Crystallization,melting behavior,and morphology of BPP/HDPE blend

The crystallization, melting behavior, and morphology of a low ethylene content block propylene–ethylene copolymer (BPP) and a high-density polyethylene (HDPE) blend were studied. It was found that the existence of ethylene–propylene rubber (EPR) in BPP has more influence on the crystallization of HDPE than on that of PP. This leads to the decreasing of the melting temperature of the HDPE component in the blends. It is suggested that the EPR component in BPP shifted to the HDPE component during the blending process. The crystallinity of the HDPE phase in the blends decreased with increasing BPP content. The morphology of these blends was studied by polarized light microscopy (PLM) and SEM. For a BPP-rich blend, it was observed that the HDPE phase formed particles dispersed in the PP matrix. The amorphous EPR chains may penetrate into HDPE particles to form a transition layer. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2469–2475, 1998     

Effect of the addition of EPM copolymers on the properties of high density polyethylene/isotactic polypropylene blends: II. Morphology and mechanical properties of extruded samples

The influence of the addition of two ethylene-propylene random copolymers (EPM) with different composition on the mechanical properties, thermal behavior and overall morphology of high density polyethylene (HDPE)/isotactic polypropylene (iPP) blends, was investigated on extruded samples. The experimental data showed that the morphology of binary HDPE/iPP blends is drastically modified by these additives and that the ultimate mechanical properties of these mixtures are greatly improved. A reasonable explanation of these results can be ascribed to the fact that these copolymers can act as “compatibilizing agents” in the amorphous regions of the two semicrystalline homopolymers. The extent of such effects is dependent on the chemical structure and/or on the molecular mass of the added copolymer as well as on the HDPE/iPP blend compositions.     

Blends of high density polyethylene and ethylene/1‐octene copolymers: Structure and properties

The morphology formation in the blends comprising a high density polyethylene (HDPE) and selected ethylene/1‐octene copolymers (EOCs) was studied with variation of blend compositions using atomic force microscopy (AFM). The binary HDPE/EOC blends studied showed well phase‐separated structures (macrophase separation) in consistence with individual melting and crystallization behavior of the blend components. For the blends comprising low 1‐octene content copolymers, the lamellar stacks of one of the phases were found to exist side by side with that of the another phase giving rise to leaflet vein‐like appearance. The formation of large HDPE lamellae particularly longer than in the pure state has been explained by considering the different melting points of the blend components. The study of strain induced structural changes in an HDPE/EOC blend revealed that at large strains, the extensive stretching of the soft EOC phase is accompanied by buckling of HDPE lamellar stack along the strain axis and subsequent microfibrils formation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1887–1893, 2007     

Adhesion of olefin block copolymers to polypropylene and high density polyethylene and their effectiveness as compatibilizers in blends

Adhesion of four ethylene-octene block copolymers (OBCs) to polypropylene (PP) and high density polyethylene (HDPE) was studied by peeling PP/OBC/HDPE microlayered tapes. The four OBCs had different comonomer composition, mechanical properties and phase morphology. Through the Irwin damage zone analysis, it was found that the stress-strain behavior of OBC was the primary factor that determined the adhesion strength. Effectiveness of these OBCs as compatibilizers in PP/HDPE blends was also investigated. Toughness of all OBC-compatibilized blends was effectively improved. The OBCs having higher adhesion strength also resulted in better mechanical performance for the compatibilized blends. A quantitative correlation was established between the adhesion strength and mechanical performance of the blends.     

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.     

Structure and properties of poly(ethylene terephthalate) crystallized by annealing in the highly oriented state. 3. Dynamic- and static-mechanical properties

Commercial undrawn and cold drawn (5 × ) poly(ethylene terephthalate) (PETP) fibers and bristles have been annealed with fixed ends for 6 h in vacuum at different temperatures between 60 and 260°C. With these samples static- and dynamicmechanical measurements have been carried out. It has been found that the α-and β-processes as well as the moduli depend on the annealing temperature (T_a) in different way, for undrawn and drawn material. The temperature position of the β-peak evaluated from tg δ and loss modulus as well as the step height of α- and β-processes are unsensitive to the T_a for the undrawn material in contrast to the drawn one for which maxima are observed. The appearance of these maxima is explained by the dominating role at the corresponding crystallization temperature of one of the two concurrent processes - crystallization and disorientation, reflected in the change of the effective density of amorphous regions. The dynamic and static measured moduli as well as the stress at break for drawn PETP decrease with the increase of annealing temperature as generally observed. The predominating significance of orientation and the state of amorphous phase in comparison with crystallinity is demonstrated. An extremely high deformation ability at room temperature (up to 200%) of previously drawn and annealed at 255 or 260°C bristles is observed. This originates from the solid state postcondensation and premelting phenomena taking place during annealing in vacuum.     

Thermal properties and crystallization behavior of polyolefin ternary blends

Crystallization behaviors, spherulite growth and structure, and the crystallization kinetics of polypropylene (PP)/ethylene‐α‐olefln copolymer (mPE)/high‐density polyethylene (HDPE) ternary blends and of mPE/HDPE binary blends have been studied using polarizing optical micrography (POM) and differential scanning calorimetry (DSC). In mPE/HDPE blends, large pendant groups of mPE disturbed spherulite growth of HDPE, leading to a different crystallite morphology and isothermal kinetics. Non‐isothermal properties, morphology, and isothermal crystallization kinetics of PP in ternary blends were significantly influenced by the composition and crystallization behavior of the mPE/HDPE binary blends as well as the crystallization condition. Polym. Eng. Sci. 44:1858–1865, 2004. © 2004 Society of Plastics Engineers.     

Crystallization kinetics and tensile modulus of blends of metallocene short‐chain branched polyethylene with conventional polyolefins

In this study, blends of metallocene short‐chain branched polyethylene (SCBPE) with low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), polystyrene (PS), ethylene–propylene–diene monomer (EPDM), and isotactic polypropylene (iPP) were prepared in weight proportions of 80 and 20, respectively. The crystallization behaviors of these blends were studied with polarized light microscopy (PLM) and differential scanning calorimetry. PLM showed that SCBPE/LDPE, SCBPE/HDPE, and SCBPE/EPDM formed band spherulites whose band widths and sizes were both smaller than that of pure SCBPE. No spherulites were observed, but tiny crystallites were observed in the completely immiscible SCBPE/PS, and the crystallites in SCBPE/iPP became smaller; only irregular spherulites were seen. The crystallization kinetics and mechanical properties of SCBPE were greatly affected by the second polyolefin but in different way, depending on the phase behavior and the moduli of the second components. SCBPE may be phase‐miscible in the melt with LDPE, HDPE, and EPDM but phase‐separated during crystallization. A big change in the crystal morphology and crystallization kinetics existed in the SCBPE/iPP blend. The mechanical properties of the blends were also researched with dynamic mechanical analysis (DMA). DMA results showed that the tensile modulus of the blends had nothing to do with the phase behavior but only depended on the modulus of the second component. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1816–1823;2005     

Co‐crystallization in ternary polyethylene blends: tie crystal formation and mechanical properties improvement

Understanding the co‐crystallization behavior of ternary polyethylene (PE) blends is a challenging task. Herein, in addition to co‐crystallization behavior, the rheological and mechanical properties of melt compounded high density polyethylene (HDPE)/low density polyethylene (LDPE)/Zeigler ? Natta linear low density polyethylene (ZN‐LLDPE) blends have been studied in detail. The HDPE content of the blends was kept constant at 40 wt% and the LDPE/ZN‐LLDPE ratio was varied from 0.5 to 2. Rheological measurements confirmed the melt miscibility of the entire blends. Study of the crystalline structure of the blends using DSC, wide angle X‐ray scattering, small angle X‐ray scattering and field emission SEM techniques revealed the formation of two distinct co‐crystals in the blends. Fine LDPE/ZN‐LLDPE co‐crystals, named tie crystals, dispersed within the amorphous gallery between the coarse HDPE/ZN‐LLDPE co‐crystals were characterized for the first time in this study. It is shown that the tie crystals strengthen the amorphous gallery and play a major role in the mechanical performance of the blend.© 2016 Society of Chemical Industry     

Blends of ethylene–octene copolymers with different chain architectures – Morphology,thermal and mechanical behavior

Blends of two elastomeric ethylene–octene copolymers with similar octene contents having a random (ORC) and a blocky architecture (OBC) are prepared by melt mixing. The thermal and mechanical properties of ORC, OBC and their blends are investigated by DSC, dynamic mechanical analysis and tensile tests. The morphology of the semi-crystalline samples is studied by AFM and WAXS. Two types of crystals have been observed: (i) Orthorhombic crystals forming lamellae with an estimated thickness of about 13 nm composed mainly of long polyethylene-like sequences of OBC that melt a temperature of about 120 °C and (ii) fringed micellar crystals with a thickness of 2–4 nm formed basically by short polyethylene-like sequences of ORC that have melting temperatures between 30 and 80 °C. The amorphous phase contains a relatively homogeneous mixture of segments of both components indicated by the relatively uniform shape of the loss modulus peaks from dymamic-mechanical measurements for all investigated copolymers and blends. ORC crystallization is hindered in blends as indicated by lower melting enthalpies. This might be related to the high octene content of the amorphous phase at the relevant crystallization temperature as well as geometrical constraints since ORC crystallization occurs in an already semi-crystalline polymer. The results of tensile tests show that the mechanical behavior can be tailored via blend composition and morphology of the semi-crystalline material. The findings clearly indicate that blending is a powerful strategy to optimize the properties of polyolefin-based copolymers.     

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     

Effect of the viscosity ratio on the morphology and properties of PET/HDPE blends with and without compatibilization

The influence of the molecular weight of polyethylene on the morphology and mechanical properties of blends of high‐density polyethylene (HDPE) dispersed as droplets in a poly(ethylene terephthalate) (PET) matrix at various compositions was investigated. The difference of morphologies can be easily explained by the influence of the molecular weight on the viscosity ratio and therefore, on the critical capillary number. The compatibilizing efficiency of copolymers containing glycidyl methacrylate groups was also addressed in relation to their nature, the protocol for their drying and the molecular weight of the HDPE phase. The increase of adhesion between PET and HDPE was found to have a larger influence on tensile properties than the reduction of interfacial tension. The amount of compatibilizer needed for adhesion improvement depends on the interfacial area that is defined by both the interfacial tension and viscosity ratio of the components. A qualitative relation between the optimum amount of compatibilizer and the critical capillary number can be written. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structure and properties of PP/POE/HDPE blends

This work was aimed to counteract the effect of ethylene‐α‐olefin copolymers (POE) by reinforcing the polypropylene (PP)/POE blends with high density polyethylene (HDPE) particles and, thus, achieved a balance between toughness and strength for the PP/POE/HDPE blends. The results showed that addition of HDPE resulted in an increasing wide stress plateau and more ductile fracture behavior. With the increase of HDPE content, the elongation at break of the blends increased rapidly without obvious decrease of yield strength and Young's modulus, and the notched izod impact strength of the blends can reach as high as 63 kJ/m² at 20 wt % HDPE loading. The storage modulus of PP blends increased and the glass transition temperature of each component of the blends shifted close to each other when HDPE was added. The crystallization of HDPE phase led to an increase of the total crystallinity of the blend. With increasing HDPE content, the dispersed POE particle size was obviously decreased, and the interparticle distance was effectively reduced and the blend rearranged into much more and obvious core‐shell structure. The fracture surface also changed from irregular striation to the regularly distant striations, displaying much obvious character of tough fracture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Epitaxial crystallization of olefin block copolymers (OBCs) on uniaxially oriented isotactic polypropylene and high-density polyethylene films

The epitaxial crystallization behavior of olefin block copolymers (OBCs) on uniaxially oriented isotactic polypropylene (iPP) and high-density polyethylene (HDPE) films has been investigated by transmission electron microscopy (TEM). The crystallizable blocks of the OBCs under investigation were epitaxially nucleated by both iPP and HDPE substrates and epitaxial growth of OBC lamellae was observed. Epitaxial crystallization of the OBCs has been found for slow and fast cooling conditions from the melt which pointed to the strong interaction between the polyolefin substrates and the OBCs. However, the epitaxial morphology of the OBCs strongly depends on their octene concentration difference (Δ_C8) between crystallizable and non-crystallizable blocks, which probably is related to the OBC segregation strength in the melt. With high Δ_C8 the development of epitaxial crystallization of the OBC was restricted within isolated crystalline domains surrounded by the amorphous phase. In contrast, with low Δ_C8 the oriented lamellae of the OBC were distributed homogeneously on iPP but formed separated crystalline domains on HDPE, which has a stronger nucleation capability than iPP on the crystalline OBC blocks because of its similar molecular architecture. Our study points to epitaxy as another reason for the strong interaction between OBC and polyolefins which causes the advanced compatibilization behavior of OBCs when compared with conventional random copolymers.     

Improving poly(ethylene terephthalate)/high-density polyethylene blends by using graft copolymers

The synthesis and the application of graft copolymers prepared from ozonized polyethylene (HDPE) are described. The homopolymer was treated with ozone and then copolymerized with monomers, such as methyl methacrylate, hydroxy ethyl methacrylate, glycidyl methacrylate, maleic anhydride, and ethyl acrylate. The products were used as compatibilizers in HDPE/PET [poly(ethylene terephthate)] blends. The mechanical properties and the influence of graft comonomers are described. The copolymers were characterized by the grafting rate and FTIR spectroscopy.     

Influence of crosslinking on crystallization,rheological, and mechanical behaviors of high density polyethylene/ethylene‐vinyl acetate copolymer blends

High density polyethylene (HDPE)/ethylene‐vinyl acetate copolymer (EVA) blends with selective crosslinking the EVA phase were prepared and the crystallization, rheological, and mechanical behaviors were studied. Selective crosslinking of EVA component could greatly improve both tensile and impact strengths of the HDPE‐rich blends and influence melting enthalpy at different annealing temperature in successive self‐nucleation and annealing procedure. Dynamic mechanical analysis reveals that glass transition temperatures of both the HDPE and EVA components are lowered upon blending and are raised upon crosslinking. The uncrosslinked HDPE/EVA blends are unstable in the melt and show increment in storage modulus (G′) and decay in loss tangent (tanδ) with annealing time associated with phase coarsening. However, morphology of selectively crosslinked blends in the melt state is highly unstable, characterized by a fast migration of uncrosslinked HDPE component out of the crosslinked EVA phase to the surface resulting in a rapid decay in G′ and an increment in tanδ at the early stage of annealing. POLYM. ENG. SCI., 54:2848–2858, 2014. © 2014 Society of Plastics Engineers     

Adhesion of propylene–ethylene copolymers to high‐density polyethylene

The adhesion of some propylene–ethylene (P/E) copolymers to polypropylene (PP) and high density polyethylene (HDPE) was studied in order to compare them with other olefin copolymers as compatibilizers for PP/HDPE blends. A one‐dimensional model of the compatibilized blends was fabricated by layer‐multiplying coextrusion. The microlayered tapes consisted of many alternating layers of PP and HDPE with a thin tie‐layer inserted at each interface. The thickness of the tie‐layer varied from 0.1 to 15 μm, which included thicknesses comparable to those of the interfacial layer in a compatibilized blend. In the T‐peel test, the P/E copolymers delaminated at the HDPE interface. An elastomeric P/E with higher ethylene content exhibited substantially higher delamination toughness than a more thermoplastic P/E with lower ethylene content. Inspection of the crack‐tip damage zone revealed that a change from deformation of the entire tie‐layer to formation of a localized yielded zone was responsible. By treating the damage zone as an Irwin plastic zone, it was demonstrated that a critical stress controlled the delamination toughness. The temperature dependence of the delamination toughness was also measured. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

十八烷基缩水甘油醚的合成及其增容尼龙6/高密度聚乙烯共混体系的研究

利用十八醇和环氧氯丙烷反应合成了十八烷基缩水甘油醚(OGE),并将其作为熔融共混方法中的增容剂,制备了尼龙6(PA6)/高密度聚乙烯(HDPE)共混材料。研究了OGE用量对共混物的热性能、结晶行为、形态结构、力学性能及吸水性的影响。结果表明,OGE促进了HDPE在PA6基体中的分散,在保持共混材料吸水率的同时,有效改善了共混物的力学性能,与未加入增容剂的PA6/HDPE共混物相比,OGE含量为2.9%(m/m)时,共混材料的缺口冲击强度、拉伸模量、断裂伸长率、弯曲强度分别提高了12%、33%、95%、6%,拉伸强度基本保持不变,而弯曲模量下降了8%。     

Effect of copolymers containing glycidyl methacrylate functional groups on the rheological,mechanical, and morphological properties of poly(ethylene terephthalate)

The aim of this work was to investigate the effect of ethylene‐glycidyl methacrylate (EGMA) and ethylene‐methyl acrylate‐glycidyl methacrylate (EMAGMA) copolymers on the rheological, mechanical, and morphological properties of Poly(ethylene terephthalate) (PET). The results of torque rheometry showed an increase in the torque of PET with the addition of EGMA and EMAGMA copolymers due to the reactions between the GMA groups present in the copolymers and the carboxyl and hydroxyl groups present in PET. The torque of PET/copolymer blends increased with the increase in the copolymer content and was more pronounced for the blends containing EGMA copolymer. X‐ray diffraction and differential scanning calorimetry analyzes showed that neat PET and the PET in PET/copolymer blends are amorphous. The addition of EGMA and EMAGMA copolymers delayed the crystallization of PET. Rheological measurements showed an increase in the viscosity at low frequencies with the addition of EGMA and EMAGMA copolymers to PET. This increase was more pronounced for PET/copolymer blends containing higher amount of copolymers and for the blends containing EGMA, corroborating the results obtained by torque rheometry. The impact strength of PET/EMAGMA blends was higher than that of PET/EGMA blends. Morphology analysis by SEM showed that PET/EMAGMA blends presented higher average dispersed phase domains size than PET/EGMA blends. POLYM. ENG. SCI., 59:683–693, 2019. © 2018 Society of Plastics Engineers     

Polymer blends with a crystallizable diblock copolymer: Thermal properties and phase behavior

We report on the thermal behavior of polymer blends comprising a block copolymer and random copolymers of styrene and acrylonitrile (SAN). The block copolymer constituents are ε-caprolactone (CL) and a carbonate. Melting as well as crystallization behavior of the blocks are strongly influenced by addition of amorphous SAN, which is miscible only with PCL block. Blends under discussion can undergo different phase changes as macro- and microphase separation and crystallization. Hence, morphology formation is controlled by different transitions and even a cooperative interplay between them. Phase behavior of the blends is discussed and correlated with results of morphological studies.