Identification basis of several easy-to-mix plastics

(1) Identification basis of polyethylene and polypropylene plastics

Polyethylene and polypropylene plastics are both milky white translucent bodies, light in weight and can float on the water surface, and the burning phenomenon is basically the same. However, there are also obvious differences between the two: polyethylene has a waxy and greasy feel to the hand, and the texture is soft and bendable, while the polypropylene feels smooth and delicate, but has no waxy and greasy feel, and has a hard and tough texture; polyethylene plastics are used in It softens significantly in boiling water, but polypropylene plastic does not soften significantly in boiling water; polyethylene plastic strips have "thin necks" when stretched, but polypropylene does not.

(2) Identification basis of 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 blow molding; from the perspective of color and transparency: polyethylene is milky white and translucent. The surface is brighter, the hand feels waxy and smooth, and the layers are still milky white and translucent, while the transparency of polyvinyl chloride is higher than that of polyethylene, the color is slightly yellow, and the layers are yellow when stacked together, and the hand is smooth. , but it has a sticky feeling, and there are mold fine lines when carefully observed; the burning phenomenon is different: polyethylene is flammable, melts and drips, and has a paraffin smell, while polyvinyl chloride is inflammable, the flame root is green, and there is a pungent odor of hydrochloric acid. Released; polyethylene with a small specific gravity can float on the water surface, while polyvinyl chloride sinks in water.

(3) Identification basis of 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 and brown, and urea-formaldehyde plastics are mostly light-colored and brightly colored; The structure is tight; when burning, phenolic odor emits phenol, and carbonization cracking occurs in the part in contact with the flame;

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

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

1. Color and Transparency

Polystyrene plastics are bright in color and have transparency like glass; PVC plastics are inferior in color and transparency to polystyrene; polyethylene plastics are translucent and look like wax products, and dyes are easy to seep out.

2. Feel

Polystyrene has a smooth hand and a hard surface, which is afraid of bumping and extrusion; PVC has a smooth hand, and film products have a sticky feeling; there are soft and hard products; polyethylene has a waxy and greasy feel. , The product is soft and resistant to bending.

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 rigid plastic is 1.35~1.45, so it will sink rapidly in water. The relative density of high-density polyethylene is 0.94~0.97, and the relative density of low-density polyethylene is 0.91~0.93, so it floats in water.

4. Sound

When hit by a hard object, 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, the flame is orange-yellow, flocculent black smoke, and has a pungent and unpleasant odor of styrene monomer; polyvinyl chloride cannot spontaneously ignite, it goes out from the fire, the flame is yellow, the roots are green, and there is a smell of hydrochloric acid released ;Polyethylene is flammable, the flame is yellow, the root is blue, emits a small amount of black smoke, softens when burning, drips wax tears like a candle, and emits paraffin odor.