Polypropylene (PP)
The methyl group has to point the same way every time. Catalysts that get that right make a polymer that melts at 165 °C, floats on water and turns up in everything from bumper fascia to nappy topsheet.
Molecular Structure
What is Polypropylene (PP)?
Polypropylene's repeat unit carries a methyl group on every second backbone carbon, and the polymer only works if those methyls are arranged regularly. Isotactic polypropylene, with all methyls on the same side of the chain, crystallises into a helix and melts at 160 to 165 °C. Atactic polypropylene, with the methyls arranged randomly, is a soft tacky material of no structural value. The whole commercial history of PP is the history of catalysts that control that arrangement.
Modern plants use high-activity Ziegler-Natta catalysts with external electron donors, or metallocenes, in bulk loop, gas phase or hybrid processes. Isotactic index above 95% is routine, and the residual atactic fraction is measured as xylene solubles.
Three families cover almost all demand. Homopolymer is the stiffest and clearest but turns brittle near 0 °C. Random copolymer, with a few percent of ethylene distributed along the chain, lowers the melting point and improves clarity and impact. Impact or block copolymer disperses a rubber phase through the matrix and stays tough well below freezing, which is what automotive and appliance applications require.
Polypropylene degrades by chain scission where polyethylene crosslinks. The tertiary hydrogen on every second carbon is easy to abstract, so oxidation cuts chains rather than joining them — melt index rises through the extruder, and unstabilised PP loses properties in sunlight within weeks. Antioxidant and UV packages are not optional extras on this polymer.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
A polyethylene-like backbone with a methyl group on every second carbon. In the commercial isotactic form those methyls all point the same way, which lets the chain coil into a regular helix and crystallise — the difference between a structural polymer and a sticky by-product.
Chain architecture — isotactic, methyl on every second carbon
Structural Identity
- PolymerPolypropylene, isotactic
- Repeat unit(C₃H₆)ₙ — propylene
- Repeat unit mass42.08 g/mol
- TacticityIsotactic — methyls on one side
- Crystal form3₁ helix, α-monoclinic
- Made byZiegler-Natta with donors, or metallocene
- ProcessesBulk loop, gas phase, hybrid
- Atactic fractionMeasured as xylene solubles
- Degradation modeChain scission — melt index rises
- CAS Number9003-07-0
- Specified byMFR, family, modulus, impact
Product Specifications
Chelora supplies Polypropylene (PP) in standard and custom grades. Contact us for specification sheets tailored to your process.
| Polymer | Polypropylene |
|---|---|
| CAS Number | 9003-07-0 |
| Repeat unit | (C₃H₆)ₙ |
| Families | Homopolymer, random copolymer, impact copolymer |
| Density | 0.895 – 0.920 g/cm³ (ISO 1183) |
| Melt flow rate | 0.3 – 100 g/10 min at 230 °C / 2.16 kg (ISO 1133) |
| Melting point (DSC) | 160 – 165 °C homopolymer; 140 – 155 °C random |
| Flexural modulus | 1100 – 1700 MPa homopolymer; 700 – 1300 MPa impact |
| Tensile strength at yield | 25 – 38 MPa |
| Notched Izod at 23 °C | 2 – 8 kJ/m² homopolymer; 15 – 60 kJ/m² impact |
| Heat deflection temperature | 95 – 110 °C at 0.45 MPa |
| Xylene solubles (max) | ≤ 4.0 wt% homopolymer |
| Ash (max) | ≤ 0.03 wt% |
| Volatiles (max) | ≤ 0.10 wt% |
| Additive package | Antioxidant and acid scavenger; nucleator, clarifier, UV to order |
| Food contact | FDA 21 CFR and EU 10/2011 declarations available |
| Packaging | 25 kg bags, 500 – 1250 kg jumbo bags, bulk |
| Transport classification | Not regulated as dangerous goods |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Polypropylene (PP).
BOPP & CPP Film
Biaxially oriented film for snack packaging, labels, tape and lamination, plus cast film for retort pouches and textile overwrap. High clarity, good barrier and excellent printability.
Fibre & Nonwoven
Spunbond and meltblown nonwovens for nappy and hygiene topsheet, medical gowns and filtration, plus staple fibre for carpet and geotextile. PP dominates hygiene nonwovens.
Automotive Compounds
Talc- and glass-filled impact copolymer for bumper fascia, instrument panels, door trim, battery cases and under-bonnet parts — the highest-volume plastic in a modern car.
Injection Moulding
Housewares, crates, thin-wall food containers, caps and closures, furniture and appliance parts, where the balance of stiffness, gloss and cycle time is hard to beat at the price.
Raffia & Woven Sacks
Slit-film tape for woven sacks, FIBC bulk bags, ropes and tarpaulin — high tenacity from orientation and effectively no moisture uptake.
PP-R Pipe & Medical
Random copolymer pipe for hot and cold water plumbing and radiator systems, and autoclavable medical devices, syringes and labware where steam sterilisation is required.
Why source Polypropylene (PP) through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market or off-spec prime passed as prime.
Grade Flexibility
Homopolymer, random and impact copolymer supplied across film, fibre, moulding and pipe grades. We match on family, melt flow rate and the mechanical target, not on MFR alone.
Full Documentation
Technical data sheet, CoA against the grade specification, SDS, REACH compliance, food-contact declarations, and medical or potable water documentation where the grade supports it.
Logistics Support
Experienced in polymer resin logistics — 25 kg bags, jumbo bags, containerised and bulk silo delivery, with pellet-loss controls in line with Operation Clean Sweep, for Indian and international delivery.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Store pellets dry, indoors and strictly out of direct sunlight. Polypropylene is markedly more UV-sensitive than polyethylene, and prolonged light exposure degrades the resin and consumes the stabiliser package before processing.
- Rotate stock and record production dates. Antioxidant depletion in storage is invisible on inspection and shows up as a melt flow rate shift at the extruder.
- Contain pellets rigorously. Spilled pellets reach watercourses through drains and are a recognised marine litter source — catch trays, drain screens and Operation Clean Sweep procedures at every transfer point.
- Control processing temperature carefully. Polypropylene degrades by chain scission, so excess heat or residence time raises melt flow rate and quietly changes the material you are moulding.
- Avoid copper and copper alloys in contact with hot polypropylene. Copper catalyses oxidative degradation, and metal-deactivator additives exist specifically for wire-coating applications because of it.
- Ground and bond pneumatic conveying, and control fines. Pellet fines cause gels and die build-up and present a dust explosion risk in silos and dust collectors.
- Extract at the die and hopper. Degrading polypropylene releases aldehydes, ketones and organic acids, all respiratory irritants, and the odour threshold is low enough to be a housekeeping signal.
- Treat molten polymer as a serious thermal burn hazard — it adheres to skin and retains heat, so die changes and purging need forearm and face protection.
- Segregate families and grades. Homopolymer, random and impact copolymer are visually identical as pellets and produce very different parts.
Hazard Summary
Classification: polypropylene in pellet form is not classified as hazardous under CLP. It is chemically inert, non-toxic and widely used in food contact and medical applications. The hazards are physical and process-related.
Thermal burns: molten polypropylene at 200–280 °C adheres to skin and continues transferring heat. Purging and die work are where these injuries occur; protection must cover forearms and face.
Processing fume: polypropylene oxidises more readily than polyethylene because of its tertiary hydrogens, releasing aldehydes, ketones and organic acids on degradation. These are respiratory irritants, and the characteristic sharp odour is a reliable indication that the melt is too hot or residence time too long.
Degradation raises melt flow rate: unlike polyethylene, which tends to crosslink, polypropylene breaks chains when it degrades. Regrind, excessive drying, hot spots and long residence time all raise the melt flow rate, and the resulting part is weaker without looking any different. This is the most common quiet quality failure in PP processing.
UV sensitivity: unstabilised polypropylene loses mechanical properties in sunlight within weeks. Anything for outdoor service needs a specified UV package, and storage in daylight is not neutral.
Dust and fines: pellet fines are combustible and can form explosible clouds in silos, conveying and dust collection. Grounding, bonding and accumulation control apply as for any organic solid.
Pellet loss and slips: polypropylene pellets persist in the marine environment and are an identified microplastic source, and loose pellets on hard flooring cause falls. Both are controlled by the same containment discipline.
PPE minimum: safety glasses and gloves for pellet handling; heat-resistant gloves, arm protection and face shield for work at the die or on molten material.
Consult the full SDS and the grade technical data sheet for processing temperature limits, and confirm food-contact or medical status for your specific application before use.
Frequently Asked Questions
Technical and commercial questions about Polypropylene (PP) sourcing and specifications.
What is polypropylene used for?
It has the widest application spread of any commodity polymer. Film — BOPP for snack packaging and labels, CPP for retort pouches. Fibre and nonwoven, where PP dominates hygiene topsheet, medical gowns and filtration media. Automotive, where filled impact copolymer is the highest-volume plastic in a modern car. Injection moulding for housewares, crates, thin-wall food packaging and closures. Raffia tape for woven sacks and bulk bags. And PP-R pipe for hot and cold water plumbing.
What is the difference between homopolymer, random copolymer and impact copolymer?
Homopolymer is propylene alone — the stiffest and highest melting, with the best clarity when nucleated, but brittle as it approaches 0 °C. Random copolymer distributes a few percent of ethylene along the chain, which disrupts crystallinity, lowers the melting point to 140–155 °C, improves clarity and gives better impact at ambient — it is what clear thin-wall containers and PP-R pipe use. Impact or block copolymer is different in kind: a separate ethylene-propylene rubber phase is dispersed through the matrix, which sacrifices stiffness and clarity but keeps the material tough well below freezing. Automotive and appliance parts are almost always impact copolymer for that reason.
What does xylene solubles measure?
The fraction of the polymer that is not properly isotactic. Regular isotactic chains crystallise and are insoluble in xylene at controlled temperature; atactic and low-tacticity material stays in solution. So the xylene solubles figure is a direct measure of how much of the batch failed to build a regular chain. For homopolymer it is typically held below 4%. High xylene solubles means a sticky, low-modulus fraction that migrates to the surface, causing blocking in film, plate-out on moulds and reduced stiffness. For random and impact copolymers the figure is naturally much higher and has to be read against the grade rather than as an absolute.
Why is PP melt flow measured at 230 °C when polyethylene is at 190 °C?
Because polypropylene melts around 165 °C, well above polyethylene's 130 °C or so, and a test at 190 °C would sit too close to the melting point to give a reliable flow reading. The standard therefore specifies 230 °C and a 2.16 kg load for polypropylene. The practical consequence is that a melt flow number from a PP data sheet cannot be compared directly with one from a PE data sheet — different temperature, different material, no meaningful ratio between them. Always quote the test condition with the number.
Why does polypropylene need more stabilisation than polyethylene?
Because of the methyl group. Every second backbone carbon in PP carries a tertiary hydrogen, which is far easier to abstract than the secondary hydrogens along a polyethylene chain. Once abstracted, the resulting radical breaks the backbone rather than crosslinking it, so oxidation cuts molecular weight — melt flow rate rises and mechanical properties fall. That is why PP always ships with an antioxidant and acid scavenger package, why outdoor grades need specific UV stabilisation, and why copper contact is avoided in hot service. Polyethylene under the same insult tends to crosslink instead, which is far more forgiving.
What documentation does Chelora provide?
Every shipment includes the grade technical data sheet, a Certificate of Analysis against the grade specification covering melt flow rate, density, xylene solubles, ash and volatiles; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; food-contact declarations under FDA 21 CFR and EU Regulation 10/2011 where applicable; medical or potable water documentation for grades that support it; an origin certificate; and destination-market certificates where required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Polypropylene (PP) grade, volume, logistics, documentation, and lead times. We respond within one business day.
