Grade High Density Polyethylene Research Articles

Improving Environmental Stress Cracking Resistance of High-Density Polyethylene Grades by Comonomer Addition and Nanocomposite Approach.

The aim is to determine the effect of polymer density, correlated to the comonomer content, and nanosilica addition on the mechanical and Environmental Stress Cracking Resistance (ESCR) characteristics of high-density polyethylene (HDPE). In this regard, five HDPE samples with similar Melt Flow Index (MFI) and molar mass but various densities were acquired from a petrochemical plant. Two polymerization reactors work in series and differ only in the amount of 1-buene comonomer fed to the second reactor. To ascertain the microstructure of the studied samples, GPC and SSA (successive self-nucleation and annealing) analyses were accomplished. All samples resulted having similar characteristics but slightly various SCB/1000C=7.26-9.74 (SCB=Short Chain Branching). Consequently, meanwhile studied HDPEs reveal similar notched impact and stress at yield values, the tensile modulus, stress-at-break, and elongation-at-break tend to demonstrate different results with the SCB content. More significantly, ESCR characteristic varied considerably with SCB/1000C extent, so that higher amount of SCB acknowledged advanced ESCR. Notably, blending HDPE sample containing higher amount of SCB/1000C, with 3 wt.% of chemically modified nanosilica enhanced ESCR characteristic by 40%. DFT (Density Functional Theory) calculations unveiled the role of the comonomer, quantitatively by binding energies and qualitatively by Non Covalent Interaction (NCI) plots.

Modelling Fatigue Crack Growth in High-Density Polyethylene and Acrylonitrile Butadiene Styrene Polymers.

Prior studies into fatigue crack growth (FCG) in fibre-reinforced polymer composites have shown that the two methodologies of Simple-Scaling and the Hartman-Schijve crack growth equation, which is based on relating the FCG rate to the Schwalbe crack driving force, Δκ, were able to account for differences observed in the measured delamination growth curves. The present paper reveals that these two approaches are also able to account for differences seen in plots of the rate of crack growth, da/dt, versus the range of the imposed stress intensity factor, ΔK, associated with fatigue tests on different grades of high-density polyethylene (HDPE) polymers, before and after electron-beam irradiation, and for tests conducted at different R ratios. Also, these studies are successfully extended to consider FCG in an acrylonitrile butadiene styrene (ABS) polymer that is processed using both conventional injection moulding and additive-manufactured (AM) 3D printing.

A data-driven analysis of HDPE post-consumer recyclate for sustainable bottle packaging

The packaging industry faces mounting demand to integrate post-consumer recyclate (PCR). However, the complex structure-property relationships of PCRs often obscure their performance compared to virgin equivalents, posing challenges in selecting suitable PCRs for applications. Focused on extrusion blow moulding grade high-density polyethylene (HDPE), this study presents the most extensive characterisation of HDPE PCR to date, encompassing 23 resins (3 virgin, 20 PCR). Employing Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), rheology, colour analysis, and mechanical testing, we established a feature-rich dataset with 56 distinctive characteristics. Utilising a data science approach based on principal component analysis, with the virgin samples as a benchmark, we identified that combining FTIR, TGA and mechanical testing provided effective identification of PCRs that closely match the properties of virgin HDPE. The pipeline created can be utilised for new PCRs to determine suitability as a replacement for virgin plastic in a desired application.

Consumer Grade Polyethylene Recycling via Hydrogenolysis on Ultrafine Supported Ruthenium Nanoparticles.

Catalytic hydrogenolysis has the potential to convert high-density polyethylene (HDPE), which comprises about 30 % of plastic waste, into valuable alkanes. Most investigations have focused on increasing activity for lab grade HDPEs displaying low molecular weight, with limited mechanistic understanding of the product distribution. No efficient catalyst is available for consumer grades due to their lower reactivity. This study targets HDPE used in bottle caps, a waste form generated globally at a rate of approximately one million units per hour. Ultrafine ruthenium particles (1 nm) supported on titania (anatase) achieved up to 80 % conversion into light alkanes (C1 -C45 ) under mild conditions (498 K, 20 bar H2 , 4 h) and were reused for three cycles. Small ruthenium nanoparticles were critical to achieving relevant conversions, as activity sharply decreased with particle size. Selectivity commonalities and peculiarities across HDPE grades were disclosed by a reaction modelling approach applied to products. Isomerization cedes to backbone scission as the reaction progresses. Within this trend, low molecular weight favor isomerization whilst high molecular weight favor cleavage. Commercial caps obeyed this trend with decreased activity, anticipating the influence of additives in realistic processing. This study demonstrates effective hydrogenolysis of consumer grade polyethylene and provides selectivity patterns for product control.

Consumer Grade Polyethylene Recycling via Hydrogenolysis on Ultrafine Supported Ruthenium Nanoparticles

AbstractCatalytic hydrogenolysis has the potential to convert high‐density polyethylene (HDPE), which comprises about 30 % of plastic waste, into valuable alkanes. Most investigations have focused on increasing activity for lab grade HDPEs displaying low molecular weight, with limited mechanistic understanding of the product distribution. No efficient catalyst is available for consumer grades due to their lower reactivity. This study targets HDPE used in bottle caps, a waste form generated globally at a rate of approximately one million units per hour. Ultrafine ruthenium particles (1 nm) supported on titania (anatase) achieved up to 80 % conversion into light alkanes (C1−C45) under mild conditions (498 K, 20 bar H2, 4 h) and were reused for three cycles. Small ruthenium nanoparticles were critical to achieving relevant conversions, as activity sharply decreased with particle size. Selectivity commonalities and peculiarities across HDPE grades were disclosed by a reaction modelling approach applied to products. Isomerization cedes to backbone scission as the reaction progresses. Within this trend, low molecular weight favor isomerization whilst high molecular weight favor cleavage. Commercial caps obeyed this trend with decreased activity, anticipating the influence of additives in realistic processing. This study demonstrates effective hydrogenolysis of consumer grade polyethylene and provides selectivity patterns for product control.

Bayesian optimization of HDPE copolymerization process based on polymer product-process integration

A framework for finding an optimal operating point of HDPE with the target properties is proposed. A bimodal high-density polyethylene (HDPE) copolymerization process is established to calculate molecular weights, dispersity, and predict properties. The process incorporates a probability-based description method with reactivity ratio to describe the content of monomer A/B and sequence distribution. A properties prediction model is established to predict glass transition temperature, melt temperature, melt index, and density. Bayesian optimization algorithm is utilized to optimize the process. This algorithm combines Gaussian process regression and an expectation improvement model to determine the optimal mass flow of feed and temperature of reactors. The objective function is modified using a penalty function to incorporate property constraints. The optimization goal is to maximize profits by identifying the optimal composition of feed and reactor temperature. Optimized bimodal HDPE copolymerization process leads to a significant increase in profit, with a 21.8 % improvement compared to the original process. The effect of melt index, is considered in determining the optimal operation range and maximizing profit. This provides valuable guidance for producing new grades of HDPE.

Effect of recycled material on failure by slow crack growth in multi-layer polyethylene pipes

Among polymer materials, high-density polyethylene (HDPE) is one of the most demanded polymers for packaging as well as in sectors with higher material requirements, such as the plastic pipe industry. The extensive use of HDPE means it is often present in municipal waste. Therefore, there is a high potential for reprocessing and exploring new applications for recycled HDPE, aiming for a circular economy. In the plastic pipe industry, recyclates have found practical use in non-pressure applications. However, the high structural and loading requirements do not allow using it for pressurized pipes yet. The presented study is focused on the possible utilization of recycled HDPE in pressurized pipes in the form of a layer in a multi-layer pipe with two protective layers made of virgin HDPE. The performance of the pipes is assessed based on numerical simulations, coupled with lifetime estimations. The lifetime assessment is based on linear elastic fracture mechanics using experimentally measured slow crack growth (SCG) rates in the virgin and recycled HDPE grades. Thanks to the numerical models, it was possible to describe damage by SCG of the multi-layer pipe as well as to find the dependency of the pipe performance on the thickness ratio and material properties of the layers.

Structure–property relationship in film and blow molding type high‐density polyethylene polymers from a slurry‐process industrial plant

AbstractIn this study, the microstructural, flow, and mechanical properties of two commercially available high‐density polyethylene (HDPE) samples with different particle sizes were quantified. Specifically, two different blow molding and film grade HDPEs produced by the same catalyst under different conditions were acquired in powder form after dryer section of an industrial plant. They were fractioned according to their particle sizes into six samples: ≤125, 125–200, 200–315, 315–400, 400–500, and ≥ 500 μm. According to sieve analysis, the film grade (D50 = 304 μm) had larger particle sizes related to the counterpart injection sample (D50 = 289 μm). A peak value in density, bulk density, viscosity molecular weight (Mv), melt flow index (MFI), and comonomer content characteristics was found in the particles with the diameter of 125–200 μm in both samples, indicating extremely non‐homogeneity of these HDPE samples. Chemical composition distribution (CCD) of the as received polymers as well as sieved fractions was surveyed via SSA or TREF analyses. The film sample represented lower MFI and density and higher Mv and comonomer content in all fractions, originated from different reactor conditions during the samples synthesis, which translate into improved mechanical properties comparing with the blow molding sample.

Effects of Binders on Physico-chemical Characteristics of Egg Albumen Paneer (EAP)

Background: An innovative food product from egg albumen analogous to the conventional paneer was developed by inclusion of different types of binders and their effects on the physico-chemical qualities of the product were studied. Methods: Different cereal flours were used as binders viz., juoha rice flour (JRF), glutinous rice flour (GRF), wheat flour (WF) and oat flour (OF) in different ratios, with the egg albumen as the base material for the production of egg albumen paneer (EAP). EAP cubes were packed in food grade high density polyethylene bags and stored at 5-7oC for physico-chemical evaluation upto 90 days. Rehydration properties of the dried products were also studied. Result: Studies of EAP revealed that pH and water activity differ significant (P less than 0.01) among the treatments groups and decreased gradually during storage irrespective of the treatment groups and days of storage. The Thiobarbituric acid and Tyrosine values also showed significant (P less than 0.01) differences among the treatment formulations as well as during the storage days. The rehydration percentage, increase in volume after rehydration and coefficient of rehydration recorded highest in T1 than the other samples. Both the rehydration ratio and rehydration percentage were recorded highest in T2 group.

Thermal and Crystallization Behaviour of Polyphenylene Sulfide in Engineering Polymer Blends with HDPE

Abstract The thermal and crystallization behaviour of polyphenylene sulfide (PPS) in its blends with high density polyethylene (HDPE) is reported. Three grades of HDPE ranging in MFI from 0.4 to 52 were used in the investigation. The effect of composition and molecular weight of HDPE on the crystallization process and morphology of PPS in the blends has been investigated by the technique of Differential Scanning Calorimetry (DSC). In the blends, PPS crystallizes in presence of molten HDPE. It is observed that the morphology of PPS in terms of crystallite size and crystallite size distribution in the blends is significantly affected by blending with HDPE. The temperature onset of melting was found to increase with increasing HDPE content and the melting peak width was found to decrease with increasing HDPE content. This indicates a larger crystallite size and a narrower crystallite size distribution of PPS in blends. The effect is more pronounced in HDPE-rich compositions. The extent of the variation in the temperature onset of melting and peak width were comparable for all the grades of HDPE. The degree of crystallinity of PPS in the blends is reduced significantly (55–70%) in HDPE-rich blends. Therefore, it is concluded that the crystallization of PPS is affected by the presence of HDPE melt. The crystallization scans of PPS in the blends, obtained in the cooling mode, did not show any evidence of accelerated nucleation. On the other hand, a marginal reduction in the temperature onset of crystallization was observed. The temperature range of crystallization of PPS in the blends was found to be less for all compositions except for 90/10 (PPS/HDPE). In summary it is concluded that blending of HDPE with PPS influences the crystal growth of PPS significantly although the effect on its homogeneous nucleation is also considerable. As a result, the morphology of PPS crystallized in blends is different from that of the homopolymer. The changes in the morphology of PPS are not sensitive to the molecular weight of HDPE probably because of the high temperature of PPS crystallization relative to the melting point of HDPE.

Facile, scalable, and universal modification strategy of polyolefin utilizing noncatalytic C[sbnd]H insertion capability of azide: Sulfonyl azide end-functionalized polystyrene to modify polyethylene

Despite a broad range of commercial uses, applications of polyolefins have often been limited because of a lack of functionality and structural diversity, which has sparked the motivation to modify polyolefins, especially postpolymerization modifications (PPMs). The CH insertion capability of nitrene intermediates has been of interest due to its universal applicability to organic macromolecules containing CH bonds. In this study, a sulfonyl azide (SA) end-functionalized polystyrene (SAPS) is prepared as a model compound by synthesizing a SA containing azo-type radical initiator. SAPS is then used to modify commercial grade high-density polyethylene (HDPE) through simple melt process, affording HDPE-graft-polystyrene. The material exhibits homogeneous fractured surface, decreased crystallinity value, increased complex viscosity value, and relatively high Young’s modulus value, suggesting the formation of the polymer hybrids. This study demonstrates the capability of SA end-functionalized polymers as a noncatalytic platform for the PPM of polyolefins.

Choosing an Effective Compatibilizer for a Virgin HDPE Rich-HDPE/PP Model Blend.

The most widely used commodity polymers in the rigid packaging industry are polypropylene (PP) and high-density polyethylene (HDPE). For example, blow molding grade of HDPE as a bottle and injection molding grade of PP as a cap are often used to produce detergent bottles. Therefore, the recycled HDPE bottles from post-consumer waste include PP as a contaminant originated from PP bottle caps. To simulate mechanical recycling of bottle waste, the mechanical properties of HDPE-rich-HDPE/PP virgin model blend were studied. For compatibilization, ethylene-based olefin block copolymer, propylene-based olefin block copolymer, ethylene propylene random copolymer, and styrene-butadiene-styrene triblock copolymer were chosen as potential compatibilizer candidates. Contact angle measurements, morphological analysis, adhesion tests of compatibilizer candidates to polymer blend components and the tensile as well as tensile impact properties of the ternary blends were studied. It was found that the ethylene-based olefin block copolymer was the most effective compatibilizer resulting in a return of mechanical properties to those of neat vHDPE due to its ability to encapsulate dispersed vPP particles in a vHDPE matrix (core-shell morphology) and the best adhesion to polymer blend components.

Applicability of the Cox-Merz Rule to High-Density Polyethylene Materials with Various Molecular Masses.

The Cox-Merz rule is an empirical relationship that is commonly used in science and industry to determine shear viscosity on the basis of an oscillatory rheometry test. However, it does not apply to all polymer melts. Rheological data are of major importance in the design and dimensioning of polymer-processing equipment. In this work, we investigated whether the Cox-Merz rule is suitable for determining the shear-rate-dependent viscosity of several commercially available high-density polyethylene (HDPE) pipe grades with various molecular masses. We compared the results of parallel-plate oscillatory shear rheometry using the Cox-Merz empirical relation with those of high-pressure capillary and extrusion rheometry. To assess the validity of these techniques, we used the shear viscosities obtained by these methods to numerically simulate the pressure drop of a pipe head and compared the results to experimental measurements. We found that, for the HDPE grades tested, the viscosity data based on capillary pressure flow of the high molecular weight HDPE describes the pressure drop inside the pipe head significantly better than do data based on parallel-plate rheometry applying the Cox-Merz rule. For the lower molecular weight HDPE, both measurement techniques are in good accordance. Hence, we conclude that, while the Cox-Merz relationship is applicable to lower-molecular HDPE grades, it does not apply to certain HDPE grades with high molecular weight.

High‐density polyethylene reinforced by low loadings of electrochemically exfoliated graphene via melt recirculation approach

AbstractThe purpose of the paper is to demonstrate the effectiveness of high‐aspect ratio electrochemically exfoliated graphene (EEG) as a filler in high‐density polyethylene (HDPE); we use an industrially viable polymer processing technique (melt blending with melt recirculation) to ensure excellent dispersion and reinforcement at low loadings. The effects of nanofiller loading were evaluated for two different HDPE grades with two different melt flow indices (MFI) based on crystallization, tensile, and rheological properties. The findings indicate improvements in mechanical properties (tensile modulus and tensile strength) for all HDPE/EEG nanocomposite samples; however, the reinforcement was more pronounced at 0.2 wt% loading, indicating a transition from excellent dispersion at lower loadings to aggregated at higher loadings. The low and high MFI HDPE/EEG nanocomposites at 0.2 wt% EEG loading displayed an improvement of 31% and 40% in tensile modulus and 19% and 33% in tensile strength, respectively. The improved mechanical response with higher MFI nanocomposites is likely due to enhanced dispersion associated with the lower melt viscosity. Similarly, the rheological results also showed maximum increase in storage and loss modulus at a loading of 0.2 wt% EEG. In conclusion, EEG can be an effective filler if proper dispersion is achieved, which is challenging at high loadings.

Evaluation and prediction of mechanical properties of HDPE grade P5300 using molecular dynamics

The present paper discusses about the dispersion of single walled carbon nanotubes (SWCNTs) in the high-density polyethylene (HDPE)-P5300, for investigation and their prediction of the important mechanical properties of grade P5300 done on the software 'Material Studio 6.0'. Modelling and simulations are performed on five different samples of single walled carbon nanotubes introducing into high-density polyethylene (SWCNTs/HDPE) composites with SWCNT variation from 0.0 to 5.0 wt.%. A maximum value of 468.91 MPa of Young's modulus with 5.0 wt.% SWCNT/HDPE composite was obtained, as compared to pure HDPE composite. Acquired most extreme estimation of flexural modulus got was 991.9 MPa. Significant addition of 0.49% and 0.28% regarding unadulterated HDPE was likewise be investigated for 5.0 wt.% sample in Young's and flexural modulus individually. This study will assist in the modelling, simulation and design of advanced nanotube reinforced HDPE composites for potential real-life applications.

A comparison between $K$ and $G$ approaches for a viscoelastic material: the case of environmental stress cracking of HDPE

According to linear elastic fracture mechanics the stress intensity factor and the energy release rate are two fracture parameters linked by the elastic modulus and Poisson’s ratio of the considered material. This concept has been extended to the analysis of linear viscoelastic materials, by introducing time-dependent quantities; it is also used for nonlinear viscoelastic polymers, even if its accuracy in this case is still an open question. In this work the slow crack growth and the environmental stress cracking resistance of two high-density polyethylene grades were investigated, differing for their molecular weight distribution and fracture resistance. The description of the fracture behavior of the two materials provided by the stress intensity factor or the energy release rate turned out to be equivalent, despite the nonlinear mechanical behavior exhibited by the two polymers. Moreover, a time-dependent effective modulus, related to the two fracture parameters, was evaluated: its value was in good agreement with the modulus experimentally determined from tensile tests. A constant relevant effective strain was found despite the different testing conditions (i.e. applied mechanical loading, temperature and presence of an active environment), its value being equal for the two considered polyethylenes.

Realizing self-reinforcement of polyethylene via high-speed shear processing

As one of the most representative polyolefins, polyethylene (PE) constitutes the largest consumption of thermoplastics in the world. Thus, the high-performance issue of PE, such as effective self-reinforcement, represents highly expected demand in both of academic and industrial areas. However, it induces a materials engineering challenge due to the difficulties in preparations of multiphase materials and technological complexities of processing. Here, we report a readily accessible self-reinforcement behavior of high-density polyethylene (HDPE) realized via using a commercially available technique, high-speed shear extrusion. A common grade of HDPE can be enhanced significantly for nearly 60%, depending on the rotation speed. The chromatography indicates that the molecular weight of HDPE is nearly constant after experiencing high-shearing effect. While a quasi-solid-like character is detected in the HDPE melt, which could be attributed to the increment of entanglement causing by severe mixing during extrusion. Subsequently, the enhanced entanglement enables the appearances of high orientation structure and specific crystalline morphology, which are responsible for the mechanical reinforcement observed. Our present study offers a promising avenue to access the manufacture of structural parts using polyolefin resins.

Methodology of Accelerated Characterization for long-term creep prediction of polymer structures to ensure their service life

Abstract Predicting long-term creep behaviour (10 or 20 years) is important in the development and design of thermoplastic structures to ensure their service life. But providing robust material data to engineers is not easy, as testing is expensive and time-consuming. The purpose of this paper is to propose a new Methodology of Accelerated Characterization for long-term creep Prediction (MACcreeP) which gives more material information much faster and at a lower cost, than Classical Methodology (CM) used today by engineers. In order to prove the effectiveness of this new method, the material used for the study is a well-known high density polyethylene grade (HDPE). More precisely MACcreeP is a characterization protocol based on creep tests performed in true tensile stress conditions over short time periods (24 h) and at different temperatures combined with the Time-Temperature Superposition Principle to construct master curves. In addition to the material data obtained over a short period of time, the data generated by the behaviour laws and the use of the CREEP law in a FEA software allows a more predictive numerical response than in CM. Finally, this methodology, which implies very few tests, allows to compare and choose the appropriate material properties to design a thermoplastic structure which will comply with end-use product requirements.

Mechanical characterization of polyethylene-based thermoplastic composite materials for radiation shielding

Abstract Polyethylene is a hydrogen-rich polymer and has been used in making composite materials for radiation shielding. It has been shown that the radiation shielding properties of polyethylene are enhanced through the incorporation of multifunctional nanostructured materials into the matrix of the polymer. In this study, composites of boron nitride added to injection-molding grade high-density polyethylene (HDPE) were prepared and physically tested for their radiation shielding capabilities. Also, the mechanical properties of these composites were also investigated using the novel technique of AFM indentation. The goal is to create a composite material which exhibits advantageous properties in areas besides radiation shielding, i.e., structural or mechanical properties, which does not inhibit the shielding properties to provide multifunctionality which pure polyethylene materials lack.

Centrifugal dewatering performance in plastic films recycling

Dewatering of plastic films is a highly energy-consuming recycling operation that largely affects the quality of the recycled product. Despite the importance of good drying, this operation has not been studied at laboratory or pilot plant scale. In this work, the mechanical dewatering of blown film grade high density polyethylene has been assessed by using a laboratory centrifuge. It is suggested that a plastic cake is formed under the centrifugal forces similar to the sludge cake after the filtration process. The water is retained within the plastic cake due to three phenomena: free water within the cake pores and voids, water maintained by capillarity (superficial and pendular) and water trapped due to the tortuosity of the plastic mass. The total moisture is a sum of an equilibrium moisture and a transient moisture. The equilibrium moisture depends on the centrifugal force (G) but it is independent of time. Conversely, the transient moisture is reliant on both the G-force and the centrifugation time. The experimental results showed that an optimum side length exists. The moisture content is minimized when the flake side lies between 1 and 2 cm. Finally, it has been found that the moisture content is a function of the plastic surface. Hence, the specific moisture content (the mass of water per total plastic surface) should be calculated to compare films with uneven thickness or made of different materials. In sum, the outcomes of this study may be fundamental for the further and more extensive research into the plastic films dewatering processes.