Phase diagrams of low-density polyethylene–alkylbenzene systems

Complete phase diagrams for mixtures of low-density polyethylene with p- and m-xylene are plotted by optical means in developing the concept of which partially crystalline polymers are microstructured liquids. It is shown that in contrast to the ones presented in the literature, both diagrams contain the solubility boundary curve of the low-molecular weight component in the polymer, above which the polyethylene has the structure of a single-phase gel (crosslinks formed by crystallites and amorphous regions saturated with xylene). At the figurative point on the diagrams, a situation is observed in which the dissolution of all the liquid contained in the initial two-phase system in the polymer is accompanied by its simultaneous complete amorphization. The parameters of the figurative point allow us to estimate the thermodynamic affinity of different alkylbenzenes toward polyethylene.     

Modification of polyethylene films by radiation grafting of glycidyl methacrylate and immobilization of β-cyclodextrin

Glycidyl methacrylate was grafted onto polyethylene films using a preirradiation method with γ rays. The effect of absorbed dose, monomer concentration, and reaction time on the degree of grafting was determined. The grafted samples were verified by FTIR-ATR spectroscopy. β-Cyclodextrin was immobilized onto polypropylene modified with glycidyl methacrylate, and the ability of the cavities of β-cyclodextrin to form inclusion complexes was demonstrated using the typically organic compound approach with m-toluic acid (3-MBA) as a probe.     

Thermal stability of high density polyethylene–fumed silica nanocomposites

High-density polyethylene-based nanocomposites were prepared through a melt compounding process by using surface functionalized fumed silica nanoparticles in various amounts, in order to investigate their capability to improve both mechanical properties and resistance to thermal degradation. The fine dispersion of silica aggregates led to noticeable improvements of both the elastic modulus and of the stress at yield proportionally to the filler content, while the tensile properties at break were not impaired even at elevated filler content. Thermogravimetric analysis showed that the selected nanoparticles were extremely effective both in increasing the decomposition temperature and in decreasing the mass loss rate, even at relatively low filler loadings. The formation of a char enriched layer, limiting the diffusion of the oxygen through the nanofilled samples, was responsible of noticeable improvements of the limiting oxygen index, especially at elevated silica loadings. In contrast with commonly reported literature results, cone calorimeter tests also revealed the efficacy of functionalized nanoparticles in delaying the time to ignition and in decreasing the heat release rate values. Therefore, the addition of functionalized fumed silica nanoparticles could represent an effective way to enhance the flammability properties of polyolefin matrices even at low filler concentrations.     

EB crosslinking of polyethylene ‘O’ rings: Optimisation of process parameters

Radiation crosslinked LDPE O rings, an inexpensive substitute for PTFE and polysilicone gaskets in high temperature applications, are widely used in the industry. Radiation crosslinking of LDPE O rings, in the finished form was carried out at the 20 kW-2 MeV, ILU — 6 type EB facility installed at the Bhabha Atomic Research Centre, Bombay to establish irradiation technique for large scale production and for an adequate and uniform dose delivery. Two irradiation geometries viz. flat bed and rotating spindle were chosen for batch processing and optimisation of process parameters. The laboratory analysis and thein situ performance showed that a minimum of 65 % gel-content is needed in the irradiated rings and that an absorbed dose of about 200 kGy is adequate to meet the industrial standards. Rotating spindle technique was found to have an edge over flat bed irradiation in terms of dose uniformity and throughput. This paper gives an account of the work carried out to optimise the process parameters for both the geometries.     

Modification of high-density polyethylene with binary mixtures of ɛ-caprolactone and ɛ-caprolactam

Modification of high-density polyethylene with binary mixtures of ?-caprolactone and ?-caprolactam was performed. The composition-property diagrams reflecting the dependences of the physicomechanical, rheological, and optical properties of the resulting polymeric compounds on the content of modifying mixture components were constructed, and the thermal oxidative degradation of the blend samples was studied. Based on the results obtained, the optimal modifier concentrations were suggested.     

Use of polyethylene glycol in the process of sol–gel encapsulation of Burkholderia cepacia lipase

Lipases from Burkholderia cepacia were encapsulated using polyethylene glycol (PEG, M _w 1500) at various concentrations (0.5–3.0 %, w/v) as an additive during the sol–gel immobilisation process. Matrixes immobilized in the presence and absences of additives were characterized by thermal analysis [thermogravimetric (TG) and differential scanning calorimetry (DSC)], scanning electron microscopy (SEM), enzymatic activity, and total activity recovery yield (Ya). The addition of PEG increased the activity values, with Ya just above 1.0 % (w/v) in the presence of PEG. The additional of 1.0 % (w/v) PEG increased enzyme activity from 33.98 to 89.91 U g^?1 and the values of recovery yield were 43.0–91.4 %, compared to values of the samples without PEG. PEG enhanced the thermal stability of the matrix structure in the temperature range 50–200 °C, as confirmed by TG and DSC analyses. This was influenced by the presence of water bound to the matrix. The SEM micrographs clearly showed an increase in the number of deposits on the material surface, producing matrices with greater porosity.     

Fabrication of rod-shaped β-FeOOH: the roles of polyethylene glycol and chlorine anion

β-FeOOH nanorods of 40 nm wide and 450 nm long were fabricated through precisely regulating the hydrolysis kinetics of Fe~(3+) in polyethylene glycol and the concentration of Cl~- as the structure-directing agent. Detailed structural and chemical analyses of the intermediates during the synthesis identified that the strong interaction between PEG and Fe~(3+) modulated the hydrolysis kinetics of Fe~(3+) and prevented the aggregation of β-FeOOH nanorods; while Cl~- provided sufficient nucleation sites, stabilized the hollow channel of β-FeOOH, and more importantly induced the growth of the nanorods along [001] direction.     

Thermal properties of chlorosulfonated polyethylene via gas–solid phase method

The thermal properties of chlorosulfonated polyethylene (CSM), which was prepared via gas–solid phase method, were studied in this article. The thermal curves were completely tested by differential thermal analysis, thermogravimetry, and differential thermogravimetry. The results showed that CSM 3550 and CSM 3570 prepared by gas–solid phase method had more excellent thermal properties (high initial/final temperature of degradation) than those via solution method, due to the uniform chlorine distribution of them in macromolecular chain. The differential scanning calorimetry curves showed that the transitions of CSM 3550 and CSM 3570 from glassy to the elastic state were also higher than those via solution method. Particularly, CSM 3570 was amorphous and no clear melting peak was observed during the melting process.     

Morphology and electrical conductivity of ultrahigh-molecular-weight polyethylene–low-molecular-weight polyethylene–carbon black composites prepared by gelation /crystallization from solutions

Composite materials based on ultrahigh-molecular-weight polyethylene (UHMWPE)–low- molecular-weight polyethylene (LMWPE) and carbon black (CB) particles were prepared by a gelation/crystallization process from dilute solution. The method was developed to obtain composite materials with an improved and reproducible positive temperature coefficient (PTC) effect. Drastic improvement of the PTC effect was achieved when specimens with a LMWPE/UHMWPE composition of 9/1 containing 13 wt% CB were treated at 170 °C without restraint before measurement. The maximum PTC intensity, defined as the ratio of the maximum resistivity to the resistivity at room temperature, was about 5 orders of magnitude, which equals that of the LMWPE-CB system prepared by a kneading method. Interestingly, electrical resistivity during the heating-cooling process showed good reproducibility in the temperature range 30–190 °C, but has never been reported before even for cross-linked LMWPE-CB compostie. Scanning electron micrographs revealed that CB particles were dispersed in the LMWPE matrix, but not on the UHMWPE fibrils. It turns out that the network structure of UHMWPE, with a very low melt index, plays an important role in removing the negative temperature coefficient effect usually observed for the LMWPE-CB system and in ensuring the quality and the reproducibility of the PTC effect. Received: 31 August 1998 Accepted in revised form: 4 January 1999     

The effect of chlorosulphonated polyethylene on thermal properties and combustibility of butadiene–styrene rubber

This article describes the test results of thermal properties and flammability of the unconventionally cross-linked blends of chlorosulfonated polyethylene (CSM) and butadiene–styrene rubber (SBR) by means of zinc oxide or nano-zinc oxide. The thermal curves have been interpreted from the point of view of the chemical transitions of elastomers and their blends. It has been found that the content of combined chlorine in CSM exerts a significant influence on the cross-linking kinetics of CSM/SBR blends, their thermal properties and flammability.     

Thermal-catalytic degradation of polyethylene over silicoaluminophosphate molecular sieves—A thermogravimetric study

The present work is aimed at recycling plastic wastes economically and efficiently, for which pure high density polyethylene (HDPE) has been initially selected for the investigations. Thermogravimetric technique has been used to investigate, analyze and compare the thermal and catalytic degradation of HDPE. The catalytic degradation was investigated over the medium pore silicoaluminophosphate, SAPO-11 molecular sieve. The thermogravimetric evaluation was performed using 2–30 wt% catalyst, and the apparent activation energies for the thermal and catalytic polymer degradation were estimated using various iso-conversional methods. The apparent activation energy was found to be lower when SAPO-11 was used compared to the direct thermal degradation of HDPE. The activation energy and coke levels are comparable to the medium pore zeolite ZSM-5 and lower than the values obtained over large pore zeolites reported in literature.     

Simulation of the random scission of C–C bonds in the initial stage of the thermal degradation of polyethylene

We performed molecular dynamics simulations to analyze the initial stage of the thermal degradation of polyethylene, which is dominated by the random scission reaction. The simulations were initiated from structures that were taken from previously equilibrated snapshots of the amorphous polymer and of a free-standing thin film. Isolated chains were also used for comparison. Our systems were coupled to a thermal heat bath, and the effect of different coupling constants was studied. Rate of random scission increases as the strength of the temperature coupling increases. Rates of reaction are almost similar in thin films and the bulk, whereas the rates are much faster in isolated chains. Expansion of the free-standing thin film accompanies degradation, producing fragments of various sizes. Chains of higher molecular weights than the initial chains can be produced due to recombination of fragments during the expansion of thin films. The polydispersity index of the resulting fragments is higher in thin films compared to the bulk. The bonds at the low density portion of the thin films have a higher probability of being broken.     

Modeling of liquid–liquid equilibrium of polyethylene glycol-salt aqueous two-phase systems—the effect of partial dissociation of the salt

The modified NRTL model proposed in the previous paper [Y.-T., Wu, D.-Q. Lin, Z.-Q. Zhu, L.-H. Mei, Fluid Phase Equilibria 124 (1996) 67–79.] is further extended to include the effect of partial dissociation of salts in polyethylene glycol (PEG)–salt aqueous two-phase systems (ATPS), and is used to calculate the liquid–liquid equilibrium phase diagrams such as PEG–(NH₄)₂SO₄ and PEG–MgSO₄ ATPS. The phase diagrams of PEG–uni-bivalent salt ATPS can be correctly represented in the cases of both complete dissociation and partial dissociation of the salt, while those of PEG–MgSO₄ ATPS can only be described in the case of partial dissociation of the salt. The analysis shows that the salts may have different existing states in the ATPS. The effect of partial dissociation of the salts on the phase diagrams should be considered, especially for systems such as PEG–MgSO₄ ATPS.     

Modeling of solid–liquid equilibria in naphthalene,normal-alkane and polyethylene solutions

A solid–liquid equilibrium (SLE) model is developed on the basis of an equation of state referred to as copolymer SAFT. This SLE model is demonstrated for hydrocarbon solutions containing totally and partially crystallizable solutes. Initially regressed and tested on the solubility data for naphthalene, normal-alkane, and polyethylene, this model is used in a sensitivity study to understand the effects of crystallizability, melting temperature, molecular weight, and pressure on solid–liquid and liquid–liquid transitions of polyethylene in subcritical and supercritical propane.     

Diffusion controlled radiochemical oxidation of low density polyethylene—II. Kinetic modelling

Various low density polyethylene (LdPE) multilayer samples were irradiated by ⁶⁰Co-γ-rays at ambient temperature. The thickness distribution of carbonyl groups concentration, determined by i.r. spectrophotometry, displays a sharp inflexion zone at an invariant depth for a given dose rate. This depth is a decreasing function of the dose rate.Experiments on thin films at various oxygen pressure are made in order to determine the rate constants for the non-diffusion controlled oxidation process. Then a kinetic model is proposed. It leads to a reciprocal dependance of the thickness of the oxidized layer on the square root of the dose rate. The experimental results agree with this model despite an unexplained superficial sharp decrease of the oxidation rate.     

Mechanical properties and heat shrinkability of electron beam crosslinked polyethylene–octene copolymer

The mechanical properties and heat shrinkability of electron beam crosslinked polyethylene–octene copolymer were studied. It was found that gel content increases with increased radiation dose. The analysis of results by the Charlesby–Pinner equation revealed that crosslinking was dominant over chain scission upon irradiation. Formation of a crosslinked structure in the electron beam irradiated sample was confirmed by the presence of a plateau of dynamic storage modulus above the melting point of the polymer. Wide-angle X-ray diffraction revealed that there was little change in crystallinity for the irradiated samples, indicating that radiation crosslinking occurs in the amorphous region of the polymer. The tensile modulus increases, whereas the elongation at break decreases with increased radiation dose. The heat shrinkability of the material increased with an increased radiation dose because the radiation-induced crosslinks serve as memory points during the shrinking process.     

High speed injection molding of high density polyethylene �� Effects of injection speed on structure and properties

Thin wall samples of high density polyethylene (HDPE) were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Young??s modulus was observed with increasing injection speed. In order to investigate the mechanism behind this decrease, the orientation, molecular weight, molecular weight distribution, melt flow rate, crystallinity and crystal morphology of HDPE were characterized using two-dimensional wide-angle X-ray diffraction (2D-WAXD), gel permeation chromatography (GPC), capillary rheometry and differential scanning calorimetry (DSC), respectively. It is demonstrated that the orientation, molecular weight, molecular weight distribution, melt flow rate and crystallinity have no obvious change with increasing injection speed. Nevertheless, the content of extended chain crystals or large folded chain crystals was found to decrease with increasing injection speed. Therefore, it is concluded that the decrease in tensile properties is mainly contributed by the reduced content of extended chain crystals or large folded chain crystals. This study provides industry with valuable information for the application of high speed injection molding.     

Dynamic properties of the polyethylene glycol molecules on the oscillating solid–liquid interface

The dynamic properties of polyethylene glycol (PEG) molecules on the solid–liquid interface oscillating at MHz were investigated using the quartz crystal microbalance (QCM). The number-average molecular weights (M_n) of the PEG molecules were systematically varied over 4 orders of magnitude. This study makes it clear that the series-resonant frequency shift, ΔF, of the QCM against the square root of the density–viscosity product of the PEG solution is linear and has the intercept. Moreover, systematical analysis reveals that the ΔF slope rapidly decreases with M_n and that the ΔF intercept becomes constant above 4.0 × 10³ g mol⁻¹. As a result, those reveal that the resonant length of the PEG molecule moving with the oscillating plate of 9 MHz is 54.2 Å. We also find that the behaviors of ΔF due to M_n are mainly caused by the length of the PEG molecule.     

Fractal analysis of polyethylene catalysts surface morphologies based on wavelet transform modulus maxima method

Surface morphologies of supported polyethylene (PE) catalysts are investigated by an approach combining fractal with wavelet. The multiscale edge (detail) pictures of catalyst surface are extracted by wavelet transform modulus maxima (WTMM) method. And, the distribution of edge points on the edge image at every scale is studied with fractal and multifractal method. Furthermore, the singularity intensity distribution of edge points in the PE catalyst is analyzed by multifractal spectrum based on WTMM. The results reveal that the fractal dimension values and multifractal spectrums of edge images at small scales have a good relation with the activity and surface morphology of PE catalyst. Meanwhile the catalyst exhibiting the higher activity shows the wider singular strength span of multifractal spectrum based on WTMM, as well as the more edge points with the higher singular intensity. The research on catalyst surface morphology with hybrid fractal and wavelet method exerts the superiorities of wavelet and fractal theories and offers a thought for studying solid surfaces morphologies. Supported by the Chinese Petroleum & Chemical Corporation Development Department (Grant No. x504024)