Properties Of High Density Polyethylene Research Articles

Role of gas delay time on the hierarchical crystalline structure and mechanical property of HDPE molded by gas-assisted injection molding

The relationship among the processing parameters, crystalline morphology, and macroscopic properties in injected molded bar becomes very complicated due to existence of temperature gradient and shear gradient along the sample thickness. To enhance the shear strength, gas-assisted injection molding (GAIM) was utilized in producing the molded bars. The aim of our research was to explore the relationship between processing conditions and the spatial variation of the hierarchy structure as well as the mechanical properties of high-density polyethylene (HDPE) obtained via GAIM. In our previous work [Wang L, Yang B, Yang W et al (2011) Colloid Polym Sci 289:1661–1671], we found that the enhancement of the gas pressure can remarkably increase the degree of molecular orientation in the HDPE samples, which turns out to improve the mechanical performances of GAIM parts. In this work, the hierarchy structure, orientation behavior, and mechanical properties of molder bars under different gas delay time were investigated using a variety of characterization techniques including rheological experiments, scanning electron microscope, tensile testing, differential scanning calorimetry, and two-dimensional wide-angle X-ray scattering. Moreover, the temperature field during the short shot stage of GAIM process was simulated using an enthalpy transformation approach. Our results indicate that these properties were intimately related to each other, and with prolonged gas delay time, GAIM samples with higher degree of orientation and improved mechanical properties were obtained.

Thermorheological analysis of blend of high- and low-density polyethylenes

The effect of temperature on dynamic viscoelastic properties of high density polyethylene and low density polyethylene blends with different weight fractions was investigated in the molten state by means of small amplitude oscillatory shear rheometry. It was found that the blends at various compositions do follow well the time-temperature superposition principle and show thermorheologically simple behavior. This behavior is attributed to both similarity in glass-transition temperature of the constituents and phase stability in the blends at various temperatures. The latter was suggested via coincidence of G′-G′′ plots and δ-G* plots at different temperatures. That was furthur supported using G′ vs. temperature curves which showed no breakdown in the linear relation. Horizontal shift factors, which reflect temperature dependence of relaxation times, obtained to draw G′ and G′′ master curves, followed an Arrhenius equation with temperature. Analysis of terminal relaxation times of components revealed that terminal dynamics of components is similar at limited particular temperatures but different at others. Moreover, depending to test temperature, dynamics of a given component in the blend may be faster or slower than in the pure state.

Morphologies and Mechanical Properties of High-Density Polyethylene Induced by the Addition of Small Amounts of Both Low- and High-Molecular-Weight Polyolefin under Shear Stress Applied by Dynamic Packing Injection Molding

This paper focuses on the mechanical properties and crystal morphology of a self-reinforced high-density polyethylene 5000S (HDPE 5000S) by simultaneously blending with 9 wt% high-molecular-weight polyethylene (HMWPE) and 9 wt% low-molecular-weight polyethylene (LMWPE) (A9) under the shear stress field which was engendered by a self-made dynamic packing injection molding (DPIM) machine. The results of mechanical properties, differential scanning calorimetry, and scanning electron microscopy characterization were as follows: (1) The tensile strength of the dynamic samples increased to 112.1 MPa, 4.85 times as much as that of static packing injection molding (SPIM) samples (23.1 MPa), as a result of realizing polyethylene's self-enhancement; (2) Shish-kebab structure was found in the dynamic samples; (3) The crystallinity of the DPIM A9 sample reached 68.6%, on increase by 18.7% compared with that of the SPIM sample. The formation of the shish-kebab structure and enhancement of mechanical properties are explained.

Mechanical properties of high density polyethylene reinforced with chemically modified coir fibers: Impact of chemical treatments

In this work, high density polyethylene (HDPE) was compounded with chemically treated coir fiber using a heated two roll mill. Three chemical treatments denoted silane, sodium hydroxide (NaOH) and dodecane bromide (C12) were selected to improve the interface adhesion between fibers and polyethylene matrix. The mechanical properties of these composites were evaluated and compared against those of neat polymer and untreated fibers composites. A fixed fiber loading of 20wt.% was used in all composites. A chemical analysis using Fourier Transform Infrared spectroscopy (FTIR) was performed to see the extent of chemical modification of the fibers. Results have shown that tensile and torsional modulus exhibited a significant increase when compared to the neat HDPE. A notable increase in the Young’s modulus was observed when C12 and silane were used, corresponding to 120% and 70%, respectively. The composites’ ductility was also evaluated by the plastic stored energy and showed a noted increase when C12 and silane were used, an increase of 55% with C12 treatment and 23% when silane treatment was used. Such results promise many applications for composite materials.

Influence of Alumina Particles on Thermal Behavior of High Density Polyethylene (HDPE)

This study evaluated the effects of alumina (Al2O3) particles on thermal properties of High Density Polyethylene (HDPE). HDPE and HDPE/5, 10 & 15 wt% Al2O3 composites were prepared by compression molding. Differential scanning calorimetery (DSC) was used to analyze the thermal and crystallization behavior of the samples. The results indicated that the alumina particles affected the crystallization behavior of HDPE matrix, significantly. However, the DSC results showed that alumina content did not influence the melting temperature of HDPE in this composite. The results also showed that the incorporation of alumina particles caused the decrease of specific heat capacity coefficient and entropy.

Morphology and tensile properties of high‐density polyethylene/natural rubber/thermoplastic tapioca starch blends: The effect of citric acid‐modified tapioca starch

AbstractThe effect of citric acid on the tensile properties of high density polyethylene (HDPE)/natural rubber (NR)/thermoplastic tapioca starch (TPS) blends was investigated. The ratio between HDPE/NR was fixed at 70/30 and used as the matrix system. TPS loadings, after modification with citric acid (TPSCA) and without modification (TPS), were varied from 0 to 30 wt %. The morphologies and tensile properties of HDPE/NR blends were evaluated as a function of TPS loadings. The tensile strength, Young's modulus, and elongation at break were found to decrease with increasing TPS loading. However, a slight improvement in the tensile strength of HDPE/NR/TPSCA blends at 5 and 10 wt % TPS loadings were observed. TPS can be partly depolymerised to produce a low viscosity product when processed with citric acid. TPS with low viscosity can easily disperse in the thermoplastic natural rubber (TPNR) system and reduce the surface tension at the interphase of TPS‐HDPE/NR as shown by scanning electron microscopy (SEM). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of Al2O3 fibers on the thermal conductivity and mechanical properties of high density polyethylene with the absence and presence of compatibilizer

AbstractAlumina (Al2O3) fiber/high density polyethylene (HDPE) composites were prepared by molding injection with or without compatibilizer, in which, maleic anhydride‐grafted polyethylene (PE‐g‐MA) and acrylic acid‐grafted polyethylene (PE‐g‐AA) were used as the compatibilizers. The thermal conductivities of the composites were anisotropic and the conductivities in the injection direction of the samples were higher than those in perpendicular direction of the injection. The anisotropic thermal conductivity for Al2O3/PE‐g‐AA/HDPE was the most obvious and this composite also gave the best mechanical performance. The SEM and DMA test revealed that PE‐g‐AA was more effective than PE‐g‐MA in improving the matrix–filler interaction. The high interfacial interaction was more favorable for the viscous flow‐induced fiber orientation, which resulted in the largest anisotropic degree of thermal conductivity of the Al2O3/PE‐g‐AA/HDPE among the studied composite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A comparative study on the effects of Coriolus versicolor on properties of HDPE/wood flour/paper sludge composites

In this study, the effects of white-rot fungus (Coriolus versicolor) on the properties of high density polyethylene (HDPE)/wood flour/paper sludge composites were examined. In addition, the effectiveness of using coupling agent on the durability of decayed and undecayed WPCs was investigated. Two different types of sludge materials, namely paper making waste water sludge (PS) and ink-eliminated sludge (IES) were used. The mechanical properties, morphology, and water absorption of fabricated composites were investigated. At a similar wood flour loading, except for modulus of elasticity, the fungi treated composites showed lower mechanical properties (such as modulus of rupture and unnotched Izod impact strength), and higher water absorption compared to untreated composites. According to the results, addition of wood flour decreased the resistance of the composites to moisture and fungal environment. The exposure of the composites to a 4-cycle (2, 24, 48 and 72h) water immersion caused serious damage to the interfacial adhesion between wood flour and polymer matrix due to contraction and swelling stresses developed during the cyclic exposure. The detrimental effect of fungal treatment on the water uptake of the composites could be explained by the degradation of lignin which made the cellulose content more accessible. Further, it makes chains of cavities that accelerate water absorption. However, the weight losses of all cases of treated composites were low (less than 2.5%), while PS filled composites were more susceptible to white-rot fungi. The addition of coupling agent during the compounding of wood flour and HDPE prevented the colonization and proliferation of fungus on the surface of the composites, and had an advantageous effect on the water uptake and mechanical properties of both treated and untreated composites.

Rheology, Crystallization Kinetics and Mechanical Properties of HDPE/Vinyl-POSS Nanocomposites

Polyhedral oligomeric silsesquioxane (POSS) is usually prepared from the hydrolytic condensation of organotrialkoxysilanes. The rheology, non-isothermal crystallization kinetics and mechanical properties of high density polyethylene (HDPE)/vinyl-containing POSS (V-POSS) nanocomposites were investigated. The results show that the molten HDPE/V-POSS belong to pseudoplastic fluid. The V-POSS can accelerate the nucleation of HDPE at starting stage of crystallization. However, it will decrease the crystallization ability of HDPE in the subsequent crystallization process. The modified Avrami analysis by Jeziorny can well explain the crystallization behaviour of HDPE/V-POSS. The yield strength and tensile modulus of nanocomposites both increase when V-POSS content is 6%.

Effect of polyethylene-grafted maleic anhydride on properties of high-density polyethylene and polystyrene blend/layered silicate nanocomposites

Effects of PE-gr-MA on properties of HDPE and PS blend nanocomposite were studied. The surface morphology, thermal stability, and mechanical properties of the composites were characterized. XRD and TEM results show that PE-gr-MA facilitated the intercalation of polymers into layered silicates. The SEM micrographs reveal that the presence of PE-gr-MA greatly increases matrices adhesion but decreases the flexibility of the nanocomposites. The thermal stability, tensile strength, and modulus are enhanced when PE-gr-MA is used.

Study on Self-Reinforcement of High-Density Polyethylene Extruded with Vibration in Low Temperature

The effect of vibration on the microstructure and mechanical properties of high-density polyethylene (HDPE) sheets, obtained through vibration plasticating extruder in low temperature, were studied systematically. Property Tests show that the tensile strength and the Vika temperature were much improved under the reciprocating axial vibration in low temperature. Differential scanning calorimetry , scanning electron microcopy and wide angle X-ray diffraction were executed to analyze the microstructure of the samples. The results indicate that the vibration extrudate in low temperature has higher crystallinity, perfect crystallite, and new crystal morphology formed , which account for enhancement of the mechanical properties and Vika temperature of sheets, compared to conventional static extrudate.

Measurement and Analysis on Dynamics Cold Crystallization Parameter of High-Density Polyethylene (HDPE) Sheet by Vibration Force Field

Physics mechanics properties of polymer materials don’t only depend on their chemical constitution, molecular weight and distribution of molecular weight, but also depend on their agglomerate configuration. The effect of vibration on the microstructure and mechanical properties of high-density polyethylene (HDPE) sheets, obtained through vibration plasticating extruder in low temperature, were studied systematically. Crystalline polymer is analyzed by differential scanning calorimetry(DSC), wide angle X ray diffraction(WAXD). The test result which represents parameters of crystalline structure is helped to judge the outside factors for crystalline structure, such as melting point, crystallinity and heat of fusion by DSC and crystallinity, crystal plane distance and grain size by WAXD, and canning electron microcopy (SEM). The results indicate that the vibration extrudate in low temperature has higher crystallinity, perfect crystallite, and strong inter-spherulite ties.

Improving electrical conductivity and mechanical properties of high density polyethylene through incorporation of paraffin wax coated exfoliated graphene nanoplatelets and multi-wall carbon nano-tubes

High Density Polyethylene (HDPE) based nanocomposites are reinforced by exfoliated graphene nanoplatelets, GNP, and multi-wall carbon nano-tubes, MWCNT, through melt extrusion and injection molding in this study. Low molecular weight paraffin wax was selected as a coating on the surface of GNP and MWCNT to improve their dispersion in HDPE. Wax coated GNP and MWCNT were fabricated by mixing wax with GNP and MWCNT in hot xylene and followed with the solvent evaporation and vacuum drying. It was found that wax coated GNP and MWCNT are much more efficient than the uncoated ones in improving the electrical conductivity and the flexural properties of HDPE nanocomposites. Morphology characterization verified that the dispersion of GNP and MWCNT in the polymer matrix was significantly enhanced by this wax coating method which was responsible for the better electrical and mechanical properties in the resulting nanocomposites.

Measurement and Analysis on Tensile Strength and Crystallinity of Vibrating Extruded High-Density Polyethylene (HDPE) Sheet

By the apparatus of differential scanning calorimetry (DSC), scanning electron microcopy (SEM) and wide angle X-ray diffraction (WAXD), The effect of vibration on the microstructure and mechanical properties of high-density polyethylene (HDPE) sheets, obtained through vibration plasticating extruder in low temperature, were measured and analysed. The result show that the tensile strength was much improved under the reciprocating axial vibration in low temperature. The phenomenon indicate that the vibration extrudate in low temperature has higher crystallinity, perfect crystallite, and strong inter-spherulite ties, which account for enhancement of the mechanical properties of sheets, compared to conventional static extrusion.

Influence of carbon nanotube–polymeric compatibilizer masterbatches on morphological, thermal, mechanical, and tribological properties of polyethylene

Study was made of the effect of multiwall carbon nanotubes (MWCNTs) and polymeric compatibilizer on thermal, mechanical, and tribological properties of high density polyethylene (HDPE). The composites were prepared by melt mixing in two steps. Carbon nanotubes (CNTs) were melt mixed with maleic anhydride grafted polyethylene (PEgMA) as polymeric compatibilizer to produce a PEgMA–CNT masterbatch containing 20 wt% of CNTs. The masterbatch was then added to HDPE to prepare HDPE nanocomposites with CNT content of 2 or 6 wt%. The unmodified and modified (hydroxyl or amine groups) CNTs had similar effects on the properties of HDPE–PEgMA indicating that only non-covalent interactions were achieved between CNTs and matrix. According to SEM studies, single nanotubes and CNT agglomerates (size up to 1 μm) were present in all nanocomposites regardless of content or modification of CNTs. Addition of CNTs to HDPE–PEgMA increased decomposition temperature, but only slight changes were observed in crystallization temperature, crystallinity, melting temperature, and coefficient of linear thermal expansion (CLTE). Young’s modulus and tensile strength of matrix clearly increased, while elongation at break decreased. Measured values of Young’s moduli of HDPE–PEgMA–CNT composites were between the values of Young’s moduli for longitudinal ( E 11) and transverse ( E 22) direction predicted by Mori-Tanaka and Halpin–Tsai composite theories. Addition of CNTs to HDPE–PEgMA did not change the tribological properties of the matrix. Because of its higher crystallinity, PEgMA possessed significantly different properties from HDPE matrix: better mechanical properties, lower friction and wear, and lower CLTE in normal direction. Interestingly, the mechanical and tribological properties and CLTEs of HDPE–PEgMA–CNT composites lie between those of PEgMA and HDPE.

Study on the structure and properties of nanocomposites based on high-density polyethylene/starch blends

The effects of nanoclay on the structure and final properties of high density polyethylene (HDPE)/thermoplastic starch (TPS) blends were investigated. Neat blends as well as nanoclay containing samples were prepared by melt blending in an internal mixer. Also, a poly (ethylene-g-maleic anhydride) (PE-g-MA) copolymer was used as compatibilizer in some of the formulations. Nanocomposites with intercalated structures were obtained in the samples lacking the compatibilizer, based on the rheological, X-ray diffraction (XRD) and transmission electron microscopy (TEM) results. However, some of the silicate layers were nearly exfoliated in the presence of the compatibilizer. The nanoclay was located preferably in the HDPE matrix as well as at the interface of the HDPE matrix and TPS dispersed phase. The ability of the nanoclays in decreasing the average size of TPS phase in the HDPE matrix was confirmed by scanning electron microscopy (SEM) observations. Furthermore, thermo-gravimetric analysis (TGA) showed that the nanoclays could enhance the thermal stability of the samples. It seems that nanoclays performed as an insulator and mass transport barrier to the small molecules generated during decomposition, and assisted in the formation of char after thermal decomposition of the polymer matrix. All the samples containing the compatibilizer possessed higher tensile strength and elongation at break, but lower modulus, compared to the corresponding un-compatibilized samples. Finally, incorporation of the nanoclays was found to be in favor of developing nanocomposites with higher biodegradability as evidenced through a biodegradation test by fungi as well as water uptake experiments.

Characterization and mechanical properties of high density polyethylene/silane montmorillonite nanocomposites

In order to understand and improve these soft and weak mechanical properties of High Density Polyethylene (HDPE), we add a silane modifier (Nanocor I.31PS) Montmorillonite (MMT) as reinforcement material, then use two kinds of different surfactant: thermoplastic polyolefin elastomers (TPO) or Maleic Anhydride (MA), to join the pieces of HDPE together, making it possess polarization. After that, use a Plastograph-Mixer by the twin-screw mixed method to obtain standard shaped specimens of Polymer-Clay Nanocomposites (PCN) to prepare HDPE/MMT nanocomposites pellets. By adding the different weight percentages (1, 3, 5 wt.%) of MMT, and 2:1 ratio of MA and MMT, the layer distance of MMT and mechanical property of nanocomposites was investigated. The chemical structure and polymer morphology of these as-synthesized PCN specimens were characterized by wide-angle powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, we prepare these experimental specimens in order to probe into its mechanical properties. These tests used are: layer distance of PCN, tensile, impact, shore-hardness, wearing tests, and so on. In addition, use XRD to accomplish the characterization analysis — comparing it to scatter and layer-distance. It is found that adding the MA into the MMT, layer-distance at 5 wt.% MMT increase from 2.11 nm to 3.55 nm; and add the TPO into the MMT, layer-distance at 5 wt.% MMT increase to the 2.66 nm. In the mechanical property, it is found that these specimens grafting with the MA have the following results: In the tensile test, the MMT weight percentage 3 wt.% has the best result, increased by 0.26%. In the shore hardness test, the MMT 3 wt.%, strengthened by 0.62%. In the wearing test, the MMT 3 wt.%, strengthened by 2.6%. Moreover, these specimens graft the TPO have the following results: In the impact test, the MMT 5 wt.% has the best result, increased by 16.96%. In the shore hardness test, the MMT 5 wt.% strengthens by 11.11%.

Thermal, Mechanical and Electrical Properties of High Density Polyethylene Composites Reinforced with Copper Powder

The thermal conductivity, electrical conductivity and mechanical properties such as tensile strength, elongation, modulus of elasticity, were experimentally investigated. Thermal and electrical conductivity measurements were performed up to filler concentration of 30 vol.%. The mechanical properties of high density polyethylene filled with up to 30 vol.% Cu particles were investigated. The tensile strength, elongation and toughness decreased with increasing Cu powder content. This was attributed to the introduction of discontinuities in the polymer structure in which modulus of elasticity increased with increasing the copper content.

Mechanical properties of HDPE/textile fibers composites

The use of natural fibers as reinforcement for thermoplastics has generated much interest due to the low cost, low density, high specific properties characteristics. In this work the mechanical properties of high density polyethylene/ textile fibers residues composites were studied. Effect of pretreatment with sulfuric acid on textile fibers to prepare composites was made to provide an improvement in mechanical properties of these materials. This treatment on fibers was evaluated by X-ray diffraction technique. Composites were produced in a thermokinetic mixer in the following composition: 5 and 10 wt% fibers. After mixing the samples were injection molding according to ASTM D-638 specification. Specimens were tested in tensile mode and composite fractures surface were analyzed in a scanning electron microscopy. Also was studied moisture absorption. Results showed that HDPE/ textile fibers residue presents good mechanical performance compared with high-density polyethylene.

The Influence of EB-Irradiated Treatment on Enhancing Barrier Property and Crystallization Behavior of Rubber-Toughened Nanocomposites

Electron beam (EB) irradiation technique was introduced to modify the crystallization and oxygen (O2) barrier properties of high density-polyethylene (HDPE)/ethylene propylene diene monomer (EPDM) matrix and HDPE/EPDM filled withorganophilic montmorillonite (OMMT). The absorbed dose for EB-irradiation was fixed at 100 kGy. HDPE/EPDM matrix and HDPE/EPDM filled with OMMT at 4 vol% loading were prepared via melt intercalation method. It was found that the barrier resistance of HDPE/EPDM filled withOMMT against oxygen (O2) transmission was significantly enhanced by EB-irradiation absorbed dose of 100 kGy as compared to the control system. The crystallization temperature,Tc, and melting temperature,Tm, were also improved with the addition of OMMT along with the aids of EB-irradiation technique. Field emission scanning electron microscope (FESEM) revealed that the stacking condition of OMMT particles was greatly reduced by EB-irradiation treatment as evidenced by finer surface and less formation of voids.