Crystallization,thermal behavior,and compatibility of poly(ethylene oxide)/poly(propylene oxide) blends

Isothermal and nonisothermal crystallization kinetics of different poly(ethylene oxide)/poly(propylene oxide) blends were investigated by means of differential scanning calorimetry (DSC). Glass transition temperature of quenched samples have also been reported. Phase morphologies and poly(ethylene oxide) spherulite growth rates were analyzed by polarizing light transmission microscopy. Results show morphological changes along with regime transitions of poly(ethylene oxide) crystal growth. Kinetic analyses of the data suggest that, although the blend behaves as a noncompatible, phase-separated system, there exists a certain degree of interaction between polymer chains. © 1996 John Wiley & Sons, Inc.     

Crystallization and melting behavior of poly(ethylene oxide)/poly(n-butyl methacrylate) blends

The phase diagram, crystallization and melting behavior of poly(ethylene oxide) (PEO)/poly(n-butyl methacrylate) (PnBMA) blends have been investigated using differential scanning calorimetry and optical microscopy. The results show that the blends are miscible up to 85 °C and show an lower critical solution temperature-type demixing at a higher temperature. The isothermal crystallization studies of the blends indicate a reduction in the overall rate of crystallization. Analysis of isothermal crystallization data by means of Avrami equation leads to average values of the Avrami index of 2.5 for pure PEO and 3.0 for the different blend compositions. The melting behavior of the blends reveals double endotherms, which is ascribed to both secondary crystallization and recrystallization. The melting point depression study yielded χ₁₂=0, indicating a relatively low interaction strength.     

Miscibility, mechanical and thermal properties of poly(lactic acid)/polyester-diol blends

We found new plasticizers with high molecular weight and low mobility for poly(lactic acid) (PLA). The new plasticizers are polyester-diols (PED) with nominal molecular weight 2000. Temperature dependence of oscillatory tensile moduli of PLA/PED blends in solid states was measured and miscible pairs of the blends were found. The miscible pairs are PLA/poly(ethylene adipate) and PLA/poly(diethylene adipate). Observation by scanning electron microscope and results of differential scanning calorimetry also indicate that these blends are miscible with PLA at weight ratio of PED less than or equal to 20%. In these blends, glass transition temperature is significantly lower than that of PLA. On the other hand, poly(butylene adipate) and poly(hexamethylene adipate) are partially miscible with PLA at weight ratio of PED 20%. The difference of the miscibility is discussed in terms of solubility parameter, which is calculated using the method by Small and configurational entropy.     

Poly(ethylene oxide)/poly(ethyl methacrylate) blends: Crystallization,melting behavior,and miscibility

Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant K_n are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account.     

Crystallization behavior and toughening mechanism of poly(ethylene oxide) in polyoxymethylene/poly(ethylene oxide) crystalline/crystalline blends

In this study, the unique crystallization behavior of poly(ethylene oxide) (PEO) in polyoxymethylene (POM)/PEO crystalline/crystalline blends was examined in detail. This study was the first to report the typical fractionated crystallization of PEO in POM/PEO blends when PEO is fewer than 30 wt.%. The delayed crystallization temperature of PEO was confirmed at about 5°C to 14°C by using differential scanning calorimetry and perturbation–correlation moving‐window 2D correlation IR spectroscopy. Wide‐angle X‐ray diffraction indicates that no new crystal structures or co‐crystals were generated in POM/PEO. The statistical calculations of scanning electron microscopy photos show that the average diameter of PEO particles is 0.227 µm to 1.235 µm and that the number of small particles is as many as 10⁹ magnitudes per cm³. Theory analysis establishes that the delayed crystallization of PEO is a heterogeneous nucleation process and not a homogeneous nucleation process. A significant toughening effect of PEO to POM was also observed. The impact strength of POM/PEO acquires a maximum of 10.5 kJ/m² when PEO content is 5%. The impact strength of the blend increases by 78.0% compared with pure POM. To improve the toughening effect, the best particle size is established between 0.352 and 0.718 µm, with a PEO particle spacing of 0.351 µm to 0.323 µm. The number of corresponding particles was 0.887 × 10⁹ per cm3 to 3.240 × 10⁹ per cm³. A PEO toughening model for POM was proposed to provide a new and effective way to solve the problem of POM toughening. Copyright © 2014 John Wiley & Sons, Ltd.     

Morphology of poly(ethylene oxide)/poly(vinyl acetate) blends

The morphology of poly(ethylene oxide)/poly(vinyl acetate) (PEO/PVAc) blends was examined using small angle X-ray scattering (SAXS) and optical microscopy. The morphological and structural parameters of the blends are dependent on both composition and crystallization conditions. Optical microscopy revealed that blend samples prepared by solution casting crystallized with volume-filling crystals up to a composition of 30/70 wt% PEO/PVAc; at higher PVAc content there was no evidence of crystallization in the temperature range studied. Pure PEO always crystallized with a spherulite-hedrite morphology. The formation of spherulites was relatively favoured at lower crystallization temperatures and by addition of PVAc to PEO. Small angle X-ray intensity profiles were analyzed using a recently developed methodology and it was found that, for a given crystallization temperature, the amorphous and interphase thicknesses increased with increasing PVAc content but that the average crystalline thickness was independent of composition. The morphological and structural properties of the PEO/PVAc blends were attributed to the presence of non-crystallizable material in both the interlamellar and interfibrillar regions.     

Crystallization kinetics and morphology of poly(vinylidene fluoride)/poly(ethylene adipate) blends

The miscibility, isothermal crystallization kinetics and morphology of the poly(vinylidene fluoride)(PVDF)/poly(ethylene adipate)(PEA) blends have been studied by differential scanning calorimetry(DSC), optical microscopy(OM) and scanning electron microscopy(SEM). A depression of the equilibrium melting point of PVDF was observed. From the melting point data of PVDF, a negative but quite small value of the interaction parameter ?PVDF-PEA is derived using the Flory-Huggins equation, implying that PVDF shows miscibility with PEA to some extent. Nonisothermal and isothermal crystallization kinetics suggest that the crystallization rate of PVDF decreases with increasing the amount of PEA, and a contrary trend was found when PEA crystallizes with the increase of the amount of PVDF. It was further disclosed that the blend ratio and crystallization temperature affect the texture of PVDF spherulites greatly, which determines the subsequent crystallization of PEA. At high temperatures, e.g. 150 ℃, the band spacing of PVDF spherulites increases with the addition of PEA content and the spherulitic structure becomes more open. In this case, spherulitic crystallization of PEA is not observed for all blend compositions. At low temperatures, e.g. 130 ℃, for the PEA-rich blends, the interpenetrated structures are eventually formed by the penetration of the spherulites of PEA growing within the pre-existing PVDF spherulites.     

Conformational changes of poly(ethylene oxide) in poly(ethylene oxide)/poly(methyl methacrylate) blends by supercritical carbon dioxide

The effects of supercritical carbon dioxide (SC CO₂) fluids on the morphology and/or conformation of poly(ethylene oxide) (PEO) in PEO/poly(methyl methacrylate) (PMMA) blends were investigated by means of differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and Fourier transform infrared (FTIR). According to DSC data for a given blend, the melting enthalpy and, therefore, degree of crystallinity of PEO were increased, whereas the melting temperature of PEO was decreased, with SC CO₂ treatment. The enhancement of PEO crystallization with SC CO₂ treatment, as demonstrated by DSC data, was supported by WAXD data. According to FTIR quantitative analyses, before SC CO₂ treatments, the conformation of PEO was transformed from helix to trans planar zigzag via blending with PMMA. This helix‐to‐trans transformation of PEO increased proportionally with increasing PMMA content, with around 0.7% helix‐to‐trans transformation per 1% PMMA incorporation into the blend. For a given blend upon SC CO₂ treatments, the conformation of PEO was transformed from trans to helix. This trans‐to‐helix transformation of PEO decreased with increasing PMMA contents in the blends because of the presence of interactions between the two polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2479–2489, 2004     

Compatible and tearing properties of poly(lactic acid)/poly(ethylene glutaric‐co‐terephthalate) copolyester blends

Fourier transform infrared and nuclear magnetic resonance results suggest that the carboxylic acid groups of poly(lactic acid) (PLA) molecules react with the hydroxyl groups of FePol (FP) molecules during the melt‐blending of PLA_xFP_y specimens. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) experiments of PLA and PLA/FP specimens suggest that only small amounts of poor PLA and/or FP crystals are present in their corresponding melt crystallized specimens. In fact, the percentage crystallinity, peak melting temperature, and onset re‐crystallization temperature values of PLA/FP specimens reduce gradually as their FP contents increase. However, the glass transition temperatures of PLA molecules found by DSC and DMA reduce to a minimum value as the FP contents of PLA_xFP_y specimens reach 6 wt %. Further DMA and morphological analysis of PLA/FP specimens reveal that FP molecules are compatible with PLA molecules at FP contents equal to or less than 6 wt %, as no distinguished phase‐separated FP droplets and tan δ transitions were found on fracture surfaces and tan δ curves of PLA/FP specimens, respectively. In contrast to PLA, the FP specimen exhibits highly deformable and tearing properties. After blending proper amounts of FP in PLA, the inherent brittle deformation and poor tearing behavior of PLA were successfully improved. Possible reasons accounting for these interesting crystallization, compatible and tearing properties of PLA/FP specimens are proposed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 913–920, 2010     

Mechano-optical behavior in poly (ethylene terephthalate)/poly (ether imide) blends

Mechano-optical behavior and related structural evolution during uniaxial stretching of melt miscible poly (ethylene terephthalate) (PET)/poly (ether imide) (PEI) blends were studied near their glass transition temperature using an instrumented machine that measures true stress, true strain and spectral birefringence simultaneously. Stretching from amorphous state, two distinct stress-optical regimes were observed at temperatures between T_g and T_cc (cold crystallization). Near T_g, a typical photoelastic behavior persists until a critical temperature above which temperature independent initial stress optical behavior is observed. At those temperatures above T_g, where glassy behavior is observed, decreasing stretching rate was also found to eliminate this glassy photo elastic regime leading to the observation of a linear initial stress optical behavior that becomes temperature independent as expected from linear stress optical rule. Increasing PEI concentration in the blends suppresses crystallizability and increases temperature at which initial elastic region disappears giving way to pure liquid behavior where linear stress optical behavior is observed. This is attributed to the increase and broadening of the glass transition temperature with the addition of noncrystallizable PEI. In PET/PEI blends, the stress-optical coefficient (SOC), determined in a linear stress optical regime, was found to increase linearly with the increase in PEI concentration.     

Compatibility of poly(ethylene oxide)/poly(vinyl chloride) blends by differential scanning calorimetry

This article refers to a study of the thermal behaviour of poly(ethylene oxide) and poly(vinyl chloride) blends in the solid state. The compatibility has been examined by differential scanning calorimetry. The influence of molecular masses of the polymers on their compatibility has been shown. The equilibrium melting temperatures decrease in the mixture, such behaviour being progressively greater with the PEO reduction. The melting temperature of blends increases linearly with the crystallization temperature for a wide range of undercooling. Values of the parameters χ₁₂ and B have been obtained.     

Transparent and ductile poly(lactic acid)/poly(butyl acrylate) (PBA) blends: Structure and properties

Poly(butyl acrylate) was prepared by the free radical polymerization of butyl acrylate as an initiator in the presence of 2,2′-Azoisobu-tyronitrile (AIBN) and the average molecular weight, polydispersity and thermal stability were evaluated. PLA and PBA were melt blended using a Haake Rheometer, and the light transmission, thermal properties, dynamic rheological properties, mechanical properties, phase morphology of blends and toughening mechanism were investigated. Dynamic rheology, SEM and DSC results show that the PLA is partial miscible with PBA. The PBA component improved the crystallization ability of PLA and the crystallinity of PLA increased with content of PBA (<15 wt.%). With the increase of PBA, the tensile strength and modulus of the blend decreased slightly while the elongation at break and toughness were dramatically increased. With the addition of PBA, the failure mode changes from brittle fracture of neat PLA to ductile fracture of the blend. Rheological results revealed the complex viscosity and melt elasticity of the blends decreased with increasing content of PBA and phase segregation occurred at loading above 11 wt.% PBA. UV–vis light transmittance showed that PLA/PBA blends with a high transparency, and the transmittance decreased with the amount of PBA.     

聚乳酸/聚苯乙烯共混物的热氧稳定性研究

通过溶液浇铸法制备了聚乳酸/聚苯乙烯共混物,以差热-热重分析研究了共混物的热氧稳定性,结果表明聚乳酸中引入聚苯乙烯,可以增强聚乳酸/聚苯乙烯共混物的热氧稳定性.采用红外光谱分析了共混物不同结构的分子链间相互作用,证实聚乳酸大分子链羰基的未共用电子对和聚苯乙烯大分子链侧基苯环的π电子形成了n-π键.     

Characterization of poly(carboxylic acid)/poly(ethylene oxide) blends formed through hydrogen bonding by spectroscopic and calorimetric analyses

The solid state of the complex between poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO), and that between poly(methacrylic acid) (PMAA) and PEO formed via hydrogen-bonding was studied by differential-scanning calorimetric (DSC) and by Fourier-transform infrared (FT–IR) spectroscopic measurements. Melting temperature T_m and the degree of the crystallinity X_c of PEO in the systems PAA (or PMAA)/PEO blends obtained from aqueous or dimethyl sulfoxide (DMSO) medium were measured in various unit mol % of PEO ([PEO]100/{[PAA(or PMAA)] + [PEO]}) where [ ] is the unit mole concentration. It was found that 50 unit mol % of PEO is a critical composition, which gives new evidence for the 1 : 1 complex formation between PAA (or PMAA) and PEO. From the FT–IR spectroscopic analysis in conjunction with DSC measurements we also found that the effects of solvent and of hydrophobic interaction (due to the α-methyl group of PMAA) are the important factors controlling the complexation in the solution and solid systems. These factors also affect the crystallization behavior and the microstructure of the PAA (or PMAA)/PEO blend in solid state.     

Morphology and interpenetrated growth of spherulites in miscible poly(ethylene succinate)/poly(ethylene oxide) blends

Morphology development and growth process of spherulites in miscible poly(ethylene succinate)/poly(ethylene oxide) blends are studied by means of polarizing optical microscopy and atom force microscopy in this paper. Thin films with different film thicknesses were used to follow the growth processes of spherulites and dendrites. It is shown that, when one component spherulite grows, the other component in the melt is always excluded from the spherulite. The excluded component may reenter into the spherulite through diffusion depending on amorphous volume fraction of spherulite and segmental mobility of molecules, which leads to the occurrence of interpenetrated growth. This mechanism was analyzed in detail in this paper.     

An analysis of the crystallization behavior of poly(ethylene oxide)/poly(methyl methacrylate) blends by spectroscopic and calorimetric techniques

Infrared spectra in conjunction with calorimetric measurements have been used to follow the crystallization process and microstructural changes of poly(ethylene oxide) (PEO) in poly(ethylene oxide) and poly(methyl methacrylate) (PMMA) blends. We have given particular attention to compositions containing low PEO concentrations. The crystallization behavior and the resultant microstructures of PEO are strongly perturbed by the presence of PMMA. In addition, we found phase separation and trans sequences of PEO to be present, especially at low PEO concentrations.     

Studies of photooxidative degradation of poly(vinyl chloride)/poly(ethylene oxide) blends

The photooxidative degradation of blends (in a full range of compositions) of amorphous poly(vinyl chloride) (PVC) with semicrystalline poly(ethylene oxide) (PEO) in the form of thin films is investigated using absorption spectroscopy (UV–visible and Fourier transform infrared) and atomic force microscopy (AFM). The amount of insoluble gel formed as a result of photocrosslinking is estimated gravimetrically. It is found that the PVC/PEO blendsí susceptibility to photooxidative degradation differs from that pure of the components and depends on the blend composition and morphology. Photoreactions such as degradation and oxidation are accelerated whereas dehydrochlorination is retarded in blends. The photocrosslinking efficiency in PVC/PEO blends is higher than in PVC; moreover, PEO is also involved in this process. AFM images showing the lamellar structure of semicrystalline PEO in the blend lead to the conclusion that the presence of PVC does not disturb the crystallization process of PEO. The changes induced by UV irradiation allow the observation of more of the distinct PEO crystallites. This is probably caused by recrystallization of short, more mobile chains in degraded PEO or by partial removal of the less stable amorphous phase from the film surface. These results confirm previous information on the miscibility of PVC with PEO. The mechanism of the interactions between the components and the blend photodegradation are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 585–602, 2004     

Morphology and properties of biodegradable poly (lactic acid)/poly (butylene adipate-co-terephthalate) blends with different viscosity ratio

Phase morphology exerts a tremendous influence on the properties of polymer blends. The development of the blend morphology depends not only on the intrinsic structure of the component polymers but also on extrinsic factors such as viscosity ratio, shearing force and temperature in the melt processing. In this study, various poly (butylene adipate-co-terephthalate) (PBAT) materials with different melt viscosity were prepared, and then poly (lactic acid) (PLA)/PBAT blends with different viscosity ratio were prepared in a counter-rotating twin-screw extruder under constant processing conditions. The influence of viscosity ratio on the morphology, mechanical, thermal and rheological properties of PLA/PBAT (70/30 w/w) blends was investigated. The experimental results showed that the morphology and properties of PLA/PBAT blends strongly depended on the viscosity ratio. Finer size PBAT phase were observed for viscosity ratio less than 1 (λ < 1) compared to samples with λ > 1. It was found that the interfacial tensions of PLA and PBAT were significantly different when the viscosity ratio was changed, the lowest interfacial tensions (0.12 mN/m) was obtained when the viscosity was 0.77. Additionally, the maximal tensile strength in PLA/PBAT blends were obtained when the viscosity ratio was 0.44, while the maximal impact properties were obtained when the viscosity ratio was 1.95.