Low Density Polyethylene Nanocomposites Research Articles

Cetylpyridinium bromide-modified montmorillonite as filler in low density polyethylene nanocomposite films

The development of clay polymer nanocomposites has been presented as an interesting alternative for design of new active food packaging materials. In this work, low density polyethylene (LDPE) nanocomposites with cetylpyridinium bromide (CPB) – modified montmorillonite (Mt) were developed. In a first stage, Mt. was modified with different CPB proportions based on cation exchange capacity (1:1 and 2:1), resulting in two different organoclays. These modified clays were hydrophobic and presented a good thermal stability that favored their capacity for extrusion to develop LDPE nanocomposites. Based on the incorporated organoclay, nanocomposite films showed important changes in morphology, and differences in mechanical properties, crystallinity, and gas permeability in comparison to polyethylene. All nanocomposites showed greater opacity than LDPE, however, their color changes did not exceed the visual perception limit. Finally, electrical conductivity (EC) measurements showed that CPB was able to migrate from the nanocomposite films to an aqueous food simulant. This behavior was dependent on the availably of free CPB in the matrix, its disposition in the organoclay and the organoclay distribution into the polymer matrix. These results highlight the migration of the surfactant from LDPE nanocomposites with Mt./CPB organoclays, making montmorillonite a potential surfactant carrier that increases compatibility and function in polymers allowing the generation of novel materials that could be used in the design of food packaging.

Electrical Breakdown Properties of Clay-Based LDPE Blends and Nanocomposites

Microstructure and electrical breakdown properties of blends and nanocomposites based on low-density polyethylene (LDPE) have been discussed. A series of LDPE nanocomposites containing different amount of organomodified montmorillonite (clay) with and without compatibilizer have been prepared by means of melt compounding. Two sets of blends of LDPE with two grades of Styrene-Ethylene-Butylene-Styrene block copolymers have been prepared to form cocontinuous structure and host the nanoreinforcement. A high degree of dispersion of oriented clay was observed through X-ray diffraction, scanning, and transmission electron microscopy. This was confirmed by the solid-like behavior of storage modulus in low frequencies in rheological measurement results. An alteration in the morphology of blends was witnessed upon addition of clay where the transportation phenomenon to the copolymer phase resulted in a downsizing on the domain size of the constituents of the immiscible blends. The AC breakdown strength of nanocomposites significantly increased when clay was incorporated. The partially exfoliated and intercalated clay platelets are believed to distribute the electric stress and prolong the breakdown time by creating a tortuous path for charge carriers. However, the incorporation of clay has been shown to diminish the DC breakdown strength of nanocomposites, mostly due to the thermal instability brought by clay.

Effect of Graphene Nanoplatelets and Paraffin Oil Addition on the Mechanical and Tribological Properties of Low-Density Polyethylene Nanocomposites

Polymeric nanocomposite materials have solved many problems due to their extensive applications such as aerospace, automobiles, coatings, and packaging materials. Low-density polyethylene (LDPE)/graphene nanoplatelets (GNPs) impregnated by paraffin oil (PO) were fabricated by a hot compression technique. Elastic modulus was calculated by results of compression test that conducted on the testing nanocomposites using a universal testing machine. Microhardness of LDPE and its composites was measured by Vickers microhardness testing machine. Tribological properties of LDPE and its composites were investigated by pin-on-disc tester at 20 N normal load, $$1.2~\hbox {ms}^{-1}$$ sliding velocity, and 212 m sliding distance. The results showed that the elastic modulus and microhardness of LDPE/GNP nanocomposites are higher than that of pure LDPE and then gradually decreased by adding PO contents. Tribological properties proved that LDPE/GNP nanocomposites have lower coefficient of friction (COF) and wear rates in comparison with pure LDPE. By adding PO contents to the LDPE and its composites, COF and wear rates were gradually increased. Wear specimens’ surfaces were imaged using scanning electron microscope.

Experimental and MD simulation study on the physical and mechanical properties of organically modified montmorillonite clay and compatibilized linear low density polyethylene nanocomposites

ABSTRACTUnderstanding the interfacial interactions plays a key role in controlling mechanical and physical properties of polymer/clay nanocomposites (PCNs). In this work, the surface interactions between constituents of experimentally prepared PCNs which are the pristine linear low density polyethylene (PE) chains, PE compatibilizers, montmorillonite clay surface layer, and surfactants were studied quantitatively by employing molecular dynamics simulation technique. The interaction energy between the polymer and the clay was found to be inversely proportional with the volume of the surfactant which decreases the electrostatic interactions between the compatibilizer and the hydrophilic clay surface. However, the van der Waals (vdW) interactions between alkyl tails of surfactants and the PE chains increase with the tail length of the surfactants. The most attractive interaction was between the surfactant's head group and the clay surface. We showed that there existed fine balance between the electrostatic and vdW type forces on the stability and the enhanced properties of the PE–organoclay nanocomposites. Calculated interaction energies were then correlated to the experimentally measured mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45817.

Sandwiched structure effect on space charge characteristics of alumina/polyethylene nanocomposites

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have been attracted more attention. In this paper, the novel sandwich-structured low-density polyethylene (LDPE) nanocomposites filled with nano-sized Al 2 O 3 particles were prepared by layer-by-layer hot pressing method. For comparison, the homo-dispersed LDPE composites with nano-Al 2 O 3 were also prepared. Morphology, breakdown strength, space charge distribution and electrical conductivity of the specimens were investigated. Morphologies of the composites were characterized by scanning electron microscopy (SEM), and their space charge profiles were measured by pulsed electro-acoustic (PEA) method. SEM images showed that there are no obvious interfaces between the adjacent layers. The breakdown strength of the sandwich-structured LDPE nanocomposites is higher than that of the homo-dispersed ones. Besides, the charge profiles indicated that space charge suppression of the sandwich-structured LDPE composites was better than that of homo-dispersed ones. Under the electrical field of 50 kV/mm at 70 °C, the conductivity of homo-dispersed nanocomposite almost approaches to 1.0 ×10−11 S/m, which is almost four-fold over that of 1%N/LDPE/1%N (i.e, 2.5 ×10−12 S/m). It was concluded that the excellent electrical insulating properties of the sandwich-structured nanocomposites were attributed to the traps existing on the interfaces, which could effectively inhibit the charge injection.

Measurement of Dielectric Properties of Low-Density Polyethylene Nanocomposites Using “Sub-Hertz” Dielectric Spectroscopy

Recently, many studies have been conducted on the dielectric properties of Low-Density Polyethylene (LDPE) nanocomposites and produced different results. However, the composition of LDPE polymer and boron nitride (BN) as nanofiller has neither been well understood nor producing a convenient result. Similarly, the dielectric spectroscopy measured at “sub–hertz” frequency has been of little interest among researchers since it is often influenced by “conduction-like” effect. This research identified the dielectric properties of LDPE nanocomposites filled with hexagonal boron nitride (h-BN) nanofillers by using dielectric spectroscopy technique. The dielectric loss and relative permittivity for three different filler concentrations were investigated under “sub-hertz” frequency ranges at room temperature. The cylindrical electrode with guard ring configuration was used to conduct the experiment, in accordance to the ASTM D150 standard. The results revealed that 5 wt% filled polymer has lower loss tangent and permittivity compared to the unfilled polymer, due to the strong interaction between nano-particle and the polymer. This strong interaction is believed to limit the movement of the polymer chain. The decrease in loss tangent also indicates lower quasi-DC at low frequency. However, further increase in the filler loading has recorded an increment in the value of permittivity and loss tangent. This higher effective permittivity is mainly due to the influence of the filler permittivity.

Effect of isolation method on reinforcing capability of recycled cotton nanomaterials in thermoplastic polymers

Cellulose extracted from recycled pulverized cotton in nanocrystalline cellulose (CNC) and nanofibrillated cellulose (NFC) forms is investigated as a reinforcing agent in low-density polyethylene (LDPE) nanocomposites. The effect of extraction processing on the pulverized cotton is shown to influence the degree of crystallinity, morphology, and thermal stability of cellulose nanomaterials. Melt compounding of CNC with LDPE resulted in polymer nanocomposites with no discoloration at 170 °C. Significant differences observed in transparency, mechanical, and thermal properties of LDPE nanocomposite films, are demonstrated to be a result of the microstructure and the content of cellulose nanomaterials. Thermal analysis using thermogravimetric analyzer and differential scanning calorimeter showed higher thermal stability and degree of crystallinity of NFC/LDPE comparing to CNC/LDPE nanocomposite films. Tensile analysis exhibited a higher elastic modulus and tensile strength for the NFC material. 10 wt% of NFC reinforcing agent showed 32% improved strength and higher transparency over the one with CNC.

New Alternative to Produce Colored Polymer Nanocomposites: Organophilic Ni/Al and Co/Al Layered Double Hydroxide as Fillers into Low-Density Polyethylene

Green (Ni2+/Al+3) and pink (Co2+/Al+3) layered double hydroxides (LDH) (molar ratio of 3:1) were intercalated with several organic anions and used as functional colored fillers into low density polyethylene (LDPE) by melt mixing in amounts of 0.2 to 7 wt.%. Scanning electron microscopic (SEM) results of LDPE nanocomposites indicated that with low percentage of filler, all the LDH samples showed efficient delamination/exfoliation in the polymer matrix. Fillers added to LDPE with concentrations of 0.2, 0.5, 2 and 5% presented, in general, maintenance of Young's modulus and tensile strength, tending to the reduction with a loading of 7%. Most of the nanocomposites presented similar elongations, although NiUS stood out, with an elongation increase of 300%. Differential scanning calorimetry (DSC) indicated the effect of the Co/Al-LDH in inducing the formation of LDPE crystalline domains, especially at higher temperature than neat LDPE.

Cavitation in strained polyethylene/aluminium oxide nanocomposites

The incorporation of metal oxide (e.g. Al2O3) nanoparticles has a pronounced positive effect on low-density polyethylene (LDPE) as an insulating material for high-voltage direct-current (HVDC) cables, the electrical conductivity being decreased by one to two orders of magnitude and charge species being trapped by the nanoparticles. The risk of debonding between the nanoparticles and the polymer matrix leading to electrical treeing via electrical discharges in the formed cavities was the motivation for this study. Scanning electron microscope (SEM), small-angle X-ray scattering (SAXS) and X-ray ptychographic tomography were used to study a series of LDPE nanocomposites which contained Al2O3 nanoparticles treated with silanes having terminal alkyl groups of different lengths (methyl, octyl and octadecyl). When specimens were subjected to a tensile strain (a typical specimen stretched beyond the onset of necking consisted of three zones according to SEM of specimens that were studied after removal of the external force: an essentially cavitation-free zone with low local plastic strain, a transitional zone in which local plastic strain showed a marked increase and the revealed concentration of permanent cavities increased with increasing plastic strain and a highly strained zone with extensive cavitation), the cavitation occurred mainly at the polymer-nanoparticle interface according to SEM and X-ray ptychographic tomography and according to SEM progressed with increasing plastic strain through an initial phase with no detectable formation of permanent cavities to a period of very fast cavitation and finally almost an order of magnitude slower cavitation. The polymer/nanoparticle interface was fractal before deformation, as revealed by the profile of the Porod region in SAXS, presumably due to the existence of bound polymers at the nanoparticle surface. A pronounced decrease in the interface fractal dimension was observed when the strain exceeded a critical value; a phenomenon attributed to the stress-induced de-bonding of nanoparticles. The strain-dependence of the interface fractal dimension value at low strain levels between composites containing differently treated nanoparticles seems to be an indicator of the strength of the nanoparticle-polymer interface.

Modelling of dielectric breakdown through charge dynamics for polymer nanocomposites

A dielectric breakdown model consisted of bipolar charge transport and free volume breakdown criterion is used to investigate the dc breakdown properties of polymer nanocomposites. In the model, we consider charge injection from electrodes, carrier migration with a constant mobility, charge trapping and detrapping associated with deep traps, charge recombination, and energy gained for charge carriers from the local distorted electric field. Since incorporating nanoparticles into a polymer can change its density and/or energy of deep traps, we calculate the dielectric breakdown properties of low-density polyethylene nanocomposites characterized by various densities and energies of deep traps. The simulated results show that the breakdown strength increases with an increase in the density and energy of deep traps, which is consistent with the experimental results. It is shown that the accumulation of homocharges, the distortion of electric field, and the energy gain of free carriers are regulated to improve the performance of breakdown.

Preparation of nanosilica-immobilized antioxidant and the antioxidative behavior in low density polyethylene

This article reports a study of the preparation of nanosilica-immobilized antioxidant (SiO2-APTMS-AO) and the thermal oxidative stability of low density polyethylene (LDPE) nanocomposites containing SiO2-APTMS-AO. SiO2-APTMS-AO was prepared based on the fumed nanosilica which was firstly modified with an aminosilane coupling agent and then reacted with 3,5-Di-tert-butyl-4-hydroxybenzoic acyl chloride. Infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis measurements confirmed that the antioxidant group was chemically immobilized onto nanosilica. LDPE/silica nanocomposites were prepared by melt mixing and then pressed into different films. The thermal oxidative stability of the nanocomposites was evaluated by thermogravimetric analysis in air atmosphere, oxidation induction time (OIT) and long-term accelerated thermal aging. The results showed that the SiO2-APTMS-AO can significant improve the thermal oxidative stability of LDPE nanocomposite. Because SiO2-APTMS-AO is based on inorganic nano-filler, in comparison to organic antioxidants, it might have advantages in thermal stability and migration stability during processing and application.

Fabrication and Properties of Polyethylene/Cellulose Nanocrystal Composites

The preparation of nanocomposites of low-density polyethylene (LDPE) and cellulose nanocrystals (CNCs) isolated from cotton or produced in situ by the dispersion of microcrystalline cellulose (MCC) is reported. The hydrophobic matrix polymer and the rather polar filler particles appear to be difficult to mix, but it is shown here that composites with significantly improved mechanical characteristics and of homogeneous appearance can be produced using an organic-solvent-free two-step process. This is achieved by first mixing an aqueous slurry of an LDPE powder with an average particle size of <600 μm with aqueous suspensions of CNCs or MCC and removing most, but not all, of the water. Compounding such water-plasticized mixtures in a roller-blade mixer and subsequent compression-molding afford highly transparent films, whose room-temperature storage modulus is increased by a factor of 2.5 upon incorporation of 15% w/w CNCs or MCC. The results demonstrate that LDPE/nanocellulose composites with improved mechanical properties can be produced by an organic solvent-free process that appears to be scalable to industrial production scale.

Influence of a novel organo-silylated clay on the morphology, thermal and burning behavior of low density polyethylene composites

Abstract The functionalization of a natural sodium montmorillonite (MMT) with (3-glycidyloxypropyl)trimethoxysilane by a silylation procedure is presented, and its use as nanofiller in the melt compounding of low density polyethylene (LDPE) nanocomposites. In particular, the effects on the thermal stability and flame retardant properties of melt compounded LDPE nanocomposites are analyzed, with and without magnesium hydroxide (MH) as an additional conventional flame retardant. The purpose was to investigate possible synergistic effects between the two inorganic fillers on fire behavior. The obtained organosilylated clay showed higher interlayer spacing than the original MMT and good thermal stability, higher than that of many commercial organoclays modified with alkylammonium salts. Its addition to LDPE allowed the production of hybrids with nanoscale dispersion of the filler, as demonstrated by X-ray diffraction. The simultaneous presence of MH, which strongly interacts with the nanoclay, hindered intercalation of the polymer chains between the clay galleries and clay layer exfoliation within the LDPE resin. The investigation of the thermal and burning behavior of the LDPE nanocomposites indicated that the organosilylated clay alone shows only a limited residual protection layer effect. In combination with MH the nanocomposites have a small adverse effect on the reaction to small flame as measured by the oxygen index and UL 94 testing, and, surprisingly, no effect on the peak heat release rate in the cone calorimeter. The quality of the fire residue was lacking on the microscopic scale. The ternary LDPE/MH/organoclay systems investigated did not open the door to reducing MH content in halogen-free flame retardant LDPE yet, but demand further research.

Fabrication and characterisation of low density polyethylene (LDPE)/multi walled carbon nanotubes (MWCNTs) nano-composites

Carbon nanotubes (CNT) have shown extraordinary electrical, mechanical properties as well as many other physical properties. The aim of this study is to explore the scope of CNT/LDPE nano-composites for engineering applications. Nano-composites of LDPE and MWCNT are generally prepared by using the melt blending method but in the present investigation these have been prepared by using solvent mixing method. Xylene has been used as a solvent which can dissolve low density polyethylene (LDPE) at about 125°C. The solution of LDPE in xylene has been ultrasonicated with various percentages of MWCNT (0, 1, 2, 5, 10wt% of MWCNT) composite to form thin film after drying. MWCNT used in this study have been synthesised by electric arc discharge method. Characteristics of these composites have been determined by Raman spectroscopy and scanning electron microscopy (SEM). Raman spectroscopy revealed variation in intensity of CNT's peak with variation in concentration of CNT. The results indicated that intensity of CNT's peak was found to increase with the increase in concentration of CNT which indicated the type of interaction between polymer and CNT. SEM analysis reveals CNT-polymer interfacial adhesion and shows agglomeration of CNT's at some locations and presence of individual tubes at other locations. These investigations show that LDPE/MWCNT composites can be fabricated using simple solvent mixing method. Further investigation on the effect of MWCNT on mechanical, electrical and thermal properties of LDPE based composites are in progress.

Charge Transport in LDPE Nanocomposites Part II-Computational Approach.

A bipolar charge transport model is employed to investigate the remarkable reduction in dc conductivity of low-density polyethylene (LDPE) based material filled with uncoated nanofillers (reported in the first part of this work). The effect of temperature on charge transport is considered and the model outcomes are compared with measured conduction currents. The simulations reveal that the contribution of charge carrier recombination to the total transport process becomes more significant at elevated temperatures. Among the effects caused by the presence of nanoparticles, a reduced charge injection at electrodes has been found as the most essential one. Possible mechanisms for charge injection at different temperatures are therefore discussed.

Structure, morphology, and properties of LDPE/sepiolite nanofiber nanocomposite

Sepiolite (SEP) nanofibers have been modified by grafting with poly(pentaerythritol diphosphonate dichloride‐hexamethylendiamine) (PSPHD) and compounded with low density polyethylene (LDPE) to form a nanocomposite. The various modified SEPs were characterized by X‐ray photoelectron spectroscopy, Fourier transform infrared, transmission electron microscopy (TEM), and thermogravimetric analysis. The Fourier transform infrared and X‐ray photoelectron spectroscopy tests show that covalent bonding exists between SEP fiber and modifiers. The nanoscale size and morphologies of SEP fiber and modified SEP nanofibers can be observed clearly by TEM. The thermogravimetric analysis results reveal that the multi‐step thermal degradation process of SEP fiber is changed by grafting modification. The various LDPE/SEP nanocomposites were characterized by scanning electron micrograph, TEM, dynamic mechanical analysis, and tensile test. The results suggest that a good interfacial modification effect has been obtained between PSPHD‐SEP and LDPE matrix. A particular improvement in tensile strength is reflected in tensile tests. Dynamic mechanical analysis shows that the storage moduli (E') of PSPHD‐SEP/LDPE nanocomposites are much higher than that of neat LDPE and a‐SEP/LDPE systems. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Preparation, microstructure and properties of polyethylene/alumina nanocomposites for HVDC insulation

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have been attracted more attention. In this paper, low density polyethylene (LDPE) nanocomposites filled with alumina nanoparticles (nano-Al2O3) were prepared employing melting blend method. Morphologies of nanoparticles and LDPE/Al2O3 nanocomposites were performed by scanning electron microscopy (SEM). Electrical properties of the LDPE nanocomposites were also investigated. Results shown that the nano-Al2O3 particles modified with vinyl silane coupling can effectively enhance the breakdown strength of LDPE nanocomposites. With the nano-Al2O3 particles loading, the volume resistivity of the LDPE nanocomposites was increased, while dielectric permittivity of the nanocomposites was decreased. Space charge of the LDPE nanocomposites was measured by pulsed electro-acoustic (PEA) method. The charge profiles indicated that space charge suppression of the LDPE nanocomposites was better than that of pure LDPE. The excellent insulation properties of the LDPE nanocomposites were attributed to the better interfacial adhesion between the surface-treated nano-Al2O3 particles and the LDPE matrix.

Effects of ENR and OMMT on barrier and tensile properties of LDPE nanocomposite film

The effects of organo-modified montmorillonite (OMMT) nanoclay and epoxidized natural rubber (ENR) content on the gas barrier, tensile, and the thermal properties of nanocomposite films based on low-density polyethylene (LDPE) are investigated. Linear low-density polyethylene-grafted maleic anhydride (LLDPE-g-MA) is used as a compatibilizer to obtain better dispersion of the nanoclay in the blends. The blends, with various amounts of ENR (0–10) wt%, are melt-compounded and extruded using a blown film extrusion single screw. The tensile properties of films are studied in machine direction (MD). The gas permeability of films is studied via constant pressure and a soap bubble flow meter. The melting and crystallization behaviors of films are examined via differential scanning calorimetry (DSC). Chemical interactions of composite blends are examined via Fourier transform infrared (FTIR) spectroscopy. An addition of 6 wt% nanoclay improved the tensile modulus by about 11 %. It further reduced the oxygen permeability by about 83 %. Although introducing OMMT decreased the percentage of crystallinity (XC), the presence of LLDPE-g-MA in the nanocomposite enhanced the property due to better intercalation between the phases. Incorporation of ENR caused an increase in the Young’s modulus for compatibilized nanocomposite systems, attributed to an interaction among clay, compatibilizer, and ENR, and cross-linking effects of ENR molecules. However, ENR decreased the permeability of the film due to the ability of amorphous regions to form crystallized structures during the blown process, and cross-linking effects of ENR. In addition, ENR reduced the XC of nanocomposites due to an interference that exists in the form of ENR molecular incorporation. The FTIR spectra showed that the maleic anhydride group in LLDPE-g-MA reacted in situ with the epoxy groups of ENR, which was an evidence of grafting reaction.

Insulating Properties of Low Density Polyethylene/Alumina Nanocomposites

High-Voltage Direct Current (HVDC) cable has become an important factor in the development of HVDC transmission. However, there are still difficulties such as space charge distribution in the development of HVDC cables. In this study, Low Density Polyethylene (LDPE) nanocomposites filled with nano alumina (nano-Al2O3) particles with or without modification were prepared by employing melting blend method. The results show that the modified nano-Al2O3 particles with vinyl silane coupling can be homogeneously dispersed in LDPE matrix. Space charge of the LDPE nanocomposites was tested by Pulsed Electro-Acoustic (PEA) method. The PEA spectrum indicated that decay charge effect of the LDPE/Al2O3 nanocomposites is better than that of neat LDPE. The space charge accumulated in the nanocomposites can be effectively decayed. The J-V curves show the nano-Al2O3 decrease the carrier mobility. The excellent insulation properties of the LDPE nanocomposites were attributed to the better interfacial adhesion between the surface-treated nano-Al2O3 particles and the matrix.

Thermal Experimental Dielectric Characterization of Cost-Fewer Low-Density Polyethylene Nanocomposites

Polymer properties can be experimentally tailored by adding small amounts of different fillers, but they are expensive with respect to the classical polymer materials. This paper has been studied the enhancement and controlling of electric and dielectric properties of low-density polyethylene (LDPE) polymer materials by cost-fewer nanoparticles. Certain percentages of clay and fumed silica nanoparticles have been enhanced electric and dielectric properties of low-density polyethylene nanocomposite. Dielectric spectroscopy has been measured the electric and dielectric properties of low-density polyethylene with and without nanofillers at various frequencies (10Hz-100kHz) and temperatures (20°C, 40°C and 60°C). Also, it has been investigated the optimum percentages of nanofillers with respect to nanofillers type, filler concentration and temperature for enhancing electric and dielectric characterization of low-density polyethylene. Experimental measurements have been carried out on dielectric breakdown strength of new polyethylene nanocomposites materials under variant electric fields (uniform, and non-uniform) and variant temperatures. It has been specified the effective nanofillers factors on dielectric breakdown strength of polyethylene nanocomposites materials.