Behavior of high density polyethylene and its nanocomposites under static and dynamic compression loadings

In this study, the deformation behavior of high density polyethylene (HDPE) and its nanocomposites under uniaxial static and dynamic compression loadings were experimentally investigated. The nanofillers used were carbon nanofibers (CNF) with surface treatments and pristine graphite nanoplatelets (GNP) respectively. The dynamic tests were performed at the strain rates of 1 × 10³, 4 × 10³, and 7 × 10³/s using the split Hopkinson pressure bar and the static tests were done at the strain rate of 1 × 10⁻²/s. In addition, microstructual examinations were performed to gain insights into the observed macroscopic behavior. It was observed that all the materials showed appreciable strain‐rate sensitivity. CNF‐based nanocomposites exhibited higher strength compared to that of the HDPE matrix material. However, the strength enhancement by GNP was very limited. The lower strength in HDPE/GNP relative to that of HDPE/CNF is likely due to the defect formation around the poor interface between polyethylene matrix and GNP reinforcement. Furthermore, the GNP with lamellate structure is also likely to create two‐dimensional interfacial cracks between the two phases, and hence weaken the strength and stability of the composites. It was also observed that for HDPE/CNF composites, different surface treatments did not seem to show significant effects on material strength. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

Static and dynamic compressive properties of polypropylene/zinc oxide nanocomposites

The effect of strain rate is widely recognized as an essential factor that influences the mechanical properties of polymer matrix composites. Despite its importance, no previous work has been reported on the high‐strain rate behavior of polypropylene/zinc oxide nanocomposites. Based on this, static and dynamic compression properties of polypropylene/zinc oxide nanocomposites, with particle contents of 1%, 3%, and 5% by weight, were successfully studied at different strain rates (i.e., 0.01 s^?1, 0.1 s^?1, 650 s^?1, 900 s^?1, and 1100 s^?1) using a universal testing machine and a split Hopkinson pressure bar apparatus. For standardization, approximately 24 nm of zinc oxide nanoparticles were embedded into polypropylene matrix for each of the tested polypropylene/zinc oxide nanocomposites. Results show that the yield strength, the ultimate strength, and the stiffness properties, of polypropylene/zinc oxide nanocomposites, were greatly affected by both particle loading and applied strain rate. Furthermore, the rate sensitivity and the absorbed energy of all tested specimens showed a positive increment with increasing strain rate, whereas the thermal activation volume showed a contrary trend. In addition, the fractographic analysis and particle dispersion of all composite specimens were successfully obtained using a field emisission scanning electron microscopy. POLYM. ENG. SCI., 54:949–960, 2014. © 2013 Society of Plastics Engineers     

Effect of bark flour on melt rheological behavior of high density polyethylene

The melt rheological behavior of neem bark flour (BF) filled high density polyethylene (HDPE) has been studied at varying volume fraction (?_f) from 0 to 0.26 at 180, 190, and 200°C in the shear rate range from 100 to 5000 s^?1 using extruded pellets of the composites. The melt viscosity of HDPE increases with ?_f because the BF particles obstruct the flow of HDPE. With the incorporation of the coupling agent HDPE‐g‐MAH, the viscosity decreased compared to the corresponding compositions in the HDPE/BF systems due to a plasticizing/lubricating effect by HDPE‐g‐MAH. The composites obeyed power law behavior in the melt flow. The power law index decreases with increase in the filler content and increases with temperature for the corresponding systems while the consistency index showed the opposite trend. The activation energy for viscous flow exhibited inappreciable change with either ?_f or inclusion of the coupling agent, however, the pre‐exponential factor increased with filler concentration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of SBA-15 on the energy absorption characteristics of epoxy resin for blast mitigation applications

The energy absorption characteristics of silica-filled epoxy composites, for potential application as a blast mitigating retrofitting polymer coating has been explored. Mesoporous silica (SBA-15) with controlled pore size of 5.4 nm was synthesized by the hydrolysis of tetraethyl orthosilicate in the presence of amphiphilic copolymer (PEO-PPO-PEO) which was characterized by nitrogen physisorption studies at 77 K. The porous siliceous rods were homogeneously dispersed in the epoxy resin by ultrasonication (0.5–7 wt%) and subsequently cured using triethylene tetra-amine hardener to prepare silica reinforced composites. Structural, thermal and mechanical properties of the composites were evaluated under dynamic as well as quasi-static conditions which revealed that introduction of SBA-15 at low loadings (1 wt%) led to an increase in the toughness of the base resin but macroporous silica led to deterioration in the properties. The results clearly revealed that the mesoporous nature of silica plays a major role towards improving the dispersion of the filler which in turn resulted in improved properties. Neat epoxy samples fractured in a brittle fashion, but in the presence of SBA-15, the sample exhibited ductile failure, which was explained on the basis of a crack pinning mechanism. High strain rate studies (~10³ s^?1) of selected compositions were performed on a Split Hopkinson pressure bar and the effect of addition of mesoporous silica on the energy absorption characteristics were established. Finite element analysis was used to predict the behavior of concrete slabs on exposure to dynamic loadings resulting from TNT explosions, both in the presence and absence of the epoxy layer, which revealed the role of the retrofit as a fragment arrestor.     

The Effects of a Silane-Based Coupling Agent on the Properties of Kenaf Core-Reinforced High-Density Polyethylene (HDPE)/Soya Powder Composites

HDPE/soya powder/kenaf-core composites were prepared by incorporation of kenaf-core powder at different loadings into HDPE/soya powder matrix with an internal mixer at 180°C and 50 rpm rotor speed. The effects of kenaf-core filler loading and chemical treatment on properties of HDPE/soya powder/kenaf-core composites were investigated by FTIR, SEM, water absorption and mechanical tests. Chemical treatment of kenaf core caused a significant increase in stabilization torque, water resistance and the mechanical properties of HDPE/soya powder/kenaf-core composites. Results from FTIR and SEM observations indicate that better adhesion was observed for the HDPE/soya powder/kenaf-core composites with chemically modified kenaf-core filler.     

Enhancing the air impermeability of a biobased poly(di‐isoamyl itaconate‐co‐isoprene) elastomer via the cocoagulation of latex and natural layered silicates

The gas‐barrier properties of elastomer are of particular importance, especially for airtight applications. Poly(di‐isoamyl itaconate‐co‐isoprene) (PDII) is a newly invented and respectable biobased elastomer, but the barrier properties of PDII and its composites with carbon black and silica are not satisfying at all. Because there are abundant ester groups in PDII macromolecules and these groups can contribute to the homogeneous dispersion of layer silicates, we applied layered silicates, including montmorillonite (MMT) and rectorite (REC), into the PDII matrix to improve the air impermeability. MMT/PDII and REC/PDII composites were prepared by a cocoagulation method, and the air impermeability of the PDII elastomer was highly improved. The smallest gas permeability index reached 1.7 × 10^?17 m² Pa^?1 s^?1 at an REC content of 80 phr; this implied a reduction of 85.5%. A comparison of the two types of silicate/PDII composites showed that the MMT/PDII composites had better properties at low filler contents, whereas the REC/PDII composites had better mechanical and gas‐barrier properties at high filler contents. Other structures and properties of the composites were investigated by X‐ray diffraction, transmission electron microscopy, and dynamic mechanical rheology. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40682.     

Effect of temperature on hygroscopic thickness swelling rate of composites from lignocellolusic fillers and HDPE

Effect of temperature on hygroscopic thickness swelling rate of lignocellolusic fillers/HDPE (high density polyethylene) composites was investigated. The composites were manufactured using a dry blend/hot press method. In this method, powder of plastic and dried powder of lignocellolusic material were mixed in high‐speed mixer and then the mixed powder were pressed at 190°C. Lignocellolusic fillers/HDPE composites panels were made from virgin and recycled HDPE (as plastic) and wood sawdust and flour of rice hull (as filler) at 60% by weight filler loadings. Nominal density and dimensions of the panels were 1 g/cm³ and 35 × 35 × 1 cm³, respectively. Thickness swelling rate of manufactured wood plastic composites (WPCs) were evaluated by immersing them in water at 20, 40, and 60°C for reaching a certain value where no more thickness was swelled. A swelling model developed by Shi and Gardner [Compos. A, 37 , 1276 (2006)] was used to study the thickness swelling process of WPCs, from which the parameter, swelling rate parameter, can be used to quantify the swelling rate. The results indicated that temperature has a significant effect on the swelling rate. The swelling rate increased as the temperature increased. The swelling model provided a good predictor of the hygroscopic swelling process of WPCs immersed in water at various temperatures. From the activation energy values calculated from the Arrhenius plots, the temperature had less effect on the thickness swelling rate for the composites including wood sawdust compared with the rice hull as filler and the composites including recycled compared with the virgin HDPE as plastic. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The comparison of properties of (rubber tree seed shell flour)‐filled polypropylene and high‐density polyethylene composites

The effect of varied rubber tree seed shell flour (RSSF) filler loadings on processing torque, mechanical, thermal, water absorption, and morphological properties of polypropylene (PP) and high‐density polyethylene (HDPE) composites has been studied. The addition of RSSF in the composites increased the stabilization torque in both PP‐ and HDPE‐based composites. Tensile strength, elongation at break, flexural strength, and impact strength show significant reduction when higher loading of RSSF was incorporated, while tensile modulus and flexural modulus were improved. The phenomenon was noted for both matrices, PP and HDPE, but HDPE‐based composites showed clear effects on the reduction of the mechanical properties compared with RSSF‐filled PP. Scanning electron microscopy of tensile fracture specimens revealed the degree of dispersion of RSSF filler in the matrices. At higher filler loadings, agglomerations and poor dispersion of RSSF particles were spotted, which induce the debonding mechanism of the system. Thermogravimetric analysis thermograms showed that both PP‐ and HDPE‐based composite systems with higher RSSF content have higher thermal stability, initial degradation temperature, degradation temperature, and total weight loss. Water absorption ability of the composites increases as the filler loading increases for both matrices. J. VINYL ADDIT. TECHNOL., 22:91–99, 2016. © 2014 Society of Plastics Engineers     

An experimental study of the influence of carbon black on the rheological properties of a polystyrene melt

A broad range of experiments on carbon black filled polystyrene melts shows the reinforcing effect of the filler. This study represents one of the most extensive investigations of a series of highly filled polymer melts. Stress relaxation and dynamic experiments characterize the small strain behavior while the steady state shear viscosity, normal stresses, and elongational flow experiments describe the large strain deformation rate response. Extrudate swell and unconstrained shrinkage of extrudates are also measured. Highly filled systems exhibit yield values. This is seen in the dynamic experiments and in the shear and elongational viscosities. Viscosity does not level off at finite values with decreasing deformation rate but continues to increase in an approximately inverse manner. This corresponds to yield values of order 5 × 10⁵ dynes/cm². The storage modulus also does not tend to zero at low frequencies. The small strain dynamic properties and stress relaxation results suggest high memories for small strain experiments. Txtrudate swell values are however small and the systems exhibit minimal delayed recovery. The implications of this are considered. Generally it is argued that at volume loadings between 10 and 20 percent, the system takes on the characteristics of a gel and the response is similar to that of a Schwedoff body.     

Rheological and morphological properties of high‐density polyethylene and poly(ethylene–octene) blends

The rheological and morphological properties of blends based on high‐density polyethylene (HDPE) and a commercial ethylene–octene copolymer (EOC) produced by metallocene technology were investigated. The rheological properties were evaluated in steady and dynamic shear experiments at 190°C in shear rates ranging from 90 s^?1 to 1500 s^?1 and frequency range between 10^?1 rad/s and 10² rad/s, respectively. These blends presented a high level of homogeneity in the molten state and rheological behavior was generally intermediate to those of the pure components. Scanning electron microscopy (SEM) showed that the blends exhibit dispersed morphologies with EOC domains distributed homogeneously and with particle size inferior to 2 μm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2240–2246, 2002     

Filler structure and tensile properties of starch xanthide-reinforced vulcanizates

Stress–strain behavior of some starch xanthide- and carbon black-reinforced styrene–butadiene elastomers was investigated as a function of filler particle size and structure. In starch xanthide systems, low strain behavior is sensitive to particle structure; high strain behavior, to particle size. Electron photomicrographs of the several starch xanthide-reinforced vulcanizates were analyzed with reference to filler particle size and structure. These parameters were then correlated with Mooney plots of [load/λ ? λ^?2] versus λ^?1, where λ is the strain ratio. Plots of samples containing highly structured filler particles were highly nonlinear, rising steeply as λ^?1 approached unity. Samples containing nonstructured filler particles were also highly nonlinear, rising steeply as λ^?1 decreased to approximately 0.4. A preliminary study of the dynamic properties of these samples, as determined in an eccentric rotating-disk rheometer, provided little additional information.     

Melt spinning flow behaviour of high-density polyethylene blended with low-density polyethylene

ABSTRACT

The melt spinning flow behaviour of a high-density polyethylene (HDPE) blended with a low-density polyethylene (LDPE) was studied using a melt spinning technique in temperature ranging from 160 to 200°C and die extrusion velocity varying from 9 to 36?mm?s^?1. The results showed that the melt apparent extension viscosity of the blends was higher than those of the LDPE and HDPE; the melt apparent extension viscosity decreased with increasing temperature; while the melt apparent extension viscosity increased with increasing extension strain rate when the extension strain rate was lower than 0.2?s^?1, and then decreased; the melt apparent extension viscosity reached up to a maximum value when extension strain rate was about 0.2?s^?1; the relationship between the melt apparent extension viscosity and the LDPE weight fraction did not follow the mixing rule.     

Thermo-mechanical properties of high density polyethylene with zinc oxide as a filler

This study investigates the microstructural, thermal, and mechanical behavior of high density polyethylene (HDPE)-based composites prepared using compression molding technique. HDPE was mixed with either micro-size zinc oxide (bulk ZnO) or zinc oxide nanoparticles (nano-ZnO) as fillers’ contents at 0, 10, 20, 30, and 40 wt%. The structural, morphological, and thermal properties of the composites were identified using X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FTIR), and thermal gravimetric analysis (TGA). The results showed good dispersion and interaction mechanisms between HDPE and the fillers at low weight percentage. The thermal stability of HDPE was enhanced by adding both bulk and nano-ZnO, especially for higher filler loading. Tensile tests at different speeds and Vickers microhardness tests conducted at different indentation loads (0.25–5 N) at t = 60 s were performed to realize how the mechanical properties of the composites were influenced. The values of stiffness, ultimate tensile strength, and yield stress increased by increasing the filler loading to 20 wt% of either bulk ZnO or nano-ZnO. The values of ultimate tensile strain and ductility were deteriorated by increasing the filler loading. Nano-ZnO, at 20 wt% content in composite, showed higher mechanical properties than bulk composite, so it has been recommended for a better tensile performance at higher strain rates. Vickers microhardness measurements showed that the tested samples exhibited reverse indentation size effect (RISE) behavior. The obtained results were analyzed using Meyer’s law which was a preferred approach for analysis of HDPE/ZnO composite.     

Effect of holding time on high strain hysteresis loss of carbon black filled rubber vulcanizates

Hysteresis loss has been measured at constant stress and constant strain, at various holding times under tensile deformation of natural rubber (NR) and styrene-butadiene rubber (SBR) vulcanizates filled with various loadings of carbon black filler. The effects of temperatures (25°C to 150°C), strain rates (3.78 × 10^?5 sec^?1 to 210 × 10^?3 sec^?1) and strain levels (20% to 300%) have been studied. Hysteresis loss and hysteresis loss ratio increase with an increase in strain rate, filler loading, strain level and holding time. It decreases with an increase of temperature. However, higher hysteresis loss and hysteresis loss ratio are observed at constant stress than at constant strain. NR and SBR vulcanizates show similar behavior. Evidence has been produced for the existence of a distinct relaxation process that occurs within first 120 second of holding time at room temperature. This process becomes less important as the strain or the temperature is increased. However, at high temperature another distinct relaxation process has been observed. The activation energy has been found to be 66.3 kJ/mole for the rates at the higher holding time, while it has been found to be 17.3 kJ/mole for the rates at the lower holding time using the data of hysteresis loss at first cycle of 40 phr black filled NR vulcanizates.     

Inelastic deformation under indentation and scratch loads in a ZrB2–SiC composite

Inelastic deformation features induced in an ultra-high temperature ceramic composite, ZrB₂–SiC, due to static indentation (rate of deformation of the order of 10^?5 s^?1), dynamic indentation (rate of deformation of the order of 10³ s^?1), and high-velocity scratch (500 mm/s) experiments are presented. It was found that this ceramic composite has up to 30% higher dynamic hardness compared to static hardness. Dynamic indentations resulted in extensive transgranular microcracking within the indented regions compared to static indentations. In addition, significant plastic deformation features in terms of slip-line formation were observed within statically and dynamically indented regions. The high-velocity scratch studies revealed extensive transgranular microcracking perpendicular to the scratch direction and slip-lines in and around the scratch path. Preliminary transmission electron microscopy (TEM) observations from regions of slip-lines surrounding the scratch grooves revealed dislocation activity in the composite.     

Influence of talc fillers on bimodal polyethylene composites for ground heat exchangers

In this study, a commercial grade of talc is used as filler in a bimodal high-density polyethylene (HDPE) used for the pressure pipe application. The composites are characterized by thermogravimetric analysis (TGA), differential scanning calorimetry, dynamic mechanical thermal analysis, and tensile testing. The results illustrate that the presence of talc has a considerable effect on the material properties and the pipe life-length. It is presented that the thermal stability measured by TGA is enhanced, while the oxidation induction time decreases in cooperation of the talc. The nucleation behavior of talc particles during crystallization has no obvious effect on melting temperature; however, an increase in crystallization temperature is evidenced. Storage modulus as recorded from the dynamic mechanical analysis is also increased in all composites, furthermore, the temperature of the α relaxation is shifted toward higher temperature and finally the strain hardening modulus for the HDPE/talc composites is assessed and compared to the neat HDPE as a measure of environmental stress crack resistance.     

Poly(phenylene oxide) composites containing crosslinked polystyrene microspheres. I. Stress–strain properties

The stress–strain properties of poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene composites containing crosslinked polystyrene microspheres have been measured at strain rates of 0.167, 1.67, and 16.7 min^?1. It is found that Young's modulus almost has no increase with the filler content. The elongation at break and tensile strength decrease with the volume fraction of the filler, but both tend to flatten out at the volume fraction ν_f > 0.25 at the strain rate of 1.67 min^?1. The two ultimate tensile properties also have maximum values in the relationship with strain rate at the same filler concentration and strain rate conditions. Considering that elongation can be brought about by both matrix and filler, the well-known equation of elongation at break becomes     

Improvements in thermal conductivity and mechanical properties of HDPE/nano-SiC composites by the synergetic effect of extensional deformation and ISBS

A new melt blending method under synergy of extensional deformation and in-situ bubble stretching for high-density polyethylene (HDPE) thermally conductive composites filled by nano silicon carbide (nano-SiC) was reported. Effects of loadings and mixing time of azodicarbonamide (AC) foaming agent on the properties of the composites were experimentally studied. Scanning electron microscopy imaging showed that the nano-SiC particles dispersed uniformly in the HDPE matrix with the addition of AC. The complex viscosity and storage modulus increased with increasing AC content and decreased with increasing mixing time. The mechanical properties of the composites improved with the addition of AC and proper mixing times. The thermal conductivity of the composites increased from 0.2 to 0.7 W m⁻¹ K⁻¹ without any damage to the mechanical properties when the mixing time increased from 2 to 6 min. These results showed that the new mixing technique enables us to prepare particle-filled thermally conductive polymer composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47648.     

Effects of filler geometry on internal structure and physical properties of polycarbonate composites prepared with various carbon fillers

BACKGROUND: The effects of filler geometry are important for understanding the internal structure and physical properties of polymer composites. To investigate the effects of filler geometry on electrical conductivity as well as morphological and rheological properties, three types of polycarbonate (PC) composites were prepared by melt compounding with a twin‐screw extruder. RESULTS: The electrical conductivity of PC/carbon black (CB) and PC/graphite (carbon) nanofibre (CNF) composites did not show a percolation threshold through the entire filler loading ranges. However, PC‐blend‐carbon nanotube (CNT) composites showed a percolation electrical threshold for a filler loading of 1.0 to 3.0 wt% and their maximum electrical conductivity approached 10^?3 S m^?1. PC‐blend‐CB and PC‐blend‐CNF composites showed Newtonian behaviour like pure PC matrix, but PC‐blend‐CNT composites showed yield stress as well as increased storage modulus and strong shear thinning behaviour at low angular frequency and shear rate due to strong interactions generated between CNT–CNT particles as well as PC molecules and CNT particles on the nanometre scale. CONCLUSIONS: The electrical conductivity of the PC composites with different carbon constituents was well explained by the continuous network structure formed between filler particles. The network structure was confirmed by the good dispersion of fillers as well as by the yield stress and solid‐like behaviour observed in steady and dynamic shear flows. Copyright © 2009 Society of Chemical Industry     

Elasticity at large deformations and high strain rates in injection molded polypropylene

The deformation behavior of isotactic polypropylene (PP) as a function of strain rate was investigated at 50°C in uniaxial tension. Injection molded dogbone specimens were tested at high strain rates, ε = 10^?1 – 10² s^?1, and the local deformation in the neck was studied using fast tensile videometry. A strong elastic recoil was observed after fracture in this strain rate range with local elastic strains as high as ?_e = 2.0 – 3.2. The recoil is very fast and takes place within 1 ms. The elastic fraction of the strain at break was found to increase with the local strain rate. The elasticity further depends on strain and temperature. The elastic deformation behavior is part of the known transition from ductile cold drawing behavior to brittle fracture that occurs with strain rate or temperature. The elasticity in PP is thought to be due to a decrease in crystallinity, resulting in a discontinuous crystalline structure comparable to that of thermoplastic elastomers.