Thermal characterisation of LDPE and LLDPE blends

Two series of film formulations are investigated comprising blends of a metallocene-catalyzed linear low-density polyethylene (mLLDPE) or a conventional linear low-density polyethylene (LLDPE) with a low-density polyethylene (LDPE). The physicomechanical and optical properties are studied at various gauge lengths to investigate the effects of downgauging the films, particularly those containing mLLDPE. The potential for downgauging is found to be optimum at higher levels of mLLDPE with the best results achieved for a film containing 40 wt.% mLLDPE at 60 mm. This formulation has significantly better properties than an analogous blend containing 40 wt.% LLDPE at 100 mm. The potential materials and cost savings associated with downgauging films is also briefly investigated.

Studies on melt flow properties of low density and linear low density polyethylene blends in capillary extrusion

Morphology and permeability of bio-based poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS) and linear low-density polyethylene (LLDPE) blend films control shelf-life of packaged bread

This paper reported the effect of starch-based additive (PSN), on the rheology, morphology and thermal behavior of low-density polyethylene (LDPE). PSN was a commercial masterbatch of corn starch and linear low-density polyethylene (LLDPE) in the ratio of 45/55. Compositions of LDPE/PSN blend ratios at 100/0, 80/20, 70/30 and 60/40 were prepared by melt blending. It was found that addition of PSN to LDPE decreased its storage modulus (G′), loss modulus (G′′) and dynamic viscosity (η′) especially at low frequency. Results of the loss tangent (tan δ) measurements indicated a tendency of forming a maximum in the low-frequency region for the samples with high PSN content. Effect of temperature on the viscosity indicated that Arrhenius-type relation with a single slope was followed by neat LDPE, while the LDPE filled with PSN followed a non-Arrhenius-type relation with multiple slopes. Differential scanning calorimeter results indicated that the blend was partially compatible. Thermogravimetric measurement results confirmed that no degradation could happen at the temperature of rheology tests. Scanning electron microscopy studies revealed that starch was uniformly distributed in the blend of LDPE and LLDPE.

A two-step isothermal annealing (TSIA) procedure is described that enables the endothermic peaks of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and their blends, to be satisfactorily resolved during analysis by differential scanning calorimetry. A modified form of multistep isothermal annealing, the TSIA procedure produces a highly characteristic profile of the blend components by facilitating the segregation of the phases based on branch density. It is proposed that the TSIA procedure may have significant merit in the identification and quantification of the components in an unknown blend as well as increasing the sensitivity in analytical procedures aimed at blend component quantification.

In this work, blends of poly(butylene terephthalate) (PBT) and linear low-density polyethylene (LLDPE) were prepared. LLDPE was used as an impact modifier. Since the system was found to be incompatible, compatibilization was sought for by the addition of the following two types of functionalized polyethylene: ethylene vinylacetate copolymer (EVA) and maleic anhydride-grafted EVA copolymer (EVA-g-MAH). The effects of the compatibilizers on the rheological and mechanical properties of the blends have been also quantitatively investigated. The impact strength of the PBT–LLDPE binary blends slightly increased at a lower concentration of LLDPE but increased remarkably above a concentration of 60 wt % of LLDPE. The morphology of the blends showed that the LLDPE particles had dispersed in the PBT matrix below 40 wt % of LLDPE, while, at 60 wt % of LLDPE, a co-continuous morphology was obtained, which could explain the increase of the impact strength of the blend. Generally, the mechanical strength was decreased by adding LLDPE to PBT. Addition of EVA or EVA-g-MAH as a compatibilizer to PBT–LLDPE (70/30) blend considerably improved the impact strength of the blend without significantly sacrificing the tensile and the flexural strength. More improvement in those mechanical properties was observed in the case of the EVA-g-MAH system than for the EVA system. A larger viscosity increase was also observed in the case of the EVA-g-MAH than EVA. This may be due to interaction of the EVA-g-MAH with PBT. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 989–997, 1999

New linear low-density polyethylene (LLDPE) blends were investigated to use as stretch and breathable films. In our investigation different types of LLDPE blends were prepared by extrusion. The characteristic melting and crystallization temperatures of these LLDPE blends were determined. Specimens were injection moulded and their tensile properties were measured. The LLDPE blends with the best thermal and mechanical results were chosen to prepare film by film blowing in laboratory conditions. Tearing properties of the films were also investigated. Our aim was to determine the most appropriate LLDPE blend for stretch film usable under industrial conditions.

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

Melt blending of linear low density polyethylene (LLDPE) and polylactide (PLLA) was performed in an extrusion mixer with post extrusion blown film attachment with and without compatibilizer-grafted low density polyethylene maleic anhydride. The blend compositions were optimized for tensile properties as per ASTM D 882-91. Based on this, LLDPE 80 (80 wt% LLDPE & 20 wt% PLLA) and M-g-L 80/4 (80 wt% LLDPE, 20 wt% PLLA and 4 parts compatibilizer per hundred parts of resin) were found to be an optimum composition. FTIR reveals that the presence of compatibilizer shifts carbonyl peak hence some increase in interaction between LLDPE and PLLA. Morphological characteristics of the fracture surface of with and without compatibilizer blends were examined by scanning electron microscopy. It shows that use of compatibilizer enhances the dispersions of PLLA in LLDPE matrix. Thermogravimetric (TG) analysis of blends shows the M-g-L 80/4 blend has higher thermal stability among studied blends. The degradation study under different pH of soil compost gives that in alkaline condition and the presence of compatibilizer was favorable for degradation. This blend may be used for packaging application.

Focusing on the study of the phase separation behavior of triblock copolymer and linear low-density polyethylene (LLDPE) systems helps to understand the influence of microstructure on the properties of poly(vinylcyclohexane)-b- poly(ethylene)-b-poly(vinylcyclohexane) (PVCH-PE-PVCH/LLDPE) blends. We prepared a series of blends of LLDPE and PVCH-PE-PVCH and explained their compatibility from the microstructure. The research findings indicate that despite having similar block compositions, PVCH-PE-PVCH with a higher molecular weight exhibits significantly stronger phase separation and crystallization ability compared to PVCH-PE-PVCH with lower molecular weight. In PVCH-PE-PVCH/LLDPE blends, the addition of 10 %, 20 %, and 30 % LLDPE induces earlier crystallization and crystal phase separation of polyethylene (PE) fragments. In addition, compared to the lower molecular weight of PVCH-PE-PVCH, the higher molecular weight of PVCH-PE-PVCH exhibits a higher tendency for independent crystallization and shows significant crystal phase separation during the cooling crystallization process when blended with LLDPE. The PE segments in the lower molecular weight of PVCH-PE-PVCH can more easily enter the nanoscale domain of LLDPE. Impact fracture electron microscopy also reveals better compatibility between the lower molecular weight of PVCH-PE-PVCH and LLDPE compared to the higher molecular weight of PVCH-PE-PVCH. Furthermore, the blends of lower molecular weight of PVCH-PE-PVCH and LLDPE exhibit a greater growth rate in elongation at break.

The kinetics of crosslinking reaction of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) using dicumyl peroxide (DCP) as the initiator and tetrakis [methylene 3-(3’,5’-di-t-butyl-4’-hydroxyl)propanoate] (Irganox 1010) as the inhibitor were studied using Brabender Plasti-Corder (BPC) and Differential Scaning Calorimeter (DSC). The crosslinking reaction in the absence of inhibitor was found to be first order with respect to initiator concentration, while in the presence of inhibitor, the reaction was first order with respect to initiator concentration and 0.21-0.31 with respect to inhibitor concentration at 446 K for BPC and 413 K for DSC. In addition, the rate constant in the presence of inhibitor was found to be around three time lower than that in the absence. The activation energy of crosslinking reaction of LDPE and LLDPE were 118 and 112 kJ/mol, respectively for BPC technique and 184 and 176 kJ/mol, respectively for DSC technique. The pre-exponential factor of crosslinking reaction of LDPE and LLDPE were respectively 3.23 x 10¹¹ and 0.82 x 10¹¹ sec⁻¹ for BPC technique and 3.56 x 10¹⁹ and 3.64 x 10¹⁸ sec⁻¹ for DSC technique. The fraction of termination was determined and found that approximately 65% was terminated by combination of polymer radicals, while 35% was terminated by disproportionation and cyclization. The amount of DCP higher than 1.6%w/w used for the crosslinking reaction gave the degree of crosslinking in polymer greater than 80%. When 0.1-0.2%w/w of Irganox 1010 was used in the preparation of compound LDPE or LLDPE containing about 2%w/w DCP, the degree of crosslinking was constant at more than 80%. For the Iragox 1010 concentration greater than 0.2%w/w, the degree of crosslinking decreased with increasing inhibitor concentration.

Linear and branched polyethylene resins are extensively used in film production for packaging. Branched polyethylenes, such as low density polyethylene (LDPE), are unique due to their high melt strength and good optical properties; while linear polyethylenes, such as linear low density polyethylene (LLDPE), exhibit excellent physical properties and drawdown capabilities The combination of both resins via blends or coextrusion provides a mix of film properties very difficult to achieve with pure materials. This paper evaluates the performance of thick blown films made from blends of LLDPE (1.0 melt index, 0.926 density) with high pressure LDPE (0.2 melt index, 0.920 density), versus three-layer coextruded films made of the same materials at the same resin ratios. A major market for these films is in pack aging free-flowing granular products. The objective is to answer which fabrication method yields superior mechanical properties, as well as outline the fundamental reasoning to understand the differences through structural and morphological analyses

Miscibility and rheological characteristics of biodegradable aliphatic polyester and linear low density polyethylene blends

The effects of cryogenically ground rubber tires (CGT) on some of the mechanical properties of blends with linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) are presented. Precoating the CGT particles with an ethylene‐acrylic acid copolymer is shown to overcome most of the deleterious effects of adding CGT to LLDPE, while still retaining composite processability. A blend of 40 wt% EAA coated CGT particles with LLDPE is shown to have impact and tensile strengths that are 90% of those for the pure LLDPE, representing increases of 60 and 20%, respectively, over blends with uncoated particles. Blends of LLDPE with ground tire bladders demonstrate that even better mechanical properties can be obtained with similar large rubber particle size but somewhat better adhesion. For HDPE, however, it is shown that with large rubber particles, moderate adhesion is not sufficient to produce useful composites.

Oriented structure and anisotropy properties of polymer blown films: HDPE, LLDPE and LDPE