Crystallization Kinetics Of PCL Research Articles

Influence of Freezing Layer on the Crystallization Kinetics of PCL on Oriented PE Film

Influence of Freezing Layer on the Crystallization Kinetics of PCL on Oriented PE Film

Bio-based semi-interpenetrating networks with nanoscale morphology and interconnected microporous structure

Creating new bio-based sustainable polymeric materials with similar or better performance than the petroleum-based counterparts has recently received considerable attention. It will have a significant positive impact on the environment and the sustainable polymer industry. This review article shows a relatively new method based on simultaneous in-situ polymerization and compatibilization of bio-based plant oil and biodegradable thermoplastic polymer to prepare semi-interpenetrating polymer networks (SINs) with unusual nano-scale morphology and interconnected porous structure will be summarized. The SINs were synthesized via cationic polymerization of tung oil in a homogenous solution of poly(ε-caprolactone) as a biodegradable, semi-crystalline, and biocompatible thermoplastic polymer. The degrees of miscibility, nanostructure morphology, and crystallinity was found to be composition-dependent. This relatively new blending method created a two-phase nanoscale morphology as small as 100 nm for blends with PCL contents of 20 and 30 wt.%. For higher PCL contents (e.g., 50 wt.% PCL blend), a co-continuous, interconnected microscale two-phase morphology was detected. The microporous structure of the SINs was also changed as a function of composition. For example, the interconnectivity and pore size was considerably decreased with increasing PCL content. Furthermore, a considerable decrease in the crystallization kinetics of PCL was observed as the PCL content is higher than or equal to 30 wt.%. While on the other hand, the crystallization kinetics accelerated significantly for 50 wt.%. This novel, low-cost strategy for preparing bio-based SINs with nanoscale morphology and interconnected three-dimensional cluster structures and desired properties should be widely used for creating new polymer systems.

Morphology, Nucleation, and Isothermal Crystallization Kinetics of Poly(ε-caprolactone) Mixed with a Polycarbonate/MWCNTs Masterbatch.

In this study, nanocomposites were prepared by melt blending poly (ε-caprolactone) (PCL) with a (polycarbonate (PC)/multi-wall carbon nanotubes (MWCNTs)) masterbatch in a twin-screw extruder. The nanocomposites contained 0.5, 1.0, 2.0, and 4.0 wt % MWCNTs. Even though PCL and PC have been reported to be miscible, our DSC (Differential Scanning Calorimetry), SAXS (Small Angle X-ray Scattering), and WAXS (Wide Angle X-ray Scattering) results showed partial miscibility, where two phases were formed (PC-rich and PCL-rich phases). In the PC-rich phase, the small amount of PCL chains included within this phase plasticized the PC component and the PC-rich phase was therefore able to crystallize. In contrast, in the PCL-rich phase the amount of PC chains present generates changes in the glass transition temperature of the PCL phase that were much smaller than those predicted by the Fox equation. The presence of two phases was corroborated by SEM, TEM, and AFM observations where a fair number of MWCNTs diffused from the PC-rich phase to the PCL-rich phase, even though there were some MWCNTs agglomerates confined to PC-rich droplets. Standard DSC measurements demonstrated that the MWCNTs nucleation effects are saturated at a 1 wt % MWCNT concentration on the PCL-rich phase. This is consistent with the dielectric percolation threshold, which was found to be between 0.5 and 1 wt % MWCNTs. However, the nucleating efficiency was lower than literature reports for PCL/MWCNTs, due to limited phase mixing between the PC-rich and the PCL-rich phases. Isothermal crystallization experiments performed by DSC showed an increase in the overall crystallization kinetics of PCL with increases in MWCNTs as a result of their nucleating effect. Nevertheless, the crystallinity degree of the nanocomposite containing 4 wt % MWCNTs decreased by about 15% in comparison to neat PCL. This was attributed to the presence of the PC-rich phase, which was able to crystallize in view of the plasticization effect of the PCL component, since as the MWCNT content increases, the PC content in the blend also increases. The thermal conductivities (i.e., 4 wt % MWCNTs) were enhanced by 20% in comparison to the neat material. The nanocomposites prepared in this work could be employed in applications were electrical conductivity is required, as well as lightweight and tailored mechanical properties.

Supernucleation and crystallization regime change provoked by MWNT addition to poly(ε-caprolactone)

In this work, the nucleation and crystallization behavior of melt mixed PCL/CNT nanocomposites has been studied. The mixtures of PCL and pristine MWNTs were prepared by extrusion with different nanofiller contents: 0.3, 0.5, 0.7, 1 and 3%. Standard DSC measurements demonstrated pronounced nucleation effects as well as increases in PCL crystallinity. The nucleation effect saturates at only 0.5% (a value much lower than those previously reported in the literature for similar nanocomposites) indicating that the dispersions obtained were excellent. This was corroborated by both TEM observations and by the determination of a very low dielectric percolation threshold (i.e., 0.3%). In self-nucleation experiments, supernucleation effects were obtained up to a maximum of approximately 200% efficiency. This is the first time that supernucleation effects of this order have been reported for PCL filled with untreated MWNTs, a result that we attribute to the excellent dispersion achieved. Isothermal crystallization experiments performed by DSC showed an increase in the crystallization kinetics of PCL with increases in MWNT content as a consequence of the supernucleation effect. The Avrami equation successfully described the overall crystallization kinetics and while neat PCL exhibited Avrami indexes close to 3, indicating that instantaneously nucleated spherulites were formed, the nanocomposite yielded mostly Avrami index values close to 2, as expected for axialites instantaneously nucleated on the surface of the MWNTs. Remarkably, the temperature dependence of the overall crystallization rate exhibited a dramatic change with MWNT content. This novel effect was described as a crystallization regime change (i.e., from Regime II to Regime III) induced by the presence of the MWNTs in terms of the Lauritzen and Hoffman theory.

Thermomechanical behavior and nonisothermal crystallization kinetics of poly(ε-caprolactone) and poly(ε- caprolactone)/poly(N-vinylpyrrolidone) blends

AbstractPoly(ε-caprolactone) (PCL) and PCL/Poly(N-vinylpyrrolidone) (PVP) blends are shown to have the potential to be used in a range of biomedical applications and can be processed with successive in-situ polymerization procedures. In this paper, the thermomechanical analysis of PCL and PCL/PVP blends was performed using dynamic mechanical analysis (DMA). The storage and loss moduli as a function of temperature and frequency were recorded. The nonisothermal crystallization kinetics of PCL and PCL/PVP blends were analyzed using Ozawa model and Mo-Liu equation, a combination equation of Avrami and Ozawa formulas. The Ozawa analysis failed to describe the nonisothermal crystallization behavior of blends, whereas the Mo-Liu equation successfully described the nonisothermal crystallization kinetics of PCL and PCL/PVP blends. In addition, the value of crystallization rate coefficient under nonisothermal crystallization conditions was calculated. The PCL/PVP blends compared with the pure PCL and PVP had a restrain effect on the crystallization kinetics of PCL in the blends. Combining the results of DMA and DSC, PVP effectively decreased the crystallinity of PCL and enhanced its damping properties, which indicated that PCL/PVP blends could be more suitable than PCL in some biomedical applications, as it might help in the dissipation of the mechanical energy generated by the patient movements.

Isothermal crystallization kinetics in binary miscible blend of poly(ε‐caprolactone)/tetramethyl polycarbonate

AbstractThe crystallization kinetics of pure poly(ε‐caprolactone) (PCL) and its blends with bisphenol‐A tetramethyl polycarbonate (TMPC) was investigated isothermally as a function of composition and crystallization temperature (Tc) using differential scanning calorimetric (DSC) and polarized optical microscope techniques. Only a single glass‐transition temperature, Tg, was determined for each mixture indicating that this binary blend is miscible over the entire range of composition. The composition dependence of the Tg for this blend was well described by Gordon–Taylor equation with k = 1.8 (higher than unity) indicating strong intermolecular interaction between the two polymer components. The presence of a high Tg amorphous component (TMPC) had a strong influence on the crystallization kinetics of PCL in the blends. A substantial decrease in the crystallization kinetics was observed as the concentration of TMPC rose in the blends. The crystallization half‐time t0.5 increased monotonically with the crystallization temperature for all composition. At any crystallization temperature (Tc) the t0.5 of the blends are longer than the corresponding value for pure PCL. This behavior was attributed to the favorable thermodynamics interaction between PCL and TMPC which in turn led to a depression in the equilibrium melting point along with a simultaneous retardation in the crystallization of PC. The isothermal crystallization kinetics was analyzed on the basis of the Avrami equation. Linear behavior was held true for the augmentation of the radii of spherulites with time for all mixtures, regardless of the blend composition. However, the spherulites growth rate decreased exponentially with increasing the concentration of TMPC in the blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3307–3315, 2007

Non‐isothermal crystallization kinetics of poly(ε‐caprolactone) in hydrogen‐bond‐coupled polymeric‐inorganic hybrid materials

AbstractSome hydrogen‐bonding‐interactions‐mediated poly(ε‐caprolactone) (PCL)/silica (SiO2) polymeric‐inorganic hybrids were prepared by the sol–gel process. The non‐isothermal crystallization kinetics of PCL in the hybrids was investigated by means of differential scanning calorimetry. The results show that the Jeziorny method, together with the combination of the Avrami and Ozawa equations, is applicable to describe the non‐isothermal crystallization kinetics of the PCL in the hybrid system, while the Ozawa theoretical method can be used just for the pure PCL and the 70/30 TEOS/PCL hybrids. Depending on the composition of the PCL/silica, the hybrids displayed microphase separation at various scales, which in turn affect the crystallization behavior and mechanism of PCL in the hybrids. On the one hand, the inorganic component (viz SiO2) could act as the nucleating agent to facilitate the crystallization of PCL in the hybrids. On the other hand, the SiO2 networks also confine the crystallization of PCL. Copyright © 2004 Society of Chemical Industry

Isothermal Crystallization of Poly(ε‐caprolactone) in Blend with Poly(styrene‐co‐acrylonitrile): Influence of Phase Separation Process

AbstractSummary: The isothermal crystallization process of poly(ε‐caprolactone) (PCL) and its blend with styrene‐acrylonitrile random copolymer containing 27.5 wt.‐% acrylonitrile has been investigated as a function of crystallization and melting temperatures for different melting times in the vicinity of the lowest critical solution temperature (LCST)‐type phase diagram using DSC. The obtained results showed that the isothermal crystallization kinetics from the melt of PCL in the blend was greatly affected by the presence of SAN. For a given crystallization temperature, the crystallization half time (t0.5) in the case of PCL/SAN = 80/20 blend was much longer than the corresponding value for pure PCL. This depression in the crystallization kinetics of PCL in the blend was mainly attributed to the favorable interaction between the two components and the reduction in chain mobility as a result of increasing the Tg by adding the amorphous component (SAN). In addition, the value of t0.5 was found to be independent of the melting temperature (Tm) and melting time for pure PCL. The isothermal crystallization kinetics for samples that were crystallized after decomposition into different stages of phase separation were also investigated. A major acceleration in the crystallization kinetics was observed isothermally for the samples that had undergone phase separation in the early and middle stages. The isothermal crystallization kinetics was also analyzed based on the Avrami approach. Although the crystallization kinetics was accelerated to a great extent by the liquid‐liquid phase separation, no change in the crystallization mechanism could be predicted. Furthermore, the phase separation process of PCL/SAN blend has been studied indirectly by following the variation in t0.5 at different melting temperatures and melting times above the LCST phase diagram.Melting temperature, Tm, dependence of crystallization half time, t0.5.magnified imageMelting temperature, Tm, dependence of crystallization half time, t0.5.