Degradation Of High Density Polyethylene Research Articles

Visible light photocatalytic degradation of HDPE microplastics using vanadium-doped titania

Efficient strategies are necessary to effectively remove microplastics (MPs), which are widely present in the environment. Among various techniques, photocatalysis using visible light has emerged as a promising ap-proach to tackle the growing concerns surrounding microplastic waste. This research explored the potential of vanadium-doped titanium oxide as a photocatalyst for degrading high-density polyethylene (HDPE) micro-plastics under visible light irradiation. Vanadium-doped titanium oxide photocatalyst was synthesized using the sol-gel method, and then characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible spectroscopy. The XRD analysis confirmed the formation of the anatase phase, while the SEM imaging provided valuable information on the catalyst’s morphology and elemental composition. The successful incorporation of vanadium ions into the structure was demonstrated by UV-visible spectrosco-py that revealed a redshift in the absorption edge. The vanadium-doped titanium oxide photocatalyst was em-ployed in the degradation of HDPE under visible light. The experimental results exhibited a significant reduc-tion in the mass of the plastic after 350 hours of illumination. V-TiO₂ achieved a maximum reduction of 5.7%, while TiO₂ nanoparticles showed only the 2% decrease. This study demonstrates the potential of V-TiO₂ as an efficient visible-light-driven photocatalyst for HDPE degradation, contributing to the mitigation of microplastics pollution in a sustainable manner.

Evaluation of the impact of natural weathering on the properties of high‐density polyethylene bottles by experimental approach

AbstractThis work presents an in‐depth experimental study aimed at assessing the impact of natural weathering on the behavior of high‐density polyethylene (HDPE) bottles. To this end, several analytical techniques were employed, including Fourier transform infrared spectroscopy (FTIR) to examine molecular changes, scanning electron microscopy (SEM) to study morphology, thermogravimetric analysis (TGA) to assess thermal properties, and tensile and compression tests to evaluate mechanical properties. The results obtained reveal significant changes in HDPE exposed to natural weathering. FTIR analysis enabled us to identify that the HDPE bottles had been subjected to an oxidation process initiated by the absorption of solar radiation during natural weathering treatments, while SEM analysis showed the presence of holes resulting from the detachment of material fragments after exposure, TGA analysis confirms the impact of natural exposure time on the decrease in the average molecular weight and chemical degradation of HDPE macromolecules, through a reduction in the initial degradation temperature and the maximum thermodegradation temperature. However, tensile and compressive tests showed a reduction in the mechanical strength of HDPE after exposure to natural conditions, with notable variations depending on environmental conditions, making the material damaged. These results enabled us to calculate the damage caused by three damage laws. These results offer important insights into the mechanisms of HDPE degradation under the influence of natural climatic factors, paving the way for the development of more resistant and durable packaging materials in the face of variable environmental conditions.Highlights The objective of this study is to analyze and describe the effects of natural weathering on high‐density polyethylene bottles. This involves evaluating the deterioration of physicochemical, mechanical, and morphological properties. Additionally, three damage laws are employed to assess the extent of damage inflicted by this material. Analytical techniques were used, including SEM, FTIR, and TGA, tensile and compressive test.

Revealing the long-term impact of photodegradation and fragmentation on HDPE in the marine environment: Origins of microplastics and dissolved organics

The extensive usage of high-density polyethylene (HDPE) materials in marine environments raises concerns about their potential contribution to plastic pollution. Various factors contribute to the degradation of HDPE in marine environments, including UV radiation, seawater hydrolysis, biodegradation, and mechanical stress. Despite their supposed long lifespans, there is still a lack of understanding about the long-term degradation mechanisms that cause weathering of seawater-exposed HDPE products. In this research, the impact of UV radiation on the degradation of HDPE pile sleeves was studied in natural as well as laboratory settings to isolate the UV effect. After nine years of exposure to the marine environment in natural settings, the HDPE pile sleeves exhibited an increase in oxygen-containing surface functional groups and more morphological changes compared to accelerated UVB irradiation in the laboratory. This indicated that combined non-UV mechanisms may play a major role in HDPE degradation than UV irradiation alone. However, UVB irradiation was found to release dissolved organic carbon and total dissolved nitrogen from HDPE pile sleeves, reaching levels of up to 15 mg/L and 2 mg/L, respectively. Our findings underscore the significance of taking into account both UV and non-UV degradation mechanisms when evaluating the role of HDPE in contributing to marine plastic pollution.

Experimental study of the degradation of HDPE packaging under accelerated thermal aging

In this work, accelerated thermal aging at different temperatures was performed on high-density polyethylene (HDPE) bottles and specimens for food packaging. The degradation of HDPE was followed macroscopically by tensile and compression tests to evaluate the decrease in mechanical properties. The data obtained from these tests are used to calculate a new static damage law and the life fraction of this polymer. A prediction of the lifetime of HDPE was determined by thermogravimetric analysis (TGA) in dynamic mode. The evolution of the crystallinity rate during accelerated thermal aging was carried out using FOURIER transform infrared spectrometry (FTIR). The results obtained show a remarkable degradation of the mechanical properties in traction and compression by calculation of the static damage, and the physical and chemical properties by the analysis of the rate of crystallinity as well as the prediction by the law of Arrhenius.

Enhancing plastic waste recycling: Evaluating the impact of additives on the enzymatic polymer degradation

While (bio)degradation of polymers is a recognized challenge, the influence of additives on this process remains poorly understood. Their presence in commercial polyethylene (PE) may inhibit the degradation process or complicate the recycling. This study aims to develop an enzymatic degradation process for post-consumer high-density polyethylene (HDPE). The HDPE degradation was performed using laccase from Trametes versicolor under mild conditions of temperature and pressure. The process was developed by exploring three key conditions: (i) the biocatalytic medium; (ii) the enzymatic mediator, and (iii) the influence of the presence of additives in the polymers. The most successful enzymatic degradation system involved HDPE from which additives were removed, with a buffer used as the reaction medium and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) employed as the enzymatic mediator. This system led to a substantial 33% weight reduction of the polymer (versus 3% for HDPE with additive under the same conditions). The characterization of the degraded polymer revealed new bands in the Fourier transform infrared spectroscopy (FTIR) spectra, including a new carbonyl band. In addition, it also showed an increased crystallinity when compared to HDPE with additive under the same conditions. These results suggest that the enzymatic degradation of HDPE occurs through an oxidation process, with the enzyme preferentially attacking the amorphous region of the polymer.

Degradation of High-Density Polyethylene (HDPE) Film by Bacterial Consortium

Degradation of High-Density Polyethylene (HDPE) Film by Bacterial Consortium

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

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

Degradation of HDPE, LLDPE, and blended polyethylene geomembranes in extremely low and high pH mining solutions at 85 °C

The durability of five 1.5-mm thick geomembranes (GMBs) is investigated in pH 0.5 and 13.5 synthetic mining solutions using immersion tests. Two high density polyethylene (HDPE), two linear low density polyethylene (LLDPE), and one blended polyethylene (BPO) GMBs are investigated at 85 °C for incubation durations of 4.5–6.5 years. It is shown that the degradation of all five GMBs in the high pH solution is faster than in the low pH solution. In the pH 0.5 solution, one of the HDPEs and the BPO GMBs exhibited polymer degradation before or at the time of the depletion of their antioxidants. In pH 13.5, four out of the five GMBs exhibited degradation and followed the conceptual three-stage degradation model until nominal failure. However, there is no correlation between the long-term performance of these GMBs and their resin type or their initial properties since one of the examined LLDPEs outperformed all the higher density/crystallinity GMBs with higher initial properties while the other LLDPE did not perform well. Thus, when selecting a GMB for a desired application, the relative performance of different candidate GMBs can be only assessed using immersion tests using the solutions expected in the field.

Degradation of high density polyethylene (HDPE) through bacterial strain from Cow faeces

The prime objective of our research was to assess the efficiency of fecal bacteria Brevibacillus parabrevis CGK45 from cow in the degradation of HDPE plastic films without any physical or chemical pre-treatment. The biodegradation studies were conducted considering various parameters such as percent weight loss and half-life of HDPE film, biomass of surface adhered cells in terms of protein content as well as viability of bacterial biofilm (CFU/cm2) on plastic surface, and hydrophobicity of bacterial culture. The extent of biodegradation was assessed by implementation of various techniques i.e., Field Emission Scanning electron microscopy (FE-SEM), Energy dispersive X-ray spectroscopy (EDX) and Fourier Transform Infrared Spectroscopy (FTIR). The bacterial strain was identified as Brevibacillus parabrevis CGK45 (Accession number MW965577) by phylogenetic analysis using 16S rRNA gene sequence homology. A significant weight loss (4.03%) in the HDPE film treated with strain CGK45 was observed after 90 days. The SEM analysis visualized remarkable bacterial colonization as well as structural changes in the surface micromorphology on HDPE surface. Furthermore, SEM-EDX analysis showed excellent reduction in the atomic percentage of carbon content (2.2%) whereas FTIR analysis confirmed the conformational shifting of peak and formation of new functional groups [ester (1290 cm−1) and alcohol (1368 cm−1)] apparently due to bacterial biofilm biodegradation. The findings of our investigation provides an insight into the ability of cow dung strain B. parabrevis CGK45 in the colonization and utilization of high density polyethylene as a sole carbon source proving its suitability for future environment friendly degradation studies.

Synergy, kinetics, and thermodynamics analysis in the valorization of waste bakelite through co-pyrolysis with HDPE

Bakelite, a thermosetting plastic, can't be recycled suitably by pyrolysis as it is charred upon heating with low conversion to useful products. So, it is required to improve the conversion before charring in order to recycle it into valuable products through pyrolysis. Co-pyrolyzing bakelite with high-density polyethylene (HDPE) should improve its conversion before charring and obtaining more useful products. The design of a co-pyrolysis process requires kinetics and thermodynamic parameters. In this context, co-pyrolysis synergy, kinetics, and thermodynamics of HDPE blended Bakelite (1:1 by wt.) are studied by a variety of kinetics models to calculate kinetics triplets and predict a suitable mechanism. The thermal degradation experimental data are taken from ambient to 1000 °C at 5, 10, 20, 30, and 50 °C/min heating rates in an inert atmosphere. The co-pyrolysis synergy is ascertained from the alteration of temperature zone and weight loss pattern in thermal degradation. HDPE blended Bakelite degraded thermally in two stages (215–420 °C and 425–550 °C). The thermal degradation of HDPE blend Bakelite for the first stage (i.e., 215–420 °C) follows the third order (F3)- based model with activation energy 154 kJ/mol while that for the second stage (i.e., 425–550 °C) follows the 1-D diffusion (D1) model with activation energy 355 kJ/mol. The order of the reaction for the first stage is in the range of 0.035–0.352 and that in the second stage is in the range of 0.110–1.048 for different temperatures. The values of change in free energy, change in enthalpy, and change in entropy for the thermal degradation of HDPE blended Bakelite in the first and the second stage is 590.303 kJ/mol, 66.745 kJ/mol, −939.958 × 10-3JK-1mol-1 and 813.062 kJ/mol, 148.574 kJ/mol, - 876.864 × 10-3 JK-1mol-1 respectively. These kinetic and thermodynamic parameters definitely contribute to the optimization of pyrolysis reactor design.

NON-BIODEGRADATION OF POLYMERIZED POLYETHYLENE RADICALS AT SELECTED DUMPSITES IN KEFFI, NASARAWA STATE NIGERIA

Polythene and plastic bags pollutes the soil because these are non-biodegradable, and so, they cannot be degraded by the action of the microbes. Therefore, they remain in the soil and will pollute the soil. Polyethylene Terephthalate (PET) is therefore belongs to the class of polymers known as polyesters. In the natural environment, PET can be degraded by thermal oxidation, but hydrolytic cleavage and photo-oxidation initiated by UV light are more common under ambient conditions. In general, polyethylene offers excellent chemical and impact resistance, electrical properties and low coefficient of friction. It is considered a dielectric material. In addition, polyethylene are lightweight, easily processed and offer near-zero moisture absorption. In this study, selected dumps were covered in Keffi. The laboratory analysis was conducted. It was found out that there are two categories of Polyethylene with different properties, characteristics and functions. These are the High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE). The analysis revealed that T4 and T5 Isolate after drying contained more density of 8-9% degradation of high density polyethylene. While in the second tests of Low Density Polyethylene the T2, T7 and T8 have the highest coefficient of degradation. The residual plot of the dry weight polyethylene T9 has the highest weight in the model.

Assessing the weathering-induced degradation on the structural integrity of high-density polyethylene

Marine plastic pollution is a growing environmental concern, with plastic debris in the ocean having negative impacts on marine life and human health. One of the major challenges in addressing this problem is the slow degradation rate of plastics in the marine environment. In this study, the degradation of high-density polyethylene (HDPE), being extremely common in marine debris, is investigated when exposed to either (a) marine or (b) atmospheric environmental exposure. The weathering effects for this type of plastic were examined through ultraviolet spectrophotometer and tensile investigations. A chain-breaking activity in the microstructure of the weathered HDPE specimens was revealed. During the investigated eight (8) months of atmospheric and sea weathering, an approximate 10 % and 6 % decrease in ultimate tensile strength σUTS was noticed for the two different environments, respectively. Higher decrease was noticed for the respective elastic modulus E (Young’s modulus) that was approximate 23 % and 21 %, respectively. Based on the available experimental test results, a linear decrease rate equation of all the investigated mechanical properties was proposed, to give valuable information regarding the residual tensile mechanical properties of HDPE after weathering exposure.

Catalytic Co-pyrolysis of empty fruit bunch and high-density polyethylene mixtures over rice husk ash: Thermogravimetric, kinetic and thermodynamic analyses

Rice husk ash (RHA) has been used as a catalyst precursor but there are lack of studies on the application of the resulting catalyst. This study allows researchers to have an insight on using RHA-sourced catalysts in pyrolysis and be encouraged to utilize waste materials in the future. The goal of this study is to examine the effect of catalysts derived from rice husk ash (RHA) using the solvent-free method, labelled as RHA-T, on the catalytic co-pyrolysis of empty fruit bunch (EFB) and high-density polyethylene (HDPE) via thermogravimetric analyser (TGA). Comparisons were then made with co-pyrolysis and catalytic co-pyrolysis over raw RHA and Hydrogen-exchanged Zeolite Socony Mobil-5 (HZSM-5). Thermogravimetric analysis was conducted (EFB-to-HDPE mass ratio of 1:1, catalyst-to-feedstock mass ratio of 1:1) in a nitrogen atmosphere, where samples were heated from 30 °C until 700 °C (heating rate 20 °C/min). The order of runs with highest mass loss in the second phase is as follows, with the term ‘BP’ indicating the biomass-plastic feedstock: BP-RHA-T (98.17 wt%), BP-RHA (96.25 wt%), BP (86.82 wt%) and BP-HZSM-5 (70.59 wt%). Kinetic analysis using Coats-Redfern method and comparing between different diffusional reaction models showed that using BP-RHA-T follows a one-dimensional diffusion reaction, similar to the non-catalytic run. Using RHA-T resulted in higher activation energy (83.03 kJ/mol to 84.91 kJ/mol) compared to the non-catalytic run (62.39 kJ/mol to 68.97 kJ/mol). Thermodynamic analysis showed the pyrolysis runs were endothermic and non-spontaneous. Using RHA-T resulted in a higher change of enthalpy, a lower change of Gibbs free energy and a less negative change of entropy. It can be concluded that applying catalysts synthesized using low-cost materials like RHA can improve the degradation of EFB and HDPE via pyrolysis, compared to commercial HZSM-5 catalysts.

Heat-Treated Wood Reinforced High Density Polyethylene Composites

This study investigated the effect of untreated and heat-treated ash and black pine wood flour concentrations on the selected properties of high density polyethylene (HDPE) composites. HDPE and wood flour were used as thermoplastic matrix and filler, respectively. The blends of HDPE and wood fl our were compounded using single screw extruder and test samples were prepared through injection molding. Mechanical properties like tensile strength (TS), tensile modulus (TM), elongation at break (EatB), fl exural strength (FS), fl exural modulus (FM) and impact strength (IS) of manufactured composites were determined. Wood fl our concentrations have significantly increased density, FS, TM and FM and hardness of composites while reducing TS, EatB and IS. Heat-treated ash and black pine fl our reinforced HDPE composites had higher mechanical properties than untreated ones. Composites showed two main decomposition peaks; one coming from ash wood flour (353-370 °C) and black pine wood fl our (373-376 °C), the second one from HDPE degradation (469-490 °C). SEM images showed improved dispersion of heat-treated ash and black pine wood flour. The obtained results showed that both the untreated and heat-treated ash/black pine wood flour have an important potential in the manufacture of HDPE composites.

Catalytic pyrolysis of petroleum-based and biodegradable plastic waste to obtain high-value chemicals

The petroleum-based plastics, high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP), and the biodegradable plastic, polylactide (PLA) were processed by thermal and catalytic pyrolysis to investigate their suitability as feedstock for chemical recycling. The influence of pyrolysis temperature (400–600 °C) and catalyst (zeolite, spent FCC, and MgO catalyst) on the pyrolysis liquid composition and yield was studied. The studied petroleum-based plastics had similar decomposition temperature ranges but produced their highest pyrolysis yields at different temperatures. Pyrolysis liquids from thermal degradation of HDPE and LDPE consisted high yield of waxes but those of PP and PLA consisted of both waxes and liquid oil. Catalysts affected not only the pyrolysis yield, but also the proportions of liquid oil and wax in pyrolysis liquids. Alkenes, alkanes, and aromatics were the main compounds in the pyrolysis liquids. Spent FCC catalyst reduced the production of waxes and increased the production of gasoline-range hydrocarbons and aromatics. MgO catalyst led to high coke formation from polyolefins and PLA. Lactic acid, lactide and propanoic acid were examples of valuable chemicals recovered from the pyrolysis of PLA. Lactide was the main product (up to 79%) of catalytic pyrolysis with zeolite at 400 °C. Spent FCC catalyst produced mostly propanoic acid at 400 °C but at 600 °C, L-lactic acid became the most abundant compound.

The Role of the Reactive Species Involved in the Photocatalytic Degradation of HDPE Microplastics Using C,N-TiO2 Powders.

Microplastics (MPs) are distributed in a wide range of aquatic and terrestrial ecosystems throughout the planet. They are known to adsorb hazardous substances and can transfer them across the trophic web. To eliminate MPs pollution in an environmentally friendly process, we propose using a photocatalytic process that can easily be implemented in wastewater treatment plants (WWTPs). As photocatalysis involves the formation of reactive species such as holes (h+), electrons (e−), hydroxyl (OH●), and superoxide ion (O2●−) radicals, it is imperative to determine the role of those species in the degradation process to design an effective photocatalytic system. However, for MPs, this information is limited in the literature. Therefore, we present such reactive species’ role in the degradation of high-density polyethylene (HDPE) MPs using C,N-TiO2. Tert-butanol, isopropyl alcohol (IPA), Tiron, and Cu(NO3)2 were confirmed as adequate OH●, h+, O2●− and e− scavengers. These results revealed for the first time that the formation of free OH● through the pathways involving the photogenerated e− plays an essential role in the MPs’ degradation. Furthermore, the degradation behaviors observed when h+ and O2●− were removed from the reaction system suggest that these species can also perform the initiating step of degradation.

Structure and catalytic activity of highly ordered AlMCM-48 materials with different Si/Al ratios on the degradation of high-density polyethylene

Catalysts of AlMCM-48 with different Si/Al molar rations were synthesized by modified hydrothermal method with respect to previous works. As a consequence, the materials showed different porous structures making them of high adsorption capacities and high efficiency to high-density polyethylene (HDPE). Samples synthesized with various Si/Al molar ratios were characterized by X-ray diffraction (XRD), nitrogen adsorption at – 196 °C, scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR) and dispersive energy X-ray spectrometry (EDX). Characterization results suggested the presence of tetrahedral Al species on AlMCM-48(x), giving highly ordered materials that exhibit thermal stability. It is important to highlight that the use pseudoboehmite as a promising Al source for the synthesis of this type of molecular sieves, leading to materials with slight morphological differences due to the formation of interconnected particles spherical. The catalytic performance showed that the high-density polyethylene (HDPE) degradation reaction occurs in complex reaction steps in the heating rates 5, 10 and 20 °C min−1. The pore diameters of the catalysts influence the degradation process under non-isothermal condition. Furthermore, on the conditions studied, the AlMCM-48(x) catalysts exhibited high conversion values and play important roles in the decrease of HDPE degradation temperature, potentially leading to an efficient process in terms of energy expenditure.

Kinetic analysis of the degradation of HDPE+PP polymer mixtures

AbstractAn in depth understanding of the kinetics of the decomposition of plastic mixtures is necessary to enhance chemical recycling approaches, in particular by pyrolysis. The fact that plastic waste is usually composed of mixtures of plastics constitutes a hindrance for secondary recycling but may not be a particular difficulty for tertiary recycling. In this study, an analysis of the thermal degradation of mixtures of high‐density polyethylene (HDPE) and polypropylene (PP), in different proportions, was carried‐out under pyrolysis conditions using thermogravimetric analysis (TGA) under nonisothermal conditions, at different heating rates. Both isoconversional and model‐fitting approaches were used to estimate kinetic parameters from the experimental information. It was found that both the degradation of HDPE and PP, as well as their mixtures, can be described by a single‐step degradation process but that the degradation process is influenced by the proportion between the two plastics. The HDPE/PP mixtures in which PP has a higher ratio than HDPE cause the degradation onset temperature for the mixture to be lower than either pure PP or pure HDPE. Also, it was found that the apparent activation energy estimated was lower for these mixtures in comparison with the pure polymers. This implies that there are extensive interactions between the plastics during the degradation procedure and, from an operational point of view, it may be actually easier to degrade plastic mixtures than the corresponding pure streams, a conclusion that is important in the context of tertiary recycling of plastic mixtures. Furthermore, it was observed that a compensation effect exists that encompasses all the kinetic data for the mixtures, regardless of the composition, indicating that, although significant changes occur in relation to the activation energy, the underlying degradation mechanism remains the same.

Comparative Study of the Degradation of the Green HDPE and Petrochemical HDPE in the Primary Recycling

Primary polymer recycling involves the reprocessing of defective parts and scraps in a processing line. The critical limitation for excessive use of primary recycling consists of the need to maintain the properties of the polymer above the required minimum level. The polymer degradation during the extrusion occurs by the combination thermal, oxidative and mechanical degradation. This work investigated the degradation of HDPE (High Density Polyethylene). Green HDPE (PV) and petrochemical HDPE (PN) were processed five times in a single-screw extruder and the flow rate, crystallinity and impact strength properties were evaluated. The increase in the number of reprocessing cycles increased the flow index and crystallinity values. The increase in the degree of crystallinity of the polymer, verified by the DSC analysis, evidenced the degradation of the material associated to the decrease of the size of the main chain (chain scission mechanism). The impact strength showed no significant change after five reprocessing cycles. Contrary variations were found in the crystallinity index considering the first and fifth processing, suggesting a change in the predominant mechanism of degradation.

A thermogravimetric study of HDPE conversion under a reductive atmosphere

The plastic waste has suffered a dramatic increase and has become one of the biggest environmental problems nowadays. The chemical transformation of plastics by catalytic cracking under hydrogen atmosphere (hydrocracking) is one of the viable solutions to this problem since it can convert plastic residues into petrochemicals and fuels. In this work a thermogravimetric study of high-density polyethylene (HDPE) conversion under hydrogen atmosphere and in the presence of catalysts with different textural and chemical features is presented. The effect of distinct micro (H-ZSM-5, H-FER and H-MOR) and mesoporous (SBA-15 and MCM-41) catalysts is studied, both in terms of energy requirements and products distribution. Moreover, the effects of sample preparation method, catalyst amount, Si/Al ratio and incorporation of a metallic function (Ni and Pt) are also analyzed. The results show that when MCM-41 and SBA-15 mesoporous silicas are added to HDPE no significant changes are observed in terms of the degradation profile. On the contrary, the use of microporous materials decreases significantly the onset of HDPE degradation temperature. The accessibility and acidic content of the materials proved to be the most important factors influencing the HDPE degradation profiles. Moreover, the introduction of a metal function results in a further shift to lower degradation temperatures and favors the liquid products distribution, promoting the formation of gasoline and diesel.