Recycling Of High-density Polyethylene Research Articles

Chemically Recyclable Linear and Branched Polyethylenes Synthesized from Stoichiometrically Self-Balanced Telechelic Polyethylenes.

High-density polyethylene (HDPE) is a widely used commercial plastic due to its excellent mechanical properties, chemical resistance, and water vapor barrier properties. However, less than 10% of HDPE is mechanically recycled, and the chemical recycling of HDPE is challenging due to the inherent strength of the carbon-carbon backbone bonds. Here, we report chemically recyclable linear and branched HDPE with sparse backbone ester groups synthesized from the transesterification of telechelic polyethylene macromonomers. Stoichiometrically self-balanced telechelic polyethylenes underwent transesterification polymerization to produce the PE-ester samples with high number-average molar masses of up to 111 kg/mol. Moreover, the transesterification polymerization of the telechelic polyethylenes and the multifunctional diethyl 5-(hydroxymethyl)isophthalate generated branched PE-esters. Thermal and mechanical properties of the PE-esters were comparable to those of commercial HDPE and tunable through control of the ester content in the backbone. In addition, branched PE-esters showed higher levels of melt strain hardening compared with linear versions. The PE-ester was depolymerized into telechelic macromonomers through straightforward methanolysis, and the resulting macromonomers could be effectively repolymerized to generate a high molar mass recycled PE-ester sample. This is a new and promising method for synthesizing and recycling high-molar-mass linear and branched PE-esters, which are competitive with HDPE and have easily tailorable properties.

Preparation and Characterization of High-Density Polyethylene (HDPE) Waste filled with Rice husk Silica (RHS) Composites in Gwagwalada metropolis, Abuja, Federal Capital Territory, Nigeria

The adverse effects of use of plastics by human beings are on the increase and become challenging with the growing population. The non-degradability of plastics products such as bottles, cans, cups, bags which resulted into blockage of culverts, drains, suffocating animal’s life. This research focused on recycling of high density polyethylene (HDPE) plastic waste with rice husk silica (RHS) from agricultural waste of rice husks to form eco-friendly polymer composites. Different proportions of 0.5 to 3.0 % rice husk silica (RHS) as filler were melt mixed with maleic anhydride grafted high density polyethylene (HDPE) material and the composite analyzed for tensile and flexural strengths. The tensile strengths ranged values from 10.49 to 13.02 MPa for the resin (vHDPE) and the recycled (rHDPE) composites presented values from 8.30 and 12.41 MPa for 0.5and 3.0% filler loading, respectively. The peak flexural strengths recorded for recycled (rHDPE) and resins (vHDPE) composites are 12.19 MPa and 12.05 MPa for 0.5 and 3.0% filler loading, respectively. The tensile strength of rice husk silica (RHS) filled HDPE waste composites are higher than that of the waste HDPE (control) and thus, the filler reinforced the HDPE. The composite prepared is suitable for use as tiles in building application to solve leaching problems associated with paint coating.

Synthesis and characterization of recycled HDPE polymer composite reinforced with nano-alumina particles

Recycling of High-density Polyethylene (HDPE) plastic is a viable and economical method to progress in the path of a sustainable and eco-friendly initiative towards the eco-sustainable environment. This work is a pilot study to synthesize a polymer nanocomposite material from recycled HDPE reinforced with aluminium oxide nanoparticles to assess its potential applications as a packaging material. The microstructure of the newly synthesized material is characterized using scanning electron microscopy (SEM) analysis, and energy dispersive X-ray spectroscopy (EDS) analysis. X-ray diffraction (XRD) analysis was done to determine the crystallographic structure, while the thermal behaviour was analyzed through Thermogravimetric analysis (TGA) and differential Scanning Calorimetry (DSC) test. Recycled HDPE is already being used in a variety of applications, however, reinforcing with nano alumina particles will alter the properties of HDPE composite which opens up a new arena of possibilities in the field of electronic packaging.

Enhanced flotation of high density polyethylene and polyvinyl chloride mixtures based on clean corona modification

The dramatic increase in waste plastics has caused harm to both human health and the environment. Due to the variety of plastic products and their complex components, it is a technical challenge to effectively separate them. High density polyethylene (HDPE) and polyvinyl chloride (PVC) both have a high detection frequency in the common solid waste streams like automobile shredder residue (ASR), and due to the similar properties of different plastics, their mixtures lack reliable separation methods. Specifically for this kind of mixtures, this work provided a novel separation strategy with prepositive corona modification and postpositive flotation units. To obtain the optimal separation parameters, flotation performance of HDPE and PVC were investigated under different modification conditions controlled by the corona polarity, discharge power and exposure time. Besides, the modification mechanism was revealed through multi-characterization tests on surface morphology, molecular weight, contact angle, and spectrums. The results showed that corona discharge can generate non-thermal plasma to activate the surfaces of HDPE and PVC, thereby increasing their floatability difference. Under the optimal conditions of 300 W positive discharge power and 8000 ms exposure time, HDPE turned into the sinking tail while PVC still accumulated in the floating product, leading to the maximum separation recovery and purity of 96.36% and 97.01%, respectively. Amorphous low-molecular weight oxidic substances emerged on the upper layer of polymers was verified by the multi-characterization, representing in varying degrees of oxidation and chain scission (HDPE > PVC). Since the corona modification is reagent-free-addition and rapid in-line process, this work showed great advantages in the total cost of separation (only 450.03 USD/t) and potential environmental benefits, which also paves a clean way for the recycling of HDPE and PVC.

A Parametric Study on the HDPE/PP and Marble Slurry Waste Utilisation Using Single Screw Extruder

Due to the increased socio-economic development, the manufacturing of different products based on various polymers for different applications such as space crafts, airplanes, automobiles, boats, and sports equipment are increasing continuously. This huge increase in solid polymer commodities is also creating the extravagant quantity of solid waste polymers (SWPs) due to their non-degradable characteristics. These SWPs, for example, high-density polyethylene (HDPE), polypropylene (PP), low-density polyethylene (LDPE), and nylon, etc., are used frequently in various applications and create new challenges to the industries, government, as well as end-users for systematic waste recycling/recovery in an eco-friendly manner. Moreover, in this modernisation era, almost all marble industries are also facing a huge problem as marble slurry (MS) yields a great burden not only due to its limited degradability characteristics but also wider environmental hazard towards water bodies, and rivers. Fine particles in the range size of 45-300 micron in the MS create air pollution which in turn increases breathing problems. Moreover, it also creates an ecological adverse impact on soil fertility and reduces the percolation rate of rain water which in turn reduces the recharging of groundwater. Therefore, keeping in view the above facts, the simultaneous recycling of HDPE, PP and marble slurry is adopted through single screw extrusion in order to reduce the burden on the environment. Moreover, the effect of various process parameters viz barrel temperature, screw speed (rpm), feed composition, and grain size of PP and HDPE on extrudate output was envisaged. It was found that the extrudate output increases steeply on increasing the average barrel temperature from 100 to 120°C and linearly with screw speed range from 65 to 85 rpm. The effect of grain size had shown decreasing trend in throughput whereas on increasing the polymer content in the feed, throughput was found to be enhanced. Additives such as HPMC were found to be effective when used in synergy with HDPE and PP along with MS. The extrudate throughput was found to be a maximum of 33.01 g/minute at 120°C, 85 screw rpm, 1.40-grain size underfeed with equal proportionate of HDPE/PP with 2% HPMC and 8% MS. This clearly opens the ways for proper utilization of HDPE, PP and MS waste by extrusion and provides the environmental protection solution by utilizing these polluted materials in the fabrication of value-added products through extrusion.

Sustainable Additive Manufacturing: Mechanical Response of High-Density Polyethylene over Multiple Recycling Processes

Polymer recycling is nowadays in high-demand due to an increase in polymers demand and production. Recycling of such materials is mostly a thermomechanical process that modifies their overall mechanical behavior. The present research work focuses on the recyclability of high-density polyethylene (HDPE), one of the most recycled materials globally, for use in additive manufacturing (AM). A thorough investigation was carried out to determine the effect of the continuous recycling on mechanical, structural, and thermal responses of HDPE polymer via a process that isolates the thermomechanical treatment from other parameters such as aging, contamination, etc. Fused filament fabrication (FFF) specimens were produced from virgin and recycled materials and were experimentally tested and evaluated in tension, flexion, impact, and micro-hardness. A thorough thermal and morphological analysis was also performed. The overall results of this study show that the mechanical properties of the recycled HDPE polymer were generally improved over the recycling repetitions for a certain number of recycling steps, making the HDPE recycling a viable option for circular use. Repetitions two to five had the optimum overall mechanical behavior, indicating a significant positive impact of the HDPE polymer recycling aside from the environmental one.

Design and analysis of cell phone case from recycling plastic bottle

Recognizing the large amount of plastic waste produced by humans today, recycling is one solution to reduce the accumulation of plastic waste. This study aims to analyze the recycling of HDPE (High Density Polyethylene) plastic waste into cell phone cases. This study compares the strength of recycled plastic cell case with other materials that are often used for cell phone cases in general. The methodology of this paper begins with the development of new 2D and 3D cellphone cases, and for processing with injection molding. The parameters are focused on the strength of the material. The simulation is presented using Autodesk Inventor with free fall analysis, and presented stress, displacement, main stress and strain. The results show that the results of stress analysis and material comparison between HDPE and other materials do not show significant differences in other words HDPE can be used as an alternative material for cell phone case materials.

Life-Cycle Assessment of Recycling Postconsumer High-Density Polyethylene and Polyethylene Terephthalate

This study aims to quantify the overall environmental performances of mechanical recycling of the postconsumer high-density polyethylene (HDPE) and polyethylene terephthalate (PET) in Jordan. The life-cycle assessment (LCA) methodology is used to assess the potential environmental impacts of recycling postconsumer PET and HDPE. It quantifies the total energy requirements, energy sources, atmospheric pollutants, waterborne pollutants, and solid waste resulting from the production of recycled PET and HDPE resin from the postconsumer plastic. System expansion and cut-off recycling allocation methods are applied. The analysis has been carried out according to the LCA standard, series UNI EN ISO 14040-14044:2006. A standard unit of output (functional unit) is defined as “one ton of PET flake” and “one ton of HDPE pellet.” The results of the production of virgin resin are compared with the “cut-off” and “system expansion” recycling results. Depending on the allocation methods applied, a nonrenewable energy saving of 40–85% and greenhouse gas emission saving of 25–75% can be achieved. Based on two allocation methods, PET and HDPE recycling offers important environmental benefits over single-use virgin PET and HDPE. LCA offers a powerful tool for assisting companies and policy-makers in the waste plastic industry. Furthermore, the “system expansion” recycling method is not easy to apply because it requires detailed data outside of the life cycle of the investigated product.

Recycling of Virgin and Post-Consumer Polypropylene and High Density Polyethylene

Abstract Recycling of plastics is becoming more important nowadays due to the increasing amount of waste that is generated worldwide. Post-consumer plastics have a large volume and their harmful effects must be considered. From this perspective, the option of recycling post-consumer plastics has become more and more necessary. The main objective of this research is the selective separation of polypropylene (PP) and high density polyethylene (HDPE). On this basis, various flotation parameters were tested on virgin plastics and optimized conditions were applied to post-consumer plastics. PP particles with a purity of 96.30% were obtained with a recovery rate of 97.4% in virgin polymer separation, while HDPE particles were obtained as the sunken product with 97.38% purity and a recovery rate of 96.3%. Besides, almost all PP and HDPE particles were selectively separated with the highest recovery rates when using 500 g/t calcium lignosulfonate (CLs) as a plasticizer in post-consumer polymer separation. Moreover, water reuse was investigated to determine the recovery and economy of plasticizer without adding extra water during the experiment. Therefore, it can be concluded that this process is environmentally friendly in terms of PP and HDPE recycling and reuse of process water.

Processability and mechanical properties of extensively recycled high density polyethylene

In plastics industry it is a common practice to mechanically recycle waste material arising from production. However, while plastics are mechanically recycled, their mechanical properties change. These changes may affect material processing conditions and quality of the end products; therefore they need to be quantified. In this study, mechanical recycling of high density polyethylene (HDPE) was simulated by one-hundred (100) consecutive extrusions cycles. During extrusion, processability of virgin HDPE and its recyclates was studied by recording the processing conditions, i.e. melt pressure and extrusion torque, while after preparation of the recyclates, melt flow index measurements (MFI), small amplitude oscillatory shear tests (rheological properties), and differential scanning calorimetry measurements (DSC) of thermal properties were performed. Also, mechanical properties in solid state were characterized in terms of hardness and modulus measured by nanoindentation, and finally, shear creep compliance was measured to characterize the materials' time-dependent mechanical properties and its durability in solid state. In addition, gel permeation chromatography (GPC) and solubility tests were implemented to study changes in the material structure.The results on rheological and MFI measurements indicate significant structural changes in the material that occurred during the first 30 extrusion cycles. Those changes affect material processability which is as well supported by the recorded processing pressure and torque. On the other hand, processing did not significantly affect material thermal properties. Results on hardness and modulus show deterioration of the material mechanical properties after 10th reprocessing cycle. Similarly, shear creep compliance measurements showed an unfavourable effect of mechanical recycling on the time-dependent mechanical properties, particularly after the 30th extrusion cycle. In addition, results suggested chain branching as a dominating mechanism through first 30 extrusion cycles, domination of chain scission afterwards and also presence of cross-linking after 60th extrusion cycle.

Life cycle analysis of distributed recycling of post-consumer high density polyethylene for 3-D printing filament

The growth of desktop 3-D printers is driving an interest in recycled 3-D printer filament to reduce costs of distributed production. Life cycle analysis studies were performed on the recycling of high density polyethylene into filament suitable for additive layer manufacturing with 3-D printers. The conventional centralized recycling system for high population density and low population density rural locations was compared to the proposed in home, distributed recycling system. This system would involve shredding and then producing filament with an open-source plastic extruder from post-consumer plastics and then printing the extruded filament into usable, value-added parts and products with 3-D printers such as the open-source self replicating rapid prototyper, or RepRap. The embodied energy and carbon dioxide emissions were calculated for high density polyethylene recycling using SimaPro 7.2 and the database EcoInvent v2.0. The results showed that distributed recycling uses less embodied energy than the best-case scenario used for centralized recycling. For centralized recycling in a low-density population case study involving substantial embodied energy use for transportation and collection these savings for distributed recycling were found to extend to over 80%. If the distributed process is applied to the U.S. high density polyethylene currently recycled, more than 100 million MJ of energy could be conserved per annum along with the concomitant significant reductions in greenhouse gas emissions. It is concluded that with the open-source 3-D printing network expanding rapidly the potential for widespread adoption of in-home recycling of post-consumer plastic represents a novel path to a future of distributed manufacturing appropriate for both the developed and developing world with lower environmental impacts than the current system.

Life Cycle Analysis of Distributed Recycling of Post-consumer High Density Polyethylene for 3-D Printing Filament

The growth of desktop 3-D printers is driving an interest in recycled 3-D printer filament to reduce costs of distributed production. Life cycle analysis studies were performed on the recycling of high density polyethylene into filament suitable for additive layer manufacturing with 3-D printers. The conventional centralized recycling system for high population density and low population density rural locations was compared to the proposed in home, distributed recycling system. This system would involve shredding and then producing filament with an open-source plastic extruder from postconsumer plastics and then printing the extruded filament into usable, value-added parts and products with 3-D printers such as the open source self replicating rapid prototyper, or RepRap. The embodied energy and carbon dioxide emissions were calculated for high density polyethylene recycling using SimaPro 7.2 and the database EcoInvent v2.0. The results showed that distributed recycling uses less embodied energy than the best-case scenario used for centralized recycling. For centralized recycling in a low-density population case study involving substantial embodied energy use for transportation and collection these savings for distributed recycling were found to extend to over 80%. If the distributed process is applied to the U.S. high density polyethylene currently recycled, more than 100 million MJ of energy could be conserved per annum along with the concomitant significant reductions in greenhouse gas emissions. It is concluded that with the open-source 3-D printing network expanding rapidly the potential for widespread adoption of in-home recycling of post-consumer plastic represents a novel path to a future of distributed manufacturing appropriate for both the developed and developing world with lower environmental impacts than the current system.

Biopolymers in the Existing Postconsumer Plastics Recycling Stream

The existing plastic bottle reclaiming industry has working technology, satisfied customers, raw material, and investors. Adding new materials to the current mix requires satisfying all four needs for those materials. Rigid plastic container recycling focuses on high-density polyethylene (HDPE) and polyethylene terephthalate (PET) bottles, the overwhelming percentage of bottles sold in North America. Bottles of other resins, including polyvinyl chloride (PVC), polypropylene and biopolymers, lack critical mass necessary for independent reclamation. To be mechanically recycled, biopolymers must be either completely fungible with existing recycled resins or be available in sufficient quantity to achieve the needed critical mass. So far, biopolymer volume projections are not encouraging. Biopolymers, like all minor bottle resins, must pay their own way in sorting and processing without subsidy from PET and HDPE recycling. Based on limited data, some biopolymers may have little effect on recycled HDPE performance, but will represent a yields loss and added economic burden at some level of occurrence. Biopolymers have not been shown to be compatible with PET and likely will represent performance problems and economic burdens at even low levels of occurrence. Applications for biopolymers should be carefully selected so as to not interfere with currently recycled materials unless critical mass can be achieved quickly.

Recycling of Polymer Waste with Fluid Catalytic Cracking Catalysts

Feedstock recycling of high-density polyethylene (HDPE) over fluid catalytic cracking (FCC) catalysts (1:6 ratio) was carried out using a laboratory fluidized bed reactor operating at 450°C. Fresh and steam deactivated commercial FCC catalysts with different levels of rare earth oxide (REO) were compared as well as used FCC catalysts (E-Cats) with different levels of metal poisoning. Fresh FCC catalysts gave the highest results of HDPE degradation in terms of yield of volatile hydrocarbon product. Meanwhile, steamed FCC catalysts and used FCC catalysts showed similar but lower yields. Overall, the product yields from HDPE cracking showed that the level of metal contamination (nickel and vanadium) did not affect the product stream generated from polymer cracking. This study gives promising results as an alternative technique for the cracking and recycling of polymer waste.

Extraction of CdS pigment from waste polyethylene

AbstractCadmium sulfide has often been used as a pigment in plastics such as high‐density polyethylene (HDPE). Removal of CdS after the useful life of plastics is desired since it poses an environmental hazard in the waste phase of these plastics. In this study, a process is investigated to convert the insoluble CdS in the polymer matrix into CdCl2 by treatment with HCl, followed by extraction of CdCl2 with 1,4‐butanediol (BDO). Since the diffusivity of CdCl2 in HDPE is low, reducing diffusion length and enhancing interfacial area by dispersing BDO by laminar mixing of molten HDPE with BDO facilitate the extraction process. The overall mass transfer process during extraction is modeled as a combination of consecutive steps: diffusion of CdCl2 through HDPE to the BDO dispersed in molten HDPE, followed by transport of the dispersed, CdCl2 containing BDO to the bulk BDO phase surrounding the HDPE. This mechanism achieves reduction of CdCl2 in HDPE from 1128 ppm to less than 100 ppm in 12 min. The somewhat higher melt flow index (MFI) of the HDPE after extraction (8.3 g/10 min) as compared with the MFI of the starting HDPE (6.3 g/10 min) shows some extent of degradation. However, the MFI is acceptable for HDPE recycling. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1024–1031, 2006

Recycling of high density polyethylene containers

The recycling of homogeneous high density polyethylene from containers for liquids gives rise to materials having mechanical properties that are strongly dependent on the reprocessing apparatus and the processing conditions. The thermomechanical degradation during processing gives rise to different modifications of the structure depending on the temperature, residence time and applied stress. In general, it is possible to say that if the reprocessing operations are carried out in apparatus with low residence time, the mechanical and rheological properties of the raw materials are only slightly influenced by the recycling operations. Significant degradation phenomena and reduction of some mechanical properties are observed on increasing the number of recycling steps in apparatus with large residence times. By adding antioxidant agents the polymer maintains the initial properties even after several recycling cycles. The competition between formation of chain branching and chain scission can be considered to be responsible for this behaviour.

The effect of multiple extrusion passes during recycling of high density polyethylene

High density polyethylene blow modling resins have been identified as a primary material for solid waste minimization and recycling. An experimental study into the effect of multiple extrusion cycles on the properties of a virgin homopolymer, virgin copolymer, natural post consumer, and mixed color post consumer blow molding resin was conducted. Rheological properties such as shear and elongational viscosity and elastic modulus were studied in the context of changes experienced during recycling. The G′-G′ (elastic storage and loss modulus) crossover point was used to measure relative changes in the polydispersity index and molecular weight distribution (MWD). It is also shown that extrudate swell and sag change after multiple extrusion passes. Environmental stress crack resistance was also measured. A rationale for the significant decrease in the environmental stress crack resistance of the virgin copolymer resin is presented. The results are analyzed in terms of known degradation mechanisms such as chain scission and crosslinking, and their relationship to the molecular structure. © 1997 John Wiley & Sons, Inc. Adv in Polym Techn 16: 11–24, 1997

5536300 Natural gas enrichment process: Reinhold Herbert E; D'Amico Joseph; Knaebel Kent, Annapolis, MD, United States assigned to Nitrotec Corporation

The growth of desktop 3-D printers is driving an interest in recycled 3-D printer filament to reduce costs of distributed production. Life cycle analysis studies were performed on the recycling of high density polyethylene into filament suitable for additive layer manufacturing with 3-D printers. The conventional centralized recycling system for high population density and low population density rural locations was compared to the proposed in home, distributed recycling system. This system would involve shredding and then producing filament with an open-source plastic extruder from post-consumer plastics and then printing the extruded filament into usable, value-added parts and products with 3-D printers such as the open-source self replicating rapid prototyper, or RepRap. The embodied energy and carbon dioxide emissions were calculated for high density polyethylene recycling using SimaPro 7.2 and the database EcoInvent v2.0. The results showed that distributed recycling uses less embodied energy than the best-case scenario used for centralized recycling. For centralized recycling in a low-density population case study involving substantial embodied energy use for transportation and collection these savings for distributed recycling were found to extend to over 80%. If the distributed process is applied to the U.S. high density polyethylene currently recycled, more than 100 million MJ of energy could be conserved per annum along with the concomitant significant reductions in greenhouse gas emissions. It is concluded that with the open-source 3-D printing network expanding rapidly the potential for widespread adoption of in-home recycling of post-consumer plastic represents a novel path to a future of distributed manufacturing appropriate for both the developed and developing world with lower environmental impacts than the current system.

Plastics recycling rates

Abstract Plastics comprise approximately 9% by weight of MSW. Of this, 39% is containers and packaging materials. The USA packaging market annually uses 6.2 × 10 9 kg of high density polyethylene (HDPE), low density polyethylene (LDPE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC). Packaging is the target of plastics recycling efforts. Depending on the material collected, plastics will comprise 4 to 14% by weight of the recyclables in a recycling program. There is a large variation in the amount of plastics collected in plastics recycling programs. A survey of mixed plastics recycling programs indicates that rigid plastic container recycling can capture 7.7–16.3 kg per year per participating household (kg/phh-yr), beverage bottle recycling can capture 3.2–8.2 kg/pph-yr, and colored HDPE bottle recycling will add 3.6 kg/phh-yr. The contribution of non-specified plastics and non-plastic contaminants to plastics recycling programs is dependent on the plastic types collected. Non-specified plastics range from as little as 1% by weight for relatively simple plastics collection (PET and clear HDPE beverage bottles) to as much as 10 to 20% for plastic bottle or colored HDPE recycling. Non-plastic contamination can be 1 to 10% by weight.