Basic properties and applications of polypropylene PP

Polypropylene PP is a polymer made from propylene as a monomer. Plastics with polypropylene PP as the base material are called polypropylene PP plastics. In addition 

to being affected by relative molecular weight and distribution, the properties of polypropylene PP are also closely related to stereoregularity. According to the different 

spatial positions of CH3 in polypropylene PP molecules, it can be divided into isotactic polypropylene PP, syndiotactic polypropylene PP and atactic polypropylene PP. 

Industrially produced polypropylene PP is mainly isotactic polypropylene PP. In addition, PP has a variety of modified products. The following is an introduction to the 

basic properties and applications of PP:

1. Main performance

The density of polypropylene PP is 0.89~0.91g/cm3. In plastics, it is only denser than poly-4-methyl-1-pentene (0.83g/cm3). It is characterized by a high softening point 

and good heat resistance. The melting point is 170~172°C, and the continuous use temperature reaches 110~120°C; the tensile strength and rigidity are good; the hardness 

is high, and the wear resistance is good; the molding shrinkage is low, which is conducive to injection molding; the stress crack resistance is excellent (greater than 1000h), 

20 to 100 times stronger than HDPE; excellent electrical insulation properties and chemical stability. The main disadvantages are poor low-temperature impact strength, 

easy brittleness, poor weather resistance, high electrostatic properties, and poor dyeability. For this reason, many countries attach great importance to research on the 

modification of polypropylene PP. Polypropylene PP can be identified by its performance characteristics. It is a white waxy substance, like PE but lighter and more transparent 

than PE. It burns easily and cannot self-extinguish after being removed from fire. The upper end of the flame is yellow, the lower end is blue, and there is a small amount of 

black smoke. When burning, it melts and drips and emits a petroleum smell.

①Physical properties

Polypropylene PP is a non-toxic, odorless and tasteless milky white highly crystalline polymer with a density of only 0.89~0.91g/cm3. It is one of the lightest varieties of 

all plastics currently. It is particularly stable to water. Its water absorption rate in water for 24 hours is only 0.01%, and its relative molecular mass is 80,000 to 150,000. 

The formability is good, but due to the large shrinkage rate (1%~2.5%), thick-walled products are easy to dent, and it is difficult to meet the requirements for some parts 

with high dimensional accuracy. The surface of the product has good gloss and is easy to color.

②Mechanical properties

Polypropylene PP has high crystallinity and regular structure, so it has excellent mechanical properties. Its yield, tensile, compressive strength, hardness, elasticity, etc. are 

higher than HDPE. However, at room temperature and low temperature, due to the regularity of its molecular structure High, so the impact strength is poor. When the relative 

molecular weight increases, the impact strength also increases, but the molding performance becomes worse. Polypropylene PP has outstanding bending fatigue resistance. 

For example, an integrated movable hinge injected with PP can withstand 7×107 times (i.e. 70 million times) of opening and closing folding and bending without any trace 

of damage. Its friction performance is also good, and its friction performance is also good. The friction coefficient is similar to that of nylon, but when lubricated with oil, 

its friction performance is obviously not as good as that of nylon. PP can only be used to make gears and bearings with low PV values and that are not subject to impact loads. 

In terms of surface effects, such as embossing, engraving, etc. on the surface of its products, it is easier than any other thermoplastic. Polypropylene PP products are particularly 

sensitive to gaps, so when designing the mold, care must be taken to avoid sharp corners, otherwise stress concentration will easily occur and affect the service life of the product.

③Thermal performance

Polypropylene PP has good heat resistance, with a melting point of 164~170℃, and the products can be sterilized at temperatures above 100℃. When not subject to external 

force, it will not deform at 150°C and has good stress relaxation resistance at 90°C. Its embrittlement temperature is -35°C, and brittleness will occur at temperatures below 

-35°C, and its cold resistance is not as good as polyethylene. If reinforced with asbestos fiber and glass fiber, it will have higher heat deformation temperature, dimensional 

stability and low temperature impact performance.

④Chemical stability

Polypropylene PP has very good chemical stability. In addition to being corroded by concentrated sulfuric acid and nitric acid, it is relatively stable to various other chemical 

reagents. However, low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can soften polypropylene PP. and swelling, and its 

chemical stability improves with the increase of crystallinity. Therefore, it is suitable for making various chemical pipelines and accessories, and has good anti-corrosion effect.

⑤Electrical performance

Polypropylene PP has excellent high-frequency insulation properties. Since it hardly absorbs water, its insulation properties are not affected by humidity. It has a high dielectric 

coefficient, and as the temperature rises, it can be used to make heated electrical insulation products. Its breakdown voltage is also very high, making it suitable for use as 

electrical accessories. It has good voltage resistance and arc resistance, but has high static electricity and is prone to aging when in contact with copper.

⑥Weather resistance

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

⑦Molding processing characteristics

Polypropylene PP has good molding and processing properties, and different products can be made by injection, extrusion, blow molding, welding, thermoforming, machining, 

electroplating, foaming and other molding processing methods. Polypropylene PP can be mainly used to make various injection products, films and monofilaments. The film 

can be made by the blown tube film method (down blowing, water cooling), or by the T-shaped die extrusion method, which can be unidirectionally or bidirectionally stretched 

into a high-strength transparent film. The injection temperature of polypropylene PP is 230~260℃, and its fluidity is greatly affected by the injection pressure. The higher the 

mold temperature, the greater the molding shrinkage. For example, when the injection pressure is 68.6MPa and the mold temperature is 60°C, the shrinkage is 1.8%. When the 

injection temperature is high (above 190°C), the fluidity increases sharply, which can easily cause flash and shrinkage cavities. When the temperature exceeds 180°C, it begins 

to decompose slowly, so the injection temperature should be low.

PP material

2. Application

Polypropylene PP is light, non-toxic, has good performance, can be steam sterilized, and has a wide range of applications.

1. In terms of household daily necessities, PP can be used as tableware, kitchen utensils such as basins, baskets, and filters, tableware such as condiment containers, snack 

boxes, and cream boxes, bathtubs, buckets, chairs, bookshelves, milk crates, and toys etc.

2. In terms of household appliances, PP can be used as refrigerator parts, electric fan motor covers, washing machine tubs, hair dryer parts for hairdressers, hair curlers, TV 

back covers, record players and radio casings, etc.

3. PP can also be used in medical syringes and containers, infusion tubes and filters, etc.;

4. Auto parts, chemical pipelines, storage tanks, equipment linings, valves, filter plates and frames, Pall ring packing for distillation towers, etc.;

5. Transportation containers, food and beverage turnover boxes, packaging films, heavy packaging bags, strapping materials and tool measuring boxes, briefcases, jewelry 

boxes, musical instrument boxes and other boxes;

6. Various clothing items, carpets, artificial lawns and artificial ski venues, etc.

7. PP can also be used as construction materials, various utensils, ropes and fishing nets for agriculture, forestry, animal husbandry, sideline production and fishery.

3. About Us

Luoyang Dema Import & Export Co., Ltd. aims to provide high-quality, cost-effective products for global factories, plastic product manufacturers, and material distributors. 

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