Viscose

Viscose (from Latin viscosus - sticky, adhesive), a viscous, jelly-like mass, capable of being drawn into threads, forming films, and adhering various objects. V. was first obtained in 1892 (Cross, Bevan and Beadle) by the action of carbon disulfide vapor on alkali-cellulose. In this process, the sodium salt of cellulose xanthogenic acid is formed, which represents viscose. V. is soluble in water; a 1% solution has the appearance of a jelly. When solutions of V. are heated to 60-80°, it is precipitated in an insoluble modification. If a solution of ammonium sulfate or sulfuric acid is added to it, cellulose precipitates, which is used for the preparation of artificial silk. V. is used for sizing paper in paper production, in textile printing as a thickening agent and for finishing; films are made from it, it is used in technology instead of celluloid, sometimes replaces horn and even ivory, etc. The raw material for the preparation of V. consists of cotton, straw, wood cellulose in the form of sawdust, chips, twigs, etc. (on professional hazards - see Silk). V. in the form of thin sheets is used as an insulating material protecting medicines from moisture, and is also used as compress paper. A mixture of V. with a celluloid solution is used for impregnating orthopedic corsets. Viscosity measurement (from Latin viscosus - sticky and Greek metron - measure), the measurement of viscosity (see), or internal friction of liquids. For V., various principles can be used; most often two are applied: measuring the rate of fall of a body in the liquid being tested or determining the time for a certain volume of liquid to flow through a capillary tube. The first principle, based on Stokes' law, which establishes the relationship between the rate of fall of a spherical body and the viscosity of the liquid, is rarely used (mainly for determining the viscosity of very thick liquids, like resin). The viscometers commonly used are based on the second principle. The simplest and most common is the Ostwald viscometer (see Figure 1). A certain amount of the liquid to be tested is introduced through a, it is sucked through b (somewhat above mark c) and allowed to flow freely, noting with a stopwatch the time elapsed between the moment the upper meniscus passes between marks c and d. Since relative viscosity is usually of interest, taking the viscosity of water as 1, the outflow time of the test liquid (t) is compared with the outflow time of pure water (t₀) in the same instrument. In this case, the relative viscosity η is expressed by the formula η=St, where S is the specific gravity of the liquid being tested. The temperature coefficient of viscosity is very high - an increase of 1° corresponds to a change of about 1-2%; therefore, in V., it is important to maintain constant temperature as much as possible. For clinical purposes, the Hess and Determann instruments are most commonly used. The Hess viscometer consists of two graduated, equal capacity, thin glass tubes, which on one side pass into capillaries, and on the other side are connected to each other by means of a T-shaped tube

FIG. 1.

and simultaneously with a rubber bulb, which serves for sucking or pumping air. Water is sucked into one of the tubes up to a certain mark on the tube, and blood (in the same amount as water) into the other up to the same mark. Then, by pumping air with the rubber bulb, both liquids are made to pass through identical capillaries under the same pressure. When the blood in its capillary reaches mark 1, the meniscus of the standing water is noted, which immediately indicates on the scale the value of relative viscosity. Accuracy up to 4%. When using different pressures and temperatures, the % error increases. - The Determann viscometer consists of a capillary tube having at its ends expansions containing exactly 0.1 cubic cm, again passing into identical capillaries on both sides. The tube is placed in a cylinder with water at 20°. Blood is sucked up to a certain mark, and then the apparatus is placed in a vertical position and the time it takes for the blood to pass through the capillary to the next mark, located at the other end, is observed. The experiment is repeated with water, and the relative viscosity η is calculated by the formula: __time for blood to pass _η η = time for water to pass

Subsequently (1911), Determann proposed an instrument combining the principles of the first two, which is now the most common (see Figure 2). The apparatus consists of two, equal capacity, parallel Determann tubes (see above), into one of which water is drawn up to mark O, and into the other - blood, also up to O. The tubes are placed in a glass sleeve filled with water at 20°. When the apparatus is turned vertically, both liquids (blood and water) begin to pass through the capillaries from mark O to the graduated ends under the influence of gravity. The relative viscosity η of the blood that has reached mark 1 is indicated by the number of the water meniscus. Blood for research is taken by pricking the pulp of a finger or the earlobe. The drop should appear freely. To prevent clotting, it is recommended to add a speck of hirudin to the blood being tested. The apparatus is simple, portable, and convenient for clinical purposes. The readings of this viscometer are accurate.