Spin drawing

Combinations of two or more of the above steps into consecutive processes, such as spin—draw or spin—draw—texture, reduces manufacturing costs. In addition to continuous-fHament yam, nylon is also offered in staple, tow, and flock forms. Staple is made by cutting crimped continuous-fHament yam into 3—20-cm lengths. In manufacturing, tow is made by combining many yam ends, either flat or crimped, to give a total tow size of 6—111 ktex. 

Fig. 7. Spin-drawing processes for nylon yam (a) draw-twisting process, (b) conventional spinning process, and (c) coupled process.

Platinum, palladium and the normal alloys of platinum used in industry are easily workable by the normal techniques of spinning, drawing, rolling, etc. To present a chemically clean surface of platinum and its alloys after fabrication, they may be pickled in hot concentrated hydrochloric acid to remove traces of iron and other contaminants —this is important for certain catalytic and high-temperature applications. In rolling or drawing thin sections of platinum, care must be taken to ensure that no dirt or other particles are worked into the metal, as these may later be chemically or elec-trolytically removed, leaving defects in the platinum. 

Nylon yarn, melt spin-draw processes for, 19 752... 

PTT polymer pellets must be dried to a moisture level of <30 ppm, preferably in a close-loop hot air dryer, to avoid hydrolytic degradation during melt processing. Drying is carried out with 130 °C hot air with a dew point of < -40 °C for at least 4 h. Because of the faster crystallization rate, PTT pellets are already semicrystalline after pelletizing, and do not require pre-crystallization prior to drying as with PET. The dried polymer is extruded at 250-270 °C into bulk continuous filaments (BCFs), partially oriented yam (POY), spin-draw yam (SDY) and staple fiber. 

Fibers oriented by stretching to 4 x original length by cold drawing (two pulleys at different speeds) or by spin drawing as it is being cooled... 

Benzobisthiazole random copolymers (X) [38] were also prepared using 2-methyl terephthalic acid and terephthalic acid with l,4-dimercapto-2,5-diamino-1,4-benzene dihydrochloride. Various copolymers provided materials with a wide range of crosslink densities. High quality fibers with spin draw ratios as high as 50 to 1 were obtained by dry-jet wet spinning of anisotropic polymerization mixtures. Heat treatment of the fibers was carried out in a tube oven... 

Another effect of the variation of the extensional viscosity is the maximum extend-ibility. For polymers like high-density polyethylene, the rapid increase of the extensional viscosity during the spinning process limits the obtainable spin-draw ratio that is the ratio between the winding velocity and the velocity in the orifice. Examples can be found in an article of Han and Lamonte (1972). 

The classic researches of Wallace Hume Carothers on polymer synthesis started in the Du Pont (USA) in 1928 and bulk scale production of nylon 6 and nylon 6,6 started in 1939. J.R.Whinfield and J.T.Dickson discovered polyester in 1941 and was commercially manufactured by 1954. Yam texturising and spin draw yams produced at super high speeds have further increase the popularity of synthetic fibres [75, 76]. Polyster fibre accounts for more than 50% of the total synthetic fibre production. 

The results of spin-drawing experiments of both polymers should be compared here for illustration. Polyfilaments have been generated consisting of 12 monofilaments with a respective diameter of 30m at a take-up speed of 2,000 mmin Table 2 shows the textile physical parameters and data of the crystallinity of the PHB and PLA multifilaments. 

These results show explicitly the influence of different processing, especially spin drawing, conditions on the structure-property relationships of samples, especially fibers. 

PLA Fambri et al. [27] compiled a list of present literature data on PLA fibers, which were spun under quite different technological conditions, dry spinning, solution spinning, melt spinning, and spin drawing. 

Further differences result in the crystallization behavior. Under high stress which may be reached in a spin-drawing process, PLA crystallizes in the course of an orientation initiating mechanism in one defined crystalline modification, regarding PHB two crystalline modifications have been detected in the course of the stress-induced crystallization. 

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