The identification of plastics can use scientific methods such as infrared spectroscopy, paramagnetic resonance, and X-ray, but it can also be identified by simpler methods. The following briefly introduces the simple identification method:

　　 sensory appraisal

　　 Sensory appraisal (organize students to participate in the identification of plastics)

(one look

　　 First look at the color and transparency of the product.

　　Transparent products include: polystyrene and plexiglass.

　　 Translucent products include: low-density polyethylene, cellulose plastic, polyvinyl chloride, polypropylene, epoxy resin, and unsaturated resin.

　　Opaque products include: high-density polyethylene, polyurethane and various colored plastics.

　　 (two) listen

　　 When hit with hard objects, the sound is different. Polystyrene sounds like metal, while organic glass sounds thicker and dull.

　　 (three) touch

　　The product feels waxy when touched by hand, it must be a polyolefin material. Secondly, the degree of softness and hardness can be simply expressed as follows:

　　 hard → soft

　　 Polystyrene→Polypropylene→Polyamide→Plexiglass→High Density Polyethylene→Rigid Polyvinyl Chloride→Low Density Polyethylene→Soft Polyvinyl Chloride

　　 Then test the surface hardness and draw the surface with pencils of different hardness to make a difference:

　　 Polyethylene plastics can draw lines with HB pencil;

　　 Polypropylene plastic ZH pencil can draw lines.

　　Due to the differences in people's physiological conditions, the feelings obtained by sensory evaluation are not the same, so this method is only for reference.

Identification basis for several miscible plastics

　　 (1) Identification basis for polyethylene and polypropylene plastics

　　 Both polyethylene and polypropylene plastics are milky white translucent, light in weight and able to float on the water surface, and the burning phenomenon is basically the same. However, there are obvious differences between the two: polyethylene has a paraffin waxy feel to the touch, soft and bendable, while polypropylene is smooth and delicate to the touch, but has no waxy and slippery feel, and the texture is very hard and tough; polyethylene plastic is Remarkably softened in boiling water, polypropylene plastic is not significantly softened in boiling water; polyethylene plastic strips have "neck" when stretched, but polypropylene does not.

　　 (2) Identification basis for polyvinyl chloride and polyethylene plastic film

The processing methods of polyvinyl chloride and polyethylene are different: polyvinyl chloride is pressed into a single film by a calendering method, and polyethylene is made into a cylindrical double-layer bag by a blow molding method; from the perspective of color and transparency: polyethylene is milky white and translucent, The surface is brighter, and the hand feels waxy and slippery. Multi-layers stacked together are still milky white and translucent. Polyvinyl chloride is more transparent than polyethylene, and its color is slightly yellow. Multi-layers stacked together are yellow and smooth to the touch. , But it has a sticky feeling, carefully observe the fine lines of the mold; the burning phenomenon is different: polyethylene is flammable, melts and drips, and has a paraffin smell, while polyvinyl chloride is non-flammable, the flame root is green, and there is a pungent odor of hydrochloric acid Released; polyethylene has a small specific gravity and can float on the water, while polyvinyl chloride sinks in the water.

　　 (3) Identification basis for phenolic and urea-formaldehyde plastics

Both are thermosetting plastics, which are hard and opaque. The main differences are as follows: phenolic plastics are generally black-brown, urea-formaldehyde plastics are mostly light-colored and bright in color; phenolic plastics have a loose section structure, while urea-formaldehyde plastics have a loose section. The structure is tight; when burning, phenolic aldehyde emits the odor of phenol, carbonization and cracking occur in the part in contact with the flame, urea-formaldehyde has the odor of urea, and whitening and cracking occurs in the area in contact with the flame.

　　 (4) Identification basis for polystyrene, polyvinyl chloride, and polyethylene plastics

　　 The identification basis of these three plastics is based on the following five aspects:

1. Color and transparency

　　 Polystyrene plastic is bright in color and its transparency is like glass; polyvinyl chloride plastic is inferior to polystyrene in color and transparency; polyethylene plastic is translucent, looks like wax products, and dyes are easy to bleed out.

2. Feel

The feel of polystyrene is smooth, the surface is hard, and it is afraid of bumps and squeezing; the feel of polyvinyl chloride is also relatively smooth, and the film products have a sticky feel; there are soft and hard products; the feel of polyethylene has a waxy and slippery feel , The product is soft and durable.

　　3. Relative density

The relative density of polystyrene is 1.05~0.06, and it sinks slowly in water; the relative density of polyvinyl chloride soft plastic is 1.24~1.45, and the relative density of hard plastic is 1.35~1.45, so it drops quickly in water Shen; The relative density of high-density polyethylene is 0.94~0.97, and the relative density of low-density is 0.91~0.93, so it floats in water.

　　4. sound

　　 When a hard object hits, polystyrene has a crisp metallic sound, polyvinyl chloride is loud but not brittle, and polyethylene is stuffy but not brittle.

　　 5. Flammability

Polystyrene is flammable, flame is orange, flocculent black smoke, pungent and unpleasant styrene monomer odor; polyvinyl chloride is not spontaneously combustible, it is extinguished from the fire, flame is yellow, the roots are green, and the odor of hydrochloric acid is released ; Polyethylene is flammable, the flame is yellow, the roots are blue, and a small amount of black smoke is emitted. It softens when burned, drips wax tears like a candle, and emits a paraffin odor.