Surface modification of polyethylene by electrical discharge treatment and the mechanism of autoadhesion

A reexamination of previous studies concerning the electrical (‘corona’) discharge treatment of polyethylene and the resulting enhancement of autoadhesion has been carried out. X-ray photoelectron spectroscopic data provide new insight into the phenomenon by showing surface oxidation to result from treatment in ‘inert’ gases. Treatment in hydrogen is an exception and results in no autoadhesion enhancement even though energy input into the film is more efficient than in air. Autoadhesion theories based on electret formation are rejected; those based on hydrogen bonding are largely up-held and shown to be more generally applicable than at first imagined.     

Compression characteristics of pharmaceutical powder mixtures

A study has been made of the compression characteristics of binary, ternary and quaternary mixtures of the ingredients of a typical griseofulvin tablet formulation. The results have been analysed in terms of the compression equations of Heckel and of Cooper and Eaton and in terms of Cheng's equation for tensile strength.The terms in these equations vary systemactically with the composition of the mixtures and they can be employed as a measure of the hardness and compressibility of the different mixtures.     

E.s.r. study of annealing and melting effects on the molecular motion of spin trapped chain-end radicals located on the polyethylene surface

E.s.r. spectra of chain-end spin labels on the surface of polyethylene powder were obtained for high and low density polyethylene samples at various stages of heat treatment process. The subsequent crystalline structures of the samples were examined with wide angle and small angle X-ray diffraction spectra. The effects of annealing on the motion of the labels were dependent on annealing temperature and the type of the samples. Higher temperature annealing decreased the rotational correlation times (τ_c) and their activation energy in high density polyethylene but did not affect those of low density polyethylene. Melting decreases the values of τ_c and ΔE for both high an low density polyethylene samples. The cause of these decreases were attributed to the changing of the sites of the chain-end labels. The motion of the labels appeared to be influenced by the local segmental motion of the polymer main chains.     

Comparison of methods for assessing powder attrition

For materials with broad size distributions, it is recognized that the small fractions of the large-size particles are few in population counts. However, these particles represent a major fraction in the total solid weight. The small errors in number—size measurements for these large sizes will magnify in orders of magnitude in the volume—size distribution data. It is for this reason that use of number—size distribution data in evaluating classification performances of a separator is preferred. Formulations of the grade efficiency function G(x) based upon the number—size distribution data are derived. It has also been demonstrated that the results are more consistent and reliable.     

On the application of the Heckel and Kawakita equations to powder compaction

The densification of powders at compression is described by the Kawakita equation up to some critical pressure Π_c and by the Heckel equation above Π_c. At the transition point, the condition is imposed that the incremental densification (first derivative of apparent volume or porosity by pressure) is continuous. If elastic effects are taken into account, additional terms have to be included in the formulae. However, it can be shown theoretically and experimentally that under conditions which in most cases are fulfilled, the Kawakita equation represents a good overall approximation if ‘zero-pressure’ data (i.e. after ejection) are used. This ‘spurious’ Kawakita equation also provides a formula for the compressional energy.     

On the modelling of continuous emulsion polymerization using a population balance with instantaneous radical termination

An analytical solution of a population balance is used to mathematically describe continuous emulsion polymerization. Steady state performance is examined. The assumption of instantaneous free radical termination within particles is made. The desorption mechanism is included. Particle size distribution information is obtained, and the effect of the desorption mechanism is noted. A desorption rate constant is calculated when the model is fit to data found in the literature.     

Redox reaction of tri(2-deoxy-2-L-ascorbyl)amine. Formation of a persisting free radical species in water

Electrochemical studies showed that tri(2-deoxy-2-L-ascorbyl)amine ($\text{1}$), a new compound isolated as one of the products of reaction of dehydro-L-ascorbic acid with phenylalanine (with added L-ascorbic acid) in ethanol, is oxidized in aqueous solution in two reversible one-electron transfer steps, on mercury or platinum electrode. The first step occurs through the dianion, and its product is an unusually stable blue anion radical giving a characteristic ESR signal. The product of the second step of oxidation is labile and is slowly converted into the oxidized form of di(2-deoxy-2-L-ascorbyl)amine, presumably by hydrolysis with splitting of L-ascorbic acid.     

Evaluation of force—displacement measurements during one-sided powder compaction in a die — the influence of friction with the die wall and of the diameter of punches and die on upper and lower punch pressure

On an instrumented single-punch press, working at an overall rate of 30 strokes per minute, the influence of diameter of punches and die on upper and lower punch pressure, measured during the densification of a powder with an initial height of 8.0 mm, has been investigated.The upper punch pressure necessary to effect a certain state of density, proved to decrease with increasing diameter, whereas the lower punch pressure proved to be independent of the diameter. The upper punch pressure differences, found for diameters ranging from 11 to 17 mm, could not be accounted for by differences in the actual speed of compaction between the individual force displacement measurements and it could be concluded that these pressure differences were exclusively due to an influence of the diameter on the process of compaction.By using a number of hyportheses concerning friction with the die wall, it was possible to derive a mathematical model for the pressure distribution on the upper punch which qualitatively agreed with the experimental results.     

Rheo-optical studies on the deformation mechanism of semi-crystalline polymers. IX. Dynamic birefringence behaviour of a high-density polyethylene film having row nucleated crystalline texture of c-axis orientation

The dynamic birefringence behaviour of a high-density polyethylene film having a row-nucleated crystalline texture of cylindrites oriented along the machine direction of fabrication was investigated over frequency and temperature ranges covering the α mechanical dispersion of this material. The results are discussed in combination with the dynamic X-ray diffraction behaviour of the material so as to explore the structural origins of the α mechanical dispersion, not only for this particular material, but also for bulk-crystallized polyethylene having a spherulitic texture. Two deformation processes contribute to the α₁ mechanism, corresponding to the lower temperature relaxation process in the α mechanical dispersion; i.e. (i) a lamellar detwisting process involving the rotation of crystal grains within the crystal lamellae or of lamellar segments around the crystal b-axis or the lamellar axis, which predominates in the MD (machine direction) specimen, and (ii) lamellar shearing associated with the rotation of the crystal grains or the lamellar segments around the crystal a-axis, which is accentuated in the TD (transverse direction to fabrication) specimen. An additional deformation process, lamellar bending, is also observed in the MD specimen as being likely elastic in the dynamic response, and its contribution is found to be substantial, not to the α dispersion, but rather to the β dispersion of this material. The α₂ mechanism corresponding to the higher temperature relaxation process in the α mechanical dispersion is observed to be more pronounced in the TD than in the MD specimen. The apparent dynamic crystal lattice compliance shows a definite dispersion during activation of the α₂ mechanism, but a slight dispersion during activation the α₁ mechanism, suggesting that the α₂ mechanism must be related to an intracrystal relaxation process whereas the α₁ mechanism must be associated with an intercrystal relaxation process at their boundaries.     

Error analysis and modelling of non-linear stress-strain behaviour in measuring dynamic mechanical properties of polymers with the Rheovibron

The Rheovibron is widely used for measuring the dynamic mechanical properties of polymers. Poor reproducibility and data variation which have been considered inherent to the Rheovibron operation necessitate both instrument modifications and modelling of the instrument operation for quantitative interpretation of the experimental data. The instrument modifications that have been made in this study include electronic modifications, a new clamp design that eliminates sample mounting and slippage problems, and the design of an environmental chamber, which, along with a nitrogen purge, eliminates moisture condensation on the sample at low temperatures. A previously-developed mathematical model for the instrument has also been extended to account for the effect of the static stress and the stress rate imposed on the sample during measurement. Based on a simple constitutive relation for non-linear stress-strain behaviour of polymers, this model has been applied to a number of polymeric materials including polyethylene, polyimide, poly (ethylene terephthalate), and polypropylene, among others. The instrument modifications and modelling of the influence of static stress and the stress rate imposed on the sample during dynamic mechanical testing allows for reproducible (within 5%) and accurate use of the Rheovibron.     

Comparison of comminution data with analytical solutions of the fragmentation equation

Analytical solutions to the fragmentation equation are presented for specific rates of breakage and primary breakage distribution functions often used to correlate comminution data. These solutions, obtained by similarity arguments, compare favorably with the experimental data of Austin et al., and suggest that correlation of data via similarity techniques may facilitate determination of function parameters.     

PtSiO2: II. Characterization of the gel and the platinum particles by X-Ray diffraction

Modern techniques for analysis of X-ray diffraction profiles have been applied to several of the platinum-silica gel catalysts described in Part I to determine average platinum crystallite size, percentage exposed, crystallite shape, size distribution, lattice parameter, residual stresses and strains, presence or absence of faulting, and mean-square amplitude of vibration. In addition the surface area of the gel was determined with small-angle scattering (SAS). There is good agreement between the percentage exposed of platinum measured by gas adsorption in Part I and the results reported here, calculated from crystallite sizes, indicating the crystallite size is the true platinum particle size. Crystallites to sizes as small as ≈25 Å have been examined. Furthermore, the crystallites are equiaxed in shape (and definitely not cuboidal) and are strain and defect free, except in the case where the average size is near the pore size of the gel. Size distributions are sharper when the catalyst preparation is by impregnation rather than by ion exchange. The size distributions indicate that there is coalescence of some surface species during preparation rather than coarsening (Ostwald ripening). The meansquare amplitude of vibration of platinum increases by ≈30% as the particles decrease in size from ≈100 to ≈25 Å. There is no change in the lattice parameter greater than ≈0.1%. The gel surface areas determined by SAS are in agreement with those determined in Part I by physisorbtion of nitrogen.     

Electrooxidation of terpenes—I. Synthesis of dihydrocarvone and 1-hydroxyneodihydrocarveol by anodic oxidation of limonene

The oxidation of (+) and (?) limonene, 1, in THF-H₂O (25:1), NaClO₄ on a graphite electrode gives, with a relative stereoselectivity, (+) and (?) dihydrocarvone, 5 and (+) and (?) 1-hydroxyneodihydrocarveol, 7, respectively as the major products. A logical route for this oxidation via a protonated epoxide as intermediate is proposed.     

A Revision of multiplicity and parametric sensitivity concepts in nonisothermal nonadiabatic packed bed chemical reactors

One-phase models including axial as well as axial and radial dispersion effects were analyzed. Reliable numerical methods based on the finite-ditterence approach and the Newton-Raphson method were proposed to solve these models. It was shown that two stable steady states may exist in very long nonadiabatical packed bed reactors. A relation between parametric sensitivity and multiplicity was discovered. Practical conclusions important for design of industrial nonadiabatical packed bed reactors are drawn.     

On the correlation of minimum porosity with particle size distribution

It has long been recognised that the major factors which influence the density of cohesionless material are the type of distribution of particle size, and particle shape. However, the difficulty of measuring particle shape and of expressing a particle size distribution comprehensively has proved a stumbling block to the determination of a successful correlation with porosity. None of the correlations so far has yielded an empirical relationship which can be employed with confidence to a wide range of types of particle size distribution.This paper examines some of the difficulties which are encountered with such correlations when attempting to describe the particle size distribution by Gaussian measures, and develops a new method of expression, by a single ‘offset‘ value, of a particle size distribution. A good empirical relationship is found between minimum porosity and this value, having taken due account of particle shape. It is suggested that the method will give engineers greater appreciation of the grading curve of cohesionless materials.     

Bubble dissolution with chemical reaction

The dissolution of an isolated stationary gas bubble, enhanced by a chemical reaction, in a large body of liquid is investigated. A theoretical model which properly accounts for the movement of the interface due to dissolution is formulated and solved using the method of finite differences. The finite difference results are used as a standard of comparison for the testing of various approximate solutions. These include a perturbation expansion, a quasi-stationary approximation and a quasi-steady approximation. The results of this work indicate that the quasi-steady approximation, which provides very simple analytical solutions, is an excellent one in the presence of a sufficiently rapid chemical reaction.     

Nucleophilic substitution reactions on 3-bromo- and 3-nitrobenzanthrones

Nucleophilic substitution reactions of 3-bromobenzanthrone and 3-nitrobenzanthrone have been studied. Reaction of 3-bromobenzanthrone with different arylamines gave rise to 6-arylamino-3-bromobenzanthrones. Anomalous behaviour was observed with 2-aminobenzothiazole, when the bromine atom underwent displacement, and with thiourea, when 3-mercaptobenzanthrone was obtained. Reactions of 3-nitrobenzanthrone, on the other hand, gave rise to 4-substituted amino derivatives.