Formosa Plastics HDPE LH5420 is a high-molecular-weight high-density polyethylene designed for blown film extrusion. The resin combines a density of 0.954 g/cm³ under ASTM D1505 with a melt flow rate of 0.18 g/10 min under ASTM D1238 at 190°C/2.16 kg. The high-load melt flow rate, measured under ASTM D1238 at 190°C/21.6 kg, is 7.0 g/10 min. This combination yields a flow-index ratio near 39, which in blown film processing translates to a shear-thinning melt capable of sustaining a stable high-stalk bubble. The resin is intended for thin-gauge film from 12 µm to 80 µm, including T-shirt grocery sacks, star-sealed trash can liners, industrial liners, and packaging films where stiffness and moisture barrier are dominant requirements.

Typical property values in the following table are obtained from compression-molded plaques or 25 µm blown film and are not to be read as specification limits. Film values depend on blow-up ratio, frost-line height, melt temperature, and die gap.

The molecular architecture is linear, with only short-chain branches from comonomer; this is distinct from high-pressure LDPE, which contains long-chain branches. Under ASTM D1238, melt flow rate values are not directly comparable across LDPE and HDPE because long-chain branching alters flow behavior. In blown film, LH5420 develops a high, stable stalk at 190–220°C, while a broad-MWD HDPE of lower molecular weight cannot sustain a stalk above 4 die diameters. This difference permits high BUR operation and balanced orientation without the bubble breaks typical of medium-MW HDPE at 5:1 BUR.

On a high-output blown-film line, the grade is processed on a single-screw extruder with a 24:1 to 30:1 barrier screw and a grooved feed section. Feed throat temperatures are set at 180°C, progressing to 200°C at the metering zone and 210°C at the adapter. The melt is conditioned through a screen pack of 20/40/60 mesh before entering a spiral mandrel die with a die gap of 1.0–1.5 mm. At a 75 mm extruder running 120 kg/h, melt pressure at the breaker plate is commonly 28–35 MPa; pressures above 40 MPa indicate screen blinding or excessive die restriction and must be addressed to prevent barrel wear. The bubble is formed with a blow-up ratio of 3:1 to 5:1, with the frost line maintained at 8–12 die diameters. When high stalk extrusion is used, the stalk is held between 6 and 10 die diameters below the frost line; premature crystallization in the stalk produces MD tear loss and visible die lines.

At 120 kg/h on a 75 mm extruder, specific energy input is typically 0.25–0.30 kWh/kg. The high shear thinning of LH5420 means that increasing screw speed from 80 rpm to 120 rpm raises melt temperature by 8–12°C rather than 20°C. Barrel cooling on the grooved feed section must be maintained with water at 40–50°C to prevent premature melting and loss of feed conveying. The melt temperature at the die should be checked with a hand probe before each shift, not inferred from barrel set points; a deviation above 220°C indicates excessive backpressure or a worn screw/barrel clearance beyond 0.25 mm.

When flow-index ratio approaches 39, what happens to die pressure under high-stalk conditions?

The broad molecular weight distribution associated with a flow-index ratio near 39 produces non-Newtonian behavior: apparent viscosity falls steeply as shear rate increases. On a 250 mm spiral die with 1.2 mm die gap, the die pressure may be 30 MPa at 100 kg/h, but the increase to 140 kg/h is not linear; pressure rises by roughly 10%, not 40%, because shear heating lowers viscosity. This allows higher throughputs without a proportional increase in melt temperature. However, this same shear thinning reduces melt strength at the die exit. The operator must maintain a stable high stalk with a dual-lip air ring; insufficient lower air flow causes bubble sag, while excessive upper air flow can freeze the stalk and elevate film haze. The practical upper limit is reached when film thickness variation across the web exceeds ±5% under ASTM D8136 or equivalent inline capacitance gauging.

Thickness variation in high-stalk film production is controlled by die gap, air-ring geometry, and frost-line height. On a 250 mm die, a die gap reduction from 1.5 mm to 1.0 mm improves MD thickness uniformity by increasing draw-down; however, it also raises die pressure and may initiate melt fracture at high output. Melt fracture appears as alternating rough and shiny bands near the die exit and can be suppressed by raising die temperature to 220°C or by lowering output 10%. If film thickness variation exceeds ±7% across the web, the bubble is typically asymmetric due to uneven air-ring flow; this is measured by an online capacitance gauge and corrected by selective air-ring port adjustment.

Mechanical performance at 25 µm blown film reflects the resin density. The secant modulus is 900 MPa MD and 950 MPa TD under ASTM D882; these values decline by 10–15% when the film is blown at 5:1 BUR because chain orientation shifts toward the transverse direction. Dart drop impact, measured by ASTM D1709A, is typically 160 g at 25 µm. At 12 µm, dart impact can fall to 70–90 g, and MD Elmendorf tear under ASTM D1922 can fall below 10 g. Raising the BUR from 3:1 to 5:1 rebalances the tear envelope; TD tear rises from 38 g toward 60 g, while MD tear may fall by 20%. For high-speed conversion, this balance is critical because bag-making machines orient film in the machine direction during unwind and sealing.

How does LH5420 differ from medium-molecular-weight HDPE in the same density class?

A medium-molecular-weight HDPE film resin at similar density may carry a melt flow rate of 0.7 g/10 min and a high-load melt flow rate near 20 g/10 min. The lower flow-index ratio of LH5420 indicates longer chains and higher melt strength. In practice, LH5420 supports downgauging: a 14 µm film can exhibit comparable stiffness and tensile yield to a 20 µm medium-molecular-weight grade. The cost is extrusion pressure and shear heating. The medium-molecular-weight grade may process at 15–20 MPa die pressure in similar conditions, while LH5420 runs at 28–35 MPa. Dart drop impact improves from roughly 90 g to 160 g at 25 µm, but Elmendorf tear in the MD remains a limiting property. Converters must not assume all HDPE film grades are interchangeable; the higher shear viscosity of LH5420 demands longer metering zones and higher torque drive motors.

Commercial HMW-HDPE film resins often use bimodal molecular weight distributions. LH5420’s flow-index ratio near 39 is consistent with a broad distribution, and the high-load melt flow rate of 7.0 g/10 min indicates the presence of a low-molecular-weight fraction that plasticizes the melt during extrusion. This low-MW fraction enables high throughput, while the high-MW fraction contributes to melt strength and dart impact. If the low-MW fraction is excessive, die lip build-up and smoke production increase; if the high-MW fraction is excessive, die pressure rises and frost-line height becomes unstable. The balance is maintained by the polymerization process.

What distinguishes LH5420 from metallocene LLDPE replacement candidates?

Relative to metallocene-catalyzed LLDPE at density 0.918 g/cm³, LH5420 offers higher modulus and lower water-vapour transmission, but lower Elmendorf tear and dart drop impact. The modulus difference is a direct consequence of crystallinity; HDPE at 0.954 g/cm³ has a crystalline fraction above 70%, whereas an mLLDPE of 0.918 g/cm³ remains near 55–60%. For a 25 µm film, water-vapour transmission under ASTM F1249 at 38°C and 90% RH is roughly 2.5 g/m²/day for HDPE and 6–8 g/m²/day for LLDPE. The trade-off appears in tear: mLLDPE typically delivers MD tear values above 50 g at 25 µm, while LH5420 is near 18 g MD. Converters selecting LH5420 therefore do so for stiffness, downgauging, and barrier, not for puncture-dominated service.

The data show a property inversion: LH5420 is selected when stiffness, downgauging, and moisture barrier are the primary control variables; mLLDPE is selected when tear, impact, and low-temperature puncture dominate. The moisture-barrier advantage of HDPE is measurable by ASTM F1249. At equivalent thickness, HDPE transmits roughly one-third to one-half the water vapour of LLDPE; the exact ratio depends on film crystallization and orientation. The lower tear of LH5420 means that side-gusset transitions and sharp bag corners can initiate crack growth under rapid filling; the converter may need to modify seal geometry or blend 10–20% mLLDPE to restore tear.

Commercial conversion of LH5420 occurs on both inline and off-line bag-making lines. T-shirt grocery sacks at 14–18 µm gauge are run with post-industrial regrind levels up to 20%; higher regrind reduces dart impact by approximately 10–15% per 10% addition. Sealing conditions on standard side-weld and bottom-seal machines range from 150°C to 175°C at 0.3–0.5 s seal time for 25 µm film. Heat-seal strength measured under ASTM F88 is controlled more by seal geometry and jaw pressure than by resin alone. In star-sealed trash can liners, the grade is processed at 20–30 µm with a higher BUR to prevent MD tear propagation from the star seal.

The supplied grade is formulated with a phenolic antioxidant and a phosphite processing stabilizer; no slip or antiblock additives are normally included. This allows converters to control surface properties independently. Addition of a fluoroelastomer processing aid at 200–500 ppm may be required to delay melt fracture at high output; the processing aid must meet the applicable food-contact condition. Use of zinc stearate at 0.05–0.10% can act as an acid scavenger but may interact with certain inks and should be validated for print adhesion under ASTM F2252.

Haze of LH5420 film at 25 µm is typically 8–12% under ASTM D1003, depending on frost-line height and die lip cleanliness. High stalk extrusion with a low frost-line creates slower cooling and larger spherulites, increasing haze. If film clarity is required, the die gap may be reduced to 1.0 mm, melt temperature raised to 215°C, and a dual-lip air ring with high internal air flow used; however, clarity remains below LLDPE because of internal scattering from HDPE crystallites. Some converters add an external slip/antiblock masterbatch at 2–4% by weight to lower film coefficient of friction from a 0.45 range down to 0.15–0.20 under ISO 8295. The selection must be verified for food contact if the final film is used in food packaging.

Environmental stress-cracking resistance of the base resin under ASTM D1693 condition B may exceed 100 h in 10% Igepal CO-630; however, blown film ESCR is thickness- and orientation-dependent. Industrial liner applications involving solvents or surfactants require end-use testing because the high density of 0.954 g/cm³ increases stiffness but lowers ESCR relative to a lower-density HDPE. For aggressive surfactant packaging, a lower-density grade or an LLDPE blend may be substituted; LH5420 should not be used when cracking precedent exists in similar liners without qualification.

Film produced from LH5420 has a Vicat softening temperature near 124°C under ASTM D1525. This supports brief hot-fill contact, but the resin is not rated for sustained service above 60°C under load. In bag-making, hot-knife sealing operations require careful temperature control between 180°C and 220°C; above 230°C the polymer degrades and leaves residue on the knife, increasing maintenance intervals. If the line uses ultrasonic welding for handle cut-outs, amplitude of 40–60% on a 20 kHz system at 75 kPa pressure provides acceptable bond quality for 25 µm film.

For food-contact evaluations, HDPE LH5420 is positioned under FDA 21 CFR 177.1520 as an olefin polymer. That citation permits use in contact with food types described in the regulation when extractives and end-use conditions are met. Under EU Regulation 10/2011, the material must satisfy an overall migration limit of 10 mg/dm² and any specific migration limits tied to additives or monomers. Under REACH, the polymer itself is exempt from registration, but constituent monomers and additives require registration or exemption; the supplied pellets should not contain substances of very high concern above 0.1% w/w. RoHS risk assessment under EU 2015/863 is generally limited to categories such as Pb, Hg, Cd, Cr(VI), PBB, and PBDE; packaging materials are outside the original electrical and electronic equipment scope, but the homogeneous material limits of 0.1% by weight for lead and 0.01% for cadmium are common supply-chain checks. Processors should obtain a compliance declaration from the resin manufacturer for each specific end market.

Operational boundaries with moisture, regrind, and high-temperature residence

Although HDPE is not hygroscopic, condensed surface moisture on cold pellets can occur when silo-to-production transfer crosses relative humidity above 60%. That surface water can generate pinholes in film below 15 µm and fluctuation in melt pressure. If condensation is present, drying at 80°C for 2 h in a desiccant dryer with a dew point below -20°C restores pellet handling. Prolonged melt residence at 220°C beyond 10 min may consume the phenolic stabilization package and produce yellowing, measurable as an increase in yellowness index under ASTM D6290. The resin should not be combined with amine-based antistatic packages that can poison or react with the phenolic system; any external lubricant should be limited to 0.5–1.0 phr mineral oil to avoid grooved-feeding slippage and output oscillation.

When post-consumer recyclate is introduced into LH5420 film, the density and melt flow rate shift because the recyclate fraction carries LDPE, LLDPE, and adhesive residues. At 20% PCR, extrusion pressure often falls by 5–10%, dart impact at 25 µm may fall below 120 g, and gel counts under ASTM D6290 visual inspection increase. Converters should raise BUR to 4.5:1 and reduce die gap to 1.2 mm to rebalance MD/TD properties. Published data for mixed-source PCR formulations is limited; each lot must be qualified on the target line before production release.

Pellet storage should be under ambient dry conditions. The resin is not hygroscopic but can develop condensation. Keep material away from direct sunlight to prevent UV degradation of the additive package. On silo discharge, ceramic-coated elbows minimize pellet fracture and angel hair formation. Angel hair generated during high-speed conveying can plug screen packs and produce gels, so dilute-phase conveying velocity should be kept below 25 m/s and mass loading above 5 kg/kg air. Screen pack inspection after start-up is recommended to monitor contamination.

Lot-to-lot variability is controlled by the supplier’s in-process limits. Density is typically controlled to ±0.002 g/cm³, and melt flow rate to ±0.02 g/10 min. Film converters should request certificate of analysis values for each silo and track high-load melt flow rate, because the ratio of HLMFR to MFR is more sensitive to polymer chain architecture than either value alone. A flow-index ratio shift below 35 can reduce melt strength and alter stalk height; a shift above 43 can increase die pressure and consumption of processing stabilizers.