Polypropylene(PP)

Views: 0 Author: Site Editor Publish Time: 2020-08-03 Origin: Site

Polypropylene(PP) (Fig.1.10) is a thermoplastic prlymer used in a wide variety of a pplications including packaging and labeling, textiles (e.g.,ropes, thermal underwear and carpets, stationery plastic parts and reusable containers of various types, laboatory equipment, automotive components, and polymer banknon.

Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low-density polyethylene and high-density polyethylene. Polypropylene is normally tough and flexible, especially when copolymerized with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS. Polypropylene is reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic, or certain other plastics. It is often opaque or colored using pigments Polypropylene has good resistance to fatigue

(1) Physical and chemical properties The melting of polypropylene occurs as a range, so a melting point is determined by finding the highest temperature of a differential scanning calorimetry chart. Perfectly isotactic PP has a melting point of 171'C Commercial isotactic PP has a melting point that ranges from 160C to 166C, depending on atactic material and crystallinity Syndiotactic PP with a crystallinity of 30% has a melting point of 130C.

The melt flow rate(MFR)or melt flow index(MFD) is a measure of molecular weight of olypropylene. The measure helps to determine how easily the molten raw material will flow during processing. Polypropylene with higher MFR will fill the plastic mold more easily during the injection or blow-molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease

Polypropylene is liable to chain degradation from exposure to heat and UV radiation such that present in sunlight. Oxidation usually occurs at the tertiary carbon atom present in every repeat unit. For external applications, UV-absorbing additives must be used. Carbon black also provides some protection from UV attack. The polymer can also be oxidized at high temperatures which is a common problem during molding operations. Anti-oxidants are normally added to prevent polymer degradation.

There are three general types of polypropylene: homopolymer, random copolymer, and block copolymer. The comonomer is typically used with ethylene. Ethylene-propylene rubber or EPDM added to polypropylene homopolymer increases its low temperature impact strength. Randomly

polymerized ethylene monomer added to polypropylene homopolymer decreases the polymer crystallinity and makes the polymer more transparent.

(2)Applications Carpets(or rugs, mats)to be used at home, and ropes, insulation for electrical cables, roofing membranes as the waterproofing top layer, injection moldings to form complex shapes at relatively low cost and high volume such as bottle tops, bottles. Sheet form is widely used for the production of stationery folders, packaging, and storage boxes. Polypropylen fibres are used as a concrete additive to increase strength and reduce cracking and spalling.

Since polypropylene is resistant to fatigue, most plastic living hinges, such as those on flip-top bottles, are made from this material. However, it is important to ensure that chain molecules are orientated across the hinge to maximise strength Polypropylene is often chosen for its resistance to corrosion and chemical leaching, its resilience against most forms of physical damage, including impact and freezing, its environmental benefits, and its ability to be joined by heat fusionrather than gluing.

Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave. Its heat resistance also enables it to be used as the manufacturing material of consumer-grade kettles.

Plastic pails, car batteries, wastebaskets, pharmacy prescription bottles, cooler containers dishes and pitchers are often made of polypropylene or HDPE, both of which commonly have rather similar appearance, feel, and properties at ambient temperature.

A common application for polypropylene is being as biaxially oriented polypropylene(boPp). These BOPP sheets are used to make a wide variety of materials including clear bags. When polypropylene is biaxially oriented, it becomes crystal clear and serves as an excellent packaging material for artistic and retail products.

Expanded polypropylene(EPP)is a foam form of polypropylene. EPP has very good impact characteristics due to its low stiffness. This allows EPP to resume its shape after impacts. EPP is extensively used in model aircraft and other radio controlled vehicles by hobbyists. This is mainly due to ability to absorb impacts, making this an ideal material for RC aircrat for beginners and amateurs.

Polypropylene(PP)

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