Abstract
Polymer melts, combining high elasticity with high viscosity and a non-linear response to imposed stress, have provided rheology with two major stimulants during the last two decades: first was the question of how to characterize such materials; second was the requirement to express that characterization within the framework of continuum mechanics. These challenges have borne considerable fruit which the plastics industry has exploited by improving the processing characteristics of the resins and optimizing the processing technologies used to shape these resins. Those responses, which have largely effected the quantitative aspects of the plastics business in terms of increased output at higher efficiency, have themselves been checked by the combined brakes of recession and overcapacity. If the industry is to continue to advance we must change the emphases of our research from the quantitative aspects-how much-to the qualitative- how good.
In this paper I shall consider three rheological challenges: the modification of existing commodity plastics to enhance the quality of the product as exemplified by acrylic processing aids in PVC; the exploitation and control of new molecular states as exemplified by liquid crystalline order in melts; and the extension of high performance resins into the field of composites as exemplified by the development of continuous fibre reinforced thermoplastics. The common thread through these diverse topics-and the thread which will be common to the new challenges of the next decade-is the close interaction between morphology and rheology: the microstructure of the material determines the flow processes and is itself determined by the flow history.
