Extrusion draw ratio

The ribbon was placed between two split billet halves of the same polyethylene, and the assembly coextruded through conical brass dies which had an included entrance angle of 20 and nominal extrusion draw ratios, EDR, of 12, 25, and 30. No lubricant was used. The EDR calculated from the displacement of the line mark was in good agreement with the nominal EDR defined as the ratio of entrance to exit cross-sectional area of a die. The extruded films were used only for the evaluation of the effect of deformation components on the resultant morphology and properties. The semiperipheral coextrudates obtained simultaneously from the extruded assembly were used for the x-ray study of the deformation mechanism for extrusion drawing. 

Now we shall consider examples of using the dimension D for the solution of applied problems. When polymer samples are obtained by solid-phase extrusion, the macroscopic (extrusion) draw ratio is determined by the ratio [122, 142,143] ... 

E modulus of elasticity or Young s mod- EDR extrusion draw ratio... 

It is reported that the maximum achieved tensile modulus and strength, for stereocomplex PLA films with an extrusion draw ratio of 16 and prepared by solid-state coextrusion, were 9500 and 410 MPa, respectively. In addition, these films exhibited excellent thermomechanical stability showing 9500, 7000, and 3000 MPa modulus [ ] values at room temperature, 100 and 200°C, respectively [209]. 

Extrusion Pressure. The characteristic feature of the plot of extrusion pressure P vs the logarithm of extrusion draw ratio In R is that it is convex to the axis of In R (Fig. 3). In the case of the hydrostatic extrusion of metals, the dependence is practically linear (44). This difference is because with polymers there is a more intensive strain hardening, strain rate, and pressure hardening as compared to metals. At a qualitative level this is shown as follows. 

Fig. 3. Typical graphs of extrusion pressure versus extrusion draw ratio (log scale) (a) and die angle (b). (a) Rigidex SOLPE, 2a = 30° (43). (b) High density polyethylene, EDR = 6.75 (38).

The Swelling of Extrudates. In the case of SSE, a phenomenon of extrudate swelling at the die exit is observed. Taking it into account, the quantities of the actual extrusion draw ratio i a = Sb/Se and the nominal extrusion draw ratio Bn = Sb/Sd are introduced, where Sg is the area of the extrudate cross section, Sd is the area of the die exit. Parameter B correlates with the EDR value. 

Sawai et al. studied the mechanical properties of a stereocomplex PLA film prepared by casting from a solution of an equimolar blend of PLLA and PDLA [35]. The film was uniaxially drawn by solid-state coextrusion and characterized by DMA. The optimum draw temperature resulting in the highest draw and mechanical properties was 200° C. The maximum achieved tensile modulus and strength, for the samples with an extrusion draw ratio of 16 and prepared by solid-state coextrusion of a highly crystalline stereocomplex film, were 9500 and 410 MPa, respectively. Furthermore, the PLA stereocomplex films with an extrusion draw ratio of 16 exhibited excellent thermomechanical stability as evaluated by the E measured as a function of temperature. The reported E values at room temperature, 100 and 200°C, were 9500, 7000, and 3000 MPa, respectively [35]. Equimolar amounts of PLLA and PDLA stereocomplex are therefore characterized, upon orientation, by the most relevant me-... 

Figure 4.21. Variation of coefficient of linear thermal expansion of HDPE fibers with extrusion draw ratio measurement made in axial direction [from Zachariades et al. (1979), reprinted with permission of the authors].

Sun et al. [23] studied the crystallization kinetics of PET oriented by solid-state coextrusion. The cold crystallization temperature was found to decrease with the increase in the extrusion draw ratio for samples extruded at various temperatures. This suggested presence of more amorphous chains containing the trans conformation isomer than the gauche conformation isomer. Because the trans isomer can be packed into crystal lattice more... 

FIGURE 14.1 The dependences of structure fractal dimension on extrusion draw ratio X, calculated according to the Eq. (1.9) (1,2) and the Eq. (1.12) (3) for UHMPE-Al (1, 3) and UHMPE-bauxite (2,3). The shaded region shows the X range, corresponding DS spontaneous change [11]. 

FIGURE 14.2 The dependences of crystallinity degree K on extrusion draw ratio 1 for... 

FIGURE 14.3 The dependence of entanglements cluster network density on extrusion draw ratio X for polyarylates DV (1) and DF-10 (2) [22]. 

FIGURE 14.6 The dependences of elasticity modulus E ) and fracture stress (2) on extrusion draw ratio X for componors UHMPE - bauxite [44],... 

In Fig. 14.8, the change of samples limiting draw ratio corresponding to their fracture in mechanical tests, as a function extrusion draw ratio X is shown. As one can seem the X,. increase at X growth is observed. Such behavior Xj is differed from traditionally observed one for oriented polymers, when X increasing decreases X,. owing to molecular chains mobility exhausting [19], Personally, it has been established, that for matrix UHMPE X enhancement from 3 up to 5 is accompanied by reduction from 1.18 uptol.l2[44]. 

For prepared by solid-phase extmsion samples it is assumed, that the value changes proportionally to extrusion draw ratio X. 

The total componors fracture probability p in mechanical tests is obviously equal to one. Further this value is divided at the conditionp =p +P2 follows. In Fig. 14.10, the dependence of fracture stress a on extrusion draw ratio X for componor UHMPE-Al is shown. As one can see, the growth is ceased and changes to drop(compare with the plot of Fig. 14.6). Such the dependence Oj( l) type is due to interfacial boundaries pol5mier-filler fracture at > 5 [44]. Hence, at < 5 the fracture of pol5mier matrix and interfacial boundary is equally probable (p =p = 0.5) and at A, > 5 the second fracture probability is higher (p >P2)- In addition it is assumed, that at A 5 is... 

FIGURE 14.10 The dependence of fracture stress Sj. on extrusion draw ratio 1 for componor UHMPE-Al [56]. 

The Eqs. (14.21) and (14.22) together with estimated by considered above method parameters A nd allow to calculate the dimensions and [55]. In Fig. 14.11 the dependences of Renyi characteristic dimensions and on extrusion draw ratio for componors UHMPE-Al and UHMPE-bauxite. As one can see, at the definite values X XJ the componors structure transition from multifiractal (canonical spectrum, grows at q increase [59]) to regular fractal D- = occurs and then at X>X - again to multifiractal (pseudospectrum, D decreases at q growth). 

The limiting draw ratio at fracture increase at extrusion draw ratio X growth is one from the most interesting features of the amorphous polymers extrudates [26,61]. Such effect was observed and in the case of DF-10 extrudates [2], Let us consider the value theoretical estimation... 

Figure 2 Shear flow profile for low molecular weight MOPE (Alathon 7050) at extrusion draw ratio 24.

Figure 3 Variation of modulus with extrusion draw ratio at a series of different extrusion temperatures, extrusion pressure 0.23 GPa. The dashed line indicates the maximum draw ratio attainable. Ref. 14.

Addition of the pull load increases the extrusion rate until fracture occurs in the die marked on the graph. The polymer is a split billet of Alathon 7050, extrusion draw ratio 36, temperature... 

This section deals with semicrystalline thermoplastics that cannot be processed by the techniques described earlier. Perkins and Porter (22) have reviewed the solid state deformation of polymers in detail and describe the numerous reports of solid state extrusion. Aharoni (23) has reported that a number of polymers may be solid state extruded to high draw ratio (> 10) by the conventional process. These include HOPE, poly(ethylene oxide), poly(4-methyl pentene-1). Polypropylene is also readily extrudable (24). However, there are many other polymers that would be attractive if they could be obtained in high draw, particularly the established fiber-forming polymers such as the nylons and poly(ethylene terephthalate). The ma,ximum extrusion draw ratio that has been reported for nylon 6 is 5 (25). This has been attributed to the onset of strain hardening at much lower extensions than polyethylene (10). Ultrahigh molecular weight polyethylene is also of interest as a way of improving the mechanical properties. 

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