Mechanical properties and morphology of high-density polyethylene/linear low-density polyethylene blend

The binary blend of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) in the range of composition from 100% HDPE to 100% LLDPE has been investigated for tensile and flexural properties and the morphology in the deformed state on tensile fracture. Tensile properties (initial modulus, yield stress, and elongation-at-yield, ultimate tensile strength and elongation-at-break, and work of yield and work of rupture) and flexural properties (flexural modulus and flexural yield stress) are studied as a function of blend composition. Behavior, in terms of these properties, is distinguishable in three zones of blend composition, viz. (i) HDPE-rich blend, (ii) LLDPE-rich blend, and (iii) the middle zone. In zones (i) and (ii), the variations of these properties are more or less linear, whereas in the middle region [i.e., zone (iii)], there is a reversal of trends in variation or sometimes a behavior opposite to the expected one. The results are explained on the basis of the effects of cocrystallization and the presence of octene-containing segments in the amorphous phase. Scanning electron micrographs of the tensile fracture surfaces are presented to illustrate the occurrence of transverse bands interconnecting the fibrils.     

Crystallization kinetics of high-density polyethylene/linear low-density polyethylene blend

This article presents crystallization kinetics studies on a cocrystallizing polymer highdensity polyethylene (HDPE)/linear lowd-ensity polyethylene (LLDPE) blend. The nonisothermal crystallization exotherms obtained by differential scanning calorimetry (DSC) were analyzed to investigate the effect of cocrystallization on kinetics parameters, namely the Avrami exponent and activation energy. The regular change of Avrami exponent with blend composition from a value of about 3 corresponding to HDPE to a value of 2 corresponding to LLDPE is observed. A sheaf-like crystalline growth with variation of nucleation depending on blend composition is concluded from these results of DSC exotherm analysis in conjunction with the small-angle light scattering observations. The observed variation of activation energy of crystallization with blend composition suggests the role of interaction of side chains and comonomer units present in the LLDPE. © 1994 John Wiley & Sons, Inc.     

Crystallization behavior of high-density polyethylene/linear low-density polyethylene blend

Binary blend of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE), prepared by melt mixing in an extruder, in the entire range of blending ratio, is studied for crystallization behavior by differential scanning calorimetry (DSC) and X-ray diffraction measurements. Cocrystallization was evident in the entire range of blend composition, from the single-peak character in both DSC crystallization exotherms and meltingendotherms and the X-ray diffraction peaks. A detailed analysis of DSC crystallization exotherms revealed a systematic effect of the addition of LLDPE on nucleation rate and the subsequently developed crystalline morphology, which could be distinguished in the three regions of blending ratio, viz, the “HDPE-rich blend,” “LLDPE-rich blend,” and the “middle range from 30–70% LLDPE content.” Variations in crystallinity, crystallite size, and d spacing are discussed in terms of differences in molecular structure of the components.     

Crystallization of high-density polyethylene–linear low-density polyethylene blend

The crystallization studies revealed that the high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) formed strong cocrystalline mass when they were melt blended in a single screw extruder. The progress of crystallization was observed through a small-angle light scattering instrument, scanning electron microscope, and differential scanning calorimeter. Analysis showed that these constituents followed individual nucleation and combine growth of crystallites in blends. The growth of crystallites all through the blend compositions were two-dimensional. Interestingly, the crystallites resembled each other for a particular blend composition; however, they differ widely as the composition changes. The rate of crystallization depends greatly to the number of crystallites and their interfacial boundary in contact with the amorphous phase pool. The t_1/2 and percentage of crystallinity showed a mutually exclusive trend and were seen to be varied in the following three regions of blend composition: the HDPE-rich, the LLDPE-rich, and the middle region of blend composition. The percentage of crystallinity decreases in both the HDPE-rich and LLDPE-rich blends, and it showed a plateau value in the middle region of blend composition. The t_1/2 showed opposite trend to that of % crystallinity. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2599–2607, 1998     

Liquid-liquid phase separation in blends of a linear low-density polyethylene with a low-density polyethylene

A linear low-density butene copolymer, of overall branch content 3 mol %, has been blended with a low-density polyethylene. The low-density polyethylene has an overall branch content of 5 mol %, including both long and short branches. The two materials were blended in a wide range of compositions and the phase behavior investigated using indirect experimental methods, the examination of quenched blends by differential scanning calorimetry, and transmission electron microscopy. After quenching from temperatures up to 170°C, blends, of almost all compositions, show two crystal populations, separated on a micron scale. It is argued that this implies that the blends were phase separated in the melt before quenching. This behavior shows good agreement with predictions based on previous extensive studies of binary and ternary blends of linear with lightly branched polyethylenes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1921–1931, 1997     

Effect of cocrystallization on kinetic parameters of high-density polyethylene/linear low-density polyethylene blend

The isothermal crystallization kinetics of a binary melt blend of high-density polyethylene (HDPE)/linear low-density polyethylene (LLDPE) is presented. An effort was made to understand the phenomenon of cocrystallization between these two constituting components of the blend with the help of kinetic parameters. The analysis based on the Avrami exponent entails that both HDPE and LLDPE undergo individual seeding of nuclei and they merge with each other in the growth process to form cocrystallites. The incorporation of the LLDPE segment in the HDPE crystallites progressively dilutes the properties of HDPE in the blend. The half-time of crystallization (t_1/2) shows variation in three distinct stages: The t_1/2 increases slowly in the region of 0–30% LLDPE content (HDPE-rich blend), remains constant in the 30–70% LLDPE-containing region (middle region of blend composition), and increases sharply thereafter. These variations of t_1/2 quite appreciably explain the change in % crystallinity, the Avrami exponent, and crystallite-size distribution. These observations were further supported by the small-angle light-scattering experiment. © 1996 John Wiley & Sons, Inc.     

Hot tack of metallocene catalyzed polyethylene and low-density polyethylene blend

Films made of metallocene catalyzed polyethylene (mPE), low-density polyethylene (LDPE), and their blend were prepared to investigate how LDPE influences the hot tack of film. Experimental results showed hot tack is independent of film thickness. The addition of 30 wt % of LDPE can increase the hot tack of mPE film. The thermograms of differential scanning calorimetry (DSC) suggest the respective partial melting and recrystallization of those smaller size crystals at the bond forming and joint fracture stages play very important roles. The large amount of partial melting and high flow may induce a higher degree of molecular diffusion. Higher residual crystallinity and recrystallization at the hot tack testing process may induce higher resistant to bond fracture. Those two positive influences show that the mPE/LDPE film has the higher hot tack. The evidence from optical (higher optical transmission and lower haze) as well as viscoelastic (higher storage modulus and lower melt viscosity) properties further support this hypothesis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1769–1773, 1999     

Elongation viscosity estimates of linear low-density polyethylene/ low-density polyethylene blends

The elongational viscosity (EV) of two series of linear low-density polyethylene/low-density polyethylene blends was estimated using an entry flow analysis. The difference, t ? n, between the power law index t of the elongational viscosity and the power law index n of the viscosity, is proportional to the LDPE content for both series of blends investigated. Comparison of the EV of the LLDPE/LDPE blend estimated from the analysis of the flow into an orifice die to the EV value estimated from the analysis of the flow into a capillary die with a flat entry, showed that the difference in geometry had little effect on the EV estimates.     

Dynamically vulcanized thermoplastic elastomer nanocomposites based on linear low-density polyethylene/styrene-butadiene rubber/nanoclay/bitumen: morphology and rheological behavior

Dynamically crosslinked thermoplastic elastomer nanocomposites were synthesized as modifier for the bitumen binder-based asphalts. Linear low-density polyethylene (LLDPE) and styrene-butadiene rubber (SBR), with the ratio of 80/20, bitumen, and organically modified clay (OC) were all melt mixed in the presence of the sulfur curing system. The proposed mixing was carried out in an internal mixer at 160 °C with a rotor speed of 120 rpm. To enhance the molecular interactions between the polymer phases and the clay silicate layers, maleic anhydride-grafted LLDPE (PE-g-MA) with the maleiation degree of 50% was also incorporated into the mixture. Observation of the composite samples, using the scanning electron microscopy (SEM), revealed the matrix dispersed type of morphology for all dynamically vulcanized samples. X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the exfoliation of the clay silicate layers with good dispersion. Rheomechanical spectrometry (RMS) was performed on the prepared nanocomposites. All dynamically vulcanized nanocomposites comprising 2.5% of OC exhibited shear-thinning behavior and non-terminal characteristics with a low frequency range. These indicate the formation of three-dimensional physical networks by the clay nanolayers throughout the LLDPE matrix. The presence of the bitumen in the composition of the prepared nanocomposites improved the flowability of the samples. This is a promising feature of the prepared nanocomposites to be used as an elastic and resistant modifier in the composition of the bitumen-based asphalts.

     

Comparison between a linear and a branched low-density polyethylene

Two low-density polyethylenes, a linear low-pressure (LLDPE) and a branched high-pressure (LDPE), have been compared. Their shear and extensional behavior and melt fracture phenomena have been investigated, and some mechanical and optical properties of their blown films have been measured. The rheological analysis showed major differences between the samples, both in shear viscosity and in elongational viscosity. The LLDPE exhibited two types of melt fracture, the first of which—a fine scale extrudate roughness—was not shown by the LDPE and appeared at a very low shear rate. The concomitance in LLDPE of a high shear viscosity and a low elongational viscosity and the presence of melt fracture at low shear rate resulted in its more difficult processing into film. The mechanical properties of the LLDPE film approached those of high-density polyethylene while the optical characteristics were in the range of LDPE. Such a coexistence of properties makes LLDPE an interesting material for film production.     

Blending of natural rubber with linear low-density polyethylene

Blends of natural rubber (NR) with linear low-density polyethylene (LLDPE) were prepared by melt blending of the materials in a plasticorder mixer at various temperatures around the melting point of LLDPE and at various mixing rates. The optimum processing conditions were a temperature of about 135°C and a mixing rate of 55 rpm. The tensile properties, stress and strain, of the blend had improved significantly with the addition of liquid natural rubber (LNR) into the blend. For blends with compositions around 50% NR, about 10–15% LNR produced the most significant improvement in the physical properties. Welldispersed plastic particles in a rubber matrix were strongly indicated in these samples. Scanning electron micrographs (SEM) of the samples also indicated an increase in the homogeneity of the mixes with the addition of LNR. A single glass transition temperature of about?55°C for the blend was observed via dynamic mechanical analysis (DMA). Interfacial linking between the NR and LLDPE phases was attributed to the presence of active groups on the polyisoprene chain of LNR, which induced the interphase reaction between the NR and LLDPE phases. © 1995 John Wiley & Sons, Inc.     

Gas barrier and morphology characteristics of linear low-density polyethylene and two different polypropylene films

In this research, linear low-density polyethylene (PE-LLD), cast polypropylene (PPcast), and bioriented coextruded polypropylene (BOPP) were used as polymeric materials. Permeability, diffusivity, and solubility of N₂, O₂, and CO₂ through above polymers were obtained at different temperatures. The structure and thermal–mechanical features of the films were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The permeability, diffusivity, solubility, and their temperature dependency were studied by correlations with gas molecule properties. The highest permeation coefficients (>3.8 × 10⁻⁸ cm³ cm⁻¹ s⁻¹ bar⁻¹) are obtained for PPcast at 60 °C. Activation energy for permeation follows the sequence: N₂ > O₂ > CO₂ for PE-LLD and PPcast. On the other hand, the diffusion activation energy follows the order: O₂ > CO₂ > N₂ and N₂ > CO₂ > O₂ for PE-LLD and PPcast, respectively. In the case of BOPP, activation energy follows the sequence: O₂ > CO₂ > N₂; CO₂ > N₂ > O₂; and O₂ > CO₂ > N₂ for permeation, diffusion, and heat of sorption, respectively.     

Nonlinear behavior of linear low-density polyethylene

To predict the response of polyethylene thin films subjected to stress for a long time, it is necessary to understand the influence of stress on either the relaxation modulus or creep compliance. Extensive testing has been conducted on 20-micron-thick samples of a particular linear low-density polyethylene film at temperatures from 23°C to −50°C. When reduced to creep compliance and compared with results from dynamic mechanical analysis (DMA), the influence of nonlinearities in the response function is apparent. However, the use of a two-step loading procedure has produced sufficient data to discriminate between the effect of stress on amplitude and time on the creep compliance. It has been found that a master curve of compliance generated by DMA equipment may be used in conjunction with certain nonlinear functions to accurately predict the response of the polyethylene. Perhaps of more importance is the observation that the principles of simple time-temperature superposition, commonly used with linear viscoelastic characterization, are insufficient for use with polyethylene films at most stress levels of interest.     

Effects of the processing conditions and blending with linear low-density polyethylene on the properties of low-density polyethylene films

Effects of blending low-density polyethylene (LDPE) with linear low-density polyethylene (LLDPE) were studied on extrusion blown films. The tensile strength, the tear strength, the elongation at break, as well as haze showed more or less additivity between the properties of LDPE and LLDPE except in the range of 20–40% where synergistic effects were observed. The LLDPE had higher tensile strength and elongation at break than did the LDPE in both test directions, as well as higher tear strength in the transverse direction. The impact energies of the LLDPE and the LDPE were approximately the same, but the tear strength of the LLDPE was lower than that of LDPE in the machine direction. The comparative mechanical properties strongly depend on the processing conditions and structural parameters such as the molecular weight and the molecular weight distribution of both classes of materials. The LLDPE in this study had a higher molecular weight in comparison to the LDPE of the study, as implied from its lower melt flow index (MFI) in comparison to that of the LDPE. The effects of processing conditions such as the blow-up ratio (BUR) and the draw-down ratio (DDR) were also studied at 20/80 (LLDPE/LDPE) ratio. Tensile strength, elongation at break, and tear strength in both directions became equalized, and the impact energy decreased as the BUR and the DDR approached each other.     

Elongational flow properties of low-density polyethylene and linear low-density polyethylene from nonisothermal melt spinning experiments

Low-density polyethylene (LDPE) and also linear low-density polyethylene (LLDPE) resins can be characterized by the degree of strain hardening and down-gaging during elongation. A new method for the determination of the apparent elongational flow characteristics is presented. In a small scale apparatus, a molten monofilament is stretched under nonisothermal conditions similar to those found in tubular film extrusion. Measurement of resistance to elongational flow and apparent elongational strain rates permit the comparison of the process-ability of different resins under specified conditions. The effect of melt temperature and extension ratio are examined. The importance of the molecular structure of both LDPE and LLDPE resins on these properties is also outlined.     

Effects of mixing on morphology,rheology, and mechanical properties of blends of ultra-high molecular weight polyethylene with linear low-density polyethylene

Various blends of ultra-high molecular weight polyethylene (UHMWPE) with linear low-density polyethylene (LLDPE) were prepared in an internal (Banbury type) mixer, a static mixer, and by solvent blending. Two mixing techniques, namely simultaneous and sequential loading methods, were employed with the internal mixer. In the former case, the two polymer components were simultaneously loaded at 180°C and mixed. The latter method allowed the UHMWPE component to diffuse at 250°C and cooled it down to 180°C, then the LLDPE component was added subsequently and mixed. Rheological and mechanical properties of these blends are profoundly affected by the mixing techniques used. Rheological results shows yield characteristics of UHMWPE/LLDPE blends, in particular in blends of high UHMWPE contents. Tensile properties of sequentially loaded blends vary more or less linearly with blend compositions. However, negative or positive deviations are seen in the simultaneously prepared blends. Differential scanning calorimetry (DSC) studies indicate that co-crystallization takes place between UHMWPE and LLDPE components in sequentially mixed blends. DSC and small-angle light scattering (SALS) studies show that separate crystallization takes place in simultaneously blended compounds as a result of poor mixing. It seems that the sequential loading method provides more homogeneous compounds than those of simultaneous blending.     

Toughening PA1010 with a functionalized saturated polyolefin elastomer

Polyamide (PA)1010 is blended with a saturated polyolefin elastomer, ethylene‐α‐olefin copolymer (EOCP). To improve the compatibility of PA1010 with EOCP, different grafting rates of EOCP with maleic anhydride (MA) are used. The reaction between PA1010 and EOCP‐g‐MA during extrusion is verified through an extraction test. Mechanical properties, such as notched Izod impact strength, elongation at break, etc., are examined as a function of grafting rate and weight fraction of elastomer. It was found that in the scale of grafting rate (0.13–0.92 wt %), 0.51 wt % is an extreme point for several mechanical properties. Elastomer domains of PA1010/EOCP‐g‐MA blends show a finer and more uniform dispersion in the matrix than that of PA1010/EOCP blends. For the same grafting rate, the average sizes of elastomer particles are almost independent on the contents of elastomer, but for different grafting rates, the particle sizes are decreased with increasing grafting rate. The copolymer formed during extrusion strengthens the interfacial adhesion and acts as an emulsifier to prevent the aggregation of elastomer in the process of blending. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 928–933, 2000     

Effect of nanosilica on the co-continuous morphology of polypropylene/polyolefin elastomer blends

This paper reports the effect of nanosilica (SiO₂) on the morphology of co-continuous immiscible polypropylene (PP)/polyolefin elastomer (POE) blends. The unfilled blends display phase inversion and a co-continuous structure at a ratio of 50/50 PP/POE by weight. Upon addition of SiO₂ in the presence of maleated PP compatibilizer a finer structure, consisting of elongated POE particles dispersed within the PP phase is obtained. This transformation is associated to the presence of finely dispersed SiO₂ particles that are localized exclusively within the PP matrix. The impact properties, flexural and Young's moduli of the blends increase significantly, pointing to a synergistic effect arising from the presence of the reinforced PP phase, containing high amounts of the finely dispersed elastomeric phase.     

高密度聚乙烯/聚烯烃弹性体/三元乙丙橡胶热塑性弹性体的结构与性能

采用动态硫化法制备了高密度聚乙烯(HDPE)/三元乙丙橡胶(EPDM)热塑性弹性体(TPV),并在基体中添加聚烯烃弹性体(POE)以改善其性能.对所制得的TPV的力学性能、微观相结构和动态黏弹行为进行了研究.结果表明,当HDPE/EPDM(质量比)为40/60时,HDPE/EPDM TPV表现出良好的综合性能;用POE...     

Thermal analysis of polycarbonate/linear low-density polyethylene

In a cooperative testing of polymer blends of polycarbonate (PC) and linear low-density polyethylene (LLDPE), 17 laboratories from six countries contributed measurements of differential scanning calorimetry (DSC) or differential thermal analysis (DTA) and of thermogravimetric analysis (TGA). This work is part of the activity of the VAMAS* Technical Working Party–Polymer Blends (TWP–PB), which provided the samples and coordinated the tests. Thermal analysis proved to be a, rapid means of assessing the miscibility of polymers using small samples. The system PC/LLDPE investigated in this test is found immiscible. The results of this cooperative test are a basis to elaborate a standard procedure for the characterization of polymer blends.