Polypropylene- Plastjoo

Polypropylene is a tough and rigid, crystalline thermoplastic produced from propene (or propylene) monomer. It is a linear hydrocarbon resin. The chemical formula of polypropylene is (C3H6)n . PP is 100% recyclable


Molecular Structure of Polypropylene  

Molecular Structure of Polypropylene                  


Polypropylene was first polymerized by German chemist named Karl Rehn and an Italian chemist named Giulio Natta to a crystalline isotactic polymer in 1954. This discovery soon led to a large-scale production of polypropylene starting in 1957 by the Italian firm Montecatini


You might like to read: Low density polyethylene

These days, polypropylene is made from polymerization of propene monomer (an unsaturated organic compound - chemical formula C3H6) by

Ziegler-Natta polymerization, or-
Metallocene catalysis polymerization-


Structure of PP Monomer  Structure of Polypropylene�   
           Structure of Polypropylene                     Structure of PP Monomer           

Different Types of Polypropylene


Propylene Homopolymer is the most widely utilized general-purpose grade. It contains only propylene monomer in a semi-crystalline solid form. Upon polymerization, PP can form three basic chain structures depending on the position of the methyl groups:

Atactic (aPP) - Irregular methyl group (CH3) arrangement-
Isotactic (iPP) – Methyl groups (CH3) arranged on one side of the carbon chain-
Syndiotactic (sPP) - Alternating methyl group (CH3) arrangement-


Atactic -Isotactic -Syndiotactic   

Main applications include packaging, textiles, pipes, automotive and electrical applications          


You might like to read: High Density Polyethylene


Polypropylene copolymer family is further divided into random copolymers and block copolymers produced by polymerizing of propene and ethene

1.    Propylene Random Copolymer is produced by polymerizing together ethene and propene. It features Ethene units, usually up to 6% by mass, incorporated randomly in the polypropylene chains. These polymers are flexible and optically clear making them suitable of applications requiring transparency and for products requiring an excellent appearance

2.    Propylene Block Copolymer, ethene content is larger (between 5 and 15%). It has co-monomer units arranged in regular pattern (or blocks). These polymers are suitable for applications requiring high strength, such as industrial usages


Properties of Polypropylene

1.    Melting Point of Polypropylene - The melting point of polypropylene occurs at a range
Homopolymer: 160 - 165°C-
Copolymer: 135 - 159°C-

2.    Density of Polypropylene - PP is one of the lightest polymer among all commodity plastics. This feature which makes it suitable option for lightweight\weight saving applications
Homopolymer: : 0.904 – 0.908 g/cm3-
Random Copolymer: 0.904 – 0.908 g/cm3-


3.    Polypropylene Chemical Resistance
Excellent resistance to diluted and concentrated acids, alcohols-
Good resistance to aldehydes, esters, aliphatic hydrocarbons, ketones-
Limited resistance to aromatic and halogenated hydrocarbons and oxidizing agents-


4.    Flammability: Polypropylene is a high flammable material

5.    PP retains mechanical & electrical properties at elevated temperatures, in humid conditions and when submersed in water. It is a water-repellent plastic

6.    PP has good resistance to environmental stress cracking

7.    It is sensitive to microbial attacks (bacteria, mold…)

8.    It exhibits good resistance to steam sterilization


Disadvantages of Polypropylene
Poor resistance to UV, impact and scratches-
Embrittles below -20°C-
Low upper service temperature, 90-120°C-
Heat-aging stability is adversely affected by contact with metals-
Post molding dimensional changes due to crystallinity effects – this can be solved with nucleating agents-


You might like to read: Polyvinyl Chloride


Applications of Polypropylene 

1.    Packaging Applications: Good barrier properties, high strength, good surface finish and low cost make Polypropylene ideal for several packaging applications


2.    Consumer Goods: Polypropylene is used in several household products and consumer goods applications including translucent parts, housewares, furniture, luggage, toys etc


3.    Automotive Applications: Due to its low cost, outstanding mechanical properties and moldability, polypropylene is widely used in automotive parts. Main applications include battery cases and trays, bumpers, fender liners, interior trim, instrumental panels and door trims. Other key features of automotive applications of PP include low coefficient of linear thermal expansion and specific gravity, high chemical resistance and good weatherability, processability and impact/stiffness balance


4.    Fibers and Fabrics: A large volume of PP utilized in the market segment known as fibers and fabrics. PP rope and twine are very strong and moisture resistant very suitable for marine applications


5. Medical Applications: Polypropylene is used in various medical applications due to high chemical and bacterial resistance. Also, the medical grade PP exhibits good resistance to steam sterilization. Disposable syringes is the most common medical application of polypropylene. Other applications include Medical vials, diagnostic devices, petri dishes, intravenous bottles, specimen bottles, food trays, pans, pill containers, etc


6.    Industrial Applications: Polypropylene sheets are widely used in industrial sector to produce acid and chemical tanks, sheets, pipes, etc. because of its properties like high tensile strength, resistance to high temperatures and corrosion resistance


Compiler: Nasim Rashidi Nezhad

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