The present article, Reliance LDPE 16MA400 and 1070LA17: Grades Compared, addresses two high-pressure low-density polyethylene homopolymers with long-chain branching and broad molecular weight distribution. The nominal melt flow index gap of 3.0 g/10 min between the two grades, measured under ISO 1133-1:2022 at 190 °C/2.16 kg, is the principal processing differentiator. Grade 16MA400 is specified at 4.0 g/10 min and 0.916 g/cm³ density per ISO 1183-1:2019, while 1070LA17 is specified at 7.0 g/10 min and 0.917 g/cm³. These small numerical offsets produce measurable differences in flow length, bubble stability, seal initiation, and additive mixing.

Rheological Fingerprint: Melt Flow Index and Density

The melt flow index difference is not a linear index of average molecular weight because both grades retain the irregular long-chain branching of high-pressure LDPE. Under capillary rheometry at 190 °C, broad-distribution LDPE grades of this class typically show shear-thinning onset below 100 s⁻¹ and a power-law index in the 0.35–0.50 range. The precise curve depends on long-chain branch frequency and is not fixed by melt flow index alone. Density at 23 °C, measured by ISO 1183-1:2019, shifts from 0.916 g/cm³ for 16MA400 to 0.917 g/cm³ for 1070LA17. A density increase of 0.001 g/cm³ alters crystalline content enough to affect stiffness and heat seal response in coextruded film, although tensile yield differences are usually below the measurement uncertainty of ISO 527-2 when specimens are conditioned at 23 °C and 50% RH for 40 h.

The density offset of 0.001 g/cm³ alters heat seal initiation in thin films. On 50 µm blown film, seal initiation temperature under 0.3 MPa jaw pressure and 0.5 s dwell is typically 2–4 °C higher for 1070LA17 than for 16MA400. However, this is smaller than the shift produced by migratory slip additives; converter trials must use the same masterbatch loading before assigning a seal-temperature difference to the base resin alone. Differential scanning calorimetry per ISO 11357-3:2018 shows a melting peak between 104 °C and 114 °C for LDPE, but seal initiation starts below the peak due to surface melting and applied pressure.

At shear rates typical of injection moulding, 10³–10⁵ s⁻¹, the viscosity gap between the two grades narrows; spiral-flow length is therefore more useful than melt flow index for substitution trials. A 2 mm spiral mould at 190 °C and 80 MPa injection pressure may give 20–25% longer flow for 1070LA17 than for 16MA400, but gate freeze time also shortens by approximately 20–30%. Published data for spiral-flow performance of these exact grades is limited; tool trials should be performed before substituting.

On a 45 mm single-screw extruder with a 24:1 L/D feed section, 16MA400 has been observed to require a lower barrel temperature profile than 1070LA17 when producing 50 µm blown film, because the higher melt viscosity of 16MA400 generates greater shear heating at screw speeds above 70 min⁻¹. Melt temperature measured at the die adapter can rise by 8–12 °C when screw speed is increased from 50 min⁻¹ to 90 min⁻¹. This narrows the bubble cooling window on air-ring-limited towers. A switch from 16MA400 to 1070LA17 without reducing rear barrel temperature by 10–15 °C often produces unstable frost-line height and film gauge variation exceeding ±15%, as measured by a beta transmission gauge at the collapsing frame. The lower viscosity of 1070LA17 is useful for injection moulding but reduces bubble stability in blown film unless the die gap is reduced or the air ring is reconfigured.

What Occurs When 1070LA17 Is Processed Below Its Short-Shot Threshold?

The 7.0 g/10 min nominal melt flow index of 1070LA17 extends flow length in a single-cavity mould, but it does not eliminate short-shot formation when available injection pressure is below 80 MPa. In a 100-tonne clamp injection moulding machine with a 25 mm screw, a 1.2 mm wall thickness closure can be filled with 1070LA17 at barrel settings of 180–220 °C and hold pressure of 50–70 MPa; the same tool may require a 10–15 MPa higher peak pressure with 16MA400 due to its lower flowability. In high-speed injection moulding with a 0.8 mm wall thickness, the melt temperature for 1070LA17 is best held within 190–195 °C, a ±2.5 °C band, because lower values increase gate freeze and higher values raise parting-line flash risk. The critical boundary appears at the gate-land-to-part-wall junction: if gate diameter falls below 0.8 mm, shear heating increases melt temperature at the gate by 5–10 °C, but frozen-layer development is still controlled by mould cooling water at 10–15 °C. Surface sink marks and warpage are minimized by holding pressure profiles that decay within 4–6 s, not by increasing melt temperature beyond 230 °C.

Material changeovers between 16MA400 and 1070LA17 are purged with a compound having a melt flow index above 10 g/10 min. Direct changeover without purging produces visible melt-flow lines in the first 5–10 min of extrusion because the lower-viscosity 1070LA17 preferentially wets the screw root and carries unmelted 16MA400 into the die. In injection moulding, a barrel capacity of two shots is the minimum purge volume when moving from 16MA400 to 1070LA17.

Both grades fall under FDA 21 CFR 177.1520(c) as olefin polymers, provided the finished article extraction tests meet the specified heptane and xylene limits for end-use conditions. In the European Union, compliance is evaluated under Regulation (EU) No 10/2011, Annex I, Table 1, with polyethylene listed as FCM substance No 17; the overall migration limit of 10 mg/dm² applies for packaging and single-use articles. Indian food-contact certification for LDPE is typically assessed under IS 10146:1982, with overall migration into n-heptane at 38 °C measured over 24 h. Recent lot-to-lot certificates for 16MA400 and 1070LA17 have shown compliance for the specific supply-chain route, but converters must re-verify when changing slip agents, antistatic additives, or masterbatch carriers because additive migration kinetics are not identical between the 4.0 g/10 min and 7.0 g/10 min matrices.

When Melt Temperature Exceeds 300 °C in Cast Film and Extrusion Coating

Extrusion coating with 16MA400 is frequently run at melt temperatures of 300–320 °C to promote polymer oxidation and adhesion to aluminium foil or paperboard. At these temperatures, the lower melt flow index of 16MA400 provides melt strength that restricts neck-in to a narrower width than would be expected from a 7.0 g/10 min resin. However, sustained melt temperatures above 320 °C can advance oxidation to the point where gel particles appear in the coating; screen-pack pressure drop on a 90 mm extruder may increase by 0.5–1.0 MPa over a 48 h run, and die-lip build-up becomes visible on the coating edges. If 1070LA17 is used on the same line, lower viscosity reduces neck-in control and oxide adhesion can be compromised unless line speed is lowered or chill-roll nip pressure is increased. The operational boundary is therefore twofold: 16MA400 should not exceed 320 °C at the die lip for more than 24 h without a purge, and 1070LA17 is not a drop-in replacement for extrusion coating at speeds above 150 m/min without a die geometry review.

Masterbatch incorporation limits are controlled by dispersive mixing in the feed zone. With a 44:1 L/D co-rotating twin-screw compounder running at 300 min⁻¹, a 40% titanium dioxide white masterbatch is typically let down at 3–5% by mass without visible agglomeration in blown film of 16MA400. Higher loadings above 8% by mass are possible only when the screw configuration includes two kneading blocks downstream of the barrel 5 side-feeder; otherwise, optical film standards under ISO 2813 show gloss reduction greater than 10 GU at 60° geometry. The higher melt flow index of 1070LA17 gives faster distributive mixing in injection moulding, but the same low-viscosity condition can separate high-aspect-ratio metallic pigments at screw speeds above 300 min⁻¹. Pre-drying of masterbatch is not required for either grade below 60% RH, but condensation at higher relative humidity introduces steam pockets in the melt and causes surface pitting.

How Does Molecular Architecture Constrain Drawdown and Neck-In?

Long-chain branching in LDPE gives both 16MA400 and 1070LA17 greater extensional hardening than linear low-density polyethylene grades. Drawdown in extrusion coating is governed by the melt strength inferred from maximum take-off speed before web break. In 16MA400, the 4.0 g/10 min matrix stabilizes a 10–15 µm coating thickness at line speeds from 70 m/min to 180 m/min on a 70 mm extruder when the melt temperature is held at 315 °C and the air gap is set to 200 mm. Under the same conditions, 1070LA17 enters draw resonance at a lower line speed; typical observations indicate a 20–35% reduction in stable take-off speed. Neck-in is also larger for 1070LA17, with edge bead build-up increasing by approximately 10–20 mm per side on a 600 mm die. These are structural consequences of greater shear-thinning and lower extensional viscosity rather than density alone. In blown film, 16MA400 shows better bubble stability at frost-line heights between 3 and 6 die diameters, whereas 1070LA17 requires a deeper air-ring dam and a lower blow-up ratio near 2.0:1 to avoid bubble wandering.

Published data for 16MA400 tensile properties are generally reported on 50 µm blown film per ISO 527-3:2018, while 1070LA17 data are generated on ISO 527-2:2012 Type 1A injection moulded bars at 50 mm/min. The difference in specimen orientation and thickness means that tensile strength and elongation cannot be compared across the two grades without specifying the preparation route. A film of 16MA400 tested in the machine direction gives higher break stress than an isotropic Type 1A bar of 1070LA17, but the result is dominated by processing-induced orientation rather than resin quality. Conditioning per ISO 291:2008 at 23 °C and 50% RH for 40 h is required before any mechanical comparison.

Reprocessing boundaries differ measurably. Edge trim from 16MA400 extrusion coating can be reintroduced at up to 20% by mass without exceeding a 100/120/100 mesh screen-pack pressure drop of 1.5 MPa; beyond that level, gel counts increase and ASTM D1003 haze on 50 µm film rises by more than 5% absolute. 1070LA17 regrind in injection moulding tolerates up to 30% by mass when melt temperature is held below 230 °C and screw residence time is below 5 min. The higher melt flow index of 1070LA17 lowers screw-recovery shear heating, but prolonged barrel residence can still produce carbonaceous specks from adiabatic heating in the compression zone.

Part-weight variation in thin-wall injection moulding of 1070LA17 remains within 0.4% when screw recovery is set to 85% of maximum cushion and back pressure is held at 3–5 bar hydraulic. The grade is not used in direct contact with saturated steam at 121 °C for extended retort cycles unless the finished part has been validated for morphological distortion; the softening point of LDPE places the continuous-use boundary below 80 °C under load-bearing conditions. For 16MA400, reel-to-reel variation in film haze is minimized by maintaining the extruder screen pack at 100/120/100 mesh and changing it before pressure drop exceeds 1.5 MPa. Published data for specific laminating structures combining 16MA400 with oriented polyamide and ethylene-vinyl acetate tie layers is limited, particularly for seal-through-contamination performance.