Nicholas E. Hudson

Transient elongational rheology of polymeric fluids

Abstract The elongation viscosity of a high viscosity polymer fluid can be measured by equilibrium techniques. Low viscosity fluids require the use of non-equilibrium methods which produce an instantaneous value. Using two solutions of polyisobutylene in different solvents it can be shown that these instantaneous values of elongational viscosity are strongly dependent on the experimental method employed for the measurement. However, by considering the results in terms of a three-dimensional plot of elongational viscosity, strain and time of elongation, a three-dimensional surface can be produced. It is postulated that the different techniques merely trace out different lines on this surface, producing the apparently different data when projected onto a two-dimensional plot of elongational viscosity vs strain (or strain rate).

The use of a capillary rheometer to determine the shear and extensional flow behaviour of nasal spray suspensions.

The rheological profiles of four commercial nasal spray suspensions (Beconase, Flixonase, Nasacort and Nasonex) were compared using rotational viscometry. Two of the nasal sprays (Beconase and Nasonex) were further examined in both shear and extension using a capillary rheometer under conditions similar to those experienced at the spray nozzle (i.e. extremely high shear rates with significant stretching or extensional flow).

The rheology of pigment dispersions

SummaryA kinetic model is developed to relate the measured shear stress in a dispersion with the rate of deformation, and with the level of structure caused by the competing effects of flocculation and deflocculation.The model parameters are determined from experimental data obtained from equilibrium and transient oscillatory shear, using dispersions of a pigment in three different oil-based media. It is found that the model can successfully describe the flow behaviour of the dispersions under all three types of deformation, and account for different concentrations and temperatures.ZusammenfassungEs wird ein kinetisches Modell entwickelt, das die in einer Dispersion gemessene Schubspannung mit der Deformationsgeschwindigkeit in Beziehung setzt unter Berücksichtigung der im Wettbewerb stehenden Flokkulations-und Deflokkulationseffekte.Die Modellparameter werden mit Hilfe experimenteller Daten bestimmt, die zu stationären und oszillatorischen Scherströmungen unter Einbeziehung wechselnder Beanspruchungsarten erhalten wurden. Dabei wurden Pigment-Dispersionen in drei verschiedenen Medien auf Öl-Basis verwendet. Man findet, daß das Modell das Fließverhalten der Dispersionen unter allen betrachteten Deformationstypen sowie bei den verschiedenen angewandten Konzentrationen und Temperaturen erfolgreich zu beschreiben vermag.

The effect of hard segment structure on rheological properties of solutions of segmented polyurethanes

Abstract Segmented polyurethanes based on polypropylene glycol, butane diol and a mixture of (diphenylmethane diisocyanate)/(toluene diisocyanate) (MDI/TDI) were prepared and characterized. Soft segment concentration was kept constant at 50% in all polymers but the structure of the hard segment was varied by using MDI/TDI ratios from zero to pure MDI. The aim of the work was to examine solution properties as a function of the polymer composition and also the stability of polyurethane solutions in dimethylformamide. Polyurethane solutions exhibited Newtonian behaviour up to rather high concentrations of 30%. No structure formation, due to association of polyurethane molecules through hydrogen bonding, was observed in DMF up to concentrations >70%. Ageing of polyurethane solutions, manifested as decrease of viscosity with time, was observed only with two high molecular samples. Solubility of the polymer increased and rigidity decreased with increasing TDI/MDI ratio. Activation energy for viscous flow increased with solution concentration and rigidity of the hard segment.

Rotational moulding – a simplified theory

This paper considers a number of theoretical approaches to the description of the various and complex issues, which are involved in rotational moulding. Experimental rheological measurements are presented to illustrate the changes, which can occur in typical rotational moulding grade polymers when subjected to shear and also when held at an elevated temperature for a sustained period of time. The influence of temperature on the viscosity is indicated to be an important factor in bubble release and maintenance of wall thickness in thick-walled mouldings. Although it is desirable to have a low viscosity in the melt to aid bubble release and hence reduce the time that the polymer spends in the melt phase, the problem of maintaining contact with the mould wall can arise in thick moulded sections.

Synthesis and Physical Property Evaluation of a Series of Poly(N‐2‐Pyridylmethyl Methacrylamide‐ Co‐Methyl Methacrylate)s and Related Polymers

The synthesis and physical properties of a series of poly(N‐2‐pyridylmethyl methacrylamide‐co‐methyl methacrylate)s and related copolymers is presented. High yields of the copolymers were obtained starting from copolymers of methacryloyl chloride with methyl methacrylate, which reacted almost quantitatively with 2‐pyridylmethylamine or a related amine, to give copolymers that are capable of interpolymer chain hydrogen bonding. Copolymers of (N‐2‐pyridylmethylmethacrylamide) (PyMeMA) were obtained in high yield and investigated in detail. The variation in the molar mass data obtained using different methods was interpreted as being a consequence of solvent‐induced aggregation effects. Examination of the solution properties indicated that the polymers are indeed able to form transient aggregates through hydrogen bonding interactions that, when subject to shear, separate into smaller aggregates or individual polymer chains. These hydrogen bond interactions are also evident in the solid state physical properties as observed in variation of the glass transition temperature, but to a lesser extent than they are in the dynamic mechanical analysis. Adhesion measurements once more indicate the potential of these materials to exhibit enhanced properties as a consequence of hydrogen bonding interactions. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Rheology of Spray-Dried Egg Yolk-Xanthan Gum Aqueous Dispersions

Protein-polysaccharide systems have not only scientific interest in the effort to understand the behaviour of complex multicomponents systems, but they also have many technological implications, above all in the development of new food products. They are particularly useful for the formulation of low-fat stuffs and for the enhancement of the funcionality of “natural” food ingredients. In fact, they are the most important structure forming macromolecular ingredients in foods.