The basic raw materials of plastics were initially mainly agricultural and sideline products. Since the 1920s, they have shifted to coal and coal tar products, and since the 1950s, they have gradually shifted to oil and natural gas.

Plastic Manufacturing

The plastics industry includes three production systems: the production of plastic raw materials (resins or semi-finished products and additives), the production of plastic products, and the manufacture of plastic molding machinery (including molds).

Synthesis Method

1. Condensation reaction. A chemical reaction in which monomer molecules remove water or other simple molecular bonds to form polymers. It can be divided into homocondensation and cocondensation.

(1) Homocondensation: A condensation reaction of a monomer with two functional groups.

(2) Cocondensation: A condensation reaction of two or more difunctional monomers.

2. Addition reaction. A chemical reaction in which unsaturated or cyclic monomer molecules are added to form polymers. No water or other low molecular weight byproducts are released during the reaction, and the elemental composition of the generated polymer is the same as that of the original monomer. According to the type of monomers participating in the reaction and the configuration of the polymer itself, it can be divided into homopolymerization, copolymerization and directional polymerization.

(1) Homopolymerization: A polymerization reaction between unsaturated or cyclic monomer molecules. Such as polyethylene, polypropylene, polyvinyl chloride, etc.

(2) Copolymerization: A polymerization reaction between two or more unsaturated or cyclic monomers. Such as acrylate-butadiene-styrene copolymer (ABS). Copolymers made from two monomers can have the following four arrangements in the polymer chain:

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Random copolymers... -AABABBBAABA-...

Block copolymers... -AAABBBBBAAA-...

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(3) Directed polymerization:

During the polymerization process, the reaction conditions are controlled so that the monomers polymerize into products with a directional and regular structure, that is, isotactic or syndiotactic polymerization. The polymerization product is called a directed polymer.

I. Definition of plastic

Plastic refers to a material that has resin (or monomers directly polymerized during processing) as the main component and additives such as plasticizers, fillers, lubricants, colorants, etc. as auxiliary components, and can flow and form during processing.

Plastics mainly have the following characteristics: ¢Ù Most plastics are light, chemically stable, and will not rust; ¢Ú Good impact resistance; ¢Û Good transparency and wear resistance; ¢Ü Good insulation and low thermal conductivity; ¢Ý Good general formability and colorability, and low processing cost; ¢Þ Most plastics have poor heat resistance, large thermal expansion coefficient, and are easy to burn; ¢ß Poor dimensional stability and easy to deform; ¢à Most plastics have poor low-temperature resistance and become brittle at low temperatures; ¢á Easy to age; ¢â Some plastics are easily soluble in solvents.

2. Classification of plastics

The classification system of plastics is relatively complex, and various classification methods also overlap. According to conventional classification, there are mainly three types: one is classification by use characteristics; the second is classification by physical and chemical characteristics; and the third is classification by processing methods.

1. Classification by use characteristics

Based on the different use characteristics of various plastics, plastics are usually divided into three types: general plastics, engineering plastics, and special plastics.

¢ÅGeneral purpose plastics

Generally refers to plastics with large output, wide application, good formability and low price, such as polyethylene, polypropylene, phenolic, etc.

¢ÆEngineering plastics

Generally, plastics can withstand certain external forces, have good mechanical properties and high and low temperature resistance, and good dimensional stability. They can be used as plastics for engineering structures, such as polyamide, polysulfone, etc.

Engineering plastics are divided into two categories: general engineering plastics and special engineering plastics.

General engineering plastics include: polyamide, polyoxymethylene, polycarbonate, modified polyphenylene ether, thermoplastic polyester, ultra-high molecular weight polyethylene, methylpentene polymer, vinyl alcohol copolymer, etc.

Special engineering plastics are divided into cross-linked and non-cross-linked types. The cross-linked types include: polyaminobismaleamide, polytriazine, cross-linked polyimide, heat-resistant epoxy resin, etc. Non-cross-linked types include: polysulfone, polyethersulfone, polyphenylene sulfide, polyimide, polyetheretherketone (PEEK), etc.

¢Ç Special plastics

Generally refers to plastics with special functions that can be used in special application fields such as aviation and aerospace. For example, fluoroplastics and silicones have outstanding special functions such as high temperature resistance and self-lubrication, and reinforced plastics and foam plastics have special properties such as high strength and high cushioning. These plastics all belong to the category of special plastics.

¢Ù Reinforced plastics. Reinforced plastic raw materials can be divided into three types in appearance: granular (such as calcium plastic reinforced plastics), fibrous (such as glass fiber or glass cloth reinforced plastics), and flake (such as mica reinforced plastics). According to the material, it can be divided into three types: cloth-based reinforced plastics (such as rag reinforced or asbestos reinforced plastics), inorganic mineral filled plastics (such as quartz or mica filled plastics), and fiber reinforced plastics (such as carbon fiber reinforced plastics).

¢Ú Foam plastics. Foam plastics can be divided into three types: hard, semi-hard and soft foam plastics. Rigid foam plastics have no flexibility, and their compression hardness is very high. They will only deform when a certain stress value is reached, and they cannot return to their original state after the stress is released; soft foam plastics are flexible, have a very low compression hardness, are easily deformed, and can return to their original state after the stress is released, with a small residual deformation; the flexibility and other properties of semi-rigid foam plastics are between rigid and soft foam plastics.

2. Classification by physical and chemical properties

According to the different physical and chemical properties of various plastics, plastics can be divided into two types: thermosetting plastics and thermoplastic plastics.

¢ÅThermosetting plastics

Thermosetting plastics refer to plastics that can be cured or have insoluble (melting) characteristics under heat or other conditions, such as phenolic plastics, epoxy plastics, etc. Thermosetting plastics are divided into two types: formaldehyde cross-linked type and other cross-linked type.

Formaldehyde cross-linked plastics include phenolic plastics and amino plastics (such as urea-formaldehyde-melamine-formaldehyde, etc.).

Other cross-linked plastics include unsaturated polyesters, epoxy resins, and diallyl phthalate resins.

¢ÆThermoplastic plastics

Thermoplastic plastics refer to plastics that can be repeatedly heated to soften and cooled to harden within a specific temperature range, such as polyethylene, polytetrafluoroethylene, etc. Thermoplastic plastics are divided into hydrocarbons, vinyls containing polar genes, engineering, cellulose, and other types.

¢Ù Hydrocarbon plastics. They are non-polar plastics with crystalline and non-crystalline properties. Crystalline hydrocarbon plastics include polyethylene, polypropylene, etc., and non-crystalline hydrocarbon plastics include polystyrene, etc.

¢Ú Vinyl plastics containing polar genes. Except for fluoroplastics, most of them are non-crystalline transparent bodies, including polyvinyl chloride, polytetrafluoroethylene, polyvinyl acetate, etc. Most vinyl monomers can be polymerized using free radical catalysts.

¢Û Thermoplastic engineering plastics. Mainly including polyoxymethylene, polyamide, polycarbonate, ABS, polyphenylene ether, polyethylene terephthalate, polysulfone, polyether sulfone, polyimide, polyphenylene sulfide, etc. Polytetrafluoroethylene. Modified polypropylene, etc. are also included in this range.

¢Ü Thermoplastic cellulose plastics. Mainly including cellulose acetate, cellulose acetate butyrate, celluloid, cellophane, etc.

3. Classification by processing method

According to the different molding methods of various plastics, they can be divided into various types such as film pressing, lamination, injection, extrusion, blow molding, casting plastics and reaction injection plastics.

Molding plastics are mostly plastics with physical properties and processing properties similar to those of general solid plastics; laminated plastics refer to fiber fabrics impregnated with resin, which are combined into a whole material through superposition and hot pressing; injection, extrusion and blow molding are mostly plastics with physical properties and processing properties similar to those of general thermoplastics; casting plastics refer to liquid resin mixtures that can be poured into a mold without pressure or with a little pressure and can harden into a certain shape of products, such as MC nylon; reaction injection plastics are plastics that use liquid raw materials and inject them into the film cavity under pressure to react and solidify into a certain shape of products, such as polyurethane.

Modification

The first thing to know is that no matter what filler or additive is added to the plastic, the properties of the plastic itself will change accordingly, and this change will sacrifice its own certain properties. For example, adding glass fiber, glass beads and mineral powder will make the plastic molding much easier, with good dimensional stability, higher hardness and higher thermal deformation temperature, but what is sacrificed is the toughness and impact resistance of the plastic. In other words, it becomes brittle and easy to break. Fatigue resistance decreases. For example, PP fiber addition, ABS fiber addition, etc.

The performance of mineral powder modification is similar to that of glass fiber modification, but there are excellent improvements in electrification, such as dielectric constant, resistivity, etc., which will become larger.

As for the above saying that adding short fibers can increase toughness, I dare not agree. Because whether it is long fiber or short fiber in the plastic raw materials I have used, it will damage toughness and fatigue. If you don't believe it, you can test it yourself.

Market prospects

With the vigorous development of China's automotive electrical, electronic, and communication machinery industry, the demand for modified engineering plastics will increase significantly, and various high-strength and heat-resistant engineering plastics will be widely used. Polymer alloys, especially nylon alloys and PC alloys, will be favored by the market.

Experts point out that the modified engineering plastics industry will develop in the direction of high performance, specialization, and serialization of products. Chinese companies should take the road of characteristic (unique products, special after-sales service system) management.

In the development of modified engineering plastic products, reinforced engineering plastics still occupy a large market; blended alloys have become the mainstream of the development of modified engineering plastics; some high-performance engineering plastics such as products with high temperature resistance, wear resistance, conductivity, and electromagnetic shielding functions will have great development.

The manufacture and application of polymer nanocomposites is an important topic in the future. Due to the unique functions of nanomaterials, they can give polymer materials many special properties, and polymer nanocomposites will develop rapidly.

The concept of green environmental protection will be introduced into the modified engineering plastics industry, and the recycling of various waste materials will become a common concern in the industry. The concepts of reuse and environmental protection will be integrated into the design and manufacturing process of modified polymers.

Plastic Industry Video