Nonisothermal Melt Crystallization Behavior Research Articles

Eco-friendly zinc-metal-organic framework as a nucleating agent for poly (lactic acid)

Eco-friendly poly(L-lactic acid) (PLA) can be made more versatile, and its crystallization rate is accelerated by adding Zinc-based metal-organic framework (Zn-MOF) particles. Using differential scanning calorimetry (DSC), the non-isothermal melt crystallization behavior of biodegradable PLA nucleated by 0.3 to 3 wt% of Zn-MOF was examined. The non-isothermal melt crystallization kinetics parameters were determined using a modified Avrami model and Mo approach. Zn-MOF dramatically accelerated the crystallization process, as evidenced by several non-isothermal crystallization metrics, including the crystallization half-time and crystallization rate constant. The melt crystallization temperatures of the PLA-Zn-MOF composites, with contents of 0.7 and 1 wt%, were increased by 21 °C compared to the neat PLA. Using the Friedman isoconversional kinetic method, the neat PLA and PLA-Zn-MOF composites' effective activation energy values, ∆E, were determined. The ∆E values of PLA-Zn-MOF from 0.3 to 1 wt% Zn-MOF composites were lower than that of neat PLA. Moreover, polarized optical microscopy revealed the formation of numerous small-sized PLA spherulites upon Zn-MOF addition. The results indicate that the Zn-MOF (at concentrations of 0.7 to 1.0 wt%) can be used as an efficient nucleating agent for PLA, where it increases the melt crystallization temperature, nucleation density, and crystallinity without changing the crystalline structure, while also significantly reduces the effective activation energy and the size of spherulites. Additionally, scanning electron microscopy confirms good dispersion of Zn-MOF (0.3 to 1 wt%) within the PLA matrix.

Comparing non-isothermal melt and cold crystallization behavior and kinetics of poly(ethylene 2,5-furandicarboxylate-co-ethylene terephthalate) copolyesters

Comparing non-isothermal melt and cold crystallization behavior and kinetics of poly(ethylene 2,5-furandicarboxylate-co-ethylene terephthalate) copolyesters

Enhancement of the properties of poly(L-lactide)/poly(butylene adipate-co-terephthalate) blends by introduction of stereocomplex polylactide crystallites

Herein, poly(L-lactide) (PLLA), poly(butylene adipate-co-terephthalate) (PBAT), and poly(D-lactide) (PDLA) were melt compounded by a low-temperature method to prepare ternary blends with balanced properties. Differential scanning calorimetry results and torque changes during melt blending confirmed that the stereocomplex polylactide (SC-PLA) crystallites were formed. Network structure composed of SC-PLA crystallites was formed when the PDLA content was 5 wt%, at which point the melts of the blend exhibited solid-like rheological behavior. The formation of SC-PLA crystallites increased the viscosity ratio between PLLA and PBAT melt, which led to an increase of the size of dispersed PBAT phase. Furthermore, the SC-PLA crystallites could greatly promote both nonisothermal and isothermal melt crystallization behaviors of PLLA/PBAT/PDLA ternary blends because of their effective heterogeneous nucleation effect. The ternary blend containing 2 wt% PDLA showed good toughness and had an elongation at break of 211% compared to the elongation at break of 3.5% for neat PLLA. These biodegradable blends showed excellent melt crystallization abilities as well as tailored rheological and mechanical properties, which could demonstrate their potential as traditional non-biodegradable plastic substitutes.

Fully biodegradable Poly(butylene succinate-co-1,2-decylene succinate)/Cellulose nanocrystals composites with significantly enhanced crystallization and mechanical property*

Poly (butylene succinate-co-1,2-decylene succinate) (PBDS) is a promising biodegradable polyester with n-octyl being the side group (Polymer 2021, 213, 123197). The toughness of PBDS is significantly higher than that of linear poly (butylene succinate) (PBS), while the tensile strength and crystallization rate of PBDS are remarkably lower than those of PBS. In this research, fully biodegradable PBDS/cellulose nanocrystals (CNC) composites were prepared at low CNC loadings with the aim of improving the crystallization and mechanical properties. The surface morphology study suggested CNC achieved an even distribution in PBDS. As an efficient heterogeneous nucleating agent, CNC obviously enhanced the nonisothermal melt crystallization behavior and isothermal melt crystallization kinetics of PBDS, as evidenced by the upward shift of melt crystallization temperature and shorter crystallization half-time. Both the nucleation activity and nucleation efficiency of CNC were quantitively evaluated, which were 0.40 and 44.9%, respectively, at a CNC loading of 2 wt%. CNC did not change the crystallization mechanism and crystal structure of PBDS. The mechanical properties study indicated that the tensile mechanical properties (Young's modulus and tensile strength from the tensile test) and storage modulus (from dynamic mechanical analysis) of PBDS were obviously enhanced by CNC, indicating the reinforcement effect.

Crystallization Studies of Poly(trimethylene terephthalate)/Silica Nanocomposites Prepared by Sol-Gel Technique.

Poly(trimethylene terephthalate) (PTT)/silica nanocomposite films were successfully fabricated using a novel sol–gel approach. The synthesis of these nanocomposites is being carried out by hydrolysis and condensation of tetraethoxysilane using trifluoroacetic acid with a small amount of water. The scanning electron microscopy and zetasizer result showed that the silica particles with a size range of 80–100 nm were homogeneously dispersed in the PTT matrix. The effect of different amounts of silica on crystallization of PTT was investigated using X-ray diffraction, differential scanning calorimetry (DSC), and optical microscopy. Polarized light microscopic results revealed that the spherulite size gradually decreased with increasing silica loading and increased with crystallization temperature for a given nanocomposite during isothermal melt crystallization. PTT with a small amount of SiO2 melt crystallized at low temperatures showed banded spherulites. DSC results revealed that nonisothermal cold crystallization temperature decreased with silica content, whereas no significant change in nonisothermal melt crystallization behavior was observed with silica content. The crystallinity of isothermally melt crystallized PTT increased with both crystallization temperature and silica loading.

Effect of low loadings of cellulose nanocrystals on the significantly enhanced crystallization of biodegradable poly(butylene succinate-co-butylene adipate)

Biodegradable poly(butylene succinate-co-butylene adipate) (PBSA)/cellulose nanocrystals (CNC) nanocomposites were successfully prepared via a solution and casting method at low CNC loadings. The nonisothermal and isothermal melt crystallization behaviors of PBSA/CNC nanocomposites were significantly enhanced by low loading of CNC. The nonisothermal melt crystallization peak temperature obviously increased from 56 °C for neat PBSA to 63.6 °C for PBSA/CNC1 (the nanocomposite containing 1 wt% CNC) at 10 °C/min. Crystallization half-time at 80 °C significantly decreased from 31 min for neat PBSA to 8.4 min for PBSA/CNC1. CNC apparently increased the crystallization rate of PBSA; however, the crystallization mechanism remained unchanged. The crystalline morphology study verified the enhanced nucleation density of PBSA spherulites, indicating the role of CNC as an efficient nucleating agent. In addition, low loadings of CNC did not modify the crystal structure of PBSA.

Effect of content and particle size of talc on nonisothermal melt crystallization behavior of poly(l-lactide)

This work examined the effect of content and particle size of nucleating agent on nonisothermal melt crystallization behavior of poly(l-lactide) (PLLA). Two different particle sizes of talc were used as the nucleating agents of PLLA. Scanning electron microscopy observation revealed that both big and small particles of talc were homogeneously dispersed in the PLLA matrix. Talc significantly accelerated the nonisothermal melt crystallization rate of PLLA. The effect of smaller particle talc on crystallization was obviously better than that of the bigger one. The activation energy based on Friedman equation was evaluated. Lower activation energy was obtained for nucleated PLLA. Finally, addition of talc did not modify the crystal structure.

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.

Enhanced crystallization rate of biodegradable poly(ε-caprolactone) by cyanuric acid as an efficient nucleating agent

The influence of cyanuric acid (CA) as an efficient nucleating agent on the crystallization behavior and morphology of biodegradable poly(e-caprolactone) (PCL) was extensively studied in this work with several techniques for the first time. The nonisothermal melt crystallization behavior and overall isothermal melt crystallization rate of PCL were significantly enhanced by only a small amount of CA. The addition of CA apparently improved the nonisothermal melt crystallization peak temperature, overall isothermal melt crystallization rate, and nucleation density of PCL spherulites, but did not modify the crystallization mechanism and crystal structure of PCL, indicating that CA was an efficient nucleating agent for the crystallization of PCL. The possible nucleation mechanism of CA on the crystallization of PCL was also discussed on the basis of their crystal structures.

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.

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.

Nonisothermal melt crystallization of PHB/babassu compounds

Poly(3-hydroxybutyrate) (PHB)/babassu compounds were prepared in a laboratory internal mixer with 10, 30, and 50 % by mass of fiber content. Nonisothermal melt crystallization behavior of PHB/babassu compounds was investigated using differential scanning calorimetry, and crystallization parameters were determined at cooling rates ranging between 2 and 32 °C min−1. Adding babassu fiber affected the melt crystallization behavior of PHB, and increasing filler content from 10 to 30 % has significant effects on the thermal characteristics of the system. Further increase in filler content from 30 to 50 % filler content has no effect on crystallization temperature and rate, but it has important positive consequences, once there is a considerably latitude in choosing the actual filler level in highly loaded PHB/babassu compounds without affecting processing characteristics. The melt crystallization kinetics of PHB/babassu compounds was analyzed by three empirical models widely used to represent nonisothermal polymer crystallization data: Pseudo-Avrami, Ozawa, and Mo. Kinetics analyses indicate that the Pseudo-Avrami model represented well the experimental data for both compounds in a wide interval of temperature, conversion, and cooling rates; the Ozawa model with two different sets of parameters, for low and high cooling rates, was found to correlate the data equally well, but over limited ranges of the variables, and the model proposed by Mo and collaborators did not adequately represent the experimental data for the systems and conditions tested.

Effect of clay on melt crystallization, crystallization kinetics and spherulitic morphology of poly(trimethylene terephthalate) nanocomposites

Poly(trimethylene terephthalate) (PTT)/clay nanocomposite films have been prepared via a novel two-step approach. The resulting nanocomposites have been characterized by Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarized light microscopy (PLM). XRD results showed this two-step process of preparation forms predominantly exfoliated structures. The effect of nanoclay on the isothermal and nonisothermal melt crystallization behaviors of PTT has been investigated and shown that the incorporation of clay accelerates the rate of crystallization and increases the total crystallinity of PTT nanocomposites compared to neat PTT. Nonisothermal melt crystallization kinetics of neat PTT and PTT nanocomposites was analyzed using crystallization isotherm. The Avrami analysis modified by Jeziorny was successfully used to describe the non-isothermal crystallization kinetics of neat PTT and PTT nanocomposites, shown by the decrease in half time (t1/2) of crystallization and increase in rate constant (Zc) as organoclay content increased up to 10%. FTIR spectroscopy has been utilized for the first time to monitor conformational changes during the melt crystallization of PTT nanocomposites. It was demonstrated that the amorphous trans conformation transforms into the crystalline gauche conformation with increasing clay content, which suggests that nanoclay accelerates the polymer chain conformational transition from trans to gauche conformation. No significant change in amorphous gauche conformation was observed either with crystallization temperature or clay content.

Enhanced crystallization rate of biodegradable poly(butylene succinate-co-ethylene succinate) by poly(butylene fumarate) as an efficient polymeric nucleating agent

PBF may significantly enhance the nonisothermal melt crystallization behavior of biodegradable PBES by acting as an efficient polymeric nucleating agent.

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.

Effects of Preexisting Poly(butylene succinate-co-24 mol % hexamethylene succinate) Crystals on the Crystallization Behavior and Crystalline Morphology of Poly(butylene adipate) in Their Melt-Miscible Polymer Blend

The effects of preexisting poly(butylene succinate-co-24 mol % hexamethylene succinate) (PBHS) crystals on the crystallization behavior and crystalline morphology of poly(butylene adipate) (PBA) were studied in their fully biodegradable melt-miscible crystalline/crystalline blend. Regardless of crystallization conditions, PBHS crystallized first, and PBA must crystallize in the presence of preexisting PBHS crystals. The preexisting PBHS crystals may not only enhance the nonisothermal melt crystallization behavior but also favor the nucleation and growth of only α-form crystals of PBA, providing an easy method of controlling the polymorphic crystals of PBA through polymer blending; moreover, the preexisting PBHS crystals could accelerate the overall isothermal melt crystallization process of PBA in the blend. PBA must crystallize as tiny crystals at the same orientation as the crystallites of the host PBHS spherulites in the blend, unlike the spherulitic morphology in its neat state. Both components crysta...

In situ ring-opening polymerization of poly(l-lactide)-graft-graphene oxide and its effect on the crystallization kinetics and morphology of biodegradable poly(l-lactide) at low loadings

Biodegradable poly(L-lactide) (PLLA) and graphene oxide (GO) nanocomposites were prepared by blending commercial PLLA with PLLA-g-GO at low loadings, which was synthesized via ring-opening polymerization using GO as the initiator and characterized with various techniques. Both the nonisothermal cold and melt crystallization behaviors and overall isothermal melt crystallization rates of PLLA have been enhanced significantly by PLLA-g-GO in the nanocomposites, relative to neat PLLA. PLLA-g-GO is more efficient than GO as a nucleating agent for the crystallization of PLLA, because PLLA is covalently grafted onto the surface of GO in PLLA-g-GO, which may provide better compatibility with the PLLA matrix and improve the nucleation ability.

Effect of cyanuric acid on the crystallization kinetics and morphology of biodegradable poly(l-lactide) as an efficient nucleating agent

Biodegradable poly(l-lactide) (PLLA) and cyanuric acid (CA) composites were prepared via a solution and casting method at low CA loadings. The nonisothermal melt crystallization behavior, overall isothermal melt crystallization kinetics, spherulitic morphology, and crystal structure of neat PLLA and the PLLA/CA composites were investigated with various techniques. Relative to neat PLLA, the crystallization process of PLLA was accelerated obviously by the presence of CA under both nonisothermal and isothermal melt crystallization conditions, indicating that CA acted as an efficient nucleating agent for the crystallization of PLLA; however, CA did not change the crystallization mechanism and crystal structure of PLLA in the composites.

Crystallization Kinetics and Morphology of Novel Miscible Crystalline/Amorphous Polymer Blends of Biodegradable Poly(butylene succinate-co-butylene carbonate) and Poly(vinyl phenol)

Biodegradable poly(butylene succinate-co-butylene carbonate) (PBSC) and poly(vinyl phenol) (PVPh) may form novel miscible crystalline/amorphous polymer blends that exhibit a single composition-dependent glass transition temperature and a depression of equilibrium melting point of PBSC in the blends. Relative to neat PBSC, blending with PVPh has not only suppressed the nonisothermal melt crystallization behavior of PBSC at the same cooling rate but also reduced both the overall isothermal melt crystallization rates and spherulitic growth rates of PBSC in the blends at the same crystallization temperature; however, the crystallization mechanism does not change for either neat PBSC or the PBSC/PVPh blends. Neat PBSC and its blends show the same crystal structure. The apparent increase in both long period and amorphous layer thickness values indicates that amorphous PVPh resides in the interlamellar region of PBSC spherulites in the blends.

Crystallization Kinetics and Morphology of Novel Biodegradable Poly(hexamethylene succinate-co-3 mol % ethylene succinate) with Low and High Molecular Weights

The crystal structure, basic thermal behavior, nonisothermal melt crystallization behavior, overall isothermal melt crystallization kinetics, and spherulitic morphology of novel biodegradable poly(hexamethylene succinate-co-3 mol % ethylene succinate) P(HS-co-3 mol %ES) with low and high molecular weights, i.e., PHES12k and PHES58k were investigated. Both PHES12k and PHES58k have the same crystal structure as neat poly(hexamethylene succinate). The glass-transition temperatures are almost the same for both PHES12k and PHES58k. The melt point temperatures and crystallization peak temperatures are higher in PHES12k than in PHES58k; however, the equilibrium melting point temperatures are lower in PHES12k than in PHES58k. With an increase in crystallization temperature, the overall isothermal melt crystallization rates decrease gradually for both PHES12k and PHES58k; moreover, at the same crystallization temperature, PHES12k crystallizes faster than PHES58k. The spherulitic growth rates are faster in PHES12k than in PHES58k, while the nucleation densityof the spherulites is lower in PHES12k than in PHES58k.