Virgin High-density Polyethylene Research Articles

Revitalizing high-density polyethylene (HDPE) waste: from environmental collection to high-strength hybrid yarns

AbstractPlastic products are used in large quantities. However, the fact that plastics do not degrade in nature for many years causes environmental pollution. Addressing this issue, the study focuses on recycling the widespread high-density polyethylene (HDPE) plastic waste. In this study, HDPE waste was collected randomly from the environment, mirroring real-world scenarios. Then, the waste was transformed into granules. Afterward, washing and drying processes were carried out. HDPE filaments of different linear densities were successfully produced from the waste plastic granules. Tensile tests revealed that the breaking strength of the filaments from waste plastic was lower than that of virgin HDPE filaments, highlighting the challenges of recycling. Hybrid yarns were formed by twisting the filaments with cotton yarn to improve the mechanical properties of the filaments from waste plastic. Remarkably, statistical analysis demonstrated that the breaking load values of the hybrid yarns from waste plastic were statistically equivalent to those made from virgin polymer. This outcome indicated that the hybrid yarns made from waste HDPE plastic were as strong as those made from virgin HDPE polymer. In addition, both hybrid yarns exhibited a breaking load 36% higher than the reference extra-twisted cotton yarn. The hybrid yarn formation made filaments produced from waste plastic a valuable component of the high-strength hybrid yarn. Overall, this study shows that recycling HDPE plastics can lead to the production of high-strength hybrid yarns, which can contribute to reducing plastic waste pollution.

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.

Effect of cold plasma pretreatment on biodegradation of high-density polyethylene (HDPE) and polystyrene (PS)

AbstractCold atmospheric plasma (CAP) pretreatment of high-density polyethylene (HDPE) and polystyrene (PS) was investigated to evaluate its effect on biodegradation. Weight and wettability measurement, surface topography, and roughness analysis were examined for physical properties evaluation. Fourier-transform infrared spectroscopy (FT-TR) analysis was conducted to understand the possible chemical transformation. Based on biofilm formation, the highest microbial colonisation was observed on the sample treated with CAP pretreatment + biotreatment, which was 0.56 and 0.19 (at OD 595 nm) for HDPE and PS, respectively. A biodeterioration effect characterised by weight loss and changes of hydrophobicity in which hydrophobicity reductions of 5.1 ± 0.64% and 12° ± 0.35° were observed with the pretreated HDPE within 50 days, respectively. No physical weight loss was detected in the PS sample, but significant surface corrosion was observed. Atomic force microscopy (AFM) also showed a higher surface degradation of 10 and 35% for CAP pretreated HDPE and PS incubated with microorganisms compared to virgin samples incubated in the same condition. Moreover, chemical transformation indicated a new peak (C–O) in CAP-pretreated PE samples before and after 50 days of biodegradation. The experiments with virgin HDPE and PS demonstrated a positive effect of the pretreatment on the biodegradation process.

Material Characterizations of the Polymers Reinforced with Recycled Flexible Plastic Blends as Filament for 3D Printing

The high consumption of single-use plastics and the low recycling rates have seriously polluted the soil and ocean environments. Thermoplastic materials from recycling can be used to make filaments for 3D printing. This study is focused on preparing, characterizing, and comparing the polymers reinforced with recycled flexible plastic blends to be used as a filament in additive manufacturing. In this regard, two types of polymers were used to create the filament: High-Density Polyethylene (HDPE) and Polypropylene (PP), which were mixed with recycled flexible plastic (RF). The mixture was initially used to create filament by using a single extrusion machine, with various ratios of virgin HDPE and PP to recycled flexible plastic (in weight%) at temperatures of 190°C and 230°C. Then, the filament blends were characterized using infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM). TGA analyses revealed that RF can increase the thermal stability of V- HDPE and V-PP upon blending, and HDPE/RF blends show a higher decomposition temperature than PP/RF. FESEM indicated that adding 30% RF is the best percentage for both polymer blends where the structure appears ductile. It can be concluded that the HDPE 70% blend is suitable for 3D printer filament as it showed the best decomposition temperature and the ductility of the fracture structure, which meet the requirements for 3D printer filament.

Mechanical, Thermal Properties of Virgin, Recycled and Mixed High-Density Polyethylene Matrices and Wood Plastic Composites with Plywood Sanding Dust

Virgin high-density polyethylene (vHDPE), recycled (rHDPE), and mixed vHDPE/rHDPE matrices and wood plastic composites based on these mixtures + 50 wt.% of plywood sanding dust (PSD) and 3 wt.% coupling agent maleated polyethylene (MAPE) physical-mechanical properties (tensile, flexural strength and modulus, impact strength, and microhardness) were investigated. It was observed that all defined properties depend on the content of rHDPE in the pure polymer matrix and corresponding WPCs. Tensile strength and modulus decreased a bit, but flexural modulus actually had no changes. At the same time, a decrease in impact strength and a significant increase (up to 2 times) in microhardness are observed. From all the investigated matrices, the most perspective seems to be the matrix with a vHDPE/rHDPE ratio of 75/25, whose mechanical properties are acceptable for the preparation of the WPCs based on plywood sanding dust. The compatibilization possibilities tests of different mixed matrices done by the DSC method in the air showed that the mixed vHDPE/rHDPE compositions compatibility is sufficiently good at different proportions. For all mixed matrices, only one relatively symmetric band with one peak of melting was observed. Differential scanning calorimetry (DSC) tests in an inert environment showed that during the first heating cycle, HDPE components are only partially compatible (two peaks of melting temperatures are possible to fix). On the contrary, after the cooling and crystallization processes, during the second heating of the same sample, these two bands completely merge, and like in the air, only one maximum melting temperature peak was observed. The values of thermal oxidation temperature and melting temperature are the highest for virgin vHDPE but the lowest for rHDPE. The values of all corresponding parameters of mixed matrices reduce proportionally with an increase in rHDPE content in the mixtures.

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.

Improving the performance of post-consumer resin feedstocks for rigid packaging applications: A pilot-scale assessment

Various market, environmental and political drivers encourage the use of more post-consumer resin (PCR) high-density polyethylene (HDPE) in rigid packaging. However, PCR HDPE performs poorly compared to virgin HDPE, particularly in blow-moulded bottles for cleaning products which often show inadequate resistance to environmental stress cracking. In this study we evaluate and compare additives representing various strategies designed to improve the mechanical performance of PCR HDPE. Two commercially available recycled HDPE PCRs were extruded with eight candidate additives and the bottle performance of the best performing blends were tested in extrusion blow moulding trials. FTIR analysis revealed polypropylene contamination in one PCR although rheology and thermal properties were very similar. The use of strain hardening modulus as a selection criterion for pilot scale trials was demonstrated. The results revealed that particulate additives may have negative effects while polyolefin additives are more likely to succeed at the pilot scale.

An Experimental Approach to Determining the Average Diffusion Coefficient of Volatile Components in Polymer Waste Materials

One of the major challenges in recycling plastics is the removal of undesired volatile components from the polymeric phase, which may reduce process efficiency and negatively affect product quality. Accordingly, the recycling industry employs a broad range of degassing techniques, the efficiency of which often depends on the diffusion coefficient—a measure of the mass transport of volatile components in polymeric phases. The aim of this study was to develop a practically feasible experimental approach using thermogravimetric analysis (TGA) to determine the average diffusion coefficient of volatile components in polymer waste materials. First, the TGA method was validated with a pressure decay apparatus (PDA) using predefined binary material mixtures: Thin sheets were pressed from virgin high-density polyethylene (HDPE) and polypropylene (PP) and deliberately saturated with toluene in a sorption experiment. These saturated samples were then used in TGA and PDA desorption experiments at 60 °C, 80 °C and 100 °C, which yielded similar results with an average difference of 7.4% for the HDPE-toluene system and 14.7% for the PP-toluene system. When validated, TGA was employed to determine the diffusion coefficient of volatile components in post-industrial plastic waste melt at a temperature of 220 °C. The proposed method contributes to the understanding of diffusion-based mass transport in polymer waste materials and provides a key parameter for model-based process control and optimization. In practice, the diffusion coefficient results can be used to predict the degassing performance of an extrusion process in the mechanical recycling of plastic waste.

Investigating the Potential of High-Density Polyethylene and Nano Clay Asphalt-Modified Binders to Enhance the Rutting Resistance of Asphalt Mixture

This study investigates the potential of two bitumen modifiers, high-density polyethylene (HDPE) and nano clay (NC), to enhance the rutting resistance of asphalt mixture. Four HDPE asphalt binders were prepared by mixing the HDPE at percentages of 2%, 4%, 6%, and 8% with the virgin binder, while four NC asphalt binders were produced by mixing the NC at percentages of 1%, 2%, 3%, and 4%. The consistency and flow of virgin binder, HDPE binders, and NC binders were evaluated by penetration, softening point, and viscosity tests. The results show a gradual increment in the binder stiffness by increasing the percentage of both modifiers. The static creep test was conducted at a temperature of 40 °C to evaluate the rutting resistance. The results confirm that both modifiers can greatly improve the rutting resistance of the asphalt mixture, where 8% HDPE and 3% NC modifications reduce the strains provoked in the asphalt mixture under loading by about 50%. According to the correlation analysis, the mixture rutting performance is highly attributed to the binder stiffness, where the lower the penetration value of the asphalt binder, the lower the strains in the asphalt mixture and the higher the stiffness modulus of the asphalt mixture.

Thermal degradation of virgin and waste plastics: Estimation of kinetic and thermodynamic parameters using model‐free iso‐conversional methods

AbstractKinetic triplets—apparent activation energy (Ea), pre‐exponential factor (A), and the reaction model—were estimated for the thermal degradation of three primary virgin and waste plastics, as well as mixed plastics waste. Model‐free iso‐conversional FWO, KAS, Starink, Kissinger and Vyzovkin and Friedman methods were employed for the kinetic analysis. The apparent activation energy was determined by the integral methods as 206.5‐209.1 kJ mol−1 and 195.6‐198.8 kJ mol−1 for the virgin and waste high‐density polyethylene (HDPE), 211.6‐214.1 kJ mol−1 and 183.1‐186.6 kJ mol−1 for the virgin and waste polypropylene (PP), 144.0‐163.1 kJ mol−1 and 159.7‐167.1 kJ mol−1 for the virgin and waste polystyrene (PS), and 173.6‐178.9 kJ mol−1 for the mixed plastics waste respectively. Ea was found to follow the trend HDPE > PP > PS with higher values for HDPE and PP virgin samples than that for their waste and marginally smaller for the virgin PS than its waste. Degradation of all plastic samples followed Avrami‐Erofeev equation with n varying between 1.0 and 1.8. The effect of conversion on Ea suggested the degradation of both virgin and waste HDPE to consist of multiple parallel reactions while that of others to be more complex. FTIR analysis of the evolved gases was used to explain the possible reaction mechanism. A small difference between the enthalpy change and the apparent activation energy (6‐7 kJ mol−1) for all plastic samples indicated favourable pyrolysis reactions. The estimated kinetic parameters and thermodynamic properties showed the stability of different plastics as HDPE > PP > PS.

Developing Filament Extruder and Characterization of Recycled High-Density Polyethylene for 3D Printing Filament Material

With the rise of additive manufacturing, the demand for 3D printing feedstock has increased exponentially and its sustainability is critical in the future. Many scholars are now concerned about how 3D printing filaments should be reproduced from recycled plastic. This study aimed to develop a filament extruder machine and investigate the potential of using recycled high-density polyethylene (HDPE), one of the most commonly used and recyclable thermoplastic, for 3D printing filament material. Desktop sized filament extruder machine was built, and a smooth and round-shaped 1.75±0.01mm diameter recycled HDPE filament was produced. Its mechanical, thermal, chemical, and physical properties were characterized by conducting various tests and validation test was conducted by comparing its properties with its virgin counterpart. The ultimate tensile strength of the recycled HDPE filament was obtained 19.02±0.35MPa, which is comparable to the ultimate tensile strength of virgin HDPE, making it a viable 3D printing feedstock for rapid prototyping. According to Thermogravimetric analysis (TGA), the recycled HDPE filament offers significant thermal stability with an onset degradation temperature of 430℃ and a full degradation temperature of 520℃. Its Fourier Transform Infrared (FTIR) spectrum shows the same functional groups as virgin HDPE polymer. The recycled HDPE filament has also excellent water-rejecting capability. In general, the study revealed a promising result for the use of recycled HDPE plastic as a more sustainable and environmentally friendly source material for 3D printing filament. To increase the potential and market competitiveness of recycled filaments, further investigation is required to optimize the filament extrusion and 3D printing process parameters, improve the mechanical properties, and overall development methods for both the recycled HDPE filament and 3D printed products.

Unraveling the catalytic activity of CaClOH-rich incineration fly ash in the pyrolysis of single-use plastics

In recent years, increased population and economic growth have resulted in an explosion in demand, production, and disposal of non-biodegradable commodity plastics. Pyrolysis, the anaerobic thermochemical breakdown of plastics such as polyethylene (PE), polypropylene (PP), and polystyrene (PS) into lower molecular weight hydrocarbons with applications as fuels, waxes, and lubricants, has emerged as one of the most promising industrial technologies for the end-of-life treatment of plastics. While a range of inorganic materials have shown efficacy in catalyzing plastic pyrolysis and reducing their energetic demands, the use of existing inexpensive waste materials such as incineration fly ash (IFA) for this application has largely been overlooked. Herein, we demonstrate the viability of IFA as a catalyst for the pyrolysis of PE, PP, and PS, which account for almost 60% of all the waste plastics produced globally. The presence of IFA improved reaction conversions and liquid yields and resulted in positive outcomes for the pyrolysis of real-life plastic waste such as high density polyethylene (HDPE) detergent bottles and low density polyethylene (LDPE) plastic bags. Specifically, the pyrolysis of virgin HDPE pellets with IFA showed increased conversion from 46.7% to 92.8% and liquid yield from 35.1% to 81.6%, respectively. Through a set of control experiments, we determined that the catalytic activity of IFA could be attributed mainly to calcium hydroxychloride (CaClOH), which differed from other common calcium-containing minerals such as calcium oxide (CaO) and calcium chloride (CaCl2). Our findings demonstrate the unique catalytic possibilities offered by overlooked waste materials such as IFA in the upcycling of single-use plastics into liquid hydrocarbons and offer new insights on the use of different calcium-based catalysts for plastic pyrolysis.

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.

Effects of Wood Flour Reinforcement on the Warpage and Compressive Strength of 3D Printed HDPEs

The study involves the use of high density polyethylene (HDPE) as a filament for 3D printing. Considering the warpage and adhesion problem of HDPE on the build plate during 3D printing, this was addressed through the incorporation of wood flour compatibilized with styrene-ethylene-butylene-styrene grafted maleic anhydride (SEBS-gMAH). The composite wood-HDPE (cHDPE) was studied to observe warpage changes. Using different SEBS, heat bed parameters and identification of the suitable print heat beds for HDPE was conducted. Results from the mechanical testing show that the compressive strength and elastic force of virgin HDPE (vHDPE) increases with infill percentage, while the same properties for cHDPE increases up to 50% infill density/percentage then decreases as it approaches 100% infill percentage. Digital microscopy imaging shows that poor layer adhesion initiated the poor compressive performance of cHDPE. Warp studies reveal that wood flour significantly decreases warping of HDPE by 42.88% at 50% infill density. While different SEBS brands show similar effectiveness as heat beds in reducing warping of HDPE during printing.

Durability of High-Density Polyethylene (HDPE)- and Polypropylene (PP)-Based Wood-Plastic Composites—Part 1: Mechanical Properties of the Composite Materials

Wood-plastic composites (WPCs) have shown exceptional promise as a building material, especially for outdoor uses. Using renewable wood fiber as the reinforcing filler in WPCs increases the material’s environmental sustainability. While virgin commodity thermoplastics are primarily used in these composites, using post-consumer plastic further contributes to their sustainability. While they are beginning to be used in the Gulf countries, information on their performance, especially durability under harsh desert climates, is sparse. The present investigation on WPCs is based on the two most popularly used thermoplastics in WPCs, virgin high-density polyethylene (HDPE) and polypropylene (PP), with the wood content varying between 0 and 36 wt. %. These were prepared with melt processing from a masterbatch and characterized primarily using thermal methods and tensile properties of their injection molded test pieces. Variations in tensile properties, especially the tensile modulus (MPa), the tensile strength (MPa), and the ultimate extensibility (%) of the composite samples were investigated to determine an optimal wood-fiber loading. For either polymer type, exceeding 27 weight percent of wood fiber resulted in unacceptably low ultimate extensibility of the material.

An investigation into the tensile properties of recycled high-density polyethylene (rHDPE) blended with talc filler

High-density polyethylene (HDPE) is a well-established thermoplastic; however, with concerns about the fate of plastics at end-of-life, there is a growing interest in strategies to utilize recycled HDPE (rHDPE) in place of virgin HDPE (vHDPE). This study investigated the tensile properties of rHDPE/talc blends (0, 20, 28, and 38 wt% talc) and adequate talc dispersion was found in the blends using SEM imaging. Increases in tensile strength (up to 20.4%), elastic nominal stiffness (up to 93.5%), and a decrease in nominal yield strain (up to 50%) were observed for rHDPE with increasing talc content. The trends observed indicate that rHDPE could be a viable alternative/supplement to vHDPE for use in large volume structural applications. If talc filler particle dispersion can be well monitored, the rHDPE/talc blends have significant potential to be used and hence reduce the amount of virgin material needed; however, additional properties should be further explored.

To Explore the Effect of Modified Seashell on the Thermo-Mechanical Properties of Polymer Matrix Composite

This research paper proposes a sustainable and feasible technique to utilize seashell waste. The utilization of seashells offers economic and environmental benefits because of their abundant, renewable, and cheap source of calcium carbonate. The technique will reduce the hazards of seashell waste generated to the environment and landfilling that cause risk to water sources and public health. Moreover, the synthesized bio − CaCO3 will reduce the end-product cost of the polymer. The successful synthesis of bio-calcium carbonate powder (bio − CaCO3) was carried out using a calcinations technique up to 800°C from seashells. The high density polyethylene (HDPE) composite samples were prepared via the industrially preferred melt route by varying the shell powder content by 10% and 20% by weight. The composite was subjected to Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetric (DSC), and mechanical analysis. TGA confirmed the thermal behavior of synthesized bio − CaCO3. The thermal degradation temperature of bio − CaCO3 and virgin HDPE were distinctly observed at 734 °C and 443 °C, respectively, in composite samples. The thermal stability was increased by more than 37 °C in the composite sample at 20% bio − CaCO3 loadings. The percent crystallinity also increased by 14% for higher bio − CaCO3 loadings when compared to virgin HDPE. DSC analysis showed no significant changes in melting points and was not affected by the addition of bio − CaCO3 and remained at about 134 °C in virgin and composite samples. This observation is attributed to the similar crystal structures in all samples. The HDPE composite sample showed higher tensilestrength, about 25%, than virgin HDPE. In addition, HDPE10 and HDPE20 composite samples showed lowerelongation at break when compared to virgin HDPE in accordance with the literature.

Experimental Investigation on Pyrolysis of Domestic Plastic Wastes for Fuel Grade Hydrocarbons

Plastics usage is rising daily because of increased population, modernization, and industrialization, which produces a lot of plastic garbage. Due to their various chemical structures, long chain polymeric compositions, and thermal/decomposition behavior, it is challenging to recycle these plastic wastes into hydrocarbon fuels. In the current work, domestic plastic waste was pyrolyzed at 473 to 973 K in a fixed bed reactor and compared with the three virgin plastics LDPE (low-density polyethylene), HDPE (high-density polyethylene), and PP (polypropylene), as well as a mixture of the three (virgin mixed plastics). The pyrolysis results showed that maximum liquid hydrocarbons obtained from HDPE, LDPE, PP, mixed plastic, and domestic waste were 64.6 wt.%, 62.2 wt.%, 63.1 wt.%, 68.6 wt.%, and 64.6 wt.% at 773 K, respectively. The composition of liquid fuels was characterized using FTIR and GC-MS, which showed a wide spectrum of hydrocarbons in the C8–C20 range. Furthermore, liquid fuel characteristics such as density, viscosity, fire and flash point, pour point, and calorific value were examined using ASTM standards, and the results were found to be satisfactory. This study provides an innovative method for recycling waste plastics into economical hydrocarbon fuel for use in transportation.

Effects of mechanical recycling on optical properties and microstructure of recycled high‐density polyethylene pellets and bottles

AbstractThe demand for recycling high‐density polyethylene (HDPE) utilizing mechanical recycling technologies is currently felt strongly by both society and industry. However, thermal oxidation of the polymer during the recycling process may lead to irreversible changes in the material properties of recycled high‐density polyethylene (rHDPE). The effects of mechanical recycling on the optical characteristics and microstructure of rHDPE pellets and bottles were investigated in this study. The results revealed that the apparent color of the rHDPE became more yellow and gray compared to the virgin HDPE (vHDPE), and showed a signal at 670–680 nm in the solar reflectance spectrum. The thermal oxidation of rHDPE considerably raised the absorption intensities of carbonyl, ester, and hydroxyl groups in attenuated total reflection Fourier transform infrared spectrum. In addition, the presence of carbonyl and hydroxyl unsaturated chemicals might make it challenging to recognize the distinctive peaks of vHDPE in the ultraviolet–visible diffuse reflectance (UV–Vis‐DIR) spectra at wavelengths less than 400 nm. Thermal oxidation of rHDPE was also confirmed in the COH, CO, and OCO valence structures of C1s and O1s. A characteristic valence band (VB) profile at 25 eV can be used as the recognizable information for the oxidation of rHDPE. The microstructure of the surface of rHDPE pellets exhibited rough and uneven morphological defects. The higher recycled content made rHDPE bottles' surface morphology rougher and their cross‐section microstructure thinner and more porous than vHDPE bottles.

Carbon nanomaterial production using waste plastic pyrolysis over a new catalyst made from mining residues: Effect of plastic type

Pyrolysis and in-line catalytic decomposition of plastic waste were performed for the production of carbon nanomaterials (CNMs) and hydrogen. A new catalyst, Ni-UGSO (Nickel-UpGraded Slug Oxide), was used in a continuous mode, and its activity was compared to that of a typical Fe/Al2O3 catalytic formulation. Moreover, the pyrolysis-catalysis of different plastics (virgin high-density polyethylene (HDPE), used HDPE, and mixed plastics) was studied to investigate the effect of the plastic type on the quantity and quality of the produced CNMs. Ni-UGSO exhibited the highest catalytic activity for the production of CNMs and H2 of the two formulations tested, with yields of 56.6 kg/100 kgplastic and 13.2 kmol/100 kgplastic, respectively. The high activity and performance of Ni-UGSO were attributed to the synergistic effect of the Ni and Fe in Ni-UGSO. Scanning transmission electron microscopy (STEM) results revealed that most of the produced carbon was in the form of carbon nanofilaments (CNFs) of different diameters, ranging from 8 to 90 nm. The use of mixed plastics as a feedstock decreased the yield of CNMs by 10 wt%, and a layer of amorphous carbon covered the CNFs. This layer is due to the presence of polystyrene (PS), polyethylene terephthalate (PET), and other contaminants in the feedstock. Raman spectroscopy showed that the CNFs produced from used HDPE had the highest intensity ratio G/D (1.13).