Terminology

• Isotactic PP: commercial form, isotactic index 85 to 95 percent, crystallinity 30 to 60 percent
• PP-R: random copolymer with polyethylene for pipework
• Homopolymer / random copolymer / block copolymer: the three general types

History and demand

Invention

• 1951: Hogan and Banks at Phillips first polymerized propylene
• 1954: Natta and Rehn discovered isotactic stereoselective polymerization
• 1957: Montecatini began large-scale commercial production

Sourcing

• 2024 production: China about 18 million tons, the United States about 11 million, India about 7.2 million (IndexBox)
• China's capacity was about 45 million tons in 2022, 44 percent of 103.7 million tons of world capacity (Polymer Update)

Demand trend

• Second most widely produced commodity plastic after polyethylene

Properties

Physical

• Density: 0.895 to 0.93 g/cm3 (56 to 58 lb/ft3)
• Melting point: commercial isotactic 160 to 166°C (320 to 331°F); perfectly isotactic 171°C

Mechanical

• Young's modulus: 1,300 to 1,800 N/mm2 (190 to 260 ksi)
• Good fatigue resistance, used for living hinges

Thermal and moisture

• Thermal expansion significant, less than polyethylene
• Brittle below 0°C (32°F)

Fire behavior

• Flash point: 260°C (500°F); autoignition: 388°C (730°F)

Durability

• UV exposure causes cracks and crazing in external applications
• Chain degradation begins above 100°C (212°F)

Uses in buildings

Building elements

• Domestic Water Piping: potable plumbing, hydronic heating and cooling, reclaimed water
• Fibers in concrete reduce cracking and spalling; fibers mixed with soil in earthquake-prone areas
• Top waterproofing layer of some single-ply roofing membranes

Pros and cons

Pros

• Good fatigue resistance
• Thermal expansion lower than polyethylene

Cons

• Brittle below 0°C
• UV causes cracks and crazing outdoors

Sustainability

Recycled content and end of life

• Resin identification code 5; less than 1 percent of PP generated was recycled as of 2015

Manufacturing and cost

Main manufacturers and suppliers

Trade association: Plastics Pipe Institute.

Sources

• Wikipedia: Polypropylene, https://en.wikipedia.org/wiki/Polypropylene
• Wikimedia Commons: Polypropylene lid.JPG, photo by Mk2010 (CC BY-SA 3.0), https://commons.wikimedia.org/wiki/File:Polypropylene_lid.JPG
• IndexBox: polypropylene in primary forms, world market overview 2024, https://www.indexbox.io/blog/polypropylene-in-primary-forms-world-market-overview-2024-5/
• Polymer Update: polypropylene capacity, https://www.polymerupdate.com/Blogs/Details/1321276/All