Lldpe Vs Ldpe Vs Hdpe In Product Design A Property Selection Table
LLDPE vs LDPE vs HDPE in Product Design: A Property-Selection Table
Linear low-density polyethylene is a copolymer of ethylene and one or more α-olefins—typically 1-butene, 1-hexene, or 1-octene—produced in low-pressure gas-phase, solution, or slurry polymerisation. Short-chain branches disrupt crystallinity, giving a density range commonly controlled between 0.915 g/cm³ and 0.940 g/cm³ when measured under ASTM D1505-18. In product design, LLDPE is positioned between high-pressure low-density polyethylene, which contains both short-chain and long-chain branches, and high-density polyethylene, which has low comonomer content and a density range of 0.941 g/cm³ to 0.967 g/cm³. The selection framework “LLDPE vs LDPE vs HDPE in Product Design: A Property-Selection Table” converts resin architecture into end-use decisions across blown film, rotomolding, injection molding, and geomembrane applications. Early-stage screening should begin with the comparison matrix, then validate lot-specific data against the applicable ASTM or ISO clauses.
What Molecular Architecture Differences Control the Selection Table?
Branching architecture is the primary independent variable. LDPE produced in high-pressure autoclave or tubular reactors contains long-chain branches above the entanglement threshold, which imparts strain-hardening and high melt tension but limits crystallinity. LLDPE manufactured with Ziegler-Natta or metallocene catalysts contains only short-chain branches; the absence of long-chain branching reduces shear-thinning and raises viscosity at high shear rates compared with LDPE of similar melt index. HDPE is essentially linear with minimal comonomer, producing high crystallinity and high modulus. Melt index measured under ASTM D1238-20 at 190 °C and 2.16 kg does not capture this difference fully; processors commonly evaluate I10/I2 or capillary viscosity for LLDPE because its high-shear viscosity can raise backpressure in extruders designed for LDPE. ISO 1133-1:2022 is the corresponding melt mass-flow rate standard for international procurement. The property-selection table below uses data routinely published in resin technical bulletins and standard specification appendices.
| Property and test method | LDPE | LLDPE | HDPE | Product design consequence |
|---|---|---|---|---|
| Density, ASTM D1505-18 | 0.910–0.935 g/cm³ | 0.910–0.940 g/cm³ | 0.941–0.967 g/cm³ | Sets crystallinity, stiffness, permeability, and softening temperature limits |
| Melt index, ASTM D1238-20 (190 °C/2.16 kg) | 0.2–70 g/10 min | 0.5–50 g/10 min | 0.03–30 g/10 min | Controls flow length, extrusion rate, and thin-wall fill in injection molds |
| Tensile yield strength, ASTM D638-14 | 7–14 MPa | 10–20 MPa | 20–35 MPa | Indicates short-term load-bearing limit before permanent deformation |
| Ultimate tensile strength, ASTM D638-14 | 8–20 MPa | 20–35 MPa | 22–45 MPa | Sets break resistance in uniaxial tension; LLDPE exceeds LDPE while retaining ductility |
| Elongation at break, ASTM D638-14 | 300–700% | 600–1000% | 100–1000% | High LLDPE elongation supports stretch film and impact deformation |
| Secant modulus at 1% strain, ASTM D790-17 | 100–300 MPa | 200–500 MPa | 700–1400 MPa | Determines stiffness, stacking strength, and creep under static load |
| Vicat softening point, ASTM D1525-17e1 | 80–95 °C | 90–110 °C | 120–130 °C | Limits hot-fill and continuous service temperature |
| Environmental stress crack resistance, ASTM D1693-15e1, Condition B (100% Igepal CO-630, 50 °C) | <24 h commonly | >1000 h common for octene grades | widely variable; 1 h to >1000 h | Critical for detergent bottles, geomembranes, and chemical storage |
The comparison demonstrates that product design choices are not monotonic with density. LLDPE at 0.918 g/cm³ can exceed 1000 h in ASTM D1693-15e1 exposure but provides only 200–500 MPa secant modulus, whereas HDPE at 0.954 g/cm³ may reach 1000 MPa but can fail environmental stress crack testing in 10–100 h when comonomer content is low. Subsequent sections move from film properties to structural and containment applications where these trade-offs appear.
Blown film conversion of 1.0 g/10 min hexene-LLDPE on a 63.5 mm single-screw extruder with L/D 30:1 and a 200 mm spiral mandrel die typically requires a melt temperature of 190–240 °C and a die gap of 1.5–2.0 mm. Because LLDPE has lower shear-thinning than LDPE, motor load and barrel pressure can be 15–30% higher at the same screw speed when switching from a fractional-melt LDPE of equivalent density. Many film lines add 20–30 wt% LDPE to LLDPE to restore bubble stability and improve melt tension. The blend, however, reduces dart impact and tear resistance in proportion to the LDPE fraction. For a 25 µm monolayer film, LLDPE-rich blends often show higher puncture resistance than LDPE; exact values depend on frost-line height, die gap, and gauge uniformity.
Puncture, Tear, and Seal Initiation Data for Film Structures
Dart impact testing under ASTM D1709-15a for 25 µm blown film differentiates LLDPE from LDPE more consistently than tensile tests. Commercial octene-LLDPE film of 0.918 g/cm³ density and 1.0 g/10 min melt index can record dart impact values in the 150–350 g range, while an LDPE of 0.923 g/cm³ density and 1.8 g/10 min melt index often falls below 100 g. The difference is attributed to higher tie-chain density and the absence of long-chain branching, which permits plastic yield to distribute over a larger area before fracture. Heat-seal initiation is another product-design discriminator because LLDPE has a lower and broader sealing window. ASTM F1921-18 seal initiation testing for cast films commonly shows LLDPE seal initiation near 85–100 °C, while LDPE requires 95–110 °C; the actual value depends on comonomer type, film gauge, and seal-bar dwell. HDPE films used in cereal liners or twist-wrap applications seal at higher temperatures but provide higher moisture barrier due to greater crystallinity.
Hot-tack strength under ASTM F88/F88M-21 is an operating boundary on vertical form-fill-seal machines; LLDPE sealant layers widen the window between melt and burn-through. The same property permits downgauging from 50 µm to 35 µm with retained abuse resistance, although film blocking and coefficient of friction may require antiblock loading of 2000–5000 ppm synthetic silica.
Rotational molding of 5000 L chemical storage vessels from octene-LLDPE places environmental stress crack resistance above stiffness. A carousel rotomolder operating at peak internal air temperature of 260–300 °C distributes powder across a 6–12 mm wall. Because LLDPE has lower flexural modulus, a container previously satisfying sidewall deflection at 12 mm HDPE wall may require 16–20 mm LLDPE wall or external ribs to meet the same internal pressure rating. The design standard for polyethylene upright storage tanks, ASTM D1998-15, provides minimum wall thickness and hydrostatic pressure test criteria but does not prescribe raw material family. LLDPE grades with ASTM D1693-15e1 Condition B failure beyond 1000 h are preferred for detergent, surfactant, and agricultural chemical service because LDPE fails early and HDPE can be vulnerable when density exceeds 0.950 g/cm³ and comonomer content is low.
When Octene-Comonomer LLDPE Replaces HDPE in Rotationally Molded Chemical Storage Vessels
Substitution of HDPE with LLDPE in a rotationally molded tank is not a direct drop-in. The lower secant modulus requires structural compensation by adding vertical ribs, increasing nominal wall thickness, or changing the geometry from a flat sidewall to a ribbed panel. For a 10,000 L vertical tank designed to hydrostatic test at 1.3 × rated capacity under ASTM D1998-15, the required LLDPE wall is governed by the ratio of HDPE to LLDPE flexural modulus; when HDPE modulus is 1000 MPa and LLDPE modulus is 300 MPa, first-order plate theory predicts a wall thickness increase of roughly 1.5 × for equivalent deflection. Processors should verify creep rupture behavior because polyethylene tanks are long-term pressure vessels and stiffness alone is insufficient. Slow crack growth tests such as ASTM F1473-18 or notched pipe tests provide a more severe resin ranking than ASTM D1693-15e1; published data for specific LLDPE/HDPE commercial grades in tank formulations may be limited, so long-term hydrostatic validation on the molded article is required.
Injection molding of high-flow LLDPE at 20–50 g/10 min under ASTM D1238-20 is used for thin-wall lids and containers where toughness and sealability are required. On a 180-ton hydraulic injection molding machine with hot-runner cavity fill and a clamp force of 1.8 MN, a 0.8 mm nominal wall lid can run at melt temperature 200–240 °C and mold temperature 10–30 °C. LLDPE exhibits less warpage than HDPE due to lower crystallinity, but the mold must accommodate differential shrinkage; ISO 294-4:2018 defines the method for shrinkage measurement. LDPE is specified where extreme flexibility or high flow is needed because its lower tensile strength limits load-bearing. HDPE dominates threaded beverage closures due to higher modulus and creep resistance, but LLDPE or LLDPE/HDPE blends are used where the cap liner or tamper-evident hinge must resist stress cracking from essential oils or surfactants.
For food-contact and medical packaging, LLDPE is typically evaluated under FDA 21 CFR 177.1520 for olefin polymers and EU Regulation 10/2011. The material must meet overall migration limits of 10 mg/dm² or 60 mg/kg simulant for food-contact articles under EU 10/2011, with specific migration limits for each comonomer and catalyst residue. REACH compliance requires that the resin supplier has registered the polymer and any intentional additives above threshold concentrations. Unlike plasticized vinyl or some engineering plastics, LLDPE does not require phthalate plasticizers to achieve flexibility, but it may contain antioxidant packages that migrate more rapidly above 60 °C. Product designers must confirm that the chosen grade does not contain slip or antiblock systems incompatible with gamma or ethylene oxide sterilization if the device is used in medical service.
High-density polyethylene is specified over LLDPE in extrusion blow-molded containers that require low oxygen and hydrocarbon permeation. A 500 mL blow-molded bottle made from HDPE at 0.954 g/cm³ can exhibit an oxygen transmission rate several times lower than an LLDPE bottle of equal wall thickness under ASTM D3985-17 at 23 °C and 0% RH. The exact barrier improvement depends on density and crystallinity; published data for specific bottle configurations is limited because permeability is also controlled by wall thickness distribution and parison programming. In these applications, LLDPE is used only as an internal or external layer where stress-crack resistance and drop impact outweigh barrier loss.
