SABIC LLDPE 6318BE: Technical Product Introduction

SABIC LLDPE 6318BE is a butene-based linear low-density polyethylene resin supplied in pellet form and formulated with an antioxidant stabilizer, slip additive, and antiblocking mineral package. The nominal melt mass-flow rate is 1.0 g/10 min when measured according to ISO 1133-1:2022 at 190 °C with a 2.16 kg piston load, and the nominal density is 0.918 g/cm³ by ISO 1183-1:2019. These values place the grade in the low-MFR, low-density segment of the SABIC LLDPE film portfolio. The material is conventionally classified as a C4-LLDPE because the comonomer is butene-1, which introduces short-chain branching during polymerisation and produces a distinguishable balance between flow, stiffness, and film puncture resistance when compared with hexene- or octene-based LLDPE grades.

The grade is intended primarily for monolayer and coextruded blown film structures, including heavy-duty sacks, agricultural nursery films, industrial liners, and carrier bags. Because the resin contains slip and antiblock additives, downstream converters can handle high-integrity film on high-speed conversion lines without immediate blocking force exceeding ASTM D3354-15 performance thresholds. The exact additive package and its loading are specified in the grade-specific technical datasheet and should be confirmed before changing film formulations or food-contact declarations.

What Molecular Parameters Differentiate 6318BE from Metallocene and C6-LLDPE Grades?

The designation 6318BE belongs to the conventional Ziegler-Natta butene-linear low-density polyethylene category. In contrast to metallocene LLDPE, the molecular weight distribution is broader and the short-chain branching distribution is more heterogeneous. This broadens the shear-thinning response and typically reduces melt pressure at high screw speeds, but it also produces a less sharp melting peak and a different coefficient-of-friction development profile. The broader molecular weight distribution contributes to bubble stability on high-stalk blown film lines, while the heterogeneous branching can produce slightly higher haze than metallocene C6-LLDPE when film haze is measured according to ISO 14782:2021 or ASTM D1003-21.

Hexene and octene comonomers generate longer short-chain branches that participate more efficiently in tie-molecule formation during strain hardening. Consequently, at equal density and MFR, C6-LLDPE and C8-LLDPE often exhibit higher dart impact strength under ASTM D1709-16a method A and higher puncture energy under ASTM D5748-19. Published data for 6318BE in direct comparison with specific hexene or octene grades is limited; a side-by-side evaluation on a 400 mm spiral mandrel blown film die at 2.2:1 blow-up ratio and 40 µm film thickness is required to establish product-specific performance differences. At the resin level, the primary differences are comonomer type, molecular architecture, and the final additive package rather than a single numerical property.

Compared with higher-MFR LLDPE grades in the 2.0 g/10 min range, the 1.0 g/10 min melt flow rate of 6318BE favors higher melt strength and better bubble stability, but it also requires more careful control of screw-induced shear heating. When processed on a grooved-feed extruder, the lower MFR grade can develop higher melt temperature at the same screw speed because of viscous dissipation. This thermal input must be managed through barrel cooling and screw-speed adjustment to avoid exceeding the degradation threshold described below.

For production-scale monolayer blown film lines running a 60 mm grooved-feed extruder with 30:1 L/D barrier screw and a 400 mm spiral mandrel die, the processing envelope for the 1.0 g/10 min C4-LLDPE resin is commonly set with barrel zones between 180 °C and 210 °C, adapter and die zones between 210 °C and 225 °C, and melt temperature between 190 °C and 230 °C. At a die gap of 1.2 mm, high shear stress at the die lip can produce sharkskin melt fracture on very thin gauges below 25 µm; widening the die gap to 2.0 mm lowers die-land shear stress but shifts molecular orientation and may reduce machine-direction tear strength under ASTM D1922-15. A fixed-lip die with a gap of 1.6 mm is often selected as a compromise for gauges near 30 µm to 50 µm.

Melt temperature should not exceed 230 °C during normal film extrusion for this resin class because butene-LLDPE is susceptible to thermo-oxidative chain scission and crosslinking at extended residence times. Gels generated at high temperature are detectable as melt pressure variation ahead of the screen changer and as optical defects in the bubble. A clean screen pack of 20/40/60 mesh is typical for this grade; an increasing pressure drop above the clean-screen baseline by more than 30 % may indicate additive plate-out, gel accumulation, or foreign-material contamination. Resin drying is not normally required, but resin exposed to relative humidity above 60 % for extended storage can develop surface moisture. Moisture content above 0.05 % by weight, measured to ISO 15512:2019, may generate bubble pinholes and die-lip deposits during extrusion.

Bubble stability for the 1.0 g/10 min grade is generally adequate at blow-up ratios from 2.0:1 to 3.0:1. High-stalk film lines should set the frost line height between 2 and 4 die diameters while maintaining air-ring pressure and internal bubble pressure within narrow limits. In coextruded film constructions, the higher-viscosity butene-LLDPE layer can act as a load-bearing core layer, but differences in melt strength with LDPE skins may cause interfacial instability when the die temperature is below 210 °C. Processors should monitor layer thickness variation by scanning capacitance and adjust die air distribution accordingly.

When Downgauging Below 40 µm Becomes a Cost-Saving Requirement

When the target film thickness falls below 40 µm, the downgauging decision cannot be separated from the intrinsic tensile, impact, and tear limitations of a butene-LLDPE base resin. Film thickness is measured according to ISO 4593:1993 or ASTM D6988-21. Dart impact resistance is determined by ASTM D1709-16a method A; at thicknesses below 30 µm, variation in gauge uniformity contributes more to dart impact scatter than intrinsic resin toughness. Thus a blown film line with automatic gauge control and a die gap of 1.2 mm to 1.6 mm is preferred to maintain a coefficient of thickness variation below 5 % where achievable on the specific line.

The addition of high-pressure LDPE at 10 wt% to 20 wt% improves melt extension and reduces film-surface blocking in many formulations, but it generally decreases dart impact under ASTM D1709-16a and Elmendorf tear under ASTM D1922-15. When 6318BE is used as the base resin in a downgauged heavy-duty sack application, the film producer should verify that the final blend still satisfies the end-use mechanical specification. Published data for blend-specific performance of 6318BE across all LDPE types is limited; therefore, a statistically planned evaluation on the target production line is required before committing to a nominal gauge reduction.

Downgauging also increases the importance of the antiblocking package. At lower film thickness, blocking force is amplified by higher contact area and film softness. The resin’s antiblock additive reduces surface contact area through micro-roughness, but excessive antiblock loading can cause visible haze and reduce printability. Converters should measure blocking force to ASTM D3354-15 and coefficient of friction to ISO 8295:1995 before running long-length rolls through high-speed bag-making equipment.

Additive Migration, Coefficient of Friction, and Blocking Force Control

The slip additive in SABIC LLDPE 6318BE migrates to the film surface after extrusion and reduces coefficient of friction over time. The kinetic coefficient of friction of freshly produced film may be above 0.6 before migration; after 7 days at 23 °C, the value often stabilizes between 0.1 and 0.3 depending on film thickness, additive concentration, and surface treatment. Coefficient of friction is measured under ISO 8295:1995, and blocking force is measured under ASTM D3354-15. These two test results are not interchangeable because one depends on surface shear and the other on surface separation resistance.

For corona-treated surfaces, surface tension measured by ISO 8296:2003 may initially exceed 38 mN/m. Corona treatment can consume surface slip additive and delay the reduction in coefficient of friction. If the film is intended for lamination or printing, the treatment level must be selected carefully because excessive treatment can oxidize the surface, increase surface polarity, and alter heat-seal initiation temperature. Heat-seal performance of the final film should be measured according to ASTM F2029-16 or the appropriate end-user sealing specification.

Storage temperature affects migration and blocking. Film rolls should be stored below 50 °C and protected from direct sunlight. At higher storage temperatures, slip migration accelerates and blocking can increase in tightly wound rolls. Film on metal shafts in a warehouse without climate control may experience surface temperature above 50 °C, especially near the roll edges. In such cases, converters should reduce roll winding tension or use a different film structure with a higher antiblock loading.

Regulatory Compliance Requires Grade-Specific Certificate and Simulant Verification

The base resin is expected to meet food contact requirements under 21 CFR 177.1520 and Regulation (EU) No 10/2011, but the finished film is not automatically compliant without converter verification. The resin supplier’s regulatory certificate is required before food-contact use, and the converter must verify that processing aids, regrind, or added masterbatches do not alter the compliance status. For polyolefins, the relevant food-contact framework is 21 CFR 177.1520(c); the specific end-use limitations, temperature conditions, and food-type restrictions are defined in that section and must be confirmed with the grade-specific letter of assurance.

In Europe, Regulation (EU) No 10/2011 requires overall migration testing with simulants listed in Annex III for food categories. The general overall migration limit is 10 mg/dm² of contact area for plastic materials. Specific migration limits for the slip and antiblock substances in the formulation must be checked against the positive list in Annex I and the grade-specific formulation disclosure. If the final article contacts fatty foods, testing under the geometric migration factor rules and the appropriate fatty simulant designation is required, with the final migration expressed per 6 dm² contact area per 1 kg food for standard food-contact ratios.

The table is a verification checklist only; it does not replace grade-specific declarations, lot-specific certificates, or converter migration testing. For pharmaceutical, medical implant, or prolonged mucosal contact applications, additional biocompatibility evaluation is required because the grade is not marketed for those exposure conditions. Processors using regrind must document its proportion and thermal history, as repeated extrusion can alter the antioxidant protective capacity and thereby affect the final compliance profile.