The identification of plastics can use scientific methods such as infrared spectroscopy, paramagnetic resonance, and X-rays, but simpler methods can also be used for identification. 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 are: 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 struck 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 → organic glass → 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 plastic can draw line marks with HB pencil;
Polypropylene plastic ZH pencil can draw line marks.
Due to the difference in people's physiological conditions, the senses 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, and the burning phenomenon is basically the same. However, there are also obvious differences between the two: polyethylene has a waxy feel to the touch, soft and bendable in texture, while polypropylene is smooth and delicate to the touch, but has no waxy and slippery feel, and the texture is quite hard and tough; 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. The layers stacked together are still milky white and translucent, while the transparency of polyvinyl chloride is higher than that of polyethylene, and the color is slightly yellow. The layers stacked together turn yellow and the hand feels smooth. , But it has a sticky feeling, carefully observe the mold fine lines; 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 smell 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 The structure is tight; when burning, phenolic aldehyde emits a odor of phenol, carbonization and cracking occurs in the part in contact with the flame, and urea-formaldehyde has the odor of urea, and whitening and cracking occurs at the contact with the flame.
(4) Identification basis for polystyrene, polyvinyl chloride, and polyethylene plastics
The identification basis of these three kinds of plastics has the following five aspects:
1. Color and transparency
Polystyrene plastic is bright in color and has transparency like glass; polyvinyl chloride plastic is worse than polystyrene in color and transparency; polyethylene plastic is translucent, looks like wax products, and dyes are easy to seep 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 PVC soft plastic is 1.24~1.45, and the relative density of rigid 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 strikes, polystyrene has a crisp metallic sound, polyvinyl chloride is loud but not brittle, and polyethylene is stuffy but not brittle.
5. Combustibility
Polystyrene is flammable, flame is orange, flocculent black smoke, pungent and unpleasant styrene monomer odor; PVC cannot be spontaneously ignited, 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 burning, drips wax tears like a candle, and emits a paraffin smell.