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.     

Effect of zinc phenylphosphonate on the crystallization behavior of poly(l‐lactide)

The effect of zinc phenylphosphonate (PPZn) on the crystallization behavior of poly(l ‐lactide) (PLLA) was investigated using differential scanning calorimetry (DSC) and Polarized Optical Microscopy (POM) measurements. The non‐isothermal cold crystallization results showed that the addition of PPZn obviously decreased the cold crystallization temperature of PLLA and increased the degree of crystallinity of PLLA. The isothermal crystallization kinetics results showed that the crystallization rate of PLLA with small amount of PPZn was much higher than that of neat PLLA, and the half‐time (t_1/2) of PLLA/PPZn sample is far less than that of neat PLLA. As an effective nucleating agent, PPZn particles had also some influence on nucleation mechanism and crystal growth of PLLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2744–2752, 2013     

Crystallization behavior,heat resistance,and mechanical performances of PLLA/myo‐inositol blends

In this work, use of myo‐inositol as a biobased nucleating agent (NA) for PLLA was researched. Effects of myo‐inositol on non‐isothermal and isothermal crystallization behaviors of PLLA at temperatures ranged from 85 °C to 130 °C were studied by using DSC, POM and WAXD. Isothermal crystallization kinetics results showed that the incorporation of myo‐inositol enhanced significantly the crystallization rate of the PLLA samples. It was confirmed that the optimum isothermal crystallization temperature range was 100 to 110 °C. The above results were instructive to confirm proper heat treatment time and temperature for compression or injection molding to fabricate highly crystallized PLLA articles. The relations among heat treatment time, crystallinity, heat resistance, and mechanical performances of the neat PLLA and PLLA/1% myo‐inositol specimens prepared by compression molding were investigated. Compared with the PLLA specimens, the PLLA/1% myo‐inositol specimens showed a shorter heat treatment time to reach the maximum crystallinity. Vicat softening temperature, as well as tensile strength, modulus, and toughness of the PLLA/1% myo‐inositol specimens was improved when crystallinity increased from 5.4% to 38.1%. Considering the nontoxicity and biocompatibility of myo‐inositol, PLLA/myo‐inositol blends would be potential to prepare some products, which are required higher health standard and can be used in elevated temperature environments. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44732.     

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     

Nonisothermal crystallization kinetics and morphology of self‐seeded syndiotactic 1,2‐polybutadiene

Subsequent melting behavior after isothermal crystallization at different temperatures from the isotropic melt and nonisothermal crystallization kinetics and morphology of partially melting sPB were carried out by differential scanning calorimetry (DSC), polarized light microscopy (POM), respectively. Triple melting‐endothermic peaks were observed for the polymer first isothermally crystallized at temperatures ranging from 141 to 149°C, respectively, and then followed by cooling at 10°C/min to 70°C. Comparing with the nonisothermal crystallization from the isotropic melt, the nonisothermal crystallization for the partially melting sPB characterized the increased onset crystallization temperature, and the sizes of spherulites became smaller and more uniform. The Tobin, Avrami, Ozawa, and the combination of Avrami and Ozawa equations were applied to describe the kinetics of the nonisothermal process. Both of the Tobin and the Avrami crystallization rate parameters (K_T and K_A, respectively) were found to increase with increase in the cooling rate. The parameter F(T) for the combination of Avrami and Ozawa equations increases with increasing relative crystallinity. The Ziabicki's kinetic crytallizability index G_Z for the partially melting sPB was found to be 3.14. The effective energy barrier Δ? describing the nonisothermal crystallization of partially melting sPB was evaluated by the differential isoconversional method of Friedman and was found to increase with an increase in the relative crystallinity. At the same time, Hoffman‐Lauritzen parameters (U and K_g) are evaluated and analyzed from the nonisothermal crystallization data by the combination of isoconversional approach and Hoffman‐Lauritzen theory. The K_g value obtained from DSC technique was found to be in good agreement with that obtained from POM technique. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1479–1491, 2006     

Crystallization kinetics of poly(L‐lactide)/carbonated hydroxyapatite nanocomposite microspheres

Microspheres consisting of carbonated hydroxyapatite (CHAp) nanoparticles and poly(L ‐lactide) (PLLA) have been fabricated for use in the construction of osetoconductive bone tissue engineering scaffolds by selective laser sintering (SLS). In SLS, PLLA polymer melts and crystallizes. It is therefore necessary to study the crystallization kinetics of PLLA/CHAp nanocomposites. The effects of 10 wt% CHAp nanoparticles on the isothermal and nonisothermal crystallization behavior of PLLA matrix were studied, using neat PLLA for comparisons. The Avrami equation was successfully applied for the analysis of isothermal crystallization kinetics. Using the Lauritzen‐Hoffman theory, the transition temperature from crystallization Regime II to Regime III was found to be around 120°C for both neat PLLA and PLLA/CHAp nanocomposite. The combined Avrami‐Ozawa equation was used to analyze the nonisothermal crystallization process, and it was found that the Ozawa exponent was equal to the Avrami exponent for neat PLLA and PLLA/CHAp nanocomposite, respectively. The effective activation energy as a function of the relative crystallinity and temperature for neat PLLA and PLLA/CHAp nanocomposite under the nonisothermal crystallization condition was obtained by using the Friedman differential isoconversion method. The Lauritzen‐Hoffman parameters were also determined from the nonisothermal crystallization data by using the Vyazovkin‐Sbirrazzuoli equation. CHAp nanoparticles in the composite acted as an efficient nucleating agent, enhancing the nucleation rate but at the same time reducing the spherulite growth rate. This investigation has provided significant insights into the crystallization behavior of PLLA/CHAp nanocomposites, and the results obtained are very useful for making good quality PLLA/CHAp scaffolds through SLS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Crystallization of poly(3‐hydroxybutyrate) with stereocomplexed polylactide as biodegradable nucleation agent

Crystallization kinetics behavior and morphology of poly(3‐hydroxybutyrate) (PHB) blended with of 2–10 wt% loadings of poly(L ‐ and D ‐lactic acid) (PLLA and PDLA) stereocomplex crystallites, as biodegradable nucleating agents, were studied using differential scanning calorimetry, polarizing‐light optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Blending PLLA with PDLA at 1:1 weight ratio led to formation of stereocomplexed PLA (sc‐PLA), which was incorporated as small crystalline nuclei into PHB for investigating melt‐crystallization kinetics. The Avrami equation was used to analyze the isothermal crystallization of PHB. The stereocomplexed crystallites acted as nucleation sites in blends and accelerated the crystallization rates of PHB by increasing the crystallization rate constant k and decreasing the half‐time (t_1/2). The PHB crystallization was nucleated most effectively with 10 wt% stereocomplexed crystallites, as evidenced byPOM results. The sc‐PLA complexes (nucleated PHB crystals) exhibit much small spherulite sizes but possess the same crystal cell morphology as that of neat PHB based on the WAXD result. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Investigations on the morphology and melt crystallization of poly(L‐lactide)‐poly(ethylene glycol) diblock copolymers

Ring opening polymerization of L ‐lactide was realized in the presence of monomethoxy poly(ethylene glycol), using zinc lactate as catalyst. The resulting PLLA‐PEG diblock copolymers were characterized by using ¹H‐NMR, SEC, WAXD, and DSC. All the copolymers were semicrystalline, one or two melting peaks being detected depending on the composition. Equilibrium melting temperature (T_m⁰) of PLLA blocks was determined for three copolymers with different EO/LA molar ratios. T_m⁰ decreased with decreasing PLLA block length. A copolymer with equivalent PLLA and PEG block lengths was selected for melt crystallization studies and the resulting data were analyzed with Avrami equation. The obtained Avrami exponent is equal to 2.6 ± 0.2 in the crystallization temperature range from 80 to 100°C. In addition, the spherulite growth rate of PLLA‐PEG was analyzed by using Lauritzen‐Hoffmann theory in comparison with PLLA homopolymers. The nucleation constant was found to be 2.39 × 10⁵ K² and the free energy of folding equal to 53.8 erg/cm² in the range of 70–94°C, both higher than those of PLLA homopolymers, while the spherulite growth rate of the diblock copolymer was lower. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

Isothermal crystallization behavior of poly(L‐lactic acid)/organo‐montmorillonite nanocomposites

The isothermal crystallization behavior of poly(L ‐lactic acid)/organo‐montmorillonite nanocomposites (PLLA/OMMT) with different content of OMMT, using a kind of twice‐functionalized organoclay (TFC), prepared by melt intercalation process has been investigated by optical depolarizer. In isothermal crystallization from melt, the induction periods (t_i) and half times for overall PLLA crystallization (100°C ≤ T_c ≤ 120°C) were affected by the temperature and the content of TFC in nanocomposites. The kinetic of isothermal crystallization of PLLA/TFC nanocomposites was studied by Avrami theory. Also, polarized optical photomicrographs supplied a direct way to know the role of TFC in PLLA isothermal crystallization process. Wide angle X‐ray diffraction (WAXD) patterns showed the nanostructure of PLLA/TFC material, and the PLLA crystalline integrality was changed as the presence of TFC. Adding TFC led to the decrease of equilibrium melting point of nanocomposites, indicating that the layered structure of clay restricted the full formation of crystalline structure of polymer. The specific interaction between PLLA and TFC was characterized by the Flory‐Huggins interaction parameter (B), which was determined by the equilibrium melting point depression of nanocomposites. The final values of B showed that PLLA was more compatible with TFC than normal OMMT. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Thermal transitions and stability of melt mixed TiO2/Poly(L‐lactic acid) nanocomposites

Poly(L‐lactic acid) (PLLA) nanocomposites containing 5, 10, and 20 wt% titanium dioxide (TiO₂), were prepared by mixing in a co‐rotating twin‐screw extruder. By X‐ray diffraction, a transformation of less ordered (α’‐form) to better organized crystalline (α‐form) structure of PLLA was observed with increasing TiO₂ content. Differential scanning calorimetry (DSC) tests revealed that cold crystallization was facilitated, as shown by the decrease of cold crystallization temperature (T_cc). The main melting peak of PLLA phase in nanocomposites, shifted towards higher temperatures and a shoulder appeared in the lower temperature flank of the curve, revealing a second peak for 20/80 w/w TiO₂/PLLA nanocomposites. The effect of TiO₂ on the isothermal crystallization of PLLA, in the temperature range T_ic: 100–120°C, was also investigated by DSC. At lower temperatures (T_ic: 100 and 110°C), the effect of TiO₂ nanoparticles is an increase of the crystallization rate, leading to lower time for the completion of crystallization, in comparison with that of pure PLLA. The inverse effect was observed at higher crystallization temperatures (T_ic: 115 and 120°C). The kinetic analysis of the crystallization behavior of the examined nanocomposites fits the Avrami equation quite well and gives values for exponent (n) varying between 2 and 3, suggesting a spherulitic crystalline morphology. POLYM. ENG. SCI., 59:704–713, 2019. © 2018 Society of Plastics Engineers     

Crystallization behavior of biodegradable poly(L‐lactic acid) filled with a powerful nucleating agent: N,N′‐bis(benzoyl) suberic acid dihydrazide

N,N′‐Bis(benzoyl) suberic acid dihydrazide (NA) as nucleating agent for poly(L ‐lactic acid) (PLLA) was synthesized from benzoyl hydrazine and suberoyl chloride, which was deprived from suberic acid via acylation. PLLA/NA samples were prepared by melt blending and a hot‐press forming process. The nonisothermal and isothermal crystallization, spherulite morphology, and melting behavior of PLLA/NA with different contents of NA were investigated with differential scanning calorimetry, depolarized‐light intensity measurement, scanning electron microscopy, polarized optical microscopy, and wide‐angle X‐ray diffraction. With the incorporation of NA, the crystallization peak became sharper and shifted to a higher temperature as the degree of supercooling decreased at a cooling rate of 1°C/min from the melt. Nonisothermal crystallization indicated that the presence of NA accelerated the overall PLLA crystallization. In isothermal crystallization from the melt, the presence of NA affected the isothermal crystalline behaviors of PLLA remarkably. The addition of NA led to a shorter crystallization time and a faster overall crystallization rate; this meant that there was a heterogeneous nucleation effect of NA on the crystallization of PLLA. With the addition of 0.8% NA, the crystallization half‐time of PLLA/NA decreased from 26.5 to 1.4 min at 115°C. The Avrami theory was used to describe the kinetics of isothermal crystallization of the PLLA/NA samples. Also, with the presence of NA, the spherulite number of PLLA increased, and the spherulite size decreased significantly. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The Kinetics of Melting Crystallization of Poly-L-Lactide

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min^?1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min^?1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of K_g(II)/K_g(III) is 2.17 [K_g(II) = 6.025 × 10⁵K², K_g(III) = 1.307 × 10⁶ K²].     

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 crystallization kinetics and melting behavior of modified high‐density polyethylene/barium sulfate nanocomposites

The melting/crystallization behavior and isothermal crystallization kinetics of high‐density polyethylene (HDPE)/barium sulfate (BaSO₄) nanocomposites were studied with differential scanning calorimetry (DSC). The isothermal crystallization kinetics of the neat HDPE and nanocomposites was described with the Avrami equation. For neat HDPE and HDPE/BaSO₄ nanocomposites, the values of n ranges from 1.7 to 2.0. Values of the Avrami exponent indicated that crystallization nucleation of the nanocomposites is two‐dimensional diffusion‐controlled crystal growth. The multiple melting behaviors were found on DSC scan after isothermal crystallization process. The multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae caused during different crystallization processes. Adding the BaSO₄ nanoparticles increased the equilibrium melting temperature of HDPE in the nanocomposites. Surface free energy of HDPE chain folding for crystallization of HDPE/BaSO₄ nanocomposites was lower than that of neat HDPE, confirming the heterogeneous nucleation effect of BaSO₄. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Effect of poly(l‐lactide)/poly(d‐lactide) block length ratio on crystallization behavior of star‐shaped asymmetric poly(l(d)‐lactide) stereoblock copolymers

Effect of Poly(l ‐lactide)/Poly(d ‐lactide) (PLLA/PDLA) block length ratio on the crystallization behavior of star‐shaped poly(propylene oxide) block poly(d ‐lactide) block poly (l ‐lactide) (PPO–PDLA–PLLA) stereoblock copolymers with molecular weights (M_n) ranging from 6.2 × 10⁴ to 1.4 × 10⁵ g mol^?1 was investigated. Crystallization behaviors were studied utilizing differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Only stereocomplex crystallites formed in isothermal crystallization at 140 to 156°C for all samples. On one hand, the overall crystallization rate decreased as PLLA/PDLA block length ratio increased. As PLLA/PDLA block length ratio increased from 7:7 to 28:7, the value of half time of crystallization (t_1/2) delayed form 2.85 to 5.31 min at 140°C. On the other hand, according to the Lauritzen–Hoffman theory, the fold‐surface energy (σ_e) was calculated. σ_e decreased from 77.7 to 73.3 erg/cm² with an increase in PLLA/PDLA block length ratio. Correspondingly increase in nucleation density was observed by the polarized optical microscope. Results indicated that the PLLA/PDLA block length ratio had a significant impact on the crystallization behavior of PPO–PDLA–PLLA copolymers. POLYM. ENG. SCI., 55:2534–2541, 2015. © 2015 Society of Plastics Engineers     

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     

Influence of dispersed organophilic montmorillonite at nanometer‐scale on crystallization of poly(L‐lactide)

We investigated the effects of surface‐treated organophilic clay on the crystallization of poly(L ‐lactide) (PLLA) in their hybrids. The natural nano‐clay in PLLA/clay hybrids acts as a heterogeneous nucleating agent to facilitate crystallization. On the contrary, extensive distributions of induction periods for nucleation are observed in the individual spherulites of neat PLLA and PLLA/organophilic clay hybrids. Therefore, it is suggested that nucleation type of neat PLLA and PLLA/organophilic clay hybrids implies nearly growth geometry as a homogeneous one. Further, under the presence of nano‐clay in their composites, PLLA matrix form the orthorhombic lattice structure corresponded to the α‐form crystal. Since this experimental fact implies little effect of the clay particles on polymorphism of PLLA crystal, the nucleating effect of the organophilic clay seems weaker than the natural clay itself. However, an increase in clay content enhances the growth rates of spherulite for hybrids. Consequently, most of hybrids exhibit an increase in overall crystallization rates at any crystallization temperature in spite of relatively lower nucleation rate of PLLA crystallites itself. In addition, the Avrami exponents (n) obtained by relatively low crystallization temperature ranged from 4 to 6, implying that the growth geometry was dominated sheaf‐like structure in early stage of isothermal crystallization. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

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 behavior of fully biodegradable poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

Both poly(lactic acid) (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) are fully biodegradable polyesters. The disadvantages of poor mechanical properties of PLA limit its wide application. Fully biodegradable polymer blends were prepared by blending PLA with PBAT. Crystallization behavior of neat and blended PLA was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X‐ray diffraction (WAXD). Experiment results indicated that in comparison with neat PLA, the degree of crystallinity of PLA in various blends all markedly was increased, and the crystallization mechanism almost did not change. The equilibrium melting point of PLA initially decreased with the increase of PBAT content and then increased when PBAT content in the blends was 60 wt % compared to neat PLA. In the case of the isothermal crystallization of neat PLA and its blends at the temperature range of 123–142°C, neat PLA and its blends exhibited bell shape curves for the growth rates, and the maximum crystallization rate of neat PLA and its blends all depended on crystallization temperature and their component. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Crystallization behavior and morphology of polylactic acid (PLA) with aromatic sulfonate derivative

This article provides a detailed investigation of crystallization behavior and morphology of polylactic acid (PLA) in the presence of a nucleating agent: potassium salt of 5‐dimethyl sulfoisothalate, an aromatic sulfonate derivative (Lak‐301). Isothermal crystallization kinetics of PLA melt mixed with Lak at concentrations of 0.25–1 wt % was investigated at a range of crystallization temperature, 140–150 °C. To gain further insight on the effect of Lak, nonisothermal differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), polarized optical microscope (POM), heat deflection temperature (HDT), and rheology were also performed. At 0.25 wt % Lak, crystallinity of PLA increased from 10% to 45%, and in 1 wt % Lak, maximum crystallinity of 50% was achieved. With 1 wt % Lak, crystallization half time reduced to 1.8 min from 61 min for neat PLA at 140 °C. The isothermal crystallization kinetics was analyzed using Avrami model. Values of the Avrami exponent for PLA with Lak were mainly in the range of 3 indicating a three dimensional crystal growth is favored. Crystallization rate was found to increase with increase in Lak content. Observation from POM confirmed that the presence of Lak in the PLA matrix significantly increased the nucleation density. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43673.