Crystallization behavior and hydrophilicity of poly(vinylidene fluoride)/poly(methyl methacrylate)/poly(vinyl pyrrolidone) ternary blends

Ternary blends composed of matrix polymer poly(vinylidene fluoride) (PVDF) with different proportions of poly(methyl methacrylate) (PMMA)/poly(vinyl pyrrolidone) (PVP) blends were prepared by melt mixing. The miscibility, crystallization behavior, mechanical properties and hydrophilicity of the ternary blends have been investigated. The high compatibility of PVDF/PMMA/PVP ternary blends is induced by strong interactions between the carbonyl groups of the PMMA/PVP blend and the CF₂ or CH₂ group of PVDF. According to the Fourier transform infrared and wide‐angle X‐ray difffraction analyses, the introduction of PMMA does not change the crystalline state (i.e. α phase) of PVDF. By contrast, the addition of PVP in the blends favors the transformation of the crystalline state of PVDF from non‐polar α to polar β phase. Moreover, the crystallinity of the PVDF/PMMA/PVP ternary blends also decreases compared with neat PVDF. Through mechanical analysis, the elongation at break of the blends significantly increases to more than six times that of neat PVDF. This confirms that the addition of the PMMA/PVP blend enhances the toughness of PVDF. Besides, the hydrophilicity of PVDF is remarkably improved by blending with PMMA/PVP; in particular when the content of PVP reaches 30 wt%, the water contact angle displays its lowest value which decreased from 91.4° to 51.0°. Copyright © 2011 Society of Chemical Industry     

Effect of blend composition and organoclay loading on the nanocomposite structure and properties of miscible poly(methyl methacrylate)/poly(styrene‐co‐acrylonitrile) blends

Organically‐modified montmorillonite clay nanocomposites of poly(styrene‐co‐acrylonitrile) (SAN), poly(methyl methacrylate) (PMMA) and SAN/PMMA miscible blend are investigated. Structure characteristics at the nanoscale and microscale and thermal and tensile properties are studied as a function of polymer blend composition and filler loading fraction. Blend miscibility and T_g are unaffected by up to 10% by wt. organoclay. Thermal degradation stability increases with SAN content and exhibits an optimum value of clay loading. Stiffness shows significant improvement. Tensile strength and elongation‐at‐break suffer as a result of nanocomposite formation. Modulus shows a maximum enhancement of 57% (5 ± 0.06 GPa at 10 wt% filler, 20/80 SAN/PMMA) and varies linearly with clay fraction for all compositions of matrix phase. Predictions of Halpin–Tsai composite model are in excellent agreement with the experimental behavior over full range of polymer blend composition. Fundamental aspects of a polymer blend–clay nanocomposite are clarified, such as lack of additional synergy between clay platelets and matrix, and tensile ductility reduction, compared with polymer–clay system. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Crystallization behavior and mechanical properties of poly(ethylene oxide)/poly(L‐lactide)/poly(vinyl acetate) blends

Poly(vinyl acetate) (PVAc) was added to the crystalline blends of poly(ethylene oxide) (PEO) and poly(L ‐lactide) (PLLA) (40/60) of higher molecular weights, whereas diblock and triblock poly(ethylene glycol)–poly(L ‐lactide) copolymers were added to the same blend of moderate molecular weights. The crystallization rate of PLLA of the blend containing PVAc was reduced, as evidenced by X‐ray diffraction measurement. A ringed spherulite morphology of PLLA was observed in the PEO/PLLA/PVAc blend, attributed to the presence of twisted lamellae, and the morphology was affected by the amount of PVAc. A steady increase in the elongation at break in the solution blend with an increase in the PVAc content was observed. The melting behavior of PLLA and PEO in the PEO/PLLA/block copolymer blends was not greatly affected by the block copolymer, and the average size of the dispersed PEO domain was not significantly changed by the block copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3618–3626, 2001     

A high‐resolution solid‐state NMR investigation of molecular mobility of poly(methyl methacrylate)/poly(vinyl pyrrolidone)/poly(ethylene oxide) ternary blends

The ternary blends of poly(methyl methacrylate)/poly(vinyl pyrrolidone)/poly(ethylene oxide), PMMA/PVP/PEO, were prepared by melting process, using a Haake plastograph, and nuclear magnetic resonance spectroscopy (NMR) was used as a methodology to characterize the molecular mobility of blend components, because NMR has several techniques that allow us to evaluate polymeric materials in different time scales. The NMR results showed that the blends were miscible on a molecular level. The values of proton lattice relaxation time in the rotating frame (T₁ρH) indicate that the ternary blend interaction did not reduce the intermolecular distance, because it is dipole–dipole. The molecular motion of each component, even in the miscible amorphous phase and the addition of PEO, has a definitive effect on the PMMA molecular mobility. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1492–1495, 2006     

Nanodroplet formation and exclusive homogenously nucleated crystallization in confined electrospun immiscible polymer blend fibers of polystyrene and poly(ethylene oxide)

By utilizing electrospun blend fibers of polystyrene (PS) and poly(ethylene oxide) (PEO) with diameters in sub-microns, nanodroplets of the minor component (PEO) were obtained by annealing the blend fibers above the glass transition temperature (T_g) of the matrix polymer (PS), as a result of the Rayleigh-Plateau instability in the melt. However, direct thermal annealing of the PS/PEO blend fibers led to poor Rayleigh breakup of the PEO fibers in the PS matrix, and fractionated crystallization with both homogeneous and heterogeneous nucleation was observed, probably due to a broad size distribution of PEO particles. On the contrary, after confining the PS/PEO blend fibers with a high T_g polymer, poly(4-tert-butyl styrene) (P4tBS, T_g ∼ 143 °C), well-defined Rayleigh breakup of the PEO fiber was achieved by annealing the P4tBS-coated PS/PEO blend fibers at 150 °C. Consequently, exclusive homogeneously nucleated PEO crystallization was observed at −20 °C. This report could provide a universal method to achieve nano-sized droplets for the study of nanoconfinement effect by utilizing electrospun immiscible polymer blend fibers without addition of any compabitilizers.     

Compatibilization-like effect of reactive organoclay on the poly(l-lactide)/poly(butylene succinate) blends

The morphology of an incompatible polymer blend composed of poly(l-lactide) (PLLA) and poly(butylene succinate) (PBS) was examined by scanning and transmission electron microscopy, X-ray scattering, and X-ray photoelectron spectroscopy before and after the incorporation of an organoclay containing reactive functional groups, namely twice functionalized organoclay (TFC). TFC was prepared by treating Cloisite^® 25A with (glycidoxypropyl)trimethoxy silane. When a small amount of TFC was incorporated into the PLLA/PBS blend, the clay layers became fully exfoliated and were located mainly in the PLLA phase. At the low clay content, the dispersed phase had an almost constant domain size comparing with the PLLA/PBS blend, which decreased sharply as the clay content was further increased. When the clay content became high, the clay layers were dispersed not only in the PLLA phase but also in the PBS phase with intercalated/exfoliated coexisting morphology. The reactive TFC was found to play an important role in the blend similar to the in situ reactive compatibilizer. The specific interaction between the TFC and the polymer matrix was quantified by the Flory-Huggins interaction parameter, B, which was determined by combining the melting point depression and the binary interaction model. The morphology of the PLLA/PBS/clay composites was analyzed by considering the interaction parameter.     

Crystalline structures in ultrathin poly(ethylene oxide)/poly(methyl methacrylate) blend films

Amorphous poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blend films in extremely constrained states are meta-stable and phase separation of fractal-like branched patterns happens in them due to heterogeneously nucleated PEO crystallization by diffusion-limited aggregation. The crystalline branches are viewed flat-on with PEO chains oriented normal to the substrate surface, upon increasing PMMA content the branch width remains invariant but thickness increases. It is revealed that PMMA imposes different effects on PEO crystallization, i.e. the length and thickness of branches, depending on the film composition.     

Effects of hard and soft components on the structure formation,crystallization behavior and mechanical properties of electrospun poly(l-lactic acid) nanofibers

The effects of multi-wall carbon nanotubes (MWCNTs) and poly(ethylene oxide) (PEO) on the structure formation, morphology, crystallization behavior and mechanical property of electrospun poly (l-lactic acid) (PLLA) nanofiber mats were investigated by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and mechanical test. If incorporate hard filler, MWCNTs into electrospun PLLA nanofiber, the crystallinity, chain orientation, and crystallization behaviors were almost not influenced by the MWCNTs content owing to the MWCNTs mainly acted as impeding the crystal growth and chain diffusion. If incorporate small content of soft and miscible component, PEO (10 wt%) into the electrospun PLLA and PLLA/MWCNTs nanofibers, the crystallinity and crystallization rate of PLLA in nanofibers were obviously enhanced. The synergistic effect of PEO and MWCNTs in PLLA nanofibers was observed during melt-crystallization behaviors of PLLA/MWCNTs fibers. Based on those results, we found that the chain mobility is an important factor to influence the structure formation and crystallization behaviors in the electrospun nanofibers. Our results indicated that the structure and properties of electrospun nanofibers could be optimized by compounding with hard inorganic filler and soft polymer components.     

Blends of amorphous and crystalline polylactides with poly(methyl methacrylate) and poly(methyl acrylate): a miscibility study

Blends of amorphous and crystalline polylactides (PDLA and PLLA) with poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) have been prepared. Thermal behaviour and miscibility of these blends along the entire composition interval were studied by differential scanning calorimetry (d.s.c.). The results were compared with those obtained by dynamic mechanical analysis (DMTA). Only one T_g was found in PDLA/PMA and PDLA/PMMA blends, indicating a high degree of miscibility in both systems. Nevertheless, the PDLA/PMMA blend presented enlargements of the T_g width at high PMMA contents. In this case, additional evidence of complete miscibility was obtained by studying the evolution of the enthalpic recovery peaks which appear after different thermal annealing treatments. When the polylactide used was semicrystalline (PLLA), once the thermal history of the blends had been destroyed, crystallization of PLLA was disturbed in both blends PLLA/PMMA and PLLA/PMA, but in a rather different fashion: in the first case crystallization was almost prevented while in the second one it was favoured. This behaviour was explained in terms of the effect of the higher stiffness as indicated by the value of T_g for PMMA compared to that for PMA.     

Porous biodegradable polyesters. I. Preparation of porous poly(L‐lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L ‐lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution‐cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (M_w = 1 × 10³), but shifted to lower values than expected when high molecular weight PEO (M_w = 1 × 10⁵) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as‐cast PLLA and PEO blend films revealed that PLLA and PEO were phase‐separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000     

不同构型聚乳酸共混体系的立构复合结晶研究进展

左旋聚乳酸(PLLA)和右旋聚乳酸(PDLA)在共混体系中可形成立构复合(sc)结晶,与聚乳酸(PLA)同质结晶材料相比,sc 结晶材料具有良好的耐热性和耐化学稳定性。因此,sc 结晶是改善PLA 综合性能的一种有效手段。但在PLLA/PDLA 共混体系中,存在各自的同质结晶与两者之间sc 结晶的竞争,所以制备高耐热sc 型PLA 材料的关键之一是理解其sc 结晶的形成条件与机理,进而调控和促进其sc 结晶程度。在PLLA/PDLA 共混物中,sc 结晶受聚合物化学结构、结晶与加工条件等诸多因素影响,其影响规律和机理较复杂。根据PLLA/PDLA共混物sc 结晶行为影响因素的不同,从聚合物分子量、立构规整性、共混比例、分子链拓扑结构、结晶方式与条件、加工助剂和其他组分加入6 个方面出发,详细综述了PLLA/PDLA 共混物sc 结晶及其sc 材料制备的研究进展,以期为高耐热生物基PLA 材料的加工制备提供指导。     

Crystallization behavior of PEO in blends of poly(ethylene oxide)/poly(2‐vinyl pyridine)‐b‐(ethylene oxide) block copolymer

The crystallization behavior of two molecular weight poly(ethylene oxide)s (PEO) and their blends with the block copolymer poly(2‐vinyl pyridine)‐b‐poly(ethylene oxide) (P2VP‐b‐PEO) was investigated by polarized optical microscopy, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy (AFM). A sharp decreasing of the spherulite growth rate was observed with the increasing of the copolymer content in the blend. The addition of P2VP‐b‐PEO to PEO increases the degradation temperature becoming the thermal stability of the blend very similar to that of the block copolymer P2VP‐b‐PEO. Glass transition temperatures, T_g, for PEO/P2VP‐b‐PEO blends were intermediate between those of the pure components and the value increased as the content of PEO homopolymer decreased in the blend. AFM images showed spherulites with lamellar crystal morphology for the homopolymer PEO. Lamellar crystal morphology with sheaf‐like lamellar arrangement was observed for 80 wt% PEO(200M) and a lamellar crystal morphology with grain aggregation was observed for 50 and 20 wt% blends. The isothermal crystallization kinetics of PEO was progressively retarded as the copolymer content in the blend increased, since the copolymer hinders the molecular mobility in the miscible amorphous phase. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Influence of dispersed organophilic montmorillonite at nanometer‐scale on crystallization of poly(L‐lactide)

We investigated the effects of surface‐treated organophilic clay on the crystallization of poly(L ‐lactide) (PLLA) in their hybrids. The natural nano‐clay in PLLA/clay hybrids acts as a heterogeneous nucleating agent to facilitate crystallization. On the contrary, extensive distributions of induction periods for nucleation are observed in the individual spherulites of neat PLLA and PLLA/organophilic clay hybrids. Therefore, it is suggested that nucleation type of neat PLLA and PLLA/organophilic clay hybrids implies nearly growth geometry as a homogeneous one. Further, under the presence of nano‐clay in their composites, PLLA matrix form the orthorhombic lattice structure corresponded to the α‐form crystal. Since this experimental fact implies little effect of the clay particles on polymorphism of PLLA crystal, the nucleating effect of the organophilic clay seems weaker than the natural clay itself. However, an increase in clay content enhances the growth rates of spherulite for hybrids. Consequently, most of hybrids exhibit an increase in overall crystallization rates at any crystallization temperature in spite of relatively lower nucleation rate of PLLA crystallites itself. In addition, the Avrami exponents (n) obtained by relatively low crystallization temperature ranged from 4 to 6, implying that the growth geometry was dominated sheaf‐like structure in early stage of isothermal crystallization. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Casting solvent effect on crystallization behavior and morphology of poly(ethylene oxide)/poly(methyl methacrylate)

Poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends were prepared by casting from either chloroform or benzene solvents. After casting from solvents, all samples used in this study were preheated to 100°C and held for 10 min. Then, the solvent effect on the crystallization behavior and thermodynamic properties were studied by differential scanning calorimeter (DSC). Also, the morphology of spherulite of casting film was studied by polarized optical microscope. From the DSC and polarizing optical microscopy (POM) results, it was found that PEO/PMMA was miscible in the molten state no matter which casting solvent was used. However, the crystallization of PEO in the chloroform‐cast blend was more easily suppressed than it was in the benzene‐cast blend. Relatively, the chloroform‐cast blend showed the greater melting‐point depressing of PEO crystals. Also, the spherulite of chloroform‐cast film showed a coarser birefringence. It was supposed that the chloroform‐cast blend had more homogeneous morphology. It is fair to say that polymer blends, cast from solvent, are not necessarily in equilibrium. However, the benzene‐cast blends still were not in equilibrium even after preheating at 100°C for 10 min. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1627–1636, 2000     

Preparation and some properties of stereocomplex‐type poly(lactic acid)/layered silicate nanocomposites

Stereocomplex‐type poly(lactic acid)‐ [PLA]‐ based blends were prepared by solution casting of equimolar PLLA/PDLA with different amounts of organo‐modified montmorillonite. The homocrystallization and stereocomplexation of PLAs were enhanced by annealing of the blends. The stereocomplexation of PLAs, intercalation of the polymer chains between the silicates layers, and morphological structure of the filled PLAs were analyzed by wide‐angle X‐ray diffraction and transmission electron microscope. Thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and tensile test were performed to study the thermal and mechanical properties of the blends. The homo‐ and stereocomplex crystallization of neat PLLA/PDLA were enhanced by annealing. The effect of annealing on the crystallization was emphasized by the addition of clay. With this structural change, thermal stabilities properties were also improved by the addition of clay. The silicate layers of the clay were slightly stacked but intercalated and distributed in the PLA‐matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characterization and properties of poly(ethylene oxide) and its blends with poly (N-vinyl carbazole)

The calorimetric properties and dynamic mechanical behaviour of pure poly(ethylene oxide) (PEO) and its blends with poly(N-vinyl carbazole) (PNVK) have been examined as a function of composition in the range 50-100% PEO. Thermomechanical measurements indicate the presence of a phase separation in this blend. Using the Hoffman-Weeks plot no equilibrium melting point depression was found in any of the blends studied. Some kinetic interfacial effects were detected in the crystallization processes. For all blend compositions, the Avrami exponent is close to that obtained for pure PEO. The DMTA and DTA results suggest an incompatibility in this system.     

Polymer compatibility III. The system poly(methyl methacrylate)–poly(vinyl acetate). Characterization studies

Blends of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) were prepared by mixing the polymers in the melt and in the absence of a solvent. PMMA was the major constituent of the blend. The polymer blends were tested, using various methods, to determine if they are compatible as solids. Data obtained from dynamic mechanical and DSC measurements show that, when they are mixed under given Brabender mix conditions, the blends exhibit properties characteristic of polymer pairs compatible as solids. If the mix conditions are altered, a two-phase system is evidenced. Using micrographs obtained by light microscopy in phase contrast as criteria, two companion blends containing PMMA/PVAc 80/20 would be classified as incompatible as solids because of the differences in refractive index of PMMA and PVAc. The micrographs also show that, in the system that would otherwise be listed as compatible, the PVAc domains appear to be relatively uniform in size and distribution through the PMMA matrix. In its companion blend, large, irregularly shaped particles of PVAc which are poorly dispersed in the PMMA matrix are evident.     

Crystallization behavior of biodegradable poly(L‐lactide)/multiwalled carbon nanotubes nanocomposites from the amorphous state

Crystallization behavior of biodegradable poly(L ‐lactide) (PLLA) and its nanocomposites at different carboxyl‐functionalized multiwalled carbon nanotubes (f‐MWNTs) contents from the amorphous state was studied in detail in this work. For the isothermal cold crystallization, the presence of f‐MWNTs enhances the isothermal cold crystallization of PLLA in the nanocomposites compared with that of neat PLLA at the same crystallization temperature; moreover, the overall cold crystallization rate of PLLA increases with increasing the f‐MWNTs content in the PLLA matrix while the crystallization mechanism does not change. For the nonisothermal crystallization, the f‐MWNTs also accelerate the crystallization process of PLLA. In addition, the activation energies of nonisothermal cold crystallization process were calculated using both the Kissinger and Friedman methods. The cold crystallization activation energies of PLLA are higher in the nanocomposites than in neat PLLA, indicating that the addition of f‐MWNTs into the PLLA matrix acts as a physical hindrance to retard crystallization. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Isothermal and non‐isothermal crystallization of poly(L‐lactic acid)/poly(butylene terephthalate) blends

Isothermal and non‐isothermal crystallization kinetics of poly(l ‐lactic acid)/poly(butylene terephthalate) (PLLA/PBT) blends containing PLLA as major component is detailed in this contribution. PLLA and PBT are not miscible, but compatibility of the polymer pair is ensured by interactions between the functional groups of the two polyesters, established upon melt mixing. Crystal polymorphism of the two polyesters is not influenced by blending, as probed by wide‐angle X‐ray analysis. The addition of PLLA does not affect the temperature range of crystallization kinetics of PBT, nor the crystallinity level attained when the blends are cooled from the melt at constant rate. Conversely, PBT favors crystallization of the biodegradable polyester. The addition of PBT results in an anticipated onset of crystallization of PLLA during cooling at a fixed rate, with a sizeable enhancement of the crystal fraction. Isothermal crystallization analysis confirmed the faster crystallization rate of PLLA in the presence of PBT. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40372.     

High molecular weight poly( -lactide) and poly(ethylene oxide) blends: thermal characterization and physical properties

The miscibility of high molecular weight poly( -lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.