The advent of bakelite is of great significance to industrial development
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Bakelite is the first plastic product to be put into industrial production. Its chemical name is phenolic. It has high mechanical strength, good insulation, heat resistance and corrosion resistance. Headphones, phone cases, instrument cases, etc., the name “bakelite”. |
Preparation Method
Phenolic resin and aldehyde compound can be prepared by polycondensation reaction under the action of acidic or basic catalyst. Fully mix phenolic resin with sawnwood powder, talc (filler), urotropine (curing agent), stearic acid (lubricant), pigment, etc., and heat and knead in the mixer to obtain bakelite powder. The bakelite powder is heated and compressed in a mold to obtain a thermosetting phenolic plastic product.
Disadvantages
The shortcomings of phenolic resins are poor mechanical properties and are not resistant to oil and chemical corrosion. In order to overcome the above defects, people have modified phenolic resins. Adding different fillers to phenolic resins can obtain modified phenolic resins with different functions. Plastics, such as adding asbestos and mica to the ingredients, can increase its acid resistance, alkali resistance, and abrasion resistance, and can be used as materials for chemical equipment and accessories for motors and automobiles; adding glass fiber can increase hardness and can be used as machine parts After modified with nitrile rubber, the oil resistance and impact strength are greatly improved; after modified with polyvinyl chloride, it can improve the mechanical strength and acid resistance.
Source Of Raw Materials
Phenolic plastics are rich in raw materials, simple in synthesis machining bakelite, cheap in price, and have excellent performance. They are still the largest thermosetting plastics in the world.
Physical characteristics
Phenolic plastic is a hard and brittle thermosetting material.
The characteristics of bakelite are non-absorbent, non-conductive, high temperature resistant, high strength, and are mostly used in electrical appliances. Because of the high insulation and plasticity like wood, it is called “bakelite”. Bakelite is made of powdered phenolic resin, which is mixed with sawdust, asbestos or clay, and then pressed into a finished product at a high temperature. Phenolic resin is the world’s first synthetic resin.
Phenolic plastic (bakelite): The surface is hard, brittle and fragile, and there is a sound of wood when struck. Most of them are opaque and dark (brown or black). It is an insulator, its main component is phenolic resin.
Formability
- 1. Good formability, but the shrinkage and directionality are generally greater than amino plastics, and contain water volatiles. It should be preheated before molding, and should be exhausted during molding. If it is not preheated, the mold temperature and molding pressure should be increased.
- 2. The mold temperature has a great influence on the fluidity. Generally, when the temperature exceeds 160 degrees, the fluidity will drop rapidly.
- 3. The curing speed is generally slower than amino plastics, and the heat released during curing is large. The internal temperature of large thick-walled plastic parts tends to be too high, which is prone to uneven hardening and overheating.
When the formaldehyde / phenol (molar ratio) is less than 1, a thermoplastic product can be obtained, called a thermoplastic phenolic resin, that is, a novolak phenolic resin, which does not contain further polycondensation groups, and can be cured by adding a curing agent and heating. For example, using hexamethylenetetramine as the curing agent, the curing temperature is 150 ℃, and the molding powder mixed with filler is commonly known as bakelite powder. When the formaldehyde / phenol (molar ratio) is greater than 1, first-stage resin, ie thermosetting phenolic resin, can be obtained under alkali catalysis, which can be dissolved in organic solvents. The first-stage resin contains hydroxymethyl which can be further polycondensed, so no need It can be cured by adding a curing agent: the B-stage resin is obtained by reaction under heating, also known as semi-soluble phenolic resin, which is insoluble and infusible but can swell and soften. After further reaction, an insoluble and infusible body structure C-stage resin, also known as insoluble phenolic resin, is obtained. The resin in stage A can also be cured by itself for a long time.
The curing form of thermosetting phenolic resin is divided into two types: normal temperature curing and thermal curing. Normal temperature curing can use non-toxic normal temperature curing agent NL, or benzenesulfonyl chloride or petroleum sulfonic acid, but the latter two materials are more toxic and irritating.
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Link to this article：What Is Bakelite?
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