Rheological and thermal properties of binary blends of polypropylene and poly(ethylene‐CO‐1‐octene)

Dynamic viscoelastic properties of binary blends consisting of an isotactic polypropylene (i‐PP) and ethylene‐1‐octene copolymer (PEE) were investigated to reveal the relation between miscibility in the molten state and the morphology in the solid state. In this study, PEE with 24 wt % of 1‐octene was employed. The PEE/PP blend with high PEE contents showed two separate glass‐relaxation processes associated with those of the pure components. These findings indicate that the blend presents a two‐phase morphology in the solid state as well as in the molten state. The PEE/PP blend with low PEE content showed a single glass‐relaxation process, indicating that PEE molecules were probably incorporated in the amorphous region of i‐PP in the solid state. The DMTA analysis showed that the blends with low PEE contents presented only one dispersion peak, indicating a certain degree of miscibility between the components of these blends. These results are in accordance with the results of the rheological analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1634–1639, 2001     

Solvothermal process for grafting dibutylmaleate onto poly(ethylene‐co‐1‐octene)

Solvothermal process was successfully developed to graft dibutylmaleate (DBM) onto poly(ethylene‐co‐1‐octene) (POE) with dicumyl peroxide (DCP) as free radical‐initiator. FTIR spectra demonstrate that DBM is successfully grafted onto the backbone of POE by this novel method. The influences of DBM content, DCP concentration, POE concentration, reaction temperature and reaction time on the grafting copolymerization have been investigated in detail through grafting degree (GD). It is worthy to indicate that high grafting degree (above 15%) can be achieved through the one‐pot way when the graft reaction is carried out in 40 mL toluene at 150°C for 5 h with 1.6 g DBM, 6–8 g POE and 0.35 g DCP. This developed solvothermal process is becoming an effective way to prepare POE‐g‐DBM graft copolymers, and can be extended to other systems. In addition, TGA results show that the thermal properties of POE are enhanced after the grafting reaction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystallization behavior and mechanical properties of polypropylene random copolymer/poly(ethylene‐octene) blends

New polymer blends of polypropylene random copolymer (PP‐R) and poly(ethylene‐octene) (POE) were prepared by melt‐blending process using a corotating twin‐screw extruder. The POE content was varied up to 35%. The toughening efficiency of POE for PP‐R was evaluated by the mechanical properties of the resulted PP‐R/POE blends. The crystallization behavior and morphology of the blends were also studied. Results show that POE acts as nucleation agent to induce the crystallization of PP‐R matrix at higher crystallization temperature. Super‐toughened PP‐R/POE blends (Izod impact strength more than 500 J/m) can be readily achieved with only 10 wt % of POE. The high toughness of PP‐R/POE is attributed to cavitation and shear yielding of matrix PP‐R, as revealed by the morphology studies. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Poly(ethylene‐co‐vinyl acetate) blends with phenoxy

EVA was blended with phenoxy over the whole range of composition using a twin‐screw Brabender. Two‐phase separation caused by EVA crystallization was observed in the EVA‐rich blends and the dispersed domain of EVA was not clearly shown in the phenoxy‐rich blends. Differential scanning calorimetry (DSC) showed that the glass transition temperature (T_g) of EVA was increased by 5–10°C in the EVA‐rich blends but the T_g of phenoxy was superposed over the melting behavior of EVA. X‐ray diffraction measurement indicated that EVA crystallization was restricted in the phenoxy‐rich blends and the EVA crystal structure was influenced by incorporation of phenoxy into the EVA‐rich blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 227–236, 1999     

The effectiveness of magnesium carbonate‐based flame retardants for poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐ethyl acrylate)

In this report we outline recent work on the evaluation of magnesium carbonate‐based flame retardants for polymers commonly used in halogen‐free flame retardant wire and cable applications: poly(ethylene‐co‐vinyl acetate) (EVA) and poly(ethylene‐co‐ethyl acrylate) (EEA). Natural magnesium carbonate (magnesite), synthetic magnesium carbonate (hydromagnesite), and hydromagnesite/huntite blends were combined with EVA or EEA and tested for flame retardancy effectiveness with the cone calorimeter. The flammability results showed that the effectiveness of these carbonates was polymer dependent, suggesting that polymer degradation chemistry played a role in the flammability reduction mechanism. Hydromagnesites were, in general, more effective in reducing flammability, being comparable in performance to magnesium hydroxide. Finally, we report some polymer–clay (organically treated montmorillonite and magadiite) + magnesium carbonate flame retardant results which showed that the nanocomposite yielded mixed results. Specifically, the polymer–clay nanocomposite samples did not always yield the greatest reductions in peak heat release rate. Copyright © 2007 John Wiley & Sons, Ltd.     

Use of pyrolyzed oil shale as filler in poly(ethylene‐co‐vinyl acetate) with different vinyl acetate contents

Pyrolyzed oil shale (POS) obtained from the pyrolysis of bituminous rock was used as filler in poly(ethylene‐co‐vinyl acetate) (EVA). The effects of the VA content of EVA and the particle size of POS on the mechanical properties were investigated. The composites were prepared in a rotor mixer at 180°C with a concentration of POS of up to 30 wt %. The stress–strain plots of the compression‐molded composites are similar to the EVA (18% VA content) behavior for low concentrations (1–5 wt %) of POS with a particle size lower than 270 mesh. It was observed that decreasing the POS particle size and increasing the VA content of EVA produced better compatibility between the polymer and filler. The mechanical properties, differential scanning calorimetry, and dynamic mechanical analysis also demonstrated the compatibility between EVA and POS under the increase of the VA content in the EVA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1544–1555, 2002; DOI 10.1002/app.10494     

Evaluation of mechanical properties and physical interactions of a ternary blend of poly(ethylene‐co‐octene)/poly(ethylene‐co‐vinyl acetate)/poly(vinyl chloride) in the molten state

In this work, ethylene‐co‐vinyl acetate (EVA), poly(ethylene‐co‐octene) (POE), and poly(vinyl chloride) (PVC) blends were processed in a molten state process using a corotating twin‐screw extruder to assess both the balance of mechanical properties and physical interactions in the melt state. Tensile measurements, scanning electron microscopy, and oscillatory rheometry were performed. By means of flow curves, the parameters of the power law as well as the distribution of relaxation times were assessed with the aid of a nonlinear regularization method. The mechanical properties for the EVA‐POE blend approximated the values for POE, while inclusion of PVC shifted the modulus values to those of neat EVA. The rise in modulus was corroborated by the PVC phase dispersion as solid particles that act as a reinforcement for the ternary blend. The rheological properties in the molten state show that the POE does not present molecular entanglement effects and so tends both to diminish the EVA mechanical properties and increase the fluidity of the blend. However, the addition of PVC both restored the EVA typical pseudoplastic feature and promoted the increase in the viscosity and the mechanical properties of the ternary blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Morphology and mechanical properties of binary blends of polypropylene with statistical and block ethylene‐octene copolymers

In the present work, statistical (EOCs) and block (OBCs) ethylene‐octene copolymers, with similar densities and crystallinities, were used as impact modifiers of isotactic polypropylene (iPP), and the toughening effects of these two types of elastomers were compared. The viscosity curves of EOCs were similar to those of OBCs with equivalent melt flow rate (MFR), enabling a comparison of the viscosity ratio and elastomer type as independent variables. No distinct differences on the crystal forms and crystal perfection of iPP matrix in various blends were observed by thermal analysis. Morphological examination showed that OBCs form smaller dispersed domains than EOCs with similar MFRs. The flexural modulus, yield stress, stress and strain at break showed the same variation tendency for all the investigated polypropylene/elastomer blends. However, the room temperature Izod impact toughness of iPP/OBC blend was higher than that of iPP/EOC blend containing elastomer with the similar MFRs. The experimental results indicated that the compatibility of iPP/OBCs was much higher than that of iPP/EOCs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure development in melt spinning of poly(ethylene‐co‐octene) filaments with various comonomer contents

An experimental study of the spinnability and the variation in crystallinity and orientation of melt spinning of poly(ethylene‐co‐octene) with different contents of comonomers was carried out. The spinning behavior of these polymers was investigated under different draw‐down ratios and temperatures and correlated to spinline stress. The melt‐spun filaments were characterized by wide‐angle X‐ray diffraction birefringence, and differential scanning calorimetry. S‐1 is a high‐density polyethylene and S‐2, S‐3, and S‐4 have 16, 22, and 38 wt % octene. An orthorhombic unit cell was found in all four polymers, but a dominant hexagonal structure (perhaps mesophase) was found for the highest octene level (S‐4). The orientation factors for the a‐, b‐, and c‐axis of the orthorhombic crystal structure and a‐axis of the hexagonal phase were then calculated. The crystalline orientation behavior of the lower octene copolymers (S‐1, S‐2, and S‐3) are similar and can be represented as a “row‐nucleated“ structure. However, the orientation behavior of S‐4 was different. The uniaxial mechanical properties were also measured. The Young's modulus and tensile strength generally increased with birefringence for all polymers. With increasing content of octene, the Young's modulus showed a decrease from semicrystalline thermoplastic toward an elastomer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 9–22, 2004     

Viscoelasticity and morphology of poly(ethylene‐co‐vinyl acetate)/polyisobutylene blends

Blends of an ethylene/vinyl acetate copolymer (EVA) and polyisobutylene of various compositions were prepared by mechanical mixing at a temperature above the melting point of EVA (T_m^EVA) but below the upper critical solution temperature of 170°C for given blends. The rheological properties of the components and blends were studied in the region of small‐amplitude oscillating deformation at temperatures above and below T_m^EVA in the frequency range of 0.01–100 rad/s. At temperatures lower than T_m^EVA, the rheological properties were determined by the existence of the yield stress. With diminishing frequency, the viscosity increased, and the plateau in the relaxation spectrum at low frequencies broadened. The morphology of the blends depended on the conditions of sample heating. The introduction of a finely dispersed filler into the blends led to an anomalous drop in the viscosity. The morphology of the systems that arose by mechanical blending of the molten components was the important factor in the rheological behavior. The observed effects were examined in the framework of the concept of structural networks formed in melts by nonmelted crystallites of EVA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2700–2707, 2006     

Silane‐modified poly(ethylene‐co‐vinyl acetate): influence of comonomers on peroxide‐initiated vinylsilane grafting

Functionalization of poly(ethylene‐co‐vinyl acetate) (EVA) with vinyltriethoxysilane (VTEOS) has been carried out by a free‐radical melt‐grafting procedure in the presence of added comonomers. The influence of comonomers on silane graft yield and crosslink density has been assessed. Experiments were performed on masterbatches of EVA, VTEOS (5 wt %), peroxide initiator (L‐231, 0.05 wt %), and comonomer (0–1 comonomer : VTEOS mole ratio) prepared at 90°C. Melt‐grafting experiments were carried out at 145°C in an oscillating disk rheometer (ODR), which measured crosslink density during the grafting process. Silane graft yields were determined by proton NMR spectroscopy. Comonomers evaluated were maleic anhydride (MAn), 1‐vinyl‐2‐pyrrolidone (VP), and 1‐dodecene (DD). At the comonomer ratios examined, MAn suppressed both silane grafting and peroxide‐initiated crosslinking. Both VP and DD, however, exhibited greater selectivity in suppressing crosslinking than silane grafting; optimum performance was found at a comonomer : vinylsilane mole ratio of 0.2. None of the comonomers studied enhanced the level of silane grafting. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1308–1314, 2000     

Preparation and characterization of blends of high density polyethylene and poly(ethylene‐co‐1‐octene) elastomer

Mechanical, thermal, and morphological properties of blends of high density polyethylene and poly(ethylene‐co‐1‐octene) (PEO) were evaluated. The blends were prepared in a single screw extruder at 230°C and 50 rpm with volume fraction of elastomer varying in the range from 0.05 to 0.8. Factors such as chemical similarity and melt viscosity favor the interdiffusion process of phases, resulting in better interfacial adhesion. A synergistic effect on the strength at break and elongation at break for a particular range of blend composition was observed. Blends with a volume fraction of PEO higher than 5% presented a super tough behavior at room temperature. Thermal analysis showed that there is a certain degree of interaction between high density polyethylene and PEO. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1991–1995, 2001     

Improvement of compatibility of poly(ethylene terephthalate) and poly(ethylene octene) blends by γ‐irradiation

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene octene) (POE) were prepared by melt blending with various amounts of trimethylolpropane triacylate (TMPTA). The mechanical properties, phase morphologies, and gel fractions at various absorbed doses of γ‐irradiation have been investigated. It was found that the toughness of blends was enhanced effectively after irradiation as well as the tensile properties. The elongation at break for all studied PET/POE blends (POE being up to 15 wt %) with 2 wt % TMPTA reached 250–400% at most absorbed doses of γ‐irradiation, approximately 50–80 times of those of untreated PET/POE blends. The impact strength of PET/POE (85/15 wt/wt) blends with 2 wt % TMPTA irradiated with as little as 30 kGy absorbed dose exceeded 17 kJ/m², being approximately 3.4 times of those of untreated blends. The improvement of the mechanical properties was supported by the morphology changes. Scanning electron microscope images of fracture surfaces showed a smaller dispersed phase and more indistinct inter‐phase boundaries in the irradiated blends. This indicates increased compatibility of PET and POE in the PET/POE blends. The changes of the morphologies and the enhancement of the mechanical properties were ascribed to the enhanced inter‐phase boundaries by the formation of complex graft structures confirmed by the results of the gelation extraction and Fourier Transform Infrared analyses. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of hydrogen donors on peroxide‐initiated melt grafting of vinylsilane to poly(ethylene‐co‐vinyl acetate)

A technique has been examined for reducing the extent of crosslinking resulting from 1,1‐di(t‐butylperoxy)‐3,3,5‐trimethylcyclohexane (L‐231) initiating melt grafting of vinyltriethoxysilane (VTEOS) onto poly(ethylene‐co‐vinyl acetate) (EVA). Using measurements of crosslink density and VTEOS conversion, a standard of selectivity for the EVA/VTEOS/L‐231 system at 145 °C was defined and used to assess the influence of a range of additives (0.25 mol per mole VTEOS). The data indicated that compounds such as 4‐nonene, N,N‐dimethylaniline, and cumene improve reaction selectivity, whereas dodecane and cyclohexyl acetate have no effect. A strong correlation between the minimum C? H bond dissociation energy and the influence of a given compound is evident, suggesting that a labile C? H bond is the key element of an effective additive. A mechanism of additive function on the basis of hydrogen atom donation is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2397–2402, 2002     

Crystallization and melting behavior of blends comprising poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) and poly(ethylene oxide)

Blends of poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) (PHBV) and poly(ethylene oxide) (PEO) were prepared by casting from chloroform solutions. Crystallization kinetics and melting behavior of blends have been studied by differential scanning calorimetry and optical polarizing microscopy. Experimental results reveal that the constituents are miscible in the amorphous state. They form separated crystal structures in the solid state. Crystallization behavior of the blends was studied under isothermal and nonisothermal conditions. Owing to the large difference in melting temperatures, the constituents crystallize consecutively in blends; however, the process is affected by the respective second component. PHBV crystallizes from the amorphous mixture of the constituents, at temperatures where the PEO remains in the molten state. PEO, on the other hand, is surrounded during its crystallization process by crystalline PHBV regions. The degree of crystallinity in the blends stays constant for PHBV and decreases slightly for PEO, with ascending PHBV content. The rate of crystallization of PHBV decreases in blends as compared to the neat polymer. The opposite behavior is observed for PEO. Nonisothermal crystallization is discussed in terms of a quasi‐isothermal approach. Qualitatively, the results show the same tendencies as under isothermal conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2776–2783, 2006     

Porous composites of hydroxyapatite‐filled poly[ethylene‐co‐(vinyl acetate)] for tissue engineering

A novel porous composite of hydroxyapatite/poly[ethylene‐co‐vinyl acetate)] (HAP/EVA) having better osteointegration was fabricated by gas foaming technique using a non toxic gas blowing agent intended for bone replacement applications. Combined techniques of scanning electronic microscopy (SEM) and X‐ray microcomputed tomography (µCT) analysis showed that the pore size and pore volume of the porous composite decrease with the increase of HAP content. The gravimetric analysis evidenced for good pore interconnectivity within the porous composites. Energy dispersive X‐ray analysis (EDX) studies inveterated the even scattering of Ca ions which in turn indicate the uniform dispersion of HAP particles in the composites. The significant gradation in Ca ion concentration seen in EDX studies is well accordance with the amount of HAP loading in the sample. Mechanical properties of the porous composite having different HAP content were measured to have the compressive strength varying from 1.06 to 2.2 MPa. Non‐cytotoxic character of the material was observed by the cytocompatibility studies. The metabolic activity of L929 cells seeded on the material assessed by [3‐(4,5‐dimethylthiazol)‐2‐yl]‐2,5‐diphenyltertrazolium bromide (MTT) assay was found to be 91.8%. The adhesion and migration of the cells inside the pore walls were visualized by confocal microscopy. Copyright © 2010 Society of Chemical Industry     

Compatibility of low‐density polyethylene/poly(ethylene‐co‐vinyl acetate) binary blends prepared by melt mixing

The compatibility of low‐density polyethylene and poly(ethylene‐co‐vinyl acetate) containing 18 wt % vinyl acetate units (EVA‐18) was studied. For this purpose, a series of different blends containing 25, 50, or 75 wt % EVA‐18 were prepared by melt mixing with a single‐screw extruder. For each composition, three different sets of blends were prepared, which corresponded to the three different temperatures used in the metering section and the die of the extruder (140, 160, and 180°C), at a screw rotation speed of 42 rpm. Blends that contained 25 wt % EVA‐18 were also prepared through mixing at 140, 160, or 180°C but at a screw speed of 69 rpm. A study of the blends by differential scanning calorimetry showed that all the prepared blends were heterogeneous, except that containing 75 wt % EVA‐18 and prepared at 180°C. However, because of the high interfacial adhesion, a fine dispersion of the minor component in the polymer matrix was observed for all the studied blends with scanning electron microscopy. The tensile strengths and elongations at break of the blends lay between the corresponding values of the two polymers. The absence of any minimum in the mechanical properties was strong evidence that the two polymers were compatible over the whole range of composition. The thermal shrinkage of the blends at various temperatures depended mainly on the temperature and EVA‐18 content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 841–852, 2003     

Miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate)/poly(vinyl acetate) blends

The miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (P(HB‐co‐HV))/poly(vinyl acetate) (PVAc) blends have been investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that P(HB‐co‐HV)/PVAc blends were miscible in the melt over the whole compositions. Thus the blend exhibited a single glass transition temperature (T_g), which increased with increasing PVAc composition. The spherulitic morphologies of P(HB‐co‐HV)/PVAc blends indicated that the PVAc was predominantly segregated into P(HB‐co‐HV) interlamellar or interfibrillar regions during P(HB‐co‐HV) crystallization because of the volume‐filled spherulites. As to the crystallization kinetics study, it was found that the overall crystallization and crystal growth rates decreased with the addition of PVAc. The kinetics retardation was primarily attributed to the reduction of chain mobility and dilution of P(HB‐co‐HV) upon mixing with higher T_g PVAc. The overall crystallization rate was predominantly governed by the spherulitic growth rate and promoted by the samples treated with the quenched state because of the higher nucleation density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 980–988, 2006     

Morphological control of porous ethylene‐vinyl acetate copolymer membrane obtained from a co‐continuous ethylene‐vinyl acetate copolymer/poly(ϵ‐caprolactone) blend

Ethylene‐vinyl acetate copolymer (EVA)/poly(?‐caprolactone) (PCL) blend (50/50 w/w) with co‐continuous morphology was prepared via melt mixing for fabricating microporous EVA membrane materials through selective solvent extraction. Shear flow and quiescent annealing techniques were employed to control co‐continuous phase size in the EVA/PCL blend, and the time‐ and temperature‐dependent relations of phase size were then evaluated theoretically. Using these techniques, microporous EVA membrane materials with various pore sizes ranging from 2 µm to more than 200 µm were obtained. In contrast to the porous EVA membrane prepared by the traditional way of solvent casting/particulate leaching, the as‐obtained microporous membrane shows a higher level of interconnectivity and much narrower pore size distribution with uniform pore structure. © 2013 Society of Chemical Industry     

Effects of ethylene content of poly(ethylene‐co‐vinyl alcohol) on diameter of fibers produced by melt‐electrospinning

Rodlike samples were made from four kinds of poly(ethylene‐co‐vinyl alcohol) (EVAL) pellets with different ethylene contents. From these rodlike samples, fibers were produced using a melt‐electrospinning system equipped with a CO₂‐laser melting device. The effects on the fiber diameter of the ethylene content and the moisture regain of the rodlike samples were investigated. Furthermore, the physical properties of the fibers were investigated. The following conclusions were reached: (i) EVAL fibers having an average fiber diameter smaller than 1 μm can be obtained using the system developed; (ii) the diameter of EVAL fiber is influenced by the ethylene content and the moisture regain of the starting rods; (iii) the laser heating does not greatly decrease the melting point and the molecular weight of EVAL; and (iv) preferred crystal orientation can be seen in electrospun EVAL fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1368–1375, 2007