Basic Knowledge of Plastics Chapter 2

Basic Knowledge of Plastics Chapter 2

Classification of plastic materials:

A. Classification according to behavior when heated

According to behavior of plastic after heating, it can be divided into two categories:

1. Thermoplastics:

◎Doughs that can be plasticized or softened after heating, hardened and molded after cooling, and repeatable are called thermoplastics.

◎Such as: PP, PE, PS, ABS, PC, POM.PBT.PPO

2. Thermosetting plastics:

◎Those that plasticize or soften after heating and undergo chemical changes to solidify and form are called thermoset plastics, which do not undergo plasticizing deformation when heated after cooling. (Not recyclable)

◎For example: UF, MF, unsaturated polyester, epoxy

B. Classification by scope of plastic

(Super Engineering Plastics, Advanced Engineering Plastics, Engineering Plastics, Special Functions, Elastomers), General Plastics.

General plastics:

◎Large production and low price, widely used general purpose plastic

◎Can only be used as a generic non-structural

◎General plastics account for more than three-quarters of global production

◎For example: polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polystyrene (PS), ABS, phenol plastic (PF)

※But after plastic modification, some general purpose plastics can also be used as structural materials such as PP+GF

Technical plastics:

◎Engineering plastics that can be used as engineering materials and replace metals for production of various mechanical equipment or parts are called engineering plastics.

◎Excellent comprehensive properties, including mechanical, electrical, heat resistance, chemical resistance, dimensional stability, and can keep these properties well over a wide range and for a long time.

◎Mainly include:

Engineering plastics: polycarbonate (PC), polyoxymethylene (POM), nylon, PET, PBT

Advanced engineering plastics: polymethyl ether (PPO), polysulfone (PSU), polyphenylene sulfide (PPS), polyethersulfone (PES), LCP

Super technical plastics: polyetherketone (PEEK), polyamideimide (PAI), polyimide (PI)

Special plastic:

A plastic specially made for one or two functions, this type of plastic will be far superior to other plastics in its special function


Conductive plastic switches (conductive plastics), resistors, carbon powder,

Electroplated plastic

flame retardant plastic + fire retardant hard PVC

Degradable (photo/biological) plastic (bio/photodegradable plastic)

Elastomer (rubber, elastomer):

◎It has high elasticity at room temperature, that is, it is a polymer material that can deform more than ten times when subjected to a small external force, and can return to its original shape after external force is removed.< /p>

For example: styrene-butadiene rubber, butadiene rubber, etc.

◎Rubber usually crosslinks slightly during vulcanization and does not decompose when heated.

◎There is a kind of non-chemically cross-linked polymer material that has high elasticity and can be thermoplastically formed, called TPE thermoplastic elastomer

For example: SBS, SEBS, TPU, PP/EPDM, etc. C. Classify plastics by molecular arrangement

1. Amorphous plastic

Molecular shape, a plastic material in which molecules are arranged in a disordered state.

For example: PS, ABS, PC, PMMA, SAN, PPO

2. Crystal Plastic

A plastic in which certain molecular segments are stacked in correct order.

Example: PP, PE, POM, PBT, PET, PA

The temperature of crystalline plastic mold is very important,

Basic Knowledge of Plastics Chapter 2

D. Classification of plastic by chemical structure

Basic Knowledge of Plastics Chapter 2


Polyolefin is a general term for olefin polymers, usually referring to copolymers of homopolymers of hexene, propylene and butene.

Main varieties: LDPE, LLDPE, HDPE, PP, chlorinated polyethylene (CPE), ethylene propylene copolymer, ethylene vinyl acetate copolymer

Characteristics: low relative density, chemical resistance, excellent water resistance, low dielectric constant, good isolation at high frequencies.


Styrene plastics is a general term for styrene homopolymers and copolymers.

These are mainly: GPPS, HIPS, ABS, SAN, MBS, etc.

Polyvinyl chloride (PVC)

Varieties of polyvinyl chloride:

Take vinyl chloride (PVC), a copolymer of vinyl chloride and vinyl acetate, a copolymer of vinyl chloride and vinylidene chloride, a graft copolymer of vinyl chloride, ethylene and propylene, a copolymer of vinyl chloride and chlorinated rubber, etc.


Acrylic plastics refer to acrylic monomers that are obtained by homopolymerization, copolymerization or mixing, as well as grafting

Large categories of plastics. Usually include polymethacrylate (PMMA), etc.

Characteristics: can be used as an adhesive and coating, has excellent transparency and UV resistance.


A polymer compound containing many repeating amide groups (-CO-NH-) in polymer backbone is collectively referred to as a polyamide.

(PA), commonly known as nylon (nylon)

For example: PA6, PA66, PA11, etc.

Polyester, polyester

Macromolecular chains contain chains of esters (-OCO-) or ethers (-C-O-C-), and polymers without branched chains and cross-linked structures are collectively called linear polyesters or linear polyesters.

Polyester: polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.

Polyethers: polyoxymethylene (POM), polyphenylene oxide (PPO), etc.

Characteristics. Most of these plastics have good mechanical properties, dimensional stability and high temperature resistance, and most of them are engineering plastics.


Polymeric materials containing fluorine atoms in molecule are called fluoroplastics. Among all fluoroplastics, polytetrafluoroethylene (PTFE) has best chemical corrosion resistance, withstands effects of "aqua regia" (strong acid) Functions without being corroded, is known as king of plastics, but due to its high viscosity at high temperature, it cannot be in a liquid state, so it is rarely used for injection molding.

Injectable fluoroplastics include tetrafluoroethylene-hexafluoropropylene copolymer (FEP, F46), polychlorotrifluoroethylene (PCTFE), and polyvinylidenfluoride (PVDF), etc.

The characteristics of PTFE are heat resistance, frost resistance (from -218 to 260 degrees), excellent chemical corrosion resistance, excellent dielectric properties and self-lubricating properties, as well as lowest coefficient of friction compared to all engineering plastics. it has anti-stick, anti-fouling and aging properties.


Cellulose plastic is a polymeric material formed by adding a plasticizer to a polymer formed by the action of inorganic (or organic) acids.

Commonly used: nitrocellulose, cellulose acetate, cellulose acetate butyrate (CAB), cellulose acetate propionate, etc.


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