Nonisothermal Cold Crystallization Research Articles

Production and characterization of sustainable poly(lactic acid)/functionalized-eggshell composites plasticized by epoxidized soybean oil

To improve the intrinsic brittleness and crystallization capacity of poly(lactic acid) (PLA), fully sustainable PLA composites were prepared. The biodegradable PLA composites consisted of 10 wt% epoxidized soybean oil (ESO) and different amounts of functional eggshell (FES) with surface modified with calcium phenylphosphonate (PPCa) were prepared by melt blending. Mechanical and crystallization behavior were studied in terms of the weight percentage of FES. ESO-plasticized PLA showed an excellent tensile toughness with the elongation at break increased over than 160% compared to 6% of pure PLA. The elongation at break for PLA composites was still higher than 70% even filled with 30 wt% FES. Besides, the tensile and storage moduli of PLA/ESO/FES composites did not suffer significant deterioration as compared with pure PLA. For cold crystallization behavior, FES with surface modified by PPCa as a good nucleating agent improved the nucleating ability of PLA. The rates of nonisothermal and isothermal cold crystallization of PLA were improved due to the synergistic effect of plasticization and nucleation. The nonisothermal cold crystallization peak temperature (Tcc) of PLA composites decreases considerably from 118.7 °C (for pure PLA) to 90 °C. The crystallization half-time of PLA composites is lower than 10 min compared with 162 min of pure PLA after isothermal crystallized at 75 °C. As a consequence, it is encouraging that ESO and FES exhibit great viability for modifying the mechanical and crystallization properties of PLA matrix, which make PLA a promising sustainable alternative to petroleum-based polymers in conventional fields.

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.

Influence of high molecular weight poly(ethylene adipate) on the crystallization behavior and mechanical properties of biodegradable poly(l-lactide) in their immiscible polymer blend

A fully biodegradable polymer blend consisting of poly(l-lactide) (PLLA) and poly(ethylene adipate) (PEA) with relatively high number average molecular weight of 8000 g/mol (80/20 in weight ratio) was prepared through a solution and casting method. The dynamic mechanical analysis and scanning electron microscopy studies confirmed that PLLA was immiscible with PEA. The crystallization behavior, crystal structure and mechanical properties of PLLA/PEA blend were investigated and compared with those of neat PLLA. In the immiscible blend, the blending with PEA enhanced the nonisothermal cold and melt crystallization behavior, decreased the isothermal melt crystallization rate and retained the crystallization mechanism and crystal structure of PLLA. The tensile test results revealed that the ductility and toughness of PLLA phase were significantly improved by the blending with high molecular weight PEA.

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.

Enhanced crystallization and mechanical properties of biodegradable poly(ethylene succinate) by octaisobutyl-polyhedral oligomeric silsesquioxanes in their nanocomposites

Two poly(ethylene succinate) (PES) based nanocomposites containing low loadings (0.5 and 1.0wt%) of octaisobutyl-polyhedral oligomeric silsesquioxanes (oib-POSS) were prepared via a solution and casting method. The scanning electron microscopy observation demonstrated the fine dispersion of oib-POSS in the PES matrix. The nonisothermal cold and melt crystallization behaviors, isothermal melt crystallization kinetics, crystalline morphology, crystal structure, and mechanical properties of PES and its nanocomposites were studied. Oib-POSS not only enhanced the nonisothermal cold and melt behaviors but also accelerated the overall isothermal melt crystallization process of PES in the nanocomposites, indicating its nucleating agent effect. Oib-POSS did not modify the crystal structure of PES in the nanocomposites; furthermore, oib-POSS and PES crystallized separately in the nanocomposites. Oib-POSS obviously enhanced the Young's modulus and yield strength while still maintained relatively good ductility of PES in the nanocomposites, suggesting the efficient reinforcing effect of oib-POSS on the mechanical properties of PES.

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.

Effect of poly(ethylene glycol)-polyhedral oligomeric silsesquioxanes on the thermal and mechanical properties of biodegradable poly(l-lactide)

Abstract In this work, a poly( l -lactide) (PLLA)/poly(ethylene glycol)-polyhedral oligomeric silsesquioxanes (PEG-POSS) nanocomposite was first prepared; moreover, the nonisothermal crystallization behavior, thermal stability, and mechanical properties of the nanocomposite were extensively studied and compared with those of neat PLLA. PEG-POSS was miscible with PLLA, as proved by a single glass transition temperature. As PEG-POSS increased the chain mobility of PLLA as a plasticizer, the nonisothermal cold and melt crystallization behaviors of PLLA were enhanced by PEG-POSS in the nanocomposite; furthermore, the thermal stability of PLLA was not obviously affected by PEG-POSS. In addition, PEG-POSS increased the ductility of PLLA as an efficient plasticizer and still maintained high Young's modulus.

Effect of poly(ethylene glycol)-polyhedral oligomeric silsesquioxanes on the crystallization kinetics and morphology of biodegradable poly(ethylene succinate)

Biodegradable poly(ethylene succinate) (PES)/poly(ethylene glycol)-polyhedral oligomeric silsesquioxanes (PEG-POSS) nanocomposites were prepared via a solution and casting method in this work. The distribution of PEG-POSS, miscibility between PES and PEG-POSS, and crystallization behavior of PES/PEG-POSS nanocomposites were fully investigated. PEG-POSS particles were homogeneously dispersed in the PES matrix. PEG-POSS was miscible with PES to some degree, because the samples displayed a single composition dependent glass transition temperature and a depression of equilibrium melting point of PES in the nanocomposites. PEG-POSS increased the chain mobility of PES, thereby improving the nonisothermal cold and melt crystallization processes, accelerating the isothermal melt crystallization rate, and increasing the spherulitic growth rate of the nanocomposites. However, the isothermal crystallization mechanism and the crystal structure of PES were not modified by PEG-POSS. PEG-POSS enhanced the crystallization behavior of PES by acting as a plasticizer.

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.

Enhanced nonisothermal and isothermal cold crystallization kinetics of biodegradable poly(l‐lactide) by trisilanolisobutyl‐polyhedral oligomeric silsesquioxanes in their nanocomposites

ABSTRACTIn this work, the nonisothermal and isothermal cold crystallization behaviors of poly(l‐lactide) (PLLA)/trisilanolisobutyl‐polyhedral oligomeric silsesquioxanes (tsib‐POSS) nanocomposites with low tsib‐POSS contents were fully investigated. For all the samples, the variations of heating rate and the tsib‐POSS loading may influence the nonisothermal cold crystallization of PLLA. During the nonisothermal crystallization kinetics study, the Ozawa equation failed to fit the nonisothermal crystallization process of PLLA, while the Tobin equation could fit it well. For the isothermal crystallization kinetics study, the crystallization rates of all the samples increased with increasing crystallization temperature. The cold crystallization activation energy of PLLA was increased with 1 wt % tsib‐POSS. Moreover, the addition of tsib‐POSS and the increment of tsib‐POSS loading could increase the crystallization rate of PLLA, indicating the nucleating agent effect of tsib‐POSS. However, the crystallization mechanism and crystal structure of PLLA remained unchanged in the nanocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43896.

Non-Isothermal Cold-Crystallization Behavior and Kinetics of Poly(l-Lactic Acid)/WS2 Inorganic Nanotube Nanocomposites

In order to accelerate the crystallization of poly(l-lactic acid) (PLLA) biopolymer and enhance its crystallizability, biocompatible and environmentally friendly tungsten disulphide inorganic nanotubes (INT-WS2) were introduced into the polymer matrix. The non-isothermal cold-crystallization and subsequent melting behaviour of pure PLLA and PLLA/INT-WS2 nanocomposites were investigated in detail by varying both the heating rate and INT-WS2 loading. The kinetic parameters of the cold-crystallization process of PLLA chains under confined conditions, successfully described using Liu model, shows that the addition of INT-WS2 significantly increased the crystallization rate and reduced the total cold-crystallinity of PLLA, while the crystallization mechanism and crystal structure of PLLA remained unchanged in spite of the INT-WS2 loading. Similarly, the final crystallinity and melting behaviour of PLLA were controlled by both the incorporation INT-WS2 and variation of the heating rate. The differential isoconversional method of Friedman was applied to estimate the dependence of the effective activation energy on the relative crystallinity and temperature for PLLA and PLLA/INT-WS2. On the other hand, the double-melting peaks, mainly derived from melting-recrystallization-melting processes upon heating, and their dynamic behaviour is coherent with a remarkable nucleation-promoting effect of INT-WS2 involved in accelerating the cold-crystallization of PLLA. These observations have considerable practical significance for the future sustainable, economic and effective technological utilisation of PLLA, as it will enable the development of novel melt-processable biopolymer nanocomposite materials.

Preferential Stereocomplex Crystallization in Enantiomeric Blends of Cellulose Acetate-g-Poly(lactic acid)s with Comblike Topology.

Although stereocomplex (sc) crystallization is highly effective for improving the thermal resistance of poly(lactic acid) (PLA), it is much less predominant than homocrystallization in high-molecular-weight (HMW) poly(l-lactic acid)/ poly(d-lactic acid) (PLLA/PDLA) racemic blends. In this contribution, the sc crystallization of HMW PLLA/PDLA racemic blends was facilitated by using comblike PLAs with cellulose acetate as the backbone. Competing crystallization kinetics, polymorphic crystalline structure, and structural transition of comblike PLLA/PDLA blends with a wide range of MWs were investigated and compared with the corresponding linear/comblike and linear blends. The HMW comblike blend is preferentially crystallized in sc polymorphs and exhibits a faster crystallization rate than does the corresponding linear blend. The sc crystallites are predominantly formed in nonisothermal cold crystallization and isothermal crystallization at temperatures above 120 °C for the comblike blends. Except for the facilitated sc formation in primary crystallization, synchrotron radiation WAXD analysis indicates that the presence of a comblike component also facilitates the transition or recrystallization from homocrystallite (hc) to sc crystallite upon heating. Preferential sc formation of comblike blends is probably attributable to the favorable interdigitation between enantiomeric branches and the increased mobility of polymer segments. After crystallization under the same temperature, the comblike blends, which mainly contain sc crystallites, show smaller long periods and thinner crystalline lamellae than do the corresponding PLLA with homocrystalline structures.

Effect of Hydrophilicity of Clay on Cold Crystallization of Poly(trimethylene terephthalate) Nanocomposites

Poly(trimethylene terephthalate) (PTT) nanocomposites with two different clays were fabricated via a novel two-step process. Structure, morphology, and cold crystallization of these nanocomposites were studied using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). XRD results reveals that PTT-15A nanocomposites were fully exfoliated, whereas PTT-30B nanocomposites were partially exfoliated. Non-isothermal cold crystallization temperature and the crystallinity of non-isothermally cold-crystallized PTT-15A nanocomposites increased with increasing 15A content. The crystallinity of isothermally cold-crystallized PTT-15A nanocomposites was shown to increase with crystallization temperature and the clay content, but no clear trend in crystallinity was observed for PTT-30B nanocomposites. The combination of FTIR and DSC has been used to determine the conformational changes during isothermal cold crystallization. The results show that the crysta...

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.

The effect of Pglass state on the non-isothermal cold and melt crystallization processes of PET matrix

The physical state of phosphate glass (Pglass) has an influence on the non-isothermal crystallization behaviors of PET matrix in the PET/Pglass blends, which has been investigated via heating the glassy state and cooling the melt state of the blends at various scanning rates, respectively, by means of differential scanning calorimetry (DSC) technique. The kinetics models based on the Avrami and Mo equations were used to analyze the non-isothermal crystallization process. Furthermore, the activation energy of non-isothermal crystallization, according to Kissinger theory for heating process and Friedman theory for cooling process, has been evaluated. The results showed that the Pglass accelerated the non-isothermal cold crystallization rate of PET matrix due to its nucleation effect. In contrast, for the non-isothermal melt crystallization, the Pglass hindered the crystallization process due to its large melt viscosity.

Crystallization kinetics and molecular mobility of an amorphous active pharmaceutical ingredient: A case study with Biclotymol

The present case study focuses on the crystallization kinetics and molecular mobility of an amorphous mouth and throat drug namely Biclotymol, through differential scanning calorimetry (DSC), temperature resolved X-ray powder diffraction (TR-XRPD) and hot stage microscopy (HSM). Kinetics of crystallization above the glass transition through isothermal and non-isothermal cold crystallization were considered. Avrami model was used for isothermal crystallization process. Non-isothermal cold crystallization was investigated through Augis and Bennett model. Differences between crystallization processes have been ascribed to a site-saturated nucleation mechanism of the metastable form, confirmed by optical microscopy images. Regarding molecular mobility, a feature of molecular dynamics in glass-forming liquids as thermodynamic fragility index m was determined through calorimetric measurements. It turned out to be around m=100, describing Biclotymol as a fragile glass-former for Angell’s classification. Relatively long-term stability of amorphous Biclotymol above Tg was analyzed indirectly by calorimetric monitoring to evaluate thermodynamic parameters and crystallization behavior of glassy Biclotymol. Within eight months of storage above Tg (T=Tg+2°C), amorphous Biclotymol does not show a strong inclination to crystallize and forms a relatively stable glass. This case study, involving a multidisciplinary approach, points out the importance of continuing looking for stability predictors.

An incremental isoconversional method for kinetic analysis based on the orthogonal distance regression.

The parameters obtained from a kinetic analysis of thermoanalytical data often exhibit a conversion-dependent behavior. A novel incremental isoconversional method able to deal with this phenomenon is proposed. The kinetic model is directly fitted to the experimental data using nonlinear orthogonal least squares procedure. The data are processed without transformations, so their error distribution is preserved. As the objective function is based on a maximum likelihood approach, reliable uncertainties of the parameters can be estimated. In contrast to other methods, the activation energy and the pre-exponential factor are treated as equally important kinetic parameters and are estimated simultaneously. Validity of the method is verified on simulated data, including a dataset with local nonlinearity in the temperature variation. A practical application on the nonisothermal cold crystallization of polyethylene terephthalate is presented.

Effect of biodegradable poly(ethylene adipate) with low molecular weight as an efficient plasticizer on the significantly enhanced crystallization rate and mechanical properties of poly(l-lactide)

The slow crystallization rate and low elongation at break are the main drawbacks of biodegradable poly(L-lactide) (PLLA) from a viewpoint of practical application. Such disadvantages of PLLA have been successfully resolved by blending with low molecular weight biodegradable poly(ethylene adipate) (PEA) in the present work. As a biodegradable plasticizer, PEA not only formed fully miscible and biodegradable polymer blends with PLLA but also apparently reduced the glass transition temperature of the blends. The increased chain mobility favored the nonisothermal cold and melt crystallization behaviors, increased the spherulitic growth rate, and accelerated the overall isothermal melt crystallization process of the blends; however, the blends had the same crystallization mechanism and crystal structures as neat PLLA. One of the exciting results was that the elongation at break value of an 80/20 PLLA/PEA blend was dramatically increased; therefore, for a wider practical application, the preparation of PLLA-based materials with fast crystallization rate, good mechanical properties, and complete biodegradability could be accomplished by the blending with a small amount of PEA with low molecular weight as an efficient plasticizer.