High-density Polyethylene Pellets Research Articles

Optimization in Extrusion Process for Polypropylene and High-Density Polyethylene Pellets in Additive Manufacturing of 3D Printing Filament

The increasing demand for sustainable and cost-effective materials in additive manufacturing has driven research into optimizing the extrusion process for creating 3D printing filament from Polypropylene (PP) and High-Density Polyethylene (HDPE) pellets. This study explores the critical parameters in the extrusion process, including temperature, and screw speed, to enhance the quality and consistency of the resulting filament. Through a series of controlled experiments, we analyze the effects of these parameters on the filament’s diameter, mechanical properties, and printability. Our findings demonstrate that by optimizing these variables, it is possible to produce high-quality 3D printing filament with excellent mechanical strength and dimensional accuracy, meeting industry standards. This research not only contributes to the broader adoption of PP and HDPE in 3D printing but also supports the development of more sustainable manufacturing practices by utilizing recyclable materials.

Pyrolysis of high-density polyethylene: Degradation behaviors, kinetics, and product characteristics

Pyrolysis is a promising technology for converting plastic waste into valuable raw materials while offering a potential solution to the global plastic pollution crisis. In this study, the thermal pyrolysis of high-density polyethylene (HDPE) is investigated in a drop tube reactor under nearly isothermal conditions. The impact of reaction temperature and gas/volatile residence time on carbon conversion and product distribution is examined across a range of 500–900 °C and 3.6–32.2 s, respectively. Non-condensable gas products detected by online mass spectrometry are H2, CH4, C2H4, C2H6, C3H6, and C3H8. At elevated temperatures and prolonged residence time, H2 yield reaches as high as 8.6 wt% of the initial HDPE mass due to intensified cracking reactions of C2–C3 hydrocarbons and long-chain aliphatic compounds. Consequently, pyrolysis tars consist mainly of polycyclic aromatic hydrocarbons (PAHs) with 5–7 rings, accompanied by visible coke deposition within the reactor. HDPE decomposition to volatiles is an endothermic process and it is complete at a temperature between 492 °C and 525 °C, depending on the heating rate employed, from non-isothermal thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) measurements. The thermal degradation of HDPE pellets follows the two-dimensional nucleation growth model for conversion levels up to 0.8 with an apparent activation energy of 259–270 kJ/mol and a pre-exponential factor of 4.83 × 1017–1.37 × 1019 min−1, determined from various isoconversional methods such as Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Starink, along with Criado's master plots. These findings provide valuable insights into optimizing process parameters and refining reactor design for pyrolysis, which can be integrated with gasification and reforming processes to enhance hydrogen production on a larger scale.

Deciphering the seasonal dynamics of microplastic morphotypes and associated co-contaminants along the northwest coast of India

In the present study, the northwest coast of India, bordering the Arabian Sea, was selected to evaluate the microplastic (MP) abundance. This is the first study to emphasize the effects of different seasons on MP distribution. The collected MPs were dried, segregated, and evaluated based on their morphotype, size, color, and polymer type. A total of 1756.6, 7326.6, and 202 particles/kg of sand were estimated in the pre-monsoon, monsoon and post-monsoon seasons, respectively, with a dominance of polypropylene (PP) type of plastic in the pre-monsoon and high-density polyethylene (HDPE) in monsoon and post-monsoon seasons. HDPE and PP collected MPs during the monsoon season were further characterized for associated contaminants. Metal absorbance was detected using SEM-EDX mapping and ICP-MS. The presence of organic compounds (OCs) was analyzed using GC-MS. MPs exhibit distinct associations with metals, among which the HDPE pellet morphotype exhibits a higher range of metal adsorption. Total 61 different OCs were associated with MPs. The HDPE pellets contained the highest amounts of hydrophobic organic compounds. PP pellets were found to contain triglycerides, fatty aldehydes, and alkaloids, along with HOCs. Among morphotypes, pellet forms of MPs were found to adsorb more contaminants. These co-contaminants infiltrate the study area through sewage runoff and shoreline debris deposition, subsequently interacting with MPs. Furthermore, the MP diversity was studied by employing the MP diversity integrated index, which suggests that most of the MP diversity was observed in the pre-monsoon period. The pollution load index employed an MP risk assessment, which presented a low degree of MP contamination. In contrast, the polymer hazard index was calculated as 21650.3 in post-monsoon, placing the area under the extreme danger category. It is evident from the data that the types of MP is more important than their number. Thus, MP morphotypes have importance in the adsorption of co-contaminants.

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.

Laboratory investigation on the moisture susceptibility and fatigue resistance of hot mix asphalt modified with high- and low-density polyethylene plastic wastes

The demand for better management of plastic wastes all over the world is increasing. Polymers such as high-density polyethylene (HDPE) and low-density polyethylene (LDPE) are examples of these wastes. Studies showed that these could be used as polymer modifiers that could improve asphalt pavement performance. Although several studies had been conducted to evaluate the performance of asphalt mixtures with HDPE and LDPE, conflicting results had been seen. Additional research is still needed to find out the true effect of plastic on the performance of asphalt mixtures. Hence, this study assessed the performance of hot mix asphalt (HMA) modified with HDPE and LDPE pellets. The Marshall mix design was used to prepare, evaluate HMA mixtures and determine the optimum percentage of HDPE and LDPE that can be added to HMA. Moreover, wheel-tracking, and immersion-compression tests were used to evaluate rutting resistance and compressive strength of HMA mixtures, respectively. Results showed that the addition of 8% HDPE and 8% LDPE by weight of bitumen are the optimum contents. The performance of the HMA mixtures with HDPE and LDPE in terms of fatigue resistance and moisture susceptibility shows improved results. This proves the potential use of the materials as polymer modifiers in HMA. Moreover, HMA with HDPE when compared to the HMA with LDPE shows better results in reducing the moisture susceptibility and improving the fatigue resistance of HMA.

Effects of Blending Tobacco Lignin with HDPE on Thermal and Mechanical Properties.

Depletion of fossil fuels and the detrimental environmental impacts of synthetic plastics have prompted a global interest in bio-based polymers. Lignin is an abundant, unused, and low-value byproduct of pulping and biochemical operations that has the potential to decrease the need for plastics derived from petroleum. Melt blending is one of the easiest strategies for expanding the commercial applications of lignin. Concerns remain, however, regarding the negative effects of lignin on the final composite material’s performance, and the increase in manufacturing costs. This study investigates the effects of blending lignin extracted from tobacco using a novel one-step processing technique on injection molding parameters, and the mechanical, physical, and thermal properties of high-density polyethylene (HDPE). By extruding HDPE pellets and lignin powder, varying blend concentrations (0, 5, 10, 15, and 30% wt.) were produced. Scanning electron microscopy (SEM) and optical microscopy were used to investigate the compatibility of the blend morphology. Results indicated that interfacial interactions were achieved as particles of tobacco lignin were well dispersed and uniformly distributed throughout HDPE. Intermolecular interactions between HDPE and lignin were also discovered through Fourier-transform infrared (FTIR) spectral analyses. The tensile test results showed that increase in lignin content up to 15% wt. had little effect on tensile strength, but at 30% wt., a 19% reduction was observed. With the addition of 5, 10, 15, and 30% wt. of lignin, the tensile modulus increased by 4%, 29%, 25%, and 8%, respectively. TGA results demonstrated that at 15% and 30% wt., tobacco lignin acted as a thermal stabilizer. The processability study revealed that tobacco lignin could be processed easily using injection molding without requiring significant changes to the process parameters. Overall, tobacco lignin showed great promise as a biodegradable HDPE filler.

Studying the combined influence of microplastics’ intrinsic and extrinsic characteristics on their weathering behavior and heavy metal transport in storm runoff

The weathering and contaminant transport behavior of both primary (PMPs) and secondary microplastics (SMPs) are interrelated to their original physiochemical features and variations within the environment. This study examines the influence of PMPs' intrinsic characteristics (polymer structure and crystallinity) and SMPs' extrinsic features (surface oxidation and external sediments attachment) on the photodegradation kinetics, and subsequently Pb(II) and Zn(II) uptake from stormwater. For this purpose, high density polyethylene (HDPE) and low density polyethylene (LDPE) with different degrees of crystallinities were produced as PMPs, and their photodegradation behaviors were compared with original polymers. Furthermore, the SMPs generated by abrasion and surface oxidation of PMPs and the virgin PMPs underwent accelerated photodegradation, and the changes of their crystallinity, surface chemistry, and morphology were examined. Scanning electron microscopy (SEM) imaging and X-ray photoelectron (XPS) studies revealed the formation of cracks and different oxidized functionalities on MPs surface due to UV photodegradation. The vinyl and carbonyl indices calculated using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy demonstrated an elevated photodegradation rate for SMPs compared to the PMPs. Moreover, the Differential Scanning Colorimetry (DSC) demonstrated an increasing percentage of crystallinity in all MPs due to the photodegradation. The percent crystallinity of HDPE pellets increased after photodegradation from 49.8 to 62.6 and it increased from 17.2 to 38.9 for LDPE pellets respectively. The greater level of increase in crystallinity for LDPE in comparison to HDPE upon photodegradation was referred to as LDPE's greater amorphous content and branched structure. A greater level of metal uptake was obtained for photodegraded LDPE pellets as 2526 μg/m2 for Pb(II) and 2028 μg/m2 for Zn(II) respectively.

Recycle Ability of Post-Consumer Recycled Plastic (PCR) from the Chlorine Tank

Plastic waste that used in our daily life is a major problem of environmental contaminate because it produces microplastics after degradation resulting in the harmful of living organisms, including humans. Therefore, this research has an idea to solve this problem by recycling the plastic waste. High density polyethylene (HDPE) plastic waste from the chlorine tank in fishing industry is considered. This work was designed to blend it with virgin HDPE plastic pellets. The ratio of blended plastics between virgin HDPE pellets and HDPE plastic waste from the chlorine tank which was defined as post-consumer recycled plastic (PCR) was 100:0, 50:50, 40:60, 30:70, 20:80 and 0:100 wt%, respectively. The result shows unchanged thermal properties of plastic blends caused by the same type of polymer, thus the PCR without blending with the virgin HDPE plastic is selected for recycle ability studies. The PCR was rerun in the twin screw extruder in the range of 0 - 80 extruded recycle time to observe the thermal, rheological, mechanical, and physical properties. It was found from our result that 20 recycling time of PCR was appropriate for maximum recycling process due to slightly change rheological characteristics, mechanical properties as well as product’s color.
 HIGHLIGHTS
 
 Thermal properties of post-consumer recycled plastic (PCR) after recycling and its blending with virgin HDPE
 Rheological change of post-consumer recycled plastic (PCR) after recycling
 Mechanical and physical properties of post-consumer recycled plastic (PCR) after recycling to meet a customer need
 
 GRAPHICAL ABSTRACT

Decontamination efficiencies of post-consumer high-density polyethylene milk bottles and prioritization of high concern volatile migrants

High-density polyethylene (HDPE) milk bottles are well-distinguished from other plastics in the mix-collected plastic waste and have potential to be closed-loop recycled. To evaluate this option, volatile substances present in various recycled HDPE (rHDPE) pellets and flakes from postconsumer milk bottles were analysed for similarities between different industrial recycling companies and batches. All substances found were classified in five different levels based on toxicity, from level I to level V (high toxicity). Chemicals present in the samples from different recyclers varied considerably, while those from different batches of a given recycler gave similar results. However, the study of rHDPE stream mixed with high volume of non-milk-bottles provided significant differences between batches. Washing the rHDPE twice and applying extra decontamination techniques reduced to a half the intensities for most chemicals detected, including two toxicity level V substances, butylated hydroxytoluene and diethyl phthalate. Nevertheless, other two high concern compounds, octocrylene, and 2-ethylhexyl-4-methoxycinnamate were not significantly reduced and thus deserve special attention when decontaminating rHDPE and evaluating its feasibility for food contact uses. Extra decontamination was able to reduce the intensities of 1-dodecene and 1-tetradecene. In total, 265 substances were detected in migration tests (95% ethanol and 3% acetic acid) and 58 of them were prioritized by toxicity. Regarding volatile migrants, rHDPE with low content of non-milk-bottle could be safe for direct contact with low-fat content food. For high-fat foods, the main concerns could come from 1-tetradecene, octocrylene, and 2-ethylhexyl-4-methoxycinnamate.

An automatic flow-through system for exploration of the human bioaccessibility of endocrine disrupting compounds from microplastics.

This article reports on the first attempt towards investigating the leaching rates in the human gastrointestinal (GI) tract of plastic-borne contaminants that can be ingested accidentally using physiologically relevant body fluids. Oral bioaccessibility under fasted and fed states was determined in dynamic mode exploiting an automatic flow setup. The flow system is able to mimic the fast uptake of the released species from the polymeric matrix by absorption in the human digestive system by the in-line removal of the leached species. Complex GI extractants based on the Unified Bioaccessibility Method (UBM, fasted state) and Versantvoort test (fed-state) were brought through a microplastic-loaded metal microcolumn for semi-continuous leaching of plasticizers (phthalic acid ester congeners) and monomer/antioxidant species (bisphenol A, BPA) followed by in-line solid-phase extraction and clean-up of GI extracts prior to liquid chromatography analysis. The temporal extraction profiles were fitted to a first-order kinetic model for the estimation of maximum bioaccessibility pools and apparent leaching rates. Among all studied contaminants, only BPA, dimethylphthalate and diethylphthalate were appreciably released under dynamic GI conditions from high-density polyethylene pellets (average size of 110 μm), with average bioaccessibility values spanning from 51 to 84% and 48 to 87% for UBM and Versantvoort methods, respectively. No statistically significant differences in oral bioaccessibility pools were found under fed- and fasted-state dynamic extractions. The apparent kinetic constants under the fed state were greater by ≥30% as a consequence of the effect of the larger amounts of bile salts and digestive enzymes in the Versantvoort test on the leaching rates. The estimated average daily intake, in which bioaccessibility data are contemplated, indicated that plastic materials exceeding 0.3% (w/w) BPA might pose real risks to human health.

Investigation of Compositional Effects of Virgin and Recycled HDPE on Mechanical Properties of Pipe

Nowadays, High-Density Polyethylene (HDPE) polymers are widely being used and its products are preferable than metals having the properties such as lightweight, ease of manufacture, stronger and tough. This makes HDPE polymers as the top choice by manufacturers. However, one of the drawbacks is that this polymer takes time to decay and affects the environment when this material is disposed as wastes. Almost all industries use only virgin imported materials to produce HDPE pipe and fittings, and this leads to increase in manufacturing cost and extraction of virgin material. The aim of this research is to overcome this problem by recycling process. This research work focuses on investigating the compositional effects of virgin and recycled HDPE on the mechanical properties of HDPE pipe fitting. The mixing of recycled with virgin (pure) HDPE were done at different weight percentages (0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, and 100:0). In this work, 16.5 kg virgin HDPE were used, and 16.5 kg recycled HDPE pellets were prepared. Also, 11 (eleven) T-reducer pipe fitting samples were produced via injection moulding machine. Melt flow rate and ash content of the manufactured recycled materials were tested to determine the quality of the plastics. Tensile strength test was also conducted to investigate the mechanical property in order to determine the percentage which possess the optimum strength. From the experimental results, recycled contents up to 70 wt. % and virgin contents up to 30 wt. % by mass were found to meet the standard requirements. This optimum proportion will help AG Pipe fitting company to save a lot in dollars every year by using the scrap contents.

Influence of processing methods on the mechanical and barrier properties of HDPE-GNP nanocomposites

In order to improve the barrier properties of Graphene nanoPlatelets (GnP)–High-Density PolyEthylene (HDPE) composites made by melt mixing, extra processing steps were investigated (solution mixing prior to melt mixing, cryomilling of the HDPE pellets into a fine powder, coating of the GnP with low molecular weight wax or with a thermoplastic elastomer, and microlayer co-extrusion). The associated mechanical properties were characterized by a flexural test and a notched Izod impact test. The barrier properties were evaluated by the permeation to oxygen. Each method resulted in a different state of dispersion and alignment of the graphene nanoplatelets, leading to a specific evolution of the barrier and mechanical properties. Microlayer co-extrusion led to a better relative improvement of the barrier properties versus neat HDPE. Solution mixing did result in an improvement of the barrier properties only if the composite was not further processed by melt mixing and extrusion. Starting with a fine HDPE powder did improve the barrier properties but affected the flexural properties. Lastly, a coating of the GnP with a thermoplastic elastomer enhanced the resistance to impact and barrier properties, but a coating with wax did not show any improvement.

POTENCY TO RECYCLE HYDRAPULPER REJECT WASTE OF PAPER MILL INTO COMPOSITE PARTICLEBOARD

Solid waste of paper mill hydrapulper reject (HR) has a relatively high plastic content, with around 45-49% composition of the total HR. About 99% of the plastic has the catagory of High Density Polyethylene (HDPE). HDPE is a type of Polyethylene (PE) plastic which has high recyclability and may be reformed at high temperature. This study tries to discribe the potential of producing particleboards derived from HR using a hot-press method. Molded HR was being hot-pressed at a presssure of 25 kgf/cm2for 5 – 15 minutes of residence time, with a variation of of the amount of HR from 150-500 gram, and variations in hot-press temperature of 150-180°C. The resulting product is then analyzed for parameters of moisture content, density, water absorption, thickness swelling, and internal bond compared to SNI 03-2105-2006 and JIS A 5908-2003. The results showed that most of the samples were relatively accepted to the SNI. The best results are obtained at HR weight of 250 gram with 165 and 180°C pressing temperature, and pressing time more than 10 minutes. The addition of HDPE pellets shows an increment of density and decrement of moisture content of particleboard, while the addition of MA shows some decrements of moisture content and water absoption of particleboard.

Synthesis and Mechanical Characterization of High Density Polyethylene/Graphene Nanocomposites

The purpose of this work is to investigate the effects of graphene nanosheets (GNSs) addition on the mechanical and thermal properties of high density polyethylene (HDPE). The HDPE/Graphene nanocomposites were synthesized using solution blending approach. HDPE was incorporated with graphene nanosheets in a solvent at various weights of fractions (0.1, 0.2, 0.4 and 0.5 wt%), and then the micro-hardness, elastic modulus, tensile strength, strain at break and thermal properties of the nanocomposites were measured and compared. The results showed that the use of Xylene solvent at high temperature combined with mechanical stirring can fully dissolve HDPE pellets. Scanning electron microscope (SEM) showed that GNSs were homogenously dispersed in the polyethylene matrix at low weights of fractions. The addition of just 0.2 wt% GNSs resulted in 100% increase in the micro-hardness value. The elastic modulus and tensile strength properties are proportionally increased with increasing GNSs content up to 0.4 wt%. However, at higher weight of fraction, a reduction in these properties is observed. The crystallinity and strain at break properties are reduced with the addition of GNSs.

Comparison of the odorant composition of post-consumer high-density polyethylene waste with corresponding recycled and virgin pellets by combined instrumental and sensory analysis

Abstract Both, for ecological and economic reasons, the recycling of plastics for new or broader applications is currently gaining more and more attention. As high-density polyethylene (HDPE) plays an essential role in various packaging, the recycling of this material is particularly sought for. Thereby, odorous contaminants are a common obstacle when aiming at achieving high-quality HDPE recycled goods. In this respect, revealing the differences in the odorant composition of waste, recycled pellets and virgin pellets provides insights into odor sources and formation pathways and therefore supports the developing of optimized avoidance strategies. For this reason, the odor of post-consumer HDPE waste, corresponding recycled HDPE pellets and virgin HDPE granules was analyzed in the frame of the present study by comprehensive sensory analysis as well as instrumental analysis using high resolution gas chromatography-olfactometry followed by two-dimensional high resolution gas chromatography-mass spectrometry-olfactometry. In total, 32 odorous substances were identified. While some oxidation products were present in all three samples, albeit mostly with much higher smell intensity when regarding the waste and the recycled pellets, a number of terpenes as well as phenylpropanoids were found only in the HDPE waste and recycled material and, in most cases, with high sensory abundance. These odorants are likely to stem from fragrances used in cosmetics and washing/cleaning agents. Moreover, comparative odor extract dilution analysis (cOEDA) revealed that the applied conventional recycling process resulted only in a slight reduction of the odor pollution; moreover, it could be shown that no new odorants were generated to any relevant extent. Accordingly, this study shows that further optimized strategies for odorant removal from post-consumer recycled HDPE material are required.

Structural changes in HDPE produced by in-line plasma-pretreated reactive extrusion

Structure of high density poly ethylene (HDPE) was changed after Plasma-induced graft polymerization of methyl methacrylate (MMA) monomer onto HDPE. Continuous polymerization of monomer wetted HDPE pellets was carried out sequentially via in-line plasma pretreatment followed by reactive extrusion. It was influenced by plasma pretreatment times between 15 s and 120 s on degree of grafting and molecular structure of the extrudate. Maximum degree of grafting was limited to 6% after 30 s plasma pretreatment. The addition of dicumyl peroxide (DCP) increased the degree of grafting to 10% after 15 s of plasma treatment. Gel formation to levels in the range 3–5% was detected, increasing with plasma pretreatment time. The formation of long chain branched (LCB) architecture, of the extruded PMMA-g-HDPE, was confirmed by rheological test in oscillatory shear, which results in increases in low frequency storage and loss moduli and melt viscosity than that of neat HDPE, especially after DCP addition. Finally, formation of a fully crosslinked structure was observed after annealing at 210 °C for 1 h as evidenced by a change in rheological properties at lowest frequencies to solid-like behaviour. Such extensive crosslinking could be useful in producing high strength adhesive joints between HDPE and other materials.

Improvement of form accuracy and surface integrity of Si-HDPE hybrid micro-lens arrays in press molding

Press molding of silicon (Si)/high-density polyethylene (HDPE) composite is an important technology for producing thin hybrid infrared (IR) optics with microstructures. In this research, Si-HDPE hybrid micro-lens arrays were press molded under various conditions, and the form accuracy and surface integrity of the molded lenses were evaluated. Air trapping occurs inside the micro-lens cavities during molding in a non-vacuum environment, which leads to severe surface defects. To investigate the air trapping phenomenon, a new in-situ observation system was developed which enables real-time direct observation of the molding process. From the in-situ observations, it was found that air traps were formed among the HDPE pellets during melting, and an increase in the pressing force will increase the pressure of the trapped air, forming trenches on the lens surface. The trapped air also impacts the mold coating, causing trench formation on the coating surface. To minimize air trapping, the molding temperature, and pressing force must be strictly controlled. By performing press molding in a vacuum environment, trench formation was completely eliminated. Moreover, polymer shrinkage compensation was performed to improve the lens form accuracy.

Physical Characterization and Pre-assessment of Recycled High-Density Polyethylene as 3D Printing Material

3D printing has received lots of attention due to its limitless potential and advantages in comparison to traditional manufacturing processes. This study focuses on the most popular type of home 3D printers, namely fused filament fabrication (FFF) printers, which use plastic filaments as the feedstock. The rather high material cost and large amount of plastic waste generated by FFF 3D printers have driven the need for plastic filaments produced from recycled plastic waste. This study evaluates, in terms of physical characterization, the feasibility of using recycled high-density polyethylene (HDPE), one of the most commonly used plastics, as the feedstock for 3D printers, in comparison with the common acrylonitrile butadiene styrene plastic pellets. In-house extrusion using recycled HDPE pellets and flakes is possible. The diameter consistency and extrusion rate results, along with other physical characterization results, including differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and water absorption, suggest that making filaments from recycled HDPE pellets is a viable option, as the obtained filament has favorable water rejection and comparable extrusion rate and thermal stability. Existing methods for overcoming the warping and adhesion problems in 3D printing with HDPE were also reviewed. In order to increase the market competitiveness of waste-derived filaments, optimization of the extrusion process, studies on the mechanical and aging properties, and development of a standard characterization methodology and database are crucial.

Radiation-Induced Grafting with One-Step Process of Waste Polyurethane onto High-Density Polyethylene.

The recycling of waste polyurethane (PU) using radiation-induced grafting was investigated. The grafting of waste PU onto a high-density polyethylene (HDPE) matrix was carried out using a radiation technique with maleic anhydride (MAH). HDPE pellets and PU powders were immersed in a MAH-acetone solution. Finally, the prepared mixtures were irradiated with an electron beam accelerator. The grafted composites were characterized by Fourier transformed infrared spectroscopy (FT-IR), surface morphology, and mechanical properties. To make a good composite, the improvement in compatibility between HDPE and PU is an important factor. Radiation-induced grafting increased interfacial adhesion between the PU domain and the HDPE matrix. When the absorbed dose was 75 kGy, the surface morphology of the irradiated PU/HDPE composite was nearly a smooth and single phase, and the elongation at break increased by approximately three times compared with that of non-irradiated PU/HDPE composite.

Emulsification of Water and Pyrolysis Oil

Emulsification of pyrolysis oil produced from recycled high-density polyethylene (HDPE) was experimentally investigated. Pyrolysis oil was made from recycled HDPE pellets using a pyrolyzer operated under cascade heating steps and heating rates. Water-in-oil emulsion was produced with ultrasonic mixer and homogenizer using Span80 surfactant as emulsifier. The emulsion stability was assessed by water droplet size and visual observation. Rheological properties were measured to confirm the microstructure change. The emulsion viscosity follows the Einstein equation for a dilute emulsion with water content less than 10%. The ultrasonic mixer was confirmed to be more effective than mechanical homogenizer both in term of smaller water droplet size and lower viscosity. Water-in-oil emulsion was more viscous than its constituting components. A proper droplet size minimization can mitigate the viscous emulsion issue.