1. What is plastic?

Plastic is a plastic created artificially from polymeric organic compounds (resin).

Plastic is an artificial material consisting of an organic synthetic resin as main component with or without addition of other materials (auxiliary materials). Usually, under influence of heat and pressure, it is molded into a device of a certain shape.

So-called ductility refers to property that, like clay, it deforms when a force is applied to it, but does not return to its original shape when external force is removed. The so-called elasticity (strength of elasticity) means that it deforms when a certain force is applied, but returns to its original shape when applied force is removed. This property is called elasticity (for example: rubber), and an object with elasticity is called an elastic body (for example, an elastic band); plastics are shaped into various shapes by exploiting plasticity that occurs when heated.

Second, source of plastic

Plastic is a high molecular weight organic compound (polymer) formed during polymerization of low molecular weight organic compounds (such as ethylene, propylene, styrene, vinyl chloride, vinyl alcohol, etc.) under certain conditions.

The molecules that make up plastics are polymers with a molecular weight of more than 10,000, so plastics are polymer compounds (polymers). In general, plastic molecules contain carbon atoms (C) and hydrogen atoms (H), and some plastic molecular structures contain a small amount of oxygen (O) and sulfur (S) atoms. The main raw materials for plastics are low molecular weight carbon and hydrogen compounds - artificial resin , extracted and synthesized from oil, natural gas or coal cracking products.

Third, plastic development process

Terms of development and production of various plastics:

1920-1933: polystyrene (PS), polyvinyl chloride (PVC), polyethylene (PE), ethylene-vinyl acetate (EVA), polypropylene (PP)

1935: Acrylonitrile Butadiene Styrene Copolymer (ABS)

1939: Polyethylene terephthalate (ABS) copolymer

1949: polyamide (nylon)

1950: acrylic

1956: Polyoxymethylene (POM)

1958: Polycarbonate (PC)

1964: polyxylene oxide (PPO)

1965: Polysulfone (PSF)

1975: Polybutylene terephthalate (PBT)

1985: Liquid Crystal Plastic (LCP)

1994: PET modification for injection molding (PETG)

1995: Superelastic polyoxymethylene (TPOM)

1996: Transparent rigid PVC

After 1960, technologies for application and processing of plastics developed by leaps and bounds.

Fourth, classification of plastic

There are currently over 300 types of plastic, and more than a dozen types of plastic are most commonly used.

1. Classification of plastics by application

Usually divided into general purpose plastics and technical plastics:

General purpose plastics can only be used as general non-structural materials with high yield, relatively low price and general performance, and are mainly used for daily necessities. (For example: PE, PP, PVC, PS, PMMA, EVA, etc.)

Engineering plastics have high mechanical properties, high temperature resistance, corrosion resistance, can be used as structural materials and have excellent comprehensive properties (including: mechanical properties, electrical properties, heat resistance, chemical resistance and etc.), can maintain these characteristics well over a wide temperature range and for a long time, and can also be used for a long time under mechanical loads and harsh chemical and physical conditions. The recognized seven major engineering plastics are: ABS, PC, POM, PA, PET, PBT, PPO, etc. The production of engineering plastics is relatively small and price is relatively high. In addition, there are functional plastics (such as LCP, artificial organs, etc.), nanoplastics, degradable plastics, etc.

2. Classification by crystalline form of plastic

Usually divided into crystalline plastics and amorphous plastics:

Crystalline plastics are plastics whose molecules can form a certain geometric structure under appropriate conditions (for example: PE, PP, PA, POM, PET, PBT, etc.) strong>, most of which are partially crystalline.

Amorphous plastics refer to plastics in which the molecular form and molecular arrangement are not in a crystalline structure, but in a disordered state (such as: ABS, PC, PVC, PS, PMMA, EVA, AS et al.), mechanical properties of amorphous plastics are same in all directions (isotropic)

3. Classification according to basic heating behavior

Usually divided into thermoplastics and thermoplastics;

Thermoplastics are plastics that can be softened by repeated heating and hardened by cooling within a certain temperature range (e.g. ABS, PP, POM, PC, PS, PVC, PA, PMMA, etc.). ), it can be recycled.

Thermoset plastics are plastics that become infusible when heated and cease to be plastic when reheated and cannot be recycled (such as: phenolic resin, epoxy resin, amino resin, polyurethane,polystyrene foam). etc.).

4. According to light transmission of plastics

Commonly divided into transparent plastic, translucent plastic and opaque plastic

.

Plastics with a light transmission greater than 88% are called transparent plastics (such as PMMA, PS, PC, Z-polyester, etc.). Commonly used translucent plastics are PP, PVC, PE, AS, PET, MBS, PSF, etc. Opaque plastics mainly include POM, PA, ABS, HIPS, PPO, etc.

5. Classification of plastic by hardness

Commonly divided into hard plastic, semi-rigid plastic and soft plastic;

Common hard plastics: ABS, POM, PS, PMMA, PC, PET, PBT, PFO, etc.;

Semi-rigid plastics include: polypropylene, polyethylene, polyamide, PVC, etc.;

Soft plastics include soft PVC, K (BS) glue, TPE, TPR, EVA, TPU, etc.

6. Classification of plastic by chemical structure

A. Polyolefins (such as: LDPE, MDPE, HDPE, LLDPE, UHMWPE, PP, etc.)

B, polystyrene (for example: PS, AS, BS, ABS, MBS, HIPS, etc.)

C, polyamides (such as: PA6, PA66, PA610, PA1010, etc.)

D, polyester (for example: PC, POM, PSF, PPO, etc.)

E, polyester (e.g. PBT, PET, etc.)

F, acrylic (e.g. PMMA)

V. Physical properties of plastic

1. Specific Gravity (Density) ★

Specific gravity of plastic is ratio of weight of a weighed sample to weight of same volume of water at a certain temperature, unit is g/cm3, and measurement is usually buoyancy method. method.

2. Water absorption ★

Moisture absorption of plastic refers to amount of water absorbed by a sample of a certain size, immersed in distilled water at a certain temperature (25±2) °C after 24 hours; after absorbing water, its size and shape change. affects, and water absorption coefficient is used. When it is expressed by weight, it is often expressed as a %.

3. Breathability

Permeability refers to volume (cm3) of gas permeable by a plastic film of a certain thickness in an area of ​​one square meter at atmospheric pressure for 24 hours, but air permeability is not related to thickness, area, time, temperature, pressure drop, and so on.

4. Moisture permeability

Moisture permeability refers to penetration of water vapor through a plastic film. The basic principles and definitions are same as those for breathability.

5. Transparency

The ratio of amount of light passing through an object to amount of light falling on object is called transmittance; ratio of light scattered in direction of incident light to all transmitted light is called haze or haze Haze aboutUsually half transparent and diffuse with respect to incident light.

6. Tensile Strength

Tensile strength refers to maximum load when sample fails by applying a tensile load along longitudinal axis of sample at specified test temperature, humidity and tensile rate.

7. Compressive strength

Compressive strength refers to strength at which a compressive load is applied to a specimen to break (for brittle materials) or yield (for non-brittle materials).

8. Flexural strength

Bending strength refers to strength of a specimen when a concentrated load is applied to two points of support to deform specimen or until it fails.

9. Impact strength

Impact strength refers to number of joules consumed per unit area when sample is destroyed by impact. For some high impact plastics, there is often a gap of a certain size in middle of sample, which can reduce time it takes to break. required joules.

Different test methods can be used for different samples: drop ball impact test, high speed impact tensile test.

10. Coefficient of friction

The coefficient of friction refers to ratio of force of friction to normal pressure. Add positive pressure to sample to measure dynamic and static ratio of sample when it is in rigid motion.

11. Clothing

Abrasion refers to process of mechanical damage in which plastic particles are continuously separated from friction surface during friction process, resulting in a permanent change in size of rubbing parts, a process also known as wear or abrasion.

12. Hardness

Plastic hardness refers to ability of a plastic to resist penetration of other hard objects. There are two main types of hardness: Rockwell hardness and Shore hardness.

Shore hardness refers to calculation of indentation depth of an indenter at a given pressure and time.

Shore indenters can be divided into two categories, namely type A and type D. The applied load weight is 1.0kg and 5.0kg, and pressing time is 15 seconds. Type A is suitable for soft plastics and type D is suitable for semi-rigid plastics; when type A is used and measurement exceeds 95% of range, type D should be used; when D type exceeds 95% of range, it should be replaced with a Rockwell fingerprint.

13. Fatigue strength

Fatigue strength refers to plastic fracture strength under action of a static breaking force with a small number of alternating cycles; sources of fatigue loading are tension and compression, bending, torsion, impact andetc.

14. Creep ★

Creep refers to characteristics of plastics that change over time under continuous action of a fixed external force under certain conditions of temperature and humidity. The characteristics of this deformation increase with increasing load and decrease with decreasing load. and her deformity gradually recovered. Sources of creep include tensile creep, compressive creep, and flexural creep.

15. Durable strength

Long-term strength refers to a function of time of ability of plastics to withstand high to low static loads for long periods of time. For example: strength of plastics before loading is 1000 hours, but after loading it can only be between 50% and 70%.

16. Linear expansion coefficient

Coefficient of linear expansion is number of centimeters that each centimeter of plastic expands when temperature rises by 1 degree Celsius. The coefficient of linear expansion of plastic is typically about ten times higher than that of steel.

17. Specific heat

Specific heat capacity is unit of heat required to raise 1 gram of plastic by 1 degree Celsius.

18. Thermal conductivity

Thermal conductivity refers to unit of heat that plastic of a certain area and thickness can pass through. The thermal conductivity of plastic is very low, only about one percent of that of steel, so it is a good thermal insulator. .

19. Temperature resistance

Plastic heat resistance is a characteristic that reflects relationship between temperature and deformation of plastic parts, and heat resistance is more important for temperature-dependent plastic parts.

20. Glass transition temperature ★

The temperature at which a plastic changes from a liquid melt to a solid state is called glass transition temperature. At this time, segments of molecular chain basically cannot move, and it is also very difficult to rotate and rotate. fix inner links of chain. There is only a little movement and stretching between atoms. And there is a normal elastic deformation, so plastic at this time will be very brittle.

21. Embrittlement temperature

When pressure is applied to a plastic at a certain low temperature, it breaks with little deformation, and this temperature is embrittlement temperature.

22. Decomposition temperature ★

Decomposition temperature refers to temperature at which macromolecular chain of plastic breaks when it is heated, and it is also one of indicators for determining heat resistance of plastic; when melting point of material exceeds decomposition temperature, most of melting material will have a yellowish color, andproduct accuracy will be greatly reduced.

23. Melting index ★

Melting Index (MFI) MI refers to mass of molten material that flows out of thermoplastic through small opening of tester for 10 minutes at a specific temperature and pressure, and is expressed in grams/10 minutes. .

Seven, plastic characteristics

1. Advantages of plastic

(1) Easy to process, easy to manufacture (easy to shape)

(2) Can be dyed at will according to needs or made into transparent products

(3) Can be made into lightweight and high strength products

(4) Does not rust, does not corrode

(5) Not easy heat transfer, good thermal insulation performance

(6) Both conductive parts and insulating products can be produced

(7) Excellent cushioning and noise reduction performance, good light transmission

(8) Low production cost

2. Disadvantages of plastic

(1) Poor heat resistance, highly flammable

(2) When temperature changes, properties will change a lot

(3) Low mechanical strength

(4) Easily corroded by special solvents and chemicals

(5) Low wear resistance, fast aging

(6) Vulnerable to damage, dust and dirt

(7) Poor dimensional stability

Eight, plastic painting

The applications of dyes include: dry powder (toner), dyes, color masterbatches, liquid color pastes, etc., which are divided into two categories: organic pigments and inorganic pigments.

Dyes should have following good properties: strong coloring power, strong hiding power, good dispersion (compatibility), good heat resistance, good light fastness, good migration resistance, good solvent resistance, chemical resistance Good quality, low shrinkage, etc. e. As customers place more and more stringent requirements on color of plastic parts, use of colored masterbatches or granules is becoming more and more widespread.

9. POS material recycling

Regular thermoplastic bait materials can be recycled. Experiments have shown that addition ratio of nozzle materials is within 25%, and effect on characteristics (strength) of plastic is not obvious (less than 10%). nozzle material recycling - plastic. The use of hot runner molds as an industrial research topic is a pioneering work to reduce nozzle material. The amount and proportion of nozzle material recycling have different degrees of influence on color fastness of plastic products, and amount of nozzle material added must be strictly controlled in process production.