Recycled High Density Polyethylene Research Articles

Volatile organic contaminants in HDPE milk bottles along the mechanical recycling value chain, revealing origins and contamination pathways

To progress towards closed-loop recycling of plastic packages it is vital to understand the origin of contaminants and to develop effective mitigation strategies. High density polyethylene (HDPE) milk bottles were sampled at nine different locations along the recycling value chain and analysed with two gas chromatography – mass spectroscopy methods to study the presence of volatile organic compounds. The total approximated concentration of volatiles reduced over time from the production of the bottles up to the cross-docking facility for the separately collected lightweight packaging waste (from about 250 to 100 ppm), as alkanes and alkenes evaporate from the bottle. A clear maximum was observed in the number of identified of volatiles and in the total approximated concentration in milk bottles at the sorted HDPE product. Here contaminants peaked that originate from the milk, from other packaging components (labels, caps, inlays), from other packages and from the surrounding atmosphere. When only the milk bottles were manually separated out from this sorted product and these were mechanically recycled, flakes were obtained that contain the least amount of volatile compounds, much less than the freshly produced bottles (about 25-50 ppm). The type of volatiles present was, however, markedly different. In the freshly produced bottles alkanes, alkenes and intentionally added anti-oxidant were found, whereas in the recycled flakes mostly contaminants were found that originated from: the milk, the other packaging components, other packages and the surrounding atmosphere. Seven different contamination pathways were discerned. The gathered knowledge facilitates the future development of food-grade recycled HDPE.

Evaluation of the Effectiveness of Geogrids Manufactured from Recycled Plastics for Slope Stabilization-A Case Study.

This study aimed to investigate the sustainable use of recycled plastics, specifically polypropylene (PP) and high-density polyethylene (HDPE), in the manufacture of geogrids for geotechnical and civil engineering applications. Plastics were collected from a recycling center, specifically targeting containers used for food, cleaning products, and other domestic packaging items. These plastics were sorted according to the Möbius triangle classification system, with HDPE (#2) and PP (#5) being the primary categories of interest. The research methodologically evaluates the mechanical properties of PP/HDPE (0/100, 25/75, 50/50, 75/25 and 100/0% w/w) composites through tensile and flexural tests, exploring various compositions and configurations of geogrids. The results highlight the superiority of pure recycled HDPE processed into 1.3 mm thick laminated yarns and hot air welded for 20 to 30 s, exhibiting a deformation exceeding 60% in comparison to the PP/HDPE composites. Through SolidWorks® Simulation, it was shown that the adoption of a trigonal geogrid geometry optimizes force distribution and tensile strength, significantly improving slope stabilization efficiency. Based on the results obtained, a laboratory-scale prototype geogrid was developed using an extrusion process. The results underscore the importance of careful composite design and yarn configuration selection to achieve the desired mechanical properties and performance in geogrid applications. It emphasizes the potential of recycled plastics as a viable and environmentally friendly solution for stabilizing slopes, contributing to the reduction in plastic waste and promoting sustainable construction practices.

The Effect of Recycled High-Density Polyethylene (HDPE) as an Additional Binder in Porous Asphalt Pavement

Porous asphalt has excellent permeability and larger air voids. Due to the low stability strength of asphalt binder with aggregates, Malaysia uses porous asphalt roads for lightweight vehicle road transportation. Numerous studies indicate utilizing Recycled High-Density Polyethylene in porous asphalt road surface. As a result, it was utilised as an additional binder material to enhance the asphalt binder. The main purpose of this study is to investigate the stability of modified porous asphalt samples and evaluate the optimum percentage of HDPE plastic waste from 3%, 6% and 9%. The aggregates, asphalt properties, Marshall Parameters and waster absorption test are in comply with JKR Standard and PWD 2008. At 3% of plastic addition has improved the stability of porous asphalt specimens. Adding plastic waste as a binder helps strengthen asphalt binding.

Assessing the circularity of post-consumer HDPE milk bottles through open-loop recycling and their environmental impact

Plastics are key in the packaging sector, but their widespread use contributes significantly to environmental challenges, such as the short life and high daily production of HDPE milk bottles. This study therefore aims to find a solution to this plastic waste, focusing on mechanical recycling. A comprehensive characterization of this post-consumer recycled HDPE reveals significant PP contamination, which poses a significant barrier due to polyolefin incompatibility, a common challenge in mixed plastics recycling. To mitigate this, blending with virgin HDPE and the use of various compatibilizers were investigated to improve the recyclability of the material. Several extrusion cycles were performed to analyse the thermo-mechanical degradation and to measure the performance and stability of the blends. The environmental impact of incorporating recycled HDPE into new bottles was also evaluated. Comparative evaluations with virgin bottles show that incorporating 25% or 50% recycled HDPE in the bottle yields carbon footprint reductions of 3% and 14%, respectively. These benefits could amplify with a wind-powered supply chain and a 100% recycled content. The findings lay the foundation for future plastic recycling scenarios, including dedicated sorting for this waste stream, providing a pathway to address the environmental impact of HDPE milk bottle disposal through recycling practices.

Mechanical Properties of Luffa Fiber Reinforced Recycled Polymer Composite

Environmental issues over the eventual fate of post-consumer polymers can be dealt with in two separate ways which is recycling or using biodegradable polymers. However, it is evident that recycling polymers from post-consumer polymers can decrease the mechanical properties over time. Hence, to strengthen the recycled polymers, integrating fibers, such as luffa, into the High-Density Polyethylene (HDPE) matrix, was carried out to produce a fiber reinforced recycled polymer (FRrP) composite. The tensile testing of the FRrP composite shows that the 10% fiber volume fraction (FVF) composite exhibits a higher tensile strength of 3.9% than the neat recycled HDPE (RHDPE). In terms of Young’s Modulus, the 5% FVF of FRrP is shown to have a higher value than the neat RHDPE by 54%. The low density of luffa fibers also contributes to the composites lightweight character. The impact testing shows that the FRrP enhances the impact properties when compared to the neat RHDPE. The peak load, perforation energy, and the total energy absorbed by the FRrP indicate an increasing trend when luffa, of up to 15% FVF, is added as the reinforcement. Thus, the addition of luffa as reinforcement in RHDPE shows significant potential as a high-performance, sustainable, and environmentally friendly material, such as automotive parts and protective gear.

Influence of Recycled High-Density Polyethylene Fibers on the Mechanical and Electrochemical Properties of Reinforced Concrete

The quantity of different plastics generated after consumption is an impact factor affecting the environment, and the lack of recycling generates solid waste. The purpose of this work is to incorporate high-density recycled polyethylene fibers (HDPE) for possible use as concrete reinforcement. Physical and mechanical properties from recycled fibers were analyzed, such as density, absorption, and stress resistance, as well as workability, air content, porosity, concrete compression, and flexural strength properties. Samples were prepared with a low fiber content of 0.2% and 0.4%, as a substitution for sand weight, and lengths of 10 and 30 mm. To study corrosion phenomena, the specimens were exposed to a saline environment containing 3% sodium chloride for 365 days, and the electrochemical techniques including half-cell potential (HCP), electrochemical noise (EN), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were applied. The results showed a 4.8% increase in compressive strength with a low fiber percentage and short geometries, while flexural strength increased marginally by 2.3% with small quantities of HDPE fibers. All these factors contribute to greater material durability, less permeability, and crack control. A positive effect of fibers with short dimensions on the corrosion processes of a steel bar was observed, with the fibers acting as a physical barrier against the diffusion of chloride ions.

Industrialized fine physical regeneration process and economic benefit assessment for recycling waste HDPE containers

The production of waste HDPE containers is enormous, and its recycling and utilization is an inevitable trend to achieve sustainable social development. However, the engineering practice of recycling waste HDPE containers is still lacking. This study provides a detailed explanation of the principles of fine recycling for waste HDPE containers, and develops a set of physical regeneration processes. By combining visual recognition assisted sorting, alkali hot water washing, physical sorting, and regranulation processes, high-quality regenerated HDPE particles are prepared. Meanwhile, various real data (sample size 50–100) of the production line and products are tracked, statistically analyzed. The results show that regenerated HDPE particles have good physical properties, the ratio of HDPE particles containing aluminum foil and multicolored impurities are extremely low, and the ratio of HDPE particles containing black spots (d＞0.1 mm) is less than 1.61 × 10−2 wt% (mean). Economic benefit analysis shows that the gross profit of recycled HDPE particles is USD $312.05 per ton. The above conclusions prove the feasibility and progressiveness of this process for the regeneration of waste HDPE containers. Meanwhile, this study provides engineering technical guidance for the large-scale fine recycling and regeneration of waste HDPE containers.

Composite materials using recycled high-density polyethylene plastic for railway sleepers

Given the substantial increase in railway load, speed and traffic, there is a notable demand for materials with high durability, long life and good damping. Such materials can be realized through composite materials that contain recycled high-density polyethylene, polypropylene (PP), mica, glass fiber and compatibilizers. In this study, extruded pellets containing the aforementioned materials and produced using a twin-screw extruder were utilized to assess their mechanical performances and microstructures. Composite materials containing 62.5% glass fiber and 20% PP demonstrated remarkable performance for manufacturing sleepers. The addition of 62.5% glass fiber in composite materials containing PP enhanced the flexural strength, flexural modulus, tensile strength and compressive strength by 315, 623, 296 and 40%, respectively, as compared with those of the original composite materials containing PP without glass fiber. Furthermore, the incorporation of glass fiber and the subsequent improvements met the requirements stipulated by the Ministry of Housing and Urban–Rural Development of the People’s Republic of China and International Organization for Standardization standards. This favorable result can be attributed to the good compatibility between the matrix and the glass fiber, as noted from the uniform distribution of glass fiber in the resin matrix in scanning electron microscopy images. The findings of this study highlight the potential of utilizing recycled materials in rail-track-manufacturing applications.

Effects of waste high-density polyethylene (HDPE) on asphalt binder and airfield mixes

ABSTRACT Flexible airport pavements may require polymer-modified asphalt binder for their asphalt concrete (AC) mixes to withstand heavy gear loading and slow traffic moving in taxiways and aprons. Waste plastics could be repurposed as a possible alternative to Styrene–butadiene-styrene (SBS) modifiers. In this study, the feasibility of using granulated recycled high-density polyethylene (HDPE) waste was evaluated as an asphalt binder modifier for airfield pavements. A base asphalt binder was modified with waste HDPE to obtain a Superpave performance grade (PG) of 70-22. Adding waste HDPE would increase binder’s stiffness and bond to aggregate, it slightly improved ductility and elasticity; but less than SBS polymer-modified binders. The AC mixes prepared with waste HDPE-modified binder showed less potential for rutting and cracking compared control AC mixes with PG 64-22. However, the rutting and cracking potential was higher when compared to their SBS-modified PG 70–22 counterparts. On the other hand, AC mixes containing waste HDPE-modified binder were less susceptible to moisture-induced damage. It appears that using waste HDPE-modified binder is feasible where improving adhesion and resistance to moisture-induced damage AC mixes are needed and embrittlement and elastic recovery are not critical, while meeting rutting and cracking potential regional thresholds.

Catalytic conversion of post-consumer recycled high-density polyethylene oil over Zn-impregnated ZSM-5 catalysts

The catalytic conversion of post-consumer recycled high-density polyethylene (PCR-HDPE) pyrolysis oil was investigated using modified ZSM-5 zeolites, prepared under different conditions. The PCR-HDPE oil, obtained through pyrolysis at 500 °C followed by distillation at 165 °C, contained a naphtha fraction hydrocarbons suitable for catalytic upgrading. H/ZSM-5 converts PCR-HDPE naphtha fraction oil primarily into BTX, along with light paraffins and olefins. Introducing mesoporosity led to increased propylene yield at the expense of BTX. Zn impregnation onto H/ZSM-5 and H-meso/ZSM-5 enhanced BTX yield by up to 13 %. However, Zn-meso/ZSM-5 exhibited a lower BTX yield than Zn/ZSM-5 with the same Zn loadings, especially after additional steam treatment at 700 °C. Spent catalysts revealed no noticeable increase in metal contaminants such as calcium and aluminum that were present in the PCR-HDPE. The Zn/ZSM-5 catalyst was stable for more than 50 h time on stream and showed promising potential for upgrading PCR-HDPE naphtha fraction oils.

Recovery pathway assessment of recycled HDPE for circular economy: Shorter-life vs longer-life products

High Density Polyethylene (HDPE) is a highly recyclable thermoplastic comprising 17% of all plastic produced. Yet, demand for recycled HDPE (r-HDPE) has outrun availability, partly due to manufacturers’ interest in meeting sustainability goals and recycled content mandates. Given that HDPE has a variety of uses, understanding optimal allocation of the constrained r-HDPE supply across product categories and lifespans will support the challenge of addressing broader sustainability goals and establishing circular economy (CE). By utilizing systems dynamic (SD) and life cycle analysis (LCA) modeling, this work studies whether prioritizing r-HDPE for longer-life products is more environmentally beneficial, compared to shorter-life products (e.g., food-grade packaging). Specifically, this work compares the production of milk containers and drainage pipes using virgin and r-HDPE as examples of HDPE applications through three scenarios. Key findings emerged from this study including the demonstration of a slight advantage to prioritizing allocating the constrained r-HDPE supply to the longer-life product vs the shorter-life product and a distinct challenge in hitting recycled content targets with current recycling rates and 2030 goals for the United States. This highlights a need to expand current recycling infrastructure in tandem with other CE practices to reduce plastic consumption and sustain environmental health for all.

Physical Behaviour of Wood Plastice Composite Made of Recycled High-Density Polyethylene (HDPE)

This paper investigated the physical characteristics of wood–plastic composites, which were made using recycled high-density polyethylene (HDPE) and using wood flour from Pometia sp (Matoa), Intsia sp (Merbau) and Alstonia sp (Pulai) as filler. The sawdust was taken from local furniture industry and the HDPE was collected from recycled plastic bottles of mineral water. Composite panels were made from recycled HDPE through hot-press moulding produced excellent stability based on JIS and SNI Standard, especially for moisture content and swelling characteristics. The water absorption and targeted density were also measured. In this study we found that the water absorption and the density of the composite exceeded our expectation. The composites showed high variation average for water absorption. For the swelling behavior, the value is varied from 5.74% to 25.57% after 2 hours soaking and varied between 7.56% to 28.53% after 24 hours soaking. This study has shown the composites had a high possibility to be used for interior and non-structural purposes.

Sustainable WPC Production: A Novel Method Using Recycled High-Density Polyethylene and Wood Veneer

This research work is focused on the development of an alternative method for manufacturing Wood Plastic Composite (WPC) panels based on Wood Veneers (WVs) and High-Density Polyethylene (HDPE) through compression molding, which enhances the physical properties, particularly, water absorption and moisture content. The aim of the present research was to develop alternative panels to replace commercial ones, which are heavily affected by hot, humid climates. In this context, the study began with the design process, which consisted of the collection and processing of primary material, production of the additional components necessary for the manufacturing process, determination of the WV ratio, and preparation of the samples. Thereafter, physical and mechanical tests were carried out on WPC, HDPE (control), commercial gypsum boards (GBs), plywood (PW), and medium density fiberboard (MDF) samples. The results indicate that the method applied to manufacture the WPC samples improved physical properties, achieving a water uptake of less than 4% in both proportions of replacement tested, in contrast to commercial panels, which reached values between 10% and 40%. In addition, a greater load capacity was achieved for lower thick elements.

Deconstructable and Chemically Recyclable High-Density Polyethylene (HDPE)-Like Materials Based on Si-O Bonds.

Polyethylene (PE) is the most widely produced synthetic polymer. By installing chemically cleavable bonds into the backbone of PE, it is possible to produce chemically deconstructable PE derivatives; to date, however, such designs have primarily relied on carbonyl- and olefin-related functional groups. Bifunctional silyl ethers (BSEs; SiR2(OR'2)) could expand the functional scope of PE mimics as they possess strong Si-O bonds, excellent oxidative stabilities, and facile chemical tunability. Here, we report BSE-containing high-density polyethylene (HDPE)-like materials synthesized through a one-pot catalytic ring-opening metathesis polymerization (ROMP) and hydrogenation sequence. The crystallinity of these materials can be adjusted by varying the BSE concentration or the steric bulk of the Si-substituents, providing handles to control thermomechanical properties while maintaining the high thermal stability of HDPE. Two methods for chemical recycling of HDPE mimics are introduced, including a circular approach that leverages acid-catalyzed Si-O bond exchange with 1-propanol. Additionally, despite the fact that the starting HDPE mimics were synthesized by chain-growth polymerization (ROMP), we show that it is possible to recover the molar mass and dispersity of recycled HDPE products using step-growth Si-O bond formation or exchange, generating high molecular weight recycled HDPE products with mechanical properties similar to commercial HDPE.

Thermally Robust yet Deconstructable and Chemically Recyclable High‐Density Polyethylene (HDPE)‐Like Materials Based on Si−O Bonds

AbstractPolyethylene (PE) is the most widely produced synthetic polymer. By installing chemically cleavable bonds into the backbone of PE, it is possible to produce chemically deconstructable PE derivatives; to date, however, such designs have primarily relied on carbonyl‐ and olefin‐related functional groups. Bifunctional silyl ethers (BSEs; SiR2(OR′2)) could expand the functional scope of PE mimics as they possess strong Si−O bonds and facile chemical tunability. Here, we report BSE‐containing high‐density polyethylene (HDPE)‐like materials synthesized through a one‐pot catalytic ring‐opening metathesis polymerization (ROMP) and hydrogenation sequence. The crystallinity of these materials can be adjusted by varying the BSE concentration or the steric bulk of the Si‐substituents, providing handles to control thermomechanical properties. Two methods for chemical recycling of HDPE mimics are introduced, including a circular approach that leverages acid‐catalyzed Si−O bond exchange with 1‐propanol. Additionally, despite the fact that the starting HDPE mimics were synthesized by chain‐growth polymerization (ROMP), we show that it is possible to recover the molar mass and dispersity of recycled HDPE products using step‐growth Si−O bond formation or exchange, generating high molecular weight recycled HDPE products with mechanical properties similar to commercial HDPE.

Influence of Modified SiO2 Nanoparticles on the Photostability of Recycled HDPE

Influence of Modified SiO2 Nanoparticles on the Photostability of Recycled HDPE

Development and characterization of short glass fiber reinforced-waste plastic composite filaments for 3D printing applications

In the present study, a thermoplastic-reinforced composite filament for 3D printing applications was created by mixing short glass fibers (SGF) with the thermoplastic matrix made from plastic waste. Short glass fiber-reinforced recycled high-density polyethylene (rHDPE) and recycled polyethylene terephthalate (rPET) blend thermoplastic composite filaments were first prepared by a plastic extrusion machine. The produced filaments' physical, mechanical, and thermal properties were investigated. After achieving the desired filament, a 3D printing technology called material extrusion was utilized to create 3D sample parts. The mechanical properties of each printed sample were analyzed following ASTM standards, and their morphological structures were also studied at various weight percentages (pure rHDPE, rHDPE/rPET (75/25 %), rHDPE/rPET reinforced with 15 % SGF, and rHDPE/rPET reinforced with 30 % SGF wt%). From the study, a 52 % increase in tensile strength, 32 % in Young's modulus, and a 50 % reduction in elongation with the addition of 30 wt% of SGF to rHDPE/rPET were noted compared to pure rHDPE. Generally, 3D printable composite filaments can be developed through the incorporation of SGF into plastic waste. This has tremendous advantages for solving environmental pollution and achieving sustainable development.

Experimental statistical modeling of tensile properties and flexural stiffness of recycled high-density polyethylene (rHDPE) thermoplastic using response surface methodology (RSM)

The widespread use of thermoplastic polymer products, particularly high-density polyethylene (HDPE), in daily consumer goods has led to the generation and accumulation of large amounts of plastic waste. This waste poses a significant threat to the environment due to the challenges and limitations in managing plastic waste effectively. Establishing new large volume applications of recycled HDPE (rHDPE) would incentivize recycling by creating new revenue streams. Before rHDPE (specifically rHDPE-talc blends) can be used more heavily in lieu of or in addition to virgin HDPE (vHDPE), its material properties in relation to application temperatures must be better understood. This study focused on characterizing tensile and flexural properties of rHDPE-talc blends across broad talc filler content and temperature ranges. Experimentally, tensile strength, elastic modulus, storage modulus, and nominal yield strain data were collected. Tensile strength and elastic modulus were observed to increase with an increase in talc content and decrease with an increase in temperature. Conversely, yield strain was observed to decrease with an increase in talc content and increase with an increase in temperature. Response Surface Methodology (RSM) was applied using the Central Composite Design (CCD) statistical experimental design approach to study the stiffness and strength of rHDPE and the effects that temperature and talc filler content have on these mechanical properties. The surfaces generated in this analysis fit the data well, with coefficients of determination greater than 0.94 for all but one property, storage modulus, which was 0.80. The evaluation of model performance revealed that the surfaces yielded good correlation and statistical significance. The results provide useful relationships that can be considered for use in practical applications involving rHDPE-talc blends, including engineering applications.

The use of recycled high‐density polyethylene waste to manufacture eco‐friendly plastic sand bricks

AbstractHigh‐density polyethylene (HDPE) polymer is one of the largest contributors to plastic wastes causing detrimental effects on various sectors of society, and is not biodegradable in nature. In the first stage, river sand and a recycled HDPE as a binder were used to manufacture eco‐friendly plastic sand bricks with various sand(s):plastic(p) ratios: 60s:40p; 65s:35p; 70s:30p; 75s:25p; 80s:20p; 85s:15p. In the second stage, 1%, 5%, and 10% of Kaolin Clay was added to each ratio of sand:plastic, respectively. Three mechanical tests were conducted: compressive strength, impact, and short beam strength. First, the addition of 5% Kaolin Clay to 75s:25p ratio increased compressive strength significantly from 21.4 to 52.76 MPa. Second, the addition of 10% Kaolin Clay in the ratio of 75s:25p mixture increased the impact strength from 4.8 to 5 J. Finally, the addition of 5% Kaolin Clay in the ratio of 60s:40p mixture increased the short beam strength significantly from 1.84 to 2.27 MPa. SEM analysis showed a well‐compacted interface indicating effective bonding between the HDPE and river sand particles in the 75s:25p ratio. Hence, the results of this study present a potential for the use of recycled HDPE plastic to manufacture plastic sand bricks.Highlights Addition of Kaolin Clay improved the mechanical properties of the composite material.

Effect of Rice Husk and Wood Flour on the Structural, Mechanical, and Fire-Retardant Characteristics of Recycled High-Density Polyethylene.

Given the rising consumption of plastic products, it is becoming imperative to prioritize the recycling of plastic items as a solution to reducing plastic waste and environmental pollution. In this context, this research focuses on assessing the impact of incorporating rice husk and wood flour into recycled high-density polyethylene (rec-HDPE) to analyze its mechanical properties, flammability, and thermal stability. The combined rec-HDPE content of wood flour and rice husk varied between 0% and 20%. The rec-HDPE content of maleic anhydride grafted polyethylene (MAPE) was fixed at 3%. Mechanical characteristics such as flexural, tensile, and impact strengths were assessed. Cone calorimetry (CC) tests, limited oxygen index (LOI) tests, and horizontal and vertical burning tests were performed to determine the flammability or fire retardancy of these composites. On the other hand, to characterize the thermal characteristics of these composites, thermogravimetric analysis (TGA) was used. To further characterize the fluctuation in these characteristics, scanning electron microscopy (SEM) and infrared spectroscopy (FTIR) studies were carried out. The mechanical characteristics were found to be increased in response to adding rice husk or wood flour. An 8% increase in tensile strength and a 20% increase in elastic modulus enhancement were recorded for a 20% rice husk-added composite. SEM revealed the reason for the variation in tensile properties, based on the extent of agglomeration and the extent of uniform distribution of fillers in rec-HDPE. Following these lines, the 20% rice husk-added composite also showed a maximum increase of around 6% in its flexural strength and a maximum increase of 50% in its flexural modulus. A decrease in impact strength was recorded for rice husk and wood flour-reinforced composites, compared with unreinforced rec-HDPE. Hybrid composites displayed a lack of mechanical strength due to changes in their nature. FTIR tests were performed for a much more elaborate analysis to confirm these results. Twenty percent of rice husk-added rec-HDPE displayed the best thermal properties that were tested, based on TGA and derivative thermogravimetric (DTG) analysis. This 20% composite also displayed the best fire-retardancy characteristics according to UL 94 tests, cone calorimetry tests, and limited oxygen index tests, due to the barrier created by the silica protective layer. These tests demonstrated that the incorporation of both fillers-rice husk and wood flour-effectively enhanced the thermal, mechanical, and fire-retardant attributes of recycled HDPE.