Decomposition Of High-density Polyethylene Research Articles

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

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

Influence of alumina pH on properties of Fe2O3/Al2O3 catalyst for high-density polyethylene decomposition to H2 generation

Influence of alumina pH on properties of Fe2O3/Al2O3 catalyst for high-density polyethylene decomposition to H2 generation

Investigation on the co-pyrolysis of agricultural waste and high-density polyethylene using TG-FTIR and artificial neural network modelling

To realize utilization of agricultural and plastic waste to alleviate environmental pollution, the individual pyrolysis and co-pyrolysis characteristics of kidney beans stalk (KS) and high-density polyethylene (HDPE) were investigated. Thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) was used to investigate the pyrolysis behaviour, synergistic effect, kinetics and gaseous product evolution of different samples. In addition, an artificial neural network (ANN) model was established to predict the mass change with temperature during sample pyrolysis or co-pyrolysis. The results showed that the decomposition of HDPE was easier than that of KS, and synergistic and inhibitive effects occurred during co-pyrolysis. The synergistic or inhibitive effect was most significant from 470 to 510 ℃. The FTIR analysis results showed that gaseous products of KS pyrolysis were mainly oxygen-containing compounds including CO2, CO, ketones, aldehydes, esters, etc., while those of HDPE pyrolysis were mainly hydrocarbons including alkanes, alkenes, aromatic rings, etc. The co-pyrolysis of samples with different proportions promoted or inhibited the production of some gaseous products to different degrees. Moreover, the activation energy of the two stages during co-pyrolysis was lower than that of the pure sample. The established ANN model can effectively predict the mass loss of a sample with temperature.

Catalytic Pyrolysis of High-Density Polyethylene: Decomposition Efficiency and Kinetics

Organic waste is generally characterized by high volume-to-weight ratios, requiring implementation of waste minimization processes. In the present study, the decomposition of high-density polyethylene (HDPE), was studied under thermal and catalytic pyrolysis conditions on two experimental systems. Firstly, pyrolytic conditions for HDPE decomposition were optimized in a laboratory-scale batch reactor. In order to maximize gas yields and minimize secondary waste, the effects of aluminosilicate catalysts, catalyst loading, and reaction temperature on decomposition efficiency were examined. Secondly, kinetics and reaction temperatures were studied on a large capacity thermobalance, especially adjusted to perform experiments under pyrolytic conditions at a larger scale (up to 20 g). The addition of catalysts was shown to enhance polymer decomposition, demonstrated by higher gas conversions. Condensable yields could be further minimized by increasing the catalyst to polymer ratio from 0.1 to 0.2. The most prominent reduction in pyrolysis temperature was obtained over ZSM-5 catalysts with low Si/Al ratios; however, this impact was accompanied by a slower reaction rate. Of the zeolites tested, the ZSM-5 catalyst with a Si/Al of 25 was found to be the most efficient catalyst for waste minimization and organic destruction, leading to high gas conversions (~90 wt%.) and a 30-fold reduction in solid waste mass.

Co-pyrolysis of xylan and high-density polyethylene: Product distribution and synergistic effects

The thermal weight-loss characteristics and product distribution of the co-pyrolysis between xylan from corn cob (XC) and high-density polyethylene (HP) were investigated by thermogravimetry coupled with fourier transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS) and pyrolysis gas chromatography/mass spectroscopy (Py-GC/MS). Moreover, the synergistic effects in the co-pyrolysis process were explored. The co-pyrolysis of XC and HP occurs in two stages. The first stage (220–350 °C) was the decomposition of XC, and the second stage (440–525 °C) was mainly attributed to the decomposition of HP. Co-pyrolysis caused the blends to decompose more easily. The synergistic effect was confirmed during the co-pyrolysis process. The co-pyrolysis process promoted the release of hydrocarbons (CH4, C2H2, C2H6, C3H6, and C3H8) and aldehyde derivatives (CH3CHO and CHO+) and decreased the production of H2 and H2O. Moreover, co-pyrolysis suppressed the generation of CO2 only when the content of HP was 75%. The Py-GC/MS results showed that the yield of oxygen-containing compounds decreased, and the yield of alkenes and alkanes increased. The increase in alkenes was greatest when the ratio of XC to HP was 1:3. This phenomenon could be attributed to the release of hydrogen radicals from mono-molecular and bi-molecular dehydrogenation reactions during the decomposition of HP. Thus, HP could be a hydrogen donor, providing hydrogen for xylan-derived oxygenates, which served as acceptors. A reaction mechanism for the co-pyrolysis of XC and HP was also proposed.

TG-FTIR-MS study of synergistic effects during co-pyrolysis of corn stalk and high-density polyethylene (HDPE)

Co-pyrolysis corn stalk (CS) and high-density polyethylene (HDPE) is an effective method to mitigate environmental pollution and reuse the problematic plastic to produce valuable energy. The devolatilization kinetics and the evolution of gaseous species during co-pyrolysis were investigated via TG-FTIR-MS. Moreover, the possible interactions of CS and HDPE were explored. The co-pyrolysis process of CS-HDPE blends was found to be divided into two decomposition stages. The first stage (150–400 °C) was mainly associated with the decomposition of CS. The second stage (400–515 °C) was the result of combinations of the thermal degradations of CS and HDPE, with the degradation of HDPE contributing the most. Co-pyrolysis CS with HDPE could delay the decomposition of HDPE. In addition, the difference between experimental and theoretical weight loss (△W) was found to be less than zero when the percentage of CS was 80%. Furthermore, the average of the experimental activation energy was lower than that of the theoretical value for 80% CS. Thus, the positive synergy was strongest when the CS content was 80%, based on the thermal decomposition behavior and the activation energy. However, the blending ratio of CS-HDPE had little effect on the major categories of gaseous products during co-pyrolysis. Moreover, the interaction between CS and HDPE in the first stage (150–400 °C) could promote the release of H2, CO/C2H4 and C3H6 in the blends with 80%, 60%, and 60% CS, respectively. Additionally, aliphatic hydrocarbons (CH4, C2H6, C3H8, C4H10, C4H8, C2H2) and oxygen-containing compounds (aldehydes, alcohols, ketones, acids) were suppressed by the interaction when the percentage of CS was less than 60%. In the second stage (400–850 °C), the yields of aliphatic hydrocarbons (CH4, C2H6, C3H8, C4H10, C4H8, C2H2, C4H6) were inhibited, independent of the content of CS in the blends. In addition, the production of H2, CO/C2H4, and C3H6 was promoted when the percentage of CS was below 80%, 80%, and 60%, respectively.

Co-pyrolysis of biomass and plastic wastes: investigation of apparent kinetic parameters and stability of pyrolysis oils

This work is dedicated to the co-pyrolysis of real waste high density polyethylene (HDPE) and biomass (rice straw) obtained from agriculture. Mixtures of raw materials were pyrolyzed in their 0%/100%, 30%/70%, 50%/50%, 70%/30%, 100%/0% ratios using a thermograph. The atmosphere was nitrogen, and a constant heating rate was used. Based on weight loss and DTG curves, the apparent reaction kinetic parameters (e.g., activation energy) were calculated using first-order kinetic approach and Arrhenius equation. It was found that decomposition of pure plastic has approximately 280 kJ/mol activation energy, while that of was considerably less in case of biomass. Furthermore, HDPE decomposition takes by one stage, while that of biomass was three stages. The larger amount of raw materials (100 g) were also pyrolyzed in the batch rig at 550°C to obtain products for analysis focussing to their long-term application. Pyrolysis oils were investigated by Fourier transformed infrared spectroscopy and standardized methods, such as density, viscosity, boiling range determination. It was concluded, that higher plastic ratio in raw material had the advantageous effect to the pyrolysis oil long-term application. E.g., the concentration of oxygenated compounds, such as aldehydes, ketones, carboxylic acids or even phenol and its derivate could be significantly decreased, which had an advantageous effect to their corrosion property. Lower average molecular weight, viscosity, and density were measured as a function of plastic content.

Study of synergistic effects during co-pyrolysis of cellulose and high-density polyethylene at various ratios

The mechanism of synergistic effects occurred during co-pyrolysis of cellulose (CE) and high-density polyethylene (HDPE), mixed at various mass ratios (3:1, 1:1, 1:3 w/w), was studied by thermogravimetric analysis coupled with mass spectrometry (TG-MS) and pyrolysis-gas chromatography coupled with mass spectrometry (Py-GC/MS). The TG analysis showed that the co-pyrolysis process was divided into two-stages: the first stage was the decomposition of CE (at 260 °C–410 °C), and the second stage between 410 °C and 527 °C was mainly the decomposition of HDPE. The experimental mass loss values of the mixtures were greater than the estimated values, which confirmed a synergistic effect in the co-pyrolysis of CE and HDPE. The results of MS and Py-GC/MS indicated that the effects of co-pyrolysis promoted the release of small-molecule volatile (H2O, CO/C2H4, CO2), and the promotion effect was strongest when the ratio was 1:3. Hydrogen transfer from the scission of HDPE could be provided for the decomposition of CE, and the oxygen-containing compounds from CE could promote the chain scission and cracking of HDPE. When the CE/HDPE ratio was less than 1:1, the production of carbohydrate, aldehyde, ketone, and furan groups assigned to CE pyrolysis was suppressed, and the production of alkane and alkene groups was promoted. The decomposition pathways in the co-pyrolysis process of CE and HDPE were proposed.

Manufacturing and characterization of vine stem reinforced high density polyethylene composites

Abstract Vine stem is an agricultural side product and has limited economic value. Alternative uses of such agricultural powder into value-added products such as thermoplastic composites can provide remarkable environmental and economic benefits. Vine stem filler may be used as a potential reinforcement in polymeric materials. In this study, vine stem reinforced high density polyethylene (HDPE) composite materials were manufactured and characterized. Agricultural waste of vine stem was collected from Manisa region, Turkey. Vine stem was ground in a grinder and thereby turning into the powder form. Composites were obtained using twin screw extruder by adding different amounts of vine stem powder (5, 10 and 20% wt.) into HDPE. Mechanical, thermal, water absorption and crystallographic properties of waste vine stem reinforced HDPE composites were investigated. HDPE containing 10% waste vine stem exhibited the highest tensile strength and flexural strength. Vine stem powder addition into HDPE delayed the thermal decomposition of HDPE. DMA analyses showed that the storage modulus values of reinforced HDPE are higher than neat HDPE throughout the whole temperature scale.

Vacuum thermal decomposition of polyethylene containing antioxidant and hydrophilic/hydrophobic silica

Temperature-programmed desorption mass spectrometry has been used to study vacuum thermolysis of high-density polyethylene (HDPE) and its composites with hydrophilic or hydrophobic nanosilica in the presence or absence of butylated hydroxytoluene (BHT). It has been found that both surface chemistry of silica filler and the presence of immobilized BHT affect the pathway of HDPE thermal decomposition. Volatility of BHT antioxidant was shown to decrease in the following sequence: free BHT > HDPE–BHT > HDPE–hydrophobic silica/BHT > HDPE–hydrophilic silica/BHT, and the capability of the additives to inhibit chain scission reaction during thermal decomposition of HDPE in vacuum was as follows: hydrophobic silica/BHT > BHT > hydrophobic silica > hydrophilic silica/BHT > hydrophilic silica ≈ no additives.

Study on the co-pyrolysis of high density polyethylene and potato blends using thermogravimetric analyzer and tubular furnace

The interactions between high density polyethylene (HDPE) and potato during their primary and secondary co-pyrolysis process were investigated by a thermogravimetric analyzer (TGA) and a tubular furnace. Kinetic analysis has shown that the devolatilization of potato was relatively faster compared to those of cellulosic materials, which has been ascribed to the multi-side-chain structure and lower polymerization degree of starch. The pyrolysis process of potato can be divided into three stages, and the main thermal degradation took place between 178 and 378°C, while the HDPE decomposition occurred in a single stage in the temperature range of 380–517°C. In the case of blends, the weight loss differences (ΔW) between experimental and theoretical ones were less than ±8% in all cases, and the co-pyrolysis process of potato and HDPE can be described as two consecutive first order reactions, the apparent activation energies of blends were almost invariable, suggested that only physical step limitation was found in the primary co-pyrolysis process of potato and HDPE. On the contrary, the results of tubular furnace experiment showed that due to the relatively long gas resident time, the interaction occurred in the gas phase not only favored the formation of gaseous products, but also improved the bio-oil quality by significantly reducing the oxygen-to-carbon ratios (O/C) of the pyrolysis oil.

Textural changes in metallurgical coke prepared with polyethylene

The effect of high-density polyethylene (HDPE) on the textural features of experimental coke was investigated using polarized-light optical microscopy and wavelet-based image analysis. Metallurgical coke samples were prepared in a laboratory-scale furnace with 2.5%, 5.0%, 7.5%, 10.0%, and 12.5% HDPE by mass, and one sample was prepared by 100% coal. The amounts and distribution of textures (isotropic, mosaic and banded) and pores were obtained. The calculations reveal that the addition of HDPE results in a decrease of mosaic texture and an increase of isotropic texture. Ethylene formed from the decomposition of HDPE is considered as a probable reason for the texture modifications. The approach used in this study can be applied to indirect evaluation for the reactivity and strength of coke.

Experimental flash pyrolysis of high density polyethylene under hybrid propulsion conditions

The inert and oxidative flash pyrolysis of high density poly-ethylene (HDPE) is studied up to 20,000K/s, under pressure up to 3.0MPa and at temperature ranging from 1000K to 1500K. These conditions are considered to represent those waited onboard a hybrid rocket engine using HDPE as solid fuel. Recycling applications may also find some interest. The pyrolysis products are quantified by Gas Chromatograph, Flame Ionisation Detector and Mass Spectrometer to determine the effects of each physical parameter on the HDPE decomposition. The classical products distribution diene–alkene–alkane for each carbon atoms number is shown to be modified at such high temperature because of the pyrolysis of primary products. The pressure effect, which is generally neglected in HDPE pyrolysis studies found in open literature, is proved to be a major factor (up to one order of magnitude on the ethylene mass fraction). The heating rate presents noticeable consequences on the pyrolysis products distribution with a larger formation of light species while heavier ones are favoured under oxidative pyrolysis conditions. The experimental data should serve in the future to improve the accuracy of kinetic mechanisms for later use in numerical computing and to serve in related combustion studies for propulsive applications.

Performance and thermal behavior of wood plastic composite produced by nonmetals of pulverized waste printed circuit boards

A new kind of wood plastic composite (WPC) was produced by compounding nonmetals from waste printed circuit boards (PCBs), recycled high-density polyethylene (HDPE), wood flour and other additives. The blended granules were then extruded to profile WPC products by a conical counter-rotating twin-screw extruder. The results showed that the addition of nonmetals in WPC improved the flexural strength and tensile strength and reduced screw withdrawal strength. When the added content of nonmetals was 40%, the flexural strength of WPC was 23.4 MPa, tensile strength was 9.6 MPa, impact strength was 3.03 J/m 2 and screw withdrawal strength was 1755 N. Dimensional stability and fourier transform infrared spectroscopy (FTIR) of WPC panels were also investigated. Furthermore, thermogravimetric analysis showed that thermal degradation of WPC mainly included two steps. The first step was the decomposition of wood flour and nonmetals from 260 to 380 °C, and the second step was the decomposition of HDPE from 440 to 500 °C. The performance and thermal behavior of WPC produced by nonmetals from PCBs achieves the standard of WPC. It offers a novel method to treat nonmetals from PCBs.

Comparative study of the effect of different nanoparticles on the mechanical properties, permeability, and thermal degradation mechanism of HDPE

AbstractIn the present study, different series of high‐density polyethylene (HDPE) nanocomposites were prepared by melt mixing on a Haake‐Buchler Reomixer, containing 2.5 wt % of multiwall carbon nanotubes, pristine and modified montmorillonite, surface‐treated and ‐untreated SiO2 nanoparticles. From transmission electron micrographs, it was found that beyond a fine dispersion of nanoparticles into HDPE matrix, there are also some aggregates easily discriminated. As a result, there was a decrease in the tensile and impact strength of most of nanocomposites except Young's modulus, which was increased. Storage modulus as recorded from dynamic mechanical analysis was also increased in all nanocomposites, because HDPE becomes stiffer due to the incorporation of nanoparticles. The nucleation behavior of nanoparticles during crystallization was found to have no obvious effect on melting and crystallization temperature of HDPE. However, a small decrease in the heat of fusion in all nanocomposites was evidenced. Gas permeability of HDPE matrix in O2, N2, and CO2 was reduced in all nanocomposites compared with neat polymer. Thermal stability of HDPE was also enhanced due to the incorporation of different nanoparticles. From the kinetic analysis of thermal decomposition of HDPE, it was concluded that to describe the thermal degradation of HDPE and the studied nanocomposites, two consecutive mechanisms of nth‐order autocatalysis have to be considered. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synergetic pyrolysis of high density polyethylene and Jatropha and Karanj cakes: A thermogravimetric study

Coprocessing behavior of mixtures of high density polyethylene (HDPE) and deoiled cakes of Jatropha and Karanja was studied by thermogravimetric analyses under dynamic conditions in the presence of nitrogen atmosphere and compared with those of individual materials. Experiments were carried out in the temperature range of ambient temperature to 900 °C at two heating rates (5 and 20 °C/min). Kinetic studies indicated activation energies for HDPE decomposition to be 235 and 258 kJ/mol at heating rates of 5 and 20 °C/min, respectively. Values of activation energy for pyrolysis of cakes of Jatropha and Karanj and those for cake-HDPE mixtures varied with the rate of heating as well as with the three temperature ranges. This variation has been explained based on the materials’ decomposition behavior. Reduction in activation energy for decomposition of the mixtures implies synergetic effects to be existing when two materials are coprocessed together.

Thermal degradation mechanism of HDPE nanocomposites containing fumed silica nanoparticles

In the present study different series of high-density polyethylene (HDPE) nanocomposites, containing 0.5, 1, 2.5 and 5 wt.% of fumed silica (SiO 2) nanoparticles were prepared by melt-mixing on a Haake–Buchler Reomixer. From SEM micrographs it was found that even though there is a fine dispersion of nanoparticles into HDPE matrix there are also some aggregates formed and their size depends directly on the SiO 2 content. Tensile strength increases by increasing silica content up to 2.5 wt.% SiO 2, while at 5 wt.% a reduction was observed. Additionally, Young's modulus increases continuously while impact strength has the opposite trend and SiO 2 content has no monotonic effect on HDPE melting point. Thermal stability of HDPE was enhanced due to the incorporation of SiO 2 nanoparticles. From the kinetic analysis of thermal decomposition of HDPE and its nanocomposites, it was concluded that in order to describe the thermal degradation mechanism, two consecutive mechanisms of nth-order (Fn) and nth-order with autocatalysis (Cn) have to be considered. SiO 2 have no effect on decomposition mechanism but only to the activation energies, which in nanocomposites are higher, compared with neat HDPE, due to the stabilization effect of SiO 2 nanoparticles.

Kinetics of pyrolysis of high density polyethylene. Comparison of isothermal and dynamic experiments

An experimental study of the thermal decomposition of high density polyethylene in an inert atmosphere has been carried out. Both isothermal and dynamic experiments at different heating rates have been performed in a thermobalance. The objective of this work is to analyse the applicability of a simple first-order equation to the prediction of the weight loss of the material, taking into account the complex chain reaction mechanism. The corresponding kinetic parameters have been obtained and its applicability at different heating rates has been analysed. The isoconversion method of Ozawa–Flynn–Wall has been used to obtain the activation energy and the frequency factor from non-isothermal experiments and compare them with the values obtained from isothermal experiments and with the results obtained by other authors.

Effect of operating parameters on time to decomposition of high density polyethylene and chlorinated polyethylenes

An investigation was made to determine the influence of furnace temperature (500–800 °C), concentration of oxygen in the gas flow (0–100%, v v ) and sample mass (2–15 mg) on the decomposition time of several polymers. These were high density polyethylene and chlorinated polyethylenes (25, 36 and 42% by mass chlorine). Thermal oxidative degradation was undertaken in a Du Pont 951 thermogravimetric analyzer in the isothermal mode using a gas flow of 0.833 ml s −1, STP. The results indicated that the average sample heating rate influenced the decomposition time most. Operating at higher furnace temperature (⩾ 700°C) and using a small sample mass (⩽ 2.5 mg) reduced the variance in t d. The activation energy for decomposition of the polymers was 39.3 ± 0.5 kJ mol −1.