Linear Low-Density Polyethylene (LLDPE) Grade Equivalents Across Producers: 218WJ vs 7042 vs 1002AY

Across polyolefin converting lines producing thin-gauge blown film, the comparison of LLDPE grade equivalents across producers: 218WJ vs 7042 vs 1002AY normally begins with density and melt flow rate. All three grades occupy a density band of 0.917–0.919 g/cm³ and a melt flow rate band of 1.9–2.1 g/10 min when measured under ISO 1133-1:2022 at 190 °C and 2.16 kg. The declared base chemistry is a butene copolymer; this similarity is the technical basis for cross-producer substitution in high-output film extrusion. However, equivalence is not established by ASTM D1238-20 melt flow rate alone. Molecular weight distribution, catalyst residue level, primary and secondary antioxidant chemistry, acid scavenger type, and slip or antiblock additive loadings differ among production assets. These differences affect film tensile balance, dart impact, optical haze, heat seal initiation temperature, and long-term melt stability during continuous extrusion.

Comonomer content is not commonly declared on general datasheets; it is inferred from density and extractable fraction. The three materials are generally characterized as Ziegler-Natta catalyzed butene LLDPE resins with a nominal density that places them in a high-clarity, medium-impact film class. Residual metal content and gel counts are also absent from standard property tables. Converters in medical film or capacitor film therefore obtain lot-specific certificates for extractables, residual titanium, and gel distribution instead of relying on melt index and density equivalence.

Values in the table are typical published datasheet ranges, not guaranteed specification limits. Within these ranges, 25 µm blown film made from 1002AY tends to publish the highest dart drop impact and lowest haze; 7042 tends to sit at the lower optical range when no surface-modifying additives are declared. Published data for the exact additive package in 218WJ is limited to producer technical bulletins; direct replacement therefore requires documented first-article qualification rather than reliance on nominal melt index.

Mechanically, the three grades occupy a narrow property band in tensile yield and elongation. Film tensile stress at yield in the machine direction on 25 µm blown film under ISO 527-3 is generally 10.0–12.5 MPa; elongation at break in the machine direction is commonly 500–750 %. These differences are small compared with film gauge variation and blow-up ratio effects. Specimens should be conditioned at 23 ± 2 °C and 50 ± 10 % relative humidity under ISO 291 before tensile testing; failure to condition for at least 40 h introduces scatter that can exceed the grade-to-grade difference. The more consequential lot-to-lot variation is in dart drop impact, where ISO 7765-1 F50 values can separate by 20–40 % at equivalent thickness. This separation is not predicted by melt flow rate; it arises from comonomer distribution and the higher molecular weight tail. A blown film line converting 7042 with a die gap of 1.8 mm and a blow-up ratio of 2.2 may require a reduction in frost line height when switching to 1002AY to preserve bubble stability and retain the published dart impact value. No pre-drying is required at relative humidity below 60 %; pellets exposed to condensation should be purged with dry air before the hopper.

Processors raising line speed above 50 m/min take-off speed may observe motor load deviations of 2–5 % when substituting 7042 for 1002AY; this is generally within normal batch-to-batch variation but should be recorded during the first run. Continuous extrusion of these grades at melt temperatures below 210 °C is preferred to limit oxidative degradation and die-lip residue.

What Are the Measurable Differences in Melt Rheology and Film Optical Response?

Rheological differences are small but observable on a 65 mm single-screw extruder with a 30:1 L/D ratio and a 250 mm spiral mandrel die. At a constant screw speed of 80 min⁻¹, head pressure may shift by 3–8 % between 7042 and 1002AY because of differences in molecular weight distribution and short-chain branching placement. The shear viscosity at 100 s⁻¹ and 190 °C is not commonly stated in general datasheets; converter trials on the specific line are required when extruder specific energy consumption must remain within 0.18–0.24 kWh/kg. Barrel temperature profiles are typically staged from 180 °C in the feed zone to 205–210 °C at the die. The 218WJ grade, when processed at a die gap of 1.6 mm and a blow-up ratio of 2.5, is reported in film-line trials to tolerate a frost line height of 5–8 die diameters; beyond 10 die diameters bubble flapping and gauge randomness increase.

Die lip deposit formation is a recognized production variable after 24–72 h continuous extrusion. Deposit mass varies with primary antioxidant type and additive package; 218WJ and 7042 films have shown white die-lip buildup on chrome-plated spiral dies when melt temperature exceeds 210 °C, while 1002AY is generally processed at 190–205 °C to limit additive volatilization. A pressure drop across the screen pack greater than 20 % of initial value at 250 bar is used on many lines as a screen change trigger; operators then inspect the die lip for oxidized additive residue.

Optical haze is influenced by surface-additive migration and internal crystallite size. At 25 µm, haze by ASTM D1003-13 typically remains 8–18 % across the three grades, and 45° gloss by ASTM D2457-13 is 45–75 GU. The 1002AY product generally sits at the lower-haze end of this band when the film contains no external slip/antiblock concentrate; 7042 can approach 18 % haze if an external antiblock masterbatch is added at 3–5 % addition. Chill air temperature and air-ring design influence measured haze more than the small density differences among the three grades.

When Heat-Seal and Organoleptic Boundaries Dictate Grade Selection

Sealing performance differentiates these grades in lamination and form-fill-seal applications. For a 25 µm monolayer film sealed at 0.275 MPa pressure and 0.5 s dwell, seal initiation temperature for butene LLDPE is generally 90–105 °C when determined by ASTM F88/F88M-21. Hot tack strength measured by ASTM F1921-18 in the 100–115 °C range can shift by 0.3–0.8 N/25 mm among the three grades, with 1002AY typically reporting higher hot tack due to a narrower interlamellar thickness distribution. Published data for the specific configuration of 218WJ in hot tack is limited; converter trials are required for high-speed vertical form-fill-seal lines above 60 packs/min.

Coefficient of friction, measured by ISO 8295 or ASTM D1894, is sensitive to the slip additive package. The kinetic coefficient can range from 0.20–0.50 depending on storage time, blooming temperature, and external antiblock concentrate. Slip additive migration to the film surface is time-dependent; measurements taken within 24 h after extrusion may understate the stabilized coefficient of friction. Converters using 7042 with unmetallizable slip packages may require downstream corona treatment and should verify wetting tension above 38 mN/m before lamination.

Organoleptic suitability under FDA 21 CFR 177.1520 and EU Regulation No 10/2011 is commonly declared by the producer for fatty and aqueous food contact. The limiting factor is not the base resin but the additive package: amine-based volatiles that evolve above 220 °C can generate off-notes; therefore melt temperature should not exceed 210 °C unless the specific product has declared high-temperature organoleptic clearance. 1002AY is frequently selected for low-odor film; 7042 may exhibit slightly higher retained volatiles at high output if nitrogen blanketing is not used in the hopper. Do not combine these grades with pro-degradant additives intended for oxo-degradable film unless the producer datasheet explicitly allows; the acid scavenger and antioxidant package can otherwise deactivate prematurely.

Regulatory Status and Food-Contact Documentation

All three grades are generally supplied with statements of conformity covering FDA 21 CFR 177.1520, EU Regulation No 10/2011, and REACH. The relevant migration limit for plastic food-contact articles is overall migration below 10 mg/dm² under EU 10/2011 Annex II test conditions. Food contact material production is also subject to Regulation (EC) No 2023/2006 on good manufacturing practice. Heavy metal restrictions follow 94/62/EC and CONEG model legislation: the sum of lead, cadmium, mercury, and hexavalent chromium is specified below 100 mg/kg. For applications sold in the European Union, documentation should include a declaration of compliance under Commission Regulation (EU) 2020/1245 as amended, which addresses non-intentionally added substances and plastic materials. The converter remains responsible for migration testing on the final article because downstream processing and printing can alter specific migration behavior.

Industrial hygiene and storage limitations also apply. Pellets stored at ambient temperature below 40 °C and protected from direct sunlight retain additive bloom resistance for 12 months from production date; material stored beyond this period should be checked for pellet blocking and slip migration. Published data for the specific configuration of additivated 7042 under long-term tropical warehouse conditions is limited; converters in high-humidity regions should issue incoming moisture and pellet flow checks before hopper loading.