Paper (5) to the Institute of Materials 6th International Conference on Fibre Reinforced Composites, Newcastle, England, 29-31 March 1994.

Published in Plastics, Rubber and Composites Processing and Applications, Vol 24, No 3 (1995).
S F Bush with F B Yilmaz and P F Zhang

Abstract

A wide series of experiments has been undertaken to measure impact strength as a function of fibre length and concentration, the fibre/matrix interface, and induced fibre-mat structure and matrix properties. Both commercially-available long-fibre polypropylene granules and in-house polypropylene and polyethylene glass-fibre compounds have been used where the interface conditions are known and can be varied. For the fibre-mat structures achieved, notched impact strengths rise with fibre lengths and with fibre concentration, giving in all cases an improvement on the virgin polypropylenes – for some conditions a five-fold improvement at 25% w/w concentration.

Paper to the Institution of Chemical Engineers Conference, Process Intensification, 18th-19th April 1983.

S F Bush

Introduction

The relatively low growth rates, around 3% per annum or less, projected for the next ten years, contrasted with those obtaining when most of the current chemical processes were designed, prompts a re-examination of the economies of scale for a number of reasons.  In the last few years, under the spur of sharply increased energy prices, much effort has naturally been devoted to increased energy utilization efficiency.  A number of such endeavours have, by occasioning a re-examination of existing designs, enabled savings in capital as well as energy to be made. None-the-less, when design inefficiencies have been stripped out, energy is the resource we use to achieve intensification or volumetric compactness. The relationship between energy efficiency and intensity rules in an approximate way in all industries, including Man’s oldest industry, agriculture, as has been pointed out by Green (1), (Table 1):

While the detailed figures depend on precise definition, the trend is clear. Equally clear for optimal design is the need to determine the fundamental limiting relationship between energy efficiency (including availability) and intensity, for the generality of chemical processes. Le Goff (2) has recently addressed this problem in connection with the design of heterogeneous reactors.

There is additional reason to examine the design fundamentals of polymerization reactors in particular and that is because the products (i.e. polymers) are now demanded in ever-increasing variety. The period 1950-1970 of rapid scale increases has been followed to-date by a period of adaptation of the processes and modification of the basic polymers (polyethylene, PVC, polystyrene, etc) designed and introduced in the former period under basically different assumptions. Additionally a number of second-generation polymers (e.g. polycarbonates, poly(phenylene oxide)) have become fully commercial during the current period. As will be indicated, there are thus both significant similarities and differences with the general class of chemical processes and both general and particular principles to apply.

References

(1) M B Green (1976), Lecture to the Society of Chemical Industry.

(2) P Le Goff (1980), Chemical Engineering Science, 35, 2029-2063.

(3) K G Denbigh (1957), “Principles of Chemical Equilibrium”, pp 71-72.

(4) H Brauer (1982), Institute of Chemical Engineers Symposium, 78, T5/11-19.

(5) P J Tail (1980), Macromolecular Chemistry, 1, SPR, Roy. Soc. Chem. 3-21.

(6) K H Laidler (1965), “Chemical Kinetics”, p 70 ff.

(7) G I Taylor (1954), Proc. Roy. Soc. A220, 446-467.

(8) S F Bush (1969), “The Design and Operation of Jet-stirred Reactors for Chemical Kinetic Studies”, Trans. I. Chem. E. 47, 59-72.

(9) R S Brodky (1966), in Uhl and Grey “Mixing”, p 52.

Paper to the Mixing and Polymer Processing Conference of the European Federation of Chemical Engineering, Delft, Holland

S F Bush with E Jongen.

Introduction

A major problem in the manufacture of a number of important polymers such as polyethylene, polyester and nylon, is the occurrence of non uniformities which show up as streaks and blobs in film and cause breaks in filament. The major source of this problem lies in the fact that during manufacture a tiny fraction of the material is exposed to reaction conditions very significantly different from those applying to the bulk of the material, by virtue of the exceptional residence times developed at vessel walls. Such non uniformities are particularly likely to occur at cooling surfaces since the unavoidable tendency to stick there is enhanced by the increase in viscosity through the thermal boundary layer.

The present paper outlines a description of the reaction and flow of polyethylene and ethylene through tubes from which there is a substantial extraction of heat. The driving force is provided by pressure drop.

In the high pressure stirred autoclave process, the reaction in the tube is incidental to its main function of cooling the polymer and reducing pressure (by about 400 atmospheres) at the outlet from the autoclave. In the tubular process, the overall pressure drop through a tube is greater (around 2000 atmospheres), since the tube is itself the main reactor. The chemical kinetics and fluid mechanics equations have been set up to cover both cases, but the applications referred to in this paper arise from the autoclave process.

See also the section on Applications to Existing Products and Processes.