Development of nanofibrous morphology in LDPE/LLDPE/PP blends and its effect on mechanical properties of blend films

Nanofibrous morphology has been observed in ternary blends of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) when these were melt‐extruded via slit die followed by hot stretching. The morphology was dependent on the concentration of the component polymers in ternary blend LDPE/LLDPE/PP. The films were characterized by wide angle X‐ray diffraction (XRD), scanning electron microscopy (SEM), and testing of mechanical properties. The XRD patterns reveal that the β phase of PP is obtained in the as‐stretched nanofibrillar composites, whose concentration decreases with the increase of LLDPE concentration. The presence of PP nanofibrils shows significant nucleation ability for crystallization of LDPE/LLDPE blend. The SEM observations of etched samples show an isotropic blend of LDPE and LLDPE reinforced with more or less randomly distributed and well‐defined nanofibrils of PP, which were generated in situ. The tensile modulus and strength of LDPE/LLDPE/PP blends were significantly enhanced in the machine direction than in the transverse direction with increasing LLDPE concentration. The ultimate elongation increased with increasing LLDPE concentration, and there was a critical LLDPE concentration above which it increased considerably. There was a dramatic increase in the falling dart impact strength for films obtained by blow extrusion of these blends. These impressive mechanical properties of extruded samples can be explained on the basis of the formation of PP nanofibrils with high aspect ratio (at least 10), which imparted reinforcement to the LDPE/LLDPE blend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological and mechanical properties in polyethylene blends

Melt rheology and mechanical properties in linear low density polyethylene (LLDPE)/low density polyethylene (LDPE), LLDPE/high density polyethylene (HDPE), and HDPE/LDPE blends were investigated. All three blends were miscible in the melt, but the LLDPE/LDPE and HDPE/LDPE blends exibiled two crystallization and melting temperatures, indicating that those blends phase separated upon cooling from the melt. The melt strength of the blends increased with increasing molecular weight of the LDPE that was used. The mechanical properties of the LLDPE/LDPE blend were higher than claculated from a simple rule of mixtures, whiele those of the LLDPE/HDPE blend conformed to the rule of mixtures, but the properties of HDPE/LDPE were less than the rule of mixtures prediction.     

Modification of recycled high‐density polyethylene by low‐density and linear‐low‐density polyethylenes

The present study investigated mixed polyolefin compositions with the major component being a post‐consumer, milk bottle grade high‐density polyethylene (HDPE) for use in large‐scale injection moldings. Both rheological and mechanical properties of the developed blends are benchmarked against those shown by a currently used HDPE injection molding grade, in order to find a potential composition for its replacement. Possibility of such replacement via modification of recycled high‐density polyethylene (reHDPE) by low‐density polyethylene (LDPE) and linear‐low‐density polyethylene (LLDPE) is discussed. Overall, mechanical and rheological data showed that LDPE is a better modifier for reHDPE than LLDPE. Mechanical properties of reHDPE/LLDPE blends were lower than additive, thus demonstrating the lack of compatibility between the blend components in the solid state. Mechanical properties of reHDPE/LDPE blends were either equal to or higher than calculated from linear additivity. Capillary rheological measurements showed that values of apparent viscosity for LLDPE blends were very similar to those of the more viscous parent in the blend, whereas apparent viscosities of reHDPE/LDPE blends depended neither on concentration nor on type (viscosity) of LDPE. Further rheological and thermal studies on reHDPE/LDPE blends indicated that the blend constituents were partially miscible in the melt and cocrystallized in the solid state.     

Polyethylene-g-Maleic Anhydride,a Compatibility Booster in Low Density Polyethylene and Polyvinylacetate Blend Preparations

Abstract

Low density polyethylene (LDPE) and polyvinyl acetate (PVAc) blends containing different weights percentages of PVAc, were prepared. Polyethylene graft Maleic anhydride (PE-g-MA) containing 0.4 mole% of anhydride groups was used as compatibility booster in the blends. FTIR helped confirming the blend formation. Improvement in mechanical properties as a result of blending and compatibilization have been observed. The properties of these blends were compared with those of blends of LDPE with NBR and SBR. Thermal properties were examined by the use of thermogravimetric analyser.     

Binary mixtures of polyethylene and oxidized wax: Dependency of thermal and mechanical properties upon mixing procedure

The influence of the preparation procedure on the thermal and mechanical properties of linear low‐density polyethylene (LLDPE)– and LDPE–oxidized wax blends was investigated. It was found that mechanically mixed blends show reduced thermal stability as well as ultimate mechanical properties (stress and strain at break) compared to that of extrusion mixed blends. However, the structure of the blend and consequently its thermal and mechanical behavior also depend on the initial morphology of polyethylene. DSC measurements show miscibility up to high wax contents in both blend types, but increasing the amount of wax in LDPE blends induces increasing crystallinity. As a result, the LDPE/wax blends show improved thermal stability of between 20 and 50°C at low wax concentrations. Although the elasticity modulus of the blends increases, increasing the amount of wax generally degrades the mechanical properties. The main reason for this is the reduced number of tie chains. Changes in the average concentration of tie chains with increasing wax content were calculated and a correlation was made with the ultimate properties of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2446–2456, 2003     

Effect of Addition of HDPE and LDPE on Rheological,Mechanical, Elastic and Compatibility Behavior of SBR/NBR Rubber Blend System

The influence of adding low density polyethylene (LDPE) and high density polyethylene (HDPE) to different ratios of styrene butadiene copolymer (SBR) and acrylonitrile butadiene copolymer (NBR) rubber blend has been studied. The experimental methods performed are based on measurements of rheological, mechanical, elastic properties, phase morphology, density, ultrasonic studies, thermal stability and differential scanning calorimetry (DSC). Results showed that rheological and mechanical properties of the blend are improved, especially at SBR/NBR blend (50/50), when incorporated with LDPE. Results indicated also a clear stability of the cure rate index (CRI) of the blend. Morphological structure analysis obtained from scanning electron microscope (SEM) showed a reduced domain size for blends containing LDPE. Ultrasonic and density investigations revealed the efficiency of adding LDPE in improving the compatibility behavior of this blend. Results also showed an improvement in elastic properties and thermal stability by adding LDPE. DSC scans of the blends filled with LDPE showed high shift in the glass transition temperature which can be attributed to the increased strength at the interface.     

Blends of low density polyethylene/plasticized poly(vinyl chloride): The rheological,morphological, and mechanical characterization

An experimental study was conducted to investigate the rheological, morphological, and mechanical properties of a heterogeneous polymer blend system consisting of low density polyethylene (LDPE) and plasticized poly(vinyl chloride) (PVC). The components were mixed using a single-screw extruder, which was equipped with a special measuring head for the determination of rheological quantities. The morphology of blends was examined by scanning electron microscopy. Die swell was determined by photography. The velocity of ultrasound through the polymer melt was also measured. The dependencies of viscosity, die swell, and ultrasonic velocity on blend composition were qualitatively similar, exhibiting a minimum at about 70 wt % PVC. The morphology of the blend system at this blending ratio was different from morphologies of the other blends. Tensile properties of blends, except elongation at break, were not significantly inferior to those of the LDPE component.     

Degradation behavior of poly (caprolactone)–poly(ethylene glycol) block copolymer/low–density polyethylene blends

Blends of poly(carprolactone)-poly(ethylene glycol) block polymer (PCE) with low-density polyethylene (LDPE) were prepared by extrusion followed by compression molding into thin film specimens. The morphology, thermal properties, degradation, and mechanical behavior of the blends were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), water immersion, static tensile testing, and dynamic mechanical analysis (DMA). The LDPE/PCE blends were immiscible for all chemical compositions. A LDPE/PCE (75/25 wt%) blend exhibited small reductions in weight and tensile strength after immersion in a buffer solution (pH = 5.0) at 50°C for extended periods of time. However, grafting maleic anhydride onto the LDPE/PCE blends improved the compatibility between the LDPE and PCE phases. Consequently, a 75/25 wt% blend of maleated LDPE/PCE exhibited significant losses in weight and tensile strength after immersion in the buffer solution. For comparison, blends of poly(caprolactone) (PCL) with LDPE were fabricated by similar techniques. The effect of compatibilizer on the degradation of LDPE/PCE and LDPE/PCL is discussed.     

LLDPE/LDPE blends. I. Rheological,thermal, and mechanical properties

Structure and mechanical properties were studied for the binary blends of a linear low density polyethylene (LLDPE) (ethylene‐1‐hexene copolymer; density = 900 kg m⁻³) with narrow short chain branching distribution and a low density polyethylene (LDPE) which is characterized by the long chain branches. It was found by the rheological measurements that the LLDPE and the LDPE are miscible in the molten state. The steady‐state rheological properties of the blends can be predicted using oscillatory shear moduli. Furthermore, the crystallization temperature of LDPE is higher than that of the LLDPE and is found to act as a nucleating agent for the crystallization of the LLDPE. Consequently, the melting temperature, degree of crystallinity, and hardness of the blend increase rapidly with increases in the LDPE content in the blend, even though the amount of the LDPE in the blend is small. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3153–3159, 1999     

Evaluation of isocyanate functional groups as a reactive group in the reactive compatibilizer

Reactive compatibilization of an isocyanate (NCO) functional group as a reactive group was investigated. Five kinds of reactive polymers were prepared through solution graft polymerization of low‐density polyethylene (LDPE) copolymerized with acrylic acid (AA), maleic anhydride (MAH), glycidyl methacrylate (GMA), and masked and naked NCO functional monomers and were used as compatibilizers in poly(ethylene terephthalate) (PET)/LDPE and polyamide 6 (Nylon 6)/LDPE blends. The reactivity of the NCO functional group in the reactive blend was evaluated in terms of the blend morphology, adhesive test, mechanical properties, and rheological properties. It was found that GMA and NCO groups were the most effective compatibilizing agents in the PET/LDPE blends and MAH and NCO groups showed effective compatibilization of the Nylon 6/LDPE blends. We confirmed that the NCO functional group as a reactive group could be used as a universal reactive compatibilizer for PET/LDPE and Nylon 6/LDPE blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2622–2629, 2003     

Morphology and deformation of compatibilized polystyrene low density polyethylene blends

This investigation deals with the morphology and tensile behavior of polystyrene/low density polyethylene blends compatibilized by hydrogenated styrene‐b‐butadiene‐b‐styrene triblock copolymer. The stress‐strain measurements indicate that blends with excellent toughness were achieved, due to the compatibilizing role of the triblock copolymer in the system. The morphology of the blends was observed by scanning electron microscopy (SEM), and the results show that the state of polystyrene changes from continuous phase to dispersed phase with increasing LDPE content. The correlation between mechanical properties and morphology is discussed. The morphologies of the tensile bars were also examined by SEM, and the deformation mechanisms of the blend were further analysed according to fractography. © 1999 Society of Chemical Industry     

Studies on LDPE—Cyanoethylated lignocellulosics blends using epoxy functionalized LDPE as compatibilizer

Rubberwood flour and cellulose have been plasticized by cyanoethylation and then blended with low‐density polyethylene (LDPE). A small quantity of epoxy functionalized polyethylene i.e., polyethylene‐co‐glycidyl methacrylate (PEGMA) has been added to further enhance the mechanical properties. The mechanical properties were measured according to the standard ASTM methods. SEM analysis was performed for both fractured and unfractured blend specimens. The mechanical properties were improved by the addition of PEGMA compatibilizer. LDPE blends with cyanoethylated wood flour (CYWF) showed higher tensile strength and modulus than cyanoethylated cellulose CYC‐LDPE blends. However CYC‐LDPE blends exhibited higher relative elongation at break values as compared with the former. The TGA analysis showed lowering of thermal stability as the filler content is increased and degradation temperature of LDPE is shifted slightly to lower temperature. DSC analysis showed loss of crystallinity for the LDPE phase as the filler content is increased for both types of blends. Dielectric properties of the blends were similar to LDPE, but were lowered on adding PEGMA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 219–237, 2006     

Use of poly(ethylene‐co‐vinyl alcohol) as compatibilizer in LDPE/thermoplastic tapioca starch blends

Poly(ethylene‐co‐vinyl alcohol) (EVOH) was used as a compatibilizer to make blends of low‐density polyethylene (LDPE) and plasticized starch (TS). The tensile properties and impact strength were measured and compared with those of neat LDPE. The morphology of the blend specimens, both fractured and unfractured, was observed by scanning electron microscopy. Comparison of the properties showed that the impact strength of the blend improves significantly by the addition of a compatibilizer even with a high TS loading of 40 and 50% (by weight). A high elongation at break almost matching that of neat polyethylene was also obtained. The blend morphology of the etched specimens revealed fine dispersion of the starch in the polyethylene matrix, while the fracture surface morphology clearly indicate that the failure of compatibilized blends occurs mainly by the ductile mode. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3126–3134, 2002     

Basic and applied rheology of m-LLDPE/LDPE blends: Miscibility and processing features

The linear viscosity of m-LLDPE/LDPE blends is adjusted to a free volume model, conceived for miscible blends. A deviation from the model is observed at 47.5% m-LLDPE/52.5% LDPE blend, suggesting immiscibility in the molten state at this composition. Time-temperature superposition method is used to confirm miscible and immiscible cases. The effect of miscibility on practical rheological features is analysed using extrusion rheometry. The results indicate a core-sheet morphology in the immiscible blend, as the less viscous LDPE encircles the m-LLDPE phase. Miscible blends with a high LDPE content and immiscible 47.5% m-LLDPE/52.5% LDPE blend, show ‘melt fracture’, but not ‘sharkskin’. The latter is observed in miscible blends of a high m-LLDPE content. ‘Sharkskin’ is postponed in 87.5% m-LLDPE/12.5% LDPE blend, a result which is associated to the elongational viscosity enhancement, due to the presence of long chain branches. The correlation between melt spinning and blown film extrusion results is investigated, showing evidences of the technical limitations caused by immiscibilty.     

增容剂LDPE-g-MAH对木质素/聚乙烯吹塑薄膜形貌与性能的影响

研究了低密度聚乙烯与马来酸酐的接枝共聚物LDPE-g-MAH对木质素/低密度聚乙烯共混体系热性能、红外光谱分析力学性能、流变行为以及微观形态的影响.DSC-TG综合热分析表明添加增容剂的共混物的熔融温度降低,热稳定性提高;红外光谱分析表明木质素与LDPE-g-MAH之间存在分子间氢键相互作用,流变性能分析表明共混物体系具有可加工性;扫描电子显微镜（SEM）照片显示添加增容剂后分散相尺寸明显减小,分散程度提高;PE-g-MAH有效提高了木质素/聚乙烯吹塑薄膜的力学性能,且当木质素、聚乙烯和LDPE-g-MAH质量比为25/75/10时,力学性能最优.     

Effects of ultrasonic oscillations on processing behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene/low‐density polyethylene blends

The influences of ultrasonic oscillations on rheological behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene (mLLDPE)/low‐density polyethylene (LDPE) blends were investigated. The experimental results showed that the presence of ultrasonic oscillations can increase the extrusion productivity of mLLDPE/LDPE blends and decrease their die pressure and melt viscosity during extrusion. Incorporation of LDPE increases the critical shear rate for sharkskin formation of extrudate, crystallinity, and mechanical properties of mLLDPE. The processing behavior and mechanical properties of mLLDPE/LDPE blends were further improved in the presence of ultrasonic oscillations during extrusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2522–2527, 2004     

Structure and properties of polyamide 6 blends with low‐density polyethylene grafted by itaconic acid and with neutralized carboxyl groups

A comparative study of the structure and properties of two‐phase blends of polyamide 6 (PA6) and low‐density polyethylene (LDPE) modified in the course of reactive extrusion, by grafting of itaconic acid (IA) without neutralization of carboxyl groups (LDPE‐g‐IA) and with neutralized carboxyl groups (LDPE‐g‐IA^?M⁺) was carried out. It was shown that 30 wt % of LDPE‐g‐IA^?M⁺ introduced to PA6 resulted in blends of higher Charpy impact strength compared with that of PA6/LDPE‐g‐IA blends. The maximum increase was achieved when Mg(OH)₂ was used as a neutralizing agent. The blend morphology has a two‐phase structure with blurred interphases because of increased adhesion between the phases. The neutralization of carboxyl groups in grafted IA did not lead to two‐phase morphology of blends, which had a negative influence on the mechanical properties. It is believed that the differences in the impact strength were caused by the influence of the added neutralizing agents on the structure of interphases, which depends on both the interfaces adhesion and structural effects resulting from the nucleating behavior of the neutralizing agent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1702–1708, 2004     

Application of phase dispersion–crosslinking synergism on recycling commingled plastic wastes

A tetra‐component blend, consisting of low‐density polyethylene (LDPE), polyvinyl chloride (PVC), polypropylene (PP), and polystyrene (PS), was studied as a model system of commingled plastic wastes (LDPE/PVC/PP/PS, mass ratio: 70/10/10/10). Effects of chlorinated polyethylene (CPE), ethylene–propylene–diene monomer (EPDM), styrene–butadiene–styrene (SBS), and their mixture (CPE/EPDM/SBS, mass ratio: 2/2/2) on the mechanical properties and morphology of the system were investigated. With addition of several elastomers and their mixture, the tensile strength of the blends decreased slightly, although both the elongation at break and the impact strength increased. Among these elastomers, EPDM exhibited the most significant impact modification effect for the tetra‐component blends. SBS and the mixture have a good phase‐dispersion effect for the tetra‐component blend. By adding a crosslinking agent [dicumyl peroxide (DCP)], the mechanical properties of the tetra‐component blends also increased. When either SBS or the mixture was added to the blend together with DCP, the probability that the crosslinking agent (DCP) would be at the interface improved because of the phase‐dispersion effect of SBS. Therefore, more co‐crosslinked products will form between LDPE and other components. Accordingly, remarkable improvement of the interfacial adhesion and hence the mechanical properties of the tetra‐component blends occurred. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2947–2952, 2001     

Development of polybutadiene (BR)–polyethylene (LDPE) blend based microcellular soles for low‐temperature applications

Microcellular (MC) soles based on polybutadiene (BR) and low‐density polyethylene (LDPE) blends for low‐temperature applications were developed. A part of BR in BR–LDPE blend was replaced by natural rubber (NR) for property improvement. The BR–NR–LDPE blend‐based MC sole shows good technical properties. Sulphur curing and DCP curing were tried in BR–LDPE and NR–BR–LDPE blends. Study shows that sulphur‐cured MC sheets possess better technical properties than DCP‐cured MC sheets. 90/10 BR–LDPE and 60/30/10 BR–NR–LDPE blend combinations are found to be suitable for low‐temperature applications. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 277–281, 2000     

Rheological and mechanical properties of composites made from wood flour and recycled LDPE/HDPE blend

The effect of compounding method is studied with respect to the rheological behavior and mechanical properties of composites made of wood flour and a blend of two main components of plastics waste in municipal solid waste, low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The effects of recycling process on the rheological behavior of LDPE and HDPE blends were investigated. Initially, samples of virgin LDPE and HDPE were thermo-mechanically degraded twice under controlled conditions in an extruder. The recycled materials and wood flour were then compounded by two different mixing methods: simultaneous mixing of all components and pre-mixing, including the blending of polymers in molten state, grinding and subsequent compounding with wood flour. The rheological and mechanical properties of the LDPE/HDPE blend and resultant composites were determined. The results showed that recycling increased the complex viscosity of the LDPE/HDPE blend and it exhibited miscible behavior in a molten state. Rheological testing indicated that the complex viscosity and storage modulus of the composites made by pre-mixing method were higher than that made by the simultaneous method. The results also showed that melt pre-mixing of the polymeric matrix (recycled LDPE and HDPE) improved the mechanical properties of the wood–plastic composites.