Non‐isothermal crystallization kinetics of poly(L‐lactide)

The non‐isothermal crystallization kinetics of poly( L ‐lactide) (PLLA) in comparison with a polylactide stereocopolymer (PLA₉₈) containing 98% L ‐lactyl and 2% D ‐lactyl units were investigated using differential scanning calorimetry to examine the effect of the configurational structure. Avrami, Ozawa and Liu models were applied to describe the crystallization process. The Avrami analysis exhibited two stages in non‐isothermal crystallization, while the Ozawa and Liu models did not successfully describe the crystallization behaviour. The activation energy was calculated with Kissinger's method. The energy barrier was found to be the same for PLLA and PLA₉₈ with a value of 126 kJ mol^?1. Copyright © 2010 Society of Chemical Industry     

Polymorphic crystallization of poly(butylene adipate) and its copolymer: Effect of poly(vinyl alcohol)

The crystallization kinetics and crystalline structure of the biodegradable polymorphic polymers, poly(butylene adipate) (PBA) and poly(butylene adipate‐co‐hexamethylene adipate), in the microparticles and nanoparticles covered by poly(vinyl alcohol) (PVA), and those on the PVA substrate were investigated by differential scanning calorimetry, wide‐angle X‐ray diffraction, and Fourier transform infrared spectroscopy. Both the polymers crystallized in the particle state and on the PVA substrate showed higher crystallization temperatures in the nonisothermal melt crystallization and shorter crystallization times in the isothermal crystallization; this indicated a faster crystallization of the polymer in the particle state and on the PVA substrate than that of the bulk sample. Furthermore, the polymers in the particle state and on the PVA substrate showed the preferential formation of the β‐type crystalline form of PBA compared to the bulk one. The mechanism for the effects of the PVA layer or substrate on the crystallization kinetics and crystalline structure of PBA and its copolyesters are discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39600.     

Effect of nucleation mechanism on complex poly(L‐lactide) nonisothermal crystallization process,part 2: Crystallization kinetics analysis

In the first part of this article, we reported the crystalline memory effect on the nonisothermal crystallization of poly(L ‐lactide). The experiments were carried out by using polymer single crystals growth from dilute solution as standard starting material. In this article (Part II), we have analyzed in detail the effect of the melting condition on the overall crystallization kinetics by applying the Nakamura‐Avrami model to DSC results. The absence or the low concentration of foreign infusible heterogeneous nuclei in our system allowed us to exalt the self‐nuclei role in polymer crystallization, to follow their concentration decrease during the melting process and to find the limiting melting temperature for their disappearance. Below such a temperature, a stable equilibrium number of self‐nuclei was observed, probably deriving from ordered structures, persisting in the melt, and originated from the single crystals thickening process during the polymer dynamic melting in the DSC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Isothermal and nonisothermal melt crystallization kinetics of a novel poly(aryl ether ketone ether ketone ketone) containing a meta‐phenyl linkage

The isothermal and nonisothermal melt crystallization kinetics of a novel poly(aryl ether ketone ether ketone ketone) containing a meta‐phenyl linkage (PEKEKmK) were studied by differential scanning calorimetry. The Avrami equation was used to analyze the isothermal crystallization kinetics of PEKEKmK. The crystallization mechanism did not change within the crystallization temperature range, but the crystallization rate decreased with an increase in the crystallization temperature. The equilibrium melting point, T, was determined to be 327°C according to the Hoffman–Weeks equation. Moreover, the nonisothermal crystallization kinetics of PEKEKmK was also investigated by the Avrami equation as modified by Jeziorny. It was found that the nonisothermal crystallization behavior of PEKEKmK could be described well by this method at various cooling rates, although the parameters n and Z_c did not have the same clear physical meaning as for isothermal crystallization kinetics. The thermal properties and crystallization characteristics of PEKEKmK were compared with those of all‐para PEKEKK(T) and PEKEKK(T/I) with a T/I ratio of 1. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4775–4779, 2006     

Effects of supercritical carbon dioxide treatment on the morphology of poly(l‐lactide)

Synthetic l ‐lactide random copolymers can be employed as controlled release materials when prepared using supercritical carbon dioxide (scCO₂), since they are biodegradable via hydrolysis. To determine the effects of thermal properties on polymer performance following scCO₂ processing, three types of poly(l ‐lactide) having different properties were assessed. The T_m of one poly(l ‐lactide) sample (H‐100) was found to be approximately 170 °C over the processing pressure range from 8 to 18 MPa, while a second sample (H‐440) also showed a constant value of approximately 152 °C. In contrast, the poly(l ‐lactide) REVODE exhibited a T_m of 146 °C prior to processing but a higher value of 147 °C following treatment at 8 MPa. Unlike the H‐100 and H‐440, the T_m value of the REVODE tended to decrease with increasing pressure. The T_g values increased greatly under mild conditions of 8 MPa pressure and a temperature of 40 °C. In particular, the T_g values for the H‐440 and REVODE increased by 4 °C and 5 °C, respectively. All T_g values were lowest at 12 MPa and increased with increasing processing pressure, although the effect of processing temperature was minimal. The Χ_{c DSC} of the H‐100 was 18% initially but increased to 20% upon scCO₂ processing at 40 °C and 14 MPa, and showed further increases at higher processing temperatures. Although the relationship between processing temperature and Χ_{c DSC} values for the H‐440 showed the same trend as observed with the H‐100, a different trend was seen for the REVODE. The Χ_{c XRD} values obtained from the XRD analyses differed from the values generated by DSC analysis, and showed a maximum degree of crystallinity following processing at 80 °C both with and without scCO₂ treatment. ATR FT‐IR analyses identified peaks due to semicrystalline regions in poly(l ‐lactide) samples treated with scCO₂, even when applying low temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44006.     

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.     

Isothermal cold crystallization kinetics of polylactide/nucleating agents

The isothermal cold crystallization kinetics of polylactide (PLA)/nucleating agents (CaCO₃, TiO₂, and BaSO₄, content from 0.5–2.0 wt %) was investigated by differential scanning calorimetry in the temperature range of 120–124°C. With blending nucleating agents, the crystallinity of PLA had a maximum crystallinity of 14.9%. Crystallization rate decreased with increasing crystallization temperature in the researched content range. The crystallization rate followed the Avrami equation with the exponent n around 4.5. From Lauritzen–Hoffman equation, the nucleation parameter K_g was estimated. And from the value of K_g, regime II crystallization behavior can be concluded. Then the lateral and fold surface free energy were calculated from K_g. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 310–317, 2007     

Isothermal and nonisothermal crystallization kinetics of novel even‐odd nylon 10 11

Isothermal and nonisothermal crystallization kinetics of even‐odd nylon 10 11 were investigated by differential scanning calorimetry (DSC). Equilibrium melting point was determined to be 195.20°C. Avarmi equation was adopted to describe isothermal and nonisothermal crystallization. A new relation suggested by Mo was used to analyze nonisothermal crystallization and gave a good result. The crystallization activation energies have been obtained to be ?583.75 and ?270.06 KJ/mol for isothermal and nonisothermal crystallization, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1637–1643, 2005     

Isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide)

The isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide) (PA‐10T) was studied by differential scanning calorimetry. Several kinetic analyses were used to describe the crystallization process. The commonly used Avrami equation and the one modified by Jeziorny were used, respectively, to describe the primary stage of isothermal and nonisothermal crystallization. The Avrami exponent n was evaluated to be in the range of 2.36–2.67 for isothermal crystallization, and of 3.05–5.34 for nonisothermal crystallization. The Ozawa analysis failed to describe the nonisothermal crystallization behavior, whereas the Mo–Liu equation, a combination equation of Avrami and Ozawa formulas, successfully described the nonisothermal crystallization kinetics. In addition, the value of crystallization rate coefficient under nonisothermal crystallization conditions was calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 819–826, 2004     

Isothermal and non‐isothermal crystallization of poly(L‐lactic acid)/poly(butylene terephthalate) blends

Isothermal and non‐isothermal crystallization kinetics of poly(l ‐lactic acid)/poly(butylene terephthalate) (PLLA/PBT) blends containing PLLA as major component is detailed in this contribution. PLLA and PBT are not miscible, but compatibility of the polymer pair is ensured by interactions between the functional groups of the two polyesters, established upon melt mixing. Crystal polymorphism of the two polyesters is not influenced by blending, as probed by wide‐angle X‐ray analysis. The addition of PLLA does not affect the temperature range of crystallization kinetics of PBT, nor the crystallinity level attained when the blends are cooled from the melt at constant rate. Conversely, PBT favors crystallization of the biodegradable polyester. The addition of PBT results in an anticipated onset of crystallization of PLLA during cooling at a fixed rate, with a sizeable enhancement of the crystal fraction. Isothermal crystallization analysis confirmed the faster crystallization rate of PLLA in the presence of PBT. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40372.     

Crystallization and thermal properties of biodegradable polyurethanes based on poly[(R)‐3‐hydroxybutyrate] and their composites with chitin whiskers

A series of biodegradable polyurethanes (PUs) were synthesized from hydroxylated bacterial poly[(R)‐3‐hydroxybutyrate], P[(R)‐HB]‐diol, as crystallizable hard segment and hydroxyl‐terminated synthetic poly[(R,S)‐3‐hydroxybutyrate), P[(R,S)‐HB]‐diol, as an amorphous soft segment, using 1,6‐hexamethylene diisocyanate, as non‐toxic connecting agent. The P[(R)‐HB] content was varied from 30 to 70 wt %. The resulting copolymers were characterized by FT‐IR, ¹H‐NMR, DSC, and TGA. The DSC data revealed that the melting of P[(R)‐HB] segment increases with increasing its own content in the PUs. The cold and melt crystallization are enhanced with increasing P[(R)‐HB] content. The TGA data revealed that the thermal decomposition mainly occurred via a single degradation step and the thermal stability slightly increased with increasing P[(R)‐HB] content. The non‐isothermal crystallization behavior of PU sample containing 40 wt % PHB with and without α‐Chitin whiskers was studied using DSC, and their kinetics data were investigated via the Avrami, Ozawa, and Z.S. Mo methods, respectively. Crystallization activation energy was estimated using Kissinger's method. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40784.     

Properties and crystallization kinetics of poly(ether ether ketone)‐co‐poly(ether ether ketone ketone) block copolymers

A series of block copolymers composed of poly(ether ether ketone) (PEEK) and poly(ether ether ketone ketone) (PEEKK) components were prepared from their corresponding oligomers via a nucleophlilic aromatic substitution reaction. Various properties of the copolymers were investigated with differential scanning calorimetry (DSC) and a tensile testing machine. The results show that the copolymers exhibited no phase separation and that the relationship between the glass‐transition temperature (T_g) and the compositions of the copolymers approximately followed the formula T_g = T_g1X₁ + T_g2X₂, where T_g1 and T_g2 are the glass‐transition‐temperature values of PEEK and PEEKK, respectively, and X₁ and X₂ are the corresponding molar fractions of the PEEK and PEEKK segments in the copolymers, respectively. These copolymers showed good tensile properties. The crystallization kinetics of the copolymers were studied. The Avrami equation was used to describe the isothermal crystallization process. The nonisothermal crystallization was described by modified Avrami analysis by Jeziorny and by a combination of the Avrami and Ozawa equations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1652–1658, 2005     

Nonisothermal crystallization kinetics of nucleated poly(ethylene terephthalate)

Studies of the nonisothermal crystallization kinetics of poly(ethylene terephthalate) nucleated with anhydrous sodium acetate were carried out. The chemical nucleating effect was investigated and confirmed with Fourier transform infrared and intrinsic viscosity measurements. The Avrami, Ozawa, and Liu models were used to describe the crystallization process. The rates of crystallization, which initially increased, decreased at higher loadings of the additive. The activation energy, calculated with Kissinger's method, was lower for nucleated samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microstructural characteristics and crystallization behaviors of poly(l‐lactide) scaffolds by thermally induced phase separation

In this study, poly(l ‐lactic acid) (PLLA) was prepared by four typical approach systems, namely, solid–liquid phase‐separation processes from PLLA–dioxane at ?80°C, PLLA–dioxane–water at ?80°C, PLLA–tetrahydrofuran (THF) at ?80°C, and PLLA–THF at 18°C. The microstructural characteristics and crystallization behaviors of PLLA were investigated by scanning electron microscopy, differential scanning calorimetry, X‐ray diffraction, and Fourier transform infrared spectroscopy. In the PLLA–dioxane binary system and PLLA–dioxane–water ternary system, the solvent froze immediately after quenching to a low temperature, and this restricted the PLLA chain arrangement. Thus, the PLLA amorphous phase dominated in the scaffolds, and solid‐walled structures were produced. THF was liquid throughout the entire process, which enabled free PLLA chain arrangement and further crystallization. Single crystals aggregated by crystal nucleation and growth at a critical temperature (T_c) of 18°C; this resulted in its most common and stable polymorph, the α form. However, α′‐form crystals, which were assumed to be limit‐disordered crystals of the α form, were produced at a low T_c (?80°C). Scaffolds with a plateletlike structure were produced at a T_c of 18°C, whereas a nanofibrous network was obtained at ?80°C. PLLA crystallization competed with phase separation; thus, the crystal structure and scaffold morphology depended on the codevelopment of these two processes. Finally, the effects of the scaffold morphologies on the cell behaviors were studied, and the nanofibrous scaffold was found to have better cell adhesion and viability than the other three scaffolds. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39436.     

Effect of the nucleation mechanism on complex poly(L‐lactide) nonisothermal crystallization process. Part 1: Thermal and structural characterization

The effect of the holding temperature and time in the melt state of poly(L ‐lactide) (PLLA) samples on the nonisothermal melt crystallization process and on the structure have been investigated by means of DSC, polarized optical microscopy and wide angle X‐ray scattering. As standard starting material, single crystals grown from dilute solution were used. In the mild melting condition, the survived athermal nuclei favor high temperature polymer crystallization, while the more severe treatment leads the PLLA to crystallize at higher supercooling with a sporadic nucleation. At the intermediate melting temperature a distinct double nucleation mechanism was observed while at the lower nuclei concentration, a double crystallization rate was also found. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Crystallization behavior and isothermal crystallization kinetics of polylactide/polystyrene-b-polybutadiene-b-polystyrene blends compatibilized with poly(styrene-ran-methyl acrylate)

The morphology, non-isothermal and isothermal crystallization behavior, and spherulite growth of polylactide (PLA)/polystyrene-b-polybutadiene-b-polystyrene (SBS) blends were investigated in the presence of a poly(styrene-ran-methyl acrylate) (S–MA) compatibilizer synthesized using surfactant-free emulsion copolymerization. Scanning electron microscopy revealed that the SBS dispersed-phase became more uniform and refined as the amount of S–MA compatibilizer was increased from 0 to 3 wt%. Calorimetric characterization of the non-isothermal and isothermal crystallization behavior analyzed using Avrami theory shows that the SBS in PLA shows plasticization and dilution effects simultaneously. When the PLA matrix chains do not move easily and/or its effective crystallization time window is narrow, the plasticization effect of the SBS is more significant. However, when the PLA matrix chains move more easily and/or its crsytallization window is wide, the dilution effects effect of the SBS is more notable. After the addition of S–MA, the plasticization and dilution effects were enhanced.     

Non‐isothermal crystallization kinetics of cork‐polymer composites for injection molding

The non‐isothermal crystallization behavior of cork–polymer composites (CPC) based on polypropylene (PP) matrix was studied. Using differential scanning calorimetry (DSC), the crystallization behavior of CPC with 15 wt % cork powder at different cooling rates (5, 10, 15, and 20 °C/min) was studied. The effect of a coupling agent based on maleic anhydride was also analyzed. A composite (PPg) containing polypropylene grafted maleic anhydride (PPgMA) and PP was prepared for comparison purposes. Crystallization kinetic behavior was studied by Avrami, Ozawa, Liu, and Kissinger methods. The Ozawa method fails to describe the behavior of these composites. Results show that cork powder surface acts as a nucleating agent during non‐isothermal crystallization, while the addition of PPgMA decreases the crystallization rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44124.     

Effect of 1,3,5‐trialkyl‐benzenetricarboxylamide on the crystallization of poly(lactic acid)

A series of 1,3,5‐trialkyl‐benzenetricarboxylamides (BTA‐Rs) with different side‐chain lengths of n‐alkyl are synthesized to use as nucleating agents of poly (lactic acid) (PLA). Crystallization rate of PLA is detailed discussed in nonisothermal melt‐crystallization with addition of the synthesized nucleating agents. Among these BTA‐Rs, BTA‐n‐butyl (BTA‐nBu) shows the most excellent nucleation ability for PLA. The influences of BTA‐nBu on the nonisothermal melt‐crystallization and cold‐crystallization from the glassy state, isothermal crystallization, crystalline structure, and spherulite morphology of PLA are investigated. It is found that 0.8 wt % is the optimal weight fraction of BTA‐nBu to improve the crystallization of PLA. In the case of isothermal melt‐crystallization from melt, the addition of BTA‐nBu shortens the crystallization half‐time and speeds up the crystallization rate of PLA with no discernible effect on the crystalline structure. Besides, BTA‐nBu nucleated PLA exhibits smaller spherulites size and larger nucleation density than that of pure PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1328‐1336, 2013     

Effect of poly(propylene carbonate) on the crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)

The crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHBV) and a 30/70 (w/w) PHBV/poly(propylene carbonate) (PPC) blend was investigated with differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The transesterification reaction between PHBV and PPC was detected in the melt‐blending process. The interaction between the two macromolecules was confirmed by means of FTIR analysis. During the crystallization process from the melt, the crystallization temperature of the PHBV/PPC blend decreased about 8°C, the melting temperature was depressed by 4°C, and the degree of crystallinity of PHBV in the blend decreased about 9.4%; this was calculated through a comparison of the DSC heating traces for the blend and pure PHBV. These results indicated that imperfect crystals of PHBV formed, crystallization was inhibited, and the crystallization ability of PHBV was weakened in the blend. The equilibrium melting temperatures of PHBV and the 30/70 PHBV/PPC blend isothermally crystallized were 187.1 and 179°C, respectively. The isothermal crystallization kinetics were also studied. The fold surface free energy of the developing crystals of PHBV isothermally crystallized from the melt decreased; however, a depression in the relative degree of crystallization, a reduction of the linear growth rate of the spherulites, and decreases in the equilibrium melting temperature and crystallization capability of PHBV were detected with the addition of PPC. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2514–2521, 2004