Kinetic study of the thermal degradation of high density polyethylene

The thermal degradation of high density polyethylene has been modelled by the random breakage of polymer bonds, using a set of population balance equations. A model was proposed in which the population balances were lumped into representative sizes so that the experimentally determined molecular weight distribution of the original polymer could be used as the initial condition. This model was then compared to two different cases of the unlumped population balance which assumed unimolecular initial distributions of 100 and 500 monomer units, respectively. The model that utilised the experimentally determined molecular weight distribution was found to best describe the experimental data. The model fits suggested a second mechanism in addition to random breakage at slow reaction rates.     

加热速率和粒径对聚乙烯在超临界水中转化的影响

随着塑料制品的广泛使用,废塑料在中国每年呈递增趋势,在城市垃圾中特别是沿海地区废塑料的质量分数己增加到8％～10％,而体积分数达到30％以上,造成严重的“白色污染”。回收利用废塑料不仅可以解决环境污染问题,而且可以将废弃物转化为资源。废塑料降解油化可以得到价值较高的液体燃料或化工原料,是一种较为理想的回收利用方法。     

Equation of state for high density solid and melt polyethylene

Pressure‐volume‐temperature (PVT) measurements for high‐density linear polyethylene (LPE) are studied experimentally over a temperature range of 290 to 470 K and pressures up to 3.1 kbar. For melt, the results can be represented by the Tait equation within the precision of the data. It is noticed that for each isotherm, an abrupt departure from the Tait representation occurs at a particular pressure. This is ascribed to onset of solidification due to pressure. Further, variation of the degree of crystallinity with pressure at various temperatures has been investigated. Finally, the PVT data has been analyzed in terms of the LJD cell theory in its original form without any modifications or simplifications of the cell potential. Satisfactory agreement is obtained between experiment and theory over the entire range of PVT data both in solids and melt states. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1618–1623, 2005     

The effect of PVC on thermal and catalytic degradation of polyethylene, polypropylene and polystyrene by a continuous flow reactor

A continuous flow reactor was operated at atmospheric pressure and feed rate of 0–1.5 kg h⁻¹ for degradation of PE, PP and PS in presence of 1–2 wt% PVC. The degradation temperatures were between 360 and 440 °C depending on the feeding material. The influence of PVC, temperature and silica-alumina catalysts on degradation behavior and on the properties of the products was studied and discussed. Different effects were observed for binary PE/PVC, PP/PVC, PS/PVC and complex PE/PP/PS/PVC mixtures due to specific interactions between PVC and each hydrocarbon polyolefin. Silica-alumina catalysts decreased the Cl concentration in oils but it seems to generate high amounts of Cl-containing organic compounds in gases.     

The temperature window of minimum flow resistance in melt flow of polyethylene. Further studies on the effect of strain rate and branching

The existence of a narrow temperature window (150–153°C) of smooth extrudability coupled with a minimum in flow resistance (extrusion pressure) in high-molecular weight polyethylene (>4 × 10⁵ g mol^?1) was the subject of a previous article where it was associated with strain-induced formation of the mobile hexagonal mesophase. The new findings of this note show that this minimum in flow resistance only sets in above a critical strain rate; this is interpreted in terms of the requirement of a critical strain rate in order to stretch molecules to their fully extended configuration. Furthermore, this critical strain rate is shown to be higher for lower molecular weight materials, in agreement with a priori considerations. Additionally, the temperature at which the pressure minimum occurs in a polyethylene containing methyl branches shifts to a significantly lower value than that for the linear material. This is interpreted in terms of the ? CH₃ groups raising the crystal free energy, thereby lowering the temperature at which the transition to the hexagonal phase occurs.     

Adhesive effect of high density polyethylene gels on polyethylene moldings

Adhesive effect of polyethylene moldings by use of high density polyethylene gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene was investigated by shearing tests, electron microscope, and DSC measurements. All of the gels showed such a strong adhesive strength over 36 kg/cm² that polyethylene plates of 3 mm in thickness gave rise to necking sufficient for practical use, when heated at 120 °C for 2 h. In particular, the gel in tetralin showed a strong adhesive strength when heated at 110 °C. It was found that adhesive strength increases with the heating temperature; the temperatures at which adhesive strength begins to increase differ depending on the type of polyethylene sample and solvent. It is apparent that polyethylene gels exhibit an adhesive effect when they are heated at higher temperatures than the gel melting temperatures, and that the closer the SP values of solvents used for the gelation are to the molded polyethylene, the stronger the adhesion of the polyethylene molding.     

The effect of particle size on the thermal decomposition kinetics of potassium bromate

The thermal decomposition of potassium bromate (KBrO₃) has been studied as a function of particle size, in the range 53?C150???m, by isothermal thermogravimetry at different temperatures, viz. 668, 673, 678, and 683?K in static air atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of all samples of KBrO₃ at all temperatures studied. The isothermal decomposition of all samples of KBrO₃ was subjected to both model fitting and model-free (isoconversional) kinetic methods of analysis. Isothermal model fitting analysis shows that the thermal decomposition kinetics of all the samples of KBrO₃ studied can be best described by the contracting square equation. Contrary to the expected increase in rate followed by a decrease with decrease in particle size, KBrO₃ shows a regular increase in rate with reduction in particle size, which, we suggest, is an impact of melting of this solid during decomposition.     

Thermal and thermo-oxidative degradation of high density polyethylene/fullerene composites

Fullerene (C₆₀)/high density polyethylene (HDPE) composites were studied in order to understand for their behaviors on thermal and thermo-oxidative degradation. Under different atmosphere, the influences of C₆₀ on the thermal stability of HDPE are different. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) demonstrate that in N₂ the addition of C₆₀ increases the onset decomposition temperature by about 10 °C with more heavy compounds (more than 34 carbon). Also the thermal stability of HDPE in air is remarkably improved with the addition of C₆₀. When the content of C₆₀ is 2.5 wt% the onset decomposition temperature increases by about 91 °C. The results of viscoelastic behavior and gel content reveal that C₆₀ can trap the alkyl radicals and alkyl peroxide radicals to inhibit hydrogen abstraction to suppress the chain scission and preserve the long chain structure. However, in the absence of C₆₀ or with low C₆₀ concentration, hydrogen abstraction occurs, resulting in the formation of a series of alkyl radicals and alkyl peroxide radicals, which accelerates the chain scission and plays a leading role in the thermal oxidative degradation.     

Influence of chain extender on thermal properties and melt flow index of stereocomplex PLA

The effects of chain extension and melt blending temperature on the stereocomplex formation of 50/50 (w/w) poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) blends or stereocomplex polylactides (scPLAs) were investigated. Joncryl^® ADR 4368, a styrene-acrylic multifunctional oligomeric agent, was used as a chain extender. Differential scanning calorimetry and X-ray diffractometry were used to confirm the stereocomplex formation of the PLLA/PDLA blends. Melt flow indices (MFI) of the blends were also determined. The stereocomplex crystallinities gradually decreased with increasing blending temperature and Joncryl^® ADR 4368 ratio. The significant decrease in the MFI of scPLAs is believed to be attributed to chain extension at the blending temperatures of 170 °C and 200 °C. The MFI values of scPLAs decreased as the Joncryl^® ADR 4368 ratio and blending temperature increased. The results indicated that the chain extension has an effect on the stereocomplexation and it improved the melt strength of the scPLAs.     

Preparation of bone powder for FTIR-ATR analysis: The particle size effect

Fourier transform infrared (FTIR) spectroscopy using attenuated total reflection (ATR) is commonly used for the examination of bone. During sample preparation bone is commonly ground, changing the particle size distribution. Although previous studies have examined changes in crystallinity caused by the intensity of grinding using FTIR, the effect of sample preparation (i.e. particle size and bone tissue type) on the FTIR data is still unknown.This study reports on the bone powder particle size effects on mid-IR spectra and within sample variation (i.e. periosteal, mesosteal, trabecular) using FTIR-ATR. Twenty-four archaeological human and faunal bone samples (5 heated and 19 unheated) of different chronological age (Neolithic to post-Medieval) and origin (Belgium, Britain, Denmark, Greece) were ground using either (1) a ball-mill grinder, or (2) an agate pestle and mortar, and split into grain fractions (>500 μm, 250–500 μm, 125–250 μm, 63–125 μm, and 20–63 μm).Bone powder particle size has a strong but predictable effect on the infrared splitting factor (IRSF), carbonate/phosphate (C/P) ratio, and amide/phosphate (Am/P) values. The absorbance and positions of the main peaks, the 2nd derivative components of the phosphate and carbonate bands, as well as the full width at half maximum (FWHM) of the 1010 cm⁻¹ phosphate peak are particle size dependent. This is likely to be because of the impact of the particle size on the short- and long-range crystal order, as well as the contact between the sample and the prism, and hence the penetration depth of the IR light. Variations can be also observed between periosteal, cortical and trabecular areas of bone. We therefore propose a standard preparation method for bone powder for FTIR-ATR analysis that significantly improves accuracy, consistency, reliability, replicability and comparability of the data, enabling systematic evaluation of bone in archaeological, anthropological, paleontological, forensic and biomedical studies.     

Synthesis and kinetics of non-isothermal degradation of amide grafted high density polyethylene

The grafted structures from the reaction of high density polyethylene with maleic anhydride (PEgMA) was reacted further with 1,4-diaminobutane to synthesize amide grafted polyethylenes. Grafted amic-acids were partially converted to imide groups during the reaction. Grafted products were identified by titration, elemental analysis and FTIR. DSC analysis indicated that C_p for amide grafted product increased about 47% with respect to PEgMA, its crystallinity increased 50% with respect to PE and 18% with respect to PEgMA. Analysis of kinetics of degradation was performed by thermogravimetry; degradation kinetic parameters of these amide grafted products have not been evaluated or reported. The degradation of Amide grafted polyethylene is similar to HDPE but with smaller activation energy indicating that it is the most stable product. F_n and A_n kinetic models seemed more suitable than diffusion models.     

The effect of flame retardant-modified sepiolite nanofibers on thermal degradation and fire retardancy of low-density polyethylene

Flame retardant-modified sepiolite nanofiber (PSPHD-SEP) was fabricated through chemical grafting by introducing intumescent flame retardant oligomer (PSPHD) onto the surface of sepiolite fiber. Various sepiolite/low-density polyethylene (SEP/LDPE) composites have been prepared successfully via melt blending. The dispersion of various SEPs in LDPE matrix was observed by scanning electron microscope and transmission electron microscope. The thermal degradation behaviors of various SEP/LDPE composites with 3 mass% acid-modified sepiolite fiber (a-SEP) or PSPHD-SEP have been investigated employing thermogravimetric analysis/derivative thermogravimetry. The thermal degradation kinetics of neat LDPE, a-SEP/LDPE and PSPHD-SEP/LDPE systems was comparatively analyzed by means of Friedman and Flynn–Wall–Ozawa methods to further comprehend the effect of a-SEP and PSPHD-SEP on the thermal stability of LDPE. Due to the addition of PSPHD-SEP, the limiting oxygen index value of PSPHD-SEP/LDPE composite can reach 21.3%, and the UL-94V-2 rating is obtained. The cone calorimetry (CONE) tests showed that a reduced peak heat release rate can be achieved for PSPHD-SEP/LDPE composite accompanying with gas-phase fire retardant action.

     

The effects of high energy electron beam irradiation on the thermal and structural properties of low density polyethylene

Radiation is currently being exploited to modify polyethylene in order to improve properties for various applications such as hip replacements. This paper thoroughly examines the effects of high energy electron beam irradiation (10 MeV) on low density polyethylene (LDPE) material. ASTM (American Society for Testing and Materials) testing specimens were manufactured from LDPE and subjected to a broad range of doses ranging between 25 and 400 kGy at room temperature in an air atmosphere. Extensive characterisation techniques such as modulated differential scanning calorimetry (MDSC) and the Fourier transform infrared spectroscopy (FTIR) were conducted on the non-irradiated and irradiated samples. While considering the semicrystalline nature of LDPE during the MDSC experiment, the melting temperature (T_m) and the temperature crystallinity (T_c) were calculated. This revealed that the T_m and the T_c decreased in temperature as the irradiation dose increased. The FTIR analysis was implemented to evaluate the presence of polar species such as carbonyl groups and trans-vinylene double bond groups. The IR spectra illustrated that the concentration of characteristic bands for trans-vinylene bonds increased with increasing radiation dose indicating the formation of carbonyl bond groups. Furthermore, the results demonstrated an occurrence of oxidative degradation due to the formation of carbonyl groups at 1718 cm^?1.     

Low density polyethylene,expanded polystyrene and expanded polypropylene: Strain rate and size effects on mechanical properties

Polymeric foam materials may be used as energy absorbing materials for protection in impact scenarios, and design with these materials requires the mechanical properties of foams across a range of deformation rates, where high deformation rate testing often requires small samples for testing. Owing to their cellular macrostructure, and the large deformations that occur during loading of foams, the measured stress-strain response of a foam material may be influenced by the sample size. In this study, the mechanical properties of three closed-cell polymeric foams (Low Density Polyethylene, Expanded Polystyrene and Expanded Polypropylene) at two different densities were investigated over a range of deformation rates from 0.01 s⁻¹ to 100 s⁻¹. For each foam material, three different nominal sample sizes (10 mm, 17 mm and 35 mm) were tested. On average, the polymeric foam materials exhibited increasing stress with increasing deformation rate, for a given amount of strain.Density variation was identified at the sample level, with smaller samples often exhibiting lower density. Expanded Polystyrene demonstrated the highest variability in sample density and corresponding variability in mechanical response, qualitatively supported by observed variations in the macrostructure of the foam. Expanded Polypropylene exhibited variability in density with sample size, and observable variability in the material macrostructure; however, the dependence of the measured mechanical properties on sample size was modest. Low Density Polyethylene was found to have a relatively consistent cell size at the macrostructure level, and the material density did not vary significantly with sample size. In a similar manner, the dependence of measured mechanical properties on sample size was modest. The effect of sample size was identified to be material specific, and it is recommended that this be assessed using sample-specific density measurements and considering different sized samples when testing foam materials.     

Comparing the effect of nanofillers as thermal stabilizers in low density polyethylene

A study of the thermal degradation under inert and oxidative conditions of LDPE and three 5-wt% nanocomposites has been performed. The bases of comparison were the geometries of the nanofillers (spherical, fibrous and laminar) and the sample thickness. Homogeneous and well-dispersed materials were obtained with the three nanoparticles, ensuring a relevant comparative analysis.The thermal degradation curves obtained from TGA under nitrogen flow did not show significant differences in behaviour within the nanocomposites and the reference LDPE. However, the results for the thermo-oxidation study showed a strong stabilization effect for both fibrous and laminar silicates, but not for the spherical silica nanoparticles. A kinetic study of the degradation under isothermal conditions showed that the nanocomposites made from fibrous and laminar silicates degraded following the mechanisms observed for thin films independent of the sample thickness. These results suggested the occurrence of a protective layer against thermo-oxidation on the film surface. Chemical analysis of the degraded surfaces by IR and EDX measurements gave data to explain these differences in behaviour.     

Study of the abnormal late co-elution phenomenon of low density polyethylene in size exclusion chromatography using high temperature size exclusion chromatography and high temperature asymmetrical flow field-flow fractionation

The elution behaviour of linear and branched polyethylene samples in SEC was studied. For the branched samples an abnormal late co-elution of large and small macromolecules manifests itself as an abnormal re-increase of the molar mass and the radius of gyration values detected with multi angle light scattering at high elution volumes in SEC. The late co-elution of small and large macromolecules cannot be explained by the SEC mechanism alone. The influence of several experimental parameters on the late co-elution was studied. It was found that the type of SEC column and the flow rate have a significant influence. The late eluting part of the sample was fractionated and separated by HT-SEC- and HT-AF4-MALS. The different results of both methods have been discussed with the aim to find possible explanations for the late elution. The experiments indicate that especially large branched structures show an increased tendency for the phenomenon.     

Effect of the particle size and solids volume fraction on the thermal degradation behaviour of Invar 36 feedstocks

Degradation kinetics and the thermal stability of Invar 36 powder injection moulding feedstocks (PIM) based on cellulose acetate butyrate (CAB) and polyethylene glycol (PEG) binders were investigated using simultaneous thermogravimetric analysis (STA) and differential scanning calorimetry (DSC). The initial decomposition temperature (IDT) and the integral procedure decomposition temperature (IPDT) were used to analyse the thermal stability of the binder system as a function of the solid loading content and powder particle size. The degradation kinetics was studied, and the process apparent activation energies were assessed using isoconversional methods. All the methodologies revealed changes in the thermal degradation behaviours of the feedstocks for solid loadings that were previously determined to correspond to optimal solid loadings using other experimental procedures. The studies also contrast previous similar findings with a ceramic powder. Therefore these results strengthen the proposal of thermodynamic degradation studies of feedstocks as an alternative or complementary technique to determine optimal solid loading contents in metal injection moulding (MIM).     

Mechanical behavior of saturated,consolidated, alumina powder compacts: effect of particle size and morphology on the plastic-to-brittle transition

The effects of particle size and morphology on the mechanical behavior of pressure consolidated, saturated, alumina powder bodies, were determined with uniaxial compression experiments of cylindrical specimens at a fixed displacement rate. Five different α-Al₂O₃ powders, from the same manufacturer, were used. The slurries were dispersed at pH 4 and then either coagulated with additions of NH₄Cl to produce weakly attractive particle networks with short-range repulsive potentials or flocculated at the isoelectric point (iep=pH 9). These slurries were consolidated by pressure filtration using pressures ranging from 2.5 to 150 MPa. Larger particles packed to higher relative densities when compared to smaller particles. Blocky particles packed at a lower relative density when compared to particles with roundish surfaces. Bodies were plastic when consolidated below a critical consolidation pressure; above this pressure, the body was brittle. Bodies formed with large particles were brittle at a lower consolidation pressure. The effect of particle size is discussed with respect to the number of particle–particle contacts per unit volume at a given relative density. Namely, for a given applied pressure, larger forces exist between larger particles because of the smaller number of contacts per unit volume relative to smaller particles.     

The effect of particle size distribution on TG

The effect of a particle size distribution on the fractional reaction has been analysed. The analysis shows that for non-isothermal TG the activation energy and frequency factor evaluated from the fractional reaction by conventional method depend on the particle size distribution, and this may lead to a kinetic compensating effect. Particle size distribution may also lead to an erroneous conclusion about the change in the mechanism of reaction.     

The effect of the particle size on the kinetics of CO electrooxidation on high surface area Pt catalysts

Using high-resolution transmission electron microscopy (TEM), infrared reflection-absorption spectroscopy (IRAS), and electrochemical (EC) measurements, platinum nanoparticles ranging in size from 1 to 30 nm are characterized and their catalytic activity for CO electrooxidation is evaluated. TEM analysis reveals that Pt crystallites are not perfect cubooctahedrons, and that large particles have "rougher" surfaces than small particles, which have some fairly smooth (111) facets. The importance of "defect" sites for the catalytic properties of nanoparticles is probed in IRAS experiments by monitoring how the vibrational frequencies of atop CO (nu(CO)) as well as the concomitant development of dissolved CO(2) are affected by the number of defects on the Pt nanoparticles. It is found that defects play a significant role in CO "clustering"on nanoparticles, causing CO to decrease/increase in local coverage, which yields to anomalous redshift/blueshift nu(CO) frequency deviations from the normal Stark-tuning behavior. The observed deviations are accompanied by CO(2) production, which increases by increasing the number of defects on the nanoparticles, that is, 1 < or = 2 < 5 < 30 nm. We suggest that the catalytic activity for CO adlayer oxidation is predominantly influenced by the ability of the surface to dissociate water and to form OH(ad) on defect sites rather than by CO energetics. These results are complemented by chronoamperometric and rotating disk electrode (RDE) data. In contrast to CO stripping experiments, we found that in the backsweep of CO bulk oxidation, the activity increases with decreasing particle size, that is, with increasing oxophilicity of the particles.