Tieng anh nganh hoa

C. Translate into English
1. Dùng giy aming ni các phn thit b.
2. Bình này c un nóng trong b du duy trì nhit 135 - 145 0 C.
3. Cui cùng b sung thêm 2g bt st và tip tc un nóng thêm 1 gi na.
UNIT 27 : SYNTHETIC RUBBER
Synthetic rubber is produced through a process known as polymerization, which involves intermolecular
combinations. The polymers resulting from this reaction are of the elastic type, such as
synthetic rubbers, and the non-elastic types, such as synthetic plastics. The rubber-type of compounds are
known as elastomers. Actually, the elastomers do not duplicate natural rubber, and in many respects
superior to the natural product.
Among the many types of rubber like compounds, Thiokol is perhaps the most easily adapted for
school laboratory preparation. It is produced essentially from the reaction of sodium tetrasulfide with
ethylene dichloride.
Dissolve 3 grams of sodium hydroxide in 60 cc of water. Place the solution in a large beaker and
heat to boiling. To the boiling liquid, add 6 grams of finely powdered sulfur. Add small portions at a time,
stirring constantly. After all has been added, continue stirring and heating for a few minutes. Then,
remove the heat, add about 50 cc of water, stir, and filter off any unreacted sulfur. The resultant filtrate
should be a clear red liquid /sodium polysulfide/.
For an emulsifying agent, we will use a soap solution. Dissolve about one-half gram of soap
flakes in 10 cc of hot water. Heat the sodium polysulfide solution prepared above in a large beaker to a
temperature of 70 degrees, and add the soap solution into it. Next, while stirring, add 10 cc of ethylene
dichloride in small portions. It is important that you keep the temperature at 70 degrees. If it should rise,
remove the heat immediately, and if necessary, cool the beaker externally. Continue stirring at the 70
degrees temperature until the liquid becomes milky-white in color. The solution will pass through various
shades of orange, yellow and ivory. But do not be satisfied until you obtain an entirely white color. This
white emulsion is the "latex". Cool the solution and add 5 cc of concentrated ammonium hydroxide,
which will act as stabilizer. Stir again and allow the mixture to stand for a day or two.
The latex emulsion will gradually settle to the bottom of the container. Carefully pour off the
clear liquid from the top. Then add the white emulsion to 150 cc of water in a beaker. Add 5cc of
concentrated ammonium hydroxide and stir well.
Our final step is to coagulate the rubber. This can be done with dilute acetic acid/ about a 20%
solution/. Add the acetic acid in small quantities with continual stirring until the Thiokol separates out of
solution as a lump in the bottom of the container. Remove the lump and wash is thoroughly with water.
This is the crude synthetic rubber. Note that it is moderately elastic.
The elasticity can be increased by treatment with zinc oxide and carbon black. Place the lump of
rubber in a mortar. Add about one-half gram of zinc oxide and small pinch of carbon black. Work the
chemicals into the rubber by kneading with the pestle. Do not grind - rather press the chemicals in. Note
the elasticity after you have treated the rubber for about 15 minutes.
The process you have just completed is similar to that of processing natural rubber. The
difference, of course, is that the milky latex is obtained from the rubber tree instead of from chemical
reactions. The natural latex is also stabilized and then coagulated with acetic acid. This rubber is then
vulcanized and further treated with carbon black or zinc oxide which help to increase its resiliency,
strength, and toughness.
Natural rubber is a complex polymerized form of isoprene. The Thiokol that you have prepared is
actually a "substitute" rubber. It is unaffected by hydrocarbons and most solvents. Thus it is used in
making hoses used to handle such liquids.
EXERCISES
A. Read and translate into Vietnamese
synthetic rubber, polymerization, inter-molecular combinations, polymer, elastic, synthetic plastics,
elastomer, duplicate, Thiokol, sodium tetrasulfide, ethylene dichloride, filter off, sodium polysulfide,
emulsifying, milky-white in color, latex, stabilizer, coagulate, moderately elastic, elasticity, pinch,
vulcanize
B. Answer the following questions
1. What is synthetic rubber?
2. What is Thiokol?
3. Can you tell something about latex?
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