LDPE End-Use Map: Which Sector Consumes Which Grade

Low-density polyethylene is produced by high-pressure radical polymerisation in tubular or autoclave reactors at pressures from 1,200 bar to 3,000 bar and temperatures of 160°C to 320°C. Commercial LDPE spans a density range of 0.917 g/cm³ to 0.930 g/cm³ when tested per ISO 1183-1:2019 or ASTM D1505, and melt mass-flow rate from 0.2 g/10 min to more than 70 g/10 min under 190°C/2.16 kg per ASTM D1238-20. The LDPE end-use map is not a single substitution table; it is a distribution of long-chain branching, molecular weight, additive loading, and extrusion rheology across distinct converting routes. Film blowing, extrusion coating, injection moulding, blow moulding, wire jacketing, agricultural sheeting, rotomoulding, and masterbatch carrier applications consume different grades because each process imposes separate shear, draw, sag, and cooling requirements. Density alone is an unreliable selector; melt strength, die swell, and draw-down ratio are controlling parameters.

Film Extrusion Grades Dominate Packaging but Not All Films Are Equivalent

Blown film lines consume the largest volume of LDPE, predominantly grades with melt mass-flow rate 0.3–2.0 g/10 min and density 0.918–0.924 g/cm³. The melt is extruded through annular dies with die gaps commonly 1.2–2.5 mm, die diameters from 50 mm to 400 mm, and blow-up ratios between 2:1 and 4:1. In production-scale blown film, bubble stability is controlled by the high long-chain branching level of autoclave LDPE; collapse or draw resonance on a 3-layer line often originates from insufficient melt strength in the polyethylene skin layer. Tensile properties on finished film are measured by ASTM D882, tear resistance by ASTM D1922, and dart impact by ASTM D1709 or ISO 7765-1. A 25 µm LDPE liner film can exhibit dart impact values in the range of 60–120 g, but the value shifts downward when the same grade is diluted with high-MFI lotion-grade resins. Food-contact film grades are used only when the base resin and additive package conform to FDA 21 CFR 177.1520 and, in the EU, to the overall migration limits in (EU) No 10/2011.

Cast film applications consume a slightly broader MFI window, often 2.0–4.0 g/10 min, because the chill-roll process does not require the same bubble strength. Sectors consuming these grades include hygiene packaging, overwrap, surface protection film, and industrial liners. Cast film on flat-die equipment with die width up to 3,000 mm operates at melt temperatures of 230–280°C; higher MFI grades reduce extruder head pressure and allow thin gauge targets of 8–15 µm. Because LDPE is a poor oxygen barrier, with reported permeability coefficient of approximately 2–4 × 10^-13 cm³·cm/(cm²·s·Pa) at 23°C, monolayer LDPE cannot provide modified-atmosphere shelf life for oxygen-sensitive foods without additional barrier layers.

Extrusion coating and lamination lines consume a separate low-viscosity LDPE class, typically with melt mass-flow rate 4.0–15.0 g/10 min and density 0.915–0.918 g/cm³. The lower density enhances hot-tack and seal initiation. This sector consumes autoclave-based coating grades specifically designed for low neck-in and high draw-down. On a tandem extrusion laminator with line speeds of 150–600 m/min, the molten web is drawn from the die at 290–320°C onto paperboard, aluminium foil, or biaxially oriented film. Draw-down ratios can exceed 100:1; grades with insufficient long-chain branching exhibit edge weave, melt break, and poor adhesion to the substrate. Coating weight is controlled in the range 10–25 g/m² for liquid-carton structures. Seal strength is measured per ASTM F88, and hot tack is measured per ASTM F1921. Adhesion to aluminium foil is enhanced by corona or ozone treatment, which raises surface energy from 28–30 mN/m to above 38–42 mN/m.

End uses include liquid-carton board, aseptic packaging, foil-laminated pharmaceutical strips, and flexible packaging pouches. Liquid-carton structures require converters to validate organoleptic and migration compliance under FDA 21 CFR 177.1520 and (EU) No 10/2011. ASTM D1238-20 alone is insufficient to qualify these resins; melt tension and draw-down are measured on dedicated capillary or extensional rheometers to separate coating-grade candidates from ordinary film or injection grades.

What LDPE Grades Are Consumed in Injection Moulding and Closure Applications?

Injection moulding consumes LDPE grades with melt mass-flow rate from 4.0 g/10 min to 70.0 g/10 min and density 0.917–0.924 g/cm³. The high-flow design compensates for the narrow gates and multicavity tooling used in thin-wall caps, overcaps, dispensing closures, tip caps, and medical device components. On a 150-tonne hydraulic injection moulding machine, a 32-cavity closure tool operating at cycle times below 10 s requires stable melt delivery at 180–240°C; higher MFI reduces injection pressure and core deflection but also lowers environmental stress crack resistance and stiffness. Moulded part performance is evaluated by flexural modulus under ISO 178 or ASTM D790, notched Izod impact under ASTM D256, and Vicat softening under ISO 306. Mould shrinkage for LDPE injection grades is typically 1.5–2.5%; tooling design must compensate for this range with gate geometry and cooling channel placement.

Closures and consumer packaging consume LDPE when a soft, squeezable closure or tamper-evident overcap is required; the grade is frequently modified with slip and antiblock additives. Food-contact and pharmaceutical closures require verification of extractables and migration per FDA 21 CFR 177.1520 and, where applicable, USP <661.1>. High-flow grades with MFI above 50 g/10 min are used in thin-wall closures but are limited by reduced environmental stress crack resistance under ASTM D1693. Low-temperature impact data should be generated for the exact product geometry because published data for this specific configuration is limited.

Blow moulding of LDPE occupies a narrow niche between rigid HDPE and flexible film. The grades consumed are typically 0.5–2.0 g/10 min in melt mass-flow rate and 0.920–0.925 g/cm³ in density. The parison must resist sag during shuttle or reciprocating screw blow moulding; therefore medium-to-high long-chain branching is retained. Die swell is a deliberate variable in squeeze bottles and dropper bottles, where a soft tactile response and rapid recovery are required. Typical blow moulding equipment operates at melt temperatures 160–190°C and parison drop times below 5 s. Bottle wall thickness, capacity, and drop impact are measured per ASTM D2463 or ISO 2248.

End users in personal care, ophthalmic, and pharmaceutical sectors consume blow-moulded LDPE for dropper bulbs, bellows, and low-stress packaging. The selected grades require high environmental stress crack resistance under ASTM D1693 when the pack contains surfactants or nonylphenol ethoxylate-based formulations; the standard stress-cracking agent is a 10% Igepal CO-630 solution at 50°C. Regulated packaging grades must comply with FDA 21 CFR 177.1520 and, for ophthalmic droppers, with USP <661.1> plastic packaging suitability.

When LDPE Compounds Enter Wire Jacketing, Peroxide Decomposition and Density Dominate Selection

Wire and cable applications consume LDPE base resins at melt mass-flow rates of 0.2–2.5 g/10 min and densities 0.920–0.930 g/cm³. For thermoplastic insulation, the grade is often classified under ASTM D1248, which defines polyethylene sheathing compounds by density, melt index, and carbon black content. For crosslinkable LDPE, dicumyl peroxide is compounded at levels 1.5–2.5 wt%; decomposition during continuous vulcanisation in a dry-cure tube at 180–220°C generates crosslinks. Hot-set testing at 200°C and 0.2 MPa loading is performed according to IEC 60811-2-1; typical crosslinked LDPE insulation may show hot-set elongation below 175% and permanent set below 15%. To prevent scorch, compounders keep melt temperature below 130°C before die entry because dicumyl peroxide decomposition begins near 140°C.

Low-voltage power distribution cable jackets consume LDPE when low dielectric constant and low dissipation factor are required. However, LDPE jackets are limited by poor flame retardancy; halogen-free flame-retardant compounds use high filler loadings of aluminium trihydrate or magnesium hydroxide, which lowers tensile and elongation. Compounding on a 75 mm co-rotating twin-screw extruder with L/D 44:1 may require LDPE carrier grades with MFI 2–20 g/10 min to maintain torque within gearbox limits. Dielectric strength is measured per IEC 60243-1, while long-term wet ageing is evaluated under the relevant IEC 60811 series.

Agricultural and construction film applications select LDPE grades with melt mass-flow rates between 0.3 g/10 min and 1.0 g/10 min and density 0.918–0.925 g/cm³. Greenhouse film, silage cover, vapour retarder, and temporary containment liners consume blown film structures where UV stabilisation, infrared retention, and long-term tensile retention control selection. A 180 µm greenhouse cover on a high-tunnel frame is evaluated for tensile strength and elongation after accelerated weathering under ISO 4892-2:2013. Retained elongation after 2,000 h of xenon-arc exposure is specified by many regional greenhouse film buyers; because thresholds vary by supplier, a single universal value is not published. Carbon black loading of 2.0–3.0 wt% is common in long-life agricultural films.

Construction vapor retarders consume LDPE sheeting with minimum thickness 0.15 mm; puncture resistance is evaluated by ASTM D4833. ASTM D4397 provides material and dimensional requirements for polyethylene sheeting used in construction. LDPE with carbon black or titanium dioxide is used for UV-stable covers; unpigmented LDPE is not suitable for continuous outdoor exposure beyond a limited service period.

Rotational Moulding Grades and Compounding Carrier Resins

Rotational moulding consumes LDPE grades with melt mass-flow rates 2.0–20.0 g/10 min and density 0.920–0.930 g/cm³. The powder or micropellet form is tumbled in biaxial machines at oven temperatures of 260–300°C; particle size and dry-flow are measured per ASTM D1895. Sintering, bubble removal, and densification determine mechanical properties; impact at low temperature is assessed by ASTM D1998 or ISO 179. Fine powder below 500 µm is preferred for consistent melt-out and wall-thickness uniformity. Rotomoulded LDPE parts are selected for toys, tanks, and containers, but are not selected for demanding chemical tanks unless environmental stress crack resistance is validated for the intended contents.

Masterbatch producers consume LDPE as carrier resin at 2.0–20.0 g/10 min because it wets pigment and additive surfaces without competing with PP or HDPE in dilution. The carrier is compounded on twin-screw extruders; higher MFI reduces heat history and permits high pigment loadings. Dispersibility is monitored by filter pressure rise in laboratory extruders. Sectors consuming these carrier grades include all thermoplastic converters, film producers, and blow moulders.