Filament Stretching Method

Figure 3.7 Schematic diagram showing the principal features of the filament stretching method for extensional viscosity measurements (a) vertical filament stretching (b) horizontal filament stretching.

Another type of experiment involves a fluid filament being drawn upward against gravity from a reservoir of the fluid (101,213,214), a phenomenon often called the tubeless siphon. The maximum height of the siphon is a measure of the spinnabiUty and extensional viscosity of the fluid. Mote quantitative measures of stress, strain, and strain rate can be determined from the pressure difference and filament diameter. A more recent filament stretching device ia which the specimen is held between two disks that move apart allows measurements ia low viscosity Hquids (215). AH of these methods are limited to spinnable fluids under small total strains and strain rates. High strain rates tend to break the column or filament. 

The techniques used in the Ml project were those of fibre spinning, open siphon, filament stretching, contraction flows, converging channel, opposing jets, climbing constants and falling drop methods. The results led to two major findings ... 

The semisolid consistency and the occurrence of slip effects during flow could limit the use of the rotary clamp method, the conveigent flow method or even Sridhar s extensional rheometer for a large number of food products such as mayonnaises and salad dressings. A novel rheometer (15) based on the concept of filament stretching has been developed by Plucinski et al (Fig. 10) to measure the extensional properties... 

Tire Ya.rns, A method to iacrease the strength of viscose yam from the 0.2 N /tex (2.2 gf/den) standard to levels needed ia tires was first patented by Courtaulds ia 1935 (18). By raising the ziac concentration ia the spia bath to 4% the thread could be stretched more by immersing it ia a hot dilute acid bath duting extension. Filament strengths iacreased to about 0.3 N/tex (3.3 gf/den), and the cross section became rounder, with a thicker skin than regular viscose. Pairs of these yams were capable of beiag twisted iato tire cords which outperformed traditional cotton cords. 

A similar method, ASTM D3107, has been developed for measuring stretch and stretch recovery of woven fabrics made in whole or in part from stretch yams. The term stretch yams refers to thermoplastic filament or spun yams having a high degree of potential elastic stretch and rapid recovery. These yams are characterized by a high degree of yam cud. 

The early methods of spinning viscose continuous filament were based upon rapid coagulation and regeneration after extrusion. This procedure is reversed in the preparation of polynosic fibres because the coagulating liquor only decomposes the xanthate slowly so that considerable stretching... 

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