Nonisothermal Cold Crystallization Kinetics Research Articles

Chain heterogeneity of poly(lactic acid) and its influence on crystallization kinetics

Temperature rising elution fractionation (TREF) approach was used to separate a biodegradable poly(lactic acid) (PLA) resin into ten fractions and completely establish the relationship between chain microstructure and properties. The main fractions were mainly eluted at 100, 110, 114, and 118 °C, and their mass percentages were 7.98 wt%, 44.83 wt%, 19.64 wt%, and 11.90 wt%, respectively. Through the use of successive self-nucleation/annealing (SSA) thermal fractionation, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and 13C-nuclear magnetic resonance spectroscopy (13C NMR), the intermolecular and intramolecular differences of PLA were further explored. Fractions eluted at 90, 110, 118, and 126 °C were also chosen to research the non-isothermal cold crystallization kinetics, and fractions eluted at 110, 118, and 126 °C were chosen to explore the non-isothermal crystallization kinetics in order to simulate the real process. The findings demonstrated that the Liu-Mo approach were more suited the non-isothermal crystallization and non-isothermal cold crystallization kinetics of PLA. As the elution temperature increased, so did the stereoregularity of the fractions, the crystallization rate, the crystallization capacity, and the lamellar thickness. These will lay a foundation for its basic research and industrial application.

Effect of Nano Spinel Ferrites Co0.9Cu0.1Fe2O4 on Non-Isothermal Cold Crystallization Behaviours and Kinetics of Its Composites with Polylactic Acid.

Nanoparticles of spinel ferrites with a composition of Co0.9Cu0.1Fe2O4 (AM NPs) were effectively synthesized via a hydrothermal route. The structure of ferrite nanoparticles was characterized with X-ray diffraction, which showed a single cubic spinel phase. Energy-dispersive X-ray (EDX) spectroscopy and field emission-scanning electron microscopy (FE-SEM) were employed to analyse elemental composition and surface morphology, respectively. Moreover, the effects of the Co0.9Cu0.1Fe2O4 on the morphology of [PLA = polylactic acid] nanocomposites were examined through polarized light optical microscopy (POM) and X-ray diffraction (XRD). The thermal behaviours for tested samples were studied through [DSC = differential scanning calorimetry] and [TGA = thermal gravimetric analysis]. A great number of minor PLA spherulites were detected using POM in the presence of the Co0.9Cu0.1Fe2O4 ceramic magnetic nanoparticles (AM), increasing with AM nanoparticle contents. X-ray diffraction (XRD) analysis showed that the presence of nanoparticles led to an increase in the intensity of diffraction peaks. The DSC findings implied that the crystallization behaviours for the efficient PLA as well as its nanocomposites were affected by the addition of AM nanoparticles. They act as efficient nucleating agents because they shift the temperature of crystallization to a lower value. The Avrami models were used to analyse kinetics data. The experimental data were well described using the Avrami method for all samples tested. The addition of AM to the PLA matrix resulted in a decrease in the crystallization half-time t1/2 values, indicating a faster crystallization rate. TGA data showed that the occurrence of AM nanoparticles decreased the thermal stability of PLA.

Influence of rGO on the Crystallization Kinetics, Cytoxicity, and Electrical and Mechanical Properties of Poly (L-lactide-co-ε-caprolactone) Scaffolds.

Biodegradable scaffolds of poly (L-lactide-co-ε-caprolactone) (PLCL) and reduced graphene oxide (rGO) were prepared by TIPS (thermally induced phase separation). The nonisothermal cold crystallization kinetics were investigated by differential scanning calorimetry (DSC) with various cooling rates. The experimental values indicate that nonisothermal crystallization improves with cooling rate, but the increasing rGO concentration delays crystallization at higher temperatures. The activation energies were calculated by the Kissinger equation; the values were very similar for PLCL and for its compounds with rGO. The electrical conductivity measurements show that the addition of rGO leads to a rapid transition from insulating to conductive scaffolds with a percolation value of ≈0.4 w/w. Mechanical compression tests show that the addition of rGO improves the mechanical properties of porous substrates. In addition, it is an anisotropic material, especially at compositions of 1% w/w of rGO. All of the samples with different rGO content up to 1% are cytotoxic for C2C12 myoblast cells.

Mechanical and nonisothermal cold crystallization behaviors of injection molded surface‐modified chitin whiskers/poly(l‐lactide) composites

AbstractTo improve the mechanical, crystallization performances of poly(l‐lactide) (PLLA), pristine and surface grafted chitin whiskers (CWs and g‐CWs) were introduced to PLLA via melt blending. Attributed to the good interfacial compatibility between the g‐CWs and PLLA matrix, the tensile, flexural, and impact performances of the g‐CWs/PLLA composites were better than that of the CWs/PLLA composites with the same whiskers content. The whiskers acted as nucleating agents to promote the crystallization of the PLLA matrix on the one hand, and acted as obstacles to restrict the crystals growth on the other hand. The nonisothermal cold crystallization kinetics revealed that the crystallization rate and crystallinity of the PLLA matrix were improved by the addition of the whiskers, but the promotion effect of g‐CWs was more obvious than CWs.

Non-isothermal cold crystallization kinetics of cork–polymer biocomposites based on polylactic acid for fused filament fabrication

Cork–polymer composites (CPC) based on polylactic acid (PLA) matrix were prepared for the development of filaments for fused filament fabrication. The non-isothermal cold crystallization behaviours of PLA and CPC were investigated by differential scanning calorimetry. Cold crystallization kinetic behaviours of PLA and CPC with 15 mass/% of cork powder residues at different heating rates (1.25, 2.5, 5 and 7.5 K min−1) were studied. Results showed that cold crystallization temperature (Tcc) of PLA matrix decreased with the addition of cork. Crystallization kinetic behaviour was studied by Avrami and Tobin models. It was shown that cork powder surface acts as a nucleating agent during non-isothermal cold crystallization, by accelerating the crystallization rate and, therefore, by reducing the half-time crystallization (t1/2) values. Polarized optical microscopy and X-ray diffraction were used to evaluate the crystalline structure of PLA and CPC. Kissinger and Friedman methods were employed to determine the crystallization activation energy (Ec).

Effect of Organic Modifier and Clay Content on Non-Isothermal Cold Crystallization and Melting Behavior of Polylactide/Organovermiculite Nanocomposites.

In clay/polymer nanocomposites, the crystallization behavior and kinetics of the polymer can be affected by the presence of clay, its content and the degree of miscibility between the clay and the polymer matrix. The effect of two different organomodified vermiculites on the non-isothermal cold crystallization and melting behavior of polylactide (PLA) was studied by differential scanning calorimetry (DSC). In the presence of vermiculites, the cold crystallization of PLA occurred earlier, particularly for the highest content of the most miscible organovermiculite with PLA. The cold crystallinity of PLA decreased at low heating rates, notably at high organoclay loadings, and increased at high heating rates, especially at low vermiculite contents. According to the crystallization half-time, crystallization rate coefficient (CRC), and crystallization rate parameter (CRP) approaches, the cold crystallization rate of PLA increased by incorporating vermiculites, with the effect being most noteworthy for the vermiculite showing better compatibility. The Mo model was successful in describing the non-isothermal cold crystallization kinetics of the PLA/vermiculite composites. The melting behavior was affected by the heating rate and the type and content of clay. The nucleating effect of the most compatible clay resulted in the less perfect crystallites. The activation energy was evaluated using the Kissinger and Takhor methods.

Nonisothermal Cold Crystallization Kinetics of Poly(lactic acid)/Bacterial Poly(hydroxyoctanoate) (PHO)/Talc

AbstractThe effects of bacterial poly(hydroxyoctanoate) (PHO) and talc on the nonisothermal cold crystallization behaviours of poly(lactic acid) (PLA) were analysed with differential scanning calorimetry (DSC), and the thermal stability of the samples was observed with thermal gravimetric analysis (TGA). The modified Avrami’s model was used to describe the nonisothermal cold crystallization kinetics of neat PLA and its blends. The activation energies E for nonisothermal cold crystallization were calculated by the isoconversional method of Kissinger-Akahira-Sunose (KAS). The DSC results showed that the PLA/PHO blends were immiscible in the whole studied range, and as the PHO and talc content increased, the crystallization rate of PLA accelerated, and the crystallinity of PLA in the PLA samples increased. The values of the Avrami exponent indicated that the nonisothermal cold crystallization of the neat PLA and its blends exhibited heterogeneous, three-dimensional spherulitic growth. The E values were strongly dependent on PHO and talc. The TGA results showed that the presence of PHO and talc slightly influenced the thermal stability of PLA.

An investigation of PLA/Babassu cold crystallization kinetics

In this work, poly(lactic acid) (PLA)-based vegetal Babassu composites were compounded and their thermal properties ascertained. Babassu acted as a facilitator agent for the nonisothermal cold crystallization of PLA. Nonisothermal cold crystallization kinetics of PLA compounds was investigated by differential scanning calorimetry applying Ozawa and Mo models; the activation energy was evaluated by Friedman equation. Our results indicate that Mo’s model describes the experimental data successfully; the maximum crystallization rates observed for PLA/Babassu composites are higher than that found for neat PLA. Ozawa model failed to provide an adequate description for the composites, mostly due to the neglected secondary crystallization and impingement of spherulites. Friedman analysis shows that 5 wt% Babassu filler reduced the activation energy of the crystallization process greatly, leading to a shorter crystallization time.

Influence of the combination of nucleating agent and plasticizer on the non-isothermal crystallization kinetics and activation energies of poly(lactic acid)

The influence of the combination of the nucleating agent (talc, N, N′-ethylene bis-stearamide (EBS) and a commercial nucleating agent NT-20) and the plasticizer (poly(ethylene glycol), PEG) on the melting and crystallization behaviors of poly(lactic acid) (PLA) was investigated by means of differential scanning calorimetry (DSC). The Jeziorny’s, Ozawa’s and Mo’s models were used to describe the non-isothermal cold and melt crystallization kinetics of the modified PLA samples. The non-isothermal cold and melt crystallization activation energies were evaluated by Kissinger’s method and Friedman’s method, respectively. The results show that the non-isothermal cold and melt crystallization kinetics of the samples are successfully analyzed by Jeziorny’s and Mo’s models, whereas Ozawa’s model is only suitable for the non-isothermal melt crystallization kinetics of PLA/talc sample. It is shown that the combination of one nucleating agent and PEG results in the synergistic effect on the cold and melting crystallization rates of PLA. Moreover, the combination of dual nucleating agents and PEG improves the cold crystallization rate but hinders the melt crystallization rate. It is indicated that dual nucleating agents act as physical hindrance to the molecular chain movement of PLA which results in the increases in the cold and melt crystallization activation energies.

The Effect of Composite Nucleating Agent on the Crystallization Behavior of Branched Poly (Lactic Acid)

Composite nucleating agent (CNA) consisting of zinc oxide as a crystallization promoter and phenylphosphonic acid zinc salt (PPZn) as an heterogeneous nucleation agent was employed to improve the crystallization behaviors of branched poly (lactic acid) (B-PLA) which was prepared by use of multi-functional epoxy-based chain extender (CE). The differential scanning calorimeter results showed that the crystallinity and crystallization temperature of prepared B-PLA/CNA were higher than that of linear poly (lactic acid) (L-PLA) and B-PLA at a high cooling rate. The corresponding phenomena of heterogeneous nucleation of B-PLA/CNA were observed by means of polarized optical microscope. The crystalline mechanism research results show that the degradation reaction and chain extending reaction were occurred simultaneously after the addition of CE and CNA into the PLA, PPZn as an effective nucleation points could increase the nucleation density and the degraded short molecular chains with higher chain mobility would improve crystal growth during the crystallization of the branched PLA. Non-isothermal cold crystallization kinetics of various B-PLA with different content of CNA was studied. The corresponding result showed that the crystallinity and crystallization rate increased obviously with the CNA content greater than or equal to 5phr, as well as the crystallization time decreased. The similar experimental results of non-isothermal and isothermal melt crystallization kinetics also showed that CNA had a significant impact on crystallization behavior of B-PLA.

Isothermal and nonisothermal cold crystallization kinetics of poly(l-lactide)/functionalized eggshell powder composites

Functionalized eggshell powder (NES) with nucleating surface of calcium phenylphosphonic acid (PPCa) for poly(l-lactide) (PLLA) was compounded with PLLA via melt blending to improve the cold crystallization process of PLLA. The cold crystallization behavior of the PLLA/NES composites was studied by differential scanning calorimetry. The isothermal cold crystallization rates have been enhanced obviously in the PLLA/NES composites than in the neat PLLA, indicative of the excellent nucleating effects of NES on PLLA. For the nonisothermal cold crystallization, the overall crystallization rate of PLLA increased with both increasing NES loadings and heating rate. It was found that the Avrami equation and the combined Ozawa–Avrami model could describe the experiment data successfully.

Isothermal and nonisothermal crystallization kinetics of novel biobased poly(ethylene succinate-co-ethylene sebacate) copolymers from the amorphous state

In this work, the isothermal and nonisothermal crystallization kinetics of three novel biobased poly(ethylene succinate-co-ethylene sebacate) (PESSe) copolymers was systematically investigated with differential scanning calorimetry under different crystallization conditions from the amorphous state. For the isothermal cold crystallization kinetics study, the Avrami equation could well describe the crystallization process of PESSe at various crystallization temperatures. All three PESSe copolymers crystallized through the same crystallization mechanism; moreover, the overall isothermal cold crystallization rate of PESSe decreased with increasing ethylene sebacate (ESe) comonomer content. The nonisothermal cold crystallization kinetics of PESSe was also studied at different heating rates. With increasing ESe content or heating rate, the nonisothermal cold crystallization exotherm of PESSe copolymers shifted to high temperature range. Both the crystallization rate parameter and crystallization rate coefficient of PESSe copolymers decreased with increasing ESe content, indicating that PESSe copolymer with higher ESe content crystallized more slowly than that with lower ESe content. The Ozawa equation was used to analyze the nonisothermal cold crystallization kinetics of PESSe copolymers, which was found to fit the crystallization process very well.

Crystallization and relaxation dynamics of amorphous loratadine under different quench-cooling temperatures

In this paper, four amorphous samples of loratadine were prepared by quench-cooling the melted drug at different temperatures. With these samples, the crystallization tendencies were tested by powder X-ray diffraction (PXRD), and non-isothermal cold crystallization kinetics was investigated by using differential scanning calorimetry (DSC) and the molecular dynamics both in super-cooled liquid and in glassy states was analyzed by using broadband dielectric spectroscopy (BDS) at a temperature range from 213 to 393 K. From the PXRD results, it was established that the four amorphous loratadine samples were apt to crystallize at a temperature below the glass transition temperature. From the DSC results, it was found that the non-isothermal crystallization mechanism of these four loratadine forms was similar. However, the fast crystallization tendency (low physical stability) was also observed for the amorphous loratadine which was obtained at a low quench-cooling temperature. The tendency was analyzed based on the BDS results which demonstrated that rapid molecular mobility could generate a low physical stability and was closely related to Johari–Goldstein relaxation. These results suggested that loratadine had a weak frustration against crystallization and its physical stability was affected by the quench-cooling temperature. This study laid a foundation for choosing the right technique to prepare the amorphous form of loratadine and improving its physical stability.

Non-isothermal cold crystallization kinetics of poly(3-hydoxybutyrate) filled with zinc oxide

The non-isothermal cold crystallization kinetics of poly(3-hydroxybutyrate) (PHB) and PHB-ZnO composites, with ZnO content of 1%, 5% and 10% per weight, was investigated at different heating rates (5, 7.5, 10, 15, 20 and 30°C/min) using differential scanning calorimetry. Both, Kissinger and Friedman activation energies predict correctly the slowest and fastest crystallizing composition. It was further found, that ZnO can neither be classified as a crystallization accelerator, nor as a crystallization inhibitor; its action is strongly concentration dependent. The empirical Pseudo-Avrami model has the best overall capability for fitting the experimental kinetic data. However, since the Pseudo-Avrami exponent was found to vary irregularly with heating rate and filler content, this model should not be applied for kinetic predictions of an arbitrary composition or an untested heating rate. In such cases, Mo's model should be used.

Non-isothermal crystallization kinetics of sucrose palmitate reinforced poly(lactic acid) bionanocomposites

Poly(lactic acid) (PLA) bionanocomposites containing sucrose palmitate (SP), which is a non-toxic food additive, were prepared by a simple solution-casting approach. In the current work, the investigation of non-isothermal cold crystallization kinetics of PLA and PLA–SP bionanocomposites was performed using a differential scanning calorimeter under the dynamic heating regime of 2.5, 5, 7.5 and 10 °C/min. Avrami model was employed to study the effect of SP on cold crystallization kinetics of PLA. For PLA–SP bionanocomposites, Avrami coefficients obtained in the range of ~2.5–4 and decreasing trend of the t 1/2 values indicated the faster crystallization mechanism in comparison to neat PLA. The nucleation and growth mechanism involved in the non-isothermal crystallization of PLA and PLA–SP bionanocomposites were further analyzed by Tobin model. Kissinger method has been employed to determine the crystallization activation energy (ΔE) for neat PLA and PLA–SP bionanocomposite. The nucleation as well as the growth of spherulites in neat PLA and PLA–SP bionanocomposites was observed using polarized optical microscopy. After incorporation of SP in the PLA matrix, an increase in the overall crystallization rate for PLA was reflected by the decline in the nucleation induction period and subsequent enhancement in the primary nucleation sites.

A novel single-component composite based on phthalonitrile end-capped polyarylene ether nitrile: crystallization and crosslinking

A novel single-component composite based on phthalonitrile end-capped polyarylene ether nitrile (PEN-Ph) was prepared successfully via hot compression. In the PEN-Ph system, the crosslinking reactions and crystallization exist simultaneously, and the crystals are embedded in the crosslinked PEN-Ph matrix, which can work as reinforcement. Analysis of the Non-isothermal cold crystallization kinetics of the PEN-Ph system was performed by using differential scanning calorimetry (DSC), and the activation energy of the crystallization process is obtained to be 217.5 kJ · mol−1. The DSC and SEM analysis provide the evidence for that there exists crosslinking reactions as well as crystallization behavior. However, the crosslinking reaction with excessive speed will restrict the crystallization behavior of the PEN-Ph. Furthermore, the DMA and mechanical measurements indicate that the glass transition temperature and mechanical properties are influenced by not only the crosslinking degree but also the crystallinity. The tensile strength of the single-component composite is 111.0 MPa, increased by about 10 MPa than that of amorphous PEN-Ph sheet.

Non-isothermal cold crystallization kinetics of poly(lactic acid)/poly(butylene adipate-co-terephthalate)/treated calcium carbonate composites

The non-isothermal cold crystallization behaviors of poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate)/titanate-treated calcium carbonate (T-CaCO3) composites were studied by means of differential scanning calorimetry. The activation energies (E a) of non-isothermal cold crystallization were calculated by Kissinger’s method. It is found that Jeziorny’s and Mo’s methods well describe the non-isothermal cold crystallization kinetics of neat PLA and PLA composites, while Ozawa’s model fails. The cold crystallization rate and E a of PLA composites are greater than those of neat PLA. It is attributed to the dual effect (heterogeneous nucleating agent and physical hindrance) of T-CaCO3 on the cold crystallization.

Crystallization behavior, morphology, and mechanical properties of poly(lactic acid)/tributyl citrate/treated calcium carbonate composites

In this article, poly(lactic acid) (PLA) composites containing titanate coupling agent treated calcium carbonate (T-CaCO3) and tributyl citrate (TBC) were prepared via melt blending. The crystallization, morphology, mechanical properties, and nonisothermal cold crystallization kinetics of PLA composites were studied by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), polarized light microscopy (PLM), scanning electron microscopy (SEM), and mechanical tests, respectively. The results show that TBC promotes crystallization of PLA. Both T-CaCO3 and TBC significantly decrease the spherulitic size, but the crystal structure of PLA is not changed. A synergistic toughening effect is obtained by the combination of T-CaCO3 and TBC. The nonisothermal cold crystallization kinetics of PLA composites is well described by Mo's method. The activation energies (ΔE) of nonisothermal cold crystallization were calculated by Kissinger and Takhor methods, respectively. It is found that the addition of T-CaCO3 and TBC increases ΔE, but it also increases the cold crystallization rate. POLYM. COMPOS., 35:1570–1582, 2014. © 2013 Society of Plastics Engineers

Non-isothermal cold crystallization behavior and kinetics of poly(l-lactide): effect of l-lactide dimer

The effects of l-lactide dimer as additives on the crystallization behavior of poly(l-lactide) (PLLA) films were studied. Hence, neat PLLA films and PLLA containing l-lactide (5 % w/w) (PLLA/La) were prepared in dichloromethane at room temperature via solution casting. The non-isothermal cold crystallization of PLLA films were studied using differential scanning calorimetry at various heating rates including 2.5, 5, 7.5, 10 and 15 °C/min. However, the X C% was increased for PLLA/La films in comparison with neat PLLA films. The crystallization kinetics was then analyzed by the Avrami, Jeziorny, Ozawa and Mo kinetic models. It is found that all the kinetic models were established to describe the experimental data fairly well except the Ozawa model. The values of t 1/2, Z C and F(T) indicated that the crystallization rate increased with increase in heating rates for PLLA and PLLA/La films. However, l-lactide dimer incorporated in PLLA films accelerates the crystallization process of PLLA at the high heating rate. The nucleation constant (K g) and the surface free energy (σ e) based on Lauritzen–Hoffman theory indicated that these parameters for PLLA/La films is lower than neat PLLA.

Crystallization behavior of poly(lactide)/poly(β‐hydroxybutyrate)/talc composites

AbstractThe morphology and miscibility of commercial poly(lactide) (PLA)/poly(β‐hydroxybutyrate) (PHB, from 5 to 20 wt %) blends prepared by melt extrusion method, were investigated using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) observations. The results show that for all the studied blend contents, PLA/PHB blends are immiscible. The effects of PHB and talc on the nonisothermal cold crystallization kinetics of PLA were examined using a differential scanning calorimetry (DSC) at different heating rates. PHB acted as a nucleating agent on PLA and the addition of talc to the blend yielded further improvement, since significant increase in the enthalpy peak was observed for samples containing 10 wt % PHB and talc (from 0.5 to 5 phr). The crystallization kinetics were then examined using the Avrami–Jeziorny and Liu–Mo approach. The simultaneous presence of PHB and talc induced a decrease of the crystallization half time. The evolution of activation energies determined with Kissinger's equation suggests that blending with PHB and incorporating talc promote nonisothermal cold crystallization of PLA. The synergistic nucleating effect of PHB and talc was also observed on isothermal crystallization of PLA from the melt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013