| 摘要 |
Fibrous, filamentous products are prepared by stretching strips or rods of foam of predominantly stereospecific polyolefin which foam has a density below 300 g/l., and has been obtained by extrusion under such conditions of temperature and blowing agent concentration that, if cooled to ambient temperature after the cross-sectional area normal to the direction of extrusion has assumed a maximum value, it would show a shrinkage upon cooling which, measured as a percentage of said area, is at least 25. The preferred polymer is polypropylene foamed to a density of 15 to 150 g/l. by chemical and/or physical blowing agents. The stretching ratio is preferably above 5:1, and stretching is preferably effected following extrusion. The products may be worked up into woven or nonwoven fabrics, or disintegrated to form staple fibre which may be worked up into yarns. In examples polypropylene is extruded and expanded with paraffin oil, sodium bicarbonate, citric acid and/or butane or pentane. |
