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LDPE

Polietileno de Baja Densidad

LDPE·Polyethylenes·Semi-crystalline

LDPE (Low-Density Polyethylene) is the most widely used flexible plastic in the world: bags, films, soft caps, squeeze bottles, six-pack rings, bath toys and anything that needs to be "squeezed" without losing shape. What distinguishes it from HDPE is not chemistry — both are pure polyethylene — but molecular architecture: long chains with many short and long branches that prevent dense crystalline packing.

Result: lower density (0.91–0.94), lower stiffness, higher flexibility, more translucent, better blown-film processing, food-grade certified and BPA-free from its basic chemistry. But also: very high shrinkage (1.5–5%), prone to warping in flat parts, low service temperature (~80°C) and less chemical resistance than HDPE. Here we have compiled the reference ranges from the PDS, plus the questions that come up over and over on the shop floor: how to control warping, when LDPE vs LLDPE vs HDPE makes sense for injection, why it almost never needs drying, food-grade #4 and real recyclability.

Share your experience in the comments — ranges vary by manufacturer and MFI, and collective discussion is what gets us out of trouble on the floor.

The ranges shown in these data tables were compiled by the MVPS team from various parameter sheets and literature, integrating the lower and upper limits for each material type.

This information must be carefully reviewed when developing injection molding processes. Final ranges and processing tolerances are the responsibility of the engineer in charge.

These ranges are not recommended for developing specific process tolerances. MVPS always recommends requesting and consulting the supplier's data sheet.

General Properties

Chemical StructureSemi-crystalline
Specific Gravity (Density)0.94:1
L/D Ratio18 – 24
Compression Ratio3 – 4
Tonnage Factor3.09 – 4.63kN/cm²
Thermal Diffusivity0.2479mm²/s
Max Shear Rate40,0001/s
Shrinkage2 – 5%
Regrind50%
Heat Deflection (HDT) @ 1.82 MPa80°C
Glass Transition (Tg) @ 10°C/min-101°C
Vicat Softening @ 50N52°C

Drying

Drying Temperature60 – 71°C
Drying Time1 – 2h
Recommended Moisture0.5%
Recommended Dryer TypeAir
Dew Point-40°C

Temperatures

Melt179 – 191°C
Nozzle179 – 191°C
Front171 – 188°C
Middle166 – 182°C
Rear160 – 177°C
Demolding38 – 82°C
Mold (Cooling)21 – 71°C
Feed Throat10 – 49°C

Processing

Back Pressure4.8 – 14.8bar
Screw Speed40 – 80RPM
Injection SpeedMedium – High
Barrel Occupancy25 – 75%
Injection Pressure500 – 1,500Pbar
Holding Pressure125 – 1,200Pbar
Cushion6.4 – 12.7mm

Mold

Runner Diameter4.57 – 9.14mm
Gate Diameter1.02 – 2.03mm
Gate Area0.81 – 3.24mm²
Wall Thickness0.76 – 3.81mm

Venting

Depth (Vent Depth)0.0102 – 0.0203mm
Land (Vent Land)0.508 – 1.02mm
Width (Vent / Clearance)3.05 – 7.62mm
Relief (Relief Channel)0.127 – 0.2032mm

Frequently asked questions

LDPE is a semi-crystalline thermoplastic (40–55% crystallinity, low vs 60–80% for HDPE) in the polyolefin family, synthesized by polymerizing ethylene at high pressure (1000–3000 bar, 150–300°C) with radical initiators. That high pressure generates short and long branches that give the polymer its unique personality: flexible, translucent, low density (0.91–0.94 g/cm³). Invented in 1933 by ICI — it was the world's first commercial polyethylene.
LDPE: highly branched chains (free radicals at high pressure), low crystallinity, flexible, translucent. Ideal for films, bags, squeeze bottles, soft caps. HDPE: linear chains (Ziegler-Natta catalysis), high crystallinity, rigid, opaque. Ideal for bottles, pipes, crates. LLDPE: linear chains with controlled short branches (metallocene catalysis). Combines HDPE's toughness with LDPE's flexibility and processability — dominant in stretch films and premium bags. Rule of thumb: flexibility + soft touch → LDPE, rigidity + barrier → HDPE, high-strength films → LLDPE.
Yes to both. LDPE is food-grade approved by FDA (21 CFR 177.1520) and EFSA, and contains no BPA or phthalates (synthesized only from ethylene). It is one of the safest and cheapest plastics for food packaging — used in bread bags, sachet milk bags, plastic wrap films, soft coffee lids, six-pack rings and mustard/ketchup squeeze bottles. Post-consumer recycled for food contact: the FDA accepts PCR LDPE since 2025 under an approved process.
LDPE is practically non-hygroscopic (<0.01% at equilibrium with ambient air), well below the critical threshold. That's why the PDS marks 'Air' or no drying. Exception: filled grades (talc, concentrated color masterbatch, anti-fog additives) may need light drying at 60–70°C for 1–2 h. If you see silver streaks in transparent LDPE parts, suspect the masterbatch before the base material.
Very high and variable shrinkage: 1.5–5% (similar to HDPE but wider range). LDPE shrinks more in flow direction than perpendicular → severe warping tendency in large flat parts (lids, trays). Solutions: (1) uniform wall with variations <15%, (2) mold at 30–45°C for controlled cooling, (3) generous cooling time because LDPE crystallizes slower than HDPE, (4) multiple balanced gates for symmetric radial flow, (5) consider LDPE-EVA copolymer for more flexibility and less warping in thin parts.
LDPE wins on: superior clarity (more translucent), gloss, soft touch, fine blown-film processability, cost (~10% cheaper). LLDPE wins on: toughness and impact (especially at low temperature), puncture resistance, better dimensional stability. Rule of thumb: for squeeze bottles, decorative kitchen films, soft toys → LDPE. For stretch wrap, heavy industrial bags, agricultural films → LLDPE. In injection, LDPE dominates soft caps; LLDPE is rarely used pure in injection (blended with LDPE yes).
LDPE wins on: flexibility and soft touch (PP is more rigid), clarity in thin parts, lower processing temperature (160–230°C vs 200–280°C for PP) = lower energy consumption. PP wins on: service temperature (~120°C vs 80°C for LDPE), stiffness, gloss, chemical resistance, living hinges (LDPE doesn't survive repeated hinge bending). Rule of thumb: soft caps that deform when squeezed → LDPE. Hard screw or flip-top caps → PP. Squeeze bottles → LDPE almost always. Rigid containers → PP.
The PDS marks 21–60°C — cold compared to almost any other plastic. Hotter (45–60°C) = better gloss and less residual stress, but much longer cycle (LDPE crystallizes slowly). Cooler (25–35°C) = short cycle, ideal for large commodity production runs (bags/films by extrusion, not injection). For injection of caps and squeeze bottles: 30–45°C ideal balance. Below 20°C: risk of mold condensation + frozen stress.
Yes, international recycling code #4. But there's a catch: although technically recyclable, LDPE bags and films jam municipal recycling center machines (they tangle in belts and rollers). That's why many municipalities don't accept LDPE films in curbside recycling — they must go to special collection points (typically supermarkets that take bags). Rigid LDPE (caps, squeeze bottles) is generally accepted curbside. The PDS marks up to 50% regrind without significant property loss.
Without protection, no. Pure LDPE becomes brittle and cracks under UV in 6–12 months outdoors. Standard solution: LDPE with carbon black (2–3% carbon black) — extends service life to 10+ years, ideal for black irrigation pipes, geomembranes, industrial bags. For outdoor uses requiring color: grades with HALS + UV stabilizers (5–7 years typical service life). For agricultural film: specific grades with anti-UV + anti-fogging + IR-blocking depending on application (greenhouse, mulch, cover).

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