Isothermal Melt Crystallization Kinetics Research Articles

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.

Enhancing the crystallization of biodegradable poly(ε-caprolactone) using a polyvinyl alcohol fiber favoring nucleation

In this study, biodegradable poly(ε-caprolactone) (PCL)/polyvinyl alcohol (PVA) fiber composites were prepared using melt processing techniques with different PVA fiber contents. The effect of PVA fiber on the non-isothermal and isothermal melt crystallization kinetics of PCL/PVA fiber composites was studied by using differential scanning calorimetry. Non-isothermal crystallization peak temperatures were enhanced significantly, as exemplified by about 20 K increase for the composite loaded with 5 wt% PVA fiber at a cooling rate of 20 K/min compared to that of neat PCL. The crystallization half-time decreased from 1.67 min for neat PCL to 0.80 min for composite with 5 wt% PVA fiber at a cooling rate of 5 K/min. PVA fiber was also found to dramatically accelerate the isothermal crystallization rate of PCL/PVA fiber composites. The crystallization half-time of composite containing 5 wt% PVA fiber was reduced by more than 10 times compared with neat PCL. Moreover, dynamic mechanical analysis results showed that PVA fiber had a strengthening effect on the PCL.

Isothermal melt crystallization kinetics study of cellulose nanocrystals nucleated biodegradable Poly(ethylene succinate)

The isothermal melt crystallization kinetics of fully biodegradable poly(ethylene succinate) (PES)/cellulose nanocrystals (CNC) composites was studied in this research. Due to the efficient nucleating agent effect, the crystallization rate of PES was remarkably enhanced by low loadings of CNC; consequently, the composites displayed shorter crystallization half-time and greater nucleation density than neat PES. Through the self-nucleation and nonisothermal melt crystallization studies, the nucleation efficiency values of CNC were quantitively evaluated in PES/CNC composites. Despite CNC loading, the nucleation efficiency exceeded 50%. With increasing the CNC loading from 0.25 to 1 wt%, both the crystallization rate of the composites and the nucleation efficiency of CNC at different loadings first increased, reached a maximum, and then decreased, displaying the CNC loading dependence. Such dependence was attributed to the different dispersion states of CNC in the composites.

Melt Crystallization Behavior and Crystalline Morphology of Polylactide/Poly(ε-caprolactone) Blends Compatibilized by Lactide-Caprolactone Copolymer.

Lactide-Caprolactone copolymer (LACL) was added to a Polylactide/Poly(ε-caprolactone) (PLA/PCL) blend as a compatibilizer through solution mixing and the casting method. The melt crystallization behavior and crystalline morphology of PLA, PLA/PCL, and PLA/PCL/LACL were investigated using differential scanning calorimeter (DSC) and polarized optical microscopy (POM), respectively. The temperature of the shortest crystallization time for the samples was observed at 105 °C. The overall isothermal melt crystallization kinetics of the three samples were further studied using the Avrami theory. Neat PLA showed a higher half-time of crystallization than that of the PLA/PCL and PLA/PCL/LACL blends, whereas the half-time of crystallization of PLA/PCL and PLA/PCL/LACL showed no significant difference. The addition of PCL decreased the spherulite size of crystallized PLA, and the nuclei density in the PLA/PCL/LACL blend was much higher than that of the PLA and PLA/PCL samples, indicating that LACL had a compatibilization effect on the immiscible PLA/PCL blend, thereby promoting the nucleation of PLA. The spherulites in the PLA/PCL and PLA/PCL/LACL blend exhibited a smeared and rough morphology, which can be attributed to the fact that PCL molecules migrated to the PLA spherulitic surface during the crystallization of PLA.

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.

Crystallization kinetics, morphology, and hydrolytic degradation of novel bio‐based poly(lactic acid)/crystalline silk nano‐discs nanobiocomposites

ABSTRACTIn this work, novel biodegradable crystalline silk nano‐discs (CSNs) having a disc‐like morphology have been utilized for fabrication of poly(lactic acid) (PLA) nanocomposites by melt‐extrusion. The main focus is to investigate the effect of CSN on isothermal melt crystallization kinetics, spherulitic growth rates, morphology, and hydrolytic degradation of PLA. Spherulitic morphology and growth rates are examined over a wide range of crystallization temperatures (90–120 °C). With incorporation of CSN, the isothermal crystallization kinetics of PLA/CSN increases, however, the crystallization mechanism remains unaltered. The apparent activation energy and surface energy barrier for crystallization process decreases upon addition of CSNs. At lower isothermal crystallization temperatures (Tc) viz. (90–100 °C), reduced growth rates of PLA spherulites is observed. Both PLA and PLA/CSN exhibit highest crystallization rates at around ∼107 °C. The hydrolytic degradation rates calculated from molecular weight reduction shows that PLA/CSN nanocomposites' degradation rates are lower as compared to PLA in acidic, neutral, and alkaline media at pH = 2, 7, and 12, respectively, due to hydrophobic nature of CSN. Scanning electron microscopy study demonstrated the surface erosion mechanism of hydrolytic degradation of PLA and PLA/CSN nanocomposites. This work provides valuable insight for the application and reclamation of PLA/CSN bionanocomposites in moist and wet working environments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46590.

Crystallization kinetics, morphology, and hydrolytic degradation of novel biobased poly(butylene succinate-co-decamethylene succinate) copolyesters

In previous work, we synthesized three novel biodegradable poly(butylene succinate-co-decamethylene succinate) (PBDS) copolyesters with different decamethylene succinate (DS) compositions and studied their basic thermal behaviors, crystal structure, and mechanical properties (Polym. Degrad. Stab. 134 (2016) 305–310). In this work, the isothermal melt crystallization kinetics, spherulitic morphology and growth rates, and hydrolytic degradation of these PBDS copolyesters were further investigated and compared with those of their homopolymer poly(butylene succinate) (PBS). With increasing DS composition and crystallization temperature, the overall isothermal melt crystallization rates of PBDS decreased; however, the crystallization mechanism of PBDS and PBS remained unchanged. Spherulitic morphology and growth rates of PBDS and PBS were investigated in a wide range of crystallization temperatures. Increasing crystallization temperature and DS composition decreased growth rates of PBDS spherulites. Both PBDS and PBS exhibited a crystallization transition from regime II to regime III; moreover, the crystallization regime transition temperature shifted to lower temperature with increasing DS composition. The hydrolytic degradation rates of PBDS copolyesters gradually decreased with increasing DS composition. Scanning electron microscopy study demonstrated the surface erosion mechanism of the hydrolytic degradation of PBDS and PBS.

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 kinetics, mechanical properties, and hydrolytic degradation of novel eco‐friendly poly(butylene diglycolate) containing ether linkages

ABSTRACTThe basic thermal properties, isothermal melt crystallization kinetics, spherulitic morphology, mechanical properties, and hydrolytic degradation behavior of a novel eco‐friendly polyester poly(butylene diglycolate) (PBDG) containing ether linkages were systematically studied with several techniques in this research. PBDG is an aliphatic polyester with high thermal stability. It had a glass transition temperature (Tg) of −25.7 °C, a melting point temperature of 65.1 °C, and an equilibrium melting point of 73.2 °C. During the isothermal melt crystallization, PBDG crystallized slowly with increasing crystallization temperature, but the crystallization mechanism did not change. Negative spherulites were observed for PBDG. The mechanical properties of PBDG were investigated from the tensile testing. As a ductile polyester, PBDG possessed good mechanical properties. PBDG also showed a fast hydrolytic degradation rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44186.

Isothermal and non-isothermal crystallization kinetics and predictive modeling in the solidification of poly(cyclohexylene dimethylene cyclohexanedicarboxylate) melt

Isothermal and non-isothermal crystallization kinetics of polycyclohexylene dimethylene cyclohexanedicarboxylate (PCCE) were investigated via differential scanning calorimetry (DSC). Isothermal melt crystallization kinetics were analyzed using the traditional Avrami equation. Non-isothermal melt crystallization kinetics data obtained from DSC were analyzed using the extended Avrami relation and a combination of the Avrami equation and the Ozawa relationship. The glass transition temperature, equilibrium melting point, isothermal crystallization activation energy, and non-isothermal crystallization activation energy were determined. Furthermore, a predictive method based on the Nakamura model was proposed and was used to describe the non-isothermal crystallization kinetics based on the isothermal experimental data. The results suggested that the original Nakamura equation was not successful in describing the non-isothermal crystallization of PCCE over a wide range of cooling rates. It was found that the non-isothermal crystallization kinetics of PCCE, over a wide range of cooling rates, could best be described by modifying the differential Nakamura equation to include a varied Avrami index.

Crystallization kinetics and morphology of poly(ethylene suberate)

ABSTRACTThe crystallization kinetics and morphology of poly(ethylene suberate) (PESub) were studied in detail with differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray diffraction. The Avrami equation could describe the overall isothermal melt crystallization kinetics of PESub at different crystallization temperatures; moreover, the overall crystallization rate of PESub decreased with increasing crystallization temperature. The equilibrium melting point of PESub was determined to be 70.8°C. Ring‐banded spherulites and a crystallization regime II to III transition were found for PESub. The Tobin equation could describe the nonisothermal melt crystallization kinetics of PESub at different cooling rates, while the Ozawa equation failed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43086.

Crystallization kinetics, morphology, and mechanical properties of novel poly(ethylene succinate-co-octamethylene succinate)

The crystallization kinetics, morphology and mechanical properties of a novel poly(ethylene succinate-co-octamethylene succinate) (PEOS) copolyester with 82 mol% ethylene succinate (ES) units and 18 mol% octamethylene succinate (OS) units, and its homopolymer poly(ethylene succinate) (PES) were extensively investigated. The glass transition temperature, cold crystallization peak temperature and melting point of PEOS are around −24, 47.5, and 80.5 °C, respectively. The Avrami equation was used to analyze the isothermal melt crystallization kinetics of PEOS and PES. They display the same crystallization mechanism, and PEOS crystallizes slower than PES at the same degree of supercooling. The spherulitic growth rates of PEOS and PES exhibit a bell shape within the investigated crystallization temperature range, with the crystallization regime transition temperature of PEOS being lower than that of PES. In addition, PEOS has high thermal stability and good mechanical properties.

Isothermal Melt Crystallization Kinetic Behavior of Poly (vinylidene fluoride)

Isothermal melt crystallization kinetics of PVDF was investigated by differential scanning calorimetry. Thin PVDF film has been fabricated by the solvent casting technique using dimethylformamide (DMF). Then, the samples were melted and subsequently crystallized in the range of the crystallization temperature (Tc) between 138 and 145 °C. The crystallization kinetics was derived from Avrami equation. Avrami parameter (n) was found in a range from 1.5 to 2.4 and the values of the crystallization rate parameters (k) increased with decreasing Tc. So the crystallization rate parameters suggested that PVDF crystallize slower with increasing of Tc. The Hoffman–Weeks equation has used to approximate the equilibrium melting point of PVDF which was concluded to be 182 °C. Likewise, the activation energy was estimated to be 103.2 kJ/mol for isothermal crystallization. In this research, Lauritzen- Hoffmann theory was employed to analyze crystallization kinetics. Accordingly, regime I found appropriate to describe the present case of PVDF crystallization.

Thermal properties and crystallization kinetics of poly(butylene suberate)

In this work, we synthesized poly(butylene suberate) (PBSub) with a weight average molecular weight of 3.64 × 104 g/mol from the monomers of butanediol and suberic acid via a two-step melt polycondensation method. The basic thermal behaviors, overall isothermal melt crystallization kinetics, crystal structure, spherulitic morphology and growth, thermal stability, and hydrolytic degradation of PBSub were systematically investigated for the first time. PBSub has a low glass transition temperature of about −61 °C, a melting point of 55.2 °C, and an equilibrium melting point of 61.4 °C. The overall isothermal melt crystallization kinetics of PBSub was investigated at different crystallization temperature values and analyzed by the Avrami equation. PBSub has an average Avrami exponent value of about 3, suggesting that the crystallization mechanism of PBSub may correspond to three-dimensional truncated sphere growth with athermal nucleation. An obvious spherulitic morphology was observed for PBSub, and the spherulitic growth rates decrease with increasing crystallization temperature. PBSub exhibits a crystallization regime II to regime III transition on the basis of the secondary nucleation theory. The crystal structure study reveals that PBSub is highly crystalline, presenting strong diffraction peaks and a great crystallinity of about 55%. The thermogravimetric analysis study demonstrates that PBSub has both a high decomposition temperature at 5 wt% weight loss of about 377 °C and a high temperature at the maximum degradation rate of about 421 °C, suggesting its good thermal stability. PBSub may undergo a hydrolytic degradation, which may be of interest for its end use as a degradable material in some special application fields.

Isothermal melt crystallization kinetics, melting behavior, and spherulitic morphology of novel biobased poly(hexylene oxalate)

Banded spherulites were observed for novel biobased poly(hexylene oxalate) in a wide crystallization temperature range.

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 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.

Effect of Low Octavinyl-Polyhedral Oligomeric Silsesquioxanes Loading on the Crystallization Kinetics and Morphology of Biodegradable Poly(ethylene succinate-co-5.1 mol % ethylene adipate) as an Efficient Nucleating Agent

In this work, a biodegradable polymer composite was prepared by mixing poly(ethylene succinate-co-5.1 mol % ethylene adipate) (PESA) and octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) at a very low ovi-POSS loading. It is found that a fine dispersion of ovi-POSS has been achieved in the PESA matrix. The effects of ovi-POSS on the nonisothermal melt and cold crystallization behaviors, overall isothermal melt crystallization kinetics, spherulitic morphology, and crystal structure of PESA in the composite were studied in detail with various techniques. Relative to neat PESA, both the nonisothermal melt and cold crystallization behaviors and isothermal melt crystallization kinetics of PESA have been enhanced significantly in the composite. Ovi-POSS is an efficient nucleating agent for the crystallization of PESA, because the nucleation density of PESA spherulites is apparently higher in the composite than in neat PESA; however, the crystallization mechanism and crystal structure of PESA remain unchanged in the composite.

Synthesis, Crystallization Kinetics, and Morphology of Novel Biodegradable Poly(butylene succinate-co-hexamethylene succinate) Copolyesters

Biodegradable poly(butylene succinate) and a series of poly(butylene succinate-co- hexamethylene succinate) (P(BS-co-HS)) with hexamethylene succinate (HS) comonomer composition ranging from 14 to 35 mol % were prepared in the present work via a two-stage melt polycondensation method. Basic thermal behaviors, crystal structure, isothermal melt crystallization kinetics, and spherultic morphology and growth of P(BS-co-HS) copolyesters with different HS composition were studied in detail with various techniques and compared with those of neat PBS. With respect to neat PBS, the glass transition temperature of P(BS-co-HS) decreases slightly, while the melting point temperature and equilibrium melting point temperature of P(BS-co-HS) are reduced significantly with an increase in the HS composition. Both neat PBS and P(BS-co-HS) have the same crystal structure; however, the crystallinity values are slightly smaller in P(BS-co-HS) than in neat PES. The overall isothermal melt crystallization kinetics of neat PBS and P(BS-co-HS) were studied in a wide crystallization temperature range and analyzed by the Avrami equation. The experimental results indicate that the crystallization mechanism remains unchanged for both neat PBS and P(BS-co-HS); however, the overall crystallization rates of P(BS-co-HS) decrease with increasing HS composition and crystallization temperature. The spherulitic morphology of neat PBS and P(BS-co-HS) were also investigated in a wide crystallization temperature range; moreover, the spherulitic growth rates of P(BS-co-HS) also decrease with increasing HS content and crystallization temperature.

Effect of Low Thermally Reduced Graphene Loadings on the Crystallization Kinetics and Morphology of Biodegradable Poly(3-hydroxybutyrate)

Biodegradable poly(3-hydroxybutyrate) (PHB) and thermally reduced graphene (TRG) nanocomposites have been prepared successfully via a solution and coagulation method in this work at low TRG loadings. The effects of TRG on the crystal structure, spherulitic morphology, nonisothermal melt crystallization behavior, and isothermal melt crystallization kinetics of PHB in the PHB/TRG nanocomposites were investigated with various techniques. It was found that TRG does not change the crystal structure of PHB but apparently increases the nucleation density of PHB spherulites in the PHB/TRG nanocomposites. Moreover, both the nonisothermal and isothermal melt crystallizations of PHB are enhanced significantly in the nanocomposites because of the efficient nucleating agent effect of TRG. In addition, the isothermal melt crystallization kinetics of neat PHB and the PHB/TRG nanocomposites was analyzed by the Avrami equation. The overall isothermal melt crystallization rates of PHB are increased with deceasing crystallization temperature and increasing the TRG loadings in the nanocomposites; however, the crystallization mechanism remains unchanged in spite of the crystallization temperature and TRG loadings.