Phase morphology of iPP/aPS/SEP blends

Supermolecular structure and phase morphology of the ternary isotactic polypropylene/atactic polystyrene/poly(styrene-b-ethylene-co-propylene) (iPP/aPS/SEP) compression molded blends with 100/0, 90/10, 70/30, and 50/50 iPP/aPS weight ratios and with different amounts of added SEP compatibilizer were studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). SEP significantly reduced the size of dispersed aPS particles that enabled better spherulitization in the iPP matrix. Furthermore, iPP spherulites in ternary blends with 90/10 iPP/aPS weight ratio became larger in comparison with the pure iPP. TEM revealed that the SEP formed continuous interface layer around the dispersed aPS particles even when only 2.5 wt.% of SEP was added. Particle size distribution was distinctly bimodal. When the SEP content was increased to 10 wt.%, joining together smaller and bigger aPS and SEP particles formed dispersed aggregates. Additionally, both amorphous components (aPS and SEP) influenced crystallization process of iPP matrix and so modified, to some extent, its final supermolecular structure. SEP compatibilizer did not significantly affect crystallite orientation. The increase of crystallite sizes, which was more affected by the addition of aPS than by the addition of SEP, seemed to be influenced by the solidification effect rather than by the phase morphology of the blends.     

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) and poly(aryl ether ether ketone)

Rhythmic growth of ring‐banded spherulites in blends of liquid crystalline methoxy‐poly(aryl ether ketone) (M‐PAEK) and poly(aryl ether ether ketone) (PEEK) has been investigated by means of differential scanning calorimetry (DSC), polarized light microscopy (PLM), and scanning electron microscopy (SEM) techniques. The measurements reveal that the formation of the rhythmically grown ring‐banded spherulites in the M‐PAEK/PEEK blends is strongly dependent on the blend composition. In the M‐PAEK‐rich blends, upon cooling, an unusual ring‐banded spherulite is formed, which is ascribed to structural discontinuity caused by a rhythmic radial growth. For the 50:50 M‐PAEK/PEEK blend, ring‐banded spherulites and individual PEEK spherulites coexist in the system. In the blends with PEEK as the predominant component, M‐PAEK is rejected into the boundary of PEEK spherulites. The cooling rate and crystallization temperature have great effect on the phase behavior, especially the ring‐banded spherulite formation in the blends. In addition, the effects of M‐PAEK phase transition rate and phase separation rate on banded spherulite formation is discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3011–3024, 2007     

Mechanical properties and characterization of slowly cooled isotactic polypropylene/high‐density polyethylene blends

In previous studies, we found that Young's moduli of quenched isotactic polypropylene/high‐density polyethylene (iPP/HDPE) exceeded the upper bound, calculated from the Voigt model, with the moduli of the quenched homopolymers as those of the two components. We suggested that this might be due to crystallization, as the components crystallized at higher temperatures in the blend than on their own. We repeated the same set of measurements, this time on iPP/HDPE blends that were cooled slowly. We also examined crystallization at various rates of cooling with differential scanning calorimetry. At slow cooling rates, the HDPE and iPP components in the blends crystallize at lower temperatures than in the pure homopolymers, suggesting that the presence of one component inhibits rather than promotes the crystallization of the other. Electron microscopy of slowly cooled blends revealed very different interfacial morphologies depending on whether the HDPE or the iPP crystallizes first. Young's moduli of most of the blends lie on the upper bound; however, some blends with co‐continuous morphologies fall well below the lower bound. The mechanical properties are discussed in terms of the interfacial morphology, the crystallization behavior, and the large‐scale phase separation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1384–1392, 2003     

Morphology and nonisothermal crystallization of in situ microfibrillar poly(ethylene terephthalate)/polypropylene blend fabricated through slit‐extrusion,hot‐stretch quenching

This study describes the morphology and nonisothermal crystallization kinetics of poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) in situ micro‐fiber‐reinforced blends (MRB) obtained via slit‐extrusion, hot‐stretching quenching. For comparison purposes, neat PP and PET/PP common blends are also included. Morphological observation indicated that the well‐defined microfibers are in situ generated by the slit‐extrusion, hot‐stretching quenching process. Neat iPP and PET/iPP common blends showed the normal spherulite morphology, whereas the PET/iPP microfibrillar blend had typical transcrystallites at 1 wt % PET concentration. The nonisothermal crystallization kinetics of three samples were investigated with differential scanning calorimetry (DSC). Applying the theories proposed by Jeziorny, Ozawa, and Liu to analyze the crystallization kinetics of neat PP and PET/PP common and microfibrillar blends, agreement was found between our experimental results and Liu's prediction. The increases of crystallization temperature and crystallization rate during the nonisothermal crystallization process indicated that PET in situ microfibers have significant nucleation ability for the crystallization of a PP matrix phase. The crystallization peaks in the DSC curves of the three materials examined widened and shifted to lower temperature when the cooling rate was increased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 374–385, 2004     

Structure,morphology, and crystallization process of isotactic polypropylene/hydrogenated hydrocarbon resin blends

The structure, morphology, and isothermal and nonisothermal crystallization of isotactic polypropylene/low‐molecular‐mass hydrocarbon resin blends (iPP/HR) (up to 20% in weight of HR) have been studied, using optical and electron microscopy, wide‐ and small‐angle X‐ray and differential scanning calorimetry. New structures and morphologies can be activated, using appropriate preparation and crystallization conditions and blend composition. For every composition and crystallization condition, iPP crystallizes in α‐form, with a spherulitic morphology. The size of iPP spherulites increases with resin content, whereas the long period decreases. In the range of crystallization temperatures investigated, HR modifies the birefringence of iPP spherulites, favoring the formation of radial lamellae and changing the ratio between tangential and radial lamellae. Spherulitic radial growth rates, overall crystallization rates, and melting temperatures are strongly affected by resin, monotonically decreasing with resin content. This confirms miscibility in the melt between the two components of the blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3368–3379, 2004     

Semicrystalline blends of polyethylene and isotactic polypropylene: Improving mechanical performance by enhancing the interfacial structure

The low‐temperature mechanical behavior of semicrystalline polymer blends is investigated. Isotactic polypropylene (iPP) is blended with both Zeigler–Natta polyethylene (PE) and metallocene PE. Transmission electron microscopy (TEM) on failed tensile bars reveals that the predominate failure mode in the Zeigler–Natta blend is interfacial, while that in the metallocene blend is failure of the iPP matrix. The observed change in failure mode is accompanied by a 40% increase in both tensile toughness and elongation at −10 °C. We argue that crystallite anchoring of interfacially entangled chains is responsible for this dramatic property improvement in the metallocene blend. The interfacial width between PE and iPP melts is approximately 40 Å, allowing significant interfacial entanglement in both blends. TEM micrographs illustrate that the segregation of low molecular weight amorphous material in the Zeigler–Natta blend reduces the number and quality of crystallite anchors as compared with the metallocene blend. The contribution of anchored interfacial structure was further explored by introducing a block copolymer at the PE/iPP interface in the metallocene blend. Small‐angle X‐ray scattering (SAXS) experiments show the block copolymer dilutes the number of crystalline anchors, decoupling the interface. Increasing the interfacial coverage of the block copolymer reduces the number of anchored interfacial chains. At 2% block copolymer loading, the low‐temperature failure mode of the metallocene blend changes from iPP failure to interfacial failure, reducing the blend toughness and elongation to that of the Zeigler–Natta blend. This work demonstrates that anchored interfacial entanglements are a critical factor in designing semicrystalline blends with improved low‐temperature properties. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 108–121, 2000     

Miscibility enhancement and formation of interpenetrating spherulites in ternary blends of crystalline polymers

Miscible blends of three crystalline polymers, namely poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), and poly(oxyethylene) (POE), exhibited interpenetrating spherulites, where a spherulite of one component grows inside the spherulites of other components. PBS and PES were immiscible above the melting points, T_m, of these substances, while ternary blends with POE showed miscibility, which depended on the molecular weight of POE. PBS and PES exhibited the same spherulitic growth process as in a miscible binary blend when they were crystallized from a homogeneous ternary melt. Spherulites of PBS, which is the highest‐T_m component, filled the whole volume first when a miscible ternary blend was quenched below T_m of POE, the lowest‐T_m component. Then, the blends showed either two types of crystallization processes. One was successive nucleation and growth of PES and POE spherulites, that is, PES nucleated and developed spherulites inside the PBS spherulites and then POE spherulites grew inside the interlocked spherulites of PBS and PES. The other was simultaneous growth and the formation of interpenetrating spherulites of PES and POE inside the PBS spherulites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 706–711, 2010     

Structure and mechanical properties of talc‐filled blends of polypropylene and styrenic block copolymers

The structure–property relationships of isotactic polypropylene (iPP)/styrenic block copolymer blends filled with talc were examined by optical and scanning electron microscopy, wide‐angle X‐ray diffraction, and tensile‐ and impact strength measurements. The composites were analyzed as a function of the poly(styrene‐b‐ethylene‐co‐propylene) diblock copolymer (SEP) and the poly(styrene‐b‐butadiene‐b‐styrene) triblock copolymer (SBS) content in the range from 0 to 20 vol % as elastomeric components and with 12 vol % of aminosilane surface‐treated talc as a filler. Talc crystals incorporated in the iPP matrix accommodated mostly plane‐parallel to the surface of the samples and strongly affected the crystallization process of the iPP matrix. The SBS block copolymer disoriented plane‐parallel talc crystals more significantly than the SEP block copolymer. The mechanical properties depended on the final phase morphology of the investigated iPP blends and composites and supermolecular structure of the iPP matrix because of the interactivity between their components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1255–1264, 2004     

Blends of isotactic polypropylene and natural terpene resins. I. Phase structure,thermal, and dynamic‐mechanical properties

This article discusses the influence of two natural terpene resins (NTR), poly(α‐pinene) (PαP A115) and poly(d‐limonene) (PL C115), on morphology, miscibility, thermal, and dynamic‐mechanical properties of their blends with isotactic polypropylene (iPP). The NTR have interesting physical and chemical properties, and they are approved for food contact application. From the results of differential scanning calorimetry and dynamic‐mechanical thermal analysis it was deduced that both the resins were completely miscible with the amorphous iPP up to the composition investigated here (70/30 wt %). Scanning electron microscopy (SEM) analysis instead showed that the 70/30 iPP/PαP A115 blend and 80/20 and 70/30 iPP/PL C115 blends contained very small domains homogeneously distributed into the matrix. It is hypothesized that the domains are likely formed by the terpene‐rich phase, and the matrix by the iPP‐rich phase (besides the crystallized iPP phase). The iPP‐rich phase and the NTR‐rich phase would have the glass transition temperatures so close that they cannot be resolved by DSC and DMTA. Finally, for the iPP/PαP A115 system an upper critical solution temperature (UCST) is proposed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 867–878, 1999     

Crystallization-induced composition inhomogeneities in PVDF/PMMA blends

Composition profiles develop around growing PVDF spherulites in a blend with PMMA. These profiles assume stationary courses after a certain crystallization time provided that the overall degree of crystallinity is not too high. The composition-dependent growth rate and the diffusion-controlled remove of the surplus PMMA from the spherulite surface are then in a stationary equilibrium. The internal structure of the spherulites will then be homogeneous, too. Upon isothermal crystallization of a PVDF/PMMA = 60/40 (wt %) blend at 160°C for at least 4 h, the spherulites internal degree of crystallinity x_c as related to the PVDF fraction obeys the inequality 55 wt % ≤ x_c ≤ 84 wt %. The overall PMMA content within the spherulites as averaged over its whole inside has been determined by IR microscopy. It amounts to about 15 wt %. In contrast, the PMMA content of the amorphous phase within the spherulites (averaged again over its whole inside) ranges between 28 and 52 wt %. This composition jumps at the spherulite surface to 52 wt %. From the slope of the composition profiles outside the spherulites that have a width of more than 50 μm, the effective chain diffusion coefficient in blends as averaged over both components can be calculated to amount to (250 ± 100) μm²h⁻¹. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2923–2930, 1998     

Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). II. Morphology and mechanical properties

The effects of the phase‐separation temperature and time on the mechanical properties and morphology of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride with 10 wt% ethyl acrylate) (SMA) blends were studied. Two compositions (20/80 and 40/60 w/w SMA/PMMAe) were prepared with a miniature twin‐screw extruder. Compared with those of the miscible blends, the Young's modulus values of the blends increased after the phase separation of the 40/60 SMA/PMMAe blend and within the early stage of spinodal decomposition of the 20/80 SMA/PMMAe blend. The mechanical properties, in terms of the tensile strength at break and the elongation, were better for the miscible blends than for the phase‐separation blends. This was believed to be the result of changes in the composition and molecular reorganization. The changes in the phase‐separating domains of both compositions, as observed by transmission electron microscopy, had no significant influence on the tensile moduli. Detailed studies of the morphology revealed a cocontinuous structure, indicating that the blends underwent spinodal decomposition. A morphological comparison of the two compositions illustrated the validity of the level rule. The growth rate of the droplet size was determined by approximation from the light scattering data and by direct measurements with transmission electron microscopy. The discrepancies observed in the droplet size growth rate were attributed to heat variations induced by the different sample thicknesses and heat transfer during the investigation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 886–897, 2004     

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     

Structure and properties for binary blends of isotactic-polypropylene with ethylene-α-olefin copolymer. 1. Crystallization and morphology

Morphology and isothermal growth rates of spherulites for the binary blends consisting of an isotactic polypropylene (i-PP) and an ethylene-1-hexene rubber (EHR) were examined as a function of the crystallization temperature ranging from 388 K to 418 K. In this study, two types of EHR's were employed: “ethylene rich” EHR and “1-hexene rich” EHR. The blends of i-PP with the EHR of 51 mol % 1-hexene are miscible in the molten state, whereas the blends with the EHR of 33 mol % 1-hexene are immiscible in the molten state. It is found that the isothermal spherulite growth rate of the miscible i-PP/EHR blends decreases with increasing the EHR fraction, whereas the spherulite growth rate of the immiscible i-PP/EHR blends is independent of the blend composition and is the same as that of the i-PP. Optical microscope observation of the miscible blends crystallized isothermally shows that there are no rubber domains either in the intraspherulitic or in the interspherulitic contact regions. On the other hand, the immiscible i-PP/EHR blends show a phase-separated morphology. Furthermore, the number of tangential lamellae of the miscible i-PP/EHR blends is found to be increased by blending of the EHR, leading to the spherulite with negative birefringence. The sign of birefringence of spherulites is unaffected by the regime transition as well as by the fold surface free energy. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 953–961, 1997     

In‐situ microfibrillar PET/iPP blend via slit die extrusion,hot stretching,and quenching: Influence of hot stretch ratio on morphology,crystallization, and crystal structure of iPP at a fixed PET concentration

The in situ microfibrillar blend of poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) was fabricated through a slit die extrusion, hot stretch, and quenching process. The morphological observation indicates that while the unstretched blend appears to be a common incompatible morphology, the hot stretched blends present PET in situ fibers whose characteristics, such as diameter and aspect ratio, are dependent on the hot stretching ratio (HSR). When the HSR is low, the elongated dispersed phase particles are not uniform at all. As the HSR is increased to 16.1, well‐defined PET microfibers were generated in situ, whose diameter is rather uniform and is around 0.6 ～ 0.9 μm. The presence of the PET phase shows significant nucleation ability for crystallization of iPP. Higher HSR corresponds to faster crystallization of the iPP matrix, while as HSR is high up to a certain level, its variation has little influence on the onset and maximum crystallization temperatures of the iPP matrix during cooling from melt. Optical microscopy observation reveals that transcrystalline layers form in the microfibrillar blend, in which the PET microfibers play as the center row nuclei. In the as‐stretched microfibrillar blends, small‐angle X‐ray scattering measurements show that matrix iPP lamellar crystals have the same orientation as PET lamella. The long period of lamellar crystals of iPP is not affected by the presence of PET micofibers. Wide‐angle X‐ray scattering reveals that the β phase of iPP is obtained in the as‐stretched blends, whose concentration increases with the increase of the HSR. This suggests that finer PET microfibers can promote the occurrence of the β phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4095–4106, 2004     

Effect of poly(butylene succinate) crystals on spherulitic growth of poly(ethylene oxide) in binary blends of the two substances

The effects of the lamellar growth direction, extinction rings, and spherulitic boundaries of poly(butylene succinate) (PBSU) on the spherulitic growth of poly(ethylene oxide) (PEO) were investigated in miscible blends of the two crystalline polymers. In the crystallization process from a homogeneous melt, PBSU first developed volume‐filling spherulites, and then PEO spherulites nucleated and grew inside the PBSU spherulites. The lamellar growth direction of PEO was identical with that of PBSU even when the PBSU content was about 5 wt %. PEO, which intrinsically does not exhibit banded spherulites, showed apparent extinction rings inside the banded spherulites of PBSU. The growth rate of a PEO spherulite, G_PEO, was influenced not only by the blend composition and the crystallization temperature of PEO, but also by the growth direction with respect to PBSU lamellae, the boundaries of PBSU spherulites, and the crystallization temperature of PBSU, T_PBSU. The value of G_PEO first increased with decreasing T_PBSU when a PEO spherulite grew inside a single PBSU spherulite. Then, G_PEO decreased when T_PBSU was further decreased and a PEO spherulite grew through many tiny PBSU spherulites. This behavior was discussed based on the aforementioned factors affecting G_PEO. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 539–547, 2009     

The β‐crystalline form of isotactic polypropylene in blends of isotactic polypropylene and polyamide‐6/clay nanocomposites

Blends of isotactic polypropylene and polyamide‐6/clay nanocomposites (iPP/NPA6) were prepared with an internal batch mixer. A high content of the β‐crystalline form of isotactic polypropylene (β‐iPP) was observed in the injection‐molded samples of the iPP/NPA6 blends, whereas the content of β‐iPP in the iPP/PA6 blends and the iPP/clay composite was low and similar to that of neat iPP. Quiescent melt crystallization was studied by means of wide‐angle X‐ray diffraction, differential scanning calorimetry, and polarized optical microscopy. We found that the significant β‐iPP is not formed during quiescent melt crystallization regardless of whether the sample used was the iPP/NPA6 blend or an NPA6 fiber/iPP composite. Further characterization of the injection‐molded iPP/NPA6 revealed a shear‐induced skin–core distribution of β‐iPP and the formation of β‐iPP in the iPP/NPA6 blends is related to the shear flow field during cavity‐filling. In the presence of clay, the deformation ability of the NPA6 domain is decreased, as evidenced by rheological and morphological studies. It is reasonable that the enhanced relative shear, caused by low deformability of the NPA6 domain in the iPP matrix, is responsible for β‐iPP formation in the iPP/NPA6 blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3428–3438, 2004     

Shear‐Induced Crystallization in a Blend of Isotactic Poly(propylene) and Poly(ethylene‐co‐octene)

Summary: Shear‐induced crystallization in a blend of isotactic poly(propylene) and poly(ethylene‐co‐octene) (iPP/PEOc) has been investigated by means of in‐situ optical microscopy and a shear hot stage under various thermal and shear histories. Cylindrites are observed after shear in the phase‐separated iPP/PEOc blends for the first time. The nuclei (shish) come from the orientation of the entangled network chains, and the relationship between the shear rate and the network relaxation time of the oriented iPP chains is a very important factor that dominates the formation of the cylindrites after liquid‐liquid phase separation. The cylindrites can grow through phase‐separated domains with proper shear rate and shear time. In addition, the number of spherulites increases with shear rate, which is consistent with the notion of fluctuation‐induced nucleation/crystallization.

Phase‐contrast optical micrograph of the iPP/PEOc = 50/50 (wt.‐%) sample sheared during cooling with shear rate of 10 s⁻¹ and isothermally crystallized at 140 °C for 142 s after isothermal annealing at 170 °C for 420 min. The shear time is 180 s.     

Unexpectedly high young's moduli recorded for iPP/HDPE blends

Young's moduli of a series of quenched isotactic polypropylene/high‐density polyethylene blends were measured. The moduli of many of the blends exceeded the upper bound, calculated from the parallel model with the moduli of the two quenched homopolymers as those of the two components. In fact, both components crystallized at higher temperatures in the blends than they did on their own. It is argued that the higher crystallization temperatures of the components lead to higher component moduli and that this can explain the observation that the measured moduli of the blends apparently exceeded the upper bound. The implications of this work are discussed in light of other studies concerning the measurement and calculation of blend moduli. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1404–1414, 2001     

Complex phase behavior and state of miscibility in Poly(ethylene glycol)/Poly(l‐lactide‐co‐ε‐caprolactone) Blends

A miscibility and phase behavior study was conducted on poly(ethylene glycol) (PEG)/poly(l ‐lactide‐ε‐caprolactone) (PLA‐co‐CL) blends. A single glass transition evolution was determined by differential scanning calorimetry initially suggesting a miscible system; however, the unusual T_g bias and subsequent morphological study conducted by polarized light optical microscopy (PLOM) and atomic force microscopy (AFM) evidenced a phase separated system for the whole range of blend compositions. PEG spherulites were found in all blends except for the PEG/PLA‐co‐CL 20/80 composition, with no interference of the comonomer in the melting point of PEG (T_m = 64 °C) and only a small one in crystallinity fraction (X_c = 80% vs. 70%). However, a clear continuous decrease in PEG spherulites growth rate (G) with increasing PLA‐co‐CL content was determined in the blends isothermally crystallized at 37 °C, G being 37 µm/min for the neat PEG and 12 µm/min for the 20 wt % PLA‐co‐CL blend. The kinetics interference in crystal growth rate of PEG suggests a diluting effect of the PLA‐co‐CL in the blends; further, PLOM and AFM provided unequivocal evidence of the interfering effect of PLA‐co‐CL on PEG crystal morphology, demonstrating imperfect crystallization in blends with interfibrillar location of the diluting amorphous component. Significantly, AFM images provided also evidence of amorphous phase separation between PEG and PLA‐co‐CL. A true T_g vs. composition diagram is proposed on the basis of the AFM analysis for phase separated PEG/PLA‐co‐CL blends revealing the existence of a second PLA‐co‐CL rich phase. According to the partial miscibility established by AFM analysis, PEG and PLA‐co‐CL rich phases, depending on blend composition, contain respectively an amount of the minority component leading to a system presenting, for every composition, two T_g's that are different of those of pure components. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 111–121