Rheology modifier additive for enhanced processability of polyethylene for blown-Film applications

Polyethylene is a versatile polymer suitable for a large variety of flexible and rigid packaging applications. Its mechanical and rheological properties can be tuned across a wide range by controlling its molecular architecture, such as the amount and distribution of olefinic comonomers (short chain branching), long chain branching, and molecular weight distribution. Linear low-density polyethylene (LLDPE) is known for its high toughness which enables downgauged film structures and low-density polyethylene (LDPE) is known for its excellent shear thinning and melt strength which enables enhanced processability and high throughput, such as on blown film lines. In order to obtain a balance of toughness and processability on films produced on blown film lines, blends of LLDPE and LDPE are commonly used. In this paper, we describe additive-based approaches, including a new product, DOWLEX™ (TM = trademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow) GM AX01, which enhances melt strength and other rheological properties of polyethylene, enabling fabrication of films with lower LDPE content while still maintaining excellent rheological properties and higher toughness versus conventional LLDPE/LDPE blends. The higher toughness enables downgauging without loss of mechanical properties, which in turn reduces consumption of polymer resulting in a more sustainable solution.     

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.     

Effect on thermal,mechanical, and biodegradable properties of plasma-treated fish scale powder/linear low-density polyethylene polymer composite films

In the present work, we report the effect of low-temperature plasma treatment on thermal, mechanical, and biodegradable properties of polymer composite blown films prepared from carp fish scale powder (CFSP) and linear low-density polyethylene (LLDPE). The CFSP was melt compounded with LLDPE using a filament extruder to prepare 1, 2, and 3 wt.% of CFSP in LLDPE polymer composite filaments. These filaments were further pelletized and extruded into blown films. The blown films extruded with 1, 2, and 3 wt.% of CFSP in LLDPE were tested for thermal and mechanical properties. It was observed that the tensile strength decreased with the increased loading content of CFSP, and 1% CFSP/LLDPE exhibited the highest tensile strength. To study the effect of low-temperature plasma treatment, 1% CFSP/LLDP polymer composite with high tensile strength was plasma treated with O₂ and SF₆ gas before blow film extrusion. The 1% CFSP/LLDPE/SF₆-extruded blown films showed increased thermal decomposition, crystallinity, tensile strength, and modulus. This may be due to the effect of crosslinking by the plasma treatment. The maximum thermal decomposition rate, crystallinity %, tensile strength, and modulus obtained for 1% CFSP/LLDPE/SF₆ film were 500.02°C, 35.79, 6.32 MPa, and 0.023 GPa, respectively. Furthermore, the biodegradability study on CFSP/LLDPE films buried in natural soil for 90 days was analyzed using x-ray fluorescence. The study showed an increase in phosphorus and calcium mass percent in the soil. This is due to the decomposition of the hydroxyapatite present in the CFSP/LLDPE biocomposite.     

Polyethylene with MoS2 nanoparticles toward antibacterial active packaging

Molybdenum disulfide (MoS₂) nanoparticles, obtained from liquid phase exfoliation in the presence of chitosan, were melt mixed with a linear low-density polyethylene (LLDPE) matrix to produce novel antimicrobial active packaging materials. The LLDPE/MoS₂ composites presented exfoliated nanoparticles forming aggregates that are well dispersed in the polymer matrix. These 2D-layered MoS₂ nanoparticles at concentrations of 0.5, 1.0, and 3.0 wt% rendered several functionalities to the LLDPE, as for example an antimicrobial behavior against Salmonella typhi and Listeria monocytogenes bacteria that can be explained not only by the photoactivity of the filler but also by changes in the composite surface. For instance, the composites presented a reduction in the water contact angle (i.e., an increased hydrophilicity) and relevant changes in the surface topography (i.e., reduced roughness) as compared with pure LLDPE. Regarding the barrier properties, while MoS₂ dramatically increased the water vapor permeation (WVP) of the polymer matrix, until 15 times for composite with 3.0 wt% of filler, the oxygen permeation decreased around 25%. All these novel functionalities in the nanocomposites were obtained without significantly affecting the tensile mechanical properties of the pure LLDPE matrix. These results show that MoS₂ is a promising filler for the development of antibacterial active packaging films with behaviors as similar as other 2D-layered fillers such as graphene derivatives.     

Thermoplastic vulcanizate nanocomposites based on polyethylene/reclaimed rubber: A correlation between carbon nanotube dispersion state and electrical percolation threshold

A three-step melt blending process was utilized to produce linear low-density polyethylene (LLDPE)/reclaimed rubber (RR)/carbon nanotube (CNT) nanocomposites in the presence of maleic anhydride grafted polyethylene as a compatibilizer. The effect of LLDPE/RR ratio and CNT content on the morphological, thermal, mechanical, and rheological behavior of these dynamically vulcanized LLDPE/RR nanocomposites were investigated. The morphological study showed that the RR was dispersed in the LLDPE matrix, and CNT addition led to an improved morphology as smaller RR sizes inside LLDPE were observed. The mechanical results revealed that increasing the RR content decreased the hardness, modulus of elasticity, and elongation at break while CNT improved the tensile properties and other mechanical properties. The differential scanning calorimeter analysis showed that the CNT improved the LLDPE crystallization by acting as nucleation agents. Dynamic mechanical analysis showed higher storage modulus and lower loss factor as compared to the neat blend due to mobility restrictions of the polymer chains induced by the presence of CNT. For the conditions studied, the electrical percolation threshold was found to occur at a very low CNT concentration (about 1 wt %) compared to the literature because of the specific structure produced leading to CNT residing in the LLDPE matrix and at the interface between both polymeric phases. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47795.     

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.     

Preparation of Cu/OMMT/LLDPE nanocomposites and synergistic effect study of two different nano materials in polymer matrix

Cu/OMMT (organo-montmorillonite)/LLDPE (linear low-density polyethylene) nanocomposites were prepared via melt mixing combined with melt extruding process. X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectra, scanning electron microscope (SEM), and transmission electron microscopy (TEM) were employed to characterize the resultant nanocomposites. The results showed that the OMMT layers were exfoliated and the nano-Cu particles were distributed uniformly in the polymer matrix. And the introduction of nanofiller into LLDPE matrix had little effect on the crystallinity of the polymer. The salt spray tests showed that OMMT and nano-Cu could improve the anticorrosion properties of LLDPE matrix, respectively. And the coexistence of OMMT and nano-Cu in Cu/OMMT/LLDPE nanocomposites could produce a synergistic effect on enhancing the anticorrosion properties. Furthermore, the co-incorporation of OMMT and nano-Cu into the polymer matrix also increased the thermal-oxidative stability and mechanical properties of LLDPE matrix significantly, as compared with the Cu/LLDPE and OMMT/LLDPE nanocomposites due to the synergistic effect. The bactericidal properties evaluation showed that the bactericidal ability of Cu/OMMT/LLDPE increases with nano-Cu content effectively.     

New strategy for preparation of LLDPE nanocomposites through tandem catalytic system

Tandem catalytic system composed of the ethylene trimerization catalyst CrCl₃/bis(2-butylsulfanyl-ethyl)amine) (SNS) ( I ) and the ethylene copolymerization catalyst zirconocene dichloride ( II ) has been introduced for preparation of linear low-density polyethylene (LLDPE). The catalytic behavior of the novel catalyst ( I ) activated by modified methyl aluminoxane was tested that afforded 1-hexene (1-C₆) with the activity of 141,370 g 1-C₆/mol-Cr h. The butyl branches in the polymers prepared by tandem catalysis method were determined utilizing Fourier transform infrared (FTIR) spectroscopy for the first time. The higher Cr/Zr molar ratio led to increasing the butyl content within the prepared copolymer up to 10.38 butyl branches per 1000 C in the polymer chain. LLDPE nanocomposites having different types of nanofillers (TiO₂, Santa Barbara Amorphous-15, and Fe₃O₄ magnetic nanoparticles) were prepared and analyzed by FTIR, scanning electron microscopy (SEM), differential scanning calorimetry, and thermogravimetric analysis. Increasing the sonication time up to 60 min enhanced the nanoparticles dispersion in the polymeric matrix. SEM images of the nanocomposites with various amounts of nanofillers, showed the best dispersion of the nanofillers in the presence of 50 mg nanofiller in toluene solvent. The presence of the nanofillers also increased the hydrophilicity of the polymer surface. Antibacterial activity against Gram-negative bacteria was also observed for the prepared nanocomposites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47497.     

Effect of Ionomeric Compatibilizer on Clay Dispersion in Polyethylene/Clay Nanocomposites

Summary: Linear low‐density polyethylene (LLDPE)/clay nanocomposites are obtained and studied by using a zinc‐neutralized carboxylate ionomer as a compatibilizer. LLDPE‐g‐MA is used as a reference compatibilizer. Two different clays, natural montmorillonite (Closite Na⁺) and a chemically modified clay Closite 20A have been used. Nanocomposites are prepared by melt blending in a twin‐screw extruder using two mixing methods: two‐step mixing and one‐step mixing. The relative influence of each compatibilizer is determined by wide‐angle X‐ray diffraction structural analysis and mechanical properties. The results are analyzed in terms of the effect of the compatibilizing agent and incorporation method in the clay dispersion, and the mechanical properties of the nanocomposites. Experimental results confirm that the film samples with ionomer show a good mechanical performance only slightly below that of the samples with maleic anhydride (MA). The two‐step mixing conditions result in better dispersion and intercalation for the nanofillers than one‐step mixing. The exfoliation of clay platelets leads to an improved thermal stability of the composite. The oxygen permeability of the clay nanocomposites, using ionomer as a compatibilizer, is decreased by the addition of the clay.

TEM image of a PE/4 wt.‐% Closite 20A nanocomposite formed using ionomer.     

New compatibilizer for linear low‐density polyethylene (LLDPE)/clay nanocomposites

Linear low‐density polyethylene (LLDPE) is one of the most widely used polymers in many fields, but it is difficult to prepare LLDPE/clay nanocomposites because of the hydrophobic nature of LLDPE. In this study, the effectiveness of low molecular weight trimethoxysilyl‐modified polybutadiene (Organosilane) as a compatibilizer for LLDPE/clay nanocomposites was studied using X‐ray diffraction (XRD) and correlated with mechanical properties. Organosilane is known to react with dicumyl peroxide (DCP) to form free radicals, which react with LLDPE increasing the polarity of the LLDPE. Based on XRD and mechanical tests, it was concluded that Organosilane is a good compatibilizer for LLDPE and clay. Also when Organosilane was used in preparing LLDPE/clay nanocomposite foams, most mechanical properties were improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of linear low-density polyethylene and halloysite nanotube (LLDPE/HNT) composites based on two-roll calendering melt fabrication

In preparation of polymer nanocomposites, achieving good mixing and uniform distribution of nanofillers is highly desired for property enhancement. Polyethylene (PE) and its nanocomposite with halloysite nanotubes (HNTs) possesses a myriad of potentials for advanced engineering properties. A high nanoparticle loading is preferred to capitalize the nano-reinforcement, thermal, and barrier properties. The capability of a two-roll calendaring machine to disperse HNT particles into a linear low-density polyethylene (LLDPE) matrix at elevated processing temperatures was assessed. Morphological, thermal, mechanical, and rheological behavior of prepared nanocomposites were characterized. A homogeneous distribution of HNTs in concentrations up to 5 wt.% was evidenced by SEM analysis. TGA showed the 10 wt.% composite exhibited an overall outstanding thermal stability. DSC analysis revealed the 30 wt.% sample has the highest T_m and T_c, and the %crystallinity did not change much due to HNT incorporation for all samples. DMA showed the storage and loss moduli increased with increase in HNT loadings. The effect of loading HNTs into the LLDPE matrix on T_g was minimal, implying that LLDPE and HNTs are quite compatible. The results demonstrated that the two-roll mill fabrication method can efficiently keep HNT particles unagglomerated and disperse them evenly into the LLDPE matrix.     

Rheological aspects and film processability of poly (lactic acid)/linear low-density polyethylene blends

Poly (lactic acid) (PLA) and Linear low-density polyethylene (LLDPE) were compounded in a corotating twin screw extruder. PE-g-glycidyl methacrylate was also added as a reactive compatibilizer in PLA/LLDPE blend system, which lowered interfacial tension between PLA and LLDPE. Blown films were prepared by using a single-screw extruder for all compounded blends. The investigation of the rheological properties of a polymeric system is very important to study the processability and understand structure-property relationship in blown films. In the present research work, the rheological properties have been investigated to assess the processability of blown films of PLA/LLDPE blends. Oscillatory shear rheology viscoelastic spectra showed an increase in the storage and loss moduli with the increase in LLDPE and compatibilizer content, which indicated pronounced viscoelastic behavior of PLA with the addition of LLDPE and compatibilizer. A steady increase in the value of extensional viscosity as a function of time was observed with the addition of LLDPE and compatibilizer in PLA. The blends with higher LLDPE content exhibited much more prominent strain hardening characteristics than those with lower LLDPE content.     

Preparation and properties of polyethylene/montmorillonite nanocomposites formed via ethylene copolymerization

BACKGROUND: In situ formation of polyethylene/clay nanocomposites is one of the prevalent preparation methods that include also solution blending and melt blending with regard to process simplification, economy in cost, environment protection and marked improvement in the mechanical properties of the polymeric matrix. In the work reported here, the preparation of linear low‐density polyethylene (LLDPE) and fabrication of polymer/clay nanocomposites were combined into a facile route by immobilizing pre‐catalysts for ethylene oligomerization on montmorillonite (MMT). RESULTS: [(2‐ArN?C(Me))₂C₅H₃N]FeCl₂ (Ar = 2,4‐Me₂(C₆H₃)) was supported on MMT treated using three different methods. The MMT‐supported iron complex together with metallocene compound rac‐Et(Ind)₂ZrCl₂ catalyzed ethylene to LLDPE/MMT nanocomposites upon activation with methylaluminoxane. The oligomer that was formed between layers of MMT promoted further exfoliation of MMT layers. The LLDPE/MMT nanocomposites were highly stable upon heating. Detailed scanning electron microscopy analysis revealed that the marked improvement in impact strength of the LLDPE/MMT nanocomposites originated from the dispersed MMT layers which underwent cavitation upon impact and caused plastic deformation to absorb most of the impact energy. In general, the mechanical properties of the LLDPE/MMT nanocomposites were improved as a result of the uniform dispersion of MMT layers in the LLDPE matrix. CONCLUSION: The use of the MMT‐supported iron‐based diimine complex together with metallocene led to ethylene copolymerization between layers of MMT to form LLDPE/MMT nanocomposites. The introduction of exfoliated MMT layers greatly improved the thermal stability and mechanical properties of LLDPE. Copyright © 2009 Society of Chemical Industry     

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.     

Rheological and dynamic mechanical characteristics of rotationally moldable linear low‐density polyethylene fumed silica nanocomposites

In rotational molding process, polymer powders undergo a cycle of heating, melting, cooling, and subsequent solidification in the mold. Resins, like linear low‐density polyethylene (LLDPE), are used in this process on a large scale mainly because of its good mechanical properties and excellent thermal stability. Yet, incorporation of additives is necessary to further improve the visco‐elastic, thermal as well as melt flow properties of the resin. This study investigates the effects of nanocomposites of fumed silica (FS) with rotationally moldable LLDPE. Thermal transitions in the LLDPE‐FS nanocomposites were investigated and correlated with their melt flow characteristics. The effect on melt processing during rotational molding and compounding, were analyzed by melt flow index and torque rheometry studies. A suitable blend of FS in LLDPE has been recommended for rotational molding based on rheological studies and dynamic mechanical analysis. POLYM. COMPOS., 37:2995–3002, 2016. © 2015 Society of Plastics Engineers     

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.     

Effect of Back-layer on seal performance of multilayer polyethylene-based sealant films

This work studies effects of back-layer materials, thickness of sealant layer, and sealing condition on seal performance of multilayer polyethylene-based films. Multilayer films with back-layers of high-density polyethylene (HDPE), or low-density polyethylene (LDPE), or linear low-density polyethylene (LLDPE) were produced with different thicknesses of the metallocene layer. It was found that increasing the thickness of the metallocene layer improved hot tack properties. In addition, films with back-layers of LLDPE or LDPE showed higher hot tack strength compared to those with HDPE back-layer. Increasing sealing temperature reduced significantly the hot tack strength and its dependency on metallocene layer thickness. It was found that increasing delay time after sealing, before peeling test, increased hot tack strength, but the rate of hot tack evolution and the type of peeling behavior were considerably affected by the type of back-layer material. The effect of dwell time was also examined, and it was observed that increasing dwell time in the studied range did not affect the hot tack evolution. The mechanisms involved in the development of hot tack evolution were discussed, and it was shown that the back-layer effects can be explained by bulk viscoelastic energy dissipation theory.     

Preparation and Properties of Ethylene-vinyl Acetate/linear Low-density Polyethylene/Graphene Oxide Nanocomposite Films

Ethylene-vinyl acetate-based nanocomposites with 18 and 28 wt% vinyl acetate were prepared via solution casting method. To improve the mechanical and barrier properties of ethylene-vinyl acetate, linear low-density polyethylene, and graphene oxide were introduced to matrix. The morphological studies indicated that the graphene oxide diffraction peak disappeared in all prepared nanocomposites, probably due to its exfoliation; also proper dispersion and good interaction between nanofillers and polymer matrix were achieved. By introducing low amount of graphene oxide into the matrix, the mechanical and thermal properties and oxygen permeability were improved especially for those with 28 wt% vinyl acetate monomer.     

Shear and elongational behavior of linear low-density and low-density polyethylene blends from capillary rheometry

In this work we present an experimental study of shear and apparent elongational behavior of linear low-density (LLDPE) and low-density (LDPE) polyethylene blends by means of capillary rheometry. The characterization of these rheological properties is crucial in the design of a blend that combines the ease of processing of LDPE with the mechanical advantages of the LLDPE. Two different low-density polyethylenes and one common linear low-density polyethylene were used to prepare the blends. The results obtained indicate a strong sensitivity of the rheology of the blend to changes in the molecular weight of the LDPE employed. For the higher molecular weight LDPE, the shear viscosity of the blend was essentially equal to that of the LDPE homopolymer up to a concentration of 25% of LLDPE, whereas the apparent extensional viscosity was appreciably lower. For the lower molecular weight LDPE, the same trend was obtained regarding the shear viscosity, but in this case the apparent extensional viscosity of the blend was somewhat higher than that of the LDPE homopolymer.     

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.