Effects of dispersed phase composition on thermoplastic polyolefins

Ternary blends of polypropylene (PP), ethylene–octene copolymer (mPE), and high‐density polyethylene (HDPE) were prepared based on the phase behavior and physical properties of mPE/HDPE binary blends, and the results were interpreted in terms of morphology and both rheological and mechanical properties of the ternary blends as well as the binary blends. It was found that when mPE encapsulates HDPE in the PP matrix, compared to the encapsulation of mPE by HDPE, better blend properties were obtained, presumably because of the compatibilizing effect of mPE between PP and HDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 179–188, 2004     

Effects of the viscosity ratio on polyolefin ternary blends

Polyolefin binary and ternary blends were prepared from polypropylene (PP), an ethylene–α‐olefin copolymer (mPE), and high‐density polyethylene (HDPE) on the basis of the viscosity ratio of the dispersed phase to the continuous phase. In PP/mPE/HDPE blends, fibrils were observed when the dispersed‐phase (mPE/HDPE) viscosity was less than that of PP, or when the viscosity of mPE was less than that of PP, although the viscosity of mPE/HDPE was greater than that of PP. The notched impact strength and mechanical properties such as the yield strength, flexural modulus, and hardness of PP/mPE binary blends further increased with the addition of HDPE according to the type of HDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4027–4036, 2004     

Melting behavior and isothermal crystallization kinetics of polypropylene/metallocene‐catalyzed polyethylene elastomer blends

Polypropylene (PP)/metallocene‐catalyzed polyethylene elastomer (mPE) blends were prepared in a twin‐screw extruder. The melting behavior, crystallization behavior, and isothermal crystallization kinetics of the blends were studied with differential scanning calorimetry. The results showed that PP and mPE were partially miscible and that the addition of mPE shifted the melting peak of PP to a lower temperature but the crystallization temperature to a higher temperature, demonstrating a dilution effect of mPE on PP. The isothermal crystallization kinetics of the blends were described with the Avrami equation. The values of the Avrami exponent indicated that the nucleation mechanism of the blends was heterogeneous, the growth of spherulites was almost three‐dimensional, and the crystallization mechanism of PP was not affected much by mPE. At the same time, the Avrami exponents of the blends were higher than that of pure PP, and this showed that the addition of mPE helped PP to form more perfect spherulites. The crystallization rate of PP was increased by mPE because the dilution effect of mPE on PP increased the mobility of PP chains. The crystallization activation energy was estimated with the Arrhenius equation, and the nucleation constant was determined by the Hoffman–Lauritzen theory. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nonisothermal crystallization,melting behavior,and morphology of polypropylene/metallocene‐catalyzed polyethylene blends

The nonisothermal crystallization, melting behavior, and morphology of blends of polypropylene (PP) and a metallocene‐catalyzed polyethylene (mPE) elastomer were studied with differential scanning calorimetry, scanning electron microscopy, polarized optical microscopy, and X‐ray diffraction. The results showed that PP and mPE were partially miscible and could form some cocrystallization, although the extent was very small. A modified Avrami analysis and the Mo method were 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 homogeneous, the growth of the spherulites was three‐dimensional, and the crystallization mechanism of PP was not affected by mPE. The crystallization activation energy was estimated with the Kissinger method. Interesting results were obtained with the modified Avrami analysis and Mo and Kissinger methods, and the conclusions were in good agreement. The addition of less mPE increased the overall crystallization rate of PP. The relationship between the composition and morphology of the blends was examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1203–1210, 2004     

Effects of the blending sequence in polyolefin ternary blends

Ternary blends of isotactic polypropylene (PP), ethylene–octene copolymer (mPE), and high‐density polyethylene (HDPE) were prepared by melt mixing in a twin‐screw extruder with two different sequences of mixing: the simultaneous mixing of the three components (method I) and the premixing of mPE and HDPE followed by mixing with PP (method II). Regardless of the mixing sequence, mPE encapsulated HDPE in the PP matrix, although better mechanical properties were generally obtained with method II. The domain size was mainly determined by the viscosity ratio of mPE to PP in method I and by the viscosity ratio of the binary blend (mPE/HDPE) to PP in method II. Specimens prepared by injection molding gave much finer dispersions than compression‐molded specimens. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 804–811, 2004     

Non‐isothermal crystallization kinetics and segmental dynamics of high density polyethylene/butyl rubber blends

Non‐isothermal crystallization kinetics and dynamics of polymer blends are important to both theory and applications. In this work, we studied the morphology, crystal structure, non‐isothermal crystallization kinetics and dynamics of high density polyethylene/butyl rubber (HDPE/IIR) blends. The non‐isothermal crystallization kinetics is analyzed by Mo's model and the dynamics behavior is analyzed by a linear method. The results of morphology, non‐isothermal crystallization kinetics and dynamics show that the condensed structure of HDPE/IIR blends has a marked influence on their non‐isothermal crystallization kinetics and segmental dynamics. © 2015 Society of Chemical Industry     

Isothermal crystallization and spherulite nucleation in blends of polypropylene with metallocene‐prepared polyethylene

The isothermal crystallization behavior and morphology of a polypropylene (PP)‐based copolymer, a metallocene‐prepared linear low‐density polyethylene (M‐LLDPE) and their three 10/90, 30/70 and 50/50 M‐LLDPE/PP blends have been investigated. The PP and M‐LLDPE contained 5 ethylene and 3.3 mol% hexene‐1 as a comonomer, respectively. Isothermal crystallization studies revealed a different temperature‐dependence on crystallization for M‐LLDPE, PP and their blends and the crystallization half‐life for the M‐LLDPE was higher than either PP or the blends at a certain temperature. The PP‐rich blends also showed a quite similar crystallization rate to that of PP. Investigations on the variation of spherulite growth rate of PP in the blends at different temperatures revealed no significant change and was quite independent of the amount of M‐LLDPE being employed. The morphology studies revealed that the nucleation densities of the PP spherulites decreased by introducing M‐LLDPE into PP and the M‐LLDPE remained as discrete droplets dispersed throughout the PP spherulites. The results obtained were consistent with no miscibility between the two components. Copyright © 2005 Society of Chemical Industry     

Isothermal crystallization behavior of polypropylene catalloys

The isothermal crystallization behavior of polypropylene (PP) catalloys and neat PP were studied with differential scanning calorimetry and polarized optical microscopy (POM). The crystallization kinetics of the samples were described with the well‐known Avrami equation. The crystallization rate depended remarkably on the content of the ethylene component in the PP catalloys. The crystallization half‐time increased obviously with the increase of the ethylene component in the PP catalloys. We also observed by POM that in isothermal crystallization, there were many more nuclei in the PP catalloys than that in neat PP and with an increase of the ethylene component, the average size of the spherulites decreased obviously. Even when ethylene content was as high as 27%, the crystallization rate still increased apparently, and this was quite different from common PP melting blends, in which the crystallization rate decreased when the ethylene content was relatively high because of the obstruction effect of dispersed droplets to the spherulite growth of the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 877–882, 2004     

玻纤增强茂金属聚乙烯弹性体改性聚丙烯的研究

采用短玻纤（SGF）对PP／茂金属聚乙烯弹性体（mPE）共混物进行增强,制得PP／mPE/SGF三元共混复合材料,分别对PP／mPE二元共混物和PP／mPE/SGF三元共混复合材料的力学性能进行了研究。探讨了弹性体用量、SGF的用量和表面处理对共混物和复合材料拉伸性能、低温冲击韧性和蠕变性能的影响。结果表明,PP／mPE/SGF三元共混复合材料同时具有良好的刚性和韧性。     

Isothermal‐crystallization kinetics and melting behavior of crystalline/crystalline blends of poly(trimethylene terephthalate) and poly(ethylene 2,6‐naphthalate)

The isothermal crystallization and crystal morphology of poly(trimethylene terephthalate) (PTT)/poly (ethylene 2,6‐naphthalate) (PEN) blends were investigated with differential scanning calorimetry and polarized optical microscopy. The commonly used Avrami equation was used to fit the primary stage of isothermal crystallization. The Avrami exponents were evaluated to be in the range of 3.0–3.3 for isothermal crystallization. The subsequent melting endotherms of the blends after isothermal crystallization showed multiple melting peaks. The crystallization activation energies of the blends with 20 or 40% PTT was ?48.3 and ?60.9 kJ/mol, respectively, as calculated by the Arrhenius formula for the isothermal‐crystallization processes. The Hoffman–Lauritzen theory was also employed to fit the process of isothermal crystallization, and the kinetic parameters of the blends with 20 or 40% PTT were determined to be 1.5 × 10⁵ and 1.8 × 10⁵ K², respectively. The spherulite morphology of the six binary blends formed at 190°C showed different sizes and perfect Maltese crosses when the PTT or PEN component was varied, suggesting that the greater the PTT content was, the larger or more perfect the crystallites were that formed in the binary blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3316–3325, 2007     

Morphology,crystallization and melting properties of isotactic polypropylene blended with lignin

The influence of lignin (L) on the thermal properties and kinetics of crystallization of isotactic polypropylene (PP) is reported in this article. PP blends containing 5 and 15 wt % of L were prepared by mixing the components in a screw mixer. An increase of the thermal degradation temperature of the blends was observed as a function of L content. The crystallization and thermal behavior of the pure PP and of the PP/L blends were analyzed by differential scanning calorimetry (DSC). Isothermal crystallization kinetics were described by means of the Avrami equation, which suggests a three‐dimensional growth of crystalline units, developed by heterogeneous nucleation. The isothermal growth rate of PP spherulites was studied using a polarizing optical microscope. The enhancement of PP crystallization rate for the PP/L blends was observed and ascribed to the nucleating action of lignin particles. Non‐isothermal crystallization kinetics were applied, according to the results elaborated by Ziabicki and the method modified by Jeziorny. The kinetic crystallizability of the PP is not influenced by the L present in the blend. In the presence of L, PP can simultaneously crystallize in both the α and β crystalline forms, and the ratio between the α and β forms was determined by X‐ray diffraction analysis. Two melting peaks relative to the two crystalline form of PP were observed for the PP/L blends, for all isothermal crystallization temperatures investigated by means of DSC. The equilibrium melting temperature for α‐form of pure PP was obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1435–1442, 2004     

Crystallization kinetics of compatibilized blends of a liquid crystalline polymer with polypropylene

Blends of a maleic anhydride-grafted polypropylene (m-PP) and a liquid crystalline polymer (LCP) based on a copolyester of hydroxynapthoic acid and hydroxybenzoic acid were fabricated. The morphology and isothermal and nonisothermal crystallization kinetics behavior of the m-PP copolymer and m-PP/LCP blends were investigated using polarizing optical microscopy, depolarized light intensity, and differential scanning calorimetry. A polarizing optical micrograph revealed that the m-PP is very effective to promote a finer dispersion of the LCP phase in the PP matrix. Consequently, the LCP domains or fibrils acted as potential sites for the spherulite nucleation. The isothermal kinetics measurements also indicated that the rate of crystallization is enhanced in the maleated PP/LCP blends which exhibit transcrystallinity. In general, the nonisothermal kinetics results were in good agreement with those obtained from the isothermal kinetics measurements. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 707–715, 1997     

Mechanical properties and morphologies of PP/mPE/filler composites

Because of the poor impact behavior of polypropylene (PP) at low temperatures, the blending of PP with metallocene‐polymerized polyethylene (mPE) elastomers was investigated in this study. However, a reduced modulus of the overall blend was inevitable because of the addition to elastomers. To obtain a balance of the properties, we introduced rigid inorganic fillers to PP/mPE blends. The performance of the composites was characterized with tensile and Charpy notched impact tests, and the fracture morphology was examined with scanning electron microscopy. The results showed that the effects of fillers in a brittle matrix and in a ductile matrix were quantitatively different. For PP/mPE/filler ternary composites, the dependence of Young's modulus and yield strength on CaCO₃ content was not significant compared with that of PP/filler binary composites, whereas the elongation at break and tensile toughness at room temperature for PP/mPE/filler systems were more improved. The impact strength of the PP/mPE blends filled with untreated glass beads and CaCO₃ at a low temperature was lowered because of the weak interfacial bond. However, the values of the impact strength of the PP/mPE/filler composites at a low temperature remained at a high level compared with that of pure PP. In particular, a PP/mPE blend filled with surface‐treated kaolin had a higher low‐temperature impact toughness than the unfilled blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3029–3035, 2002; DOI 10.1002/app.2333     

Effect of the high‐density polyethylene melt index on the microcellular foaming of high‐density polyethylene/polypropylene blends

The effect of high‐density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high‐melt‐index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004     

Morphology and mechanical properties of biaxially oriented films of polypropylene and HDPE blends

Biaxially oriented films of blends of high-density polyethylene (HDPE) with polypropylene (PP) homopolymer and PP copolymers prepared by twin-screw extrusion and lab-stretcher have been investigated by scanning electron microscopy (SEM), polarized microscopy, differential-scanning calorimeter, and universal testing machine. Three different kinds of PP copolymers were used: (i) ethylene–propylene (EP) random copolymer; (ii) ethylene–propylene (EP) block copolymer; (iii) ethylene–propylene–buttylene (EPB) terpolymer. In the SEM study of the morphology of films of HDPE with various PP blends, phase separation is observed between the PP phase and the HDPE phase for all blends and compositions. In all blends, HDPE serves to reduce the average spherulites size, probably acting as a nucleating agent for PP. The reduction of spherulite size appeared most significantly in the blend of EPB terpolymer and HDPE. A large increase of crystallization temperature was found in the blend of EPB terpolymer and HDPE compared with the unblended EPB terpolymer. For the blend of EPB terpolymer and HDPE, the improvement of tensile strength and modulus is observed with an increase of HDPE content, and this can be considered as a result of the role of HDPE in reducing average spherulite size. © 1994 John Wiley & Sons, Inc.     

Mechanical properties and morphology of polyethylene–polypropylene blends with controlled thermal history

The effect of time–temperature treatment on the mechanical properties and morphology of polyethylene–polypropylene (PE–PP) blends was studied to establish a relationship among the thermal treatment, morphology, and mechanical properties. The experimental techniques used were polarized optical microscopy with hot‐stage, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and tensile testing. A PP homopolymer was used to blend with various PEs, including high‐density polyethylene (HDPE), low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and very low density polyethylene (VLDPE). All the blends were made at a ratio of PE:PP = 80:20. Thermal treatment was carried out at temperatures between the crystallization temperatures of PP and PEs to allow PP to crystallize first from the blends. A very diffuse PP spherulite morphology in the PE matrix was formed in partially miscible blends of LLDPE–PP even though PP was present at only 20% by mass. Droplet‐matrix structures were developed in other blends with PP as dispersed domains in a continuous PE matrix. The SEM images displayed a fibrillar structure of PP spherulite in the LLDPE–PP blends and large droplets of PP in the HDPE–PP blend. The DSC results showed that the crystallinity of PP was increased in thermally treated samples. This special time–temperature treatment improved tensile properties for all PE–PP blends by improving the adhesion between PP and PE and increasing the overall crystallinity. In particular, in the LLDPE–PP blends, tensile properties were improved enormously because of a greater increase in the interfacial adhesion induced by the diffuse spherulite and fibrillar structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1151–1164, 2000     

Study on the Phase Behavior of High Density Polyethylene – Ethylene Octene Copolymer Blends

The processes of melting and crystallization of blends based on HDPE and EOC were investigated. DSC thermograms showed that a separate crystallization and co‐crystallization occurred in the blends studied. Avrami approach was used to analyze the kinetics of crystallization in the blends. It is shown that the Avrami exponent depends on the EOC concentration of the samples studied. The difference in the Avrami parameters for HDPE, EOC and the blends indicated that the nucleation mechanism and dimension of the spherulite growth of the blends were different from that of HDPE to some extent. The crystal growth was examined in the context of the Lauritzen‐Hoffman theory. DSC traces obtained at different cooling rates were used for analyzing the non‐isothermal crystallization. It was found that the Ozawa model was rather inapplicable for the materials studied. In contrast, the Avrami equation modified by Jeziorny can be used more efficiently to describe the non‐isothermal crystallization behavior of HDPE‐EOC blends.

     

Crystallization kinetics of thermoplastic elastomeric blends based on ground tyre rubber

This work analyzes the crystallization process of thermoplastic elastomeric blends (TPE) based on ground tyre rubber (GTR). More specifically it analyzes the effect of GTR and fresh rubber materials, like ethylene propylene diene monomer (EPDM) and ethylene propylene rubber (EPR), on the crystallization of binary and ternary polypropylene (PP)‐based blends. The crystallization kinetics is studied under isothermal and nonisothermal conditions using differential scanning calorimetry (DSC). The kinetic parameters derived from the Avrami model are used to study the effect of temperature and rubber materials on the nucleation mechanism, the morphology of the crystalline structures, and the crystallization rate. Results reveal that GTR has a strong nucleating effect on PP and that its presence leads to higher crystallization rates. The EPDM presence has a slight effect on the PP crystallization process whereas EPR has no significant effect. From the DSC curves it is possible to detect an inverse relationship between temperature and the crystallization rate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42589.     

Morphology and nonisothermal crystallization behavior of PP/Novolac blends

The morphology and nonisothermal crystallization behavior of PP/Novolac blends were studied with scanning electron microscopy, differential scanning calorimeter, polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). The results showed that the crystallization of PP in PP/Novolac blends was strongly influenced by cooling rate, size of Novolac particles, crosslinking, and compatibilizer maleic anhydride‐grafted PP (MPP). In dynamically cured PP/MPP/Novolac blends, the MPP grafted on the surface of cured Novolac particles and formed a chemical linkage through the reaction of anhydride groups with the hexamethylenetetramine. The graft copolymer not only improved interfacial compatibility but also acted as an effective heterogeneous nucleating agent, which accelerates the crystallization of PP. The combination of Avrami and Ozawa equations exhibited great advantages in treating the nonisothermal crystallization kinetics in dynamically cured PP/MPP/Novolac blends. The POM results showed that the spherulite morphology and the size of PP in PP/MPP/Novolac blends were greatly affected by Novolac. WAXD experiment demonstrates that the PP and dynamically cured PP/MPP/Novolac blends showed only the α crystal form. At the same time, the addition of Novolac resin also affects the crystal size of PP. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Morphology prediction and the effect of core‐shell structure on the rheological behavior of PP/EPDM/HDPE ternary blends

In this work, the morphologies of polypropylene (PP)/ethylene‐propylene‐diene (EPDM) rubber/high density polyethylene (HDPE) 70/20/10 blends were studied and compared with the predictions of the spreading coefficient and minimum free energy models. The interfacial tension of PP/HDPE, PP/EPDM, and HDPE/EPDM blends were obtained by fitting the experimental dynamic storage modulus data to Palierne's theory. The prediction results showed core‐shell morphology (core of HDPE and shell of EPDM) in PP matrix. The PP/EPDM/HDPE blends were respectively prepared by direct extrusion and lateral injection method. Core‐shell morphology (core of HDPE and shell of EPDM) could be obtained with direct extrusion corresponding to the predicted morphology. The morphology of PP/EPDM/HDPE blends could be effectively controlled by lateral injection method. For PP/EPDM/HDPE blend prepared by lateral injection method, HDPE and EPDM phase were dispersed independently in PP matrix. It was found that the different morphology of PP/EPDM/HDPE blends prepared by two methods showed different rheological behavior. When the core‐shell morphology (core of HDPE and shell of EPDM) appeared, the EPDM shell could confine the deformation of HDPE core significantly, so the interfacial energy contribution of dispersed phase on the storage modulus of blends would be weaken in the low frequency region. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers