MELT SPINNING OF POLYPROPYLENE

The melt spinning by screw-extruder of polypropylen was carried out at 275°C, with various winding speeds (or drafts). The hot drawidg of undrawn filaments was carried out at 120°C in hot air.Some properties of undrawn filaments are as follows: The increase of draft produces the increase of tensile strength and the decrease of elongation. The birefringence of undrawn filament also increases: with the increase of draft, and the relationship of the two has the character of a saturation curve. The effect of draft on the density is not so large.Some properties of drawn filaments are as follows: The birefringence and the tensile strength increases and the elongation decreases with increasing draw ratio, varying with draft at the spinning process. The density increases by hot drawing rangeing from 0.909 to 0.911. Drawing under the above condition, tensile strength increases proportionally and elongation decreases inversely to draw ratio. By drawing the initial elasticity it also increases with the decrease of elongation.For example, as to the filament with draft 800 and draw ratio 5, the denier becomes 4 d and the tensile strength 9.7-10.3g/d.