Isothermal Melt Crystallization Rates Research Articles

Miscibility, crystallization and mechanical properties of poly[(3‐hydroxybutyrate)‐co‐(4‐hydroxyvalerate)]/poly(propylene carbonate)/poly(vinyl acetate) ternary blends

AbstractA ternary blend of poly[(3‐hydroxybutyrate)‐co‐(4‐hydroxyvalerate)] (P34HB), poly(propylene carbonate) (PPC) and poly(vinyl acetate) (PVAc) was initially melt‐blended in an effort to obtain an excellent balance of mechanical performance. The effect of PVAc content on the miscibility, phase morphology, thermal behavior, isothermal melt crystallization and mechanical properties of P34HB/PPC/PVAc ternary blends was systematically investigated. Dynamic mechanical analysis indicated that P34HB and PPC were immiscible, and PVAc exhibited immiscibility with PPC. PVAc was selectively dispersed in the P34HB matrix and phase morphology was refined by reducing the interfacial tension. Moreover, the PVAc component suppressed the cold crystallization and reduced the isothermal melt crystallization rate of P34HB in the ternary blends. Unexpectedly, marked increases of 32.7% and 3025% were achieved in the tensile modulus and elongation of the ternary blend containing 20 wt% PVAc compared to neat P34HB. Meanwhile, the strength did not deteriorate. The unusual combination of high ductility, strength and modulus is of great potential for expanding the practical application of sustainable and biological polymers. © 2021 Society of Industrial Chemistry.

Effect of Polycondensation Catalyst on Fiber Structure Development in High-Speed Melt Spinning of Poly (Ethylene Terephthalate).

We conducted a preliminary study on fiber structural development in the high-speed melt spinning of environmentally friendly polyethylene terephthalate (Ti-PET) synthesized with 25 ppm of titanium-based catalyst, which was compared with conventional PET (Sb-PET) synthesized with 260 ppm of antimony-based catalyst. Gel permeation chromatography of Ti- and Sb-PET resins of intrinsic viscosity 0.63 confirmed that both resins have similar molecular weights and distributions. However, differential scanning calorimetry revealed that the Ti-PET resin exhibited a lower melt–crystallization peak and isothermal melt-crystallization rate than the Sb-PET resin. High-speed melt spinning of the Ti- and Sb-PET was possible up to a spinning velocity of 6 km/min. Two-dimensional wide-angle X-ray diffraction analyses showed that the molecular orientation of the obtained as-spun Ti- and Sb-PET fibers increased with spinning velocity, and a highly oriented, crystalline structure by orientation-induced crystallization started to appear from 5 km/min. Notably, Ti-PET fibers showed a lower degree of crystalline structural development and lower tensile strength compared with Sb-PET fibers under the high-speed spinning conditions. Our results suggest that the catalyst in PET resins can act as nucleating agents in thermal- and orientation-induced crystallization, and that differences in catalyst content can influence PET fiber structure development under extreme conditions in high-speed melt spinning.

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.

Crystallization behaviors of poly(lactic acid) composites fabricated using functionalized eggshell powder and poly(ethylene glycol)

The eggshell power decorated with calcium phenyphosphonate (NES), an effective nucleating agent for poly(lactic acid) (PLA), was introduced into PLA simultaneously with a plasticizer, poly(ethylene glycol) (PEG), via melt blending. The morphology and melt crystallization behaviors of PLA composites were studied by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). PEG improved compatibility and interfacial adhesion between NES and PLA, which made NES dispersed more evenly in PLA matrix. The isothermal melt crystallization rate of PLA/PEG/NES was fastest in all the composites, indicative of a synergistic effect between PEG and NES. For the nonisothermal melt crystallization, the Avrami and Mo’s model could describe the experiment data successfully. Whereas the Ozawa equation failed to provide an adequate description for the composites. Moreover, the crystallization activation energy was further evaluated based on Friedman equation.

Isothermal melt crystallization and performance evaluation of polylactide/thermoplastic polyester blends with multi‐functional epoxy

ABSTRACTA multi‐functional epoxy (ADR) was used to improve compatibilization of poly(lactic acid) (PLA)/ thermoplastic polyester elastomer (TPEE) blends. Influence of ADR on isothermal melt crystallization of the blends was investigated. The results show that isothermal melt crystallization rate of the samples increases with ADR loading. It can be attributed to a nucleation enhancement resulted from an increase of molecular weight and melt viscosity created by the chain extension/branched process of PLA in the presence of ADR. In addition, the maximum crystallinity of the samples shows a decrease with increasing ADR loading because of the chain extended and branched reaction. Quenched and crystallized samples were fabricated using compression molding under different cooling conditions in‐mold. Effects of crystallinity and ADR on mechanical performances of the PLA/TPEE sample were investigated. With increasing the crystallinity, the PLA/TPEE sample shows a marked enhancement in heat resistance. However, the tensile ductility of the crystallized PLA/TPEE sample drastically decreases due to the formation of firm crystal crosslinking and the incompatibility between PLA and TPEE. It is notable that the tensile ductility of the crystallized samples is improved with the introduction of ADR owing to its reactive compatibilization effect. Finally, the crystallized PLA/TPEE/ADR samples with improved heat resistance and relative higher ductility are obtained. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46343.

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.

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.

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.

Crystallization behavior, mechanical properties, and enzymatic degradation of biosourced poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/graphene nanocomposites

Herein, through a solution and coagulation method, biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)]/graphene nanocomposites were prepared. The nonisothermal melt crystallization peak temperature values and overall isothermal melt crystallization rates in the nanocomposites are greater than in neat P(3HB-co-4HB), indicating a nucleating effect of graphene; however, the crystallization mechanism of P(3HB-co-4HB) remains unchanged in the nanocomposites, regardless of graphene level and crystallization temperature. The nonisothermal and melt crystallization processes of the nanocomposites are found to vary with the graphene loading, exhibiting a maximum at 1 mass% graphene loading. The incorporation of graphene obviously increases spherulites nucleation density values of the nanocomposites and does not modify the crystal structure of P(3HB-co-4HB) in the nanocomposites. The storage modulus has been apparently improved in the nanocomposites compared to neat P(3HB-co-4HB). Moreover, the enzymatic hydrolytic degradation rates have been enhanced obviously in the P(3HB-co-4HB)/graphene nanocomposites than in neat P(3HB-co-4HB).

Crystallization behaviors and morphology of novel poly(octamethylene adipate-co-octamethylene succinate) and poly(octamethylene adipate)

Crystallization behaviors and morphology of novel biodegradable poly(octamethylene adipate-cooctamethylene succinate) (POAS) copolymers with different octamethylene succinate (OS) contents and their parent homopolymer poly(octamethylene adipate) (POA) were extensively investigated. Compared to POA, increasing the OS unit does not modify the crystal structures but slightly decreases the crystallinity values of POAS. The glass transition temperature values of POAS are greater than that of POA. Both the nonisothermal crystallization peak temperature and melting point temperature values of POAS decrease gradually with the increment of the OS unit. The overall isothermal melt crystallization rates of POAS decrease with increasing crystallization temperature and the OS content, while the crystallization mechanism does not change. The equilibrium melting point values of POAS are reduced with increasing the OS content, with respect to POA. The nucleation densities of POAS spherulites are reduce significantly; moreover, increasing crystallization temperature and the OS content reduces the spherulitic growth rates of POAS, relative to POA.

Crystalline morphology and crystallization kinetics of melt-miscible crystalline/crystalline polymer blends of poly(vinylidene fluoride) and poly(butylene succinate-co-24mol% hexamethylene succinate)

Poly(vinylidene fluoride) (PVDF) and poly(butylene succinate-co-24 mol% hexamethylene succinate) (PBHS), both crystalline polymers, formed melt-miscible crystalline/crystalline polymer blends. Both the characteristic diffraction peaks and nonisothermal melt crystallization peak of each component were found in the blends, indicating that PVDF and PBHS crystallized separately. The crystalline morphology and crystallization kinetics of each component were studied under different crystallization conditions for the PVDF/PBHS blends. Both the spherulitic growth rates and overall isothermal melt crystallization rates of blended PVDF decreased with increasing the PBHS composition and were lower than those of neat PVDF, when the crystallization temperature was above the melting point of PBHS component. The crystallization mechanism of neat and blended PVDF remained unchanged, despite changes of blend composition and crystallization temperature. The crystallization kinetics and crystalline morphology of neat and blended PBHS were further studied, when the crystallization temperature was below the melting point of PBHS component. Relative to neat PBHS, the overall crystallization rates of the blended PBHS first increased and then decreased with increasing the PVDF content in the blends, indicating that the preexisting PVDF crystals may show different effects on the nucleation and crystal growth of PBHS component in the crystalline/crystalline polymer blends.

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.

Influence of Thermally Reduced Graphene Low-Loadings on the Crystallization Behavior and Morphology of Biodegradable Poly(ethylene succinate)

Through a solution and coagulation method, biodegradable poly(ethylene succinate) (PES) and thermally reduced graphene (TRG) nanocomposites were prepared at low TRG loadings. The nonisothermal melt crystallization peak temperature values and overall isothermal melt crystallization rates are greater in the nanocomposites than in neat PES, indicative of a nucleating agent effect of TRG; however, the crystallization mechanism of PES remains unchanged in the nanocomposites, regardless of TRG loading and crystallization temperature. The nonisothermal and melt crystallization processes of the nanocomposites are found to vary with the TRG loading, exhibiting a maximum at 0.25 wt % TRG loading. The incorporation of a small amount of TRG shows little influence on the spherulitic growth rates but obviously affects the spherulites nucleation density values of the nanocomposites. TRG does not modify the crystal structure of PES in the nanocomposites.

Miscibility and crystallization behavior of biodegradable poly(butylene succinate-co-butylene carbonate) and tannic acid blends

Biodegradable poly(butylene succinate-co-butylene carbonate) (PBSC) and tannic acid (TA) blends were prepared via a solution and casting method in this work. Miscibility and crystallization behavior of PBSC/TA blends were investigated with various techniques. PBSC is miscible with TA as evidenced by both a single composition dependent glass transition temperature and the depression of equilibrium melting point of PBSC in the blends. Relative to neat PBSC, blending with TA does not modify the crystal structure of PBSC in the blends. The nonisothermal melt crystallization of PBSC was retarded by TA in the blends. Both the overall isothermal melt crystallization rates and spherulitic growth rates of PBSC/TA blends show the similar variation trends, which become slower with increasing crystallization temperature and the TA composition. The crystallization mechanism of PBSC does not change, regardless of crystallization temperature and the TA composition in the blends.

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.

Synthesis of organic bisurea compounds and their roles as crystallization nucleating agents of poly(l-lactic acid)

A series of novel organic bisurea (BUr) compounds were facilely synthesized from phenyl isocyanate and a variety of diamines, and their roles as crystallization nucleating agents of commercial poly(l-lactic acid) (PLLA) were investigated through differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). Their crystallization accelerating efficiency depends on the methylene numbers in molecular structure: the less the CH2 number, the faster the crystallization rate. Among them, 1,1′-(ethane-1,2-diyl)bis(3-phenylurea) (BUr1) acts as the most effective crystallization accelerating agent. In the presence of ca. 2wt% BUr1, the melt crystallization enthalpy of PLLA increases from almost 0 to 31.2J/g under cooling rate of 10°C/min, and the isothermal melt crystallization rate (t1/2-1) increased by 10.5 times at 140°C. Much higher nucleation density and smaller spherulite size of PLLA were observed by POM, indicating obvious heterogeneous nucleation effect. And the crystal structure of PLLA remains unchanged after incorporation of the nucleator.

Effect of Uracil on the Isothermal Melt Crystallization Kinetics and Polymorphic Crystals Control of Biodegradable Poly(butylene adipate)

Biodegradable poly(butylene adipate) (PBA) and uracil composites were prepared via a solution and casting method at low uracil loadings in this work. The isothermal melt crystallization rate has been increased apparently in the composites by the addition of uracil, which acts as a nucleating agent for the crystallization of PBA. PBA may crystallize in the α- or β-form under different conditions. During the nonisothermal melt crystallization, the α-form crystals of neat PBA are formed at only relatively slow cooling rate; however, the formation of α-form crystals can be induced by uracil in the composites at relatively faster cooling rates. The formation of polymorphic crystals of PBA may be regulated by changing cooling rate and the uracil loading, which provides an efficient way of controlling the polymorphic crystals formation and biodegradation behaviors.

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.

Isothermal Crystallization Kinetics, Morphology, and Dynamic Mechanical Properties of Biodegradable Poly(ε-caprolactone) and Octavinyl–Polyhedral Oligomeric Silsesquioxanes Nanocomposites

Biodegradable poly(ε-caprolactone) (PCL) and octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) nanocomposites were prepared at low ovi-POSS loadings via a solution casting method in this work. Scanning electron microscopy observation reveals not only the fine dispersion but also the crystallization of ovi-POSS in the PCL matrix. The overall isothermal melt crystallization kinetics, spherulitic morphology, crystal structure, and dynamic mechanical properties of neat PCL and its nanocomposites were studied with various techniques. The presence of ovi-POSS has enhanced the overall isothermal melt crystallization rates of PCL in the nanocomposites; however, the crystallization mechanism and crystal structure of PCL remain unchanged despite the ovi-POSS loading. In addition, the storage modulus of the nanocomposites has been enhanced significantly relative to neat PCL, while the glass transition temperature varies slightly irrespective of the presence of ovi-POSS.