Melting Point Depression Analysis Research Articles

Amorphous solid dispersions in poly(ε-caprolactone)/xanthohumol bioactive blends: physicochemical and mechanical characterization.

This paper reports the obtention of amorphous solid dispersions (ASDs) of xanthohumol (XH) in PCL containing up to 50 wt% of the bioactive compound in the amorphous form thanks to the advantageous specific interactions established in this system. The miscibility of the PCL/XH blends was investigated using DSC. Melting point depression analysis yielded a negative interaction parameter indicating the occurrence of favorable inter-association interactions. XRD analyses performed at room temperature agree with the crystallinity results obtained on the heating runs performed by DSC. FTIR spectroscopy reveals strong C[double bond, length as m-dash]OO-H specific interactions between the hydroxyl groups of XH and the carbonyl groups of PCL. The AFM analysis of the blends obtained by spin-coating shows the variation of crystalline morphology with composition. Finally, tensile tests reveal high toughness retention for the blends in which XH can be dispersed in the amorphous form (containing up to 50 wt% XH). In summary, PCL is a convenient matrix to disperse XH in the amorphous form, bringing the possibility of obtaining completely amorphous bioactive materials suitable for the development of non-stiff biomedical devices.

Tailoring the isothermal crystallization kinetics of isodimorphic poly (butylene succinate-ran-butylene azelate) random copolymers by changing composition

A detailed isothermal crystallization study of biobased and biodegradable isodimorphic poly (butylene succinate-ran-butylene azelate) random copolyesters (PBS-ran-PBAz) with a wide composition range has been carried out to determine nucleation kinetics, spherulitic growth rates and overall crystallization kinetics. Differential Scanning Calorimetry (DSC) and Polarized Light Optical Microscopy (PLOM) analysis show that for the PBS-rich phase, the incorporation of BAz comonomer leads to a significant increase in nucleation density and a decrease in spherulitic growth. On the contrary, for the PBAz-rich phase, an antinucleating effect of the incorporation of BS comonomer has been observed. Both effects agree with the thermodynamic analysis of the equilibrium melting point depression as a function of composition, which predicts that only a small amount of BAz comonomer is included within the PBS-rich crystals and a larger amount of comonomer is included in PBAz-rich crystals. In addition, the enthalpy of melting of 100% crystalline PBS and PBAz were determined by a different practical approach: extrapolating real time synchrotron Wide Angle X-ray Scattering (WAXS) isothermal crystallization data and isothermal DSC data.

Antimicrobial poly(ε-caprolactone)/thymol blends: Phase behavior, interactions and drug release kinetics

Blends of poly(ε-caprolactone) (PCL) and thymol (THY) have been prepared by melt-mixing to obtain biodegradable materials with antibacterial properties. Miscibility and specific interactions have been investigated by means of DSC and FTIR, and the drug release kinetics of the PCL/THY blends have been analyzed using UV spectroscopy at 274nm. The melting points of PCL and THY have been analyzed using melting point depression analysis, and the interaction energy density has been found to vary from B=−30J/cm3inTHY rich blends to B=9J/cm3inPCL rich blends. The former value indicates a thermodynamically miscible blend, but the latter is close to critical conditions, and the dependence of B on composition has been discussed. The study of the carbonyl and hydroxyl stretching regions of the FTIR spectra for different compositions of the blend reveals strong CO⋯HO hydrogen bonding interactions, supporting the miscibility of the PCL/THY blends. Finally, the analysis of the release kinetics of THY from the PCL/THY blends in phosphate buffered saline (PBS) solution at 37°C (pH 7.4) shows that diffusion through the swelled polymeric chains is the leading mechanism for drug release.

Miscible blends of poly(ethylene oxide) with brush copolymers of poly(vinyl alcohol)-graft -poly(l -lactide)

Even though poly(ethylene oxide) (PEO) is immiscible with both poly(l-lactide) (PLLA) and poly(vinyl alcohol) (PVA), this article shows a working route to obtain miscible blends based on these polymers. The miscibility of these polymers has been analyzed using the solubility parameter approach to choose the proper ratios of the constituents of the blend. Then, PVA has been grafted with l-lactide (LLA) through ring-opening polymerization to obtain a poly(vinyl alcohol)-graft-poly(l-lactide) (PVA-g-PLLA) brush copolymer with 82 mol % LLA according to 1H and 13C NMR spectroscopies. PEO has been blended with the PVA-g-PLLA brush copolymer and the miscibility of the system has been analyzed by DSC, FTIR, OM, and SEM. The particular architecture of the blends results in DSC traces lacking clearly distinguishable glass transitions that have been explained considering self-concentration effects (Lodge and McLeish) and the associated concentration fluctuations. Fortunately, the FTIR analysis is conclusive regarding the miscibility and the specific interactions in these systems. Melting point depression analysis suggests that interactions of intermediate strength and PLOM and SEM reveal homogeneous morphologies for the PEO/PVA-g-PLLA blends. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1217–1226

High-pressure rheological analysis of CO2-induced melting point depression and viscosity reduction of poly(ε-caprolactone)

High-pressure rheology has been used to assess the effects of supercritical carbon dioxide (scCO2) on the melting point (Tm) and viscosity of poly(ε-caprolactone) (PCL) over a range of temperatures and pressures up to 300 bar over a wide range of shear rates. Plots of the storage and loss moduli against temperature show a significant shift of Tm to lower temperatures in the presence of CO2, indicating that the polymer crystals melt at temperatures much lower than the ambient pressure Tm.Furthermore, a significant decrease in the viscosity of two PCL grades with different molecular weight (Mn ∼ 10 kDa and 80 kDa) was also detected upon increasing the CO2 pressure to 300 bar. Experimental viscosity data were fitted to the Carreau model to quantify the extent of the plasticising effects on the zero-shear viscosity and relaxation time under different conditions. Similar analyses were conducted under high-pressure nitrogen, to compare the effects obtained in the presence of a non-plasticising gas.

Miscibility studies of paraffin/polyethylene blends as form-stable phase change materials

Thermal energy storage is useful to promote energy conservation in buildings or machinery. One means of achieving a form stable phase change materials (PCMs) with polymers is to utilize immiscible blend pairs, governed by blend miscibility. The degree of miscibility between the polymer pairs may also influence energy efficiency in applications. Binary polyethylene–paraffin blends were melt compounded at different ratios of high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE) using a parallel co-rotating twin screw extruder. The miscibility of the paraffin in the three types of polyethylene was evaluated using differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The DSC data demonstrated two melting temperatures with a depression of the equilibrium melting temperature for the polyethylene in the mixture. Two distinct and an intermediate phase were evident in the atomic force microscopy images. This structure verified the partial miscibility of paraffin in polyethylene. Interaction parameters between paraffin and polyethylene were obtained through melting point depression analysis via the Flory–Huggins approximation for thermodynamic mixing of two components. The crystallinity of each component depends upon the blend concentration. Two paraffin crystallization peaks for the PE/paraffin blends were observed, with the enthalpy of one peak increasing at the expense of the other. The lowest paraffin miscibility in polyethylene is found in paraffin/HDPE blend.

Novel miscible blends of poly(p-dioxanone) with poly(vinyl phenol)

Poly(p-dioxanone) (PPDO) has been blended with poly(vinyl phenol) (PVPh) and the PPDO/PVPh blends have been investigated using DSC, FTIR and POM. According to the single Tg criterion, miscibility has been found in the whole composition range for the blends obtained by solvent casting from dioxane solutions. The dependence of the Tg on composition shows negative deviation from the Fox equation. The interaction parameter, obtained from melting point depression analysis, χ12=−1.0, confirms a thermodynamically miscible blend. Specific interactions have been analyzed by FTIR. The OH stretching region of PVPh indicates that upon addition of PPDO the hydroxyl–hydroxyl autoassociation interactions are mainly replaced by hydroxyl–carbonyl interassociation contacts, in detrimental of the possible hydroxyl–ether interactions. The carbonyl stretching region of pure PPDO is sensitive to intramolecular ether-ester interactions occurring in the oxyethanoate structures (–O–CH2–CO–O–) present along the PPDO chain. The –O–CH2–CO–O– structure presents only two minimum energy conformations, trans and cis, resulting in two different absorptions in the CO stretching region located respectively at about 1757 and 1732cm−1. Blending with PVPh promotes two new contributions red shifted by about 23cm−1 relative to the “free” CO components. Finally, POM analysis shows that the addition of PVPh to PPDO significantly decreases the crystallization rate of PPDO.

Copolymers of ethyl glycolate and ω–pentadecalactone: Enzymatic synthesis and solid-state characterization

Synthesis of poly(PDL-GA) copolymers is successfully achieved via enzymatic catalysis starting from ω-pentadecalactone and ethyl glycolate. In the copolymers PDL and GA units show a significant tendency to an alternating arrangement. All copolyesters display a high degree of crystallinity (χc≈70%) regardless of their composition (GA content: 0–27mol%). Analysis of melting point depression by the Wendling–Suter model suggests inclusion of GA units in PPDL-type crystals. Accordingly WAXS results show that, with increasing GA unit content, the PPDL unit cell undergoes a gradual increase of c-axis (chain axis) periodicity, compatible with the insertion of GA units within the crystallizing PDL sequences. Poly(PDL-GA) copolymers combine typically hydrophobic (PDL) and hydrophilic (GA) monomers and are promising new tuneable drug-delivery systems for medical applications. In this perspective, poly(PDL-GA) nanoparticles are fabricated and characterized.

Synthesis and Properties of Novel Biodegradable/Biocompatible Poly[propylene‐co‐(ethylene succinate)] Random Copolyesters

AbstractRandom biocompatible/biodegradable poly[propylene‐co‐(ethylene succinate)]s were prepared. Mechanical properties and crystallization rates decreased with propylene succinate content. Glass transition temperatures (Tg) varied between those for the homopolymers. DSC and TMDSC findings showed that multiple melting behaviour of PPESu samples is related to melting–recrystallization–remelting. WAXD observations, eutectic behaviour, and thermodynamic analysis of the equilibrium melting point depression indicated isodimorphic cocrystallization. The copolymers showed enzymatic hydrolysis rates between those of the homopolymers and cytotoxicity/biocompatibility similar to PLA.magnified image

Miscibility of TPU(PCL diol)/PCL Blend and Its Effect on PCL Crystallinity

AbstractPoly(ε‐caprolactone) (PCL) was melt blended with thermoplastic polyurethane based on polycaprolactone diol (TPU(PCL diol)). The amount of PCL was varied from 20% to 50% by weight. A single composition dependent glass transition temperature (from DSC) shows the miscibility of system. Also the negative value of polymer‐polymer interaction density, obtained from the analysis of the equilibrium melting point depression, confirms the blends' miscibility. Tc and Tm of the PCL component in the blend decrease significantly with an increase in the TPU content, in comparison with that of pure PCL. The position of the diffraction peak related to (110) planes of PCL in the blends using WAXS has been shifted to lower value. This means the b‐axis of orthorhombic unit cell of PCL is spread out in the blends. On the whole, increase of TPU content in the blend decreases crystallization ability of PCL compared to pure PCL.

Crystallization behavior of poly(ϵ‐caprolactone) in poly(ϵ‐caprolactone) and poly(vinyl methyl ether) mixtures

AbstractThe morphological development and crystallization behavior of poly(ϵ‐caprolactone) (PCL) in miscible mixtures of PCL and poly(vinyl methyl ether) (PVME) were investigated by optical microscopy as a function of the mixture composition and crystallization temperature. The results indicated that the degree of crystallinity of PCL was independent of the mixture composition upon melt crystallization because the glass‐transition temperatures of the mixtures were much lower than the crystallization temperature of PCL. The radii of the PCL spherulites increased linearly with time at crystallization temperatures ranging from 42 to 49°C. The isothermal growth rates of PCL spherulites decreased with the amount of the amorphous PVME components in the mixtures. Accounting for the miscibility of PCL/PVME mixtures, the radial growth rates of PCL spherulites were well described by a kinetic equation involving the Flory–Huggins interaction parameter and the free energy for the nuclei formation in such a way that the theoretical calculations were in good agreement with the experimental data. From the analysis of the equilibrium melting point depression, the interaction energy density of the PVME/PCL system was calculated to be −3.95 J/cm3. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Thermal and spectroscopy studies on ternary miscibility and phase behavior in blends comprising poly(4‐vinyl phenol) and two aryl polyesters

AbstractThermal analysis and Fourier transform infrared spectroscopy characterizations were performed on three ternary blend systems that comprise poly(4‐vinyl phenol) (PVPh) and any two of the three homologous aryl polyesters [poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT)]. Although PVPh is miscible with any one of the polyesters in forming a binary blend system, miscibility in ternary systems by introducing one more polymer of different structures to the blend system is not always expected. However, this study concludes that miscibility does exist in all these three ternary blends of all compositions investigated. Reasons and factors for such behavior were probed. Quantitative interactions in the ternary blend system were also estimated. The overall interaction energy density (B) by analysis of melting point depression for the PBT/PVPh/PET ternary blend system led to a negative value (B = −5.74 cal/cm3). Similarly, Tg‐composition analyses were performed on two other ternary blend systems, PET/PVPh/PTT and PTT/PVPh/PBT. Comparison of the qualitative results showed that the interaction energy densities in the other two ternary blend systems are similarly negative and comparable to the PBT/PVPh/PET ternary blend system. The Fourier transform infrared spectroscopy results also support the qualitative findings among these three ternary blend systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1339–1350, 2006

Glass transition behavior and miscibility in blends of poly(vinyl p-phenol) with two homologous aliphatic polyesters

New miscible blend systems comprised of poly(4-vinyl phenol) (PVPh) and a homologous series of polyesters of different CH2/CO ratios (from 4.5 to 7) was discovered. Miscibility has been confirmed using differential scanning calorimetry, Fourier-transformed infrared spectroscopy, and scanning electron microscopy. The PVPh/polyesters blends investigated exhibited a single composition-dependent glass transition and homogeneous phase morphology, and they similarly exhibited a cusp in the Tg-composition relationships. This work further extended the range of aliphatic polyesters that are known to be miscible with PVPh. The Flory–Huggins interaction parameter (χ12) or energy density (B) obtained from analysis of melting point depression for PVPh/PEAz and PVPh/PHS blends are of negative values. More interestingly, the specific interactions in the PVPh/polyester blends change with the corresponding different structures in the polyester component. For the PVPh/PHS blend whose polyester constituent possesses a lower carbonyl density in the main chain (average CH2/CO ratio=7), the energy density B was found to be −1.17calcm−3. This value is significantly lower than those for either the PVPh/PEAz (CH2/CO=4.5) blend system (B=−7.72calcm−3). Miscibility, specific interactions, and peculiar Tg-composition relationships in the blends of PVPh with selected homologous polyesters are discussed.

Miscible blends of poly(4‐vinyl phenol)/poly (trimethylene terephthalate)

AbstractA new miscible blend of all compositions comprising poly(4‐vinyl phenol) (PVPh) and poly(trimethylene terephthalate) (PTT) was discovered and reported. The blends exhibit a single composition‐dependent glass transition and homogeneous phase morphology, with no lower critical solution temperature (LCST) behavior upon heating to high temperatures. Interactions and spherulite growth kinetics in the blends were also investigated. The Flory–Huggins interaction parameter (χ12) and interaction energy density (B) obtained from analysis of melting point depression are negative (χ12 = −0.74 and B = −32.49 J cm−3), proving that the PVPh/PTT blends are miscible over a wide temperature range from ambient up to high temperatures in the melt state. FTIR studies showed evidence of hydrogen‐bonding interactions between the two polymers. The miscibility of PVPh with PTT also resulted in a reduction in spherulite growth rate of PTT in the miscible blend. The Lauritzen–Hoffman model was used to analyze the spherulite growth kinetics, which showed a lower fold‐surface free energy (σe) of the blends than that of the neat PTT. The decrease in the fold‐surface free energy has been attributed to disruption of the PTT lamellae exerted by PVPh in an intimately interacted miscible state. Copyright © 2004 Society of Chemical Industry

Calorimetric study of fluorinated methacrylic and vinyl polymer blends: part 2: correlation between miscibility, chemical structure and χ12 interaction parameter in binary systems

The miscibility of poly(methylmethacrylate) (PMMA) and (trifluoroethyl methacrylic ester–MMA) copolymers (MMA–MATRIFE) with poly(vinylidene fluoride) (PVDF) and VDF copolymers was studied by differential scanning calorimetry (DSC) as a function of the fluorinated copolymer crystallinity and fluoroalkyl methacrylic ester content in the methacrylic copolymer. Miscibility limits were found identical whatever be the blend preparation technique, although solution mixing induced some polymer fractionation, thus giving slightly higher blend glass transition temperature. The miscibility domain widths are reduced when using MMA–MATRIFE copolymers as compared to PMMA-containing blends and miscibility limits are dependent on the MATRIFE content in the methacrylic copolymer. Moreover, PVDF or VDF copolymer melting enthalpy decrease is associated to a partial dissolution of the semi-crystalline polymer in PMMA or MMA–MATRIFE copolymer above the total miscibility limit. The evolution of dynamic moduli as a function of blends composition confirms the miscibility limits determined by DSC. The Flory–Huggins interaction parameters were determined through the melting point depression analysis and compared to correlate the intensity of inter- or intra-molecular interactions between the polymers to the postulated ‘acidity’ of hydrogen atoms in various VDF-containing polymers. The interaction parameter χ12 increases with the fluoroalkyl methacrylic ester content, corresponding to a prevalence of intra-molecular on inter-molecular interactions in these blends. Similarly, PVDF offers higher χ12 values as compared to VDF–TFE or particularly to VDF–TrFE copolymers. These results highlight the importance of the nature of fluorinated polymers and of the inter- or intra-molecular character of dipolar interactions on both, copolymer miscibility and interaction parameter values.

Miscibility in blends of liquid crystalline copolyester and semicrystalline poly(ethylene-2,6-naphthalene dicarboxylate)

The miscibility in blends of random liquid crystalline copoly(oxybenzoate-ethylene terephthalate) at a molar ratio of 60:40 (P64) and semicrystalline poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) were investigated with differential scanning calorimetry, wide angle X-ray diffraction and polarized optical micrography. It was found that P64 and PEN were partially miscible as evidenced from the appearance of a single glass transition temperature for each blend at different compositions. Furthermore, the Flory–Huggins interaction parameter, χ12, for P64 and PEN was determined to be −1.13 through the melting point depression analysis, indicating miscibility in blends of P64 and PEN at the melt state. The coherence lengths of PEN in the presence of a small amount of P64, around 3%, were larger than that in pure PEN, implying the regularity of PEN crystals in the blends with low P64 content being more perfect than that of the pure PEN.

Miscibility, melting and crystallization behavior of two bacterial polyester/poly(epichlorohydrin- co-ethylene oxide) blend systems

The miscibility, melting and crystallization behavior of two bacterial polyester/poly(epichlorohydrin- co-ethylene oxide) (PECH–EO) blend systems was studied. PECH–EO containing 48 mol% of epichlorohydrin is miscible with poly(3-hydroxybutyrate) (PHB) and with poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) containing 14 mol% hydroxyvalerate. Both blend systems are characterized by the existence of a single glass transition temperature ( T g) and a depression of the equilibrium melting temperature of PHB or PHBV in each blend. The T g-composition dependence of the blends can be described by the Kwei equation. The interaction parameters obtained from melting point depression analysis are −0.089 and −0.075 for PHB/PECH–EO and PHBV/PECH–EO blends, respectively. The melting and cold crystallization behavior of PHB and PHBV during DSC heating runs is markedly affected by the addition of PECH–EO. During the non-isothermal crystallization process, the cold crystallization temperature ( T cc) of PHB first shows a slight decrease with increasing PECH–EO content from 0 to 50 wt.%, and then a significant increase with further increase of PECH–EO content to 90 wt.% in PHB/PECH–EO blends. For PHBV/PECH–EO blends, the T cc of PHBV increases with increasing PECH–EO content in the whole composition range studied during the process. For samples after cold crystallization, the phase crystallinity of PHB remains constant, while that of PHBV decreases significantly with increasing PECH–EO content. Under isothermal condition, the radial growth rates of bacterial polyester spherulites in the blends are lower than that of pure bacterial polyester samples at higher crystallization temperatures. Spherulitic growth kinetics is analyzed using the Lauritzen–Hoffman model, and the kinetic parameters are determined. Nucleation constant decreases with increasing PECH–EO content in both PHB/PECH–EO and PHBV/PECH–EO blends.

Relation for Solid−Liquid Coexistence Systems and Its Application to Melting Point Depression of Benzene in Natural Rubber

A relation that represents “solid−liquid coexistence” curves in binary equilibrium phase diagrams of solvent crystal−noncrystalline polymer systems is deduced on a more general theoretical basis, which is a counterpart of the Flory−Huggins equation representing a solution curve. The relation deduced is expressed as a function of concentration in terms of the interfacial free energy and crystal size. Next, on this relation basis, a melting point depression analysis is made by using certain experimental results on lightly chemically cross-linked NR−benzene systems whose degree of chemical crosslinking is so small that they can be regarded as uncross-linked systems. The relation is revised when considering an elastic term by chain entanglements in the good solvent and a certain concentration−temperature dependent polymer−solvent interaction parameter. Consequently, in the higher concentration range, part of the previous data of crystal size determined from X-ray fit fairly well within the upper and lower lim...

Compatibility studies of partially compatible blends through glass transition temperature and melting point depression analysis

This work deals with a compatibility study of blends based on poly(vinylidene fluoride) (PVDF) by means of the determination of the polymer–polymer interaction parameter through two different and separated methods. Firstly, the well-known Flory–Hüggins interaction parameter was determined from melting point depression analysis and subsequently from Tg measurements by applying an expression proposed by Kim and Burns. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:997–1004, 1998

Compatibility studies of partially compatible blends through glass transition temperature and melting point depression analysis

This work deals with a compatibility study of blends based on poly(vinylidene fluoride) (PVDF) by means of the determination of the polymer–polymer interaction parameter through two different and separated methods. Firstly, the well-known Flory–Hüggins interaction parameter was determined from melting point depression analysis and subsequently from Tg measurements by applying an expression proposed by Kim and Burns. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:997–1004, 1998