Recycled High Density Polyethylene Research Articles

Engineering Performance of Concrete Incorporated with Recycled High-Density Polyethylene (HDPE)-A Systematic Review.

Incorporating recycled plastic waste in concrete manufacturing is one of the most ecologically and economically sustainable solutions for the rapid trends of annual plastic disposal and natural resource depletion worldwide. This paper comprehensively reviews the literature on engineering performance of recycled high-density polyethylene (HDPE) incorporated in concrete in the forms of aggregates or fiber or cementitious material. Optimum 28-days’ compressive and flexural strength of HDPE fine aggregate concrete is observed at HDPE-10 and splitting tensile strength at HDPE-5 whereas for HDPE coarse aggregate concrete, within the range of 10% to 15% of HDPE incorporation and at HDPE-15, respectively. Similarly, 28-days’ flexural and splitting tensile strength of HDPE fiber reinforced concrete is increased to an optimum of 4.9 MPa at HDPE-3 and 4.4 MPa at HDPE-3.5, respectively, and higher than the standard/plain concrete matrix (HDPE-0) in all HDPE inclusion levels. Hydrophobicity, smooth surface texture and non-reactivity of HDPE has resulted in weaker bonds between concrete matrix and HDPE and thereby reducing both mechanical and durability performances of HDPE concrete with the increase of HDPE. Overall, this is the first ever review to present and analyze the current state of the mechanical and durability performance of recycled HDPE as a sustainable construction material, hence, advancing the research into better performance and successful applications of HDPE concrete.

Catalytic pyrolysis of recycled HDPE, LDPE, and PP

Plastic waste has been growing every year, and as a result, environmental concern has been a topic of much attention. Many properties of plastics, such as their lightweight, durability, and versatility, are significant factors in achieving sustainable development. The exponential increase of plastic production produces every year approximately 100 million tons of waste plastic, which could be converted into hydrocarbon fuels by employing a process appropriately called pyrolysis. Pyrolysis, which is thermal or catalytical, can be performed under different experimental conditions that affect the type and amount of product obtained. With the pyrolysis process, products can be obtained with high added value, such as fuel oils and feedstock for new products. In this study, magnesium silicate (MgO3Si) and Cloisite 30B were used as catalysts for the decomposition of different plastics, and the results were compared with the zeolite catalyst. In the case of high-density polyethylene (HDPE), the oil yield with a zeolite catalyst was found to be 71%, whereas with MgO3Si and Cloisite 30B, this was 68% and 67%, respectively. Zeolite produced better results in the decomposition of polypropylene (PP) compared to MgO3Si and Cloisite 30B. Fourier-transform infrared spectroscopy (FTIR), and gas chromatography (GC) were conducted in this work. The spectra results for all samples were consistent and in the fuel range.

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.

Use of virgin/recycled polyethylene blends in rotational moulding

Abstract Aiming to further plastics recycling via rotational moulding plastics processing, blends of virgin and recycled polyethylene sourced from post-consumer plastics were developed. Three different kinds of recycled high density polyethylene – from bottles, pipes and mixed household waste – were compounded with virgin medium density polyethylene in an extruder. The ideal amount of recyclate was chosen based upon the impact resistance of different contents (25, 50 and 75%) of recycled plastic with the 50/50 blend found to have the best performance. Compression-moulded and rotationally-moulded samples were analysed through falling dart impact test, flexural test, melt flow rate and differential scanning calorimetry analysis. The impact results of the compression-moulded samples showed an increase in the impact resistance of the blends with a higher melt flow index and lower degree of crystallinity. The rotationally-moulded specimens displayed much lower impact resistance than the pure virgin plastic and a 20–30% reduction in the flexural moduli, which were ascribed to the crystalline structure of the part and issues in the blends’ rotomoulding process. It was concluded that blending virgin and recycled polyethylene for rotational moulding can be an effective way to further plastics recycling inside the Circular Economy context.

Influence of processed waste bagasse fibre-stone dust-6063 aluminium alloy particle on the characteristics of hybrid reinforced recycled HDPE composites

ABSTRACT A novel hybrid composite material was developed through the compression moulding technique by adding bagasse fibre, stone-dust and 6063 aluminium alloy (Al-Mg-Si) particles to recycled high-density polyethylene (rHDPE) matrix. The bagasse fibres were treated while the stone-dust and 6063 aluminium alloy (Al-Mg-Si) particles were sieved to particle sizes of ˂75 µm and ˂250 µm, respectively, before blending with the matrix. The work investigates comparatively, the influence of bagasse fibre-stone dust (hybrid-of-2) and bagasse fibre-stone dust-Al-Mg-Si particles (hybrid-of-3) on composite formation systems for reinforced rHDPE composites. The properties of recycled HDPE and rHDPE composites were thoroughly investigated through selected mechanical properties, wear resistance and thermal conductivity tests. The results show that the addition of bagasse fibre-stone dust-Al-Mg-Si alloy particles improves the mechanical, wear and thermal properties of the composites. The ultimate tensile strength was enhanced by 39% having a UTS value of 32 MPa, tensile modulus by 13% with a value of 98 MPa and wear resistance by 53% with a value of 0.8 g. SEM images showed that these reinforcements blended more properly when lower contents were added. This is responsible for the enhancement observed in the mechanical properties of the hybrid-of-3 reinforced composite.

Morphological, thermal and mechanical properties of recycled HDPE foams via rotational molding.

In this study, foamed recycled high density polyethylene (rHDPE) parts were produced by rotational molding using different concentration (0 to 1% wt.) of a chemical blowing agent (CBA) based on azodicarbonamide. From the samples produced, a complete morphological, thermal and mechanical characterization was performed. The morphological analysis showed a gradual increase in the average cell size, while the cell density firstly increased and then decreased with increasing CBA content. As expected, increasing the CBA content decreased the foam density as well as the thermal conductivity. Although increasing the CBA content decreased both tensile and flexural properties, the impact strength showed a similar trend as the cell density with an optimum CBA content around 0.1% wt. Finally, neat rHDPE samples were also produced by compression molding. The results showed negligible differences between the rotomolded and compression molded properties indicating that optimal rotomolding conditions were selected. These results confirm the possibility of using 100% recycled polymers to produce rotomolded foam parts.

Rotational molding parameters of wood-plastic composite materials made of recycled high density polyethylene and wood particles

Recent investigations have demonstrated that it is possible to incorporate different natural fibers in the rotational molding process. In this perspective, the main purpose of this work is to study the influence of rotational molding parameters on the sintering process of composite materials made of recycled high density polyethylene and wood particles. To achieve this, an experimental procedure of three molding stages was elaborated to make wood-plastic composite materials. At each stage, it was studied the effect of a certain molding parameter on mechanical properties, while the other parameters remain constant during the molding process. The composite materials made during each stage were tensile tested to identify which of them have suitable mechanical properties and to find the most convenient molding parameters for making them. Using a stereoscope, pictures of composite materials' morphologies were taken to study the degree of sintering and determine its influence on mechanical properties. Results show that there is a very close relationship among composite materials’ morphologies, degree of sintering, rotational molding parameters and mechanical properties. In addition, it has been found that composite materials that reached the most convenient properties have a tensile strength which decreases up to 17% and an elastic modulus which increases up to 16%, in regard to a material made of neat recycled polyethylene that was molded under the same conditions.

Comparison of Composite Quality from PP Plastic with Recycled HDPE Through The Screw Extruder Process

This study examines the composite quality of PP and HDPE plastic waste materials using Microfiber Oil palm empty fruit bunches (OPEFB) as filler, the fiber used is 90 µm. The ratio of matrix: filler used is 60:40 and 70:30 for each type of PP and HDPE polymer. The method used is a melt blending screw extruder, where plastic and fiber materials are dissolved with a compatibilizer and then melt blended in an extruder by providing temperatures of 160 and 170 oC. Tensile tests showed the strength of the PP composite with a filler ratio of 60:40 and 70:30, respectively, of 313.25 N and 336.35 N, while the HDPE composite with a filler ratio of 60:40 and 70:30, respectively are 392.93 N and 187.90 N. The maximum force required to break HDPE composites reaches 21.10 Mpa while for PP composites it reaches 18.56 Mpa. From the morphology of the PP and HDPE composite samples, the overall surface structure of HDPE looks regular with a width from 1 to 13.5 mm. The PP composite shows a uniform and regularly arranged surface structure and the bond between the fibers and the filler looks more compatible but the surface pores are rougher. Heat resistance can be seen from the melting point of PP composites which can reach 163.81oC while HDPE composites only reach 134.21oC.

Effect of processing condition and antioxidants on visual properties of multilayer post-consumer recycled high density polyethylene films

Mechanical recycling is a promising approach to reduce the environmental impact of plastic packaging waste. However, the presence of defects in recycled materials results in final products with relatively poor visual and/or mechanical properties. In this work, the origin of the visual defects in post-consumer recycled HDPE (PCR HDPE), as well as the effects of processing method, processing condition and the addition of antioxidants on the visual defects were studied in multilayer flexible polyethylene films. The nature of the defects in the film samples were investigated by combining optical microscopy, energy dispersive X-ray (EDX), hot stage microscopy, solvent extraction, and differential scanning calorimetry (DSC) techniques. It was found that the defects in PCR film samples can be mainly categorized as fiber defects and point gels. Hot stage microscopy results show that point gels can be subcategorized in two groups: (a) non-melting, non-deformable gels, and (b) melting, deformable defects. In addition, it was found that deformation of molten, deformable defects increased at higher temperatures specifically above 200 °C. Further characterizations showed that the observed deformable defects are highly entangled high molecular weight HDPE. The effect of processing temperature, processing with a twin-screw extruder and the addition of antioxidant on the visual defects in film samples were also discussed in detail. It was shown that increasing processing temperature and using twin-screw extruders were two approaches that could reduce considerably the number of defects. The addition of antioxidants was also shown to improve the film quality especially at lower processing temperatures.

The Effect of Recycled HDPE Plastic Additions on Concrete Performance

This study examined HDPE (high-density polyethylene) plastic waste as an added material for concrete mixtures. The selection of HDPE was based on its increased strength, hardness, and resistance to high temperatures compared with other plastics. It focused on how HDPE plastic can be used as an additive in concrete to increase its tensile strength and compressive strength. 156 specimens were used to identify the effect of adding different percentages and sizes of HDPE lamellar particles to lower, medium, and higher strength concrete for non-structural applications. HDPE 0.5 mm thick lamellar particles with sizes of 10 × 10 mm, 5 × 20 mm, and 2.5 × 40 mm were added at 2.5%, 5%, 10%, and 20% by weight of cement. The results showed that the medium concrete class (with compressive strength equal to 10 MPa) had the best response to the addition of HDPE. The 5% HDPE addition represented the optimal mix for all concrete types, while the 5 × 20 mm size was best.

Mechanical Properties of Bamboo on Virgin and Recycled High-Density Polyethylene Matrix

Natural fiber-reinforced polymer composites are considered to have advantages over synthetic fibers, namely that they are more environmentally friendly but with better mechanical properties. The purpose of this study was to make a pure / recycled HDPE (High-Density Polyethylene) composite with bamboo fiber reinforcement by analyzing the mechanical properties of the composite. The method used in this research is experimental with a quantitative approach. Experiments are carried out by creating or manipulating certain conditions and by providing control over the test specimen. Pure / recycled HDPE plastics and bamboo fibers will be mixed in a machine extrusion molding with a temperature heater (160, 165, 170, 175) ° C. Before fabrication, bamboo fibers are treated with alkaline treatment, namely by immersing 5% NaOH. The ratio of mass fraction between vHDPE/rHDPE and bamboo fiber was 70%: 30%. This study evaluated the mechanical properties of HDPE-bamboo composites using Izod Impact testing with ASTM D 256-05 standards. Tests were carried out to analyze the differences between pure HDPE and recycled HDPE matrices on bamboo fiber reinforced composites. The mechanical test results showed that the impact strength on bamboo composites with recycled HDPE matrix was 2.69 (KJ / m2) while bamboo composites with pure HDPE matrices had an impact strength of 1.6 (KJ / m2). Thus, the mechanical properties measured by impact strength on composites with recycled HDPE matrices were better than composites with pure HDPE matrices. In accordance with the results of research that has been done, recycled HDPE can be used as a matrix composite with mechanical properties that are not too different from composites with pure HDPE matrices. This can be done as a means of utilizing recycled HDPE waste instead of pure HDPE.

Characteristics of recycled HDPE/bamboo fibre composite

Increasing the mechanical properties of recycling can be done by adding natural fibers into composite materials. The focus of this research is to develop a composite using bamboo as a reinforcing material and recycled High Density Polyethylene (HDPE) as a matrix using the extrusion method. This study aims to analyze the mechanical analysis between bamboo fiber-based composites using a pure HDPE matrix and composites using recycled HDPE matrices at a matrix volume fraction: 70%: 30% fiber. Mechanical tests were performed using the tensile testing machine model RAY-RAN Test Equipment M500-50CT with ASTM D 638 standards to evaluate the tensile strength and modulus of the composite. The results showed that the tensile strength and Young’s modulus of bamboo fiber reinforced rHDPE composites were 8.764 MPa and 52.0152 MPa, respectively. While the bamboo composite with a vHDPE matrix has a tensile strength of 9.3312 MPa and a Young Modulus value of 94.8468 MPa. Thus, bamboo fiber reinforced composites with pure HDPE matrix have better mechanical properties than bamboo composites with recycled HDPE matrices. Differences in matrix shape can affect composites resulting from such fibers.

Development of hemp fiber composites with recycled high density polyethylene grocery bags

AbstractThis research focuses on the development of an environmentally friendly composite directly from recycled high density polyethylene (rHDPE) grocery bags without changing their film form. Untreated and alkali‐treated hemp fibers are used as reinforcement for a composite with recycled High Density Polyethylene (rHDPE) and a combination of rHDPE and virgin HDPE (vHDPE). Grocery bags and hemp fibers are characterized using Fourier transform infrared spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and thermogravimetric analysis (TGA). Fiber preforms are produced using a hydro‐entanglement method and compression molded with HDPE and/or rHDPE at weight fractions of 30, 40, and 50%. The hemp fiber HDPE composites are characterized and tested for their tension and flexure performance. The results show an improvement in mechanical properties when using treated fibers as well as the addition of vHDPE to the polymer matrix. The highest tensile and flexural strength values for the pure rHDPE composite were acquired after adding 40 and 50% weight fraction of treated fibers, respectively. An increase of around 10 MPa on both of these properties was found when using the optimized combination of the recycled and virgin matrix materials with 40 and 50% weight fraction of reinforcement, respectively. It is concluded that the composite made of hemp fibers and recycled plastic bag has relatively good mechanical properties and can be potentially used for secondary structural use.

Experimental Study on Utilization of Recycled HDPE Aggregate as A Partial Replacement for Coarse Aggregate in Conventional Concrete

Experimental Study on Utilization of Recycled HDPE Aggregate as A Partial Replacement for Coarse Aggregate in Conventional Concrete

Effect of MWCNT on Mechanical Properties of Polymer Based Composite Brick

This paper investigates the mechanical properties of wood plastic composite which was made by using recycled High-Density Polyethylene (HDPE) and Polypropylene (PP) with Teak wood flour. Multi-Walled Carbon Nanotubes were used as additional filler. The composite was made using single screw extruder having L/D ratio 20. The RPM of the screw was fixed at 15 RPM and the temperature of the feed, metering and transition zone was maintained at 130°C, 1900c and 220°C respectively. Dimensional stability and mechanical properties of the composite were improved by coupling agents. Wood floor was used at 10wt% and MWCNTs were taken between 0.1 to 1 wt %. Increasing filler load improves compressive strength of the composite. The addition of MWCNT to HDPE/WF composite results in significant increment in compressive strength of the composite.

Mechanical Testing of Recycled HDPE Extruded Hollow Section

High density polyethylene (HDPE) is a thermoplastic polymer which is classified as one of the highly consumed types of plastics. One major advantage of thermoplastic materials is their ability of recycling and reprocessing which will bring considerable economicand environmental benefits. The present paper, therefore, endeavours to explore the practical possibility of using recycled HDPE hollow section as a replacement of virgin HDPE made by the extrusion process. The main focus of the study was to evaluate the mechanical performance of the recycled HDPE and compare the results with virgin or non-recycled HDPE. The modulus of elasticity, tensile yield and ultimate strength, compressive yield and ultimate strength, flexural yield and ultimate strength and the coefficient of thermal expansion were the main parameters to be checked against the respective mechanical properties. Thus, pursuant to the rsults, it was found out that the modulus of elasticity and the tensile yield strength are lower in recycled HDPE compared to the non-recycled HDPE. However, there is no significant difference between the recycled and non-recycled HDPE for the tensile ultimate strength, compressive yield strength and compressive ultimate strength. The flexural yield strength and flexural ultimate strength properties of the recycled HDPE proved to be superior to those of the non-recycled HDPE. The coefficient of linear thermal expansion of the recycled HDPE sample was 130 μm/(m.°C) and that for the non-recycled HDPE was 142 μm/(m.°C).

Modification of Recycled HDPE Composite with OPEFB Microfibers Through the Melt Blend Extruder Process

Oil palm empty fruit bunches (OPEFB), have not many been used as a have economic value material. OPEFB fiber content can be using as a filler to composites fabrication. The fiber contained in the OPEFB can be increase composites quality because have high thermal and mechanical properties. SEM analysis shows that OPEFB waste with a size of 63 and 90 ?m is suitable to be use as a filler because of the compatibility of the fiber and matrix matrix. As with the results of the DSC analysis, the melting point of HDPE-TKKS composite with 63 ?m fiber size reaches 133.58 0 C while the melting point of HDPE-TKKS composite with 90 ?m fiber size reaches 134.41 0 C. The FTIR test results also show that the indications of the two samples have the same chemical composition, namely lignicellulose. The best tensile strength is obtained which is equal to 21.11 MPa and the force required to break the composite is 391.56 N, these results were obtained from composites with a ratio of 60: 40 (matrix : filler) and 90 µm fiber size. Key words : Plastic, HDPE, fiber, OPEFB, composit e

Effect of wood particle size on the water absorption of wood-plastic composites

The main aim of this paper is to present the research findings which come out from the experimental determination of the influence of input raw material properties and composition on the water absorption of wood-plastic composites. During the WPCs production, important raw material parameters such as wood sawdust particle size, wood/plastic concentration ratio or type of plastic matrix can be recognized. In this research study, the aim was to produce WPCs of an acceptable and competitive level of quality which is determined from the final mechanical properties of WPCs. Particle size of wood sawdust used for production of WPC has significant influence on mechanical properties of composites and also on other important properties (water absorption, hardness, frost resistance, etc.). Using a variety combination of influencing variables the final quality of composites and also the operating parameters of the injection molding press can be improved. Their effect can be seen from the quality indicators and from the operating parameters of the injection press which has a direct impact on the production costs. The paper deals with the determination of the impact and the relationship between the input wood sawdust particles sizes, wood/plastic concentration ratio and water absorption of composites. By side intention of authors is to determine the possibilities of waste raw materials usage. The experimental research findings were obtained using a semi-operational injection molding press where the injection is provided by a working screw. As the input raw material, spruce sawdust, HDPE plastic matrix and recycled HDPE, represented by lids from PET bottles, was used. The effect of the input wood sawdust particle size on water absorption was determined according to a combination and default levels of wood/HDPE concentration ratio, using recycled HDPE instead of virgin HDPE and particle size of wood sawdust.

Hydrological Behaviour of Extensive Green Roofs with Native Plants in the Humid Subtropical Climate Context

Different mitigation measures with vegetation have been proposed to sustainably manage rainwater, among which green roofs have demonstrated to be a valid solution in urbanized areas. Green roofs have gained interest also in Italy, but their spreading is generally based on application of ready-to-use packages, poorly tested in the specific climate conditions. A study was carried out to evaluate the green roof solution most suitable in the humid, subtropical climate context of Veneto Plain (north-eastern Italy) to reduce outflow volumes from building roofs into the urban drainage systems. Twelve different microcosm combinations of extensive green roof (three plant mixtures × two substrates × two storage/drainage layers) were tested and compared with gravel (considered as a conventional flat roof with gravel ballast). The tested drainage/storage layers were a preformed layer in recycled HDPE (PL) and an expanded perlite mineral layer (ML), and the growth medium layers were recycled brick substrate (RS) and volcanic substrate (VS). Three different mixtures of native plant species were transplanted: Sedum (SE), herbaceous perennial (HE), and suffruticose (SF). Results showed that all the green roof systems have a good ability to manage rainwater, with a retention ranging on average from 46.2% (SE-RS-PL microcosms) to 62.9% (SF-RS-ML microcosms) of the precipitation in the two-year period (September 2014–August 2016), against 15.4%, retained by gravel. Over the two-year period, the retained rainfall volumes were about 100% for all the light rainy events (<10 mm) and varied within a range of 48–95% for medium rainy events (≥10 and <25 mm) and 20–88% for heavy rainy events (≥25 mm), depending on rainfall depth and the antecedent weather period. The layer that gave the highest relative contribution to the stormwater retention was the vegetation layer, followed by the drainage/storage layers and then the substrate layer. In particular, SF plants decreased the outflows by 15.2% on average compared to SE, and ML layer retained more than 10% of precipitation compared to PL layer. At last, the analysis of variance showed that, within each layer, the more effective in water retention, able to generate less outflow volumes, was similarly suffruticose and herbaceous mixtures, the crushed bricks substrate, and the mineral drainage/storage layer.

New methods to remove volatile organic compounds from post-consumer plastic waste

While the annual European demand for polyolefins is 25 million tonnes, only 3 million tonnes of recycled polyolefins find their place in the market, despite collecting 15 million tonnes of post-consumer polyolefins every year. Brand owners of care products are showing their interest in using post-consumer recycled plastics for their packaging. However, there is a general concern in using these materials, as recycled polymers can contain unwanted substances that may expose the consumer to health risks or make the packaging unattractive. Accordingly, the presence of these contaminants narrows the market opportunity of recycled plastics to applications with low-quality requirements and in which the product is not in direct contact with the consumer.Though mechanical recycling is the most widespread solution presents limitations in terms of decontamination, as only superficial substances are removed. Thereby, the volatile organic compounds (VOCs) migrated to the polymer matrix remain inside. Consequently, there is a need to find a solution to purify recycled plastics and increase their market share.This study focuses on removing VOCs from post-consumer recycled HDPE through two innovative methods applied for the first time in this field, steam stripping and polyethylene glycol (PEG) extraction. The methodology implemented to analyze the volatile organic compounds in HDPE was HS-SPME-GC/MS. Both methods showed a decrease above 70% in the VOCs content compared to extrusion-degassing. Moreover, these were compared to hot air stripping, a new technology developed at an industrial scale for the removal of VOCs. As a result, steam stripping improved efficiency in reducing the overall VOCs compared to hot air stripping. The PEG extraction method lowered the volatile polar compounds further than using hot air stripping. Additionally, none of these technologies modified the HDPE melting flow index.