Thermal and mechanical properties of linear low‐density polyethylene/low‐density polyethylene/wax ternary blends

The thermal and mechanical properties of uncrosslinked three‐component blends of linear low‐density polyethylene (LLDPE), low‐density polyethylene (LDPE), and a hard, paraffinic Fischer–Tropsch wax were investigated. A decrease in the total crystallinity with an increase in both LDPE and wax contents was observed. It was also observed that experimental enthalpy values of LLDPE in the blends were generally higher than the theoretically expected values, whereas in the case of LDPE the theoretically expected values were higher than the experimental values. In the presence of higher wax content there was a good correlation between experimental and theoretically expected enthalpy values. The DSC results showed changes in peak temperature of melting, as well as peak width, with changing blend composition. Most of these changes are explained in terms of the preferred cocrystallization of wax with LLDPE. Young's modulus, yield stress, and stress at break decreased with increasing LDPE content, whereas elongation at yield increased. This is in line with the decreasing crystallinity and increasing amorphous content expected with increasing LDPE content. Deviations from this behavior for samples containing 10% wax and relatively low LDPE contents are explained in terms of lower tie chain fractions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1748–1755, 2005     

Dynamic mechanical behavior of high‐density polyethylene/ethylene vinyl acetate copolymer blends: The effects of the blend ratio,reactive compatibilization,and dynamic vulcanization

The effects of the blend ratio, reactive compatibilization, and dynamic vulcanization on the dynamic mechanical properties of high‐density polyethylene (HDPE)/ethylene vinyl acetate (EVA) blends have been analyzed at different temperatures. The storage modulus of the blend decreases with an increase in the EVA content. The loss factor curve shows two peaks, corresponding to the transitions of HDPE and EVA, indicating the incompatibility of the blend system. Attempts have been made to correlate the observed viscoelastic properties of the blends with the blend morphology. Various composite models have been used to predict the dynamic mechanical data. The experimental values are close to those of the Halpin–Tsai model above 50 wt % EVA and close to those of the Coran model up to 50 wt % EVA in the blend. For the Takayanagi model, the theoretical value is in good agreement with the experimental value for a 70/30 HDPE/EVA blend. The area under the loss modulus/temperature curve (LA) has been analyzed with the integration method from the experimental curve and has been compared with that obtained from group contribution analysis. The LA values calculated with group contribution analysis are lower than those calculated with the integration method. The addition of a maleic‐modified polyethylene compatibilizer increases the storage modulus, loss modulus, and loss factor values of the system, and this is due to the finer dispersion of the EVA domains in the HDPE matrix upon compatibilization. For 70/30 and 50/50 blends, the addition of a maleic‐modified polyethylene compatibilizer shifts the relaxation temperature of both HDPE and EVA to a lower temperature, and this indicates increased interdiffusion of the two phases at the interface upon compatibilization. However, for a 30/70 HDPE/EVA blend, the addition of a compatibilizer does not change the relaxation temperature, and this may be due to the cocontinuous morphology of the blends. The dynamic vulcanization of the EVA phase with dicumyl peroxide results in an increase in both the storage and loss moduli of the blends. A significant increase in the relaxation temperature of EVA and a broadening of the relaxation peaks occur during dynamic vulcanization, and this indicates the increased interaction between the two phases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2083–2099, 2003     

Effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on thermal properties,morphology, and tensile properties of low‐density polyethylene (LDPE) and corn starch blends

The effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on the thermal properties, morphology, and tensile properties of blends of low‐density polyethylene (LDPE) and corn starch were studied with a differential scanning calorimeter (DSC), scanning electron microscope (SEM), and Instron Universal Testing Machine, respectively. Corn starch–LDPE blends with different starch content and with or without the addition of PE‐g‐MA were prepared with a lab‐scale twin‐screw extruder. The crystallization temperature of LDPE–corn starch–PE‐g‐MA blends was similar to that of pure LDPE but higher than that of LDPE–corn starch blends. The interfacial properties between corn starch and LDPE were improved after PE‐g‐MA addition, as evidenced by the structure morphology revealed by SEM. The tensile strength and elongation at break of corn starch–LDPE–PE‐g‐MA blends were greater than those of LDPE–corn starch blends, and their differences became more pronounced at higher starch contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2904–2911, 2003     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

Rheological behavior and mechanical properties of high‐density polyethylene blends with different molecular weights

The dynamic rheological and mechanical properties of the binary blends of two conventional high‐density polyethylenes [HDPEs; low molecular weight (LMW) and high molecular weight (HMW)] with distinct different weight‐average molecular weights were studied. The rheological results show that the rheological behavior of the blends departed from classical linear viscoelastic theory because of the polydispersity of the HDPEs that we used. Plots of the logarithm of the zero shear viscosity fitted by the Cross model versus the blend composition, Cole–Cole plots, Han curves, and master curves of the storage and loss moduli indicated the LMW/HMW blends of different compositions were miscible in the melt state. The tensile yield strength of the blends generally followed the linear additivity rule, whereas the elongation at break and impact strength were lower than those predicted by linear additivity; this suggested the incompatibility of the blends in solid state. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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

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

Mechanical properties and water absorption of low‐density polyethylene/sawdust composites

The mechanical properties and water absorption of low‐density polyethylene/sawdust composites were investigated. The relationship between the filler content and the composite properties was also studied. Different degrees of esterification of the sawdust with maleic anhydride were obtained with different reaction times. The experimental results demonstrated that the treatment of sawdust by maleic anhydride enhanced the tensile and flexural strengths. The water absorption for maleic anhydride treated sawdust indicated that it was more hydrophobic than untreated sawdust. The effects of the addition of benzoyl peroxide during the preparation of composite samples on the water absorption and mechanical properties were also evaluated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Modification of properties of CaCO3‐polymerization‐filled polyethylene

CaCO₃–polyethylene (PE) compositions, containing an ultrahigh molecular polyethylene (UHMPE) interlayer between the filler surface and the PE matrix, were synthesized by two‐step polymerization of ethylene on a filler surface activated with a suitable catalyst. The properties of the compositions were studied depending on the molecular weight of the PE matrix and the thickness of the UHMPE intermediate layer at the filler particles. It was shown that the presence of UHMPE as an interlayer in chalk–UHMPE–PE compositions leads to an increase of plastic deformation of the materials as long as the M_w value of the PE matrix is higher than is the brittleness threshold for PE. Chalk–UHMPE–PE compositions exhibit a higher ability for plastic deformation compared to chalk–PE compositions based on a PE matrix of a molecular weight equal to the molecular weight of the total polymer phase (UHMPE–PE) in the first case. There is no improvment of the mechanical properties when the UHMPE is dispersed in the compositions and not as an interlayer between a filler and a matrix. This means that the method of polymerization filling allows one to incorporate the polymer interlayer with a desired nature and properties between a filler surface and polymer matrix in filled polyolefin compositions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 577–583, 2003     

Rheological and thermal properties of single‐site polyethylene blends

Branched polyethylenes, low‐density polyethylenes (LDPE1 and LDPE2) or long‐chain‐branched very low density polyethylenes (VLDPE2), were blended with very low density polyethylenes containing short branches (VLDPE1 and VLDPE3). The rheological and thermal measurements of the pure copolymers and their blends (VLDPE1–LDPE1, VLDPE1–LDPE2, VLDPE1–VLDPE2, and VLDPE2–VLDPE3) were taken by controlled stress rheometry and differential scanning calorimetry, respectively. The shear‐thinning effect became stronger with increasing long‐chain‐branched polymer compositions when it was correlated with the flow behavior index, and the extent of shear thinning was different for each blend set. Stronger shear thinning and a linear composition dependence of the zero‐shear viscosity were observed for the VLDPE1–LDPE1 and VLDPE1–LDPE2 blends. These blends followed the log additivity rule, and this indicated that they were miscible in the melt at all compositions. In contrast, a deviation from the log additivity rule was observed for the VLDPE1–VLDPE2 blend compositions with 50% or less VLDPE2 and for the VLDPE3–VLDPE2 blends with 50% or more VLDPE2. The thermal properties of the blends were consistent with the rheological properties. VLDPE1–LDPE1 and VLDPE1–LDPE2 showed that these blends were characteristic of a single‐component system at all compositions, whereas the phase separation (immiscibility) was detected only for VLDPE1–VLDPE2 blends with 50% or less VLDPE2 and for VLDPE3–VLDPE2 blends with 50% or more VLDPE2. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1549–1557, 2005     

Thermal,dielectric, and mechanical properties of SiC particles filled linear low‐density polyethylene composites

A thermally conductive linear low‐density polyethylene (LLDPE) composite with silicon carbide (SiC) as filler was prepared in a heat press molding. The SiC particles distributions were found to be rather uniform in matrix at both low and high filler content due to a powder mixing process employed. Differential scanning calorimeter results indicated that the SiC filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites displays a high thermal conductivity of 1.48 Wm^?1 K^?1 and improved thermal stability at 55 wt % SiC content as compared to pure LLDPE. The surface treatment of SiC particles has a beneficial effect on improving the thermal conductivity. The dielectric constant and loss increased with SiC content, however, they still remained at relatively low levels (<10² Hz); whereas, the composites showed poorer mechanical properties as compared to pure LLDPE. In addition, combined use of small amount of alumina short fiber and SiC gave rise to improved overall properties of LLDPE composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure and properties of ultraviolet‐irradiated high density polyethylene at different environmental temperatures

C? O, C?O, and C(?O)O oxygen‐containing groups were introduced onto the molecular chain of high‐density polyethylene (HDPE) through ultraviolet irradiation in air. The introduction rate of the oxygen‐containing groups onto HDPE increased with increasing environmental temperature. After ultraviolet irradiation, the molecular weight of HDPE decreased, and its distribution became wider; the melting temperature, contact angle with water, and impact strength decreased; the degree of crystallinity and yield strength increased; and their variation amplitude increased with environmental temperature. The environmental temperature had an effect on the gel content of irradiated HDPE. HDPE‐irradiated for 48 h at 35° and 50°C were not crosslinked. However, gelation took place in HDPE irradiated for 24 h at 70°C. HDPE irradiated at a high environmental temperature was more effective than that irradiated at a low environmental temperature in compatibilizing HDPE with PVA. Compared with the 83/17 HDPE/PVA blend, the yield and notched impact strength of the 73/17 HDPE/PVA blend compatibilized with 10% HDPE irradiated for 24 h at an environmental temperature of 70°C increased from 30.8 MPa and 110 J/m to 34.9 MPa and 142 J/m, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2966–2969, 2003     

Very high modulus high‐density polyethylene and high‐modulus polypropylene obtained by solid‐state roll drawing

This article describes results obtained with a process developed for rolling and drawing simultaneously polymer profiles in the solid state. Solid‐state roll drawing has the advantage of being continuous, which allows relatively high production rates and the generation of high deformation ratios with some degree of biaxial orientation. The roll‐drawing process allows the extent of biaxial orientation to be controlled by the adjustment of the tension and compression loads applied to the polymers, in particular semicrystalline thermoplastics. Some experimental results obtained with a four‐station roll‐drawing apparatus are presented, particularly on high‐density polyethylene (HDPE) and polypropylene. The effect of process parameters, such as the gap between the rolls and tension, are discussed. Aspects discussed also include relaxation; structure development in terms of orientation and crystallinity as a function of draw ratio (λ); λ as a function of process parameters; and finally, mechanical and thermal properties as a function of λ. Moduli as high as 25 GPa in the longitudinal direction and about 4 GPa in the transverse direction were obtained with successively rolled, initially thick, HDPE profiles. © 2006 Government of Canada. Exclusive worldwide publication right in the article have been transferred to Wiley Periodicals, Inc. J Appl Polym Sci 102: 3391–3399, 2006     

High‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blend. I. The processing,thermal, and mechanical properties

Various blend ratios of high‐density polyethylene (HDPE) and ultrahigh‐molecular‐weight polyethylene (UHMWPE) were prepared with the objective of determining their suitability as biomaterials. Although the presence of HDPE in the blends enabled melt processing, the presence of UHMWPE helped to improve the toughness of the resulting blends. The processability of the blends was investigated with the Brabender torque, which was used as an indication of the optimum blend conditions. The blends were characterized with differential scanning calorimetry. The mechanical tests performed on the blends included tensile, flexural, and impact tests. A 50:50 (w/w) blend yielded optimum properties in terms of the processability and mechanical properties. The tensile property of the 50:50 blend was intermediate between those of HDPE and UHMWPE, but the strain at break increased 200% in comparison with that of both neat resins. The energy at break of the 50:50 blend revealed an improvement in the toughness. The fracture mechanism was also investigated with scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 413–425, 2005     

Mechanical and thermo‐physical properties of high‐density polyethylene modified with talc

The aim of this study was to examine the physical, mechanical, and thermo‐physical properties of high‐density polyethylene (HDPE) modified with talc. Different weight fractions of talc (up to 35 wt %) were compounded with an HDPE matrix containing 2.5 wt % of carbon black (CB) in a twin‐screw compounder. The composites were then processed by injection moulding to obtain specimens for testing. The results indicate that CB causes a significant decrease in the toughness, while talc not only enhances the thermal conductivity and thermo‐physical properties of the composites but can also play a role in compensating for the negative effects of CB on impact resistance. The experimental data show that the presence of CB reduces the impact resistance of HDPE by up to 34%, while addition of up to 8 wt % talc can return this value to close to that of pure HDPE. No significant effect on the composite tensile yield and fracture strength was observed for either component at all concentrations. The thermal conductivity, thermal diffusivity, and specific density values of the composites increased almost linearly, but the increase in moisture absorption in the long term showed nonlinear behavior in the concentration range of the experiment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Bi‐axial self‐reinforcement of high‐density polyethylene induced by high‐molecular weight polyethylene through dynamic packing injection molding

Previously, bi‐axial self‐reinforcement of high‐density polyethylene (HDPE) was achieved through a uni‐axial shear stress field introduced by dynamic packing injection molding technology. Here, further improvement of tensile strength along the flow direction (MD) was achieved by blending a small amount of high‐molecular‐weight polyethylene (HMWPE) with HDPE, while the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional moldings. Tensile strengths in both flow and transverse directions were considerably enhanced, with improvements from 23 MPa to 76 MPa in MD and from 23 MPa to 31 MPa in TD. The effect of HMWPE content and molding parameters on tensile properties was also investigated. The tensile strength along MD was highly dependent on HMWPE content, oscillating cycle, mold temperature, melt temperature and packing pressure, while that along TD was insensitive to composition and processing parameters within the selected design space. According to the stress–strain curves, samples with HMWPE produced by dynamic packing injection molding had a special tensile failure mode in MD, different from both typical plastic and brittle failure modes. There were no yielding and necking phenomena, which are characteristic during tensile testing of plastic materials, but there was still a considerably higher elongation compared to those of brittle materials. However, in TD, all dynamic injection molding samples exhibited plastic failure as did typical conventional injection molding samples. Copyright © 2006 Society of Chemical Industry     

Surface modification of ultra‐high‐molecular‐weight polyethylene. II. Effect on the physicomechanical and tribological properties of ultra‐high‐molecular‐weight polyethylene/poly(ethylene terephthalate) composites

We performed surface modification of ultra‐high‐molecular‐weight polyethylene (UHMWPE) through chromic acid etching, with the aim of improving the performance of its composites with poly(ethylene terephthalate) (PET) fibers. In this article, we report on the morphology and physicomechanical and tribological properties of modified UHMWPE/PET composites. Composites containing chemically modified UHMWPE had higher impact properties than those based on unmodified UHMWPE because of improved interfacial bonding between the polymer matrix and the fibers and better dispersion of the fibers within the modified UHMWPE matrix. Chemical modification of UHMWPE before the introduction of PET fibers resulted in composites exhibiting improved wear resistance compared to the base material and compared to unmodified UHMWPE/PET composites. On the basis of the morphological studies of worn samples, microploughing and fatigue failure associated with microcracking were identified as the principle wear mechanisms. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Characterization of the free volume in high‐impact polystyrene/polypropylene and high‐impact polystyrene/high‐density polyethylene blends probed by positron annihilation spectroscopy

The free‐volume properties of high‐impact polystyrene (HIPS)/polypropylene (PP) and HIPS/high‐density polyethylene (HDPE) blends were investigated by means of positron annihilation lifetime spectroscopy (PALS). The measured results show that the free‐volume holes in the semicrystalline polymers, such as PP and HDPE, were not large enough to accommodate the branched chains and the end groups of the macromolecular chains in HIPS to produce favorable interactions between the semicrystalline polymers and the HIPS polymer in these blends; thus immiscible blends were formed. The weak interaction between two dissimilar polymer molecules only took place in the regions between two amorphous phases. In addition, the observed negative deviations of the longest lifetime intensity and the free‐volume fraction were attributed to the influence of the interfacial polarization during PALS measurement. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1507–1514, 2003     

Biaxially self‐reinforced high‐density polyethylene prepared by dynamic packing injection molding. I. Processing parameters and mechanical properties

Uniaxial oscillating stress field by dynamic packing injection molding (DPIM) is well established as a means of producing uniaxially self‐reinforced polyethylene and polypropylene. Here, the effects on the mechanical properties of high‐density polyethylene (HDPE) in both flow direction (MD) and transverse direction (TD) of packing modules and processing parameters in DPIM are described. Both biaxially and uniaxially self‐reinforced HDPE samples are obtained by uniaxial shear injection molding. The most remarkable biaxially self‐reinforced HDPE specimens show a 42% increase of the tensile strength in both MD and TD. The difference of stress–strain behavior and impact strength between MD and TD for the DPIM moldings indicates the asymmetry of microstructure in the two directions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1584–1590, 2004     

Improving low‐density polyethylene/poly(ethylene terephthalate) blends with graft copolymers

Blends of low‐density polyethylene (LDPE) and poly(ethylene terephthalate) (PET) were prepared with different weight compositions with a plasticorder at 240°C at a rotor speed of 64 rpm for 10 min. The physicomechanical properties of the prepared blends were investigated with special reference to the effects of the blend ratio. Graft copolymers, that is, LDPE‐grafted acrylic acid and LDPE‐grafted acrylonitrile, were prepared with γ‐irradiation. The copolymers were melt‐mixed in various contents (i.e., 3, 5, 7, and 9 phr) with a LDPE/PET blend with a weight ratio of 75/25 and used as compatibilizers. The effect of the compatibilizer contents on the physicomechanical properties and equilibrium swelling of the binary blend was investigated. With an increase in the compatibilizer content up to 7 phr, the blend showed an improvement in the physicomechanical properties and reduced equilibrium swelling in comparison with the uncompatibilized one. The addition of a compatibilizer beyond 7 phr did not improve the blend properties any further. The efficiency of the compatibilizers (7 phr) was also evaluated by studies of the phase morphology (scanning electron microscopy) and thermal properties (differential scanning calorimetry and thermogravimetric analysis). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical properties and structure of high‐density polyethylene samples prepared by injection molding with low‐frequency vibration

To better understand the formation of different crystal structures and improve the mechanical properties of high‐density polyethylene samples, melt vibration technology, which generally includes shear vibration and hydrostatic pressure vibration, was used to prepare injection samples. Through melt vibration, the crystal structure changed from typical spherulites of the traditional injection sample to obviously orientated lamellae of vibration samples. Sizes and orientation degrees of lamellae were different according to different vibration conditions. Crystallinity degrees of vibration samples increased notably. Therefore, the tensile strength of vibration samples increased with increasing vibration frequency and vibration pressure, whereas elongation of vibration samples decreased during the first stage and then continued to increase as the vibration frequency increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 818–823, 2005