Polypropylene is generally produced through a reaction of chain-growth polymerization that involves propylene. The polymer can also be known as a type of polypropylene and sometimes it is represented with the abbreviation form of ‘PP’. This type of polymer is called thermoplastic polymer, and it guides to soften by heating and can be remoulded.

Definition: Polypropylene

Polypropylene is a particular form of polypropylene and it is used for different ranges of purposes. It is mainly made from monomer propylene through a particular process.

This type of plastic refers to the thermoplastic that is crystalline in form and it is commonly used as the main ingredient of packaging trays along with different types of household products, cases of battery as well as different types of medical devices.

Classifications Of Polypropylene

Three different kinds of polypropylene can be seen, they are homopolymer, random and block copolymer. The term co-monomer is mainly applied to ethylene and it is added to thermosetting polymer that guides to increments its temperature.

Polypropylene is mainly categorized in different forms.

  • Atactic polypropylene can be represented as PP-at.

  • Syndiotactic polypropylene is another form that is denoted by PP-st.

  • Isotactic polypropylene is denoted as PP-it.

The group of methyl can be aligned uniformly within a polypropylene of atactic that alters for syndiotactic. It also affects the isotactic form of polypropylene and the thermal properties of this type of chemical compound are crystalised. Atactic is another type of polypropylene that is amorphous as well as lacks regularity and making difficult to crystallisation.

Polypropylene: Physical Properties

The distribution of the molecular weight refers to the crystallinity in the form of a comonomer and it has a great influence on the physical properties of this chemical compound.

  • Polypropylene has a similarity with polyethene in several forms particularly in terms of solubility as well as electrical characteristics.

  • The chemical resistance mainly decreases when the group of methyl increase its mechanical properties along with the resistance in thermal power.

  • The density of this chemical compound varies from 0.895 to 0.92 g/cm3. Therefore, PP has the lowest density in plastic products. The parts that can mould in the lower weight along with more parts of the provided mass in plastic are created with a lower amount of density. The density of this compound is variable significantly.

  • The range of PP in terms of Young’s modulus varies between 1300 and 1800 N/mm2.

  • The thermal expansion of these materials is significant but a little less compared to polyethene.

Polypropylene: Chemical Properties

The chemical properties of polypropylene are slightly different from other types of polythene in several ways.

  • It comprises heavy oxidants, but this chemical compound has full resistance to fats along with organic solvents at normal temperatures. The chemical properties vary from different bases of polyethene like acid-base as well as the non-oxidizing base. It is fully dissolved in non-polar types of solvents such as xylene and tetralin at higher temperatures. The chemical resistance power of the chemical compound is lower because of the tertiary atom of carbon.

  • The majority of this chemical compound is isotactic with the crystallinity intermediates between two types of polythene such as lower and higher density. At the temperature of 140°C isotactic as well as atactic types, compounds can easily dissolve within p-xylene. After cooling, the temperatures to 25°C the isotactic parts mainly precipitate and stay soluble in the solution of p-xylene.

Synthesis of Polypropylene

Polymer is entirely built around the particles of heterogeneous catalysts within a gaseous phase along with the slurry reactors. Propene can be passed over a bed that contains solid catalysis at the time of gaseous polymerization. Then the resulting polymer can be easily separated like a powder and transformed into pellets.

Gas is not a reacting ingredient that is recycled and pumped back into the reactor. Liquid propane can be applied like a solvent in bulk polymerization for keeping its precipitating form. It mainly takes place at the temperature of 60 to 80°C and the pressure will be 30 to 40 atm.

Applications of Polypropylene

Several applications are seen of this material in different sectors for different purposes.

  • Different types of plastic products are made of this ingredient like flip-top water containers due to the feature of fatigue resistance.

  • Polypropylene is applied in the making of piping systems and it requires a higher purity along with strength and rigidity.

  • It is very used for different purposes, as it is corrosion resistant with chemical leaching. Besides this, it has a resistance power to different physical damage.

  • It is used in the making of plastic chairs and different types of medical or laboratory products.


Polypropylene is generally tough or versatile and it is helpful to compete with different materials like acrylonitrile butadiene styrene like engineering plastic. The increment in temperature also increased the strength of the polypropylene. Randomly polymerized ethylene monomers are mainly used as the homopolymer as the crystallinity of the reduced polymer. The melting point of this type of polymer generally becomes more transparent.


Q1. Why polypropylene is used in the food industry?

Ans. It has a higher resistance power to heat and that is why it is used in the food industry. It does not melt with a dishwasher, so it is effective for this industry.

Q2. What is the fatigue resistance of this chemical compound?

Ans. The fatigue resistance of this chemical compound is generally higher and the melting point is 171°C or 340°F. The melting point of isotactic PP for commercial purposes varies between 160 and 166°C.

Q3. What are the disadvantages of polypropylene?

Ans. The scratch-resistant power of polypropylene is low and it embrittles at -20°C. The actions with different metals mainly harm the stability of heat ageing and the dimensions of this material are changed.

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