Thermal Degradation Of Polyethylene Research Articles

Conversion of Polyethylene to Low-Molecular-Weight Oil Products at Moderate Temperatures Using Nickel/Zeolite Nanocatalysts.

Polyethylene (PE) is the most widely used plastic, known for its high mechanical strength and affordability, rendering it responsible for ~70% of packaging waste and contributing to microplastic pollution. The cleavage of the carbon chain can induce the conversion of PE wastes into low-molecular-weight hydrocarbons, such as petroleum oils, waxes, and natural gases, but the thermal degradation of PE is challenging and requires high temperatures exceeding 400 °C due to its lack of specific chemical groups. Herein, we prepare metal/zeolite nanocatalysts by incorporating small-sized nickel nanoparticles into zeolite to lower the degradation temperature of PE. With the use of nanocatalysts, the degradation temperature can be lowered to 350 °C under hydrogen conditions, compared to the 400 °C required for non-catalytic pyrolysis. The metal components of the catalysts facilitate hydrogen adsorption, while the zeolite components stabilize the intermediate radicals or carbocations formed during the degradation process. The successful pyrolysis of PE at low temperatures yields valuable low-molecular-weight oil products, offering a promising pathway for the upcycling of PE into higher value-added products.

A modification to the Friedman and Ortega isoconversional methods for evaluation of the activation energy as a function of conversion and temperature

The Friedman and Ortega isoconversional methods typically apply linear regression to the isoconversional kinetic data for calculation of activation energy solely as a function of extent of conversion. However, in complex reactions, activation energy depends on both conversion and temperature. Our modification involves quadratic curve fitting instead of linear regression, resulting in the determination of activation energy as a function of conversion and temperature. The new technique enables the calculation of the temperature dependence of activation energy for different heating rates, making it a valuable addition to isoconversional analysis. The conventional and modified approaches were utilized on the isoconversional kinetic data concerning polyethylene thermal degradation. The results provided a more detailed representation of the variations in activation energy when nonlinear regression was used.

SULFONYL CHLORIDES - NOVEL SOURCE OF FREE RADICALS

Novel free radicals source based on sulfonyl chlorides is discovered. The radical mechanism is confirmed by 2,3-dimethyl-2,3-diphenylbutane formation under chlorosulfonated polyethylene heating in the isopropylbenzene solution. Concerted homolytic C-S and S-Cl bond scission of chlorosulfonated polyethylene thermal degradation mechanism proved by kinetic analysis. The proof of the two bonds simultaneous breaking is provided by the threefold activation energy reduction (83 kJ/mol) in comparison to the C-S and C-Cl bond dissociation energy (280 and 286 kJ/mol respectively), the 6 orders lower preexponential factor (2,46 ∙ 10 s) in Arrhenius equation in comparison to one bond cleavage (≈10-10 s) as well as the strongly negative activation entropy value (-134 J/mol∙K).

Thermal degradation of polyethylene in the presence of a non-acidic porous solid by a continuous flow reactor

Thermal degradation of polyethylene (PE) in the presence of a non-acidic porous solid (silicalite) was performed under atmospheric pressure in a continuous flow reactor, at 420 °C and feeding rate of 0–1.5 kg h−1. Conducting pyrolysis at steady state allowed observations on the behavior of polymers during thermal degradation. Based on collected information about reaction rates and the composition of pyrolysis products as well as of reactor content we could distinguish between the random and the chain-end scissions of polymer macromolecules and we showed that porous silicalite favored the later ones. Although silicalite had no acid reactive centers, it influenced the equilibrium attained at steady state and changed the composition of pyrolysis products. As a result, the rate of double bonds formation strongly increased with the silicalite amount; however the mass rate of pyrolysis was not significantly affected. The macroscopic mechanism for the thermal degradation of polymer explained why the amount of silicalite does not contribute to the improvement of the mass rate of volatilization.

Influence of ionic liquids on mechanical and thermal properties of polyethylene from renewable resources

Polyethylene from renewable resources produced using sugarcane as raw material was modified with phosphonium ionic liquids. Tensile properties and thermal behavior of modified biopolyethylene in air and nitrogen atmosphere were studied. The thermal degradation of ionic liquids and their influence on thermal degradation of polyethylene from renewable resources were studied by thermogravimetric analysis (TGA). In general, modification of biopolyethylene with phosphonium ionic liquids resulted in improvement of tensile properties, i.e., tensile strength and Young’s modulus. Thermal degradation of biopolyethylene modified with phosphonium ILs proceeds in one step in the range of 400–500 °C in nitrogen atmosphere. Modification of polyethylene with trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate ionic liquid resulted in increase in DTGpeaks and T10% temperatures toward higher temperature for modified polyethylene in comparison with unfilled PE sample both in air and nitrogen atmosphere.

Degradation of fundamental polymers/plastics used in daily life: a review

Polymers are made from the monomers that are used for packaging purposes. The degradation of polymers can take place either abiotic or biotic pathways. Abiotic pathway occurs from thermal, photo-degradation, and catalytic methods whereas, biotic occurs in presence of different types of microorganisms. The degradation of polymers (polyethylene and polylactic acid) was explained by the thermal, catalytic, and biodegradation process. The thermal degradation of polyethylene and polylactic acid was explained by the thermogravimetric analysis (TGA) curve. Catalysts such as zeolites and amorphous silica-alumina are used for the degradation of polyethylene whereas, tin for polylactic acid. Microorganisms such as bacteria, fungus, and actinomycetes help for the degradation of polyethylene and polylactic acid.
 BIBECHANA 18 (2021) 240-253

Modeling the Rate of Batch-Mode Thermal Degradation of Polyethylene Suspended in an Oven

This study presents dynamic modeling of the thermal degradation of polyethylene (PE) in an oxidizing atmosphere. The purpose of the work is to calculate the degradation rate of samples placed in a macro-thermobalance. The model is composed of two coupled sub-models: the first one describes the processes occurring in the condensed phase (where termal degradation of PE in lighter molecule occurs) while the second one accounts for the processes occurring in the gaseous phase. The condensed phase model allows for the evaluation of the rate at which combustible gas is produced by PE pyrolysis and the gas phase model computes the gaseous oxidation of the products of pyrolyse and subsequent heat flux transferred back to the sample. This second model relies on the use CFD (Ansys Fluent) where turbulent combustion of octane (which is supposed to be the product of PE Pyrolysis) is accounted for thanks to eddy dissipation approximation. The effect of the filling height in the sample crucible containing the polyethylene is studied. The experimental results from macro TGA (MTGA) and from the mathematical model are compared. Three different behaviors associated to crucible filling height are highlighted. For small ones, kinetics of pyrolysis is the overall limiting phenomenon, whereas heat transfer to the sample is the limiting one for high filling heights. Both experimental and numerical findings show that the position of the flame in the vincity of the crucible (inside or outside and surrounding it) is the key parameter in polyethylene’s degradation rate.

Polyethylene high-pressure pyrolysis: Better product distribution and process mechanism analysis

Pyrolysis is currently an effective way to recycle plastics. High-pressure conditions can change the pyrolysis product component distribution, but the microscopic mechanism has not been well elucidated. To explore the relationship of product distribution versus pressure and explain the microscopic mechanism of polyethylene high-pressure pyrolysis, experiments under a large initial pressure range from 1 bar to 51 bar at initial temperatures of 330–380 °C were carried out in an autoclave. In the process of polyethylene high-pressure pyrolysis, the temperature within the reactor exceeded the set temperature by 100 °C at a rate of 150 °C/min. The thermal runaway phenomenon was caused by the polymerization of concentrated olefins in liquid form, which was initiated by hydrocarbon radicals. As the pressure increased, the reaction peak temperature was risen and more small molecules were produced. Under an initial temperature of 340 °C and high-pressure conditions, polyethylene was completely converted into liquid and gas products. The experimental results also revealed that high-pressure conditions led to the production of aromatic compounds and isoparaffins, as well as more cycloalkanes and fewer olefins in the liquid product, making the product characteristics closer to the fuel standard. Finally, this paper proposes the radical microscopic mechanisms of polyethylene thermal degradation under atmospheric-pressure and high-pressure conditions.

Influence of the Chemical Nature and Structural Characteristics of Nanofillers on the Mechanism of Polyethylene Pyrolysis

The influence of different types of nanofillers on the mechanism of polyethylene thermal degradation is studied. The composition of the products of pyrolysis of composite material was evaluated using gas chromatography–mass spectrometry (GC–MS). It has been found that incorporating carbon nanofillers (carbon nanotubes, graphite nanoplates, and reduced graphite oxide) into polyethylene leads to increase in the fraction of heavy hydrocarbons of the pyrolysis products. The varying influence of carbon fillers on the pyrolysis process is explained in terms of the surface defectiveness of the fillers and their specific effect on the segmental mobility of the polyethylene macroradicals within the framework of the previously proposed theory. The use of montmorillonite-layered silicate as a filler leads to a qualitative change in the composition of pyrolysis products, which is caused by the presence of catalytic acid sites and the ionic character of the polyethylene thermal degradation mechanism.

The combustion of polyolefins in inert and catalytic fluidised beds

Abstract The thermal degradation of polyethylene and polypropylene were performed in three types of fluidised bed consisting of sand, inert hollow microspheres (cenospheres) with a density of 3 , or the same cenospheres covered with Fe 2 O 3 . For the first time, the cenospheres were proposed as material of fluidised bed that allowed the immersion of polymeric material. With regard to combustion, this is organised inside a fluidised bed reactor consisting of sand as the bed material; the combustion of polyolefins occurs in the freeboard with considerable soot formation. Based on acoustic and video analyses, it was proven that the combustion of polyolefins in the cenospheric fluidised bed reactor occurs inside the fluidised bed. It takes the form of explosions in the bubbles or takes place in the emulsion phase. In the cenospheric fluidised bed, a 97–99% yield of polyolefin conversion can be achieved at 800 °C. Catalytic combustion in the fluidised bed reactor was also proposed, for this, catalytic bed material was prepared by chemical Fe 2 O 3 deposition on the cenospheres. As precursor Fe(CO) 5 was used. As a consequence of changing the non-catalytic fluidised bed into a catalytic bed, conversion to CO 2 increased from 57-59% to 80–85% at temperatures as low as 500 °C. Furthermore, at 800 o C–900 °C, the CO 2 yield increased from 97-99% to 98–99%, these small differences caused the CO concentration in the catalytic process to be 2–4 times lower than in the case of the process conducted in the inert fluidised bed. The use of a catalytic bed led to the complete elimination of explosions, thus it is safer and also leads to lower NO X emissions. Based on experimental data, NOx concentration did not exceed 6 mg in a cubic metre of dry exhaust gases containing 11% vol. O 2 at all tested temperatures (500–900 °C).

Improved thermal stability of polyethylene with rare earth trifluoromethanesulfonate

Abstract The thermal degradation of polyethylene (PE) is a free radical chain reaction, in other words, free radicals are the primary cause of combustion and degradation. Discovering proper compounds with radical trapping ability is critical for developing flame retardant PE composites. Herein, we introduced rare earth trifluoromethanesulfonate (RE(OTf) 3 ), with radical trapping ability, into PE. The effects of ytterbium (Yb(OTf) 3 ) and lanthanum (La(OTf) 3 ) on the thermal stability and flammability properties of polyethylene (PE) were investigated systemically. Electron spin resonance (ESR) spectroscopy proved the free radical-trapping ability of La(OTf) 3 and Yb(OTf)3 . The results of thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) showed that Yb(OTf) 3 could improve the thermal stability of PE more significantly compared with La(OTf)3. The flame retardancy of PE/intumescent flame retardant (IFR) composite was improved when 0.4 wt% IFR was substituted by RE(OTf)3. It changed the PE/IFR26 from UL-94 non-rated to V-0. Vertical flame test, limited oxygen index (LOI) and microscale combustion calorimeter (MCC) indicated that the effect of Yb(OTf)3 on the flame retardancy of PE was better than La(OTf)3. The improvement on the thermal stability and flame retardancy of PE is due to the combined action of anion and cation of RE(OTf)3. However, the different effects are attributed to the different reactivity of rare earth elements.

Molecular and Kinetic Models for High-Rate Thermal Degradation of Polyethylene.

Thermal degradation of polyethylene is studied under the extremely high rate temperature ramps expected in laser-driven and X-ray ablation experiments-from 1010 to 1014 K/s in isochoric, condensed phases. The molecular evolution and macroscopic state variables are extracted as a function of density from reactive molecular dynamics simulations using the ReaxFF potential. The enthalpy, dissociation onset temperature, bond evolution, and observed cross-linking are shown to be rate dependent. These results are used to parametrize a kinetic rate model for the decomposition and coalescence of hydrocarbons as a function of temperature, temperature ramp rate, and density. The results are contrasted to first-order random-scission macrokinetic models often assumed for pyrolysis of linear polyethylene under ambient conditions.

Spray process to styrene grafting onto polyethylene film surface for paintability enhancement

Abstract A direct and fast post-processing method to modify polyethylene (PE) film surface is proposed in order to improve its paintability performance without changing its bulk properties. This goal is achieved by grafting styrene onto the PE film surface using a macrocarbocationic copolymerization reaction where both catalysts and reagents are sprayed directly on softened film respectively. Pure styrene as grafting molecule and aluminium chloride suspended in n-heptane as catalyst are used. Grafting reaction occurrence was assessed by analyzing the reacted film surface before and after extraction of non-grafted reaction products. The results confirmed by three independent analytical techniques evidence reaction occurrence. A graft-copolymer layer remains onto the PE film surface even when physically adhered reaction products were extracted. This layer enhances PE film water-affinity and paintability either with water or acrylics paints because of the grafted aromatic group and roughness increase. Besides, this modification increments PE thermal degradation temperature giving another beneficial effect for future film applications. The proposed modification film methodology has potential application in continuous film production as reagents spraying onto softened films could be applicable in a cast film extrusion line.

Autocatalysis in thermal decomposition of polymers

Possibility of replicating polymer decomposition by a single global reaction greatly simplifies pyrolysis modeling. Apparent kinetic parameters are normally derived from the microscale experiments with linear heating program, and the n-th order reaction is routinely assumed thereby strongly affecting the numerical values of the kinetic parameters. In this work, we demonstrate inconsistency of the n-th order reaction assumption and reveal the autocatalytic behavior in thermal degradation of polyethylene, polystyrene and polycarbonate. The autocatalysis manifests itself in non-monotonicity of the conversion function, which markedly increases in a wide range of conversions. Although the iso-conversional approach makes it possible to explicitly recover the conversion function from the measurements, this option has not been used in most of the previous studies. Meanwhile, proper approximation of the experimentally derived conversion function results in excellent replication of the measured reaction rates, with the same kinetic parameters, in a range of the heating rates. Thus developed thermal decomposition kinetic models are provided in this paper for three kinds of polyethylene (LDPE, HDPE, and UHMWPE), seven kinds of polystyrene, polycarbonate, and two kinds of polymethylmethacrylate with different molecular weights. Although the pyrolysis of the polymers with different molecular weights proceeds differently, no systematic correlation of the pyrolysis characteristics (conversion-averaged apparent activation energy, heat of combustion, peak reaction rates and temperatures etc.) with the molecular weight has been observed for polystyrene. Peak reaction rates and temperatures varied in opposite directions for polyethylene and polymethylmethacrylate.

Chromatographic study of the recovered gases from hydropyrolytic de-polymerization of LDPE, MDPE and HDPE mix type of waste polyethylene

The thirst of energy is one of the biggest challenges the world is facing today. The search for new alternative and renewable source of energy is being studied worldwide. The emission of harmful gases such as NO x , SO x , CO and CO2 and other greenhouse gases in the environment contributes to the global warming and also causes health related problems. Polyethylenes are substances which take longer time for its decomposition and are one of the biggest threats to the environment. The waste polyethylene was thermally de-polymerized and during such process the gases recovered were studied. The study was carried out on low-medium and high-density polyethylene mix. The study of the waste polyethylene into useful hydrocarbon products provides scope for further investigation on this field for the production of domestic fuel. The comparisons of the recovered gases with the LPG gas components were also studied and there fuel property is discussed. This paper describes the gaseous hydrocarbon components recovered during the process of thermal degradation of polyethylene. The component recovered and their importance as fuel is also studied.

Comparative effect of metal stearates as pro-oxidant additives on bacterial biodegradation of thermal- and photo-degraded low density polyethylene mulching films

The effect of Iron, Cobalt and Manganese stearates are examined on the post-bacterial photochemical and thermal degradation of polyethylene (LDPE). The activity of stearates has been evaluated by ATR-FTIR, chemiluminescence and GPC of polyethylenes. A significant increase in carbonyl index for PE containing stearates was determined by FTIR together with a marked decrease in molecular weight as measured by GPC. All three metal stearates induced the development of drastic photo- and thermal-degradation processes for polyethylenes containing metal stearates except in the case of LDPE-Fe film which did not exhibit any significant thermocatalytic effect on degradation.In a second post bacterial study step, a mixture of three Bacillus MIX (Bacillus cereus, Bacillus megaterium and Bacillus subtilis) as well as Brevibacillus borstelensis were tested for biodegradation (90 days at 45 °C) of the highly photo- and thermo-degraded polyethylene films. Biodegraded materials were characterized using different techniques and mineralization was evaluated by carbon dioxide measurement using an indirect impedance technique. The biodegradation of degraded LDPE films by B. borstelensis and the mixture of Bacillus MIX was highly effective following the order LDPE-Co > LDPE-Mn > LDPE-Fe and in the range of 9.0–59.2% of mineralization after only 90 days of bacterial bioassay at 45 °C. The approach studied in this work showed much higher degradable efficacy than that already reported in the literature.

High-density polyethylene thermal degradation and gaseous compound evolution in a cone calorimeter

In this paper, the thermal degradation of pure high-density polyethylene (HDPE) has been studied in a cone calorimeter (CC) under well-ventilated conditions with a piloted ignition. Ten CC irradiance levels (from 15 to 80kWm−2) have been applied to HDPE sample to characterize their influence on the thermal degradation parameters (ignition time (tig), critical heat flux (CHF), mass loss rate (MLR) and specific mass loss rate (SMLR)) as well as on the concentrations of exhaust gases emitted during the combustion process. During our experiments, gaseous compound mole fractions have been quantified simultaneously by a Fourier transformed infrared (FTIR) spectrometer and another gas analyzer. Thus, several main species (CO, CO2, H2O, NOx, lightweight hydrocarbons and O2) with concentrations and emission yields of high or non-negligible consistency have been encountered, regardless of the external heat flux considered. Furthermore, using the oxygen consumption method, heat release rate (HRR), total heat release (THR) and effective heat of combustion (EHC) have been calculated for each irradiance level. Therefore, these different results (thermal properties, emission yields, HRR, THR and EHC) are in quite good accordance (same order of magnitude) with those found in previous studies.

Degradation of Polyethylene Film Samples Containing Oxo-Degradable Additives

The introduction of the so called oxo-biodegradable additives in the Argentine market motivated the assessment of the effects of abiotic and biotic factors on the structure and mechanical behavior of polyethylene (PE) with oxo-degradable additives (PE+AD). Samples of oxo-degradable packaging films found in local shops together with polyethylene films with and without d2ẅ additive were annealed at different temperatures between 50 and 110¼C and submitted to ultraviolet radiation at different irradiances (0,35; 0,45; 0,89 and 1,20W/m2). Furthermore, aged oxo-degradable films were set in a controlled compost bioreactor in order to evaluate their biodegradation ability. Experimental results showed that elongation at break was the mechanical property more sensitive to the polymeric degradation. The structural changes determined by FT-IR remarked the importance of the UV degradation time over the irradiation rate; the carbonyl index of the degraded samples pointed out that chain scission was a thermally activated process. Regarding degradation due to UV radiation, at the same dose, the elongation at break is lower at lower irradiance both in PE and PE+AD samples. On the other hand, thermal degradation of PE without additive is more susceptible to degradation than PE + AD. At the beginning of the biodegradation tests, PE + AD showed a higher CO2 production rate with respect to PE; however, this rate reduced along the first 30 days, reaching the CO2 production of PE without additive. The maximum biodegradation observed for both PE and PE+AD samples was 24% after 90 days of incubation.

Influence of copper chloride for the formation of aromatic compounds during polyethylene pyrolysis

Infrared image furnace ion-attachment mass spectrometry (IIF-IAMS) experiments have been conducted to elucidate the effects of copper(II) chloride on the formation of aromatic compounds during the pyrolysis of polyethylene. Under the time-resolved pyrolysis conditions of IIF-IAMS, the effects of CuCl 2 were measured to compare the variation in ratios of alkenes and aromatics during polyethylene thermal degradation when pyrolysis temperature was increased. Thermogravimetry experiments and X-ray powder diffraction analysis conducted under similar conditions to those used for IIF-IAMS enabled us to characterize the oxidation states of copper prevailing during the thermal degradation process of polyethylene in the presence of CuCl 2. Reduction of Cu(II) into Cu(I) during the pyrolysis process was characterized. The IIF-IAMS method demonstrates its advantage for on-line detection of reaction products during time-resolved pyrolysis experiments.

Thermal degradation of polyethylene into fuel oil over silica–alumina by a continuous flow reactor

A continuous flow reactor was operated at 420 °C and feed rate of 0–1.5 kg h −1 for catalytic degradation of polyethylene (PE) over SA-1 silica–alumina in order to investigate the effect of catalyst on the reaction rate and the quantity and quality of degradation products. SA-1 was either mixed with the PE inside reactor or placed in a catalyst cage, the efficiency being slightly higher in the first case. The catalyst did not have a significant effect on the reaction rates but the volatile products clearly had lower molecular weights. More gases were produced on SA-1 compared to thermal degradation, containing higher amounts of C 4 and less amounts of C 2 compounds.