GB1132406A - Polypivalolactone yarn - Google Patents

Abstract

1,132,406. Producing polypivalolactone yarns. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 21 Aug., 1967, No. 38434/67. Heading B5B. Polypivalolactone filaments having a tenacity of at: least 7 g/den and an elongation at break of not more than 20% may be produced by melt-spinning polypivalolactone having an intrinsic viscosity of not less than 0À75 (measured in trifluoroacetic acid at 25‹ C.), preferably between 2 and 4, through a spinneret having orifices of at least 0À2 mm. diameter, but in particular having orifices of 0À7 to 2À5 mm. diameter, preferably of 1À0 to 1À5 mm. diameter while applying drawdown at a ratio of 50 to 500, preferably of 100 to 300. It is essential that the extruded filaments after having been drawn down, are quenched, i.e. shock-cooled, by means of a liquid medium having a temperature below 100‹ C. The solidified filaments (usually formed into a yarn before or after the quenching step by passing them through a convergence guide) are then annealed at a temperature between 110‹ and 220‹ C., preferably between 140‹ and 180‹ C., without applying stretch. The annealing time is usually at least <SP>1</SP>/ 10 th of a second, e.g. 3-120 minutes, in particular 10 to 30 minutes. The filaments may be allowed to shrink freely or to a certain extent, but are advantageously kept at constant length during annealing. Lastly, the filaments are stretched to 65-95%, preferably to 70-85%, of the elongation at break of the annealed filaments. Thus, if the filaments possess an elongation of 70% (i.e. the filaments or yarn will break when stretched to 1À7 times its original length) it will, upon stretching at a draw ratio of 1À6 : 1, provide a yarn stretched to 85% of the elongation at break of the annealed yarn. Suitable stretch ratios are in the range of 1À1 : 1 to 2 : 1, preferably of 1À4 : 1 to 1À75 : 1. Stretching may be carried out at a temperature from room temperature up to 210‹ C. but is preferably effected at temperatures between 150‹ and 200‹ C. The stretched yarn is subsequently wound up. on known means. The term " polypivalolactone " is defined as a linear polyester consisting essentially of recurring ester structural units having the formula The application of draw down to the. extruded. filaments may be applied to them while they are passing through a zone, e.g., a " hot box" situated immediately next to the spinneret and.. maintained at a temperature between 175‹ and 305‹ C., in particular between 250‹ and 300‹ C. and in which the diameter of the filaments is reduced to a diameter of between <SP>1</SP>/ 7 and <SP>1</SP>/ 20 . of the diameter at which. the filaments. are. extruded. The " hot box " may have a length of 10 to 30 cm. and the quenching zone is preferably not more than 35 cm. below the. hot box.