Classification, characteristics and applications of polypropylene (PP) plastics


(1) Polypropylene (PP) production process Polypropylene is made by addition polymerization of propylene, CH2=CHCH3, under the action of Z-N metal catalyst.

(2) Production method of polypropylene (PP)
① Slurry method. Polymerization in a diluent (such as hexane) is the earliest industrialized method and the largest production method so far.
② Liquid phase bulk method. Polymerize in liquid propylene at 70°C and 3MPa.
③Gas phase method. Polymerize under gaseous conditions of propylene. The latter two methods do not use diluent, the process is short, and the energy consumption is low. The liquid phase bulk method has now shown the advantage of coming from behind, and the gas phase method is also developing rapidly.

Polypropylene classification

According to different structures, it is divided into isotactic polypropylene and atactic polypropylene.

The commonly used polypropylene is isotactic polypropylene.

Characteristics of PP

Its molecular structure is similar to polyethylene, but the interphase carbon atoms on the carbon chain carry a methyl group (–CH3). Polypropylene is slightly more brittle than polyethylene and has a melting temperature of 160°C.
Usually a translucent colorless solid, odorless and non-toxic.
Due to the regular structure and high degree of crystallization, the melting point is as high as 167°C, heat-resistant, and the product can be steam sterilized is its outstanding advantage.
With a density of 0.90g/cm3, it is the lightest general-purpose plastic.
Corrosion resistance, tensile strength 30MPa, strength, rigidity and transparency are better than polyethylene.
The disadvantage is poor low-temperature impact resistance and easy aging, but it can be overcome by modification and addition of antioxidants.

Application of PP

(1) Injection molded products: It is the largest application field of polypropylene. The products include turnover boxes, containers, suitcases, auto parts (car interior parts, such as dashboards; mudguards, ventilation ducts, fans; bumpers), Household appliances parts, medical equipment (disposable syringes), equipment (dishwasher door liners, dryer vent pipes, washing machine frames and covers, refrigerator door liners, etc., consumer goods (lawn and garden equipment such as grass cutting) Machines and sprinklers, etc.) and furniture.

(2) Extruded products: It can be made into polypropylene fiber or polypropylene film. The strength and transparency of biaxially stretched film are greatly improved, making it an important polymer material for packaging.

Polypropylene is the most versatile general-purpose plastic. It can be used as plastic or spun into fibers (polypropylene). Polypropylene is a fiber with low water absorption and high corrosion resistance. It can be used in clothing and furniture, and is especially suitable for weaving carpets. It can also be extruded or blown into a film, and then cut into flat filaments by drawing to make a woven bag, or used as a binding material-packing tape. In recent years, the polypropylene composite film has developed rapidly, which can prevent moisture, gas and steam, and be used as a flexible packaging for food and beverages.
Polypropylene pipes are used to transport hot water—PPR pipes, industrial waste water and chemicals.
Sheets are used to make containers.

(3) Thermoformed products: Thin-walled products are made into thin-walled products after thermoforming, which are used as disposable food containers-drinking cups.

Others, such as blow molding products, polypropylene is widely used in food packaging, such as yogurt containers, hot-filled beverage bottles. toy. Through a special catalytic method (metallocene catalytic technology), block polypropylene with identical and random segments can also be made. The properties of this polypropylene are similar to rubber.

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