Biaxial drawing

Several more recent variations of the film-to-fiber approach result in direct conversion of film to fabric. The film may be embossed in a controlled pattern and subsequently drawn uniaxiaHy or biaxiaHy to produce a variety of nonwoven products (47). Addition of chemical blowing agents to the film causes fibrillation upon extmsion. Nonwovens can be formed directly from blown film using a unique radial die and control of the biaxial draw ratio (48)... 

Figure 7. A. Schematic of an elliptic flaw initially at right angles to the draw direction. For a uniaxial draw, the draw ratio D = at. At a critical draw ratio D = I/R the ellipse becomes circular. For higher draw ratios (D > I/R), the ellipse forms with a 90° change in its orientation. B. Schematic of the effect of increasing draw ratio on an ellipse initially at some angle other than 90° to the draw direction. C. A general biaxial draw (al9 a2) acting on an ellipse at initial orientation pto the, major drawm direction (a. > as).

Films can be uniaxially drawn on roll mills. Such drawn films have increased tensile strengths along the draw direction, but decreased tensile strengths perpendicular to the draw direction. Actual improvements are first obtained by biaxial drawing (Table 36-10). Biaxial drawing is achieved by up to eight-sided drawing machines which draw in both directions simultaneously. 

Under biaxial drawing conditions of the small punch test (Edidin and Kurtz 2001), the large-deformation mechanical behavior of polyethylene also... 

A drawn film was also included in the analysis [66]. The quasi-isothermal TMDSC of this drawn sample is reproduced in Fig. 6.109. It was produced out of practically amorphous PET by biaxial drawing at 368 K. The sample retains no residual cold crystalhzation and has a higher rigid-amorphous fraction than the semicrystalline reference PET of Fig. 3.92. Long-time aimealing causes an aimealing peak of the crystals, as described in Sect. 6.22, but displays no hysteresis peak, as was also observed for the slowly cooled, undrawn PET samples with similar crystallinity used as an example in Fig. 6.129. 

There are many factors within the cast film process that can affect the final quality of the film. The semicrystalline nature of SPS requires special attention to draw ratios and annealing temperatures. The effect of annealing temperature and biaxial draw ratio on the fracture mechanics of SPS homopolymer can be seen in Figure 14.20. The orientation draw was conducted at a typical SPS draw temperature of 110°C. 

By simple modification of the shape of the die holes, these three techniques can be adapted to the production of films and membranes. In such cases, the monoaxial stretching of fibers is replaced by a biaxial drawing that improves the two-dimensional mechanical properties. 

Under biaxial drawing conditions of the small punch test [8], the large-deformation mechanical behavior of polyethylene also displays strong molecular weight dependence. Representative small punch test data, shown in Figure 2.3, were conducted at room temperature at a rate of 0.5 mm/min. 

Several polymer forming processes are dominated by uni- or biaxial drawing, such as FS and film blowing. These forming processes contrast with IM, where there is hardly any control over the physical and mechanical properties, which will vary over the whole product. With... 

Figure 4. Plots of true stress versus nominal strain of equi-biaxial drawing of PET films.

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