Introduction to Plastics

Introduction to Plastics

1. What is plastic

Plastic consists of polymer synthetic resin as main raw material and a certain amount of additives.

Synthetic resins are among them, as opposed to natural resins. (eg sticky resin of pine bark, tree fat) Synthetic resin is a high molecular weight compound resulting from polymerization of monomers.

For example, polyethylene: from ethylene at 100 MPa and 200 °C, double bonds of molecule open and recombine, forming long carbon single bonds to form polyethylene, as shown in figure below.

Introduction to Plastics

2. Plastic composition

Resin

Fillers: reduce resin content, change properties. For example, calcium, toner, fiberglass, carbon fiber, etc.

Plasticizer: Increases fluidity, ductility and other molding properties, but reduces strength.

Dyes: color change

Lubrication: improves formability.

Stabilizer: Increases stability, such as heat resistance, for longer life.

3. Plastic classification

1. By molecular structure

Thermoplastics: molecular structure is linear and can be recycled.

Thermosetting plastics: molecular structure consists of a network and a body. Can only be used once after molding.

4. Common plastic

PE polyethylene, such as mineral water bottles, is used at a temperature of 80°C, and if temperature exceeds 80°C, deformation will occur.

PVC, e.g. electrical wire insulation

Polystyrene PS

PP polypropylene

PF Phenolic Resin, which is a thermosetting plastic such as a shovel handle

5. Engineering plastics

Polyamide PA, commonly known as nylon

PC polycarbonate

PTFE, good corrosion resistance

6. Characteristics of plastic

-Low density 0.83kg/dm3～2.2kg/dm3

-High specific strength (δb/ρ), high specific stiffness (E/ρ)

-Good chemical stability

-Good electrical insulation, heat insulation and sound insulation

-Good wear resistance and self-lubrication

-Good grip

-Good molding characteristics, good coloring characteristics

-Good vibration absorption, good anti-static

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