What is PP?

PP: Polypropylene English name: Polypropylene, abbreviated as: PP, commonly known as: 100-fold glue. Polypropylene is a representative of poly-α-olefins, a thermoplastic resin made by propylene polymerization, and its monomer is propylene CH2=CH-CH3. According to the different initiators and polymerization processes, polypropylene can be divided into three configurations: isotactic polypropylene, random polypropylene and syndiotactic polypropylene.

Isotactic polypropylene is easy to form a crystalline state, with a crystallinity of more than 95% and a molecular weight between 80,000 and 150,000, giving it good heat resistance and solvent resistance; random polypropylene is a non-crystalline, slightly sticky white wax at room temperature, with a low molecular weight of 3000-10000, irregular structure and lack of cohesion, and is less used.

PP is a semi-crystalline material. It is harder and has a higher melting point than PE. Since homopolymer PP is very brittle when the temperature is above 0°C, many commercial PP materials are random copolymers with 1~4% ethylene or block copolymers with a higher ethylene content.

Copolymer PP materials have a lower heat distortion temperature (100°C), low transparency, low gloss, and low rigidity, but have stronger impact strength. The strength of PP increases with the increase of ethylene content. The Vicat softening temperature of PP is 150°C. Due to the high crystallinity, this material has good surface stiffness and scratch resistance. PP does not have environmental stress cracking problems. Usually, PP is modified by adding glass fiber, metal additives or thermoplastic rubber. The flow rate MFR of PP ranges from 1 to 40. Low MFR PP materials have better impact resistance but lower ductility. For materials with the same MFR, the strength of copolymers is higher than that of homopolymers. Due to crystallization, the shrinkage of PP is quite high, generally 1.8~2.5%. And the directional uniformity of the shrinkage is much better than that of materials such as PE-HD. Adding 30% of glass additives can reduce the shrinkage to 0.7%.

Both homopolymer and copolymer PP materials have excellent resistance to moisture absorption, acid and alkali corrosion, and solubility. However, it has no resistance to aromatic hydrocarbon (such as benzene) solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, etc. PP is not as resistant to oxidation at high temperatures as PE.

Polypropylene (PP) is one of the lighter common plastics with excellent electrical properties. It can be used as a moisture-resistant high-frequency insulation material. PP is a crystalline polymer. When the melt condenses, it shows a large shrinkage rate (1.0%-1.5%) due to the large change in specific volume and high degree of molecular orientation. In the molten state, it is not very effective to reduce the viscosity of PP by increasing the temperature. Therefore, in the molding process, the injection pressure and shear rate should be increased to improve the molding quality of the product.

Physical properties

PP is a non-toxic, odorless, milky white, highly crystalline polymer. It is one of the lightest varieties of all plastics at present. It is particularly stable to water, and the water absorption rate in water for 14 hours is only 0.01%. The molecular weight is between 80,000 and 150,000, and the moldability is good. However, due to the large shrinkage rate, the original wall products are easy to dent, the surface gloss of the products is good, and it is easy to color.

Mechanical properties

PP has high crystallinity and regular structure, so it has excellent mechanical properties. Its strength, hardness and elasticity are higher than high-density PE (HDPE). The outstanding feature is the bending fatigue resistance (7×10^7) times of opening and closing folding and bending without damage marks. The dry friction coefficient is similar to nylon, but not as good as nylon under oil lubrication.

Thermal properties

PP has good heat resistance, the melting point is 164~170℃, and the products can be sterilized at a temperature above 100℃. Without the influence of external forces, it will not deform at 150℃. The embrittlement is -35℃, and embrittlement will occur below -35℃. The heat resistance is not as good as PE.

Chemical stability

PP has good chemical stability. In addition to being corroded by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable to various other chemical reagents. However, low molecular weight aliphatic hydrocarbons and aromatic hydrocarbons can soften and swell PP, and the chemical stability is improved with the increase of crystallinity. Therefore, PP is suitable for making Russian-Chinese chemical pipelines and accessories, and has good anti-corrosion effect.

Electrical properties

Polypropylene has excellent high-frequency insulation performance. Since it hardly absorbs water, its insulation performance is not affected by humidity. It has a high dielectric constant and can be used to make heated electrical insulation products with high breakdown voltage as the temperature rises. It is suitable for electrical accessories, etc. It has good voltage resistance and arc resistance, but high static electricity and is easy to age when in contact with copper.

Weather resistance

Polypropylene is very sensitive to ultraviolet rays. Adding zinc oxide thiopropionate dilauryl, carbon black-like milky white fillers, etc. can improve its aging resistance.

Characteristics

Non-toxic, odorless, low density, strength, stiffness, hardness and heat resistance are better than low-pressure polyethylene, and can be used at around 100°C. It has good dielectric properties and high-frequency insulation and is not affected by humidity, but becomes brittle at low temperatures, is not wear-resistant, and is easy to age. It is suitable for making general mechanical parts, corrosion-resistant parts, and insulating parts. Common organic solvents such as acids and alkalis have little effect on it and can be used for tableware.

Polypropylene has many excellent properties:

1. The relative density is small, only 0.89-0.91, and it is one of the lightest varieties of plastics.
2. Good mechanical properties. Except for impact resistance, other mechanical properties are better than polyethylene, and the molding and processing performance is good.
3. It has high heat resistance, and the continuous use temperature can reach 110-120℃.
4. Good chemical properties, almost no water absorption, and no reaction with most chemicals.
5. Pure texture and non-toxic.
6. Good electrical insulation.
7. The transparency of polypropylene products is better than that of high-density polyethylene products.

It has many advantages but also disadvantages:

1. The product has poor cold resistance and low low-temperature impact strength.
2. The product is susceptible to aging due to light, heat and oxygen during use.
3. Poor colorability.
4. Easy to burn.
5. Poor toughness, high static electricity, poor dyeing, printing and adhesion.

Application

1. Chemical and chemical storage tank manufacturing and processing
2. High acid and alkali solution storage
3. Processing equipment building materials
4. Electronic electroplating equipment containers
5. Experimental equipment and utensils
6. General processing instruments and equipment
7. Scrubber, air filtration system, duct system
8. Waste gas treatment washing system
9. Circuit board pickling equipment
10. Plating tank
11. Medical application components
12. Computer digital processing center and precision equipment components
13. Transportation

Application industry

1. Chemical processing industry
2. Surface treatment industry
3. Medicine
4. Life science