Structure development and viscoelastic properties in silane‐crosslinked ethylene–octene copolymer

The development of structure and viscoelastic properties during silane crosslink reaction in metallocene ethylene–octene copolymer has been investigated. Using attenuated and transmission infrared spectroscopy, the concentrations of certain functional groups and change in sample thickness were monitored, giving the information on the progress of crosslink reaction. The evolution of crosslink content and viscoelastic properties was analyzed using a parallel‐plate rheometer. The results showed that crosslinking process started with the hydrolyzation of methoxy groups in the near‐surface layer, proceeding in a diffusion manner. At this stage no silanol groups could be detected, revealing that the condensation occurred promptly after hydrolyzation. The internal crosslink could not begin until there are sufficient water molecules in the surrounding. A water by‐product from the condensation reaction played an essential part in the center region. The rheological data showed a reduction in magnitude of creep compliance. As the reaction proceeded, more networks took place within an existing gel. The materials, then, acted more like elastic and exhibited an improvement in ability for recovery process. The immobilization of chain segments, due to the presence of tight network, disallowed conformations necessary for crosslink reaction and a certain amount of hydrolyzable groups and silanol groups remained after a long crosslinking process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal stability of polyoxymethylene and its blends with poly(ethylene‐methylacrylate) or poly(styrene‐butadiene‐styrene)

Polyoxymethylene (POM) copolymer and its blends with poly(ethylene‐methylacrylate) (EMA) or poly(styrene‐butadiene‐styrene) (SBS) up to 5 wt % were conducted to thermooxidative ageing in oven at 140°C for 111 days. POM showed continued degradation as seen from the gradual decrease in the crystallization temperature from differential scanning calorimetry (DSC) study, while no change in Fourier transform infrared spectra (FTIR) and low weight loss were observed (2.5% after 111 days' ageing). The POM degradation was characterized by the initial increase of crystallinity due to crystal perfection, which then kept nearly unchanged until 35 days' ageing, and lastly increased again to result in embrittlement and decrease in tensile strength. Increase in the tensile stress and strain was observed up to 35 days' ageing. POM blends with SBS or EMA had similar degradation behavior as POM, but addition of SBS accelerated the POM degradation significantly, while POM blend with 1 or 3% EMA just showed slightly lower thermal stability than POM. Degradation in POM and SBS/POM occurred in amorphous phase while EMA/POM degraded in both amorphous and crystal phase. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic rheological and morphological study of the compatibility of thermoplastic polyurethane/ethylene–octene copolymer blends

Two grafted ethylene–octene copolymers [POEs; i.e., POE‐g‐maleic anhydried (MAH) and aminated POE (denoted by POE‐g‐NH₂) were used as compatibilizers in immiscible blends of thermoplastic polyurethane (TPU) and POE. The effects of the compatibilizers on the dynamic rheological properties and morphologies of the TPU/POE blends were investigated. The characteristic rheological behaviors of the blends indicated that the strong interactions between the two phases were due to the compatibilization. Microstructural observation confirmed that the compatibilizers were located at the interface in the blends and formed a stable interfacial layer and smaller dispersed phase particle size. Compared with POE‐g‐MAH, POE‐g‐NH₂ exhibited a better compatibilization effect in the TPU/POE blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal and crystallization behavior of silane‐crosslinked polypropylene

Silane‐crosslinked polypropylene (PP) has been prepared first by the grafting of silane onto the backbone of PP in a melt process and then by crosslinking in warm water. The effects of type and concentration of silane and peroxide on the silane grafting on PP were investigated. The thermal behavior of the silane‐crosslinked PP was studied by thermogravimetric (TG) and differential scanning calorimetry (DSC) methods. TG results show that PP prepared via silane crosslinking increases its thermal stability greatly. It has been found from DSC measurements that the crystallization temperatures, ie the onset temperature and peak temperature of the exotherm of the silane‐crosslinked PP, increase compared with those of the pure PP. The silane crosslinking hardly changes the crystallinity degree of PP. The crystallization behavior of the silane‐crosslinked PP was also studied by wide‐angle X‐ray diffraction analysis. Copyright © 2004 Society of Chemical Industry     

Melting,nonisothermal crystallization behavior and morphology of polypropylene/random ethylene—propylene copolymer blends

The melting, nonisothermal crystallization behavior and morphology of blends of polypropylene (PP) with random ethylene–propylene copolymer (PP‐R) were studied by differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy, and X‐ray diffraction. The results showed that PP and PP‐R were very miscible and cocrystallizable. Modified Avrami analysis was 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 heterogeneous, the growth of the spherulites was tridimensional, and the crystallization mechanism of PP was not affected by PP‐R. The crystallization activation energy was estimated using the Kissinger method. An interesting result was obtained with the modified Avrami analysis and the Kissinger method, whose conclusions were in good agreement. The addition of a minor PP‐R phase favored an increase in the overall crystallization rate of PP. Maximum enhancing effect wass found to occur with a PP‐R content of 20 wt %. The relationship between the composition and the morphology of the blends is discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 670–678, 2006     

Nonisothermal crystallization kinetics of ethylene–butene copolymer/low‐density polyethylene blends

Nonisothermal crystallization kinetics of the blends of three ethylene–butene copolymers with LDPE was studied using differential scanning calorimetry (DSC) and kinetic parameters such as the Avrami exponent and the kinetic crystallization rate (Z_c) were determined. It was found that the pure components and the blends have similar Avrami exponents, indicating the same crystallization mechanism. However, the crystallization rate of the blends was greatly influenced by LDPE. The Z_c of all the blends first increases with increasing LDPE content in the blends and reaches its maximum, then descends as the LDPE content further increases. The crystallization rate also depends on the short‐chain branching distribution (SCBD) of the ethylene–butene copolymers. The Z_c of the pure component with a broad SCBD is smaller, but its blends have a larger crystallization rate due to losing highly branched fractions after blending with LDPE. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 123–129, 2001     

Comparison in processability and mechanical and thermal properties of ethylene–octene copolymer crosslinked by different techniques

The crosslinking of metallocene ethylene–octene copolymer was investigated. The crosslinked polymers were prepared using two different techniques, i.e., peroxide crosslinking and silane–water crosslinking. In the former, the crosslinking reaction was conducted in a twin‐screw extruder, in the presence of dicumylperoxide. In the latter, the polymer was first grafted with vinyl trimethoxysilane in the extruder and subsequently crosslinked with water. The paper aims at investigation of the differences between these two techniques, in terms of processing and product mechanical and thermal properties. The results showed that the silane‐crosslinked polymers could be prepared with much higher gel contents than the peroxide‐crosslinked samples. The silane‐crosslinked polymers also retained the elastomeric characteristics of the pure polymer and showed remarkably higher extensibility, better thermal stability, and energy storage capacity. An explanation for the property differences between peroxide‐crosslinked and silane‐crosslinked polymers was proposed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1179–1185, 2004     

Modeling of flow‐induced crystallization in blends of isotactic polypropylene and poly(ethylene‐co‐octene)

Poly(ethylene‐co‐octene) (PEOc) has been shown to provide a high toughening contribution to isotactic polypropylene (iPP). The theoretical modeling of flow‐induced crystallization (FIC) of blends of iPP and PEOc is not much reported in the literature. The aim of the present work is to clarify the FIC of iPP upon addition of PEOc in terms of theoretical modeling. The crystallization of iPP and PEOc blends in flow is simulated by a modified FIC model based on the conformation tensor theory. Two kinds of flow fields, shear flow and elongational flow, are considered in the prediction to analyze the influence of flow field on the crystallization kinetics of the polymer. The simulation results show that the elongation flow is much more effective than shear flow in reducing the dimensionless induction time of polymer crystallization. In addition, the induction time of crystallization in the blends is sensitive to the change of shear rate. In comparison with experimental data, the modified model shows its validity for the prediction of the induction time of crystallization of iPP in the blends. Moreover, the simulated relaxation time for the blends becomes longer with increasing percentage of PEOc in the blends. Copyright © 2012 Society of Chemical Industry     

Rheological,mechanical, thermal,and morphological properties of polypropylene/ethylene‐octene copolymer blends

Rheological and morphological studies were performed on polymer blends of ethylene‐octene copolymer [polyethylene elastomer (PEE)] and polypropylene (PP). The viscosities of PEE, PP, and PEE/PP blends were analyzed using an Instron capillary rheometer and a Rheometrics Dynamic Stress Rheometer, SR 200. A non‐Newtonian flow behavior was observed in all samples in the shear rate range from 27 to 2700 s⁻¹, whereas at shear rates in the range from 0.01 to 0.04 s⁻¹, a Newtonian flow behavior was verified. The scanning electron micrographs showed that dual‐phase continuity may occur between 50 and 60 (wt %) of PEE. This result is consistent with the Sperling's model. The mechanical analysis showed that PEE/PP, with 5 wt % of PEE, presented an increase on the mechanical properties and as the PEE content increased, a negative deviation in relation to an empirical equation was observed. Thermal analysis showed that there were no change in the crystallization behavior of the matrix when different elastomer contents were added. Dynamic mechanical thermal analysis showed that samples with low PEE contents presented only one peak, indicating a certain degree of miscibility between the components of these blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 692–704, 2000     

Thermal property improvement of ethylene‐octene copolymer through the combined introduction of filler and silane crosslink

In many applications, e.g., wire and cable insulation, hot water pipe, high‐temperature properties of polymer are essential. This article presents the use of silane crosslinking together with the addition of particular filler in improving the thermal and mechanical properties of ethylene‐octene copolymer (EOC). The effects of filler surface characteristics on siloxane network structure developed and final properties of the crosslinked products are discussed. The results show an increase in the decomposition temperature of EOC more than 50°C after modification. Only crosslinked composites are able to withstand the high‐temperature environment of aging test which is beyond the melting temperature of the matrix polymer. The crosslinked composites filled with calcium carbonate show superior properties to those with silica, due to a higher crosslink density and tighter network structure formed. The silane coupling mechanism and the presence of bound polymer on silica surfaces cause difficulties for the crosslink formation in the silica filled systems. However, an advantageous influence of both silane coupling and crosslink reaction in the silica filled composites is seen on the enhanced tensile strength and modulus of the materials. © 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     

Thermal,mechanical, and surface characterization of starch–poly(vinyl alcohol) blends and borax‐crosslinked films

Starch–poly(vinyl alcohol) (PVA) blends with different compositions were prepared and crosslinked with borax by in situ and posttreatment methods. Various amounts of glycerol and poly(ethylene glycol) with a molecular weight of 400 were added to the formulations as plasticizers. The pure starch–PVA blends and the crosslinked blends were subjected to differential scanning calorimetry, thermogravimetry, and X‐ray photoelectron spectroscopic studies. Broido and Coats–Redfern equations were used to calculate the thermal decomposition kinetic parameters. The tensile strengths and elongation percentages of the films were also evaluated. The results suggested that the glass‐transition temperature (T_g) and the melting temperature strongly depended on the plasticizer concentration. The enthalpy relaxation phenomenon was dependent on the starch content in the pure blend. The crosslinked films showed higher stability and lower T_g's than pure PVA and starch–PVA blends, respectively. High‐resolution X‐ray photoelectron spectroscopy provided a method of differentiating the presence of various carbons associated with different environments in the films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1313–1322, 2005     

Effect of hot air aging on the properties of ethylene‐vinyl acetate copolymer and ethylene‐acrylic acid copolymer blends

The aim of this investigation is to evaluate the effect of hot air aging on properties of ethylene‐vinyl acetate copolymer (EVA, 14 wt % vinyl acetate units), ethylene‐acrylic acid copolymer (EAA, 8 wt % acrylic acid units), and their blends. Attenuated total reflection‐Fourier transform infrared spectroscopy, differential scanning calorimeter (DSC), wide angle X‐ray diffraction, and mechanical tests are employed to investigate the changes of copolymer blends' structures and properties. Increase of carbonyl index derived from ATR measurements with aging time suggests the incorporation of oxygen into the polymeric chain. By DSC measurements, the enthalpy at low temperature endothermic peak (T_m2) of EAA becomes less and disappears after 8 weeks aging, but enthalpy at T_m2 of EVA is not influenced by the hot air aging and remains stable despite of the aging time. For various proportions of EAA and EVA blends, enthalpy at T_m2 decreases as the EAA proportion increases when aging time is 8 weeks; after several weeks of hot air aging, the various blends appear a same new peak just over the aging temperature 70°C which is due to the completion of crystals which are not of thermodynamic equilibrium state. Mechanical tests show that increase of crystallinity and hot air aging deterioration both have influence on the hardness, tensile strength, and elongation at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Crystallization behavior of partially crosslinked poly(β‐hydroxyalkonates)/poly(butylene succinate) blends

Partially crosslinked poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)/poly(butylene succinate) (PHBV/PBS) and poly(β‐hydroxybutyrate)/poly(butylene succinate) (PHB/PBS) blends were prepared by melt compounding with dicumyl peroxide. The effect of partial crosslinking on crystallization of the PHBV/PBS and PHB/PBS blends was investigated systematically. Differential scanning calorimetry results showed that the overall crystallization rates of both PHBV and PBS in their blends were enhanced considerably by the partial crosslinking. Similar results were also detected in the PHB/PBS blends. The polarized optical microscope observation displayed that the nuclei density of PHBV was increased while the spherulitic morphology did not change much. Conversely, the PBS spherulites turned into cloud‐like morphology after the partial crosslinking which is a result of the decrease in spherulite size, the reduction in interspherulite distance and the interconnection of fine PBS domains. Wide angle X‐ray diffraction patterns confirmed the enhancement in crystallization of the PHBV/PBS blends after the partial crosslinking without modification on crystalline forms of the PHBV and PBS components. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41020.     

Rheology,structure, and properties of ethylene–vinyl acetate/metallocene‐catalyzed ethylene–α‐olefin copolymer blends

The rheology, morphology, thermal, mechanical, and adhesive properties of blends containing ethylene–vinyl acetate and metallocene‐catalyzed ethylene–α‐olefin copolymers, containing butene and octene comonomers, were investigated. On the basis of the thermal and rheological properties and scanning electron microscopy observations, we deduced that these blends were immiscible, both in the solid and melt states over the whole range of compositions. Rheological properties were correlated to blend morphology with the Palierne emulsion model. The butene‐based blends had better mechanical properties, which was attributed to their finer morphology, lower interfacial tension, and better adhesive properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 881–889, 2004     

Properties of dynamically vulcanized ethylene–propylene–diene copolymer/polypropylene blends

In this study, vulcanized thermoplastic elastomers were produced through the formation of crosslinks with peroxide for different ratios of ethylene–propylene–diene copolymer to polypropylene. Mixing was performed with a twin‐screw extruder. Afterward, the yield, tensile strength, elastic modulus, elongation, Izod impact strength, hardness, melt flow index, Vicat softening point, heat deflection temperature, and density of the crosslinks were determined. The thermal transition temperatures and microstructure were determined with differential scanning calorimetry and scanning electron microscopy, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3895–3902, 2007     

Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Isothermal crystallization

Poly(ethylene‐octene) (POE), maleic anhydride grafted poly(ethylene‐octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE, PBT/mPOE, and PBT/mPOE/POE blends by a twin‐screw extruder. Observation by scanning electron microscopy revealed improved compatibility between PBT and POE in the presence of maleic anhydride groups. The melting behavior and isothermal crystallization kinetics of the blends were studied by wide‐angle X‐ray diffraction and differential scanning calorimeter; the kinetics data was delineated by kinetic models. The addition of POE or mPOE did not affect the melting behavior of PBT in samples quenched in water after blending in an extrude. Subsequent DSC scans of isothermally crystallized PBT and PBT blends exhibited two melting endotherms (T_mI and T_mII). T_mI was the fusion of the crystals grown by normal primary crystallization and T_mII was the melting peak of the most perfect crystals after reorganization. The dispersed second phase hindered the crystallization; on the other hand, the well dispersed phases with smaller size enhanced crystallization because of higher nucleation density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystal structure transformations and orientation in crosslinked elastic fibers of an ethylene‐octene copolymer in response to deformation and heat treatment

Crosslinked elastic fibers, made from a low density (0.875 g/cc) ethylene‐octene copolymer, were studied after constrained at 300% elongation and annealed at different temperatures (40–80°C) to simulate conditions encountered in yarn and textile processing. It is surprisingly found that the transition from pseudo hexagonal to orthorhombic structure is much faster under simultaneously constraining and annealing than that without strain. Almost a neat orthorhombic structure can be produced when the fiber is annealed at 60°C. Annealing above 60°C leads to mixed orthorhombic and pseudo‐hexagonal structures. The average melting point increases with an increase in the fraction of orthorhombic phase. It is also surprisingly noted that the simultaneously constraining and annealing of the fiber can produce highly oriented crystals, even annealed at 80°C (above the average melting point of 65°C). The unique effect of annealing under large strain can be attributed to the crosslinking of the fiber, which makes it possible for the fiber to have strong chain orientation (even in molten state) under large strain. The strong chain orientation in melt leads to a faster structural transition from pseudo hexagonal to more stable orthorhombic structure. The strong chain orientation is also very likely the reason why highly oriented crystal and amorphous phases are formed, including the case where the fiber is annealed above melting point. These findings could be leveraged for improving thermal and mechanical properties of the fabrics made with such fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3565–3573, 2013     

Toughening of recycled poly(ethylene terephthalate)/glass fiber blends with ethylene–butyl acrylate–glycidyl methacrylate copolymer and maleic anhydride grafted polyethylene–octene rubber

The aim of this study was to improve the toughness of recycled poly(ethylene terephthalate) (PET)/glass fiber (GF) blends through the addition of ethylene–butyl acrylate–glycidyl methacrylate copolymer (EBAGMA) and maleic anhydride grafted polyethylene–octene (POE‐g‐MAH) individually. The morphology and mechanical properties of the ternary blend were also examined in this study. EBAGMA was more effective in toughening recycled PET/GF blends than POE‐g‐MAH; this resulted from its better compatibility with PET and stronger fiber/matrix bonding, as indicated by scanning electron microscopy images. The PET/GF/EBAGMA ternary blend had improved impact strength and well‐balanced mechanical properties at a loading of 8 wt % EBAGMA. The addition of POE‐g‐MAH weakened the fiber/matrix bonding due to more POE‐g‐MAH coated on the GF, which led to weakened impact strength, tensile strength, and flexural modulus. According to dynamic rheometer testing, the use of both EBAGMA and POE‐g‐MAH remarkably increased the melt storage modulus and dynamic viscosity. Differential scanning calorimetry analysis showed that the addition of EBAGMA lowered the crystallization rate of the PET/GF blend, whereas POE‐g‐MAH increased it. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polypropylene/polypropylene‐grafted acrylic acid copolymer/ethylene–Acrylic acid copolymer ternary blends for hydrophilic polypropylene

Ternary blends of polypropylene (PP), a polypropylene‐grafted acrylic acid copolymer (PP‐g‐AA), and an ethylene–acrylic acid copolymer (EAA) were prepared by melt blending. The surfaces of films with different contents of these three components were characterized with contact‐angle measurements. Scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis were used to characterize the microstructure, melting and crystalline behavior, and thermal stability of the blends. The contact angles of the PP/PP‐g‐AA blends decreased monotonically with increasing PP‐g‐AA content. With the incorporation of EAA, the contact angles of the PP/PP‐g‐AA/EAA ternary blends decreased with increasing EAA content. When the concentration of EAA was higher than 15 wt %, the contact angles of the ternary blends began to increase. Scanning electron microscopy observations confirmed that PP‐g‐AA acted as a compatibilizer and improved the compatibility between PP and EAA in the ternary blends. Differential scanning calorimetry analysis suggested that acrylic acid moieties could act as nucleating agents for PP in the polymer blends. Thermogravimetric analysis and differential thermogravimetry confirmed the optimal blend ratio for the PP/PP‐g‐AA/EAA ternary blends was 70/15/15. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 436–442, 2006