Thermal behaviour of polyethylene‐block‐poly(methyl methacrylate) block copolymer: effect of multiple heating and cooling rates versus mathematical artefact

The melting and crystallization behaviours of a polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer and a PE homopolymer were investigated using multiple heating and cooling rate differential scanning calorimetry (DSC) experiments, and modelling of the crystallization kinetics and lamellar thickness distribution. This new model was first validated applying literature and experimental data. The model‐predicted morphology (n = 3.2) closely matched the spherulitic morphology (n = 3), which was determined using polarized optical microscopy. For each experimental cooling rate, the model predicted diblock copolymer crystallinity that well matched the entire DSC crystallinity curve, notably for an Avrami–Erofeev index of n = 2; and apparent crystallization activation energy that hardly varied with the cooling rates used, relative crystallinity (α), and crystallization temperature or time. This disfavours the concept of variable activation energy. The use of the right crystallization model and parameter estimation algorithm is important for addressing the mathematical artefact. Under non‐isothermal cooling, the PE‐b‐PMMA diblock copolymer, as per the model prediction, crystallized without confinement (n ≠ 1), preserving the cylindrical structure. From the characteristic shapes of the crystallization function f(α(T)) versus 1/T and crystallization rate versus α plots, the resulting T_cmax and narrow α_max range can guide the search for an appropriate crystallization model. The overall treatment illustrated in this study is not restricted to a PE homopolymer and a PE‐b‐isotactic PMMA block copolymer. It can be generally applied to crystalline homopolymers and copolymers (alternating, random and block), as well as their blends. The block copolymers and blends can be crystalline–amorphous as well as crystalline–crystalline. © 2014 Society of Chemical Industry     

Thermal properties and non‐isothermal crystallization behavior of biodegradable poly(p‐dioxanone)/poly(vinyl alcohol) blends

Blends of two biodegradable semicrystalline polymers, poly(p‐dioxanone) (PPDO) and poly(vinyl alcohol) (PVA) were prepared with different compositions. The thermal stability, phase morphology and thermal behavior of the blends were studied by using thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). From the TGA data, it can be seen that the addition of PVA improves the thermal stability of PPDO. DSC analysis showed that the glass transition temperature (T_g) and the melting temperature (T_m) of PPDO in the blends were nearly constant and equal to the values for neat PPDO, thus suggesting that PPDO and PVA are immiscible. It was found from the SEM images that the blends were phase‐separated, which was consistent with the DSC results. Additionally, non‐isothermal crystallization under controlled cooling rates was explored, and the Ozawa theory was employed to describe the non‐isothermal crystallization kinetics. Copyright © 2006 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.     

Crystallization study on absorbable poly(p‐dioxanone) polymers by differential scanning calorimetry

An investigation was carried out on the crystallization behavior of p‐dioxanone polymers using differential scanning calorimetry (DSC). Kinetic analyses were performed on data collected primarily during isothermal crystallization. Isothermal data were treated within the framework of the classical Avrami equation. Using this approach, both the Avrami exponent, n, and the crystallization half‐time, t_1/2, were evaluated and their implications are discussed for each system studied. It is shown that a small change in the polymer's composition greatly affects the crystallization kinetics, as well as the crystallizability of the materials. Additionally, nonisothermal crystallization under controlled heating and cooling rates was explored. In the case of cooling from the melt, the Ozawa theory and the recently proposed Calculus method were employed to describe the nonisothermal crystallization kinetics. In view of our results, the validity of these two estimation techniques for determining important kinetic and morphological parameters is also discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 742–759, 2001     

Crystallization kinetics for simulation of processing of various polyesters

The approach to determine crystallization kinetic parameters based on the DSC nonisothermal crystallization experiments is applied to poly(butylene terephthalate) (PBT) and poly(ethylene‐2,6‐naphthalate) (PEN). The differential form of the Nakamura equation and master curve approach are used. The isothermal induction times are obtained from nonisothermal induction times according to the concept of induction time index. The correction of temperature lag between the DSC furnace and the sample is incorporated. The corrected nonisothermal crystallization kinetic data is shifted with respect to an arbitrarily chosen reference temperature to obtain the master curve. By fitting the obtained master curve with the Hoffman‐Lauritzen equation, the model parameters for the crystallization rate constant are obtained. The relative crystallinity measured at different cooling and heating rates is described by these model parameters. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2847–2855, 2006     

Crystallization and melting behavior of iPP studied by DSC

This article is a part of a study of model and bulk composites, based on isotactic polypropylene (i-PP) and glass (or carbon) fibers, produced from knitted textile preforms of hybrid yarns. First, we report the results on crystallization and fusion of textile-grade i-PP, used for the processing of hybrid yarns and the corresponding knitted fabrics. The kinetics of the crystallization process, in the dynamic and isothermal regime, was followed by DSC, and the results were analyzed by Avrami, Ozawa, and Harnisch-Muschik methods. Isothermal crystallization of i-PP was carried out at 388–400 K, and values for the Avrami exponent ranging from 1.93 to 4.39 were determined. The equilibrium melting temperature was determined by the Hoffman-Weeks method, and γ = 2.54 was found. Double melting peaks were observed both when the crystallization was performed at lower temperatures (isothermal regime) and at higher cooling rates (nonisothermal regime). A single melting peak appeared upon melting following isothermal crystallization at 400 K. The nonisothermal kinetics data showed that the peak crystallization temperature changes from 377 to 386 K as the cooling rate decreases from 20 to 3 K/min. Applying the Ozawa method, a value of the exponent n = 2.33 was determined, which is in agreement with the results for isothermal crystallization at 391–400 K. The Harnisch-Muschik approach was also applied to compare the results for n, and a similar trend in the results of isothermal and nonisothermal crystallization was found, due to the predominant homogeneous mechanism of nucleation at lower cooling rates (lower isothermal T_c) in spite of being heterogeneous at higher cooling rates (higher isothermal T_c). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 395–404, 1998     

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     

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.     

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

Melting behavior and crystallization kinetics of easy processing polyethylene (EPPE) and the blends of EPPE/mLLDPE were studied using differential scanning calorimetry at various crystallization temperature and cooling rates. The Avrami analysis was employed to describe the isothermal and nonisothermal crystallization process of pure polymers and their blends, and a method developed by Mo was applied for comparison. Kinetic parameters such as the Avrami exponent (n), the kinetic crystallization rate constant (k and k_c), the peak temperatures (T_p), and the half-time of crystallization (t_1/2), etc. were determined. The appearance of double melting peaks and the double crystallization peaks of the polymers showed that the main chain and the branches crystallize seperately, but the main chains of two polymers can crystallize together and mLLDPE act as nuclei while EPPE crystallizes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Non‐isothermal crystallization and multiple melting behavior of syndiotactic polystyrene—pre‐melting temperature effects

This work investigated how pre‐melting temperature (T_max) and cooling rate (C) affected the non‐isothermal melt crystallization, melting behavior and crystal structure of syndiotactic polystyrene (sPS) by using differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) techniques. Experimental results indicated that raising T_max or C decreased the crystallization peak temperature (T_p) and crystallization initiating temperature (T_i). The crystallization kinetics was analyzed through the Ozawa equation. Although the Ozawa exponent n and cooling function K(T) were determined for T_max = 340°C and T_max = 315°C specimens, for T_max = 290°C specimens, the Ozawa equation was not applicable. Activation energies for the non‐isothermal crystallization processes of different T_max specimens were estimated to be approximately 418 kJ/mol. As T_max was raised the nucleation rate of sPS became slower. The multiple melting peaks were associated with different polymorphs as well as recrystallized crystals that formed during heating scans. The percentage content of α polymorph formed in the crystals under various crystallization conditions was estimated through WAXD experiments.     

Cure kinetics and properties of epoxy/dicyanate blends

The cure behavior and properties of epoxy/dicyanate blends containing a stoichiometric amount of an amine curing agent for epoxilde groups were investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic and isothermal cure behavior of the blends. The cure rate of the blend increased with increasing dicyanate content. A second order autocatalytic reaction mechanism described the cure kinetics of the blends. The kinetic parameters were determined by fitting the dynamic DSC data to the model kinetic equation. The k₁₀ and E₁ values were mainly affected by the change of dicyanate content. The glass transition temperature of the blend decreased with increasing dicyanate content. The thermal decomposition characteristics of the blends were investigated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were used to investigate the mechanical properties of the blends. With increasing dicyanate content, the cure rate increased but the thermal and mechanical properties of the cured blends were not improved.     

Crystallization behavior and isothermal crystallization kinetics of PLLA blended with ionic liquid, 1‐butyl‐3‐methylimidazolium dibutylphosphate

The crystallization behavior and isothermal crystallization kinetics of neat poly(l ‐lactic acid) (PLLA) and PLLA blended with ionic liquid (IL), 1‐butyl‐3‐methylimidazolium dibutylphosphate, were researched by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X‐ray diffraction (WXRD). Similar to the non‐isothermal crystallization behavior of neat PLLA, when PLLA melt was cooled from 200 to 20°C at a cooling rate of 10°C min^?1, no crystallization peak was detected yet with the incorporation of IL. However, the glass transition temperature and cold crystallization temperature of PLLA gradually decreased with the increase of IL content. It can be attributed to the significant plasticizing effect of IL, which improved the chain mobility and cold crystallization ability of PLLA. Isothermal crystallization kinetics was also analyzed by DSC and described by Avrami equation. For neat PLLA and IL/PLLA blends, the Avrami exponent n was almost in the range of 2.5–3.0. It is found that t_1/2 reduced largely, and the crystallization rate constant k increased exponentially with the incorporation of IL. These results show that the IL could accelerate the overall crystallization rate of PLLA due to its plasticizing effect. In addition, the dependences of crystallization rate on crystallization temperature and IL content were discussed in detail according to the results obtained by DSC and POM measurements. It was verified by WXRD that the addition of IL could not change the crystal structure of PLLA matrix. All samples isothermally crystallized at 100°C formed the α‐form crystal. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41308.     

Crystallization kinetics and melting behavior of poly[(trimethylene terephthalate)‐co‐(29 mol % ethylene terephthalate)] copolyester

The copolyester was characterized as having 71 mol % trimethylene terephthalate units and 29 mol % ethylene terephthalate units in a random sequence according to the NMR spectra. Differential scanning calorimeter (DSC) was used to investigate the isothermal crystallization kinetics in the temperature range (T_c) from 130 to 170°C. The melting behavior after isothermal crystallization was studied using DSC and temperature‐modulated DSC by varying the T_c, the crystallization time, and the heating rate. The DSC thermograms and wide‐angle X‐ray diffraction patterns reveal that the complex melting behavior involves melting‐recrystallization‐remelting and different lamellar crystals. As the T_c increases, the contribution of recrystallization gradually falls and finally disappears. A Hoffman‐Weeks linear plot yields an equilibrium melting temperature of 198.7°C. The kinetic analysis of the growth rates of spherulites and the change in the morphology from regular to banded spherulites indicate that a regime II→III transition occurs at 148°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of molecular weight on crystallization and melting of poly(trimethylene terephthalate). 1: Isothermal and dynamic crystallization

The crystallization behavior of poly(trimethylene terephthalate) as a function of molecular weight was investigated under isothermal and dynamic cooling conditions using a differential scanning calorimeter (DSC) and polarized light optical microscopy (POM). THe overall rate of bulk crystallization increased with molecular weight. An Avrami analysis of the isothermal crystallization kinetics indicated that the crystallization rate constant increased with increasing molecular weight. The Avrami exponent, n, approached 2 and was nearly independent of both molecular weight and temperature. The modified Avrami analysis developed by Jeziorny and Ozawa was applied to the dynamic crystallization data. At the same cooling rate, higher molecular weight resulted in a narrower crystallization peak, higher onset crystallization temperature, and larger rate constant (Z_t)^1/n. Higher molecular weight resulted in larger cooling function of dynamic crystallization K(T) and lower Ozawa exponent m. For dynamic crystallization, the average value of the Avrami exponent varied from 3.4 to 3.8 and the average value of the Ozawa exponent changed from 2.3 to 2.6 as the number‐average molecular weight changed from 13,000 to 67,000. Morphology studies indicated that both the isothermal crystallization and the dynamic crystallization of PTT from the melt were thermal nucleation processes, and for a fixed temperature between 190°C and 210°C, the nucleation density increased with increasing the molecular weight.     

The DSC thermal analysis of crystallization behavior in high erucic acid rapeseed oil

DSC isothermal analysis is used to investigate the crystallization behavior of high erucic acid rapeseed oil (HEAR oil) in conjunction with usual cooling and heating methods. The crystallization of HEAR oil is found to be in two stages and which are accounted for by the crystallization of the α form and its transformation to theβ form under isothermal cooling conditions. Theα form is also transformed to theβ form under constant heating rate conditions (10 K/min), but this transformation is governed by the heating rate. The crystallization behavior of HEAR oil appears to be dominated by its characteristic triglyceride structure as the transformation is completely altered by random interesterification. Further, when HEAR oil is blended with SBO, the crystallization is changed as the SBO component is increased.     

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     

Thermal behavior of transparent poly(etheretherketone)(PEEK) film

The thermal behavior of poly(etheretherketone)(PEEK) film heated in an open differential scanning calorimetry (DSC) pan at 20°C/min is distorted by relaxation of the strained film. PEEK film in a closed pan or quenched PEEK in open or closed pans shows a glass-transition temperature (T_g) around 144°C, cold crystallization (～22 J/g) at 177°C, melt-temperature (T_m) peaking at 335–340°C, with an enthalpy of fusion of 32–34 J/g, and recrystallization on cooling at 285°C, with a crystallization exotherm of about 40 J/g. The enthalpy of fusion decreases with increasing heating rate from 2–100°C/min and approaches the enthalpy of cold crystallization. With increasing heating rate, further crystallization of PEEK during the DSC scan is suppressed. With increasing cooling rate, PEEK melt crystallizes at larger supercoolings to a lesser extent. Crystallization on cooling the melt was more complete than cold crystallization and annealing on heating.     

Multiple recrystallization behavior of poly(1,1-dimethysilacyclobutane): A combined calorimetric and small angle X-ray scattering study

The crystallization and melting behavior of a series of poly(1,1-dimethysilacyclobutane) (PDMSB) samples accessible via living anionic polymerization protocols with different molar masses were studied by differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and X-ray diffraction (XRD). It has been found that in the cooling process only one crystallization exotherm was observed by using DSC, but in subsequent heating two clear endotherms appeared. DSC measurements additionally revealed that there will be two melting peaks when the isothermal crystallization temperature, T_c, is low enough, but only one melting peak could be obtained when T_c is high. The value of the lower melting peak T_m1 increased with T_c, showing the increase of lamella thickness due to increase of T_c, which was also evidenced by using SAXS measurements. However, the value of the higher melting peak T_m2 stayed almost constant with T_c. XRD analysis showed that there is only one crystal form independent of T_c. While SAXS results revealed only one long range order, indicating this multiple endotherms phenomenon was caused by the recrystallization process during heating, but not isothermal thickening and thinning process as observed for e.g. poly(ethylene oxide)s (PEOs) with low molar masses. Heating rate dependent DSC experiments showed that there are two recrystallization processes with different time scales. The recrystallization at low temperature always showed up independent of heating rate while the recrystallization at high temperature showed up only when the heating rate was very low. This interesting phenomenon was explained by the different energy barrier for the recrystallization process at low and high temperature as shown by in situ SAXS measurements during heating.     

Kinetic thermal behavior of nanocellulose filled polylactic acid filament for fused filament fabrication 3D printing

Fused filament fabrication (FFF) with thermoplastic filaments is the most popular 3D printing technology. The continuous polymer filaments undergo a series of thermal processes, including heating, melting, cooling, and solidification. Therefore, it is necessary to investigate the thermal behavior of polymer filaments. The present study aims to provide a fundamental study of the thermal decomposition behavior and the isothermal melting crystallization behavior of nanocellulose filled polylactic acid (PLA) filaments. The influences of nanocellulose contents on the thermal decomposition properties such as onset temperature (137_onset), the temperature at 20-wt % conversion (T_α20), and the temperature at the peak decomposition rate (T_p) were examined by thermogravimetric analysis (TGA). The effects of nanocellulose contents on the glass transition temperature (T_g) and the melting temperature (T_m) were studied by differential scanning calorimetry (DSC). Effects of nanocellulose and polyethylene glycol (PEG) incorporation on the thermal decomposition activation energy, isothermal melting crystallization rate, and semi-crystallization time are also investigated. The addition of nanocellulose improves the thermal stability of PLA filament, whereas the addition of plasticizer PEG decreases the thermal stability. TGA and DSC kinetic analyses indicate that nanocellulose alone or together with PEG could drastically increase the crystallization rate and shorten the semi-crystallization time. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48374.     

Temperature and shear rate distributions of gas-assisted injection molded (GAIM) polypropylene and the application in forecast of cooling time

An umbrella handle product of polypropylene molded by gas-assisted injection molding (GAIM) was studied from both aspects: theoretical modeling and simulation as well as in situ temperature measurement. The simulation was primarily through the use of the commercial software Moldflow (version 6.1) coupled with enthalpy transformation method (ETM) in an attempt to investigate the shear rate and temperature fields during GAIM process. A four-parameter model (FPM) was used to nonlinearly fit the temperature decays during the GAIM cooling stage on the basis of a three-parameter model (TPM) raised previously in our group. The FPM showed perfect fitting effect as well as presented fairly acceptable cooling time (t_c) prediction in comparison to experimental data, which could better reflect the nature of crystalline polymers during melt crystallization process. The understanding of the shear rate and temperature fields would be of practical importance to the further research on relationship of “processing–structure–property” as well as the optimization of cooling parameters for industrial GAIM operations of crystalline polymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47390.