Low-density polyethylene (LDPE) is produced in tubular or autoclave reaction systems, yielding a branched macromolecular structure with a solid-state density between 0.917 g/cm³ and 0.930 g/cm³ measured at 23 °C per ISO 1183-1:2019. In trade, Sinopec LDPE Grades: 2426H, 2420H and 2102TX00 in Trade are routinely offered as pelletized film-extrusion resins, but the grade suffix does not encode a single melt index. Commercial equivalence is instead established through certificates of analysis, sampling procedures, and agreed acceptance windows. Granulate is usually packed in 25 kg multi-wall bags, palletized at 1,375 kg net, and shipped with lot traceability documents that list melt mass-flow rate, density, ash content, and optical test data.

Procurement specifications for these grades commonly reference ASTM D1238-23 or ISO 1133-1:2022 for melt mass-flow rate, with the test performed at 190 °C under 2.16 kg load. Certificate values for a single lot may differ between the ASTM and ISO methods due to die geometry and thermal equilibrium differences, so cross-border trade documents often state which method has been applied and whether the result falls within the producer’s ±0.3 g/10 min release window. For density, ISO 1183-1:2019 is the most commonly cited method in Sinopec-issued documentation, although older certificates may list ASTM D1505-18. A density shift of 0.001 g/cm³ is analytically small but can alter film stiffness and bubble cooling behavior at high throughput.

Why Melt Rheology Controls Trade Equivalence Among 2426H, 2420H and 2102TX00

Melt rheology differentiates the three grades more decisively than density. In blown film extrusion, the extensional viscosity of LDPE is controlled by long-chain branching concentration and molecular weight distribution; a grade with a nominally identical melt index can exhibit different drawdown force on high-stalk bubble configurations. For 2426H, 2420H and 2102TX00, traders and converters therefore compare shear viscosity curves rather than relying on a single melt index point. Capillary rheometry in the shear range 100 s⁻¹ to 1,000 s⁻¹ at 190 °C typically shows that 2102TX00 retains higher low-shear viscosity than 2420H, although published data for this specific configuration is limited. Converters are advised to run a full shear sweep before substituting one grade for another on a stabilized line.

At the blending or extrusion stage, melt temperature should be held between 160 °C and 190 °C for LDPE film grades. Above 200 °C, oxidative degradation accelerates, producing aldehydes and reducing film gloss. Machine-direction melt pressure on a 60 mm single-screw extruder with an L/D of 28:1 typically falls in the range 20 MPa to 35 MPa for these pellets at screw speeds above 80 rpm. When switching among 2426H, 2420H and 2102TX00, a pressure deviation greater than 10% from the baseline lot usually indicates a difference in pellet preheat, feed zone friction, or molecular weight distribution rather than a simple melt index offset.

The table below summarizes commonly quoted trade windows for the three grades. The values are not producer guarantees; they represent acceptance ranges typically distributed by sellers and should be verified against the certificate of analysis for each lot.

On a conventional blown film line, the die gap is usually set between 0.8 mm and 1.2 mm, and the blow-up ratio is maintained from 2.0 to 3.0. These conditions generate balanced film orientation for 2426H and 2420H, but 2102TX00 may require the die gap to be opened to 1.5 mm when the line runs high-strength sack film at thicknesses above 80 µm. The frost line height is a key control variable: for LDPE grades with the same melt index, a higher frost line increases machine-direction tear resistance but reduces transverse-direction dart impact. Operators avoid moving the frost line by more than 10% when swapping grades without re-qualifying the film. Actual output on a 90 mm extruder running 50 µm film at 120 kg/h is often limited by bubble instability rather than plastication capacity, especially when 2102TX00 is run in a high-stalk configuration.

Blown Film Bubble Stability and Frost-Line Management with Sinopec LDPE Grades

Bubble stability is governed by extensional strain hardening, which in LDPE increases with long-chain branching density. Sinopec 2426H and 2420H are typically run in a conventional in-pocket bubble geometry, while 2102TX00 is frequently quoted for high-stalk lines where the melt is drawn upward over a greater distance before the frost line. In high-stalk operation, the stalk height may reach 5 to 10 die diameters, increasing melt relaxation and improving transverse-direction tear balance. The cooling air ring must supply chilled air at 10 °C to 20 °C with sufficient differential pressure to stabilize the bubble; excessive air velocity at the die lip can induce draw resonance, especially below 25 µm film thickness. Operators record bubble diameter variation with a laser micrometer and typically reject production when diameter variability exceeds ±2% over a 10 min interval.

Lot-to-lot variation in LDPE from different Sinopec plants may appear as changes in bubble height or neck geometry even when the certificate values are within specification. In a production-scale trial on a 3-layer blown film line, substituting 2420H with 2102TX00 in the core layer required a 5 cm reduction in frost line height to maintain a stable neck. Without this adjustment, the bubble oscillated at a frequency of 0.3 Hz and generated film thickness variation above ±6% per ISO 4593:2019.

When film is downgauged from 50 µm to 25 µm, dart impact resistance measured per ASTM D1709-16a and Elmendorf tear resistance measured per ASTM D1922-15 become limiting values for acceptance. For 2426H in 25 µm monolayer film, the minimum dart impact requirement is often set at 80 g, but published data for this specific configuration is limited. Converters commonly run a capability study with at least 30 rolls before accepting the downgauged structure. Haze measured per ASTM D1003-13 may shift from 6% at 50 µm to 4% at 25 µm, although optical performance also depends on die lip cleanliness and melt temperature.

When a Converter Switches from 2420H to 2102TX00 for High-Drawdown Monolayer Film

If a converter replaces 2420H with 2102TX00 on a high-drawdown monolayer line, the first measurable change is usually an increase in motor load at constant screw speed, reflecting a higher melt viscosity at low shear. The extruder control system should be set to maintain melt temperature below 190 °C; if melt temperature rises above 195 °C, gel particles can form through oxidative crosslinking and appear as fisheyes in the film. Drawdown force measured at 190 °C at a draw ratio of 10:1 can differ by 15% to 25% between lots of 2102TX00 depending on storage age. Pre-drying is generally unnecessary at relative humidity below 60%, but surface moisture condensation can occur when cold pellets are transferred into a warm production hall. In such cases, hopper drying at 60 °C for 2 h is applied before extrusion.

The melt curtain in extrusion lamination is another trade application for 2102TX00. At a line speed of 150 m/min, the melt web must resist neck-in and draw resonance; a high-molecular-weight fraction in the resin stabilizes the web, but excessive viscosity limits the minimum coat weight. Lamination coat weight is typically controlled to 15 g/m² for paper-liner structures, and the melt must be extruded through a slot die with a lip gap of 0.5 mm to 0.8 mm. The maximum draw ratio for 2102TX00 at 190 °C is often quoted between 20:1 and 25:1; beyond that, draw resonance appears as periodic thickness bands visible in the coated substrate.

Although the three grades have similar density and melt index windows, their additive packages are not identical. 2426H is commonly supplied with a hindered phenolic antioxidant and a slip/antiblock package for agricultural film, while 2420H may carry a lower slip load for general packaging. 2102TX00 is often supplied with a higher molecular weight antioxidant system for extrusion lamination and heavy-duty sacks, where melt residence time can exceed 10 min at 200 °C. The presence of erucamide slip additives at 500 ppm to 1,000 ppm can lower the coefficient of friction of the film surface, but migration to the sealing interface may reduce seal strength in high-speed form-fill-seal lines. Converters should avoid using fluoropolymer processing aids as a substitute for grade-specific bubble stability validation, because the resulting melt fracture suppression may mask viscosity differences that are required for stable high-stalk operation.

A Trade Lot Is Not a Single Number: Documentation and Traceability Requirements

Cross-border trade in Sinopec LDPE grades requires documentary verification of food-contact status, hazardous substance compliance, and inventory traceability. For food-contact film, converters must verify that the specific grade and lot comply with FDA 21 CFR 177.1520 for olefin polymers or the relevant European Commission regulation. The certificate of compliance should state the resin density range and the end-use condition of use. REACH compliance is documented through a safety data sheet under Regulation (EC) No 1907/2006, and RoHS compliance is often demonstrated by IEC 62321-8:2017 screening for phthalates and heavy metals. Bills of lading should retain the producer lot number, not only the grade name, because antidumping or preferential origin documentation can be rejected if the lot number is absent.

Warehouse inspection before unloading includes checking pallet stability, bag integrity, and contamination by external polymer fines. LDPE pellets do not require drying in normal storage, but exposure to direct sun for more than 6 months can increase yellowness index measured per ASTM E313-20 beyond 2 in tropical storage environments. Incoming quality control should draw samples from 5% of the pallets or at least 3 bags per lot, then test melt mass-flow rate and density before the material is released to silo storage. If the melt index deviates more than 0.5 g/10 min from the purchase specification, the lot is quarantined for a full rheological comparison and possible downgrading to less critical film applications.

Trade disputes involving 2426H, 2420H and 2102TX00 frequently arise from comparing certificates against different test methods. A lot that fails an ASTM D1238-23 melt index specification may still be acceptable under ISO 1133-1:2022 if the conversion bias is documented. Purchase contracts should therefore fix the exact test method, conditioning temperature, and specimen preparation. For density, conditioning at 23 °C for 40 h is specified in ISO 1183-1:2019 for referee testing. Without that conditioning step, molded plaques and pellets may show apparent density differences up to 0.001 g/cm³ due to crystallinity relaxation, which is analytically significant in trade acceptance.