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Basic knowledge of engineering plastics
2020/7/14 18:21:53   238

Plastic-a polymer material that is composed of resin as the main component, with or without other matching materials (auxiliaries), and is plasticized under heating and pressurizing conditions.

It is one of the world's three largest organic polymer materials (the three largest polymer materials are plastic, rubber, and fiber).


1. The English name of plastic is plastic, commonly known as: plastic.


Second, the source of plastic

The basic raw materials of plastics are low molecular carbon and hydrogen compounds.

It is an artificial resin refined and synthesized from cracked petroleum, natural gas or coal.


Third, the classification of plastics

1. Classified by application of plastics

——General Plastics and Engineering Plastics:

General-purpose plastics: large output, low price, and average performance. (Such as: PE, PP, PVC, PS, ABS, etc.)

Engineering plastics: excellent comprehensive properties, can be used as structural materials. (Such as: PC, POM, PA, PET, PBT, etc., the output of engineering plastics is relatively small and the price is more expensive)

2. According to the physical and chemical properties of plastics

-Thermoplastics and thermosetting plastics:

Thermoplastics: Plastics that can be repeatedly heated to soften and cool to harden within a specific temperature range. (Such as: ABS, PP, POM, PC, PS, PA, etc.). It can be recycled again.

Thermosetting plastics: plastics that become infusible after being heated, and no longer have plasticity when heated again, and cannot be recycled. (Such as: phenolic resin, epoxy resin, amino resin, polyurethane, expanded polystyrene, etc.).


Fourth, the characteristics of plastic

advantage:

(1) One-time molding, processing efficiency is higher than metal, and low cost.

(2) Light weight (1/6-1/7 of steel, 1/3-1/4 of aluminum), which can save energy.

(3) Any color can be matched to increase the value of goods.

(4) Resistant to chemicals, unlike metals that are easy to rust and corrode.

(5) It is not easy to transfer heat and has good heat preservation.

(6) It can make both conductive parts and insulating products.

Disadvantages:

(1) Compared with metals, it has poor heat resistance and is easy to burn.

(2) As the temperature changes, the performance will greatly change.

(3) Compared with the same volume of metal, the mechanical strength is lower.

(4) Poor durability and easy aging.

(5) The surface hardness is low and it is easy to scratch.

(6) High shrinkage rate and poor dimensional stability.


5. Introduction to commonly used plastics

1. Polyethylene (PE)

Monomer: Ethylene-a gas refined from petroleum

According to different synthesis processes, it is divided into three categories:

LDPE—low density polyethylene (chemical resistance, excellent electrical insulation, toughness at low temperatures)

LLDPE—Linear low density polyethylene (soft and tough, but slightly harder than LDPE)

HDPE—High-density polyethylene (lower mechanical strength than LDPE, close to PP, and surface finish lower than PP)

Uses: films, cables, low-grade shells, containers and bottles.


2. Polypropylene (PP) commonly known as 100% plastic

Monomer: Propylene-a gas refined from petroleum

Category: Homo-PP (polymerization of single propylene monomer, good heat resistance)

Copolymerized PP (mixed with a small amount of ethylene polymerization, high impact strength)

Performance: PP is the lightest plastic with a density of 0.9g/cm3 which is lighter than water (which can float on the surface). The pellets are milky white or translucent. Heat resistance (can be used at around 100 degrees), corrosion resistance, good toughness (can withstand tens of thousands of bends)

Uses: woven bags, packaging films, tableware, household appliances shells.


3. Polystyrene (PS) commonly known as ordinary hard rubber

Monomer: Styrene-a colorless liquid synthesized from petroleum.

Distinguish: Hard and brittle colorless transparent plastic (imitating glass), density 1.05g/cm3, basically the same as water. The upper end of the burning flame is golden yellow, while softening and bubbling, without dripping, there are thick smoke and black pillars, and it emits the "sweet fragrance" taste of styrene monomer.

Performance: High transparency, high gloss, hard and brittle quality, crisp sound, easy to scratch and crack, and can be broken by hand.

Uses: transparent lenses, transparent tableware, daily necessities and toy shells.


4. High impact polystyrene (HIPS) commonly known as high impact hard rubber

Monomer: Copolymerization of styrene and rubber

Discrimination: Sub-white opaque, density 1.04g/cm3, golden yellow at the upper end of the burning flame, will soften and foam, no dripping, thick smoke and black columns, and fly ash.

Performance: HIPS is a modified material of PS, and its toughness is four times higher than that of PS. The product is opaque, easy to color, and has low water absorption. It does not need to be dried in advance during processing.

Uses: home appliance shells, toy shells, hollow products, bottles.


5. Acrylonitrile-styrene copolymer (AS) commonly known as transparent viscose

Monomer: Copolymerization of styrene (S) and acrylonitrile (A)

Identification: Transparent pellets, density 1.07g/cm3, slightly heavier than water. The burning flame flashes, yellows bright, emits black smoke, and when it is extinguished, there is a pungent smell (fishy smell) like PS.

Performance: It has high transparency, good mechanical properties, chemical resistance, grease resistance, and good printing performance. It is the raw material of excellent transparent products.

Uses: cosmetic outer boxes, lighter shells, food containers, lenses, home appliances


6. Acrylonitrile-butadiene-styrene copolymer (ABS resin), commonly known as super non-breaking glue

Monomer: Acrylonitrile (A)-butadiene (B)-styrene (S) copolymerized into

Identification: light yellow opaque particles, density 1.05, high gloss surface, burning flame yellow, emitting black smoke, plastic softening and scorching, no melting and dripping.

Performance: It has the comprehensive performance of "tough, hard and rigid", high strength, good rigidity, hardness, impact resistance, and good surface gloss.

Uses: used for the shells of household appliances and various products.


7. Polyoxymethylene (POM) commonly known as Saigang

Monomer: formaldehyde-from natural gas

Identification: White opaque pellets with a high density of 1.42. The burning flame is blue, does not emit smoke, and has a strong pungent smell of formaldehyde (easy to shed tears) after being extinguished.

Performance: Tough and elastic, high hardness, high strength, excellent wear resistance, fatigue resistance, good surface gloss, and a greasy feeling when touched by hand. POM is an engineering plastic with high rigidity, also known as metal plastic.

Uses: gears, interlocking levers, bearings, bushings, blades.


8. Polycarbonate (PC) commonly known as bulletproof glue

PC is an engineering plastic with excellent comprehensive performance.The density of pure PC is 1.20g/cm3, which is heavier than water.

Identification: PC particles are light yellow or colorless and transparent. When the PC burns, the upper part of the flame is golden yellow, and the lower part is blue, emitting a lot of black smoke, bubbling, carbonization, self-extinguishing phenomenon after leaving the fire, and a slightly pungent phenol (fragrance) smell.

Performance: PC products are transparent and glossy, have high impact resistance, good temperature resistance (120°C), good toughness, and high hardness and rigidity.

Uses: transparent lens, electrical housing, communicator housing

General ABS:

Grades: BASF GP22, LG Yongxing HI-121H, Taiwan Chemical AG12A1/15A1, Chi Mei 757K, etc.

Uses: Microwave oven facade/control box/knob, front and rear housing of fan and other appearance parts, appearance parts of air conditioner, modified base materials, etc.

AS:

Grades: LG Yongxing 80HF (white background), 80HF-ICE (blue background); Chi Mei 127H, 138H, etc.

Uses: transparent fan blade, transparent shell, display light mirror, juicer cup body, water purification bucket, etc.

HIPS:

Grades: Chevron MA5210/MB5210, Chi Mei PH88/PH888G, Dow Chemical 1300/1180, etc.

Uses: Matte HIPS is used for the chassis and rear cover of part of the air conditioner; high gloss HIPS is used for the air outlet frame, front shell panel, air outlet frame panel, and some shell parts of the hanger.

POM:

Grades: BASF N2320, DuPont Asahi Chemicals 4520, Korean Engineering F20-03, Polyplastics M90-04, Yuntianhua M90, etc.

Uses: fan gear components, sliding parts, microwave oven door hooks, switch brackets, etc.

Domestic PP:

Grades: Maoming Petrochemical EPC30R-H, N-MPHM160; Guangzhou Petrochemical J641, S700; CNOOC and Shell EP503M, HP500N.

Uses: Modified base material for the base of induction cooker, upper cover of water dispenser housing, base material for modified material of electric rice cooker components, plastic parts for fans, etc.

Imported PP:

Brands: Samsung HJ730L, Korea Dalin HA748L, HP602N, Singapore TPC AW564, AR564, Exxon 7033N, AP03B, etc.

Uses: Kettle body, fan blades, motor front and rear shells, water dispenser water storage boxes, bases, microwave ovens are used for fan blades/fan bracket modified base materials, etc.