Spherulitic growth in block copolymers and blends of miscible crystalline polymers

Spherulitic morphology and growth rate of block copolymers comprised of miscible crystalline constituents, namely poly(ethylene succinate) (PES) and poly(ethylene oxide) (PEO), were investigated. The results of the copolymers were compared with those of the blends with the same composition and molecular weight. Interpenetrating spherulites, where spherulites of one component grow in those of the other component, were observed in the copolymers as in the blends. Copolymerization, namely the connectivity of the PES and PEO blocks, reduced the spherulitic growth rate in the melt for both components. The growth inside the spherulites of the other component was discussed based on the lamellar and fibrillar (or lamella‐stack) structures, which are influenced by the interblock connectivity. Suppression of molecular mobility in the interlamellar regions resulted in the reduced nucleation and growth rate of the component growing in the spherulites of the other constituent. PES of the copolymer showed dendrites around 60 °C or above. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

The competition between crystallization and demixing in polymer blends. IV. Detection of composition inhomogeneities around growing spherulites

In polymer blends of an amorphous and a semicrystalline component, the crystallization kinetics and the resulting morphology are heavily determined by the diffusion ability of the whole chains and by the dwelling site of the amorphous polymer. Depending on the relative rates of spherulite growth and chain diffusion, radial composition profiles around the growing spherulites and a gradual increase of the melt bulk composition can develop. The resulting change in composition, particularly at the crystallization front, causes a corresponding temporal variation of the spherulite growth rate. In the present article, two experimental techniques are introduced to prove the existence and to determine the course of these concentration profiles. They are based on the composition dependences of the spherulite growth rate and the number density of primary nuclei. Their efficiency is demonstrated by measurements on PVDF/PEA blends. The blend composition at the crystal growth front was found to change by absolute 25%, and the width of the profile can amount to up to 70 μm. © 1996 John Wiley & Sons, Inc.     

Cracking in polylactide spherulites

A polylactide of high optical purity was crystallized between 100 and 140 °C, in‐between two glass slides, and its morphology was investigated by polarizing optical microscopy, scanning electron microscopy, and atomic force microscopy, during subsequent heating and cooling cycles between ?15 °C and the crystallization temperature. It was found that dark circular rings show up on cooling on top of the spherulites and represent cracks of about 300 nm in width. This phenomenon is completely reversible, and the heating–cooling curves are centered at about 56 °C, which coincide with the T_g of polylactide. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3308–3315, 2005     

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     

Morphology and crystallization kinetics of dilute binary blends of two monodisperse n‐alkanes with a length ratio of two

The crystallization kinetics and morphologies of dilute binary blends of the monodisperse alkane n‐C₁₂₂H₂₄₆ in n‐C₂₄₆H₄₉₄ and vice versa have been investigated. With a molecular length ratio close to two, this pair of n‐alkanes does not produce permanent cilia when once‐folded C₂₄₆H₄₉₄ molecules cocrystallize with extended chains of C₁₂₂H₂₄₆. In this condition, the supplementary splaying of adjacent dominant lamellae and the consequently more spherulitic textures, which are present in previous blends for which a longer guest molecule gives permanent cilia, are absent, although other features of blend crystallization remain. Specifically, the isothermal radial growth rate is constant for cocrystallizing blends, although less than for their pure hosts, but becomes nonlinear with cellulation when C₁₂₂H₂₄₆ forms a segregated population within extended‐chain C₂₄₆H₄₉₄. Increased nucleation in the blends give smaller scale textures than for the host materials, but the presence of a second component reduces splaying and thereby disfavors spherulitic growth. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2874–2887, 2001     

Crystallization kinetical and morphological peculiarities in binary crystalline/crystalline polymer blends

A survey is presented on the crystallization kinetics and the morphology of miscible crystalline/crystalline polymer blends. There are only few corresponding systems. In them, however, a number of strange kinetic and structural phenomena can be observed: (i) spherulitic crystallization of the components side‐by‐side, (ii) “interpenetrating crystallization,” (iii) “interlocking spherulitic crystallization,” and (iv) “interfilling crystallization.” Cocrystallization is forbidden for crystallographic reasons. The blend partners grow instead in their own lamellar stacks, and mixed lamellar stacks are a seldom and questionable exception. They crystallize also usually stepwise and not simultaneously. Upon step crystallization, the crystallization of the second component is determined by its redistribution with crystallization of the former. Those composition inhomogeneities are an independent issue that arises also with the development of the morphology in crystalline/amorphous blends, and a corresponding survey is yielded, too. The blend poly (vinylidene fluoride)/poly‐β‐hydroxybutyrate is a convenient model system as it can show all of these morphological and kinetic features after suitable thermal treatment. Some of them are demonstrated in the present publication. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1917–1931, 2007     

Crystal orientation switching in spherulites grown from miscible blends of poly(3‐hydroxybutyrate) with cellulose tributyrate

Fully miscible blends over the whole composition range are obtained by melt mixing bacterial poly(3‐hydroxybutyate) (PHB) and tri‐substituted cellulose butyrate [cellulose tributyrate (CTB)]. Blends containing up to 50 wt % CTB are partially crystalline. Isothermal crystallization experiments show formation of PHB spherulites that grow until impingement. Depending on composition, radial growth rate is either constant or it suddenly increases in a very unusual manner leading to peculiar morphologies. In the latter case, in concomitance to the crystal growth acceleration, the sign of birefringence changes and rotation of the PHB unit cell orientation is observed. These results are discussed in terms of the influence of both composition and T_c on the relative crystallization kinetics of the two blend components. A strong effect played by the not yet crystallized CTB component that in the presence of the highly mobile PHB component forms a liquid crystal‐like phase is proposed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Composition distributions within poly(vinylidene fluoride) spherulites as grown in blends with poly(methyl methacrylate)

Upon crystalline solidification of one component in a homogeneously molten polymer blend, composition profiles develop outside (i.e., in the rest melt) and behind (i.e., within the spherulites) the crystal growth front. The present article is devoted to the detailed verification and the interpretation of these distributions and their temporal development inside growing spherulites. To this end, the energy dispersive X‐ray emission (EDX) of suitable elements has been recorded locally resolved in a scanning electron microscope and evaluated correspondingly. The investigations were performed at the melt homogeneous blend of poly(vinylidene fluoride) (PVDF) as crystallizing and poly(methyl methacrylate) (PMMA) as steadily amorphous component. If the spherulites are not volume filling, the mean PMMA content 〈?_PMMA〉 inside the PVDF spherulites is for all blends about 0.2 below the starting composition. ?_PMMA increases however slightly from the center of a spherulite to its border. That increase reflects the PMMA concentration in front of the spherulite surface, which increases likewise with time, and is clearly above the initial composition. There is at the spherulite surface, consequently, a remarkable jump in composition from the spherulite internal to its amorphous surroundings. It may amount up to 0.5. With volume filling spherulites, a slight variation of the composition from the center of a spherulite to its border is observed, too. This proves that also at these conditions composition profiles develop in the spherulite's surroundings. They remain however so weak that they do not inhibit crystallization even in its later stages. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 338–346, 2006     

Phase behavior and structure formation in ternary blends: studies on blends of PVDF/PMMA/PVAC

The phase behavior of ternary blends was analyzed on the basis of the lattice approach. Both compatibilization and incompatibilization effects are predicted to occur depending on the relative magnitudes and the sign of the interaction parameters of the binary subsystems. Thermodynamic, structural and kinetic properties were investigated for a ternary model blend composed of poly(vinylidene fluoride), poly(methyl methacrylate) and poly(vinyl acetate). This particular ternary system is characterized by a specific symmertry with respect to the interactions in the binary subsystems. This symmetry affects both thermodynamic and structural properties. The experimentally determined interaction parameters were used to model the phase diagram on the basis of the lattice model: the theoretical phase diagram was found to be close to the experimental one. The crystallization processes were analyzed both for the binary and the ternary systems on the basis of a modified Turnbull–Fisher equation. The conclusions are that the properties of the ternary systems can be understood to a first approximation on the basis of those of the corresponding binary systems and the symmetry of the interactions.     

Thermal properties and crystalline structure of syndiotactic polystyrene‐based miscible blends

This work examined the effect of the pre‐melting temperature (T_max) on the thermal properties and crystalline structure of four miscible syndiotactic polystyrene (sPS)‐based blends containing 80 wt % sPS. The counterparts for sPS included a high‐molecular‐weight atactic polystyrene [aPS(H)], a medium‐molecular‐weight atactic polystyrene [aPS(M)], a low‐molecular‐weight atactic polystyrene [aPS(L)], and a low‐molecular‐weight poly(styrene‐co‐α‐methyl styrene) [P(S‐co‐αMS)]. According to differential scanning calorimetry measurements, upon nonisothermal melt crystallization, the crystallization of sPS shifted to lower temperatures in the blends, and the shift followed this order of counterpart addition: P(S‐co‐αMS) > aPS(L) > aPS(M) > aPS(H). The change in T_max (from 285 to 315 °C) influenced the crystallization of sPS in the blends to different degrees, depending on the counterpart's molecular weight and cooling rate. The change in T_max also affected the complex melting behaviors of pure sPS and an sPS/aPS(H) blend, but it affected those of the other blends to a lesser extent. Microscopy investigations demonstrated that changing T_max slightly affected the blends' crystalline morphology, but it apparently altered that of pure sPS. Furthermore, the X‐ray diffraction results revealed that the α‐form sPS crystal content in the blends generally decreased with an increase in T_max, and it decreased with a decrease in the cooling rate as well. The blends showed a lower α‐form content than pure sPS; a counterpart of a lower molecular weight more effectively reduced the formation of α‐form crystals. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2798–2810, 2006     

Miscibility of crystalline and amorphous polymers: Poly-ethylene/polyisobutylene blends

Blends were prepared from a linear low density polyethylene and a polyisobutylene in the entire composition range. Flory-Huggins interaction parameters were determined from DMTA and DSC measurements. The usual technique had to be modified in the case of DSC data, since the T_g of PE cannot be determined by this technique. The two methods yielded identical results and indicated good interaction of the components, which was supported also by a SEM study and the mechanical properties of the blends.     

Morphological development of melt crystallized poly(propylene oxide) by in situ AFM: formation of banded spherulites

The morphology of poly(propylene oxide) (PPO) crystals grown from the melt was investigated. The spherulites of the optically pure S polymers displayed a regular pattern of concentric rings as observed by polarizing optical microscopy, while the stereocopolymer developed irregularly banded, or non-banded spherulites depending on the degree of undercooling. The organization of the lamellar crystals within the spherulites was examined by means of atomic force microscopy (AFM). For all cases, the lamellar structures appeared to adopt an alternating flat or edge-on orientation. Examination of the morphology of single crystals in the melt of the stereocopolymer revealed truncated-lozenge crystals, which were elongated in shape. Results from crystallization kinetics, obtained by in situ AFM observations, showed that the elongated habit is related to differences in the growth rates of the {2 0 0} and {1 1 0} facets. Interestingly, the melt-grown RS-PPO crystals developed a curved asymmetrical three-dimensional shape. Based on these observations it can be proposed that the chiral nature of the chain is transmitted to higher structural levels of ordering in the crystal aggregates.     

Miscibility level and mechanical characterization of blends of two liquid‐crystalline polymers based on p‐hydroxybenzoic acid

Injection‐molded blends composed of two liquid‐crystalline polymers (LCPs) based on 60/40 p‐hydroxybenzoic acid/ethylene terephthalate (R3) and 73/27 p‐hydroxybenzoic acid/2,6‐hydroxynaphthoic acid (VA) copolymers, respectively, were obtained across the whole composition range. The two amorphous phases of the blends contained only slight amounts of the minority component, and the occurrence of some chemical reaction, mainly at high VA contents, was detected by Fourier transform infrared. Synergisms in the modulus of elasticity and in the tensile strength were seen in most of the blend compositions. The largest synergism was in the 50/50 R3/VA blend, which showed a modulus of elasticity 26% higher than that of either of the two components and a 17% positive deviation in the tensile strength with respect to the rule of mixtures. The different orientation of the LCPs in the blends explains the differences in the mechanical behavior. However, contrary to previous works on LCP blends and despite the almost complete immiscibility, the observed negative volume of mixing appears to be the main parameter that determines the synergistic mechanical behavior. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1022–1032, 2003     

Morphology of Nylon-6 blends with styrenic polymers

The morphology of blends of styrenic polymers in a matrix of 75% Nylon-6 prepared in a Brabender Plasti-Corder was examined by scanning electron microscopy. Styrene/acrylonitrile copolymers (SAN) form smaller particles as the AN level increases owing to the corresponding decrease in the SAN–polyamide interfacial tension. Various styrenic polymers containing functional groups, maleic anhydride or oxazoline type, that can react with Nylon-6 during melt processing were added to the SAN phase which also led to a decrease in the particle size owing to the graft copolymer formed in situ. The effects of functional group type, amount of functional groups per chain, amount of functional polymer added, and the miscibility of the styrene/maleic anhydride (SMA) and SAN copolymers on the morphology of the styrenic phase in the Nylon-6 matrix are described. © 1992 John Wiley & Sons, Inc.     

Non-isothermal crystallization and crystalline structure Of PP/POE blends

Polypropylene (PP) /ethylene-octene copolymer (POE) blends with different content of POE were prepared by mixing chamber of a Haake torque rheometer. The crystallization behaviors and crystal structure of PP/POE blends were systematically investigated by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). The results showed that PP spherulites became defective and the crystallization behavior was influenced intensely with the introduction of POE. At the low content of POE, the addition of POE decreases the apparent incubation period (Δt _i) and the apparent total crystallization period (Δt _c) of PP in blends due to the heterogeneous nucleation of POE, and small amount of β-form PP crystals form because of the existence of POE. However, at high content of POE, the addition of POE decreases the mobility of PP segments due to their strong intermolecular interaction and chain entanglements, resulting in retarding the crystallization of PP, decreasing in the amount of β-form PP crystals, and increasing in Δt _i and Δt _c of PP in blends.     

Miscibility and crystallization behavior of solution-blended PEEK/PI blends

Miscibility and crystallization behavior of solution-blended poly(ether ether ketone)/polyimide (PEEK/PI) blends were investigated by using DSC, optical microscopy and SAXS methods. Two kinds of PIs, YS-30 and PEI-E, which consist of the same diamine but different dianhydrides, were used in this work. The experimental results show that blends of PEEK/YS-30 are miscible over the entire composition range, as all the blends of different compositions exhibit a single glass transition temperature. The crystallization of PEEK was hindered by YS-30 in PEEK/YS-30 blends, of which the dominant morphology is interlamellar. On the other hand, blends of PEEK/PEI-E are immiscible, and the effect of PEI-E on the crystallization behavior of PEEK is weak. The crystallinity of PEEK in the isothermally crystallized PEEK/YS-30 blend specimens decreases with the increase in PI content. But the crystallinity of PEEK in the annealed samples almost keeps unchanged and reaches its maximum value, which is more than 50%. The spherulitic texture of the blends depends on both the blend composition and the molecular structure of the PIs used. The more PI added, the more imperfect the crystalline structure of PEEK. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2267–2274, 1998     

Formation of new banded spherulites in polyimides

The crystalline morphology and structural development of aromatic polyimides during an optimum continuous thermal imidization procedure were examined by means of polarized optical microscopy and X‐ray diffraction. During thermal imidization, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimide samples formed complicated spherulites, which, in addition to zigzag Maltese crosses, also showed concentric extinction rings, which are characteristic of banded spherulites. The factors affecting the formation of banded spherulites were studied. The initial imidization conditions dramatically affected the formation of the banded spherulite morphology: slow heating (0.5 °C/min) or fast heating (20 °C/min) led to relatively small polyimide spherulites and less identifiable extinction rings. The morphological features were also affected by the molecular weight of the polyimide: higher molecular weight samples showed typical banded spherulites, whereas low‐molecular‐weight samples formed degenerated banded spherulites. In all the spherulites formed in 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride/1,3‐diaminobenzene polyimides, special zigzag Maltese crosses, instead of normal Maltese crosses, were observed. The relationship between the imidization procedure and the spherulite morphology formation was also studied. X‐ray and Fourier transform infrared together revealed that after several minutes of thermal treatment, the crystallization was nearly complete, with a 42.5% degree of crystallinity; meanwhile, only some poly(amic acid) converted to the corresponding polyimide, with a 27% degree of imidization. The crystalline morphology and structure formed in the initial stage of the imidization process were maintained during the following imidization processing at an elevated temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1997–2004, 2005     

Morphology and crystallization of blends of linear low density polyethylene with a semiflexible liquid crystalline polymer

The morphology and the crystallization behavior of blends of linear low density polyethylene (LLDPE) with an experimental sample of a semiflexible liquid crystalline polymer (SBH 112 by Eniricerche, Italy) have been studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The blends possess a two-phase morphology, due to immiscibility of the two components. SEM observations show that dispersion of the minor SBH phase is favored at low (相似文献   

Effect of crystallization temperature on the crystalline phase content and morphology of poly(vinylidene fluoride)

The effect of temperature on the crystallization of α, β, and γ phases of PVDF from dimethylacetamide (DMA) solution was studied. Variation in the crystallinity content of these three phases was obtained as a function of temperature using infrared spectroscopy, differential scanning calorimetry (DSC) and x-ray diffraction techniques. Such variation is related to the dependence of the crystallization rate of each phase with temperature, and allowed a better understanding of some results found in the literature about the crystallization and interconversion of these phases. Micrographs of samples present morphologies that corroborate with the proposed explanations. © 1994 John Wiley & Sons, Inc.     

Effect of dispersed phase composition on morphological and mechanical properties of PET/EVA/PP ternary blends

Immiscible ternary blends of PET/EVA/PP (PET as the matrix and (PP/EVA) composition ratio = 1/1) were prepared by melt mixing. Scanning electron microscope results showed core‐shell type morphology for this ternary blend. Binary blends of PET/PP and PET/EVA were also prepared as control samples. Two grades of EVA with various viscosities, one higher and the other one lower than that of PP, were used to investigate the effect of components' viscosity on the droplet size of disperse phase. The effect of interfacial tension, elasticity, and viscosity on the disperse phase size of both binary and ternary blends was investigated. Variation of tensile modulus of both binary and ternary blends with dispersed phase content was also studied. Experimental results obtained for modulus of PET/EVA binary blends, showed no significant deviations from Takayanagi model, where considerable deviations were observed for PET/PP binary blends. Here, this model that has been originally proposed for binary blends was improved to become applicable for the prediction of the tensile modulus of ternary blends. The new modified model showed good agreement with the experimental data obtained in this study. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 251–259, 2010