Extrusion solid-state, HDPE

In this chapter the solid state extrusion of different grades of polyethylene is discussed. The term coprdyetfaylene stands as weU for short and long branched PE as for the nearly alternating 1 1 oipolymer poly(ethjdene-aj-chlorotrifluoroethylene) (PECTFE). It is well known that even HDPE cxsitains a certain amount of ort branches. Therefore, it isi of interest to note that already one butyl side group per thousand main diain carboni atoms effects the solid state extrusion properties of PE remarkably. 

In ram extrusion experiments, the pressure is applied directly to the semicrystalline billet by use of a piston. Ram extrusion was used by Imada and coworkers for the extrusion of PP13 and of HDPE19 and for the coextrusion of HDPE withn-parafBns2 . Figure 1 gives a schematical representation of the apparatus used for ram extrusion. To decrease the friction of the billet during the extrusion experiment, a lubricant was added. A similar technique, however without lubricant, was applied for the solid-state extrusion of thermoplastic elastomers of the block copoly(ether ester) type by Drdscher and co-workers21-23. ... 

Table 2.5 clearly Indicates that the mechanical properties of solid-state extruded HOPE are much superior to the melt extruded HDPE. In fact, the tensile strength of solid-state extruded HDPE is about the same as carbon steel There are some other interesting benefits associated with solidstate extrusion of polymers. There is essentially no die swell at high extrusion ratios (extrusion ratio is the ratio of the area in the cylinder to the area in the die). Thus, the dimensions of the extrudate closely conform to those of the die exit. The surface of the extrudate produced by hydrostatic extrusion has a lower coefficient of friction than that of the un-oriented polymer. Above a certain extrusion ratio (about ten), polyethylene and polypropylene become transparent. Further, solid-state extruded polymers maintain their tensile properties at elevated temperatures. Polyethylene maintains its modulus up to 120°C when it is extruded in the solid state at a high extrusion ratio. The thermal... 

We wish to review here a series of developments made in this laboratory that have extended the range of the solid state extrusion technique for HDPE and also allows the extrusion of materials previously found to be difficult to process by conventional solid state extrusion. The properties of materials produced by these unconventional processing methods will also be described. 

The processing and properties of HDPE rods produced by solid state extrusion will be briefly described for more detail, the reader is referred to the original papers (6-8) and an extensive review by Zachariades, et al. (9). The polyethylene used was a duPont grade Alathon 7050 Mw = 57,000, Mw/Mn = 3. Melt crystallized billets were prepared by melting at 160 C and subsequent crystallization under the combined effects of temperature and pressure. The billets were extruded through a conical brass die, with an included entrance angle of 20°, in a 1 in. bore Instron capillary rheometer. 

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