There are many kinds of plastics, and plastics commonly used in injection moldings mainly include: PE, PP, PS, AS (SAN), BS, ABS, POM, PA, PC, PVC, ABS or AS+glass. fiber reinforcement, etc.

The molecular structure and composition of plastics are very complex, especially copolymers, blends and modified materials, as well as plastics containing various additives (such as fillers, stabilizers, plasticizers, flame retardants, mixed materials, etc.). Often they cannot be identified. simple method, and its composition can only be determined using chemical tests, instrumentation (spectrometers) and other means.

Different types of plastics need to know their categories. The laboratory usually uses sophisticated analytical and test instruments to identify them, such as infrared photometers, chromatographs, color spectrometers, nuclear magnetic resonance instruments, etc. Since these test instruments are very expensive, conventional plastic parts manufacturers can be unable to purchase them. However, there are many practical (empirical) methods for identifying plastics, two of which are most commonly used: Specific Gravity Method and Combustion Characteristics Method.

In absence of testing instruments and analytical laboratories, can be distinguished by density, combustion phenomenon, external color and product characteristics;after plastic is dyed, it is difficult to see directly with naked eye To know what it's plastic, use "see, hear, smell, press, fall, bite" method for comprehensive identification. Now, take a quick look at characteristics, product characteristics, and identification methods of various commonly used plastics so that you can be guided in identification of plastic materials.

1. Polypropylene (PP), commonly known as folded adhesive

PP is lightest plastic with a density of 0.9-0.91 g/cm3, it is lighter than water and can float on water in water. Polypropylene material is milky white, translucent and waxy. It burns slowly. The upper end of flame is yellow, with blue in middle, and phenomenon of burning drops is observed. After flame goes out, paraffin will appear. smell. PP products are light and hard, have excellent heat resistance, corrosion resistance, fatigue resistance and good toughness (withstand tens of thousands of bending and folding), and PP products are easy to age.

Notes: PP and PE (polyethylene) have similar properties, but density of PE is 0.91～0.95g/cm3, density is slightly higher than that of PP, and hardness is slightly lower than that of PP. should be carefully distinguished from PE.

2. Styrene (PS), commonly known as a hard adhesive

Pure PS is a hard and brittle colorless transparent plastic with a density of 1.05 g/cm3, which is close to specific gravity of water. PS has a low burning rate, bright yellow flames, flashes, black smoke and a special smell of gas after extinguishing; PS products have high hardness and brittleness, are easily scratched and cause stress cracking, they can be broken by hand (brittle failure); Polystyrene products have good surface gloss and low impact strength.

3. Acrylonitrile-styrene copolymer (AS or ASN), commonly known as clear superglue

AS particles

SAN (AC) is a light blue transparent tablet modified with PS, with a density of 1.08 g/cm3 and slightly heavier than water, SAN burns slowly, flame flashes, bright yellow, black smoke, extinguishes PS-like sometimes appears irritating odor (fishy smell), strength of SAN products increases and fragility of polystyrene products improves.

4. Acrylonitrile butadiene styrene copolymer (ABS resin), commonly known as a super strong adhesive

ABS is a kind of general purpose engineering plastic, ivory yellow grain (ivory white), opaque plastic, density 1.06 g/cm3, slightly heavier than water. ABS can burn slowly, flame is yellow and bright, flashes and emits black smoke. After it is extinguished, there is a sharp fishy smell like polystyrene. Non-flammable ABS is difficult to burn, and it will self-extinguish after exiting ABS fiberglass material is rough and has a light gray color with poor gloss. ABS products have comprehensive properties of "strength, hardness and rigidity", high strength, good rigidity, hardness, impact resistance and good surface gloss.

5. Polyoxymethylene (POM), commonly known as Saigan

POM is white, opaque granules with a high density, typically 1.42 g/cm3, heavier than water.

When burning, flame is blue, almost colorless (no smoke), after extinguishing there is a strong pungent smell of formaldehyde (it is easy to water). POM products have high hardness, good rigidity, wear resistance and high strength, surface of products has good gloss, hand-molded, there is a greasy feeling. POM is a kind of engineering plastic with high rigidity, metal-like performance.

6. Polycarbonate (PC), commonly known as bulletproof rubber

PC is an engineering plastic with excellent complex properties. Pure PC has a density of 1.20 g/cm3, which is heavier than water. PC granules are yellowish and transparent. When PC burns, flame is bright, emits a lot of black smoke, foams and chars. Self-extinguishes after leaving fire and has a slightly irritating phenolic (aromatic) smell. PC products have high impact resistance and good performance. temperature resistance (120 ℃), good toughness, high hardness and rigidity. Polycarbonate products often experience stress cracking.

7. Polyamide (PA), commonly known as nylon

There are many varieties of PA, such as PA6, PA66, PA1010, etc. The density of pure PA is 1.051.15 g/cm3. PA is a light yellow translucent particles with a rough (not smooth) surface. When burning PA, flame is yellow at top and blue at bottom, crackles and flows into fibers, self-extinguishes (no black smoke) after leaving fire, has a smell of burnt horn (nails, hair).

8. Polyvinyl chloride (PVC)

PVC is a type of plastic with poor heat resistance. There are many types including soft, semi-rigid and rigid PVC. PVC is mainly white powder or flakes, granules, etc. Pure PVC is colorless and transparent granules with a density of 1.25–1.45 g/cm3 and is heavier than water. It burns slowly, flame is yellow above, green below, smokes black, self-extinguishes after leaving fire, has a sharp (HCL↑) smell of burning. {To test if plastic contains chlorine, a normal copper wire is heated to a colorless red-hot state on a damp lamp (spirit lamp), then a small amount of test plastic is taken and placed on copper wire to heat, flame appears blue-green (CuCL2), is considered that plastic contains chlorine}, and strength and rigidity of PVC products are low.

9. Plexiglas (PMMA)

Plexiglas is also called acrylic, most of particles of its material are colorless and transparent (some slightly bluish), and density is about 1.20 g/cm3. The transparency of product is better and it is more rigid and less brittle than polystyrene, however, compared to polycarbonate, its toughness/strength is lower, surface hardness is low, and it is easy to be scratched by hard objects.

PMMA burns easily, blue colored flame (yellow top), does not smoke, tends to drip and foam, may continue to burn after leaving fire, gives off a strong smell of flowers and fruits (similar to smell of durian) or the stench of rotting vegetables.