Influence of thermal history on crystalline morphologies of isotactic polypropylene in its miscible blends with polybutene‐1

The miscibility behaviors in blends of isotactic polypropylene (iPP) and polybutene‐1 (PB) have been studied using in‐situ FTIR imaging. The heterogeneous melt of 3/7 iPP/PB blends were formed at 250, 220, and 180°C and then quenched to the same crystallization temperature of iPP at 125°C, respectively. Evolution processes of composition distribution during crystallization were monitored according to their characteristic peaks, and the results suggest a trend from local concentration to uniform dispersion of PB fraction. Further studies of the PB fraction as the distance from the growth front of iPP spherulite indicate an irreversible phase behavior with the progress of thermal history. The cyclic melting and crystallization favor the mixing of iPP/PB blend. Meanwhile, the nonlinear growth rate of iPP spherulite is mainly responsible for compatible promotion of iPP/PB blend, which hinders the transportation of iPP chains to its growth front. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43282.     

The phase diagram and morphology of blends of poly(vinylidene fluoride) and poly(ethyl acrylate)

The phase diagram and crystallization behaviour of the polymer blend system consisting of poly(vinylidene fluoride) (PVF₂) and poly(ethyl acrylate) (PEA) have been examined. The melt exhibits phase separation upon heating to 10°C–50°C above the melting point of the PVF₂, depending on the composition. The cloud point and equilibrium melting point curve (for α-PVF₂) intersect at about 180°C and a composition of 50% (by weight) PVF₂. The polymer-polymer interaction parameter, χ, was calculated from the equilibrium melting point depression data and found to be −0.16 (at 170°C). Spherulite growth rate data have been measured as a function of composition and temperature. Assuming regime II crystallization a value of the product of the surface free energies of the α-PVF₂ crystals was calculated to be 4.4 × 10⁻⁴J²m⁻⁴. In blends crystallized from the one phase melt the texture of spherulites becomes more open and the spherulite extinction ring spacing (due to lamaller twist) becomes larger with increasing crystallization temperature. In addition the ring spacing increases with PEA content at constant crystallization temperature.     

Effect of poly(propylene carbonate) on the crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)

The crystallization and melting behavior of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHBV) and a 30/70 (w/w) PHBV/poly(propylene carbonate) (PPC) blend was investigated with differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The transesterification reaction between PHBV and PPC was detected in the melt‐blending process. The interaction between the two macromolecules was confirmed by means of FTIR analysis. During the crystallization process from the melt, the crystallization temperature of the PHBV/PPC blend decreased about 8°C, the melting temperature was depressed by 4°C, and the degree of crystallinity of PHBV in the blend decreased about 9.4%; this was calculated through a comparison of the DSC heating traces for the blend and pure PHBV. These results indicated that imperfect crystals of PHBV formed, crystallization was inhibited, and the crystallization ability of PHBV was weakened in the blend. The equilibrium melting temperatures of PHBV and the 30/70 PHBV/PPC blend isothermally crystallized were 187.1 and 179°C, respectively. The isothermal crystallization kinetics were also studied. The fold surface free energy of the developing crystals of PHBV isothermally crystallized from the melt decreased; however, a depression in the relative degree of crystallization, a reduction of the linear growth rate of the spherulites, and decreases in the equilibrium melting temperature and crystallization capability of PHBV were detected with the addition of PPC. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2514–2521, 2004     

Blends of bacterial poly[(R)‐3‐hydroxybutyrate] with oligo[(R,S)‐3‐hydroxybutyrate]‐diol

The miscibility, melting and crystallization behaviour of poly[(R)‐3‐hydroxybutyrate], PHB, and oligo[(R,S)‐3‐hydroxybutyrate]‐diol, oligo‐HB, blends have been investigated by differential scanning calorimetry: thermograms of blends containing up to 60 wt% oligo‐HB showed behaviour characteristic of single‐phase amorphous glasses with a composition dependent glass transition, T_g, and a depression in the equilibrium melting temperature of PHB. The negative value of the interaction parameter, determined from the equilibrium melting depression, confirms miscibility between blend components. In parallel studies, glass transition relaxations of different melt‐crystallized polymer blends containing 0–20 wt% oligo‐HB were dielectrically investigated between ?70 °C and 120 °C in the 100 Hz to 50 kHz range. The results revealed the existence of a single α‐relaxation process for blends, indicating the miscibility between amorphous fractions of PHB and oligo‐HB. © 2002 Society of Chemical Industry     

Melting and curie transition behavior of blends of vinylidenefluoride-tetrafluoroethylene copolymer and polymethylmethacrylate

Thermal properties were investigated using differential scanning calorimetry of blends of vinylidenefluoride-tetrafluoroethylene (VDF-TFE) copolymer and polymethylmethacrylate. Curie transition behavior was strongly dependent on the crystallization temperature. A Curie temperature was shown in pure VDF-TFE copolymer and in the blend with 91 wt % VDF-TFE copolymer, which were crystallized above the Curie temperature. The samples crystallized above the Curie temperature showed higher melting temperatures than those crystallized below the Curie temperature, resulting in an upturn of slope at high temperatures in the Hoffman-Weeks plot. The polymer-polymer interaction parameter was calculated to be ?0·165 at 130°C from the equilibrium melting temperatures, indicating miscibility of the two components.     

Physical characterization of isotactic polypropylene/ethylene-propylene copolymer blends

The properties of solution-mixed blends of isotactic polypropylene (iPP) and an amorphous ethylene-propylene copolymer (EPM), containing 40 wt.-% of ethylene, were studied throughout the composition range. The techniques used were differential scanning calorimetry (DSC), dynamic mechanical spectroscopy, and optical microscopy. Morphological examination revealed a heterogeneous structure. The dynamic mechanical technique at isochronous conditions (110 Hz) between -120 and 160°C confirmed the heterophase nature of the blends and revealed limited phase mixing of the amorphous components of the two constituents. DSC measurements of specimens quenched at 0°C, indicated that EPM rubber promotes crystallization of the iPP phase. Appropriate mechanics models tested in the complete composition range led to the conclusion that the system is incompatible, with rubber spherical inclusion strongly adhering to the iPP matrix, up to an EPM volume fraction Φ (EPM) ? 0.70. At higher EPM compositions, matrix reversal occurs — a fact corroborated by the available mechanical data for this blend.     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/propylene‐g‐styrene blends

Optical microscopy, differential scanning calorimetry, and small angle X‐ray scattering techniques were used to study the influence of the crystallization conditions on morphology and thermal behavior of samples of binary blends constituted of isotactic polypropylene (iPP) and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) isothermally crystallized from melt, at relatively low undercooling, in a range of crystallization temperatures of the iPP phase. It was shown that, irrespective of composition, no fall in the crystallinity index of the iPP phase was observed. Notwithstanding, spherulitic texture and thermal behavior of the iPP phase in the iPP/uPP‐g‐PS materials were strongly modified by the presence of copolymer. Surprisingly, iPP spherulites crystallized from the blends showed size and regularity higher than that exhibited by plain iPP spherulites. Moreover, the amount of amorphous material located in the interspherulitic amorphous regions decreased with increasing crystallization temperature, and for a given crystallization temperature, with increasing uPP‐g‐PS content. Also, relevant thermodynamic parameters, related to the crystallization process of the iPP phase from iPP/uPP‐g‐PS melts, were found, composition dependent. The equilibrium melting temperature and the surface free energy of folding of the iPP lamellar crystals grown in the presence of uPP‐g‐PS content up to 5% (wt/wt) were, in fact, respectively slightly lower and higher than that found for the lamellar crystals of plain iPP. By further increase of the copolymer content, both the equilibrium melting temperature and surface free energy of folding values were, on the contrary, depressed dramatically. The obtained results were accounted for by assuming that the iPP crystallization process from iPP/uPP‐g‐PS melts could occur through molecular fractionation inducing a combination of morphological and thermodynamic effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2286–2298, 2001     

Influence of the method of mixing on homogeneity and crystallization kinetics of blends of linear and branched polyethylene

The influence of mixing method—solution and melt mixing—on the homogeneity and crystallization kinetics of a series of blends of single‐site materials of linear polyethylene and ethyl‐branched polyethylene was studied by differential scanning calorimetry. Data obtained for heats of melting and crystallization, melting and crystallization peak temperatures, and melting and crystallization temperature profiles were essentially the same for the samples obtained by the two mixing methods. The results obtained can be interpreted as indicating that melt mixing is capable of producing homogeneous melts of these relatively low molar mass polymers, given that solution mixing is considered to give perfectly homogeneous blends. The heat associated with the high temperature melting peak after crystallization at 125°C of the blend samples, obtained by the two preparation methods, was higher than that of the linear polyethylene included in the blends, suggesting that a part of the branched polyethylene crystallized at 125°C. The unblended branched polyethylene showed no crystallization at 125°C. Samples obtained by powder mixing showed independent crystallization and melting of the linear and branched polyethylene components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1730–1736, 2004     

Nonisothermal crystallization of isotactic polypropylene blended with poly(α-pinene). I. Bulk crystallization

The influence of a natural terpene resin, poly(α-pinene) (PαP), on the nonisothermal crystallization process of isotactic polypropylene (iPP) was investigated. The solidification process strongly depends on cooling rate, composition, and miscibility of the system. For the blends containing PαP up to 30 wt %, the overall nonisothermal crystallization rate is depressed with respect to plain iPP. This is probably the result of the diluting effect of the polyterpene because the two components are miscible. The 50/50 blend presents, instead, two amorphous phases: an iPP-rich phase and a PαP-rich phase. For this composition, solidification starts at temperatures higher than those for plain iPP and blends with lower PαP content, given that the diluting effect of PαP in the iPP-rich phase is counterweighted by an increased number of nuclei that originate from the polyterpene-rich phase domains. PαP also influences the morphology of iPP spherulites, which are spherical in plain iPP and become more irregular with increasing PαP content. The number and dimension of iPP spherulites depend on blend composition and miscibility of the components. Moreover, the nonisothermal crystallization kinetics of iPP/PαP blends was analyzed with the Ozawa equation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 358–367, 2001     

Morphology and thermal properties in the binary blends of poly(propylene-co-ethylene) copolymer and isotactic polypropylene with polyethylene

The morphology and thermal properties of isothermal crystallized binary blends of poly(propylene-co-ethylene) copolymer (PP-co-PE) and isotactic polypropylene (iPP) with low molecular weight polyethylene (PE) were studied with differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). In PP-co-PE/PE binary blends, however, the connected PE acted as a phase separating agent to promote phase separation for PP-co-PE/PE binary blends during crystallization. Therefore, the thermal properties of PP-co-PE/PE presented double melting peaks of PE and a single melting temperature of PP during melting trace; on the other hand, at cooling trace, the connected PE promoted crystallization rate because of enhanced segmental mobility of PP-co-PE during crystallization. At isothermal crystallization temperature between the melting points of iPP and PE, the binary blend was a crystalline/amorphous system resulting in persistent remarkable molten PE separated domains in the broken iPP spherulite. And then, when temperature was quenched to room temperature, the melted PE separated domains were crystallized that presented a crystalline/crystalline system and formed the intra-spherulite segregation morphology: these PE separated domains/droplet crystals contained mixed diluent PE with connected PE components. On the other hand, in the iPP/PE binary blends, the thermal properties showed only single melting peaks for both PE and iPP. Moreover, the glass transition temperature of iPP shifted to lower temperature with increasing PE content, implying that the diluent PE molecules were miscible with iPP to form two interfibrillar segregation morphologies: iPP-rich and PE-rich spherulites. In this work, therefore, we considered that the connected PE in PP-co-PE functioned as an effective phase separating agent for PP and diluent PE may be due to the miscibility between connected PE and diluent PE larger than that between PP and dispersed PE.     

Crystallization characteristics of isotactic polypropylene with and without nucleating agents

Nucleation effects of two sorbitol derivatives on the crystallization of isotactic polypropylene (iPP) were studied by means of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). A nonisothermal crystallization kinetic equation was employed to analyze the crystallization characteristics of iPP with or without the nucleating agents from DSC crystallization thermograms. The equilibrium melting temperature of iPP necessary for the kinetic study was obtained by the extrapolation method to be 209°C. The nonisothermal crystallization kinetic analysis for the unnucleated iPP at different cooling rates was possible by assuming the spherulite growth initiated simultaneously by heterogeneous and homogeneous nucleation. On the other hand, the crystallization kinetics of the nucleated iPP could be described by the heterogeneous nucleation and growth process alone. The addition of the nucleating agents up to their saturation concentrations in iPP increased the crystallization peak temperature by 17°C, and the number of effective nuclei by three orders of magnitude. A high concentration of the nucleating agents caused agglomeration of the agents to lower the number of effective nuclei.     

Poly(ethylene glycol)/poly(methyl methacrylate) blends as novel form‐stable phase‐change materials for thermal energy storage

In this study, we focused on the preparation and characterization of poly(ethylene glycol) (PEG)/poly(methyl methacrylate) (PMMA) blends as novel form‐stable phase‐change materials (PCMs) for latent‐heat thermal energy storage (LHTES) applications. In the blends, PEG acted as a PCM when PMMA was operated as supporting material. We subjected the prepared blends at different mass fractions of PEG (50, 60, 70, 80, and 90% w/w) to leakage tests by heating the blends over the melting temperature of the PCM to determine the maximum encapsulation ratio without leakage. The prepared 70/30 w/w % PEG/PMMA blend as a form‐stable PCM was characterized with optical microscopy and Fourier transform infrared spectroscopy. The thermal properties of the form‐stable PCM were measured with differential scanning calorimetry (DSC). DSC analysis indicated that the form‐stable PEG/PMMA blend melted at 58.07°C and crystallized at 39.28°C and that it had latent heats of 121.24 and 108.36 J/g for melting and crystallization, respectively. These thermal properties give the PCMs potential LHTES purposes, such as for solar space heating and ventilating applications in buildings. Accelerated thermal cycling tests also showed that the form‐stable PEG/PMMA blend as PCMs had good thermal reliability and chemical stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystallization,melting, and rheology of reactive polyamide blends

The crystallization and melting characteristics of a series of polyamide blends based on PA 4,6 and PA 6I were investigated by calorimetric methods; preparation of the samples was conducted so as to control the extent of transamidation occurring in the melt before crystallization. Blend samples with minimal prior thermal history displayed a modest degree of melting point depression compared to the equilibrium melting temperature of PA 4,6 (T = 309.5°C). Application of the Nishi–Wang equation indicated a value of χ = ?0.25 for the blends. PA 4,6 and the blends followed Avrami crystallization kinetics with exponents in the range 2.0 to 2.5; no systematic variation of n with blend composition was observed. The influence of transamidation was investigated for samples exposed to varying melt temperatures and melt times with the extent of transreaction quantified using ¹³C‐NMR. Increasing extents of transreaction led to a decrease in both the rate of crystallization and the overall bulk crystallinity of the blends owing to a reduction in the length and number of crystallizable blocks present along the polymer chains. Capillary rheometry studies indicated a strong sensitivity to time in the melt for the PA 4,6 homopolymer, and the mechanism responsible for the observed decrease in apparent viscosity was also operative in the blend samples. As such, it was not possible to independently assess the influence of transreaction on the rheology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1245–1252, 2004     

Poly(hydroxybutyrate)/poly(butylene succinate) blends: miscibility and nonisothermal crystallization

Four blends of poly(hydroxybutyrate) (PHB) and poly(butylene succinate) (PBSU), both biodegradable semicrystalline polyesters, were prepared with the ratio of PHB/PBSU ranging from 80/20 to 20/80 by co-dissolving the two polyesters in N,N-dimethylformamide and casting the mixture. Differential scanning calorimetry (DSC) and optical microscopy (OM) were used to probe the miscibility of PHB/PBSU blends. Experimental results indicated that PHB showed some limited miscibility with PBSU for PHB/PBSU 20/80 blend as evidenced by the small change in the glass transition temperature and the depression of the equilibrium melting point temperature of the high melting point component PHB. However, PHB showed immiscibility with PBSU for the other three blends as shown by the existence of unchanged composition independent glass transition temperature and the biphasic melt. Nonisothermal crystallization of PHB/PBSU blends was investigated by DSC using various cooling rates from 2.5 to 10 °C/min. During the nonisothermal crystallization, despite the cooling rates used two crystallization peak temperatures were found for PHB/PBSU 40/60 and 60/40 blends, corresponding to the crystallization of PHB and PBSU, respectively, whereas only one crystallization peak temperature was observed for PHB/PBSU 80/20 and 20/80 blends. However, it was found that after the nonisothermal crystallization the crystals of PHB and PBSU actually co-existed in PHB/PBSU 80/20 and 20/80 blends from the two melting endotherms observed in the subsequent DSC melting traces, corresponding to the melting of PHB and PBSU crystals, respectively. The subsequent melting behavior was also studied after the nonisothermal crystallization. In some cases, double melting behavior was found for both PHB and PBSU, which was influenced by the cooling rates used and the blend composition.     

Spherulite nucleation in blends of isotactic polypropylene with isotactic poly(butene-1)

The phase morphology and the influence of composition on the primary nucleation of isotactic polypropylene in isotactic polypropylene/isotactic poly(butene-1) (iPP/iPB) blends were investigated by electron and light microscopy and small-angle light scattering. It was found that iPP and iPB are miscible but the thermal treatment induces partial phase separation of components and the formation of iPP-rich and iPB-rich phases. The complete phase separation needs high temperatures and/or a long time of melt annealing. In samples crystallized isothermally at low undercooling the heterogeneous primary nucleation in blends is depressed as compared to plain iPP. In blends the less active heterogeneities lose their activity because of an increase of the energy barrier for critical size nucleus formation due to phase separation of blend components during crystallization. For the same reason the rate of homogeneous nucleation in blends decreases, as observed in samples crystallized at very high undercooling. At very high undercooling iPP and iPB are able to crystallize with similar rates, which results in the formation of a fraction of iPB spherulites in addition to iPP spherulites. Consequently the number of spherulites in the blend is larger than that in plain iPP, in spite of the decrease in the homogeneous nucleation rate of iPP in the blend. © 1994 John Wiley & Sons, Inc.     

Multiple melting and partial miscibility of ethylene‐vinyl acetate copolymer/low density polyethylene blends

Multiple melting behaviors and partial miscibility of ethylene‐vinyl acetate (EVA) copolymer/low density polyethylene (LDPE) binary blend via isothermal crystallization are investigated by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). Crystallization temperature T (°C) is designed as 30, 50, 70, 80°C with different crystallization times t (min) of 10, 30, 60, 300, 600 min. The increase of crystallization temperature and time can facilitate the growth in lateral crystal size, and also the shift of melting peak, which means the completion of defective secondary crystallization. For blends of various fractions, sequence distribution of ethylene segments results in complex multiple melting behaviors during isothermal crystallization process. Overlapping endothermic peaks and drops of equilibrium melting points of LDPE component extrapolated from Hoffman–Weeks plots clarify the existence of partial miscibility in crystalline region between EVA and LDPE. WAXD results show that variables have no perceptible influence on the predominant existence of orthorhombic crystalline phase structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Miscibility and crystallization behavior of poly(ether ether ketone ketone)/poly(ether imide) blends

The miscibility and crystallization behavior of poly(ether ether ketone ketone) (PEEKK)/poly(ether imide) (PEI) blends prepared by melt‐mixing were investigated by differential scanning calorimetry. The blends showed a single glass transition temperature, which increased with increasing PEI content, indicating that PEEKK and PEI are completely miscible in the amorphous phase over the studied composition range (weight ratio: 90/10–60/40). The cold crystallization of PEEKK blended with PEI was retarded by the presence of PEI, as is apparent from the increase of the cold crystallization temperature and decrease of the normalized crystallinity for the samples anealed at 300°C with increasing PEI content. Although the depression of the apparent melting temperature of PEEKK blended with PEI was observed, there was no evidence of depression in the equilibrium melting temperature. The analysis of the isothermal crystallization at 313–321°C from the melt of PEEKK/PEI (100/0, 90/10, and 80/20) blends suggested that the retardation of crystallization of PEEKK is caused by the increase of the crystal surface free energy in addition to the decrease of the mobility by blending PEI with a high glass transition temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 769–775, 2001     

Melting and crystallization behavior of copolymer from cyclic butylene terephthalate and polycaprolactone

In this study, we investigated the nonisothermal crystallization kinetics, crystallization morphology, and melting behavior of polymerized cyclic butylene terephthalate (pCBT) copolymerized with polycaprolactone (PCL). The results of this experiment indicated that the Ozawa exponent varied between 2 and 3 for pCBT, but between 1 and 2 for blends of pCBT/PCL. At the same temperature (185°C), the crystallization rate constant K_T for pCBT/PCL blend was much lower than for pCBT homopolymer. These results indicated a strong hindrance on the crystallization of pCBT/PCL blends. The pCBT and pCBT/PCL samples exhibited no visible difference in morphology or microstructure. However, the crystallization and melting peak temperature of pCBT/PCL blends was ～20°C lower than that of pCBT homopolymer. Crystal morphology confirmed that the mechanism of simultaneous polymerization and crystallization found applicable to pCBT homopolymer did not apply for blends of pCBT/PCL. It therefore appears that crystallization should be delayed until after the completion of pCBT/PCL copolymerization. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Kinetics of isothermal and non‐isothermal crystallization of poly(butylene terephthalate)/ liquid crystalline polymer blends

The melting behavior and isothermal and non‐isothermal crystallization kinetics of poly(butylene terephthalate) (PBT)/thermotropic liquid crystalline polymer (LCP), Vectra A950 (VA) blends were studied by using differential scanning calorimetry. Isothermal crystallization experiments were performed at crystallization temperatures (T_c), of 190, 195, 200 and 205°C from the melt (300°C) and analyzed based on the Avrami equation. The values of the Avrami exponent indicate that the PBT crystallization process in PBT/VA blends is governed by three‐dimensional morphology growth preceded by heterogeneous nucleation. The overall crystallization rate of PBT in the melt blends is enhanced by the presence of VA. However, the degree of PBT crystallinily remains almost the same. The analysis of the melting behavior of these blends indicates that the stability and the reorganization process of PBT crystals in blends are dependent on the blend compositions and the thermal history. The fold surface interfacial energy of PBT in blends is more modified than in pure PBT. Analysis of the crystallization data shows that crystallization occurs in Regime II across the temperature range 190°C‐205°C. A kinetic treatment based on the combination of Avrami and Ozawa equations, known as Liu's approach, describes the non‐isothermal crystallization. It is observed that at a given cooling rate the VA blending increases the overall crystallization rate of PBT.     

Isothermal crystallization kinetics of AB<Subscript>3</Subscript> hyperbranched polymer (HBP)/polypropylene (PP) blends

In this paper, the isothermal crystallization kinetics of pure isotactic polypropylene (iPP) and iPP with 5% AB₃ hyperbranched polymer (HBP) added had been investigated by differential scanning calorimetry (DSC). During isothermal crystallization, the crystallization rate of the blends was higher than those of iPP remarkably. Moreover, the value of t _½ became smaller with increasing the HBP molecular weight in blends, however, the crystallization rate of the blend decreased when the higher molecular weight HBP (\( \bar{M}_{n} \) = 12,500) was added. The crystallization rate of the blends was more sensitive to temperature than that of iPP. An increase in the Avrami exponent may be attributed to the fractal structure of hyperbranched polymer.