Flash DSC crystallization study for blown film grade bimodal HDPE resins. I. Isothermal kinetics and its application of the blown film modeling

Isothermal ultra‐cooling crystallization tests were conducted on three blown film grade bimodal HDPE resins using an ultrafast scanning calorimeter, the Flash DSC. Isothermal tests were performed to study the regime transition, the thermal nucleation and the spherulitical growth using the Hoffman‐Lauritzen theory in a range between 90 °C and 116 °C. Temperature profile estimations using such data were in good agreement with actual blown film process data. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2425–2431     

The crystallization of polypropylene with reduced density of entanglements

The crystallization of polypropylene with different density of macromolecular entanglements was studied in isothermal and non‐isothermal conditions. The growth rate of spherulites increased with reduced concentration of entanglements. Reduction of entanglements shifted the temperature of transition between Regimes II and III, which means that more regular growth of crystals was possible at lower temperature. The range of temperatures at which polypropylene cavitated in regions of melt occluded by spherulites was limited to 137–139°C, with weak dependence on entanglements density. DSC studies showed that isothermal crystallization is faster in less entangled polymers, however the crystallinity degree and long period of structure (by SAXS) were similar for studied materials. When the crystallization was completed during fast cooling, the differences between individual samples were more significant. The partial disentangling, overcoming some limitation for movements of macromolecules, made possible easier crystallization, even at low temperature of Regime III. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 748–756     

Isothermal and nonisothermal crystallization kinetics of poly(propylene terephthalate)

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

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

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

Crystallization kinetics and morphology of poly(butylene succinate‐co‐adipate)

The crystallization kinetics of biodegradable poly(butylene succinate‐co‐adipate) (PBS/A) copolyester was investigated by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The Avrami and Ozawa equations were used to analyze the isothermal and nonisothermal crystallization kinetics, respectively. By using wide‐angle X‐ray diffraction (WAXD), PBS/A was identified to have the same crystal structure with that of PBS. The spherulitic growth rates of PBS/A measured in isothermal conditions are very well comparable with those measured by nonisothermal procedures (cooling rates ranged from 0.5 to 15 °C/min). The kinetic data were examined with the Hoffman–Lauritzen nucleation theory. The observed spherulites of PBS/A with different shapes and textures strongly depend on the crystallization temperatures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3231–3241, 2005     

Quiescent crystallization of polypropylene: Experiments and modeling

The quiescent crystallization of several polypropylenes (PPs) was examined using Differential Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). The half‐times of crystallization were obtained from the DSC thermographs employing the Avrami/Nakamura equation to fit and predict crystallization kinetics under isothermal and nonisothermal conditions. The induction times under nonisothermal conditions were estimated from isothermal crystallization data and used in conjunction with the Nakamura model in order to capture the crystallization behavior of the studied PPs. The Avrami/Nakamura model is found to fit and predict the nonisothermal crystallization data of the various PPs well over a range of cooling rates supporting its use in the simulation of polymer processes of industrial relevance. POM was used in line with parallel plate rheometry (Anton Paar, MCR 502) under no flow conditions to study the shape and growth rate of crystals of various PP resins at different temperatures or cooling rates. The growth rate of crystals is impeded exponentially with increase of temperature. The various PP resins of different molecular architecture have shown different nucleation and growth rate characteristics behavior under similar processing conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1259–1275     

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

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

CO2‐delayed crystallization of isotactic polypropylene: A kinetic study

The effect of CO₂ on the nonisothermal crystallization of isotactic polypropylene (iPP) was studied with high‐pressure differential scanning calorimetry at cooling rates of 0.2–5 °C/min. CO₂ significantly delayed the melt crystallization of iPP, and both the crystallization temperature and the heat of crystallization decreased with increasing CO₂ pressure. The crystallization rate of iPP, as characterized by the half‐time, was also prolonged by the presence of CO₂. With a modified Ozawa model developed by Seo, the Avrami crystallization exponent n of iPP was calculated. This value was depressed by the addition of CO₂ and was strongly dependent on the CO₂ pressure at low cooling rates. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1518–1525, 2003     

Miscibility and crystallization behavior of PBT/epoxy blends

The miscibility and the isothermal crystallization kinetics for PBT/Epoxy blends have been studied by using differential scanning calorimetry, and several kinetic analyses have been used to describe the crystallization process. The Avrami exponents n were obtained for PBT/Epoxy blends. An addition of small amount of epoxy resin (3%) leads to an increase in the number of effective nuclei, thus resulting in an increase in crystallization rate and a stronger trend of instantaneous three‐dimensional growth. For isothermal crystallization, crystallization parameter analysis showed that epoxy particles could act as effective nucleating agents, accelerating the crystallization of PBT component in the PBT/Epoxy blends. The Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT/Epoxy 97/3 had lower nucleation constant K_g than 100/0, 93/7, and 90/10 PBT/Epoxy blends. Analysis of the crystallization data of PBT/Epoxy blends showed that crystallization occurs in regime II. The fold surface free energy, σ_e = 101.7–58.0 × 10^?3 J/m², and work of chain folding, q = 5.79–3.30 kcal/mol, were determined. The equilibrium melting point depressions of PBT/Epoxy blends were observed and the Flory–Huggins interaction parameters were obtained. It indicated that these blends were thermodynamically miscible in the melt. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1320–1330, 2006     

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

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

Isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone)

The isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone) are investigated by differential scanning calorimetry over two temperature regions. The Avrami equation describes the primary stage of isothermal crystallization kinetics with the exponent n ≈ 2 for both melt and cold crystallization. With the Hoffman–Weeks method, the equilibrium melting point is estimated to be 406 °C. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter (K_g) of the isothermal melt and cold crystallization is estimated. In addition, the K_g value of the isothermal melt crystallization is compared to those of the other poly(aryl ether ketone)s. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1992–1997, 2000     

Transient and athermal effects in the crystallization of polymers. II. Nonisothermal crystallization

Nonisothermal crystallization of several polymers was investigated with differential scanning calorimetry and optical microscopy. The results indicated that as in the case of isothermal processes, crystallization starts with nucleation on noncompletely melted crystalline residues. It is assumed that if the crystalline residues are subcritical at melting temperatures, they can become stable by an athermal mechanism during cooling. There is also some contribution of nucleation on heterogeneities. The next mechanism of nucleation is a classical homogeneous process occurring by thermal fluctuations. The results showed the non‐steady‐state character of the nonisothermal crystallization of polymers. In the investigated range of cooling rates, the non‐steady‐state character of nonisothermal crystallization of polymers is dominated by the transient thermal effects. In the range of high temperatures, the transient homogeneous nucleation can be interpreted with the Ziabicki model, and the steady‐state rate determined from nonisothermal experiments coincides with the rate determined in isothermal crystallization. The athermal nucleation occurring at the beginning of crystallization from noncompletely melted aggregates seems to be independent of the applied cooling rate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 68–79, 2003     

Isothermal and nonisothermal crystallization kinetics of irradiated nylon 1212

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

Nonisothermal crystallization kinetics of polypropylene/montmorillonite nanocomposites

The nonisothermal crystallization kinetics of poly(propylene) (PP) and poly(propylene)/organic‐montmorillonite (PP/Mont) nanocomposite were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by previous research was used to describe the nonisothermal crystallization process of PP and PP/Mont nanocomposite very well. The values of half‐time and Z_c showed that the crystallization rate increased with increasing cooling rates for both PP and PP/Mont nanocomposite, but the crystallization rate of PP/Mont nanocomposite was faster than that of PP at a given cooling rate. The activation energies were estimated by the Kissinger method, and the values were 189.4 and 155.7 kJ/mol for PP and PP/Mont nanocomposite, respectively. PP/Mont nanocomposite could be easily fabricated as original PP, although the addition of organomontmorillonite might accelerate the overall nonisothermal crystallization process. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 408–414, 2002; DOI 10.1002/polb.10101     

Nonisothermal crystallization kinetics of poly (phenylene sulphide) in composites with a liquid crystalline polymer

The article deals with the melting and nonisothermal crystallization behavior of neat poly (phenylene sulphide) (PPS) and its composites with a thermotropic liquid crystalline polymer (TLCP)—Vectra A950, prepared by melt mixing and probed by differential scanning calorimetry. The various macrokinetic models namely, the Ozawa, the modified Avrami, the Tobin, and the Mo models were applied to describe the crystallization kinetics under nonisothermal conditions. The kinetic crystallizabilty of PPS/TLCP composites calculated using the approach of Ziabicki varies depending on these two composite composition‐induced effects. Similarly Mo model predicts that to obtain a higher degree of crystallizabilty for PPS/TLCP composites, a higher cooling rate should be used. The effective energy barrier based on the differential isoconversional method of Friedman is found to be an increasing function of relative degree of melt conversion. The effect is explained in terms of nucleation theory proposed by Wunderlich to crystallization of polymers. The Lauritzen–Hoffman parameters are estimated using G = 1/t_0.5 effective activation energy equation proposed by Vyazovkin and Sbirrazzuoli. The K_g values estimated from latter equations are more comparable with values obtained using isothermal crystallization data than 1/t_0.5 method. Furthermore, the kinetic analysis using this equation shows a regime transition from regime II to regime III for 100/00, 90/10, 80/20 PPS/TLCP composites, basically attributed to reduced mobility of PPS chains in composites. This regime II to III transition is accompanied by a morphological transition from defective spherulitic sheaf‐like structures to ordered sheaf‐like structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1070–1100, 2010     

Crystallization kinetics study of poly(L‐lactic acid)/carbon nanotubes nanocomposites

Effects of carbon nanotubes (CNT) on the isothermal crystallization kinetics of poly(L ‐lactic acid) (PLLA) were quantitatively investigated using the Avrami equation and the secondary nucleation theory of Lauritzen and Hoffman. CNT via grafting modification with PLLA could well disperse in the PLLA matrix and give significantly enhanced crystallization rate and crystallinity of PLLA as analyzed by differential scanning calorimetry and polarized optical microscopy. Analysis of isothermal crystallization kinetics using the Avrami equation demonstrated that CNT significantly enhanced the bulk crystallization of PLLA. Analysis of spherulite growth kinetics using the secondary nucleation theory of Lauritzen and Hoffman found that CNT could expand the temperature range of the crystallization regime III of PLLA. Values of the nucleation constant (K_g) in crystallization regimes III and II of PLLA both increased with increasing CNT contents. The K_g III/K_g II ratios were found to be close to the theoretical value 2 but were not clearly found to depend on the CNT contents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 983–989, 2010     

Crystallinity of poly(3‐hexylthiophene) in thin films determined by fast scanning calorimetry

Using fast scanning calorimetry, we determined the crystallinity of thin films of poly(3‐hexylthiophene) crystallized from the melt from measurements of the specific melting enthalpy. A broad range of film thicknesses from 10 µm down to 26 nm was covered. The sample mass was determined from measurements of the specific heat capacity in the molten state allowing a quantitative analysis of the heat flow data. Films with a thickness 400 nm slowly cooled from the melt showed the same crystallinity as bulk samples measured with conventional DSC. Below 350 nm the melting enthalpy decreased strongly. We assign this strongly reduced crystallinity to the restricted crystallization kinetics originating from hindered spherulitic growth under thin film confinement. A higher crystallinity could be partially regained by extended isothermal crystallization at elevated temperatures. Much faster cooling, with rates above about 100 Ks^?1 led to a partial suppression of crystallization even for thick films. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1791–1801     

Crystallization kinetics of a thermotropic liquid crystalline polyimide derived from 1,3-bis[4-(4′-aminophenoxy) cumyl] benzene

We have studied the nonisothermal and isothermal crystallization kinetics of an aromatic thermotropic liquid crystalline polyimide synthesized from 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) and 1,3-bis[4-(4′-aminophenoxy) cumyl] benzene (BACB) by means of differential scanning calorimetry (DSC). Polarized light microscopy (PLM) and wide-angle X-ray diffraction (WAXD) results confirm that this polyimide exhibits a smectic texture. Nonisothermal crystallization showed two strong and one weak exothermic peaks during cooling. The phase transition from isotropic melt to liquid crystalline state is extremely fast which completes in several seconds. The mesophase transition has a small Avrami parameter, n, of approximate 1. The isothermal crystallization of 253–258°C has been examined. The average value n is about 2.6 and the temperature-dependent rate constant k changes about two orders of magnitude in the crystallization temperature range of 6°C. The slope of ln k versus 1/(T_cΔT) is calculated to be −2.4 × 10⁵, which suggests nucleation control, via primary and/or secondary nucleation for the crystallization process. During the annealing process, a new phase (slow transition) is induced, which grows gradually with annealing time. At lower annealing temperatures (220–230°C), the slow transition process seems not to be influenced by the crystals formed during cooling process and its Avrami parameter n is ca. 0.3–0.4. However, the slow transition was hindered by the crystals formed during cooling process when annealed at higher temperature (230–240°C). © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1679–1694, 1998     

Nonisothermal crystallization kinetics of biodegradable poly(butylene succinate‐co‐propylene succinate)s

Poly(butylene succinate) (PBSu) and two poly(butylene succinate‐co‐propylene succinate)s were synthesized via the direct polycondensation reaction. The copolyesters were characterized as having 7.0.and 11.5 mol % propylene succinate (PS) units, respectively, by ¹H NMR. A differential scanning calorimeter (DSC) and a polarized light microscope (PLM) adopted to study the nonisothermal crystallization of these polyesters at a cooling rate of 1, 2, 3, 5, 6, and 10 °C/min. Morphology and the isothermal growth rates of spherulites under PLM experiments were monitored and obtained by curve‐fitting. These continuous rate data were analyzed with the Lauritzen?Hoffman equation. A transition of regime II → III was found at 95.6, 84.4, and 77.3 °C for PBSu, PBPSu 95/5, and PBPSu 90/10, respectively. DSC exothermic curves show that all of the nonisothermal crystallization occurred in regime III. DSC data were analyzed using modified Avrami, Ozawa, Mo, Friedman, and Vyazovkin equations. All the results of PLM and DSC measurements indicate that incorporation of minor PS units into PBSu markedly inhibits the crystallization of the resulting polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1299–1308, 2010     

Crossover behavior in crystal growth rate from n‐alkane to polyethylene

A crystal growth rate equation, parameterized from molecular dynamics simulations of n‐alkanes, is compared to recent experiments on growth rates for polyethylene at high undercooling. The analysis reveals that the growth rate of alkanes and polyethylene can both be described by the same relationship. The appropriate relaxation time is used to describe the kinetic barrier to crystallization. For chains shorter than the entanglement length, this is the Rouse time. For chains longer than the entanglement molecular weight, kinetic limitations are modeled by the local relaxation of an entangled segment at the interface. This model supports a different mechanism for fast crystal growth at high undercooling than that usually inferred from slow growth data near the melting temperature. Use of the crystal growth rate model is illustrated for polyethylene crystallizing under conditions of slow cooling and fast cooling. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2468–2473, 2005