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.     

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.     

Performance of multilayer films using maleated linear low-density polyethylene blends

Blends of linear low-density polyethylene (LLDPE) and linear low-density polyethylene grafted maleic anhydride (LLDPE-gMA) were prepared by melt mixing and then coextruded as external layers, with a central layer of polyamide (PA) on three-layer coextruded flat films. Blends with contents of 0% to 55 wt% of maleated LLDPE, on the external layers, were analyzed. The T-peel strength and oxygen and water vapor transmission rate of the films were measured. The surfaces of the peeled films were characterized using attenuated total reflection infrared spectroscopy (FTIR-ATR) and scanning electron microscopy (SEM). The observed increase in T-peel strength of the films with 10% and higher levels of maleated LLDPE in the blend suggests good interfacial adhesion between layers. This sharp increase in peel strength appears to be associated, besides interdiffusion, with specific interactions between polymers, as the bond formation between maleic anhydride and the polyamide end groups by in situ block copolymer formation across the interface. No significant modifications in oxygen barrier properties of the films were observed; however, the use of higher contents of LLDPEgMA, even though it increases the adhesion performance, also increases the water vapor transmission rate by a reduction in the degree of crystallinity.     

Crystallization,structure, morphology,and properties of linear low-density polyethylene blends made with different comonomers

Linear low-density polyethylene (LLDPE) 7042, which has a butene comonomer, is widely used but has poor tear and dart strengths. For practical applications, small amounts of other materials can be blended with 7042 to effectively improve its properties. In this study, four blend resins and films (cast and compressed films) were prepared by blending 7042 with four LLDPEs (2045G, 9030, 23F, and 9085) in 8:2 ratios. The results indicated that after blending 2045G, 23F, or 9030 with 7042, the crystallization ability of the three blends was significantly suppressed and crystal size decreased. Moreover, the molecular chain can pass though more lamellar stacks in the blends, leading to an increased tie-chain concentration. Therefore, the tear and dart impact strength of the blend films improved. In contrast, the crystallization ability of the 7042/9085 blend was only slightly suppressed and did not significantly impact its properties. These findings contribute to our understanding of the relationship between material structures and properties, demonstrating that LLDPE blends can be used to improve the tear and dart strengths of 7042.     

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.     

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.     

Compatibilized linear low-density polyethylene/isotactic polypropylene blends studied by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS), capable of probing free volume, is used to study the effect of compatibilizer concentration, compatibilizer type, and the effect of blend processing on the morphology and properties of an immiscible linear low-density polyethylene/polypropylene system. It is proposed that improvement of fracture toughness due to compatibilization can be attributed to the packing (and bonding) at interfaces. Improved interfacial packing and bonding result in lower free volume concentration than expected from component additivity, with a concomitant increase in plastic deformation on impact.     

Crystal and morphology development in immiscible nonpolar polymer blend nanocomposite based on low-density polyethylene and linear low-density polyethylene in presence of clay and compatibilizer

In this work, polyolefin-blend/clay nanocomposites based on low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and organically modified clay (OC) were prepared by melt extrusion. Various grades of maleic anhydride (MA) grafted polyethylene (PE-g-MA) were used and examined as compatibilizers in these nanocomposites. Differential scanning calorimetry analysis showed that OC and compatibilizer affect the crystallization behavior of LDPE/LLDPE with different mechanisms. Thermodynamic calculations of wetting coefficient based on interfacial energy between OC, LD, and LL, Morphological characterization based on field emission scanning electron microscopy, X-ray diffraction, small angles X-ray scattering, and dynamic rheology measurements revealed that the compatibilizer and OC were localized at the interface of LDPE and LLDPE phases with a preferred tendency toward one phase. Results demonstrated that at a specific amount of OC, there is an optimum compatibilizer concentration to achieve nanodispersed OC and beyond that the compatibilizer causes a structural change in the polymer crystalline morphology. It was also found that the tensile property enhancement of LDPE/LLDPE/OC nanocomposites is closely related to the crystalline structure development made by incorporation of both OC and compatibilizer.     

Structure-property relationships in blends of linear low- and conventional low-density polyethylene as blown films

Three-layer coextruded blown (either blend or composite) films, made of low-density polyethylene and linear lowdensity polyethylene (1:1 ratio) of identical density, were compared. The tensile properties of both systems are nearly as high as those of the linear polyethylene while high strain rate properties including impact strength and tear resistance of the composite film are superior. Some structural insight was obtained by thermal analysis and thermoelastic measurements. Structure property relationships are discussed in light of the unique behavior, structure, and morphology of linear low-density polyethylene. The two polyethylenes are only compatible to a rather limited extent mainly affecting their blend behavior. However, a strong mutual reinforcement effect was observed.     

Viscoelastic,thermal and environmental characteristics of poly(lactic acid), linear low-density polyethylene and low-density polyethylene ternary blends and composites

Poly(lactic acid) (PLA)/(linear low-density polyethylene (LLDPE)–low-density polyethylene (LDPE)) PLA/(LLDPE-LDPE) ternary blends were prepared and characterized as function of the PLA content. (50/50) PLA/(LLDPE–LDPE) blend was also compatibilized using maleic anhydride grafted low-density polyethylene (PE-g-MA) incorporated with a concentration of 5 wt.%. PLA/(LLDPE–LDPE) blend composites have been prepared by dispersing 5 wt.% of an organophilic montmorillonite (Org-MMT), added according to two different mixing methods. These materials were subjected to several investigations such as X-rays diffraction (XRD), dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry, and environmental tests. In the PLA glassy region, DMTA results showed that the storage modulus of PLA/(LLDPE–LDPE) blends decreases upon decreasing the PLA content. When PE-g-MA and Org-MMT were added, PLA exhibited a noticeable increase in the storage modulus across the glass transition region due the interface reinforcement and the enhancement of the blends stiffness. The decrease in the magnitude of the PLA tan δ peak was attributed to the decrease in the molecular mobility that could result from the increase in the interfacial resistance. XRD analysis showed that the method of dispersion of the nanoclay controls the final structural properties of the composites. (50/50) PLA/(LLDPE-LDPE) blend and composites revealed a satisfactory aptitude to biodegradation.     

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.     

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     

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 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.     

Nonisothermal crystallization,melting behavior,and morphology of polypropylene/linear bimodal polyethylene blends

The nonisothermal crystallization, melting behavior, and morphology of isotactic polypropylene (PP)/linear bimodal polyethylene (LBPE) blends were studied with differential scanning calorimetry, scanning electron microscopy, and polarized optical microscopy. The results showed that PP and LBPE were miscible to a certain extent, and there was no obvious phase separation in the blends. The modified Avrami analysis, Ozawa equation, and Mo method were 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 homogeneous, the growth of spherulites was three‐dimensional, and the crystallization mechanism of PP was not affected much by LBPE. The crystallization activation energy was estimated by the Kissinger method. The results obtained with the modified Avrami analysis, Mo method, and Kissinger method agreed well. The addition of a minor LBPE phase favored an increase in the overall crystallization rate of PP, showing some dilution effect of LBPE on PP. The PP spherulites decreased obviously with increasing content of LBPE. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improvement in volume resistivity and morphology of a blend of polyolefin elastomer with linear low-density polyethylene

A silane moisture-cured polyolefin elastomer/linear low-density polyethylene (LLDPE) blend was prepared through a two-step silane-grafting method (Sioplas Process) in an industrial scale twin-screw extruder. The silane-grafted compound was used to make wire and cable coatings. In this work, the effect of some interactive parameters on quality of the products prepared by the above method has been studied, while so far, there have been less experimental investigations. The volume resistivity of cross-linked compound was changed from 2.96 × 10¹⁴ to 7.41 × 10¹⁴ Ω cm with increasing LLDPE component by maximum 10 wt%. Surface morphology of the product was corrected with reduction in benzoyl peroxide (BPO) concentration from 0.2 wt% to 0.13 wt%. BPO at this level acted as an initiator in grafting reaction of vinyl trimethoxysilane. The curing condition and specimen preparation method by injection molding and/or extrusion were factors which influenced the hot-set test results at 200 °C. The results of tensile and elongation studies showed a maximum value of 9 MPa and 397% for the tests, after 6 h curing. With increases in curing time at a specified temperature, the gel content of the cross-linked compound was increased and reached its maximum value. The maximum gel content values were found to be approximately 60%, 80%, and 82% at temperatures of 25, 60, and 85 °C, respectively. The hardness, density, and tear strength of the samples did not vary significantly with the curing temperature.

     

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.     

Study of deformation mechanism for linear low-density polyethylene

The deformation mechanism for linear low-density polythylene (LLDPE) has been studied by electron microscopy, infrared spectroscopy, and pulsed nuclear magnetic resonance. Morphologically, the lamellae in the polar region of a spherulite are aligned in parallel to the drawing direction and then unfolded into microfibrils with drawing. The lamellae in the equatorial region are curved, corrugated, and unfolded partially. Actually, microfibrils are formed with transformation of both lamellae and some amorphous molecules throughout the drawing. Restraint of molecular mobility for the amorphous region increases with drawing, but mobility for the immobile region (lamellae and microfibrils) remains constant. Orientation of the trans-methylene sequences in amorphous regions proceeds with extension. These results can explain the changes of the s-s curve behavior.     

Maleation of linear low-density polyethylene by reactive processing

The reaction of maleic anhydride (MAH) with molten 2 MI poly(ethylene-co-butene-1) (LLDPE) at 160°C in the presence of peroxyesters (t_1/2 < 10 s) as catalysts resulted in the formation of a mixture of cross-linked and trichlorobenzene-soluble LLDPE-g-MAH. The soluble fraction constituted more than 50% of the mixture and had an MI of 0.0 and an MAH content ranging from 0.3 to 1.8 wt %. The presence of tri(nonylphenyl) phosphite (TNPP) in the LLDPE–MAH–t-butyl peroctoate (tBPO) reaction at 160°C increased the MI of the soluble product to 0.7–2. The amount of soluble polymer increased at higher TNPP concentrations while its MAH content ranged from 0.05 to 0.54 wt %, with most contents in the 0.2–0.3 wt % range. The color development that usually occurs in polyolefin–MAH reactions was reduced by the presence of TNPP. However, the reaction of TNPP with the peroxide and from the thermal decomposition thereof reduced the availability of the excited species necessary for the appendage of MAH units onto the polyofin.     

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.