Classification standards for polyethylene and PET

Classification criteria for polyethylene and PET: Transparency: PET has high transparency, with a light transmittance typically reaching 88% to 92%. Products made from PET, such as beverage bottles, appear clear and transparent. However, the transparency of polyethylene varies greatly. Low density polyethylene (LDPE) has a certain degree of transparency with a light transmittance of about 80% to 90%, while high-density polyethylene (HDPE) is mostly milky white with poor transparency, with a light transmittance of generally 60% to 70%.

Color and texture: The surface of PET products is smooth and glossy; Polyethylene products have a relatively soft texture, HDPE has a slightly harder texture, and LDPE is softer and has a waxy feel.

Density.

PET: The density is generally 1.38 1.41 g/cm ³.

Polyethylene: has a wide density range, with LDPE having a density of 0.91 0.94 g/cm ³ and HDPE having a density of 0.94 0.97 g/cm ³. By accurately measuring density, it is possible to distinguish between the two with greater precision.

Combustion characteristics.

PET: After ignition, the flame turns yellow with a small amount of black smoke. When burning, it curls up and melts, producing a special sweet odor that can continue to burn after leaving the source of fire.

Polyethylene: When burned, the flame appears yellow at the top and blue at the bottom. During the combustion process, it melts and drips, with a smell of paraffin burning. LDPE is easier to burn than HDPE, and the degree of continued combustion after leaving the fire source varies.

Chemical properties.

Acid and alkali resistance: PET has good tolerance to acid and alkali, but hydrolysis occurs in high temperature and high concentration acid-base environments. Polyethylene has good tolerance to most acids and bases, but may undergo oxidation reactions under the action of strong oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid.

Hardness and tensile properties.

Hardness: The hardness of PET is relatively high, with a Shore hardness of generally 80-90D; the hardness of polyethylene is relatively low, with a Shore hardness of about 40-60D for LDPE and 60-70D for HDPE. Tensile strength: The tensile strength of PET is relatively high, usually around 50-70 MPa; The tensile strength of LDPE is 7.15 MPa, and the tensile strength of HDPE is 20.35 MPa. By testing hardness and tensile strength, the two can be distinguished.