Low Density Polyethylene (LDPE)
Made at three thousand bar by letting ethylene radicals do whatever they like. The tangled, long-chain-branched result has melt strength nothing else can match, which is why it still owns extrusion coating and blown film bubbles.
Molecular Structure
What is Low Density Polyethylene (LDPE)?
LDPE is polyethylene, but the description that matters is architectural rather than chemical. It is made by free radical polymerisation of ethylene at 1,000 to 3,000 bar and 150 to 300 °C, in autoclave or tubular reactors with peroxide or oxygen initiation. Under those conditions the growing radical chain does not simply add monomer in a line — it abstracts hydrogens from other chains and from itself, producing long branches off the main backbone and short butyl and ethyl branches from backbiting.
That branching is the whole product. Long branches prevent the chains from packing into crystals, which is why the density sits at 0.910 to 0.925 g/cm³ and the resin is soft, clear and flexible. More importantly they entangle, which gives LDPE melt strength and strain hardening in extension — the properties that hold a blown film bubble stable and let molten polymer be drawn onto moving paper at high speed without tearing.
Nothing about LDPE is defined by its CAS number, which covers polyethylene generically. A grade is specified by melt flow index, density and additive package, and two resins sharing all three can still behave differently depending on whether they came from an autoclave or a tubular reactor.
LDPE and LLDPE share CAS 9002-88-4, because polymer CAS numbers identify a class rather than a substance. The two resins are made by entirely different processes and behave differently in every converting operation. Specify by melt flow index, density, reactor type and additive package — the CAS tells a supplier almost nothing about what you need.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
The repeat unit is ethylene and nothing else — but the chains carry long branches produced by intermolecular chain transfer, and shorter branches from backbiting within the same chain. That irregular, tree-like architecture is what separates LDPE from every other polyethylene.
Chain architecture — long branches, themselves branched
Structural Identity
- PolymerPolyethylene, high-pressure process
- Repeat unit(C₂H₄)ₙ — ethylene
- Repeat unit mass28.05 g/mol
- ArchitectureLong-chain branched, irregular
- Short branchesButyl and ethyl, from backbiting
- Made byFree radical, 1,000 – 3,000 bar
- Reactor typesAutoclave and tubular
- InitiatorOrganic peroxide or oxygen
- Defining propertyHigh melt strength, strain hardening
- CAS Number9002-88-4 — generic to polyethylene
- Specified byMFI, density, additive package
Product Specifications
Chelora supplies Low Density Polyethylene (LDPE) in standard and custom grades. Contact us for specification sheets tailored to your process.
| Polymer | Low density polyethylene |
|---|---|
| CAS Number | 9002-88-4 (generic) |
| Repeat unit | (C₂H₄)ₙ |
| Repeat unit mass | 28.05 g/mol |
| Density | 0.910 – 0.925 g/cm³ (ISO 1183) |
| Melt flow index | 0.2 – 70 g/10 min at 190 °C / 2.16 kg (ISO 1133) |
| Melting range (DSC) | 105 – 115 °C |
| Vicat softening point | 85 – 95 °C |
| Tensile strength at yield | 8 – 12 MPa |
| Elongation at break | 200 – 600% |
| Dart drop impact (film) | Grade dependent — specify with film gauge |
| Volatiles (max) | ≤ 0.10 wt% |
| Ash (max) | ≤ 0.02 wt% |
| Gel count | Grade dependent — specify for optical film |
| Additive package | Antioxidant; slip, antiblock and processing aid to order |
| Food contact | FDA 21 CFR and EU 10/2011 declarations available |
| Bulk density (pellets) | ≈ 550 – 600 kg/m³ |
| 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 Low Density Polyethylene (LDPE).
Blown & Cast Film
The largest outlet. High melt strength gives a stable bubble at high blow-up ratios, and the clarity and softness suit bread bags, produce bags, liners, laundry and general packaging film.
Extrusion Coating
The dominant resin for coating paper, board and foil. Nothing else draws down as thin at line speed without edge tear, which is a direct consequence of long-chain branching.
Agricultural Film
Greenhouse covering, mulch film and silage wrap, where flexibility at low temperature, UV-stabilised durability and puncture tolerance matter more than raw tensile strength.
Wire & Cable
Insulation and jacketing, including crosslinkable grades for medium and high voltage cable, where LDPE's dielectric properties are excellent and consistent.
Injection & Blow Moulding
Closures, squeeze bottles, lids and flexible mouldings where softness and stress crack resistance are wanted rather than rigidity.
Foam & Shrink Film
Crosslinked and non-crosslinked LDPE foam for protective packaging and insulation, and collation shrink film where high shrink force and bubble stability are required.
Why source Low Density Polyethylene (LDPE) 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
Film, extrusion coating, cable and moulding grades supplied. We match on melt flow index, density, reactor type and additive package, because a CAS number and a density figure do not describe a polyethylene grade.
Full Documentation
Technical data sheet, CoA against the grade specification, SDS, REACH compliance, and food-contact declarations under FDA 21 CFR and EU 10/2011 with every shipment.
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 out of direct sunlight. LDPE does not absorb much moisture, but surface condensation on cold pellets causes bubbles and haze in film and coating.
- Keep bags off the ground and away from external walls, and rotate stock. Prolonged UV exposure degrades the resin and consumes the antioxidant package before the material reaches the extruder.
- Contain pellets rigorously. Spilled pellets travel through drains into watercourses and are a recognised marine litter source — Operation Clean Sweep procedures, catch trays and drain screens should be standard at every transfer point.
- Treat spilled pellets on the floor as a slip hazard, and clear them immediately rather than at shift end.
- Ground and bond pneumatic conveying. Pellet transfer generates significant static, and pellet fines and dust are combustible.
- Control fines and dust generation with low-velocity conveying and correctly specified bends — fines cause gels, die build-up and dust explosion risk in equal measure.
- Extract at the die and hopper. Thermal degradation of polyethylene above about 300 °C generates aldehydes including acrolein, plus organic acids, all of which are respiratory irritants.
- Treat molten polymer as a serious thermal burn hazard. It sticks to skin, retains heat and cannot be brushed off — die changes and purging need face and arm protection.
- Segregate grades and colours. Cross-contamination between film and coating grades, or between natural and masterbatched material, is a common and avoidable cause of rejected production.
Hazard Summary
Classification: LDPE in pellet form is not classified as hazardous under CLP. It is chemically inert, non-toxic and used throughout food packaging. The hazards that matter are physical and process-related rather than toxicological.
Thermal burns: molten polyethylene at 180–320 °C adheres to skin and continues to transfer heat after contact. Burns from purging, die changes and screw pulls are the most common serious injury in polyolefin processing, and protection has to cover the forearms and face, not just the hands.
Processing fume: polyethylene degrading above roughly 300 °C releases aldehydes — including acrolein — organic acids and hydrocarbon fragments. These are respiratory irritants, and the risk rises sharply with melt temperature and residence time. Local extraction at the die and hopper is the appropriate control.
Dust and fines: pellet fines are combustible and can form explosible dust clouds in silos, conveying systems and dust collectors. Grounding, bonding and accumulation control apply as they would for any organic solid.
Pellet loss to the environment: polyethylene pellets are persistent in the marine environment and are a significant identified source of microplastic pollution. Containment at every transfer point, drain screening and spill recovery procedures are the expected standard, and customers increasingly audit against them.
Slip hazard: loose pellets on a hard floor behave like ball bearings and cause falls. This sounds trivial and is a frequent cause of lost-time injury in resin handling areas.
Fire: polyethylene burns readily once ignited, with a high heat release, producing dense black smoke and carbon monoxide. Bulk pellet storage fires are difficult to extinguish and should be designed against.
PPE minimum: safety glasses and gloves for pellet handling; heat-resistant gloves, arm protection and face shield for any 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 status for your specific application before use.
Frequently Asked Questions
Technical and commercial questions about Low Density Polyethylene (LDPE) sourcing and specifications.
What is LDPE used for?
Film is the largest outlet by far — blown and cast film for bread and produce bags, liners, laundry film and general packaging, plus collation shrink film. Extrusion coating of paper, board and foil is the second, and it is a segment LDPE effectively owns. Beyond that, LDPE goes into agricultural film for greenhouses and mulching, wire and cable insulation including crosslinkable grades, closures and squeeze bottles, and protective foam.
What is the difference between LDPE and LLDPE?
The process, and therefore the chain architecture. LDPE is made by free radical polymerisation at very high pressure, which produces long branches off the backbone and an irregular, tree-like molecule. LLDPE is made at low pressure over a Ziegler-Natta or metallocene catalyst by copolymerising ethylene with an alpha-olefin, giving a straight backbone with short branches of uniform length and no long-chain branching. The practical result is that LDPE has far better melt strength and processes more easily, while LLDPE has better tensile strength, puncture and tear resistance and can be run at thinner gauges. They are frequently blended to get both.
Why does LDPE dominate extrusion coating?
Because of strain hardening in the melt. In extrusion coating a molten curtain of polymer is drawn down from a die onto substrate moving at high speed, and the film has to thin uniformly without tearing or drawing in at the edges. Long-chain branches entangle, so as LDPE is stretched the extensional viscosity rises and thin spots resist further thinning — the melt effectively self-corrects. Linear polymers have no such mechanism, so they neck in and tear at the line speeds coating economics require. This is one of the clearest cases in polymer processing where architecture, not composition, determines the application.
Why do LDPE and LLDPE share a CAS number?
Because polymer CAS numbers identify a class of substance, not a discrete molecule. CAS 9002-88-4 covers polyethylene generically — it says the material is made of ethylene repeat units and nothing more. Density, branching, molecular weight distribution and comonomer content are all specification properties rather than identity properties, so LDPE, LLDPE, HDPE and their many grades all fall under the same number. For regulatory paperwork the CAS is what gets quoted; for actually buying the right resin it is close to useless, which is why enquiries need to specify melt flow index, density, reactor type, additive package and intended process.
How should I specify an LDPE grade?
Start with melt flow index and density, since those two set the broad processing and property envelope — lower MFI for melt strength and toughness in film, higher MFI for injection moulding and coating. Then state the process, because autoclave and tubular reactor grades at the same MFI and density have different molecular weight distributions and behave differently in extensional flow. Then the additive package: antioxidant level, and whether you need slip, antiblock, processing aid or UV stabilisation, since ordering natural resin and adding these later is not always equivalent. Finally, state any food contact, optical or gel-count requirement, as those narrow the field considerably.
What documentation does Chelora provide?
Every shipment includes the grade technical data sheet, a Certificate of Analysis against the grade specification covering melt flow index, density, volatiles and ash; a Safety Data Sheet to GHS and REACH format; REACH polymer compliance confirmation; food-contact declarations under FDA 21 CFR 177.1520 and EU Regulation 10/2011 where applicable; confirmation that the material is not regulated as dangerous goods; an origin certificate; and destination-market certificates where required.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Low Density Polyethylene (LDPE) grade, volume, logistics, documentation, and lead times. We respond within one business day.
