Two-stage, drawing

Cansfield et al. [221] have also studied the slow two-stage drawing of polypropylene. A series of polymers with different molecular weights and molecular weight distributions were examined. 

FIGURE 3.60 Modulus versus draw ratio for polypropylene fibers. (From Taylor, W.N. Clark, E.S. Polym. Eng., 1978, 18, 518. With permission.) 

The fibers produced by Porter and Clark are transparent, indieating the absence of structural units larger than about 0.5 pm. In addition, the fibers took a permanent set when bent. The bending caused internal fibrillation. 

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Fig. 8. x,ra 5ltaos versus opl for PET drawn at 85 °C O single-stage draw A two-stage draw. Reproduced from Polymer by permission of the publishers, Butter-worth Co (Publishers) Ltd. (C)... 

Figure 12.11 Schematic of a modern staple drawline for PET fibers 1, spun yarn supply cans 2, lubricating bath 3, two-stage drawing 4, heatsetting 5, cooling 6, reheating 7, crimping 8, dyeing 9, cutting 10, baling...

Spectacular results have been obtained with two-stage drawing of polyoxymethylene by Clark and Scott (1974). In the first stage and polymer is drawn to the natural draw ratio of about 7. The second stage takes place at a very low velocity (50% elongation per minute) up to an ultimate draw ratio of about 20. The optimum temperature for the second step is about 30 °C below the standard melting point. A modulus of 35 GPa, about 70% of the theoretical value has been obtained in this way. The drawn material did not show folded chain periodicity anymore. 

Fig. 8. Modulus-draw ratio relationship for POM samples drawn at 14S °C. Single-stage drawing was performed at 10 cm/min (A) and 1 cm/min (O). In the two-stage drawing experiment ( ) the samples were first drawn for 72 s at 10 cm/min and then at 1 cm/min...

Figure 4. Tensile modulus vs. DR for UHMW-PE films prepared drawing of SGC mats and by two-stage drawing of initial ED extrudates.

The effect of draw technique and conditions, and sample Mv on the drawability of UHMW-PP SGC mats has been studied. It was found that these mats also was most deformable by two-stage drawing, as was observed for UHMW-PE SGC mats. Furthermore, the initial EDR also had a major effect on the drawability for the second-stage tensile drawing. Thus, the SGC mats of PP with different Mv s were initially coextruded at 130°C and a low EDR of 6, followed by tensile drawing at optimum temperatures of 150-165°C, depending on the sample Mv. The maximum achievable DR increased slightly with Mv, from 60 for a Mv of 3 x 10 to 80 for a Mv of 36 x 10, Such an increase in drawability with Mv is not so remarkable as found in PE. 

Figure 6. Tensile modulus (a) and strength (b) ys. DR for a range of PP molecular weights. The SGC mats were drawn by two-stage drawing.

The SGC mats of UHMW-P4M1P was also found to be ultradrawable up to a DR of 80 by a two-stage drawing technique. Although the mechanical properties of this helical polymer are substantially poor compared to the... 

Hot drawing of the extruded ( as-spun ) fibres was carried out on a small-scale drawing unit consisting of two pairs of advancing rollers and a hot plate. One- or two-stage drawing procedures were used. More detailed accounts of the extrusion and drawing conditions are published elsewhere (17,18). 

It is clear from Table I that in all cases the overall draw ratio was considerably increased by two-stage drawing. For pure PP fibres, there was a large increase in initial modulus and a small increase in fibre tenacity in comparison with one-stage drawing. For the... 

Fig. 10. Staple fiber line (1) spim yam supply cans, (2) lubricating bath, (3) two-stage drawing, (4) heatsetting, (5) cooling, (6) reheating, (7) crimping, (8) drying, (9) cutting, and (10) baling.

A two-stage drawing process of the paracrystalline as-spun fibers of low orientation yields drawn fibers of very high tenacity (85 cN/tex) with linear density around 0.4 tex. 

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