PP plastics are often used in custom materials for disposable cups. The chemical name for PP plastics is polypropylene. Polypropylene is a semi-crystalline thermoplastic. It has high impact resistance, strong mechanical properties, resistance to various organic solvents and acid-base corrosion. It has a wide range of applications in the industry and is one of the commonly seen polymer materials.

First, pp plastic molding characteristics:

1. Crystallized material, low hygroscopicity, easy to melt fracture, long-term contact with hot metal is easy to decompose.

2. Good fluidity, but the shrinkage range and shrinkage value are large, and shrinkage, dent and deformation are easy to occur.

3. The cooling rate is fast, the pouring system and the cooling system should be slowly dissipated, and the molding temperature should be controlled. The material temperature is easy to orient at low temperature and high pressure. When the mold temperature is lower than 50 degrees, the plastic parts are not smooth, and it is easy to produce poor welding and flow marks. More than 90 degrees is prone to warp deformation

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

Second, pp plastic properties:

Physical properties

Polypropylene is a non-toxic, odorless, odorless, milky white, highly crystalline polymer with a density of only 0.90--"0. 91g/rm. It is one of the lighter varieties of all plastics. It is particularly stable to water. The water absorption rate in water is only 0. O1, the molecular weight is about 80,100,000. The moldability is good, but the shrinkage rate is large (1~2.5). The thick-walled products are easy to be sunken, and some parts with higher dimensional accuracy are also It is difficult to meet the requirements, the surface of the product is good in gloss and easy to color.

2. Mechanical properties

Polypropylene has high crystallinity and regular structure, and thus has excellent mechanical properties. The mechanical properties of polypropylene are higher than that of polyethylene, but it is still a low grade in plastic materials, and its tensile strength can only reach 30 MPa or slightly higher. Polypropylene with a higher isotactic index has higher tensile strength, but as the isotactic index increases, the impact strength of the material decreases, but does not change after falling to a certain value.

Temperature and loading rate have a great influence on the toughness of polypropylene. When the temperature is higher than the glass transition temperature, the impact fracture is ductile fracture, brittle fracture below the glass transition temperature, and the impact strength value is greatly reduced. Increasing the loading rate increases the temperature at which the ductile fracture transitions to brittle fracture. Polypropylene has excellent bending fatigue resistance, and its product can be bent 106 times at normal temperature without damage.

However, at room temperature and low temperature, the impact strength is poor due to the high degree of molecular structure regularity. The performance of polypropylene is resistance to bending fatigue, commonly known as a hundred fold plastic.