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一. What kind of plastic is PP

PP plastic, chemical name: Polypropylene

English Name: polypropylene (PP for short)

Weight: 0.9-0.91 g / cm3 molding shrinkage: 1.0-2.5 molding temperature: 160-220 ℃

Features: non toxic, tasteless, small, strength, stiffness, hardness and heat resistance are better than low-pressure polyethylene, can be used in about 100 degrees. With good electrical properties and high-frequency insulation, not affected by humidity, but brittle at low temperature, not wear-resistant, easy to aging. Suitable for manufacturing general mechanical parts, corrosion-resistant parts and insulation parts. The common organic solvents of acid and alkali have little effect on it and can be used in tableware.

PP plastic molding features:

1. Crystal material, hygroscopicity is small, easy to form melt fracture, long time contact with hot metal is easy to dissolve

2. Good fluidity, but large shrinkage range and shrinkage value, easy to form shrinkage cavity, dent and deformation

3. The cooling speed is relatively fast, the pouring system and cooling system should slow heat dissipation, and pay attention to control the molding temperature. When the material temperature is low temperature and high pressure, it is very easy to orientate. When the mold temperature is less than 50 ℃, the plastic parts are not smooth, which is easy to form poor fusion and flow marks, and more than 90 ℃ is easy to form warping deformation

4. The thickness of the plastic wall must be uniform to avoid the lack of glue and sharp corners to prevent stress concentration.

二. Properties of PP plastics

physical property

Polypropylene is a non-toxic, odorless and tasteless milky white high crystalline polymer with a density of only 0.90-- "0.91g/rm, which is one of the lighter varieties of all plastics at present. It is very stable to water. Its water absorption rate is only 0.01 and its molecular weight is about 80.15 million. It has good formability, but because of the large shrinkage rate (1 ~ 2.5), thick wall products are easy to sag, and some parts with high dimensional accuracy can not meet the requirements. The surface luster of the products is good, and it is easy to dye.

mechanical property

Polypropylene has good mechanical properties because of its high crystallinity and regular structure. The mechanical properties of PP are higher than that of PE, but PP still belongs to the lower variety in plastic materials, and its tensile strength can only reach 30MPa or slightly higher level. Polypropylene with higher isotactic index has higher tensile strength, but with the increase of isotactic index, the impact strength of the material decreases to a certain extent, but it will not change after falling to a certain value.

Temperature and loading rate have great influence on the toughness of polypropylene. When the temperature is higher than the glass transition temperature, the impact failure is ductile fracture, and when the temperature is lower than glass transition temperature, it is brittle fracture, and the impact strength value decreases greatly. With the increase of loading rate, the temperature of transition from ductile fracture to brittle fracture increases. Polypropylene has excellent bending fatigue resistance, and its products can be bent at room temperature.