Abstract: A method for producing hollow articles comprises extruding a thermoplastic material, initially in a molten state, through a lubricated die having a mandrel for constraining the material into a tubular shape, cooling the outer surface of the material during its passage through the die so that said material emerges therefrom as a tubular extrudate having its inner surface molten and its outer surface at a temperature below its freezing temperature, squeezing the extrudate at suitable intervals to fuse the molten inner surface together and thereby seal discrete lengths, and inflating the sealed lengths to conform to a surrounding mould to produce a shaped article.

Abstract: the process for the production of an oriented fibrillar product from a polyarylene-oxadiazole which is heat-softenable without substantial degradation when in an air-free inert atmosphere comprises extruding contiguously disposed particles of the polymer, which particles are heat-softened but non-molten and are blanketed in an air-free atmosphere of an inert fluid, through a die to produce a substantially non-degraded oriented fibrillar product. Means are provided, if necessary, to substantially prevent relaxation of the orientation resulting from the extrusion.Particularly preferred polyarylene-oxadiazoles for use according to the process are the amorphous and non-crystallizable copolymeric polyphenylene-1,3,4-oxadiazoles having the characteristic repeating units ##STR1## where R.sub.1 is a p-phenylene radical, R.sub.2 is a m-phenylene radical, the ratio of R.sub.1 radicals to R.sub.2 radicals is within the range 60/40 to 10/90, and the R.sub.1 and/or R.sub.