What Is Polypropylene?
Polypropylene (PP) is a semi-crystalline thermoplastic polyolefin. A methyl group on every other carbon gives it greater stiffness, higher service temperature, and better resistance to organic solvents compared to HDPE.
Stiffer, stronger, higher service temperature. Standard for chemical tanks, duct systems, and structural fabricated components.
More impact-resistant, especially at lower temperatures. Used for outdoor enclosures and equipment experiencing mechanical shock.
Key Properties
Chemical resistance: Resistant to most organic solvents, oxidizing acids, polar chemicals, strong acids, bleaches, and laboratory chemicals.
Weldability: Welds readily with hot gas and extrusion welding — creating strong, chemically homogeneous joints. The standard material for fabricated chemical tanks and duct systems.
Low density: ~0.90 g/cm³ — it floats in water. Significantly lighter than PVC, HDPE, or metal.
Moisture resistance: Absorbs essentially no moisture. Maintains dimensional stability in wet environments.
Service temperature: Homopolymer PP at ~200°F (93°C) — higher than standard PVC (140°F), comparable to CPVC.
Two limitations: high thermal expansion requiring design allowances for temperature cycling, and poor resistance to chlorinated solvents and aromatic hydrocarbons. Always confirm chemical compatibility for the specific environment.
PP vs HDPE for Corrosive Environments
PP offers superior resistance to oxidizing acids (nitric, chromic), bleaches, and polar organic solvents that attack HDPE. HDPE offers better resistance to aliphatic hydrocarbons and performs better at low temperatures.
For most strong acid environments — sulfuric acid tanks, acid scrubbers, plating equipment, laboratory fume hoods — polypropylene is preferred. For hydrocarbon storage, food contact, or outdoor UV-exposed components, HDPE is often more appropriate.
Applications
Frequently Asked Questions
What is the difference between homopolymer and copolymer PP?
Homopolymer is stiffer with higher service temperature — standard for tanks and ducts. Copolymer is more impact-resistant at lower temperatures — correct for mechanical shock or cold conditions.
How does PP compare to PVC for chemical tanks?
PP offers broader acid resistance and higher service temperature (200°F vs 140°F). PVC is less expensive and easier to fabricate. For hot chemical processes, PP is required. For ambient-temperature applications, PVC may suffice.
Can polypropylene be welded?
Yes — reliably using hot gas and extrusion welding with compatible PP welding rod. Plastic-Craft offers in-house plastic welding.
Is PP UV-resistant?
Standard PP has limited UV resistance. UV-stabilized grades are available. For outdoor structural use, black HDPE with carbon black is often more practical.
Where can I buy polypropylene?
Plastic-Craft Products stocks PP in homopolymer and copolymer grades at West Nyack, NY. No minimum orders. Call (845) 358-3010 or email [email protected].
Ready to Order Polypropylene?
Plastic-Craft stocks homopolymer and copolymer PP — cut to exact dimensions or fabricated to print with no minimum orders. In-house plastic welding and CNC fabrication.
(845) 358-3010