High Density Polyethylene Nanocomposites Research Articles

Thermal Stability of High Density Polyethylene-Clay Nanocomposites Produced by in situ Solvent Polymerization

High density polyethylene and high density polyethylene-clay nanocomposites were produced using direct solvent polymerization and a Ziegler catalyst system (TiCl4 and triethylaluminum in hexane). The produced polymer has a high average molecular weight and a multimodal molecular weight distribution composed of four distributions including a very high molecular weight component. The laboratory polymer has a thermal stability in inert atmosphere similar to the commercial high density polyethylene produced by Braskem. In oxidant atmosphere the produced polymer presents three thermal oxidation events above 400ºC due to the combustion of low, medium and high molecular weight molecules. The thermal oxidation of the nanocomposites is shifted and reduced for high temperatures indicating an improvement in the thermal stability of the polymeric matrix due to the clay barrier effect for gases and volatile compounds.

Preparation and antimicrobial assessment of zinc-montmorillonite intercalates based HDPE nanocomposites: A cost-effective and safe bioactive plastic

Zinc-montmorillonite intercalates based high density polyethylene (HDPE) nanocomposites were prepared by melt compounding route as an affordable and non-toxic substitute for silver based antimicrobial plastics, which are costly and sometimes toxic to human tissues. Zn is an essential trace element important for growth in humans and shows acceptable antimicrobial behavior, but its antimicrobial attribute has been largely unutilized. Zn ion exchanged montmorillonite (Zn-MMT) and ZnO nanoparticles (NPs) decorated MMT (ZnO-MMT) were synthesized in lab using a combination of simple ion exchange and reduction reactions. The synthesized intercalates were melt mixed in HDPE at different concentrations to obtain HDPE/Zn-MMT and HDPE/ZnO-MMT nanocomposites with uniform dispersion of incorporated nano-additive. For comparison, HDPE/ZnO nanocomposite without MMT was also synthesized. A mixture of intercalated and exfoliated microstructure at lower loadings and intercalated morphology at higher loadings was confirmed by both TEM and WAXD studies in the nanocomposites. The antibacterial properties and antifungal properties were evaluated against gram-negative E. coli, gram-positive S. aureus and black mold fungi A. niger. Remarkable reduction in bacterial colonies and significant zone of inhibition was obtained for the Zn-montmorillonite intercalates and HDPE nanocomposites at 5 wt% of loading. The nanocomposites demonstrated no lysis of human RBC cells in hemolytic assay and no effect in human dermal fibroblast cell proliferation in MTT assay asserting its non-toxic nature, in contrast with HDPE/ZnO nanocomposite which showed mild cytotoxic behavior.

Mass‐produced graphene—HDPE nanocomposites: Thermal, rheological, electrical, and mechanical properties

Economically viable high‐density polyethylene (HDPE)/graphene nanocomposites were produced using mass produced graphene powder and an industrial twin‐screw melt‐compounding machine. Rheological and electrical properties were investigated and scanning electron microscopy was carried out to investigate graphene dispersion and its network formation in the matrix. Mechanical properties of the nanocomposites were evaluated using tensile, flexural and impact tests. Differential scanning calorimetry analysis indicated that the crystalline structure of the polymer might be affected by high loadings of graphene. SEM evaluation revealed reasonable graphene dispersion in the matrix. In addition, the amount of graphene required to form a percolated network was similar for both rheological and electrical networks. The nanocomposites exhibited a significant increase in Young's and flexural moduli without a notable reduction in impact strength up to 14 wt% graphene loading. In these experiments, compounding graphene powder with HDPE produced a clear and distinct improvement in mechanical properties at an industrially suitable low cost. POLYM. ENG. SCI., 59:675–682, 2019. © 2018 Society of Plastics Engineers

Mechanical properties of composite thermoplastic hdpe / natural rubber and palm oil boiler ash as a filler

This study aims to determine the mechanical properties of natural rubber and High-density polyethylene (HDPE) nanocomposites using 72 nm Palm Oil Boiler Ash (POBA) as filler. The Open mill method is used in the preparation of SIR 20 compounds. Nanocomposite preparation was carried out by varying the composition of nanoparticles (0,5,10,15,20)%. Sample preparation was carried out using 60 cc volume internal mixers with JIS K 6781 standard. The results showed that Young’s modulus of thermoplastic elastomer with 20% POBA composition increased to 551.47 MPa and exceeded the pure HD Modulus Young value of 423.58 MPa. Morphological analysis showed that with the addition of nanoparticles, the morphology of the mixture was homogeneous

Observations of a novel strengthening mechanism in HDPE nanocomposites

Previous strengthening mechanisms described in literature for high density polyethylene (HDPE) carbon nanotubes composites are typical of those observed in fibre reinforced polymeric micro composites. Here, we present a new molecular level strengthening mechanism based on HDPE carbon nanotubes composite, which has not been reported before to the best of authors’ knowledge. The HDPE nanocomposite was produced by melt intercalation technique via twin-screw extrusion. Thereafter, the samples were subjected to mechanical tensile tests and scanning electron microscope (SEM) examination. Carbon nanotubes (CNTs) were found to be disentangled from the polymer molecules after yielding and prior to breaking. SEM and optical microscopic observations revealed visible black agglomerate bands at 45° appeared after yielding and prior to the breaking of the ductile HDPE. It was observed that CNTs were pushed out from the intricate mechanical interlocking with the thermoplastic polymeric chains of HDPE during strain hardening.

Photooxidative degradation of graphene‐reinforced high‐density polyethylene nanocomposites

ABSTRACTNatural weathering of high‐density polyethylene (HDPE) and its graphene nanocomposites was studied. The nanocomposites, prepared by in situ polymerization of ethylene, were exposed to the natural environment for 30, 60, and 90 days. The effects of weathering on the crystallinity, melting temperature, and lamellar thickness distribution were studied using differential scanning calorimetry. The changes in chain microstructure and molecular weight were determined by crystallization analysis fractionation and gel permeation chromatography, respectively. The effects of weathering on the dynamic mechanical properties and the morphology of the nanocomposite were also determined. The parent HDPE suffered severe degradation as expected. However, graphene‐reinforced HDPE nanocomposites show resistance to degradation. The changes in the crystallinity, lamellar thickness, molecular weight, and dynamic mechanical properties of graphene nanocomposites were less pronounced as compared to the parent HDPE. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47030.

Nanocomposites of acid free CNC and HDPE: Dispersion from solvent driven by fast crystallization/gelation

Among several applications, the use of cellulose nanocrystals (CNC) as reinforcement in composite materials with thermoplastic matrix stands out. However, both the conventional method for CNC production and the processes for composite production with non-water-soluble matrix show several drawbacks. The common method for CNC preparation based on the hydrolysis of cellulose with high concentrated sulfuric acid produces sulfated nanocrystals with low thermal stability and generates large amounts of acidic effluents. Although the presence of ionic groups on the surface of the nanocrystals prepared in sulfuric acid increases the stability of their suspensions in water, it promotes the degradation of the CNC in melt processing temperatures of thermoplastic composites, such as extrusion or injection molding. Here we describe the use of high thermal stable cellulose nanocrystal prepared by subcritical water as reinforcement for high density polyethylene (HDPE) using a three step processing: i) solvent exchange in order to produce a suspension of CNC in xylenes, ii) dissolution of HDPE followed by iii) the fast crystallization/gelation/flocculation, leading to the isolation of the composite. This process leads to the production of a well-dispersed nanocomposite with higher thermal stability (higher than 250 °C) and improved mechanical properties. An increase of ~20% in Young's modulus was observed when compared with the neat matrix.

Nano indentation and morphology study of the polypropylene and high density polyethylene nanocomposites based on exfoliated graphite Nano platelets/Nano- magnesium oxide

Polypropylene (PP) and high density polyethylene (HDPE) were successfully fabricated using injection molding machine, by the addition of exfoliated graphite nanoplatelets composites reinforced with 2wt.t% of nano-magnesia. The nanoindentation properties and microstructure of the composites were investigated, in the current study. The XRD patterns of both composites showed the peaks of xGnP and n-MgO, where their intensity became stronger with increasing the concentration of xGnP added into both polymers. In addition, the SEM micrographs revealed a good dispersion of fillers within the matrix. The nanoindentation properties of both nanocomposites revealed better properties with compared to the virgin polymers. The PP nanocomposites showed an improvement of hardness up to 22 % and 118% with the compositions of 1xGnP/2n-MgO and 5xGnP/2n-MgO respectively. In addition, HDPE/1xGnP/2n-MgO and HDPE/5xGnP/2n-MgO represented a dramatic improvement of hardness up to 146% and 341% respectively with compared to virgin polymer. In addition, the enhancements in reduced modulus of PP and HDPE were proportional to the xGNP loading.

Effect of TiO2 Nanofiller Concentration on the Mechanical, Thermal and Biological Properties of HDPE/TiO2 Nanocomposites

The necessity for advanced and effective biomimetic tissue engineering materials has increased massively as bone diseases such as osteoporosis and bone cancer have become a major public health problem. Therefore, the objective of this study is to develop titanium dioxide (TiO2) nanoparticles-enriched high-density polyethylene (HDPE) nanocomposites that could serve as potential biomaterials. HDPE/TiO2 nanocomposites with varying TiO2 nanoparticles content were fabricated by using injection molding technique and were subjected to mechanical, thermal and biological characterization. SEM–EDS analysis confirmed even dispersion of TiO2 nanoparticles into the HDPE matrix. It was observed from the mechanical testing that the addition of TiO2 nanoparticles to HDPE noticeably improved the stiffness (from 345 to 378 MPa) while maintaining almost similar yield strength of pure HDPE. The thermal analyses revealed that TiO2 nanoparticles inclusion to HDPE matrix enhanced the thermal stability of nanocomposites, as the overall rate of crystallization increased by almost 4%. Furthermore, biocompatibility of nanocomposites was also studied by means of various cell culture experiments; human osteoblasts (hFOB) were seeded on the HDPE/TiO2 nanocomposites and were visualized through SEM after 72 h of incubation; surface morphology revealed normal cell growth and spreading with more attachment on PNC-10 that contains 10 wt.% of TiO2. Moreover, cell viability assays (i.e., MTT and cell attachment) revealed consistent increase in cell count and metabolic activity when triplicate cultures were incubated for 1, 3 and 7 days.

Insights into crystallization and melting of high density polyethylene/graphene nanocomposites studied by fast scanning calorimetry

Graphene nanoplatelets (5 wt%) with different diameters (5 and 25 × 10−6 m in diameter, 6 × 10−9 m in thickness) filled high density polyethylene nanocomposites were prepared by the melt-mixing method and the effect of graphene nanoplatelets on the polymeric matrix are then investigated by X-ray diffraction, polarized light microscopy, differential scanning calorimetry, fast scanning calorimetry, and rheology. Polarized light microscopy revealed that graphene nanoplatelets of 5 × 10−6 m promote the decrease in the size of the spherical aggregates during crystallization compared to larger nanoplatelets. From rheological measurements, it was found that even though the viscosity of the nanocomposites with increasing filler diameter was increased significantly compared to the neat polymer, the processability of these materials was not affected. Several melting events for neat high-density polyethylene and graphene nanocomposites were observed by fast scanning calorimetry associated with the small imperfect crystals grown at large supercooling, the nucleation efficiency and the diameter size of the filler. The activation energy values versus the relative extent of crystallization revealed that graphene nanoplatelets block the movement of the molecular segments and make crystallization difficult, especially at the final stage of the process. Based on this work, it can be concluded that the nanocomposite with the smaller diameter showed the most enhanced crystallization kinetics as graphene increased the number of nucleation sites, while the larger ones hindered the melted molecules in reaching full isotropization above the melting temperature.

특수 설계된 마찰교반도구(Friction Stir Process Tool)를 사용한 HDPE 나노복합체 제조방법

Polymer nanocomposites are being increasingly used in a variety of tribological applications owing to their structural features. In this study, high density polyethylene (HDPE) composites with three different nanoparticles such as alumina (Al₂O₃), multi-walled carbon nanotubes (MWCNT) and graphene were fabricated using a newly designed friction stir processing tool and fixture. Mechanical test results showed that the fabricated polymer nanocomposites possess enhanced mechanical properties at higher tool rotational speed and traverse feed. The frictional coefficient and wear properties of the fabricated polymer nanocomposites were evaluated under dry sliding conditions using a pin-on-disc tribometer. Further the surfaces of the fabricated samples before and after wear studies were evaluated using scanning electron microscope. The wear test results showed that the HDPE/MWCNT has a very low mass loss as compared with HDPE/graphene, HDPE/Al₂O₃ composites and HDPE parent material. Moreover MWCNT particles act as a lubricant during wear test causing the worn surface of HDPE/MWCNT nanocomposites to be smoother as compared to other fabricated nanocomposites. The higher reflection peak between 23.71o to 23.95° obtained using X-ray diffraction (XRD) for the HDPE nanocomposites fabricated with the nanoparticles MWCNT, Al₂O₃ and graphene reveal a uniform mixture of the polymer matrix with the nanoparticles. The XRD results also show that the addition of nanoparticles does not significantly alter the crystal structure of the HDPE matrix.

Strategy for the Improvement of the Mechanical Properties of Cellulose Nanofiber-Reinforced High-Density Polyethylene Nanocomposites Using Diblock Copolymer Dispersants

Cellulose nanofibers (CNFs) hold great potential as sustainable reinforcement fillers with excellent mechanical, thermal, and chemical properties. However, in polyolefin nanocomposite materials, the rational control of dispersion and the improvement of interfacial strength remain challenging. Herein we propose the tuning of the interface between CNF and high-density polyethylene by the design of polymer dispersants on the basis of surface free energy and the glass transition temperature. The former is related to the wettability against the polymer matrix and is therefore critical to the dispersion of CNF whereas the latter is related to the interfacial strength between CNF and HDPE. As a result of this investigation, we discovered a suitable dispersant for CNFs, poly(dicyclopentenyloxyethyl methacrylate)-block-poly(2-hydroxyethyl methacrylate), which played a pivotal role in achieving both a uniform dispersion of CNF and greatly improved mechanical properties, including a 4-fold increase of the Young's modulus over that of neat HDPE with 10 wt % CNF loading.

Effect of inorganic nanofillers on the impact behavior and fracture probability of industrial high-density polyethylene nanocomposite

The main purpose of this work is to study how the morphology of nanofillers and dispersion and distribution level of inorganic nanofiller influence the impact behavior and fracture probability of inorganic filler filled industrial high-density polyethylene nanocomposites. For this study, nanoclay and nano-CaCO3 fillers–high-density polyethylene mixings (0, 1, 3, 5 wt.% high-density polyethylene) was prepared by melt-mixing method using a compounder system. The impact behavior was examined by charpy impact test, scanning electron microscopy, and probability theory and statistics. The level of the dispersion was characterized with scanning electron microscopy energy dispersive X-ray spectroscopy analysis. The results showed rather good dispersion of both of inorganic nanofiller, with a mixture of exfoliated and confined morphology. The results indicated that the impact strength of the industrial nanocomposite decreased with the increase of inorganic particulate content. The impact reliability of the industrial nanocomposites depends on the type of nanofillers and their dispersion and distribution in the matrix.

Influence of mixing methods on the properties of high density polyethylene nanocomposites with different carbon nanoparticles

In this paper, nanocomposites with multiwalled carbon nanotubes (MWCNT) or graphene nanosheets were prepared using a high density polyethylene (HDPE) matrix. Two different processes were employed: a solution method and a melt mixing method. The crystallinity index of the HDPE showed similar levels in nanocomposites after the addition of carbon nanotubes. It can be seen that the preparation process modified the degree of crystallinity of the HDPE matrix with graphene nanosheets. Nanocomposites prepared by the solution method showed a decrease in the crystallinity index. The addition of carbon nanotubes led to an increase of Young´s Modulus with an increase in the MWCNT quantity, regardless of the preparation process used, with a 22.8 % increase for composites with 0.5 wt% of CNTs. The nanocomposites with graphene nanosheets exhibited a different behavior with each mixing method. Nanocomposites prepared by the solution method showed a higher Young´s Modulus than those prepared by melt mixing. Results of transmission electronic microscopy and field emission scanning electronic microscopy indicated homogeneous dispersion for carbon nanotubes in melt mixing. Graphene nanocomposites showed some agglomerates, with smaller platelets in the nanocomposites prepared by solution mixing compared to that prepared by the melt mixing. Keywords: nanocomposites, high density polyethylene, graphene, carbon nanotube, mixing methods

Improved electrical heating properties for polymer nanocomposites by electron beam irradiation

Nowadays, light weight heating materials are attractive and conductive polymer nanocomposites (CPC) were potential applications in being used as Joule heating materials. To prepare CPCs with high efficiency and stable heating, nanocomposites of high density polyethylene (HDPE) and carbon nanotubes (CNTs) were treated by electron beam (EB) irradiation. The influence of EB irradiation on the composites was characterized by DSC, TGA, TMA, SEM, and DMA. The results showed that gel content and thermal decomposition temperature increased and the thermal expansion coefficient decreased with increasing the irradiation dose. Meanwhile, electrical and thermal conductivity of irradiated samples also increased. These were attributed to crosslinking of HDPE by EB irradiation. As a result, surface temperature (T s) of samples after irradiation was heightened and the correspondence heat efficiency was improved. Mechanical properties of the composites were significantly improved after irradiation, especially at the temperatures which were higher than melting point of HDPE, indicating the improvement of thermal stability by irradiation crosslinking. It made the irradiated HDPE/CNTs composites good candidates for application in the electrical heating.

Prediction of barrier properties of HDPE/PA-6/nanoclay composites by response surface approach: effects of compatibilizer type and the contents of nanoclay, PA-6 and compatibilizer

This research presents study of barrier properties of the injection moulded bottles based on high-density polyethylene, polyamide-6 and nanoclay (HDPE/PA-6/NC) nanocomposites. In fact, the effects of compatibilizer type and contents of nanoclay, PA-6, and compatibilizer were assessed using response surface methodology. Investigation of individual effects showed that increase in nanoclay and PA-6 contents leads to improvement of the barrier properties, whereas compatibilizer content had an optimal level. Among three types of compatibilizers, Fusabond had the best performance. The interaction of effects of the nanoclay and PA-6 contents was very considerable. The highest barrier properties are obtained when these parameters were in high and low levels (in the range of study), respectively. Analysis of variance revealed that compatibilizer type was the most significant parameter. Eventually, using MINITAB software, a correlation for predicting the rate of mass reduction in the nanocomposites was developed.

Processing-property relationships of biaxially stretched binary carbon nanofiller reinforced high density polyethylene nanocomposites

Different dimensional carbon nanofillers, such as carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and carbon black (CB), are often incorporated into polymers in a hybrid form to fabricate multifunctional nanocomposites. In this paper, biaxial stretching of binary carbon nanofiller reinforced high density polyethylene (HDPE) nanocomposites was carried out at various stretching ratios in order to investigate the influence of carbon nanofillers on material deformation behaviour and the influence of biaxial deformation on the structure and properties of the deformed material. It is shown that the strain hardening behaviour of nanocomposites upon biaxial stretching is gradually enhanced with increasing aspect ratios of the nanofillers. The deagglomeration and reorientation of nanofillers in the polymer matrix can be observed during deformation. Furthermore, biaxial stretching significantly affects the final tensile, electrical and barrier properties of the deformed nanocomposites, depending on the components of carbon nanofillers introduced. The stretched HDPE/GNP/CNT and HDPE/GNP/CB nanocomposites exhibit greatly improved tensile and barrier properties.

Effect of Cloisite 30B nanoclay on the mechanical properties of HDPE nanocomposites

In the past decades the study of nanocomposites has held the interest of researchers due to their better mechanical properties by the addition of small amounts of filler material called nanoclay. In this study, high-density polyethylene (HDPE) was chosen as matrix material and nanoclay as reinforcement material, i. e., Cloisite 30B. HDPE grafted with maleic anhydride (HDPE-g-MA) with 3 wt.-% compatibilizer was used to provide better adhesion between the high-density polyethylene and nanoclay. The nanocomposite materials were prepared by melt compounding in a twin screw extruder with a spindle speed of 50 rpm with zone temperatures. The addition of nanoclay to HDPE was in the range of 0 to 4 wt.-%. The specimens were prepared according to ASTM standard for various mechanical tests like flexural, tensile, hardness, and impact tests using respective dies in the injection molding machine. The scanning electron microscope analysis was used to characterize the ditribution of particles in the nanocomposites. In addition, the effect of five different amounts of nanoclay (0 to 4 wt.-%) on the mechanical properties of HDPE was examined to identify the most effective amount of nanoclay for improving the strength of nanocomposites.

Thermal conductivity and degradation behavior of HDPE/graphene nanocomposites

Graphene-filled high-density polyethylene nanocomposites varying filler’s size (5, 10 and 25 × 10−6 m in diameter) were prepared by the melt-mixing method, and their thermal properties are then investigated by TG, Py–GC/MS and thermal conductivity measurements. Thermal and thermo-oxidative degradation temperatures of HDPE/graphene nanocomposites were substantially improved with increment of filler content and graphene size. According to kinetic analysis of thermal decomposition, the thermal degradation mechanism of HDPE/graphene nanocomposites may efficiently be described by an nth-order model with autocatalysis (Cn). Meanwhile, the activation energy values versus the partial mass loss revealed that graphene nanoparticles take up the heat and obstruct transport of HDPE degradation products efficiently. It was also found that the decomposition in nanocomposites is taking place mainly via chain scission reaction, followed by β-scission propagation reactions, radical reactions and the termination process. Graphene nanocomposites achieved significant improvements in thermal conductivity at low filler concentrations, while the experimental data are in good agreement with the Hatta–Taya theoretical model. Summing up the influence of filler size on thermal properties of polymer matrix, graphene nanoparticles with the higher diameter (25 × 10−6 m) affect more than graphene of 5 × 10−6 and 15 × 10−6 m.

Investigation of thermal and dielectric properties of Fe3O4/high-density polyethylene nanocomposites

High-density polyethylene nanocomposites containing Fe3O4 nanoparticles were prepared by employing melt mixing process. The amorphous Fe3O4 nanoparticles with average size about 50 nm were prepared by the conventional coprecipitation method from iron (ΙΙ and ΙΙΙ). Thermal and dielectric properties of high-density polyethylene and its nanocomposites were investigated via differential scanning calorimetry and electrochemical impedance spectroscopy. The crystalline structure of high-density polyethylene and Fe3O4/high-density polyethylene nanocomposite were studied by wide-angle X-ray diffraction, which confirmed orthorhombic crystalline structure. The results of thermal and dielectric analysis indicated that the addition of Fe3O4 nanoparticles to high-density polyethylene matrix leads to decreasing degree of crystallinity and improvement of dielectric constant.