content, which was related to the better dispersion of POE and the interaction between PA 6 and the in situ formed POE-g-MAH. Additionally, the spherulite morphology was observed by polarized optical microscopy (POM).     

Melting,crystallization behaviors,and nonisothermal crystallization kinetics of PET/PTT/PBT ternary blends

The melting, crystallization behaviors, and nonisothermal crystallization kinetics of the ternary blends composed of poly(ethylene terephthalate), poly(trimethylene terephthalate) (PTT) and poly(buthylene terephthalate) (PBT) were studied with differential scanning calorimeter (DSC). PBT content in all ternary blends was settled invariably to be one‐third, which improved the melt‐crystallization temperature of the ternary blends. All of the blend compositions in amorphous state were miscible as evidenced by a single, composition‐dependent glass transition temperature (T_g) observed in DSC curves. DSC melting thermograms of different blends showed different multiple melting and crystallization peaks because of their various polymer contents. During melt‐crystallization process, three components in blends crystallized simultaneously to form mixed crystals or separated crystals depending upon their content ratio. The Avrami equation modified by Jeziorny and the Ozawa theory were employed to describe the nonisothermal crystallization process of two selected ternary blends. The results spoke that the Avrami equation was successful in describing the nonisothermal crystallization process of the ternary blends. The values of the t_1/2 and the parameters Z_c showed that the crystallization rate of the ternary blends with more poly(ethylene terephthalate) content was faster than that with the lesser one at a given cooling rate. The crystal morphology of the five ternary blends investigated by polarized optical microscopy (POM) showed different size and distortional Maltese crosses or light spots when the PTT or poly(ethylene terephthalate) component varied, suggesting that the more the PTT content, the larger crystallites formed in ternary blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Crystallization and melting behavior of partially miscible six‐armed poly(l‐lactic acid)/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) blends

The crystallization kinetics and spherulitic morphology of six‐armed poly(L‐lactic acid) (6a‐PLLA)/poly(3‐hydroxybutyrate‐co?3‐hydroxyvalerate) (PHBV) crystalline/crystalline partially miscible blends were investigated with differential scanning calorimetry and polarized optical microscopy in this study. Avrami analysis was used to describe the isothermal crystallization process of the neat polymers and their blends. The results suggest that blending had a complex influence on the crystallization rate of the two components during the isothermal crystallization process. Also, the crystallization mechanism of these blends was different from that of the neat polymers. The melting behavior of these blends was also studied after crystallization at various crystallization temperatures. The crystallization of PHBV at 125°C was difficult, so no melting peaks were found. However, it was interesting to find a weak melting peak, which arose from the PHBV component for the 20/80 6a‐PLLA/PHBV blend after crystallization at 125°C, and it is discussed in detail. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42548.     

乙烯-醋酸乙烯酯共聚物对茂金属聚乙烯的改性研究

以添加不同比例的茂金属聚乙烯 (mLLDPE) /乙烯 醋酸乙烯酯 (EVA)共混物为研究对象 ,考察了EVA含量对mLLDPE/EVA共混物的力学性能、热性能、流变性能、动态力学性能和形态结构的影响。研究结果表明 ,EVA添加到mLLDPE中 ,增加了mLLDPE的剪切敏感度、降低了mLLDPE的熔融粘度、改善了mLLDPE的流动性和加工性 ;在一定的添加比例范围内mLLDPE和EVA具有很好的相容性 ,可以在改善mLLDPE加工性能、引入极性基团的同时又保持与纯mLLDPE相近的力学性能 ,但会导致共混物材料的刚性下降 ,柔性增加。热分析数据说明 ,mLLDPE/EVA共混体系中 ,在EVA含量较小时共混物存在大量共晶 ,与mLLDPE有很好的相容性 ,无论是熔融曲线还是降温曲线都只出现一个峰。当EVA含量增大时 ,mLLDPE/EVA共混物出现相分离 ,曲线出现双峰 ,但两峰值呈现靠近趋势 ,预示mLLDPE/EVA共混物中仍存在少量共结晶     

Effect of cooling rate on crystallization behavior of milk fat fraction/sunflower oil blends

The effect of cooling rate (slow: 0.1°C/min; fast: 5.5°C/min) on the crystallization kinetics of blends of a highmelting milk fat fraction and sunflower oil (SFO) was investigated by pulsed NMR and DSC. For slow cooling rate, the majority of crystallization had already occurred by the time the set crystallization temperature had been reached. For fast cooling rate, crystallization started after the samples reached the selected crystallization temperature, and the solid fat content curves were hyperbolic. DSC scans showed that at slow cooling rates, molecular organization took place as the sample was being cooled to crystallization temperature and there was fractionation of solid solutions. For fast cooling rates, more compound crystal formation occurred and no fractionation was observed in many cases. The Avrami kinetic model was used to obtain the parameters k _n and n for the samples that were rapidly cooled. The parameter k _n decreased as supercooling decreased (higher crystallization temperature) and decreased with increasing SFO content. The Avrami exponent n was less than 1 for high supercoolings and close to 2 for low supercoolings, but was not affected by SFO content.     

Crystallization kinetics of a PEEK/LCP blend

The crystallization kinetics of a polyetheretherketone (PEEK)/liquid crystalline polymer (LCP) blend was studied by using differential scanning calorimetry. Nonisothermal runnings were performed on heating and on cooling at different rates. Isothermal crystallization experiments at 315, 312, 310, and 307°C, from the melt state (380°C) were performed in order to calculate the Avrami parameters n and k and the fold surface free energy, σ_e. Polarized light optical micrographs were also obtained to confirm the Avrami predictions. It was observed that the LCP retarded the PEEK crystallization process and that the PEEK melting temperature decreased with the amount of LCP, but the LCP melting temperature increased with the amount of PEEK. Probably the PEEK improves the perfection of the LCP crystalline domains. A spherulitic morphology in pure PEEK and its blends was predicted by the Avrami analysis; however this morphology was only observed for pure PEEK and for the 80/20 composition. The other compositions presented a droplet and fibrillar-like morphology. The overall crystallization rate was observed to decrease with the crystallization temperature for all compositions. Finally, σ_e was found to decrease with the increase of LCP in the blends, having unrealistic negative values. Thus, calculations were made assuming σ_e constant at all compositions. It was observed that δ, the interfacial lateral free energy, decreased but still remained positive. It was concluded that in these blends neither σ_e nor σ could be considered constant. © 1995 John Wiley & Sons, Inc.     

Nonisothermal crystallization kinetics of ethylene–butene copolymer/low‐density polyethylene blends

Nonisothermal crystallization kinetics of the blends of three ethylene–butene copolymers with LDPE was studied using differential scanning calorimetry (DSC) and kinetic parameters such as the Avrami exponent and the kinetic crystallization rate (Z_c) were determined. It was found that the pure components and the blends have similar Avrami exponents, indicating the same crystallization mechanism. However, the crystallization rate of the blends was greatly influenced by LDPE. The Z_c of all the blends first increases with increasing LDPE content in the blends and reaches its maximum, then descends as the LDPE content further increases. The crystallization rate also depends on the short‐chain branching distribution (SCBD) of the ethylene–butene copolymers. The Z_c of the pure component with a broad SCBD is smaller, but its blends have a larger crystallization rate due to losing highly branched fractions after blending with LDPE. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 123–129, 2001     

Structure,nonisothermal crystallization behavior,and thermal property study of poly(trimethylene terephthalate)/cellulose acetate butyrate blends

Poly(trimethylene terephthalate) (PTT)/cellulose acetate butyrate (CAB) blends were prepared by melting blending through a co‐rotating twin screw extruder. The structures of PTT/CAB blends were characterized by scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectra, and the results showed that CAB phase dispersed homogeneously in the PTT matrix and there existed evident phase interface between PTT and CAB. The nonisothermal crystallization behavior was investigated by differential scanning calorimetry (DSC) and was described with modified Avrami equation of Jeziorny and Mo equation, respectively. The results indicated that the half crystallization time (t_{1/ 2}) is much shorter, the nonisothermal crystallization kinetic rate constant (Z_c) is bigger at a given cooling rate, the cooling rate [F_z(T)] is smaller at a given relative crystallinity (X _t) of PTT/CAB blends than those of PTT, which proved that the addition of CAB improved the crystallization of PTT and made PTT crystallize more perfect and faster than pure PTT. In addition, thermogravimetric analysis (TGA) curves of PTT and PTT/CAB blends showed that effects of CAB content on the thermal decomposition of PTT/CAB blends were little. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Synthesis and characterization of monomer‐casting polyamide 6/polymethacrylic ionomer blends

Monomer‐casting polyamide 6 (MCPA6)/polymethacrylic ionomer blends were synthesized by the in situ anionic ring‐opening polymerization of ?‐caprolactam. The polymethacrylic ionomer used in this study was a copolymer of methyl methacrylate and sodium or zinc methacrylate. Because the polymethacrylic ionomer strongly interacted with polyamide 6 (PA6) chains, it influenced the alignment of the polyamide chains. The change in the degree of the order of hydrogen bonding in MCPA6 caused by the addition of the polymethacrylic ionomer was studied with Fourier transform infrared. The change in the interaction between PA6 chains was studied with rheological measurements. The influence of the polymethacrylic ionomer on the crystallization behavior of MCPA6 was also studied with differential scanning calorimetry. The isothermal crystallization and subsequent melting behavior were investigated at the designated temperature. The commonly used Avrami equation was used to fit the primary stage of the isothermal crystallization. The Avrami exponent (n) values were evaluated to be 2 < n < 3 for the neat MCPA6 and MCPA6/polymethacrylic ionomer blends. The polymethacrylic ionomer, acting as a stumbling‐block agent in the blends, decelerated the crystallization rate with the half‐time of crystallization increasing. The polymethacrylic ionomer made the molecular chains of MCPA6 more difficult to crystallize during the isothermal crystallization process. More less perfect crystals formed in the MCPA6/polymethacrylic ionomer blends because of the interaction between the MCPA6 molecular chains and polymethacrylic ionomer. The crystallinity of the blends was depressed by the addition of the polymethacrylic ionomer. The thermal stability was also studied with thermogravimetric analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nonisothermal crystallization kinetics of linear metallocene polyethylenes

The effect of weight‐average molecular weight (M_w) on the nonisothermal crystallization kinetics of linear metallocene polyethylene (m‐PE) was studied with modulated differential scanning calorimetry. Six linear m‐PEs of molecular weights in the range 122–934 kg/mol were prepared by gas‐phase polymerization. The cooling rate (R) was varied in the range 2–20°C/min, and it significantly affected the crystallization behavior. M_w had a weak influence on both the peak crystallization temperature and the crystallization onset temperature. All m‐PEs showed primary and secondary crystallizations. At both low and high R's, the crystallinity showed a significant drop (～ 30%) when M_w was increased from 122 to 934 kg/mol. At low R's (< 10°C/min), the rate parameters in the modified Avrami method [primary rate constant (k_R)] and Mo method [F(T)] of analyses agreed in suggesting that an increased M_w slowed the rate of crystallization. The M_w dependency of k_R followed the Arrhenius type (k_R = k_Roe²⁸¹/M_w, where k_Ro is a rate‐dependent constant). However, at higher R's, k_R approached a constant value. The order parameters obtained by the different methods of analysis (n and α) were independent of M_w, which suggests that the crystal type remained the same. Hoffman–Lauritzen theory was used for data analysis, and activation energy per segment showed a significant decrease, from 225.0 to 11.8 kJ/mol, when M_w was increased from 152 to 934 kg/mol. Finally, all methods of analysis suggested a significant effect of M_w on slowing the overall crystallization process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal properties and non‐isothermal crystallization behavior of poly(trimethylene terephthalate)/poly(lactic acid) blends

Thermal properties and non‐isothermal melt‐crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(lactic acid) (PLA) blends were investigated using differential scanning calorimetry and thermogravimetric analysis. The blends exhibit single and composition‐dependent glass transition temperature, cold crystallization temperature (T_cc) and melt crystallization peak temperature (T_mc) over the entire composition range, implying miscibility between the PLA and PTT components. The T_cc values of PTT/PLA blends increase, while the T_mc values decrease with increasing PLA content, suggesting that the cold crystallization and melt crystallization of PTT are retarded by the addition of PLA. The modified Avrami model is satisfactory in describing the non‐isothermal melt crystallization of the blends, whereas the Ozawa method is not applicable to the blends. The estimated Avrami exponent of the PTT/PLA blends ranges from 3.25 to 4.11, implying that the non‐isothermal crystallization follows a spherulitic‐like crystal growth combined with a complicated growth form. The PTT/PLA blends generally exhibit inferior crystallization rate and superior activation energy compared to pure PTT at the same cooling rate. The greater the PLA content in the PTT/PLA blends, the lower the crystallization rate and the higher the activation energy. Moreover, the introduction of PTT into PLA leads to an increase in the thermal stability behavior of the resulting PTT/PLA blends. Copyright © 2011 Society of Chemical Industry     

Kinetics and crystal structure of poly(lactic acid) crystallized nonisothermally: Effect of plasticizer and nucleating agent

The kinetics of neat poly(lactic acid) (PLA) and its composites with triphenyl phosphate (TPP) and/or talc crystallized nonisothermally at different cooling rates of 1, 2.5, 5, 7.5, and 10°C/min was analyzed by differential scanning calorimetry and described by Avrami equation and combined Avrami‐Ozawa equation. The results showed that talc acted as PLA nucleating agent accelerated crystallization rate by decreasing the crystallization half‐time t_1/2 or rate parameter F(T), whereas TPP acted as PLA plasticizer decreased crystallization rate. For neat PLA and plasticized PLA, the average values of Avrami exponent n were almost close to each other, but added TPP decreased crystallization rate constant k. As for PLA composites with talc, the crystallization process was relatively complex, and was divided into three regimes. At a given cooling rate, the value of n₂ was almost larger than that that of n₁ or n₃, whereas the value of k₂ was less than that of k₁ or k₃. The effective activation energy ΔE_x calculated from Friedman formula increased with the increase of relative crystallinity and TPP content, whereas decreased with the presence of talc. Wide angle X‐ray diffraction verified that all samples crystallized nonisothermally in cooling rate range of 1–10°C/min form α‐form. POLYM. COMPOS., 31:2057–2068, 2010. © 2010 Society of Plastics Engineers