Correlation between crystallization kinetics and melt phase behavior of crystalline-amorphous block copolymer/homopolymer blends

We show that the phase behavior of the strongly segregated blend consisting of a crystalline-amorphous diblock copolymer (C-b-A) and an amorphous homopolymer (h-A), which depends on the degree of wetting of A blocks by h-A, can be probed by the crystallization kinetics of the C block. A lamellae-forming poly(ethylene oxide)-block-polybutadiene (PEO-b-PB) was blended with PB homopolymers (h-PB) of different molecular weights to yield the blends exhibiting ‘wet brush’, ‘partially dry brush’, and ‘dry brush’ phase behavior in the melt state. The crystallization rate of the PEO blocks upon subsequent cooling, as manifested by the freezing (crystallization) temperature (T_f), was highly sensitive to the morphology and spatial connectivity of the microdomains governed by the degree of wetting of PB blocks. As the weight fraction of h-PB reached 0.48, for instance, T_f experienced an abrupt rise as the system entered from the wet-brush to the dry-brush regime, because the crystallization in the PEO cylindrical domains in the former required very large undercooling due to a homogeneous nucleation-controlled mechanism while the process could occur at the normal undercooling in the latter since PEO domains retained lamellar identity with extended spatial connectivity. Our results demonstrate that as long as the C block is present as the minor constituent the melt phase behavior of C-b-A/h-A blends can also be probed using a simple cooling experiment operated under differential scanning calorimetry (DSC).     

Glass transition behavior of polypropylene/polystyrene/styrene-ethylene-propylene block copolymer blends

Summary The glass transition behavior of ternary blends of polypropylene (PP), polystyrene (PS) and styrene-ethylene-propylene-styrene block copolymer (SEPS) was investigated. The blends were prepared by an internal mixer, and their dynamic mechanical properties and morphology were measured. The blends showed phase inversion at around 75wt% PS composition. The glass transition temperature (T_g) of the PP phase shifted to lower temperature as the PS contents were increased in PP/PS binary blends, probably due to the mismatch of thermal expansion coefficients between two components. As the SEPS copolymer contents were increased, the T_g's of the PP phase in the blends increased. In particular, the large increase in T_g of the PP phase was observed in the PP/PS (25/75) blends where the phase inversion takes place. Received: 2 February 1998/Revised version: 24 March 1998/Accepted: 13 April 1998     

Crystallization and coalescence of block copolymer micelles in semicrystalline block copolymer/amorphous homopolymer blends

Crystallization of two oxyethylene/oxybutylene block copolymers (E₇₆B₃₈ and E₁₅₅B₇₆) from micelles in block copolymer/amorphous homopolymer blends was studied by differential scanning calorimetry (DSC) and time-resolved small angle X-ray scattering (SAXS). Unlike the simultaneous crystallization and formation of superstructure in crystallization from an ordered structure, crystallization of block copolymer from micelles can be divided into two steps. The core of the micelles firstly crystallizes individually, with first-order crystallization kinetics and homogeneous nucleation mechanism. The SAXS revealed that crystallization-induced deformation occurs for the micelles, which strongly depends on microstructure of the block copolymers. For the shorter block copolymer E₇₆B₃₈, larger deformation induced by crystallization was observed, leading to coalescence of the micelles after crystallization, while for the longer block copolymer E₁₅₅B₇₆ the micelles show little deformation and the morphology of micelle is retained after crystallization.     

Crystallization behavior of polypropylene/ethylene butene copolymer blends

One polypropylene (PP) was mixed with two ethylene butene copolymers (EBM). EBM1 had 12.5 mol % of butene and was immiscible with the PP. EBM2 had 51.6 mol % of butene and was miscible with the PP. The dispersed PP in EBM1 showed fractionalized crystallization behavior with a crystallization temperature at around 45°C and a much slower isothermal crystallization rate comparing to the neat PP. The PP did not exhibit fractionalized crystallization behavior in EBM2. EBM1 did not decrease both the crystallization and melting temperatures of the continuous PP. However, EBM2 could decrease both the two temperatures. It was found that EBM2 could largely suppress the epitaxial lamellar branching of the PP. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Temperature-composition phase diagrams of binary blends of block copolymer and homopolymer

The temperature-composition phase diagrams for six pairs of diblock copolymer and homopolymer are presented, putting emphasis on the effects of block copolymer composition and the molecular weight of added homopolymers. For the study, two polystyrene-block-polyisoprene (SI diblock) copolymers having lamellar or spherical microdomains, a polystyrene-block-polybutadiene (SB diblock) copolymer having lamellar microdomains, and a series of polystyrene (PS), polyisoprene (PI), and polybutadiene (PB) were used to prepare SI/PS, SI/PI, SB/PS, and SB/PB binary blends, via solvent casting, over a wide range of compositions. The shape of temperature-composition phase diagram of block copolymer/homopolymer blend is greatly affected by a small change in the ratio of the molecular weight of added homopolymer to the molecular weight of corresponding block (M_H,A/M_C,A or M_H,B/M_C,B) when the block copolymer is highly asymmetric in composition but only moderately even for a large change in M_H,A/M_C,A ratio when the block copolymer is symmetric or nearly symmetric in composition. The boundary between the mesophase (M₁) of block copolymer and the homogeneous phase (H) of block copolymer/homopolymer blend was determined using oscillatory shear rheometry, and the boundary between the homogeneous phase (H) and two-phase liquid mixture (L₁+L₂) with L₁ being disordered block copolymer and L₂ being macrophase-separated homopolymer was determined using cloud point measurement. It is found that the addition of PI to a lamella-forming SI diblock copolymer or the addition of PB to a lamella-forming SB diblock copolymer gives rise to disordered micelles (DM) having no long-range order, while the addition of PS to a lamella-forming SB diblock copolymer retains lamellar microdomain structure until microdomains disappear completely. Thus, the phase diagram of SI/PI or SB/PB blends looks more complicated than that of SI/PS or SB/PS blends.     

Melting,nonisothermal crystallization behavior and morphology of polypropylene/random ethylene—propylene copolymer blends

The melting, nonisothermal crystallization behavior and morphology of blends of polypropylene (PP) with random ethylene–propylene copolymer (PP‐R) were studied by differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy, and X‐ray diffraction. The results showed that PP and PP‐R were very miscible and cocrystallizable. Modified Avrami analysis was used to analyze the nonisothermal crystallization kinetics of the blends. The values of the Avrami exponent indicated that the crystallization nucleation of the blends was heterogeneous, the growth of the spherulites was tridimensional, and the crystallization mechanism of PP was not affected by PP‐R. The crystallization activation energy was estimated using the Kissinger method. An interesting result was obtained with the modified Avrami analysis and the Kissinger method, whose conclusions were in good agreement. The addition of a minor PP‐R phase favored an increase in the overall crystallization rate of PP. Maximum enhancing effect wass found to occur with a PP‐R content of 20 wt %. The relationship between the composition and the morphology of the blends is discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 670–678, 2006     

Effect of various added compatibilizers on the crystalline structure of polypropylene homopolymer/polybutylene terephthalate and polypropylene copolymer/polybutylene terephthalate polymer blends

Blends of semicrystalline isotactic polypropylene homopolymer and polypropylene copolymer with polybutylene terephthalate with different compatibilizers [i.e., styrene acrylonitrile, Surlyn, styrene–ethylene–butadiene styrene (SEBS), block copolymer and SEBS block copolymer grafted with maleic anhydride] were prepared by melt blending. Wide angle‐X‐ray scattering patterns of injection moldings were obtained. The crystallinity index and d‐spacing were calculated with different concentrations of different compatibilizers. X‐ray results in the structural investigation of the compatibilized blends correlated well with the different compatibilizer concentrations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1190–1193, 2003     

Crystallization of double crystalline block copolymer/crystalline homopolymer blends: 1. Crystalline morphology

The crystalline morphology formed in binary blends of poly(ε-caprolactone)- block-polyethylene (PCL-b-PE) copolymers and PCL homopolymers has been examined using synchrotron small-angle X-ray scattering (SR-SAXS) and differential scanning calorimetry (DSC) as a function of the homopolymer fraction in the blend. The PE block crystallized first on quenching from a lamellar microdomain structure to set a hard lamellar morphology (PE lamellar morphology) in the blend, followed by the crystallization of PCL chains (i.e., PCL homopolymers + PCL blocks). Two binary blends were studied by considering the miscible state of PCL homopolymers in the microdomain structure: when the PCL homopolymers were uniformly mixed with PCL blocks, they formed a mixed crystal. When the PCL homopolymers were localized between PCL blocks in the microdomain structure, DSC results suggested the possible formation of separate PCL crystals in the PE lamellar morphology. The effect of the advance crystallization of PE blocks on the subsequent crystallization of PCL chains was discussed as compared with the crystalline morphology formed in PCL-block-polybutadiene copolymer/PCL homopolymer blends, where the crystallization of PCL chains started directly from a microdomain structure without forming the hard lamellar morphology.     

Baroplastic behavior of miscible block copolymer blends

Pressure dependence of various phase transitions for the miscible block copolymer (BCP) blends was evaluated by depolarized light scattering (DPLS) and small-angle neutron scattering (SANS) measurements, in which the blends consist of a polystyrene-b-poly(n-butyl methacrylate) (PS-b-PnBMA) and a deuterated polystyrene-b-poly(n-hexyl methacrylate) (dPS-b-PnHMA). Excellent baroplasticity was observed in nearly symmetric blends of PS-b-PnBMA/dPS-b-PnHMA, leading to the most outstanding pressure coefficients, |dT/dP|, in a closed-loop type phase behavior between a lower disorder-to-order transition (LDOT) and an order-to-disorder transition (ODT) type phase behavior. Together with the estimated pressure coefficients based on the values of enthalpic and volumetric changes at phase transitions, we demonstrate that the entropic compressibility for the miscible BCP blends is a baroplastic indicator, which was characterized by the negative volume change on mixing (ΔV_mix) at transitions.     

Effects of vibration blending on the subsequent crystallization behavior of polycarbonate/polypropylene blends

The effects of blending in a novel vibration internal mixer on the subsequent multiple crystallization of 70/30 w/w polycarbonate (PC)/polypropylene (PP) were investigated by differential scanning calorimetry, wide‐angle X‐ray diffractogram, and microscopy. The vibration internal mixer was reformed from a conventional internal mixer through parallel superposition of an oscillatory shear on a steady shear. For this polypropylene‐minor phase blend, three possible crystallization peaks were observed. The crystallization behavior was sensitive to the sizes and the size distribution of the dispersed polypropylene droplets. Larger amplitude and/or higher‐frequency vibration produced more small droplets (<2 μm) and increased the number of medium droplets (2–8 μm) as a result of the spatially wider and temporally quicker variation of shear rate. The resulting subsequent low‐temperature crystallization peak became larger and shifted to lower temperature, and the intermediate‐temperature peak became obvious. On the contrary, the coalescence of small droplets, resulting from the heating treatment, weakened the low‐temperature peak but strengthened the intermediate‐temperature peak and rendered the high‐temperature peak to be wider. Mixing at the too high amplitude produced the unstable, partially cocontinuous phase morphology restricting the medium droplets and enlarging the surface area, such that the intermediate‐temperature crystallization peak did not appear. Multiple crystallization was related to phase morphology and the nucleation density as well as surface effects. Double‐fusion endotherms of the PP component were also observed, corresponding to the melting of different forms of polypropylene crystals. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 92–103, 2002     

Compatibilization of polypropylene/polystyrene blends with poly(styrene-b-butadiene-b-styrene) block copolymer

The compatibilizing effect of the triblock copolymer poly(styrene-b-butadiene-b-styrene) (SBS) on the morphology and mechanical properties of immiscible polypropylene/polystyrene (PP/PS) blends were studied. Blends with three different weight ratios of PP and PS were prepared and three different concentrations of SBS were used for investigations of its compatibilizing effects. Scanning electron microscopy (SEM) showed that SBS reduced the diameter of the PS-dispersed particles as well as improved the adhesion between the matrix and the dispersed phase. Transmission electron microscopy (TEM) revealed that in the PP matrix dispersed particles were complex “honeycomblike” aggregates of PS particles enveloped and joined together with the SBS compatibilizer. Wide-angle X-ray diffraction (WAXD) analysis showed that the degree of crystallinity of PP/PS/SBS slightly exceeded the values given by the addition rule. At the same time, addition of SBS to pure PP and to PP/PS blends changed the orientation parameters A₁₁₀ and C significantly, indicating an obvious SBS influence on the crystallization process in the PP matrix. SBS interactions with PP and PS influenced the mechanical properties of the compatibilized PP/PS/SBS blends. Addition of SBS decreased the yield stress and the Young's modulus and improved the elongation at yield as well as the notched impact strength in comparison to the binary PP/PS blends. Some theoretical models for the determination of the Young's modulus of binary PP/PS blends were used for comparison with the experimental results. The experimental line was closest to the series model line. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2625–2639, 1998     

Ductile tear behavior of multilayered polypropylene homopolymer/ethylene 1‐octene copolymer sheets

The tear resistance of the polypropylene homopolymer (HPP)/ethylene 1‐octene copolymer (POE) alternating multilayered sheets, which were prepared through multilayered coextrusion, was evaluated. Polarized optical microscope (POM) photographs revealed that HPP and POE layers aligned alternately vertical to the interfaces and continuously parallel to the extrusion direction. Tear results demonstrated the conventional blends had less tear‐resistant than the multilayered samples. Large plastic deformation of HPP layer occurred in the multilayered structure during the stable crack growth, causing the tear energy to increase with the number of layers increasing. The measurements of PCMW2D IR and WAXD revealed that the large plastic deformation had a direct relationship with the crystal structure and termination of micro‐cracks by interface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43298.     

氯化聚乙烯橡胶改性聚丙烯的非等温结晶行为研究

用示差扫描量热仪(DSC)对氯化聚乙烯橡胶(CM)改性聚丙烯(PP)的非等温结晶行为进行了研究。结果表明,随着降温速度上升,样品结晶温度下降,结晶速度上升。在以15k/min与20k/min速度降温时,发现两者的结晶行为相一致。采用TCHC交联剂的1#样品的结晶温度与速度都大于采用DCP交联剂的2#样品,前者的硫化效率低,对结晶影响小。本文又通过求解非等温结晶动力学参数与结晶活化能,进一步解释了1#与2#样品的结晶行为。     

Viscoelastic and elastic behavior of polypropylene and ethylene copolymer blends

Thermorheological properties of an incompatible polymer blend of polypropylene inclusions dispersed in a ethylene copolymer matrix were discussed from the emulsion model developed by Palierne. Due to the different rheological behaviors with temperature of the two phases, such a system proved to be a judicious blend in order to consider the special cases of the model applications: (1) the two phases are viscoelastic liquids, (2) the dispersed phase is a solid elastic assimilated to rigid spheres in comparison with viscoelastic liquid behavior of the matrix, and (3) the two phases are elastic solids. At low frequencies, the rheological behavior of the blend was not correctly predicted by the model. So interactions other than hydrodynamics can exist in the intrafacial region, and physical entanglements between the chains of the two constituents leading to topological interactions may be assumed at the interphase. © 1995 John Wiley & Sons, Inc.     

Performance of talc/ethylene-octene copolymer/polypropylene blends

Polypropylene-based compounds are increasingly attractive because of low cost, processability, and good balance of properties. In recent years, metallocene ethylene-octene copolymers have started displacing EPR and EPDM as an impact modifier for PP. This study examines the effect of compounding conditions and composition on the properties of talc/ethylene-octene copolymer/PP compounds. The mechanical properties of the compounds were not significantly affected by the mixing conditions on a laboratory twin screw extruder. The use of 30 wt% of talc provided a twofold increase in tensile modulus compared with pure PP. Impact resistance of filled and unfilled compounds was found to increase rapidly once the copolymer concentration reached around 20 wt% based on the polymer phase. Modulus and tensile strength decreased linearly with copolymer concentration. Four different commercial maleic anhydride-grafted PPs were tested as interfacial modifiers. In the best cases, a slight tensile strength increase was observed when using between 2 and 10 wt% of modified PP.     

Studies on simultaneous crystallization of polypropylene/nylon 12 blends

The effect of the morphology of polypropylene (PP)/nylon 12 (PA12) blends on their crystallization behaviour is studied using differential scanning calorimetry and scanning electron microscopy. In PP/ maleated polypropylene (PP-MA)/PA12=65/10/25 blend, simultaneous phase (PA12) is smaller than 0.5 μm, PP crystallizes first and its crystals induce the crystallization of PA12. When some of the PA12 particles are larger than 0.5 μm, this part of PA12 crystallizes first. Then this part of the PA12 crystals induces the crystallization of PP, and PP crystals induced the crystallization of PA12 fine droplets in turn.     

Studies on miscibility in homopolymer/ random copolymer blends by equation of state theory

The miscibility of poly(methyl methacrylate) (PMMA) and styrene-acrylonitrile random copolymers (SAN) blends was investigated on the basis of the Flory—Orwoll—Vrij equation of state theory. To obtain the equation of state parameters (P*, V*_sp, T*: characteristic parameters), the pressure—volume—temperature (PVT) behaviour was measured for PMMA and a series of SANs with various acrylonitrile contents. The exchange energy parameter X_ij was also calculated by fitting the theory to some phase diagrams of PMMA/SAN blends. The Flory—Huggins interaction parameter χ was separated into two contributions based on the equation of state theory for mixtures: the exchange energy term χ_inter and the free volume term χ_free. Both the temperature and copolymer composition dependences of χ_inter and χ_free were estimated by calculations using the equation of state parameters. There exists a region in which χ_inter is negative, leading to a miscibility window in PMMA/SAN blends. However, the immiscibility at high temperatures in the blends cannot be explained only by χ_inter; it is caused by the free volume contribution, χ_free. The miscibility window behaviour in PMMA/SAN blends may be explained within the framework of the equation of state theory.     

Isothermal crystallization behavior and properties of polypropylene/EPR blends nucleated with sodium benzoate

The effect of sodium benzoate on the isothermal crystallization behavior of isotactic polypropylene (iPP)/ethylene–propylene rubber(EPR) blends was investigated using differential scanning calorimetry. Dynamic mechanical and physical properties of the iPP/EPR blends nucleated with sodium benzoate were also measured. It was found that the crystallization behavior and physical properties such as heat deflection temperature (HDT), flexural modulus, and impact strength were strongly affected by the competition between the nucleating effect of EPR attributed to its partial compatibility with iPP and the simple addition of the amorphous component, as well as the nucleating effect of sodium benzoate. High impact strength was achieved by addition of EPR and sodium benzoate to iPP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 201–211, 2002