A review on tertiary recycling of high-density polyethylene to fuel

Plastics have become an indispensable ingredient of human life. They are non-biodegradable polymers of mostly containing carbon, hydrogen, and few other elements such as chlorine, nitrogen etc. Rapid growth of the world population led to increased demand of commodity plastics. High density poly ethylene is one of the largest used commodity plastics due to its vast applications in many fields. Due to its non bio degradability and low life, HDPE contributes significantly to the problem of Municipal Waste Management. To avert environment pollution of HDPE wastes, they must be recycled and recovered. On the other hand, steady depletion of fossil fuel and increased energy demand, motivated the researchers and technologists to search and develop different energy sources. Waste to energy has been a significant way to utilize the waste sustainably, simultaneously add to meet the energy demand. Plastics being petrochemical origin have inherently high calorific value. Thus they can be converted back to useful energy. Many researches have been carried out to convert the waste plastics into liquid fuel by thermal and catalytic pyrolysis and this has led to establishment of a number of successful firms converting waste plastics to liquid fuels. This paper reviews the production and consumption HDPE, different methods of recycling of plastic with special reference to chemical degradation of HDPE to fuel. This also focuses on different factors that affect these degradations, the kinetics and mechanism of this reaction.     

The effects of recovering fibre and fine materials on sludge dewatering properties at a deinked pulp mill

The manufacture of deinked pulp generates large amounts of waste for disposal. The yield loss in the production of recycled paper can be up to 25%. The use of landfills for waste disposal is very expensive and will be prohibited in Europe in the next few years. Thus, there is a great pressure to improve the material efficiency and to reduce the amount of waste that is produced at deinked pulp mills. However, the issue is complex because an improvement of the material efficiency at one process unit may deteriorate the performance of other stages. For example, the attempts to increase the fibre yield in the deinking processes can lead to poor sludge dewatering properties, resulting in that there are no added advantages for the mill anymore.This work aims to determine the limitations between the sludge dewatering properties and the improvements in material efficiency at a deinked pulp mill by investigating the dewatering properties of sludge samples that contained variable amounts of fine screening and flotation froth rejects. The results show that the deinked pulp mill material efficiency can be increased without weakening the sludge dewatering properties if the fibre content is not reduced below a certain limit. The material efficiency can be increased either by (1) recovering fibres at an acceptable quantity where the fibre content does not decrease below the limiting point or by (2) recovering fine materials simultaneously with fibres in a way that maintains the fibre content above a limiting point. The first method provides an opportunity for deinking mills to increase the yield, even though the increase is less than 2 percentage units. With the simultaneous recovery of fibres and fine materials using the second method, it would be possible to improve the material efficiency at the deinked pulp mill by approximately 5 percentage units without affecting the dewatering of the combined sludge.     

Degradation of greenhouse twines derived from natural fibers and biodegradable polymer during composting

Commercial composting operations generally do not accept organic wastes with plastic twines from the greenhouse vegetable industry and the bulk of the waste materials ends up in landfills. The objectives of this paper are to identify environmentally compatible substitutes that could replace the current use of petrochemically derived plastic twines in greenhouse vegetable production, thus diverting them from landfills, and to assess the extent of their degradation via composting. Physical properties of the twines, including linear density, percent weight loss and tensile strength were monitored for the biodegradation tests. A pilot-scale composting trial was conducted in an in-vessel composting system. Results showed that the three biodegradable twine materials (cotton, jute and EcoPLA) could degrade readily in a composting environment within a reasonable time frame. Specifically, at the end of 105 days of composting, 85.3%, 84.8% and 81.1% of weight loss was observed for cotton, jute and EcoPLA, respectively. Furthermore, EcoPLA exhibited a slower decline in tensile strength with time, when compared to jute and cotton.     

Diversion from landfill: quality products from valuable plastics

Mechanical recycling of 100% post-consumer plastic waste into high-quality products has been performed. The chemical and physical properties of these recycled materials have been compared with similar products manufactured from virgin resins. The properties of a blow-moulded bottle prepared from 100% post-consumer high-density polyethylene (HDPE) showed that this recycled polymer exceeded the materials specifications for virgin plastic designs. Similarly, a sample of thermoplastic polyolefin (TPO, 100% polypropylene), obtained entirely from shredder residue (SR) displayed sufficient material strength for future separation and reprocessing.     

Life cycle assessment of biofibres replacing glass fibres as reinforcement in plastics

This article aims to determine the environmental performance of China reed fibre used as a substitute for glass fibre as reinforcement in plastics and to identify key environmental parameters. A life cycle assessment (LCA) is performed on these two materials for an application to plastic transport pallets. Transport pallets reinforced with China reed fibre prove to be ecologically advantageous if they have a minimal lifetime of 3 years compared with the 5-year lifetime of the conventional pallet. The energy consumption and other environmental impacts are strongly reduced by the use of raw renewable fibres, due to three important factors: (a) the substitution of glass fibre production by the natural fibre production; (b) the indirect reduction in the use of polypropylene linked to the higher proportion of China reed fibre used and (c) the reduced pallet weight, which reduces fuel consumption during transport. Considering the whole life cycle, the polypropylene production process and the transport cause the strongest environmental impacts during the use phase of the life cycle. Since thermoplastic composites are hardly biodegradable, incineration has to be preferred to discharge on landfills at the end of its useful life cycle. The potential advantages of the renewable fibres will be effective only if a purer fibre extraction is obtained to ensure an optimal material stiffness, a topic for further research. China reed biofibres are finally compared with other usages of biomass, biomaterials, in general, can enable a three to ten times more efficient valorisation of biomass than mere heat production or biofuels for transport.     

Utilization of waste foundry sand (WFS) in concrete manufacturing

Due to ever increasing quantities of waste materials and industrial by-products, solid waste management is the prime concern in the world. Scarcity of land-filling space and because of its ever increasing cost, recycling and utilization of industrial by-products and waste materials has become an attractive proposition to disposal. There are several types of industrial by-products and waste materials. The utilization of such materials in concrete not only makes it economical, but also helps in reducing disposal concerns. One such industrial by-product is waste foundry sand (SFS). Waste foundry sand is a by-product of ferrous and nonferrous metal casting industries. Foundries successfully recycle and reuse the sand many times in a foundry. When the sand can no longer be reused in the foundry, it is removed from the foundry and is termed as waste foundry sand.Published literature has shown that WFS could be used in manufacturing Controlled Low-Strength Materials (CLSM) and concrete. This paper presents an overview of some of the research published on the use of WFS in concrete. Effect of WFS on concrete properties such as compressive strength, splitting tensile strength, modulus of elasticity, freezing-thawing resistance, and shrinkage are presented.     

Recycle of bio-waste banana and sisal fiber filled harmlessness epoxy hybrid composite for automotive roof application

Insists of polymer matrix composite is prepared by using natural fiber facilitates high tensile, flexural, and impact toughness properties. The natural fiber utilization in the polymer matrix can overcome the synthetic fiber demerits of poor compatibility, high moisture absorption, and high cost. The present research investigates developing a low-cost, environmentally eco-friendly epoxy hybrid composite using different volume percentages of chopped natural waste banana (0Vol%, 5Vol%, 10Vol%, and 15Vol%) and sisal fiber (0Vol%, 15Vol%, 10Vol%, and 5Vol%) through hand mould hot compression technique. The presence of natural waste banana and sisal fiber on tensile strength, flexural strength, and thermal adsorption properties of the epoxy hybrid composite are evaluated by ASTM test standards. The ASTM standard measured test results of epoxy hybrid composite with and without natural waste banana and sisal fiber were compared and sample three was identified by good tensile strength, flexural strength, and better thermal adsorption properties compared to all others. The sample three epoxy hybrid sample is recommended for automotive roof application.     

Waste-based composites—Poverty reducing solutions to environmental problems

This paper highlights an innovative model of waste management combined with poverty reduction, which has been developed by the organisation Waste for Life (wasteforlife.org) - a network of academics, students, practitioners and on the ground cooperative partners in low income communities. The Waste for Life teams work with local cooperatives to create waste-based composites, which may be sold in local markets, thereby creating an income stream. The application of this model to the context of cartoneros (waste picker) cooperatives in Buenos Aires, Argentina, reveals that viable products can be made from paper and plastic waste, with low-impact material preparation that circumvents the need for chemically intensive, polluting and mechanically degrading procedures, preserving recycled fibre integrity. Tests on material samples indicate mechanical properties comparable to products made with more complex processing. The production model is based on the philosophy that not only the waste materials, but also the production equipment should be locally sourced and manufactured and products created to suit local markets. A simple reproducible model has been developed for the local manufacture of composites from waste, which can provide an income source for waste pickers as well as providing an innovative waste management solution.     

Optimization of the high-pressure, near-critical liquid-based microsortation of recyclable post-consumer plastics

High-pressure, near-critical liquids were used as float-sink separation media for the microsortation of polyolefin mixtures and PET/PVC mixtures. Near-critical carbon dioxide was used for the refinement of the polyolefins, and sulfur hexafluoride was used to separate post-consumer PVC from PET. Preliminary experiments indicated that there was no overlap in the density ranges of post-consumer HDPE, LDPE and PP containers. There was no overlap in the PET and PVC densities, with the exception of a single PVC packaging material with a density in the PET range. These initial results indicated that a float-sink separation was a viable means of microsortation. Separations of 91% LDPE (1/8′ beads)/9% PP (1/8′ chopped strands) resin mixtures and mixed post-consumer polyolefin flakes were then conducted in a laboratory-scale, 1-I batch apparatus. This apparatus not only permitted the observation of the separation, but also enabled the separated fractions to be removed from the high-pressure environment. The results indicated that LDPE purity of greater than 98.9% was obtained in 3 min or less if (a) the fluid density was 0.018 g/cm³ greater than the PP density and only 0.002 g/cm³ less than the LDPE density, thereby providing the greatest buoyancy force for the removal of the PP, (b) the fluid was recirculated upward through the bed of mixed plastics, facilitating the upward movement of the PP, and (c) the loading was kept at levels below 40% by volume. HDPE purity of 99% was also attained with clean, dry, post-consumer mixed plastic flakes. The loadings for these separations were very low, however, due to the difficulty in agitating the mixed bed of plastics using fluid recirculation. An economic analysis of these microsortation processes indicated that the value of the sorted plastics relative to the mixed feed must increase by approx. $0.08/lb for the CO₂-based separation and approx. $0.27/lb for the SF₆-based separation to justify the implementation of these high-pressure processes.     

Assessment of plastic packaging waste: Material origin,methods, properties

The global plastics production has increased annually and a substantial part is used for packaging (in Europe 39%). Most plastic packages are discarded after a relatively short service life and the resulting plastic packaging waste is subsequently landfilled, incinerated or recycled. Laws of several European and Asian countries require that plastic packaging waste collected from households has to be sorted, reprocessed, compounded and reused. These recycling schemes typically produce milled goods of poly(ethylene terephthalate) (PET), poly(ethylene) (PE), isotactic poly(propylene) (PP), mixed plastics, and agglomerates from film material. The present study documents the composition and properties of post-consumer polyolefin recyclates originating from both source separation and mechanical recovery from municipal solid refuse waste (MSRW). The overall composition by Fourier transform-infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC) were determined and compared with the sorting results of the sorted fractions prior to the reprocessing into milled goods. This study shows that the collection method for the plastic packaging waste has hardly any influence on the final quality of the recyclate; however, the sorting and reprocessing steps influence the final quality of the recyclate. Although the mechanical properties of recyclate are clearly different than those of virgin polymers, changes to the sorting and reprocessing steps can improve the quality.     

Closed loop recycling of plastics containing Flame Retardants

Annually 2.7 million tonnes of plastics containing Flame Retardants (FRs) are globally discarded in Waste Electrical and Electronic Equipment (WEEE). Little is known on the feasibility of closing material loops for FR plastics. Therefore, series of experiments were set up to analyze the feasibility of separating plastics containing FRs from one specific product category, namely End-of-Life (EoL) Liquid Crystal Display (LCD) TVs. The characterization of the housings of this waste stream indicated a concentration of 18 wt% Bromine based (Br) FRs and 31 wt% Phosphor based (P) FRs, the remainder not containing FRs. With practical tests it was demonstrated that, after disassembly and plastic identification, the co-polymer poly-carbonate (PC)/acrylonitrile-butadiene-styrene (ABS) containing PFR can be recycled in a closed loop system. Based on the determined plastic density distributions and separation efficiencies of optical sorters, a purity of 82% was calculated for PFR PC/ABS separated from EoL LCD TVs after size-reduction (shredding). Performed miscibility tests indicated that for this fraction at least a factor 10 dilution with virgin material is required. In addition, higher waste volumes are required for a size-reduction based treatment to become economically viable and technical challenges still need to be faced, whereas closed loop recycling of PFR PC/ABS from the current waste stream of EoL LCD TVs of different brands in a disassembly based treatment is found to be technically feasible and economically viable under European boundary conditions.     

A comprehensive waste collection cost model applied to post-consumer plastic packaging waste

Post-consumer plastic packaging waste (PPW) can be collected for recycling via source separation or post-separation. In source separation, households separate plastics from other waste before collection, whereas in post-separation waste is separated at a treatment centre after collection. There are also two collection schemes, either curb side or via drop-off locations. These different schemes have impact on total costs of collection at the municipal level. It can also influence the facility choices and network design. Therefore, a method which can compare costs of various collection schemes is needed.A comprehensive cost model was developed to compare costs of municipal collection schemes of PPW. The ‘municipal waste collection cost model’ is based on variables including fixed and variable costs per vehicle, personnel cost, container or bag costs as well as on emission costs (using imaginary carbon taxes). The model can be used for decision support when strategic changes to the collection scheme of municipalities are considered. The model takes into account the characteristics of municipalities, including urbanization degree and taxation schemes for household waste management.The model was applied to the Dutch case of post-consumer plastic packaging waste. Results showed that that in general post-separation collection has the lowest costs and curb side collection in urban municipalities without residual waste collection taxing schemes the highest. These results were supported by the conducted sensitivity analysis, which showed that higher source separation responses are negatively related to curb side collection costs. Greenhouse gas emission costs are a significant part of the total costs when collecting post-consumer plastic packaging waste due to the low density to weight ratio of the materials collect. These costs can amount to 15% of the total collection costs.     

Characterization of aromatic hydrocarbon formation from pyrolysis of polyethylene-polystyrene mixtures

Design and operating parameters, and cause and effect relationships among feedstocks and products in the pyrolysis of waste polymers are needed if this method of processing is to be used for energy recovery from waste plastics. The purpose of this study was to quantify the effect of various operating factors for the pyrolysis of common polymeric wastes. Experiments were performed using a conventional retort tube as a batch reactor. The operating factors considered were temperature and reaction time at constant heating rate. High density polyethylene (PE) and polystyrene (PS), the most common plastic waste in Korea, were used singly and in mixture.The pyrolysis time for maximum oil production from a PE-PS mixture was shorter than in the case of PE alone, showing an enhancement effect from the PS. The maximum gas production time from PE-PS mixtures was shorter than for PE alone at 500° C; above 600° C, this does not occur. Small aromatic compounds (which can be valuable) are produced at maximum with an 1:1 mixture of PE and PS at 600° C, showing the possibility of process control for the maximum recovery of desirable pyrolysis products. The maximum yield of toluene, xylene, styrene, and 1-propenyl benzene were 8.6, 8.9, 51.0 and 7.4 wt.% of feed for pyrolysis PS at 700° C, respectively. For naphthalene, it was at 700° C with 1:1 PE:PS (by wt.). The maximum recovery was 1.3 wt.%. Diels-Alder theory can explain the formation of aromatic compounds in the pyrolysis products. The yield of these secondary pyrolysis products can be controlled by reaction time, pyrolysis temperature and mixing ratio of plastic wastes in the pyrolysis feed.     

Carbon storage potential in natural fiber composites

The environmental performance of hemp based natural fiber mat thermoplastic (NMT) has been evaluated in this study by quantifying carbon storage potential and CO₂ emissions and comparing the results with commercially available glass fiber composites. Non-woven mats of hemp fiber and polypropylene matrix were used to make NMT samples by film-stacking method without using any binder aid. The results showed that hemp based NMT have compatible or even better strength properties as compared to conventional flax based thermoplastics. A value of 63 MPa for flexural strength is achieved at 64% fiber content by weight. Similarly, impact energy values (84–154 J/m) are also promising. The carbon sequestration and storage by hemp crop through photosynthesis is estimated by quantifying dry biomass of fibers based on one metric ton of NMT. A value of 325 kg carbon per metric ton of hemp based composite is estimated which can be stored by the product during its useful life. An extra 22% carbon storage can be achieved by increasing the compression ratio by 13% while maintaining same flexural strength. Further, net carbon sequestration by industrial hemp crop is estimated as 0.67 ton/h/year, which is compatible to all USA urban trees and very close to naturally, regenerated forests. A comparative life cycle analysis focused on non-renewable energy consumption of natural and glass fiber composites shows that a net saving of 50 000 MJ (3 ton CO₂ emissions) per ton of thermoplastic can be achieved by replacing 30% glass fiber reinforcement with 65% hemp fiber. It is further estimated that 3.07 million ton CO₂ emissions (4.3% of total USA industrial emissions) and 1.19 million m³ crude oil (1.0% of total Canadian oil consumption) can be saved by substituting 50% fiber glass plastics with natural fiber composites in North American auto applications. However, to compete with glass fiber effectively, further research is needed to improve natural fiber processing, interfacial bonding and control moisture sensitivity in longer run.     

Waste electric and electronic toys: Management practices and characterisation

The main objective of this paper is to characterise, both physically and chemically, waste electric and electronic toys, belonging to the category 7 of the Directive, 2012/19/UE, in order to obtain information about the generation and composition of this waste which is not widely found in the literature. For this, a campaign was designed with the aim of collecting a representative sample of waste toys in different schools in a Spanish town. Altogether 1014.25 kg of waste toys were collected, of which 31.83% corresponded to the electric and electronic fraction, which is the object of study. The collected wastes were divided into subcategories and a representative sample of each was one used to characterise them physically and chemically. Physical characterisation provided information about the materials they were made of, the electrical and electronic parts, fixing and assembly systems, and so forth. The results showed that the weight of a toy is comprised of 72.30% of plastics, 12.07% of electrical and electronic components, 4.47% of metals, and 11.15% other materials. In general, the most common types of polymers were PS, PP and ABS. Chemical characterisation made it possible to analyse the composition of the plastic components, which is information that is essential to be able to determine the feasibility of recovering the resulting fractions. The results showed that the content of hazardous substances in these plastics is far below the limits stipulated in Directive 2002/95/EC (RoSH Directive). The findings of this study show a need for a specific management system for this fraction of domestic wastes and a wide range of potential reusability of the discarded toys since 65% of the toys from the collected sample worked in perfect condition. We also found that the end-of-life is one of the aspects that have not been considered during their design as both materials and disassembly sequence do not facilitate the end-of-life of this type of wastes. This information could be used to improve the ecodesign of electrical and electronic equipment toys regarding their end-of-life.     

Analysis of products from the pyrolysis and liquefaction of single plastics and waste plastic mixtures

Waste plastics in the form of two examples of real world municipal solid waste plastics and a simulated mixture of municipal waste plastics were pyrolysed and liquefied under moderate temperature and pressure in a batch autoclave reactor. In addition, the five main polymers which constitute the majority of plastics occurring in European municipal solid waste comprising, polyethylene, polypropylene, polystyrene, polyethylene terephthalate and polyvinyl chloride were also reacted. The plastics were reacted under both a nitrogen (pyrolysis) and hydrogen pressure (liquefaction) and the yield and composition of products are reported. The hydrocarbon gases produced were mainly methane, ethane, propane and lower concentrations of alkene gases. A mainly oil product was produced with the mixed plastic waste with significant concentrations of aromatic compounds, including single ring aromatic compounds. The composition of the oils and gases suggested that there was significant interaction of the plastics when they were pyrolysed and liquefied as a mixture compared to the results expected from reactions of the single plastics.     

Application of recycled paper sludge and biomass materials in manufacture of green composite pallet

Rice straw, rice husk and paper sludge are by-products and industrial waste, and are beneficial resources as raw biomass materials used for manufacturing value-added composite products. We investigated the effect on selected mechanical properties of adding rice straw, rice husk and paper sludge to wood composites to replace wood particles for manufacturing green pallets. Results showed that increasing the contents of rice straw and rice husk dramatically decreased the mechanical strength of the composites. This is because the wax and silicate coating of these materials obstructed the strong bonding with UF resin. When 10 wt.% of wood particle was replaced with 10 wt.% of paper sludge, the wood–paper sludge composites showed similar mechanical properties to those of wood particle. Wood particle can be replaced by 10 wt.% of dried paper sludge in accordance with the minimum requirement recommended by standards in green pallet manufacturing.     

Evaluation of recycling efforts of aircraft companies in Wichita

The number of manufactured aircraft has been continuously increasing worldwide because of the high demand for airline transportation. During manufacturing, many advanced materials and devices are used to build various sizes and shapes of aircraft. However, most of these materials and devices require considerable energy and labor to produce, so reusing these at any life stage of the aircraft offers many economic and environmental benefits, and is considered lucrative and environmentally responsible. Several recyclable materials—composites, metals and alloys, wires, wood, paper, plastics, electronics, and avionics—emerge as waste streams during the manufacturing of aircraft. Many aircraft companies have been recycling these materials to remanufacture aircraft parts or other products for more sustainable production. In the present study, we evaluated the recycling efforts of local aircraft companies in Wichita, KS. These efforts were considered in terms of recycling efficiency/rate and environmental benefits. These included cradle-to-gate (CTG) life-cycle inventory analysis of the materials, carbon dioxide emissions, virgin material replacement with recycled materials, and natural resources usage. Our findings show that there exists a significant potential for contributions to sustainability as well as environmental and health benefits in the region from recycling by aircraft manufacturing plants.     

Recycling of gneiss rock waste in the manufacture of vitrified floor tiles

The present study focuses on the recycling of gneiss rock waste generated by the ornamental rock industry for manufacturing vitrified floor tile products. The gneiss rock waste came from a rock-cutting plant located in Santo Antônio de Pádua-RJ, Brazil. Initially the waste sample was characterized for chemical composition, X-ray diffraction, particle size, morphology, and pollution potential. Floor tiles containing up to 47.5 wt.% waste were prepared. The tiles were tested to determine their physical-mechanical properties (linear shrinkage, water absorption, apparent density, and flexural strength). Microstructural evolution was carried out by scanning electron microscopy. The results indicate that the gneiss rock waste could be used for vitrified floor tile production, resulting in a new possibility for recycling this waste and conserving natural resources.     

An approach for analysing the potential for material efficiency improvement

Material efficiency improvement saves energy and reduces the consumption of primary resources and reduces the volume of waste. In this article an approach for analysing the potential for material efficiency improvement is proposed and discussed. In this approach the product functions performed by the materials and various improvement measures are taken into account. The potential for material saving and associated energy saving is assessed and evaluated economically. In this paper the approach is tested in an analysis of the potential for material efficiency improvement with respect to plastic packaging in the Netherlands. The technical reduction potential is found to be 34 ± 7% (157 ± 30 ktonne virgin plastics). Realization of this potential would improve the energy efficiency of the lifecycle of plastic packaging by 31% (10 PJ in 1988). From our study we conclude that our approach can indeed be used to investigate the potential for material efficiency improvement. However, a reliable technical and particularly an economical assessment of reduction measures cannot be made until more detailed data become available.