LDPE Blends Research Articles

Effect of blending high‐pressure low‐density polyethylene on the crystallization kinetics of linear low‐density polyethylene

AbstractIt is well known that the addition of a small amount of high‐pressure low‐density polyethylene (HP‐LDPE) to linear low‐density polyethylene (LLDPE) can improve the optical properties of LLDPE, and LLDPE/HP‐LDPE blend is widely applied to various uses in the field of film. The optical haziness of polyethylene blown films, as a result of surface irregularities, is thought to be as a consequence of the different crystallization mechanisms. However, not much effort has been directed toward understanding the effect of HP‐LDPE blending on the overall crystallization kinetics (k) of LLDPE including nucleation rate (n) and crystal lateral growth rate (v). In this study, we investigated the effect of blending 20% HP‐LDPE on the crystallization kinetics of LLDPE polymerized by Ziegler‐Natta catalyst with comonomer of 1‐butene. Furthermore, by combining depolarized light intensity measurement (DLIM) and small‐angle laser light scattering (SALLS), we have established a methodology to estimate the lateral growth rate at lower crystallization temperatures, in which direct measurement of lateral growth by polarized optical microscopy (POM) is impossible due to the formation of extremely small spherulites. This investigation revealed that HP‐LDPE blending leads to enhanced nucleation rate, reduced crystal lateral growth rate, and a slight increase in the overall crystallization kinetics of pure LLDPE. From the estimated crystal lateral growth rate, it was found that the suppression in v from HP‐LDPE blending is larger at lower temperatures than at higher temperatures. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of electron beam irradiation and vinyl acetate content on the physicochemical properties of LDPE/EVA blends

The radiation-induced crosslinking, compatibility, and surface modification of low density polyethylene/ethylene vinyl acetate blends (LDPE/EVA) were investigated. The structural and physical properties were characterized in terms of gel content, hot set, mechanical properties, contact angle, and surface free energy. The highest crosslink density was obtained at 20 wt % of EVA. Gel content of LDPE/EVA blends was increased with increasing irradiation dose, vinyl acetate (VA), and EVA contents. The hot set results are consistent with the gel content data. Mechanical testing showed that the tensile strength of samples increased with increasing irradiation dose up to 180 kGy, whereas the elongation at break was decreased with increasing irradiation dose. Contact angle measurements showed that the surface hydrophillicity of LDPE blend was increased with increasing irradiation dose and contents of both VA and EVA. The surface free energy was greatly dependent on irradiation dose and content of both VA and EVA. The total surface free energies of different LDPE formulations were in the range 17.25–32.51 mN/m, in which the polar (pσ) and disperse (dσs) values were within the range 16.52–26.6 and 0.9–5.91 mN/m, respectively. In conclusion, electron beam irradiation and blending LDPE with EVA improved the wettability or adhesion properties of LDPE/EVA blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

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.

Influence of branching characteristics on thermal and mechanical properties of Ziegler–Natta and metallocene hexene linear low‐density polyethylene blends with low‐density polyethylene

AbstractThe effect of the branch content (BC) and composition distribution (CD) of linear low‐density polyethylene (LLDPE) on the thermal and mechanical properties of its blends with LDPE were studied. All blends and pure resins were conditioned in a Haake PolyDrive blender at 190°C and in the presence of adequate amounts of antioxidant. Two metallocene LLDPEs (m‐LLDPE) and one Ziegler–Natta (ZN) hexene LLDPE were melt blended with the same LDPE. The effect of the BC was investigated by blending two hexene m‐LLDPEs of similar weight‐average molecular weights and molecular weight distributions but different BCs with the same LDPE. The effect of the CD was studied by using a ZN and an m‐LLDPE with similar weight‐average molecular weights, BCs, and comonomer type. Low‐BC m‐LLDPE blends showed separate crystallization whereas cocrystallization was observed in the high‐BC m‐LLDPE‐rich blends. However, ZN‐LLDPE/LDPE blends showed separate crystallization together with a third population of cocrystals. The influence of the crystallization behavior was reflected in the mechanical properties. The BC influenced the modulus, ultimate tensile strength, and toughness. The addition of a small amount of LDPE to a low‐BC m‐LLDPE resulted in a major improvement in the toughness, whereas the results for the high‐BC pair followed the additivity rule. ZN‐LLDPE blends with LDPE blends were found to be more compatible and exhibited superior mechanical properties compared to m‐LLDPE counterparts with the same weight‐average molecular weight and BC. All mechanical properties of ZN‐LLDPE blends follow the linear rule of mixtures. However, the CD had a stronger influence on the mechanical properties in comparison to the BC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2488–2498, 2005

Dielectric spectroscopy using dielectric probes: a new approach to study glass transition dynamics in immiscible apolar polymer blends

Dielectric relaxation spectroscopy using dielectric probes was applied to study the (glass transition) dynamics in binary blends of isotactic PP, PS and LDPE. The blends were prepared by melt-mixing and doped with 0.5% of the dielectric probe 4,4′-( N, N-dibutylamino)-( E)-nitrostilbene (DBANS) (van den Berg O, Sengers WGF, Jager WF, Picken SJ, Wübbenhorst M. Macromolecules 2004;37:2460. [17]). Due to the selective amplification of the dielectric relaxation processes related to the dynamic glass transition of the polymers, accurate relaxation data were obtained, even for the minor phases. No substantial influence of the blend composition and the blend morphology on the glass transition dynamics was found, indicating that both blend constituents behave like homogeneous bulk materials. The normalised relaxation strength of glass transition processes remained constant, regardless of the blend type and blend composition. This indicates that the probe molecule, DBANS, was equally distributed over the two blend components in all three polymer combinations PE–PP, PE–PS and PP–PS.

Rheological study of heterogeneities in melt blends of ZN-LLDPE and LDPE: Influence of Mw and comonomer type, and implications for miscibility

The influences of molecular weight and LLDPE comonomer type on the heterogeneity (immiscibility) of Ziegler-Natta LLDPE and LDPE blends are investigated with rheological methods. Dynamic and steady shear measurements were carried out in a Rheometrics Mechanical Spectrometer 800.

Foaming of Electron-Beam Irradiated LDPE Blends Containing Recycled Polyethylene Foam

An experimental study concerning the recycling of slightly crosslinked polyethylene foams produced in the manufacturing process was conducted. The recycled polyethylene (RPE) was blended with virgin low-density polyethylene (PE) and irradiated by electron-beams and expanded by heat to make regenerated foams. Four RPE/PE blends with different RPE contents ranging from 0 to 15 phr were foamed and the amount of blowing agent was varied in order to make foams of various densities. The mean cell size of the RPE/PE blend increased with an increase in the RPE content and the degree of anisotropy was generally higher for foams with larger RPE contents. The homogeneity of cell distribution and the type of cell distribution seem to be independent of the expansion ratio at a low RPE content. Furthermore, RPE/PE blends with 0∼5 phr of RPE were capable of producing good regenerated foams without losses of tensile and tear strength and other properties such as compression set, resiliency, dimensional change on heating, and Asker C hardness.

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

A steady rise for metallocene

Capillary extrusion experiments involving a number of polyethylenes with emphasis on assessing the effect of long chain branching (LCB) are performed. None of the metallocene catalyzed linear low density polyethylenes (mLLDPE) produced by Dow Chemicals, which are believed to have some level of LCB, show temperature dependence on the viscosity at the gross melt fracture regime. Furthermore, these materials do not show spurt or stick-slip flow, in contrast with most linear polyethylenes. LDPE and blends of LDPE with LLDPE having LCB also show the absence of stick-slip flow, but show temperature dependence on the viscosity. From these observations, we conclude that the stick-slip flow is very sensitive to the existence of LCB.

Effects of granule size and shape on morphology and tensile properties of LDPE and starch blends

Effects of granule size and shape on morphology and tensile properties of LDPE and starch blends

Foamed crosslinked LDPE/PP blends made by hot mold injection molding

Foamed and crosslinked blends of LDPE and i-PP were investigated. The specimens were made by hot mold injection molding process at the temperature of the mold of 210°C. Azodicarbonamide as foaming agent and 2,5-dimethyl-2,5-di(tert.-butylperoxy)hexane as crosslinked agent were used. The chemical changes as a result of the crosslinking were determined by gel content. Thermal behavior of the blends was studied by DSC. The difference of influence of crosslinking agent on chemical changes of both polymers was established. An improvement of the mechanical properties due to crosslinking between PE and PP on their interface was observed. The interaction on the PE/PP interface was confirmed by phase transition parameters determined on the basis of DSC-curves.

Neoalkoxy Titanate and Zirconate Coupling Agent Additives in Thermoplastics

Ti or Zr coupling agents chemically bridge two dissimilar species such as an inorganic filler/particulate and organic polymer via proton coordination on non-silane reactive substrates such as CaCO3 and carbon black without the need of water of condensation as with silanes. Minor amounts of thermally stable neoalkoxy titanate and zirconate additives provide a means for post reactor, in-situ metallocene-like repolymerization catalysis of a filled or unfilled polymer during the plastication phase resulting in: significantly faster thermoplastic processing at lower temperatures; lower polymer recrystallization time; and the copolymerization of dissimilar polymers. Examples: both 40% CaCO3 filled and unfilled PP compounds experienced respective reductions of 35.5% and 42% in injection mold cycle time and 22% and 11% in process temperature; 17% “pyrophosphato titanate coupled conductive carbon black (CB)” in LDPE provides the same Positive Temperature Coefficient effect as 25% untreated CB; a 39.7% reduction in the recrystallization time of PPS; a ten-fold increase in the elongation of a PET/PC regrind alloy; and the regeneration of recycled blends of LDPE and PP regrinds. The catalysis effect is shown to be permanent and recyclable. Coupling agent liquid, powder and pellet forms; dosage; data and applications methodology in compounding, injection and blow molding are discussed. New and novel transparent and permanent antistatic agents based on the formation of bipolar layers of dissimilar trineoalkoxy zirconates are shown to be non-blooming, non-moisture dependent providing volume as well as surface ESD effects.

Rheological study of the influence of Mw and comonomer type on the miscibility of m-LLDPE and LDPE blends

The influences of molecular weight and m-LLDPE comonomer type on the miscibility of m-LLDPE with LDPE in the melt state were investigated with rheological methods. Dynamic, steady shear and transient measurements were carried out in an ARES rheometer at 190 °C. The M w of the shortly branched m-LLDPE has influenced its miscibility with LDPE and immiscibility has increased with the increase in M w of m-LLDPE. The miscibility of the high- M w m-LLDPE with LDPE was non-symmetric with respect to composition as revealed by the dependence of their η 0, η′( ω), G′, N 1( γ ̇ ), and N 1( t) on blend composition. Addition of a small amount of the hexene m-LLDPE to LDPE was more likely to cause immiscibility than the addition of a small amount of LDPE to m-LLDPE. Increasing the m-LLDPE branch length (comonomer) from butene to hexene did not influence the miscibility of m-LLDPE/LDPE blends. Agreement was observed between the measured rheology and theoretical predictions of Einstein, Scholz et al., Palierne and Bousmina emulsion models. The ratio of interfacial tension to droplet radius was estimated to be ∼10 3 N/m 2.

Preparação e Avaliação Térmica e Reológica de Misturas de PEBD/PELBD

Misturas de Polietileno de Baixa Densidade (PEBD) com diferentes tipos e proporções de Polietilenos Lineares de Baixa Densidade (PELBD) foram preparadas em extrusora de rosca simples e dupla a fim de verificar a influência destes últimos na viscosidade e cristalinidade das misturas. As misturas de PEBD com PELBD foram avaliadas através de reometria capilar e calorimetria (DSC). As misturas de PEBD com PELBD com comonômero de 1-buteno e de 1-octeno, preparadas em extrusora de rosca simples ou dupla, não apresentaram diferenças no perfil das curvas reológicas. Entretanto, as misturas de PEBD com PELBD com comonômero 1-hexeno apresentaram diferenças nas curvas de viscosidade. Verificou-se que a adição de PELBD na mistura modifica significativamente a viscosidade principalmente em altas taxas de cisalhamento. Pela avaliação das curvas de fusão, observou-se que o aumento da concentração de PELBD nas misturas provoca uma variação no comportamento térmico das mesmas com o conseqüente alargamento da faixa de fusão.

Biodegradation studies of LDPE filled with biodegradable additives: Morphological changes. I

AbstractLow‐density polyethylene (LDPE) samples filled with three commercial biodegradable additives (Mater‐Bi, Cornplast, and Bioefect) have been subjected to an accelerated soil burial test in a culture oven for 1 year. By means of Differential Scanning Calorimetry (DSC), the effect of the degradation in soil in the samples morphology has been analyzed, in terms of their melting temperature, their crystalline content, and their lamellar thickness distribution. These morphological parameters evolve in different stages, depending on the additive used. It has been found that the LDPE–Mater‐Bi samples are the ones exhibiting faster changes in their crystalline content. However, the LDPE blends with Cornplast and Bioefect display more significant changes in their lamellar thickness distribution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1683–1691, 2002

Rheological study of the miscibility of LLDPE/LDPE blends and the influence of Tmix

AbstractThe miscibility of LLDPE and LDPE blends and the influence of mixing temperature (Tmix) are discussed. Adequate amounts of antioxidants were added during melt blending. Dynamic and steady shear measurments were carried out at 190°C in a Rheometrics Mechanical Spectrometer 800.The dependence of rheological properties on blend composition indicated that blends of LLDEPE (butene) and LDPE mixed at 190°C and 220°C are only partially miscible; immiscibilty is likely to occur around the 50/50 composition and in the LDPE‐rich blends. Blends at 190°C are likely miscible in the LLDPE‐rich range. Tncreaasing Tmix did improve the miscibility of LLDPE/LDPE blends at 190°C or influence the dynamic sher properties (η′ or G′) of the “pure” resins of blends. Suggested that the molecular order [see Hussein and Williams, J. Non‐Newt. Fluid Mech., 86 105 (1999); Hussein and Williams, Macromol. Rapid Commun., 19, 323 (1998)] and mismatch of the molecular conformations of different polyethylene structures provide an explanation for the immiscibility of polyethylenes. Agreement was observed between themeasured dynamic properities and theortical predictions of Palierne and Bousmina‐Karner emulsion models.

Chemical modification of cassava starch for degradable polyethylene sheets

Cassava starch was chemically modified by radiation grafting with acrylic acid to obtain cassava starch graft poly(acrylic acid), which was further modified by esterification and etherification with poly(ethylene glycol) 4000 and propylene oxide, respectively. The modified product was characterized by NMR spectroscopy and contact angle measurement. The blends of LDPE with EBS wax had properties similar to the LDPE blends with the modified starch in terms of surface wettability, tensile properties, and hardness, but with a much better degradation in soil due to the much higher water absorption. This article describes the chemical modifications of hydrophilic cassava starch to become partially hydrophobic, which was then used for blending with LDPE sheets for evaluations of mechanical, thermal and degradation properties.

Studies on biodegradability, morphology and thermo-mechanical properties of LDPE/modified starch blends

Starch was converted to a hydrophobic derivative by phthalation. The starch phthalate (stath) thus obtained was found to show highly crystalline nature and sharp melting point. The potential of stath as a substitute for starch in the development of biodegradable blends was investigated. Blends of LDPE containing upto 30% starch were prepared and the latter was gradually replaced by stath. It was observed that the tensile strength and elongation at break increased while the modulus decreased as the starch was substituted by stath. Morphology of binary LDPE/stath blends showed improved adhesion leading to enhanced mechanical properties compared to LDPE/starch blends. DSC analysis showed no significant change in the T m of LDPE by incorporation of 30% stath in spite of a wide difference in the T m of the two components. Biodegradation of starch was found to decrease on esterification. However, the LDPE/stath blends showed greater degradation in soil compared to LDPE/starch blends.

Electrical Properties of Electron Beam Modified Films of Thermoplastic Elastomeric LDPE and EVA Blends

Electrical Properties of Electron Beam Modified Films of Thermoplastic Elastomeric LDPE and EVA Blends

BENEFITS OF COEXTRUDED LLDPE/LDPE FILM VS. BLENDED LLDPE/LDPE FILM

The benefits of three-layer coextrusion versus a mono-layer blend of the same resins are explored. Good design considerations of the coextruded structure can allow a processor to take advantage of the performance characteristics of the resins and the equipment. These performance characteristics can be compromised in a mono-layer blend of the same materials. Expected benefits of coextrusion can be improved physical properties and reduction in additives required for good processing. These are accomplished by eliminating blends of LDPE and LLDPE, reducing the draw-down ratio and taking advantage of the rheological differences between LDPE and LLDPE.