Degradation Of High Density Polyethylene Research Articles

Analysis of surface degradation of high density polyethylene (HDPE) insulation material due to tracking

In the present work, tracking phenomena has been studied with HDPE material under a.c. voltage, with ammonium chloride as the contaminant. It is noticed that the tracking time depends on the conductivity and flow rate of the contaminant. The diffusion coefficient of the material was obtained. The thermal and chemical stability of the material were identified by carrying out a methodical experimental study. The physico-chemical analyses viz. wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), were carried out and it was concluded that the mechanism of tracking process is due to the surface degradation. The surface condition of the insulation structure was characterized for any surface discharges or tracking, using the leakage current measurement, utilizing the wavelet concepts.

Liquid-phase catalytic degradation of mixtures of waste high-density polyethylene and polystyrene over spent FCC catalyst. Effect of mixing proportions of reactants

The catalytic degradation of waste high-density polyethylene (HDPE) and polystyrene (PS) mixtures with a different mixing proportions over spent FCC catalyst has been studied using a stirred semi-batch reactor at 400 °C. The cumulative amount distribution, the degradation rate into liquid products, the carbon number distribution, and the paraffin, olefin, naphthene and aromatic (PONA) distribution in the liquid product were determined as a function of time or mixing proportion of reactants. The cumulative amount distribution of liquid product depended on the mixing proportion of both HDPE and PS. The degradation rate in the range of initial lapsed time (initial degradation rate) increased exponentially with PS content whereas that for the range of final lapsed time (final degradation rate) increased slowly with HDPE content. An increase of PS content in the reactants showed an increase of gasoline fraction, from about 85 wt.% (0 wt.% PS content) to about 98 wt.% (100 wt.% PS content). Liquid PONA product distributions revealed the interaction of the degraded intermediates from HDPE and PS degradation. The addition of PS to the catalytic degradation of HDPE accelerated the production of aromatic components with mono-cyclic species in liquid products and moreover showed the highest selectivity of above 60 wt.% for ethylbenzene and styrene (C 2 benzene) in aromatic products

Mechanochemical degradation kinetics of high-density polyethylene melt and its mechanism in the presence of ultrasonic irradiation

In this paper, the effect of ultrasonic intensity on the degradation of high-density polyethylene (HDPE) melt, degradation mechanism, ultrasonic degradation kinetics of HDPE melt as well as the development of molecular weight distribution of HDPE melt during ultrasonic degradation were studied. In the initial stage, the ultrasonic degradation of HDPE melt shows a random scission process, and the molecular weight distribution broadens. After that, the ultrasonic degradation of HDPE melt shows a nonrandom scission process, and the molecular weight distribution of HDPE melt narrows with ultrasonic irradiation time. The average molecular weight of HDPE decreases with the increase of ultrasonic intensity and increases and trends forward that of undegraded HDPE with the increase of distance from ultrasonic probe tip, indicating that attenuation of ultrasonic intensity in HDPE melt is very quick. Ultrasonic degradation kinetics of HDPE melt obeys the equation: M t = M ∞+ Ae − kt . The theoretic calculation by this equation accords well with the experimental results. The plausible ultrasonic degradation mechanism of polymer melt based on molecular relaxation was also proposed in this paper.

Mineral filler influence on the photo-oxidation mechanism degradation of high density polyethylene. Part II: natural exposure test

Weathering tests were carried out on high-density polyethylene (HDPE) HDPE–CaCO3 composites exposed to tropical humid climate of Yucatan peninsula of Mexico, in two different environments: a rural–urban (RU) and marine–coastal (MC) one. The samples were analyzed for changes of physical and chemical properties, with respect to their thermal behavior, infrared absorption and molecular weight. Data obtained in this study, by means of FT-IR, DSC, and viscometry techniques, show that the actual weathering process can be extremely complex, involving a number of weathering factors acting together and resulting in other process interactions within or on the material. Despite the differences between RU and MC temperature–relative humidity daily values, the environmental temperature seems to be the key factor that impacts the rate of aging more than the ambient humidity. The presence of the mineral filler CaCO3 influences the HDPE degradation mechanism, whereas the environmental conditions only modify the rate of polymer degradation.

Mechanical, thermal and microstructure evaluation of HDPE after weathering in Rio de Janeiro City

The weathering of high-density polyethylene (HDPE) specimens, with and without additives, submitted to natural atmosphere of Rio de Janeiro City, was studied and mechanical, thermal and structural changes were evaluated. The results indicated an impressive environmental oxidative degradation of non-stabilized HDPE. The impact resistance showed an abrupt drop up to 2520 h of aging and continued to decrease slowly after this time. The elongation at break also presented a pronounced drop and after 2520 h of exposure the value was close to zero revealing the loss of ductility up to this exposure time. We also observed a progressive increase in Young's modulus. The reduction of molecular weight and to some extent the increase of crystallinity were the main factors which caused the changes in properties. The microstructural FT-IR absorptions at 888, 909–991, 964, 1715–1740 cm −1 were detected and compared using a reference band (1368 cm −1). For non-stabilized HDPE, all these absorbances showed a progressive increase and after 3000 h of exposure, we observed an abrupt increase which could represent an auto-acceleration process of reaction of the photo-oxidation. The properties of stabilized HDPE remained practically constant at the same exposure time, revealing the effectiveness of the additives present in this sample.

Investigation of catalytic degradation of high-density polyethylene by hydrocarbon group type analysis

Catalytic degradation of waste high-density polyethylene (HDPE) to hydrocarbons by ZSM-5, zeolite-Y, mordenite and amorphous silica–alumina were carried out in a batch reactor to investigate the cracking efficiency of catalysts by analyzing the oily products including paraffins, olefins, naphthenes and aromatics with gas chromatography/mass spectrometry (GC/MS). Catalytic degradation of HDPE with zeolite-Y, mordenite and amorphous silica–alumina yielded 71–82 wt.% oil fraction, which mostly consisted of C 6–C 12 hydrocarbons, whereas ZSM-5 yielded much lower 35% oil fraction, which mostly consisted of C 6–C 12 hydrocarbons. Both all zeolites and silica–alumina increased olefin content in oil products, and ZSM-5 and zeolite-Y particularly enhanced the formation of aromatics and branched hydrocarbons. ZSM-5 among zeolites showed the greatest catalytic activity on cracking waste HDPE to light hydrocarbons, whereas mordenite produced the greatest amount of coke. Amorphous silica–alumina also showed a great activity on cracking HDPE to lighter olefins in high yield, but no activity on aromatic formation.

Catalytic degradation of polyethylene over SAPO-37 molecular sieve

The degradation of high-density polyethylene (HDPE) was studied alone and in presence of silicoaluminophosphate type silicoaluminophosphate (SAPO-37) as catalyst. This material was synthesized by the hydrothermal method using tetrapropylammonium hydroxide and tetramethylammonium chloride as organic templates. The characterization by X-ray diffraction, infrared spectroscopy, thermogravimetry and scanning electron microscopy showed that typical faujasite structure for the SAPO-37 was obtained. The total acidity, determined by n-butylamine adsorption, it was equivalent to 0.558mmolg−1, corresponding to moderate acid strength. For catalytic reaction, a physical mixture of 25%SAPO-37/HDPE was decomposed in a thermobalance at heating rates of 5, 10 and 20°Cmin−1, from 380 to 520°C. At the maximum degradation rate, the products were collected in a cold trap and analyzed by a coupled gas chromatograph/mass spectrometer. The degradation of HDPE without catalyst was carried out at the same conditions for comparison with the obtained data with SAPO-37. The HDPE alone suffers decomposition to a wide range of hydrocarbons (C5–C25) while in the presence of catalyst, light hydrocarbons (C2–C12) were obtained. By the application of the Vyazovkin model-free kinetic method, it was observed that the activation energy decreased from 290kJmol−1 for HDPE alone, to 220kJmol−1 for 25%SAPO-37/HDPE, evidencing that SAPO-37 is an effective catalyst for polyethylene degradation.

Polymer waste recycling over “used” catalysts

Catalytic degradation of high-density polyethylene (HDPE) was carried out under nitrogen using a laboratory fluidised bed reactor operating at 360°C with catalyst to polymer feed ratio of 2:1 and at 450°C with catalyst to polymer feed ratio of 6:1 under atmospheric pressure. The catalysts used in this study were ZSM-5, US-Y, ASA, fresh FCC (fluid catalytic cracking) commercial catalyst (Cat-A) and equilibrium FCC catalysts with different levels of metal poisoning were studied. The initial results for polymer degradation at 360°C (catalyst to polymer ratio of 2:1) in a fluidised bed reactor in terms of the yield of volatile hydrocarbon products were: model catalysts>commercial FCC catalyst>E-Cats. However, when the process conditions more closely resembled to FCC conditions, the fresh commercial FCC catalyst was more favourable in terms of the yield of volatile hydrocarbon products. The degradation of HDPE over E-Cats although reduced was similar to ASA in product selectivity and yield, and the level of metal contamination did not affect the product stream generated. A simple economic evaluation of polymer recycling process is reported showing that a catalytic system based on E-Cats appears comparable in costs to a commercial thermal cracking plant.

Friction and wear of hydroxyapatite reinforced high density polyethylene against the stainless steel counterface.

Hydroxyapatite (HA) reinforced high density polyethylene (HDPE) was invented as a biomaterial for skeletal applications. In this investigation, tribological properties (e.g. wear rate and coefficient of friction) of unfilled HDPE and HA/HDPE composites were evaluated against the duplex stainless steel in dry and lubricated conditions, with distilled water or aqueous solutions of proteins (egg albumen or glucose) being lubricants. Wear tests were conducted in a custom-built test rig for HDPE and HA/HDPE containing up to 40 vol % of HA. It was found that HA/HDPE composites had lower coefficients of friction than unfilled HDPE under certain conditions. HA/HDPE also exhibited less severe fatigue failure marks than HDPE. The degradation and fatigue failure of HDPE due to the presence of proteins were severe for low speed wear testing (100 rpm) as compared to high speed wear testing (200 rpm). This was due possibly to the high shear rate at the contact which could remove any degraded film instantaneously at high sliding speed, while with a low sliding speed the build-up of a degraded layer of protein could occur. The degraded protein layer would stay at the contact for a longer time and mechanical activation would induce adverse reactions, weakening the surface layer of HDPE. Both egg albumen and glucose were found to be corrosive to steel and adversely reactive for HDPE and HA/HDPE composites. The wear modes observed were similar to that of ultra-high molecular weight polyethylene. Specimens tested with egg albumen also displayed higher wear rates, which was again attributed to corrosion accelerated wear.

A kinetic approach to the temperature-programmed pyrolysis of low- and high-density polyethylene in a fixed bed reactor: determination of kinetic parameters for the evolution of n-paraffins and 1-olefins

The thermal degradation of both low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have been investigated under non-isothermal conditions. The weight loss data have been analyzed by Flynn and Wall methods. The activation energies for overall degradation of LDPE and HDPE were determined. In addition, the recovery of carbon as 1-olefins and n-paraffins was determined by temperature-programmed pyrolysis of polyethylene. A fixed bed reactor under argon flow was used to pyrolyze small samples of LDPE and HDPE. A special gas-phase sampling technique was used to determine the composition of products eluted from the reactor as a function of temperature and time. Hydrocarbon evolution data have been analyzed by Coats–Redfern and Chen–Nuttall combinations. It must be emphasized that the evaluation of temperature-programmed pyrolysis data by combined use of Coats–Redfern and Chen–Nuttall methods provide satisfactory mathematical approaches to obtain kinetic parameters for 1-olefin and n-paraffins formation from degradation of polyethylene. Using this method, it is possible to identify every stage of pyrolysis and derive values for kinetic parameters.

Degradation of high density polyethylene, polypropylene and their mixtures in supercritical acetone

The degradation of high density polyethylene (HDPE), polypropylene (PP) and their mixtures was carried out in supercritical acetone under the reaction temperature ranging from 450 ‡C to 470 ‡C, pressure ranging from 60 atm to 100 atm and reaction duration time as 60 min. The yields of gas, oil and wax components and the compositions and distributions of liquid-like products were measured by means of gas chromatography and gas chromatography/mass spectrometer. In every run, the reaction was completed in 30 min after reaching the prescribed temperature. The yields of oil and gas degraded from PP were not greatly influenced by the temperature, whereas in HDPE, the yields of oil decreased and that of gas increased, respectively, with rising temperature. The yields of oil from HDPE and PP increased with increasing pressure up to 7 atm and the values under higher pressure remained almost constant, i.e., 88% for HDPE and 96% for PP. Correspondingly, the yields of wax from HDPE and PP decreased with increasing pressure below 75 atm and above the value they remained almost constant, especially zero with PP. Generally, the degradation performance was influenced by the temperature rather than applied pressure. For the degradation of mixtures of HDPE and PP, with increasing PP composition, the yield of oil increased, whereas that of wax decreased, and above 80% of PP composition, it decreased to zero. For example, the yields of oil, wax and gas from a 52 wt% HDPE-48 wt% PP mixture, amounted to 90 wt%, 1 wt% and 9 wt%, respectively. The yield of wax decreased with increasing PP percentage.

CATALYTIC DEGRADATION OF HIGH DENSITY POLYETHYLENE USING ZEOLITES

Plastic wastes, which cause a serious environmental problem in urban areas, can serve as sources of energy. Catalytic treatment of High Density Polyethylene (HDPE) has shown that the degradation of HDPE resulted in the production of a stream of gaseous hydrocarbons varied in the range C1-C8. The degradation was carried out using diluted forms of zeolites ZSM-5, USY and Mordenite (MORD) using a fluidized bed reactor (FBR). Effect of coke formation on the activity of the catalysts was screened by thermogravimetric (TGA). ZSM-5 showed a significant resistance to deactivation because of the nature of its small pore size compared with USY and MORD.

Catalytic degradation of high density polyethylene and polypropylene into liquid fuel in a powder-particle fluidized bed

Catalytic degradation of high density polyethylene (HDPE) and polypropylene (PP) were carried out in this work in a powder-particle fluidized bed with inside diameter of 25 mm. Two kinds of catalysts (F9; Silica/Alumina,SA) were used as medium particles fluidized by nitrogen. The yields of liquid fuel, gas product and solid residue were investigated under different operating conditions, including catalyst type, bed temperature, superficial gas velocity. The compositions of liquid and gas products were also determined by gas chromatography. Between two kinds of catalyst, SA can produce higher yield of liquid fuel and more valuable gas product under temperature range from 400 to 550°C. Over 86 wt.% conversion of liquid fuel, containing hydrocarbons from C-5 to C-11, was reached from both HDPE and PP under 500°C with a residue yield level of less than 8 wt.%. Gas product under appropriate operating conditions contains over 59 wt.% ethylene and propylene.

Structure development and property changes in high density polyethylene during pan-milling

A new self-designed mechanochemical reactor, inlaid pan-mill, was used in studying high density polyethylene (HDPE). The effects of pan-milling stress on the structure and properties of HDPE were investigated. Gel permeation chromatography, melt indexer, Fourier transformed infrared spectroscopy, electron spectroscopy for chemical analysis, differential scanning calorimetry, X-ray diffraction, capillary rheometer, and Instron material testing system were used to characterize the structures and evaluate the properties of HDPE. The results showed that mechanochemical degradation of HDPE occurred under the stress fields of pan-mill, the molecular weight of HDPE was reduced, and HDPE with higher initial molecular weights were easier to degrade under the stress fields. Oxygen-containing groups such as COOH, C=O, and C-O were introduced to HDPE chains as a result of degradation during milling. Crystallinity of HDPE first decreased slightly followed by gradual increases with increasing milling times; monoclinic crystals appeared after four cycles of milling and increased markedly with increasing milling times. Pressure oscillation in capillary flow occurred at significantly higher shear stress and shear rate for milled HDPE than unmilled HDPE. After milling, mechanical properties were improved.

HDPE liquefaction: Random chain scission model

Liquefaction of commodity polymers to oils and gases can be used to recover the energy value of these materials. This article reports liquefaction data for high-density polyethylene (HDPE), one of the major plastics in recycled material. Thermal degradation of HDPE to oil–gas mixtures required higher temperatures (450–490°C) than low-density polyethylene (LDPE) (430–460°C) because of fewer chain branching points for HDPE, which are more susceptible to chain scission reactions. The addition of hydrogen (0.1–1.5 MPa) had negligible effect on product distribution. HDPE thermal degradation is consistent with a random chain scission mechanism. Product distributions for degradation at 450°C were modeled assuming random chain scission with a rate constant k(x) dependent on the molecular weight x by a power law model dependence, k(x) = kbxb, where kb is the pseudo-first-order rate constant, and b is the power index of dependence on molecular weight. Degradation rates dropped rapidly after initial breakup of the chains, and 2 sets of coefficients were needed to describe the molecular weight distributions as functions of reaction time. The error in model was about 10%. This model can be used to optimize the production of oils from thermal degradation of HDPE. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1239–1251, 1998

HDPE liquefaction: Random chain scission model

Liquefaction of commodity polymers to oils and gases can be used to recover the energy value of these materials. This article reports liquefaction data for high-density polyethylene (HDPE), one of the major plastics in recycled material. Thermal degradation of HDPE to oil–gas mixtures required higher temperatures (450–490°C) than low-density polyethylene (LDPE) (430–460°C) because of fewer chain branching points for HDPE, which are more susceptible to chain scission reactions. The addition of hydrogen (0.1–1.5 MPa) had negligible effect on product distribution. HDPE thermal degradation is consistent with a random chain scission mechanism. Product distributions for degradation at 450°C were modeled assuming random chain scission with a rate constant k(x) dependent on the molecular weight x by a power law model dependence, k(x) = kb xb, where kb is the pseudo-first-order rate constant, and b is the power index of dependence on molecular weight. Degradation rates dropped rapidly after initial breakup of the chains, and 2 sets of coefficients were needed to describe the molecular weight distributions as functions of reaction time. The error in model was about 10%. This model can be used to optimize the production of oils from thermal degradation of HDPE. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1239–1251, 1998

Production of hydrocarbons by catalytic degradation of high density polyethylene in a laboratory fluidised-bed reactor

High density polyethylene (HDPE) was pyrolysed over different catalysts using an in-house designed laboratory fluidised-bed reactor operating in the 290–430°C range under atmospheric pressure. The catalysts used were HZSM-5, Silicalite, HMOR, HUSY and SAHA and the yield of volatile hydrocarbons (based on the feed) was typically HZSM-5>HUSY≈HMOR>SAHA. Product streams varied markedly with catalysts type and structure. The sodium form of siliceous ZSM-5, silicalite, containing very few or no catalytically active sites, gave very low conversions of polymer to volatile hydrocarbons. HZSM-5 and SAHA produced more olefinic streams with HZSM-5 yielding over 80 wt% olefins in the C 3–C 5 range compared with around 40 wt% with SAHA. However, both HMOR and HUSY produced more paraffinic streams with large amounts of C 4 (19 and 14 wt%, respectively) and both catalysts deactivated during the course of the degradation. Observed differences in product yields and product distributions under identical reaction conditions can be attributed to the microstructure of catalysts.

Catalytic degradation of high density polyethylene: An evaluation of mesoporous and microporous catalysts using thermal analysis

Catalytic degradation of waste polymers offers the potential for the selective recovery of useful chemical fractions by influencing the product distributions. Thermogravimetric analysis has been used to investigate the activity of various aluminosilicate catalysts in the degradation of high density polyethylene (HDPE). Amorphous silica-alumina significantly reduced the apparent activation energy as compared with uncatalysed thermal processes. Zeolites Y and ZSM-5 further reduced the activation energy resulting in more rapid degradation. Aluminium containing MCM-41 was found to be active in the degradation of HDPE at a rate similar to that of HZSM-5, confirming the potential of this family of materials in the cracking of heavier hydrocarbons.

Deactivation of US-Y zeolite by coke formation during the catalytic pyrolysis of high density polyethylene

Abstract Catalytic pyrolysis of waste polymers over zeolitic catalysts has the potential to recover valuable hydrocarbons. Thermogravimetric analysis has been used as a tool to characterise the activity, regenerability and deactivation behaviour of zeolite US-Y in the degradation of high density polyethylene (HDPE). Deactivation of the catalyst occurs due to the deposition of coke. Analysis of the TGA results allowed a relationship between catalyst activity and coke content to be derived. The catalyst activity was found to fall exponentially with coke content.

Thermal and catalytic degradation of high density polyethylene and commingled post-consumer plastic waste

High density polyethylene (HDPE) and commingled post-consumer plastic waste (CP#2) were thermally and catalytically depolymerized in both a 27-cm 3 tubing reactor and a 150-cm 3 autoclave reactor at 400–435°C, 60 min. under N 2 or H 2, with or without TiCl 3 or HZSM-5 as catalyst. For both HDPE and CP#2, no significant non-catalytic reactions occurred until the reaction temperature reached 430°C. For depolymerization reactions of HDPE and CP#2 in the autoclave reactor at 435°C, the optimum oil yields (88.7% for HDPE and 86.6% for CP#2) were obtained over TiCl 3 catalyst, while the maximum gas yields (21.2% for HDPE and 17.6% for CP#2) were produced over HZSM-5 catalyst. HZSM-5 catalyzed cyclization and aromatization reactions while TiCl 3 catalyzed recombination and disproportionation reactions. Detailed product analyses and characterization lead to a reasonable explanation of reaction pathways and mechanisms.