Glass transition study of blends of poly(N-methyldodecano-12-lactam) with poly(styrene-co-acrylic acid)

The blends of poly(N-methyldodecano-12-lactam) (MPA) with poly(styrene-co-acrylic acid) (PSAA) prepared from dioxane solutions were studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The experimental DSC data of glass transition temperature T_g as a function of composition of amorphous phase were fitted for the as-prepared and re-scanned samples using theoretical approaches. The as-prepared blends show monotonic single-T_g dependence. The values of the Gordon-Taylor coefficient not far from unity suggest miscibility of the blend system in amorphous phase in the whole concentration range. As documented by FTIR, this miscibility is associated with hydrogen bonds between COOH groups of the acrylic acid units in PSAA molecules acting as the H-bond donor and CO groups of MPA acting as the H-bond acceptor. The T_g-dependencies obtained form the second runs have a profound sigmoid character. The Schneider treatment induced an idea of partial limited miscibility in the MPA/PSAA blends caused by prevalence of homogeneous contacts. The difference in T_g between the first and second run can partly be attributed to higher crystallinities in the former.     

Crystallization behavior of polyethers containing odd numbers of methylene spacers from the isotropic and liquid crystalline states

A series of thermotropic polyethers synthesized from 1-(4-hydroxyphenyl) - 2 - (2 - methyl - 4 - hydroxyphenyl) - ethane and α,ω-dibromo-n-alkanes with odd numbers of methylene units (MBPE-n = odd) shows monotropic mesophase behavior. In isothermal differential scanning calorimetry (DSC) experiments, two—sometimes even three—exothermic transition processes can be observed when the crystallization temperature is below the mesophase transition temperature, while only one exothermic process is present above the mesophase transition temperature. The melting behavior of the crystals grown from the mesophase and from the isotropic melt states is different. The crystals grown from the mesophase state exhibit a larger overall heat of transition and a higher transition temperature compared with those grown from the isotropic melt. This may be attributed to the molecular interfacial connections between the crystal and amorphous regions when MBPEs crystallize from the mesophase state. The difference in morphology between the crystals grown from the different states has also been studied with polarized light microscopy (PLM) and transmission electronic microscopy (TEM). The structures of the crystals grown from the different states are, however, the same, as evidenced through wide-angle X-ray diffraction (WAXD) measurements. From the banded morphology of MBPE samples observed from PLM, the defect textures observed through TEM and the results of WAXD experiments, this mesophase can be identified as a nematic liquid crystal state.     

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.     

Crystallization,melting and structure of polypropylene/poly(vinylidene-fluoride) blends

Blends were prepared from isotactic polypropylene (iPP) along with its b-nucleated form and poly(vinylidene-fluoride) (PVDF). Melting, and crystallization characteristics as well as structure of the blends were studied by polarized light microscopy (PLM) and differential scanning calorimetry. According to PLM studies, the phase structure of these blends is heterogeneous in the molten state. The temperature range of crystallization of PVDF during cooling is higher than that of iPP. PVDF has a strong α-nucleating effect on iPP. The crystallization of iPP starts on the surface of dispersed PVDF droplets and an α-transcrystalline layer forms on the surface of the crystalline PVDF phase. The iPP matrix crystallizes predominantly in a-form in spite of the presence of a highly active b-nucleating agent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Crystallization behavior and thermal properties of blends of poly(3-hydroxybutyate-co-3-valerate) and poly(1,2-propandiolcarbonate)

Crystallization behavior of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(1,2-propandiolcarbonate) (PR(CO₂)) has been investigated by polarized light microscopy (PLM). The spherulite growth rates (SGR) of all blends were faster than that of pure PHBV, and the spherulite growth rates of PHBV in the PHBV/PR(CO₂) blends reduced with increasing PR(CO₂) weight fraction. There are two melting peaks in both the pure PHBV and the PHBV/PR(CO₂) blends. The melting peak of PHBV/PR(CO₂) blends was reduced by lower temperature about 20K as compared to PHBV and the higher temperature melting peak was increased by about 10K in the blends.     

Multiple melting behavior of poly(butylene succinate)

The multiple melting behavior of poly(butylenes succinate) (PBS) isothermally crystallized from the melt was investigated using differential scanning calorimetry (DSC), temperature modulated DSC (MDSC) and polarized optical microscopy. PBS exhibits at most four melting endotherms (denoted as T_m1, T_m2, T_m3, and T_m4 from high to low temperatures) and a crystallization exotherm (denoted as T_re) in the DSC heating trace. Multiple melting endotherms were observed even at high heating rates. The origins of each endothermal and exothermal peak were discussed in detail. It is suggested that: (i) the crystallization exothermic peak, T_re, relates to the recrystallization of the melt of the crystallites with lower thermal stability; (ii) the T_m1 is ascribed to the melting of crystallites formed through recrystallization; (iii) two crystal populations with different thermal stability are responsible for the T_m2 and T_m3; (iv) the T_m4, which is the annealing peak, represents the transition of the rigid amorphous fraction (RAF) from solid-like RAF into liquid-like amorphous fraction.     

聚苯硫醚/尼龙6共混物界面对结晶行为的影响

高分子作为材料时 ,其力学性能受其结晶形态的影响 ,而其结晶形态与其结晶行为有关 .结晶性聚合物共混物中结晶组分由于第二组分存在 ,改变了结晶组分在熔体时的化学与物理环境 .因此 ,其结晶组分的结晶行为不仅取决于两组分在熔体时的相容性 ,而且与第二组分是否起到异相晶核作用和 /或两组分间界面是否诱导成核作用有关 ,从而影响共混物中结晶组分的结晶行为 ,导致共混物力学性能的改变[1～ 4] .在ＰＰＳ/ＰＡ6共混物中 ,由于ＰＰＳ的熔点和熔体结晶温度都比ＰＡ6的高 ,共混物熔体降温结晶ＰＰＳ是在ＰＡ6熔体存在下发生结晶 ,而ＰＡ6是在…     

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.     

Thermal characterization of polycarbonate/polycaprolactone blends

In this work, we prepared blends of bisphenol A polycarbonate (PC) and poly(ϵ‐caprolactone) (PCL) in a wide composition range by melt mixing and solution mixing. Two different molecular weights of PCL were used (nominally, 10.000 g/mol, PCL10, and 80.000 g/mol, PCL80). The thermal behavior of both systems was studied via differential scanning calorimetry under dynamic and isothermal conditions. The blends were miscible in the entire composition range in the liquid and amorphous states, as indicated by the single glass‐transition temperature (T_g) exhibited by both the PC/PCL10 and PC/PCL80 blends. The compositional variation of the T_g was accurately described by the Fox equation for the PC/PCL80 blends, whereas slight deviations from this equation were exhibited by the PC/PCL10 blends. For blend compositions containing 40% or more PCL, either one or both blend components crystallized. Crystallization occurred during cooling from the melt or during subsequent heating in the form of cold crystallization. Although PCL crystallization was reduced and its crystallization rate decreased with the addition of PC, PCL was a very effective macromolecular plasticizer for PC, to the extent that crystallization during the scan was detected for some blend compositions. Isothermal crystallization experiments allowed the determination of equilibrium melting points (T) by the Hoffman–Weeks extrapolation method. A T depression was found for both PCL and PC components as the content of the other blend component was increased. The Avrami equation was closely obeyed by both blend components during the isothermal overall crystallization kinetics up to crystalline conversion degrees of 60–70% and with values of Avrami indices ranging from 3 to 4, depending on the crystallization temperature employed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 771–785, 2001     

Poly(butylene terephthalate)–polyarylate blends

In this paper we focus on miscible blends of two engineering polymers: poly(butylene terephthalate) (PBT) and a polyarylate (PAr). The issue of transesterification in these blends will be addressed, followed by a discussion of the crystallization kinetics of PBT, poly(ethylene terephthalate) and several PBT/PAr blends. The ability to estimate polymer–polymer interaction parameters in blends from melting point depression will also be discussed. The amorphous phase behavior of the PBT/PAr blends has been explored primarily using dielectric spectroscopy. For blends in which PBT has crystallized, we observe two relaxations associated with T_g-like motion, and this behavior is interpreted in light of our recent work on order–disorder interphases in crystalline blends.     

Miscibility and isothermal crystallization behavior of polyamide 6/poly(vinyl alcohol) blend

An investigation of miscibility and isothermal crystallization behavior of Polyamide 6 (PA6)/Poly(vinyl alcohol) (PVA) blends was conducted. Fourier transform infrared spectra (FTIR) analysis indicated that the interactions between the carbonyl groups of PA6 and hydroxyl groups of PVA increase as the weight ratios of PA6 to PVA of PA6/PVA specimens increase. This interaction between PA6 and PVA leads to their miscibility in the amorphous region and even some extent effects on their crystal phase, respectively. Further isothermal crystallization behavior of PA6/PVA indicate that the miscibility of PVA in PA6 leading difficulty in crystallization of PA6. Several kinetics equations are employed to describe the effects of PVA on the crystallization properties of PA6 in PA6/PVA blends in detail. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1360–1368, 2008     

X-ray scattering and thermal analysis study of the effects of molecular weight on phase structure in blends of poly(butylene terephthalate) with polycarbonate

Blends of Poly(butylene terephthalate), PBT, with Polycarbonate, PC, were studied for a range of molecular weights and blend compositions. Blends were available in PBT/PC compositions 80/20 and 40/60, and with M_w designated by H (high) or L (low). Samples were prepared by melt crystallization, or by cold crystallization following a rapid quench from the melt. Addition of PC reduces the crystallization kinetics of PBT so that the resulting crystals are more perfect than those which form in the homopolymer. Degree of crystallinity of the blends followed the rank ordering: L/L > L/H > H/L = H/H. The glass transition behavior was investigated using dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC). All blends exhibited two glass transitions at intermediate temperatures between the T_gs of the homopolymers, indicating existence of a PBT-rich phase and a PC-rich phase. Blends L/L were most, and H/H the least, miscible. Small-angle X-ray scattering was performed at room temperature on cold crystallized blends, or at elevated temperature during melt crystallization. The long period was consistently larger, and the linear stack crystallinity was consistently smaller, in blends L/L or H/L. These results indicate that in blends containing low M_w PC, there is more PC located within the PBT-rich phase. The long period was consistently smaller in cold crystallized samples, while the linear stack crystallinity was nearly the same, regardless of melt or cold crystallization treatment. Reduction of the average long period in cold crystallized samples could result from crystallization of PBT within the PC-rich phase. This is consistent with thermal analysis results, which indicate that cold crystallized samples have greater overall crystallinity than melt crystallized samples. A hypothetical liquid phase diagram is presented to explain the differences between melt and cold crystallized blends. © 1996 John Wiley & Sons, Inc.     

Miscibility in crystalline/amorphous blends of poly(3-hydroxybutyrate)/DGEBA

A differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) study of miscibility in blends of the semicrystalline polyester poly(3-hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) was performed. Evidence of the miscibility of PHB/DGEBA in the molten state was found from a DSC study of the dependence of glass transition temperature (T_g) as a function of the blend composition and isothermal crystallization, analyzing the melting point (T_m) as a function of blend composition. A negative value of Flory–Huggins interaction parameter χ_PD was obtained. Furthermore, the lamellar crystallinity in the blend was studied by SAXS as a function of the PHB content. Evidence of the segregation of the amorphous material out of the lamellar structure was obtained. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. III. Crystallization and phase diagram by differential scanning calorimetry

The crystallization of poly(vinylidene fluoride) (PVDF)/poly(3‐hydroxybutyrate) (PHB) blends was studied with differential scanning calorimetry, from which the phase diagram was derived. Strong miscibility was underlined by the large negative Flory–Huggins interaction parameter (?0.25). The crystallization of the blend components differed remarkably. Whereas PVDF always crystallized in the surroundings of a homogeneous melt, PHB crystallized in a volume that was confined by the already existing PVDF spherulites, partly in their surroundings and partly inside. Under isothermal conditions, PVDF usually crystallized regularly in three dimensions with predominant quench‐induced athermal nucleation. The Avrami exponent for PVDF dendritic spherulitic growth was, however, distinctly smaller than that for compact growth, and this revealed the two‐dimensional lamellar growth inside. This deviation from ideal Avrami behavior was caused by the development of compositional inhomogeneities as PVDF crystallization proceeded, and this decelerated the kinetics. PHB crystallized three‐dimensionally with mixed thermal and athermal nucleation outside the PVDF spherulites. Inside the PVDF spherulites, PHB crystallization proceeded in a fibrillar fashion with thermal nucleation; the growth front followed the amorphous paths inside the dendritic PVDF spherulites. The crystallization was faster than that in the melt of uncrystallized PVDF. Solid PVDF acts possibly heterogeneously nucleating, accelerating PHB crystallization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 287–295, 2005     

Chemical modification of poly(lactic acid) and its use as matrix in poly(lactic acid) poly(butylene adipate-co-terephthalate) blends

Poly(lactic acid), PLA, was chemically modified with maleic anhydride (MA) by reactive extrusion. The effect of this modification on molar mass (MM) and acidity was assessed by means of size-exclusion chromatography (SEC) and titration, respectively. PLA MM decreased in the presence of MA solely and of MA and peroxide. Reduction in MM was monitored by the increase in acidity. PLA blends containing poly(butylene adipate-co-terephthalate) (PBAT) were prepared through different mixing protocols, PLA/PBAT, PLA-g-MA/PBAT and PLA/PBAT/MA/peroxide (PLA/PBAT in situ). SEC results and rheological properties revealed reduction in MM and viscosity of the modified blends. PLA/PBAT presented increase in MM and bimodal MM distribution. The calculated interfacial tension was significantly lower for the modified blends, despite the lower average particle area of PLA/PBAT. Surprisingly, the modified blends presented higher yield strength than that predicted by the rule of mixtures, which might indicate interfacial reactions.     

Isothermal crystallization kinetics of poly(ethylene terephthalate) in blends with a liquid crystalline polyester (Vectra A)

The isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) in blends with a fully aromatic liquid crystalline copolyester (Vectra A) were studied with differential scanning calorimetry. PET crystallization rates decreases with increasing Vectra fractions in the blends, and the percentage of PET that is crystalline also decreases with increasing Vectra. The equilibrium PET melting temperature for blends containing 40% or more Vectra is unambiguously below that of pure PET. Attenuated total reflectance Fourier-transform infrared spectroscopy measurements indicate that PET/Vectra transesterification does not take place. The results are consistent with a scenario based on prior NMR data in which there is some interphase mixing between the liquid crystalline and flexible polymers and an increase in the fraction of gauche conformers in the PET.     

Crystallization measurements via ultrasonic velocity: Study of poly(lactic acid) parts

Crystallization has significant effects on the physical and mechanical properties of polymer products; therefore, crystallization measurements are important for understanding and predicting polymer products' properties. However, traditional crystallization measurement methods have disadvantages in practical applications because they can be destructive, offline, unsafe, and expensive. Recently, ultrasonic technology has shown great potential as a nondestructive, online, real‐time, and environmentally friendly measurement method for polymer characterization. In this study, a novel measurement method based on ultrasonic technology was proposed to study the crystallization characteristics of poly(lactic acid) (PLA) parts. An annealing process was employed to produce PLA parts with different degrees of crystallinity. A new ultrasonic water immersion method was used to measure the ultrasonic velocities of these annealed PLA parts. It has been found that the plot of the inverse ultrasonic velocity versus the degree of crystallinity shows good linearity over the whole crystallinity range for all three annealing temperatures. The linear relationship between the inverse of the ultrasonic velocity and the crystallinity observed in this study could provide a nondestructive method for investigating the degree of crystallinity of polymers, which can be implemented both offline and online. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 700–708     

Competition of phase dissolution and crystallization in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

Blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile was studied. The PCL/SAN blend having LCST (lower critical solution temperature) phase boundary above the melting point T_m of PCL offered an excellent opportunity to investigate the competition of liquid-solid phase transition (crystallization) and liquid-liquid phase transition (phase dissolution). A blend with the critical composition (80/20 PCL/SAN) underwent a temperature-jump above LCST to proceed spinodal decomposition, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below T_m at which both the crystallization and the phase dissolution could occur. By transmission electron microscopy it was found that during isothermal annealing after quenching to high temperatures close to T_m (e.g. 51 °C), the SD structure gradually disappeared, and then the crystallization started from a single-phase mixture to yield normal crystalline structure similar to that of a neat crystalline polymer. At lower temperatures (e.g. 40 °C), crystallization quickly occurred and the SD structure was preserved, implying that the crystallization prevailed over the dissolution yielding a bi-continuous structure consisting of amorphous (SAN-rich) and crystalline (PCL-rich) regions. At intermediate temperatures (e.g. 45 °C), the phase dissolution competed with the crystallization, resulting in a bi-continuous structure with longer periodic distance and a broad boundary having a gradient in composition of amorphous region between PCL crystal lamellae. Light-scattering analysis quantitatively revealed a competition of the crystallization and the phase dissolution in terms of the crystallization rate (from H_v scattering) and the apparent diffusion coefficient for dissolution (from V_v scattering).     

Crystallization and structure formation in polymer blends with strong intermodular interactions: blends of poly(ethylene oxide) and styrene-hydroxystyrene copolymers

Time-resolved synchrotron wide- and small-angle X-ray scattering experiments were used to investigate crystallization behavior and microstructure development of a nearly monodisperse poly(ethylene oxide) [PEO] (M_w = 53,500), and its melt-miscible blends with two fractionated styrene - hydroxystyrene random copolymers [SHS]. PEO crystallization rates decrease significantly in the presence of the melt-miscible SHS copolymers. All low and high molecular weight SHS blends exhibit a crystallization process at relatively short times characterized by large Avrami exponents (n), followed by a dominant process with n near that of neat PEO. A model for the crystallization of these blends is proposed.     

Study of poly(lactic-co-glycolic acid) interactions with collagen

Poly(lactic-co-glycolic acid) (PLGA) is excellent to fabricate drug delivery systems that prolong the release of recombinant human growth hormone (rhGH), with current research focusing on their possible use for bone regeneration in odontological practice.Herein, we evaluate PLGA interactions with a component of the buccal cavity, as collagen, using monolayers and differential scanning calorimetry (DSC) techniques.Our results indicate that interactions in the PLGA-collagen mixtures showed no phase separation and attraction forces were detected irrespective of the concentration ratio.