(1) Introduction
Polystyrene is a linear structure of plastic polymerized from styrene monomers. Its commercial name is referred to as "benzene plastic", and its English abbreviation is PS. The synthesis of polystyrene is usually carried out by a bulk polymerization method and an emulsion polymerization method.
Block polymerization
The styrene is heated in an inert gas at a temperature of 60 to 90 ° C and polymerized with dibenzoyl peroxide as a catalyst to obtain a transparent bulk resin. The resin has high purity and good transparency and gloss.
2. Emulsion method
Under the action of the catalyst, the aqueous emulsion temperature of the styrene monomer is controlled at 80-95 ° C to carry out polymerization, and then the polymer is separated from the mother liquid, and after treatment, a powdery resin is obtained. The heat resistance of the finished product is slightly higher than that of the bulk polymer resin, but the electrical insulation and transparency are slightly poor.
(2) Identification features
The surface is hard and smooth, the transparency is good, the coloring power is strong, the color is bright; the texture is brittle, the impact strength is low, easy to scratch, and easy to break; when tapping, the sound is crisp and easy to break when folded; the relative density is greater than 1, slightly Sink in the water.
(3) Burning phenomenon
It has good combustion performance, is flammable, continues to burn after leaving the fire, and has a styrene odor release. The flame is yellow and black smoke; it softens and foams when burned.
(four) performance
The structural formula of polystyrene is a linear structure, but there are continuously spaced bulky phenyl groups on the carbon atoms of the molecular chain. This structure determines the special properties of polystyrene.
1. The texture is rigid and the impact strength is low; the random configuration of polystyrene has good gloss, high light transmittance and good colorability.
2. The softening temperature is 80 ° C. Below 80 ° C it is a hard solid like glass. Above 80 ° C, it becomes a softer object. It has rubber-like properties and should be avoided at high temperatures.
3. Good molding performance, small shrinkage deformation and dimensional stability in the temperature range of use; good water resistance, chemical stability decreases with increasing temperature; for a certain concentration of inorganic acid, organic acid, salt solution Alkali, alcohols, vegetable oils, etc. all have good resistance. They will gradually turn yellow when exposed to sunlight for a long time, devitrification and cracking.
4. Contact with oils and insecticides often cause cracking, discoloration and viscous melting, and it is easy to age and yellow under the action of light, oxygen and heat.
5. Soluble in organic solvents such as chloroform, dichloromethane, toluene, butyl acetate, etc., should not be in contact with the above solvents during storage.
(5) Modification
Polystyrene has serious disadvantages due to its brittleness, low softening temperature and easy cracking. In order to eliminate its disadvantages, modified polystyrene has appeared; the route is to copolymerize styrene monomer with other units or miscible polystyrene with other polymers and copolymers. The modified varieties mainly include the following:
Tough polystyrene
In order to improve the shortcomings of polystyrene brittle and fragile, a blend of elastomers such as rubber (butylbenzene or nitrile) is used to form a tough modified polystyrene, which improves the impact strength of polystyrene. But it reduces the transparency and electrical performance of the product.
2. Chlorinated styrene
Two chlorine atoms are introduced into the styrene structure to prepare a dichlorostyrene monomer, which is then polymerized into a dichlorostyrene synthetic resin. The modified polystyrene is still a transparent object, and the heat resistance is greatly improved, and the impact strength is also improved.
3. Styrene and propylene guess copolymer (AS)
Due to the introduction of acrylonitrile monomer, the chemical corrosion resistance, heat resistance, mechanical strength of the material can be improved, and cracks are not generated, which is an ideal material.
4. Styrene and butadiene, acrylonitrile copolymer (ABS)
Butadiene is a good elastomer, and various monomers exert their respective excellent properties in the copolymer. Therefore, ABS plastic has a good overall performance and is an ideal engineering plastic.
(6) Use
Polystyrene plastic is widely used in optical instruments, chemical industry and daily necessities to make tea trays, sugar bowls, soap boxes, cigarette cases, student rulers, combs, etc. Due to the certain gas permeability, when made into a film product, good food packaging materials can be made.
Overshot go into the heart of the drill pipe, the slider move up, make the tube socket head can be inserted into the center, when on the slider move up tight, using friction lift drill, remove loose again after the slider, by means of the connection string to slide along the block should tighten, set aside the center pipe, but in front of the salvage must first determine the bit in the bottom of the hole position, can be in a thin plate with bolts tight end of drill pipe, Drop the drill pipe to the bottom of the hole and press it on the drill bit. After waiting for a moment, it is proposed that the relative position of the drill bit at the bottom of the hole and the center of the rotary plate of the drill can be determined by observing the indentation left by the center pipe of the drill bit on the board, and then move the drill or rotary plate so that the center of the rotary plate is directly in front of the center pipe of the injured head, so as to ensure that the fishing device can be inserted into the center pipe accurately.
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