Yield behaviour of a melt-compounded polyethylene-intercalated montmorillonite nanocomposite

The yield behaviour of a series of melt-mixed polyethylene-modified montmorillonite nanocomposites has been studied as a function of temperature and strain rate and compared to the behaviour of the base polymer. The processing conditions used gave an intercalated structure as assessed by X-ray diffraction. Although there was a modest improvement in stiffness with clay content, the yield behaviour was insensitive to the addition of the clay. Both the base polymer and the nanocomposites showed double yield points. These were analysed as activated rate processes, with the activation energies consistent with the low strain yield point being associated with the alpha(2) molecular relaxation and the higher strain yield point with W axis slip. (C) 2003 Society of Chemical Industry.

A randomised controlled study of the efficacy of hypromellose and Lacri-Lube combination versus polyethylene/Cling wrap to prevent corneal epithelial breakdown in the semiconscious intensive care patient

Objective. To compare the efficacy of two forms of eye care (hypromellose and Lacri-Lube combination vs polyethylene/Cling wrap covers) for intensive care patients. Design. Randomised-controlled trial. Setting. University affiliated, tertiary referral hospital. Patients and participants. One hundred ten patients with a reduced or absent blink reflex were followed through until they regained consciousness, were discharged from the facility during study enrolment, died or developed a positive corneal ulcer or eye infection. Interventions. All patients received standard eye cleansing every 2 h. In addition to this, group one (n=60) received a treatment combining hypromellose drops and Lacri-Lube (HL) to each eye every 2 h. Group two (n=50) had polyethylene covers only placed over the eye to create a moisture chamber. Measurements and results. Corneal ulceration was determined using corneal fluorescein stains and mobile slit lamp evaluation, performed daily. No patients had corneal ulceration in the polyethylene cover group, but 4 patients had corneal ulceration in the HL group. Conclusions. Polyethylene covers are as effective as HL in reducing the incidence of corneal damage in intensive care patients.

Polyethylene multiwalled carbon nanotube composites

Polyethylene (PE) multiwalled carbon nanotubes (MWCNTs) with weight fractions ranging from 0.1 to 10 wt% were prepared by melt blending using a mini-twin screw extruder. The morphology and degree of dispersion of the MWCNTs in the PE matrix at different length scales was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and wide-angle X-ray diffraction (WAXD). Both individual and agglomerations of MWCNTs were evident. An up-shift of 17 cm(-1) for the G band and the evolution of a shoulder to this peak were obtained in the Raman spectra of the nanocomposites, probably due to compressive forces exerted on the MWCNTs by PE chains and indicating intercalation of PE into the MWCNT bundles. The electrical conductivity and linear viscoelastic behaviour of these nanocomposites were investigated. A percolation threshold of about 7.5 wt% was obtained and the electrical conductivity of PE was increased significantly, by 16 orders of magnitude, from 10(-20) to 10(-4) S/cm. The storage modulus (G') versus frequency curves approached a plateau above the percolation threshold with the formation of an interconnected nanotube structure, indicative of 'pseudo-solid-like' behaviour. The ultimate tensile strength and elongation at break of the nanocomposites decreased with addition of MWCNTs. The diminution of mechanical proper-ties of the nanocomposites, though concomitant with a significant increase in electrical conductivity, implies the mechanism for mechanical reinforcement for PE/MWCNT composites is filler-matrix interfacial interactions and not filler percolation. The temperature of crystallisation (T.) and fraction of PE that was crystalline (F-c) were modified by incorporating MWCNTs. The thermal decomposition temperature of PE was enhanced by 20 K on addition of 10 wt% MWCNT. (c) 2005 Elsevier Ltd. All rights reserved.

Effect of exfoliation and dispersion on the yield behavior of melt-compounded polyethylene-montmorillonite nanocomposites

The yield behavior of melt-mixed nanocomposites containing 5 wt % organically modified montmorillonite in matrices of a linear low-density polyethylene (LLDPE) or a modified polyethylene was studied as a function of the temperature. and strain rate. In the melt-mixed LLDPE nanocomposite, the montmorillonite showed a slight increase in the clay spacing, which suggested that the clay was at best intercalated. Transmission electron microscopy (TEM) images showed that the dispersion in this nanocomposite was poor. The use of the modified polyethylene promoted exfoliation of the clay tactoids in the nanocomposite, as assessed by X-ray diffraction and TEM. In both nanocomposites, the yield mechanisms were insensitive to the addition of the organoclay, even though modest increases in the modulus were produced. (c) 2006 Wiley Periodicals, Inc.

Evaluation of performance reference compounds in polyethylene-based passive air samplers

Polyethylene-based passive air samplers (PSDs) were loaded with performance reference compounds (PRCs) and deployed in a wind tunnel to examine the effects of wind speed on sampler performance. PRCs could be loaded reproducibly into PSDs, with coefficients of variation only exceeding 20% for the more volatile compounds. When PSDs were exposed to low (0.5-1.5 m s(-1)) and high (3.5-4.5 m s(-1)) wind speeds, PRC loss rate constants generally increased with increasing wind speed and decreased with increasing sampler/air partition coefficients. PSD-based air concentrations calculated using PRC loss rate constants and sampler/air partition coefficients and air concentrations measured using active samplers compared closely. PRCs can be used to account for the effect of differences in wind speeds on sampler performance and measure air concentrations with reasonable accuracy. (c) 2006 Elsevier Ltd. All rights reserved.

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. (c) 2005 Elsevier Ltd. All rights reserved.