Problem V Design of a Multilayered Extrusion Die

Coextrusion is an important process for manufacturing layered plastic composites, such as film, sheet, and tubing (Middleman, 1977 Schrenk and Alfrey, 1983 Schrenketal., 1963). A costly alternative would be the fabrication of individual layers of plastics followed by conventional lamination and coating. An additional advantage of the coextrusion technique is its ability to handle extremely thin films on the order of 10 xm. One of the most colorful applications of this technique is the iridescent film, which consists of hundreds of very thin layers of alternating low and high refractive indices. A typical example of this type of film consists of 116 layers of poly(methyl methacrylate) (PMMA) with refractive index 1.49 and 115 layers of polystyrene (PS) with refractive index 1.59 and total film thickness of about 20 o.m (Radford et al., 1973). 

We seek to produce a multilayered film of two polymers from a coextrusion blown film apparatus. The die is of the annular type with the mandrel rotating (see Fig. 6.31a) and its dimensions are kR = 4.8 cm, R = 5.0 cm, and L = 15 cm. The two polymers, which are presented in the schematic by black and white colors, have the same Newtonian viscosity, fj, = 500 Pa-s, at the extrusion temperature. The pressure drop in the die is AP = 3.45 MPa (500 psi) and the total volumetric flow rate is Q = 9.43 cm /s. The feedport system consists of 20 equal-size ports in total, 10 for the first polymer (black) and the other 10 for the second polymer (white). A similar feedport system with 16 ports in total is shown in 

Polymer Processing Principles and Design, Second Edition. Donald G. Baird and Dimitris I. Collias. 2014 John Wiley Sons, Inc. Published 2014 by John Wiley Sons, Inc. 

FIGURE 6.1 Mixing in the major routes for melt processing of polymers to finished products. (Reprinted by permission of the publisher from Matthews, 1982.) 

Generally, in polymer processing we are concerned with mixing in three types of systems liquid-liquid, solid-solid. 

---