Presented before Divisions o f Industrial and Engineering Chemistrw and Paint, Varnish, and Plastics Chemistrg at the 112th Meeting of the American Chemical Societg, New York, AT. Y.
Introductory Remarks T. S. Carswell Commercial Solvents Corporation, Terre Haute, Ind.
I
T IS somewhat of a pioneering experiment to hold a symposium
is unique in t,hat the finished products are always mat,erials of extremely high viscosity and it' is in handling products which flow with such difficulty that most of t,he chemical engineering problems are met. Two of the papers in this symposium are specifically involved with t'his phase of the problem. Two other papers compare German developments with our own practices, and are particularly interesting in contrasting methods of handling which were developed abroad to those which we have doveloped. I t is to be hoped that. this symposium will lead to other and more exhaustive treatments of the subject. There is really very little information in the literature which the practical chemkal engineer can utilize in the design of equipment where flow of high viscosity plastics under pressure is concerned. The topic is a worth-while one for a more exhaustive study by some of our chemical engineering schools.
on chemical engineering techniques in the ,plastics industry. The plastics industry in this country is relatively new. The earliest synthetic plastics in the United States were the phenol aldehyde resins, which started with Baekeland's original experiments in 1909, but did not grow to a large volume of business until a number of years later. The manufacture of thermoplastics is much newer and the more important synthetic members of the latter group-styrene and vinyl chloride-began t o be important articles of manufacture in this country less than a decade ago. The organic and physical sides of the plastics industry have been thoroughly covered in recent years; there is much less information regarding the developments in chemical engineering. The processing of plastics is a branch of chemical engineering in so far as it involves handling chemical products under elevated temperatures and high pressures. I n fact, the plastics industry
Rheological Problems in the Processing of Plastics Rolf Buchdahl
H. IC. Nason
iMonsanto Chemical Company, Springfield, Mass.
Monsanto Chemical Company, Dayton, Ohio scribed. The problem of obtaining material constants which are independent of the instruments used is given particular attention. Because the viscosity coefficient of most high-polymeric systems is not only a function of temperature but also a function of time, shearing force (or rate of shear), and previous history, i t is important to obtain a complete evaluation of the flow properties, in order to establish a satisfactory correlation between them and the processing behavior. In the final section i t is shown how the flow- properties affect-and to some extent determine-the processing behavior of plastic systems. Because of the lack of extensive quantitative data it is possible to give only a qualitative discussion, The following processes are considered in some detail: extrusion, molding, calendering, and coating of surfaces,
]In the first part of this paper the various deformation mechanisms of high-polymeric substances are discussed in a general manner. Three different types of deformations are possible: ordinary elastic, highly elastic, and viscous deformation. The various constants which characterize these mechanisms are: a set of elastic moduli, a set or spectrum of relaxation times, and a viscosity coefficient. If a variable force is acting on the material, the dependence of the elastic moduli and of the viscosity as a function of the frequency must be taken into account. The relationship between the viscosity coefficient and molecular properties is considered with particular reference to Eyring's theory. I n the second part of the paper various methods of measuring the flow properties of plastic systems, covering a wide consistency range, are de-
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