The identification method of plastics is usually identified by appearance and use, density test, softening point or melting point, combustion test, and comprehensive identification method. The following commonly used methods are used to learn:
Appearance and use
To dissect an unknown polymer sample, the first thing is to look at the hand touch, to determine which category it belongs to in its appearance. If possible, understand the source and know as much as possible about the use;
â—Ž transparency and color
Crystalline → translucent / opaque (PP, PE, Nylon, POM, PET, ...)
Amorphous → Transparent (PC, PMMA, GPPS, SAN, PPO
â—Ž feel and mechanical properties
By hand, squeezing, tapping or bending the sample, you can sense the approximate strength and toughness of the material: you can use the nail scratches (or tools such as nails) to determine the hardness of the material. These can be used to initially identify the approximate type of material.
â—ŽUse of plastic products
Qualitative identification without background knowledge is very difficult. However, if the source of the sample is known, as well as other background knowledge of the use case, the scope of identification is greatly reduced.
For example: not broken inner plastic cup
Density test
Equal density method (refer to ASTM D1505; ISO R 1183 method D)
The density of the solid can be measured by suspending the solid to be tested in a liquid of known density (ie equal density).
Solution specific gravity solution specific gravity
Industrial alcohol 0.8 sodium chloride 1.22
Water 1 zinc chloride 1.63
Magnesium chloride 1.33
Combustion test
â—ŽThe method of burning test is very simple. Support a small piece of sample with a tweezers or a spatula, and directly heat it with a flame. Generally, the corner of the sample is close to the edge of the flame. For the sample that is easy to ignite, it can be distinguished first and then placed. Burning on the flame, sometimes moving away to determine whether the fire continues to burn.
â—Ž The flammability of the material is related to the elements contained.
Combustible elements - non-flammable elements such as carbon, chlorine, sulfur - halogen, phosphorus, nitrogen, antimony, boron, etc.
The color of the flame is usually related to the element
Yellow - plastic containing only carbon and hydrogen, such as PS
Blue - oxygen-only plastics such as POM
Green - chlorine-containing plastics such as PVC
White - burning plastic, such as nitrocellulose.
General plastic raw materials
a. The plastic material is thermally expanded, and the coefficient of linear expansion is much larger than that of metal;
b. The rigidity of general plastic materials is an order of magnitude lower than that of metals;
c. The mechanical properties of plastic materials will decrease significantly under prolonged heating;
d. The general plastic material will be permanently deformed under normal temperature and under the stress of its yield strength, and permanent deformation will occur;
e. Plastic materials are sensitive to gap damage;
f. The mechanical properties of plastic raw materials are usually much lower than that of metals, but some composite materials have higher specific strength and specific modulus than metals. If the product design is reasonable, it will be more advantageous;
g. Generally, the mechanical properties of plastic raw materials are anisotropic;
h. Some plastic materials will absorb moisture and cause dimensional and performance changes;
i. Some plastics are flammable;
j. The fatigue data of plastic raw materials is still very small, and should be considered according to the use requirements.
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