LyondellBasell Icorene 3560 BWG 9276 is a linear low-density polyethylene (LLDPE) grade identified in manufacturer documentation as a rotational molding and compounding feedstock. The product series carries a nominal density of 0.935 g/cm³ when determined by ISO 1183-1:2019 and a nominal melt flow rate of 6.0 g/10 min when determined at 190 °C/2.16 kg by ISO 1133-1:2022. These values are nominal series values; the BWG 9276 additive and pigmentation package can shift as-delivered density and melt flow relative to the unpigmented base resin, so the certificate of analysis is controlling. The BWG 9276 suffix is an additive and color package designation. The BWG portion is associated with black weathering-stabilized formulations, and 9276 identifies the specific stabilizer and pigment formulation. Exact additive loadings are proprietary and lot-dependent.

The material is an ethylene-alpha-olefin copolymer produced by low-pressure catalytic polymerization. The linear backbone and short-chain branching differentiate it from high-pressure low-density polyethylene, which contains long-chain branches, and from high-density polyethylene, which has lower comonomer content and higher crystallinity. These structural characteristics affect not only laboratory properties but also machine behavior: at the same nominal melt flow rate, LLDPE may exhibit higher zero-shear viscosity and slower powder coalescence in unpressurized molds than an LDPE of equivalent density class. Published data specific to the BWG 9276 package is limited in open literature; where direct data are absent, comparisons are scaled from the 3560 series or from equivalent LLDPE rotomolding grades of the same nominal density and melt flow class.

What Distinguishes This Linear Low-Density Polyethylene from High-Pressure LDPE and HDPE?

The primary difference is molecular architecture. High-pressure LDPE is produced by free-radical polymerization and contains both short-chain and long-chain branches; the long-chain branches create shear thinning but also reduce environmental stress crack resistance at a given density. HDPE is an ethylene homopolymer or low-comonomer copolymer with minimal short-chain branching, yielding high crystallinity, high flexural modulus, and lower impact resistance in thick sections. The Icorene 3560 BWG 9276 grade belongs to the LLDPE class, which is an ethylene-alpha-olefin copolymer with a controlled distribution of short-chain branches and no significant long-chain branching. At a nominal density of 0.935 g/cm³, the product is positioned at the upper end of the LLDPE density range and approaches the medium-density transition zone; this raises flexural modulus relative to 0.918–0.925 g/cm³ LLDPE while retaining higher environmental stress crack resistance than a typical HDPE homopolymer.

For mechanical comparisons, tensile properties are normally evaluated on compression-molded plaques under ASTM D638-14. LLDPE grades in this density and melt flow class typically show tensile yield stress between 17 MPa and 19 MPa, elongation at break above 800%, and flexural modulus between 600 MPa and 750 MPa when tested under ISO 178:2019. HDPE grades at 0.950 g/cm³ and above generally exceed these modulus values but may exhibit lower notched impact and environmental stress crack resistance. Rotomolded parts from LLDPE also show a different failure mode: under constant strain in detergent or surfactant solutions, the LLDPE part tends to craze and yield locally rather than undergo rapid crack propagation through spherulitic boundaries. Environmental stress crack resistance is evaluated by ASTM D1693-15; direct comparison between LLDPE and HDPE is valid only when specimen thickness, notch depth, and test temperature are identical.

In processing terms, LDPE has a broader melting range and lower zero-shear viscosity, which permits faster powder densification at lower oven settings. LLDPE requires a higher internal mold air temperature to complete particle coalescence and air removal. HDPE requires even higher peak temperatures and is more sensitive to warpage and internal void formation in thick sections due to its sharper crystallization exotherm. Therefore, a direct substitution of Icorene 3560 BWG 9276 for LDPE or HDPE without adjusting oven residence time, rotation ratio, and venting is not recommended. The product’s 6.0 g/10 min melt flow rate is one control point: higher melt flow grades of the same density reduce cycle time but may reduce environmental stress crack resistance; lower melt flow grades improve toughness but may increase cycle time and risk pinholes in thin-wall parts.

In rotational molding, the charge weight is calculated from the part wall thickness and the powder apparent density, which for this grade is typically in the 0.380–0.420 g/cm³ range when measured under ASTM D1895-96 Method A. Pulverized powder should be screened to remove fines below 35 mesh and coarse particles above 70 mesh where tight surface detail is required. Excessive fines increase dust accumulation in vent ports and produce nonuniform melt-out; oversized particles can remain unmelted in thin walls and create surface defects. The recommended peak internal air temperature for this melt flow range is between 180 °C and 210 °C. Oven air temperature is normally set between 260 °C and 320 °C depending on mold thermal mass, wall thickness, and transfer time. A nitrogen purge on the mold interior is common on production-scale carousel machines to reduce oxidative degradation of the black weathering package during extended dwell.

If the powder is stored at relative humidity above 60%, surface moisture can generate steam bubbles in thick sections. Pre-drying at 60–70 °C for 1–2 h in a desiccant dryer or heated hopper is a standard corrective action; moisture content below 0.05% is a typical control target for rotomolding powders. Production-scale process bottlenecks include uneven wall thickness in deep-draw cavities when the mold rotation ratio is below 4:1, and surface porosity when demolding is attempted before the mold surface temperature falls below 70 °C. The grade’s melt flow rate of 6.0 g/10 min balances particle coalescence and air release, but it does not remove the need for venting in enclosed mold features such as ribs, threaded inserts, or foam-filled cavities.

On a fixed-arm carousel machine with a swing diameter of 3.0 m or smaller, the colder mold shoulder in the off-side position can remain below the polymer melting range for several minutes, leading to nonuniform densification. Independent inner mold air temperature measurement with a radio telemetry probe is the accepted method to verify that all surfaces reach the required 180–210 °C window. Infrared pyrometers aimed at the mold exterior are not sufficient because dark carbon black surfaces absorb infrared differently than natural LLDPE powders.

Specification Ranges and the ISO/ASTM Methods Used to Assign Them

The properties below are given as indicative ranges for an LLDPE rotomolding grade of nominal density 0.935 g/cm³ and melt flow rate 6.0 g/10 min. They are not a substitute for the manufacturer’s certificate of analysis for the BWG 9276 package, because carbon black and stabilizer loading can shift melt flow and density relative to a natural base resin. Conditioning and specimen preparation follow the standards listed; property comparisons between suppliers are valid only when the same specimen thickness, cooling rate, and test temperature are applied.

Environmental stress crack resistance is not an intrinsic material constant; it is strongly influenced by molded-in stress, cooling rate, and part geometry. Values above 1000 h are commonly reported for compression-molded plaques but may not be reproduced on rotomolded parts with abrupt wall-thickness transitions. Flexural modulus data from ISO 178:2019 are generated on conditioned specimens at 23 °C and 50% relative humidity; modulus decreases as temperature approaches the Vicat range.

Thermal analysis by differential scanning calorimetry under ISO 11357-3:2018 typically records a broad melting endotherm for this LLDPE class, with peak melting temperatures in the 122–130 °C range and crystallization onset near 108–112 °C at a cooling rate of 10 °C/min. The broad melting range is relevant to rotational molding because it delays complete solidification and permits air bubble migration; a narrow melting metallocene grade may solidify too quickly in complex molds.

When Internal Mold Air Temperature Exceeds the Recommended Dwell Window

Prolonged exposure above 220 °C internal air temperature accelerates consumption of the weathering stabilizer package in the BWG 9276 formulation. Carbon black absorbs radiant energy more efficiently than natural resin, so dark parts develop a larger skin-to-core temperature differential. If the inner wall surface remains above 220 °C for more than a few minutes, the polymer begins to generate carbonyl species that can be monitored by infrared spectroscopy under ASTM D5576-00. A measurable increase in carbonyl index relative to the as-received powder indicates depletion of the antioxidant package and a loss of long-term oxidation resistance.

The consequence is threshold-dependent. Notched impact toughness measured by ISO 179-1:2010 may remain unchanged during the first stage of additive depletion and then fall sharply once the retained stabilizer concentration drops below the critical level. In production-scale trials on a carousel machine with 25-minute total cycle and 6 mm nominal wall thickness, internal air reached 205 °C while the exterior mold surface exceeded 235 °C; bubble formation occurred in the low-velocity region behind a threaded insert because localized viscosity reduction trapped volatiles. These observations are not unique to Icorene 3560 BWG 9276 but are representative of black rotomolding LLDPE grades in this density class.

The operational boundary for reliable molding is therefore bounded at the upper end by the degradation kinetics of the stabilizer package and at the lower end by incomplete particle coalescence. Published data for this specific BWG 9276 configuration is limited, and the boundaries above are generalized from LLDPE rotomolding grades of equivalent nominal density and melt flow. They should not replace lot-specific run sheets or the manufacturer’s technical service recommendations.

Regulatory Status and the Compliance Tests Required for End-Use Articles

For food-contact applications, polyethylene olefin polymers are regulated in the United States under 21 CFR 177.1520, which permits olefin polymers provided density, melting point, and extraction limits are satisfied. The black pigment package must meet the purity requirements of 21 CFR 178.3297 or equivalent national legislation. In the European Union, compliance is assessed under EU Regulation 10/2011 with overall migration not exceeding 10 mg/dm² for food-contact articles. These regulations apply to the finished article rather than the resin alone.

Compliance statements must be confirmed against the current formulation and the intended use temperature. A black weathering grade intended for outdoor industrial tanks is not automatically suitable for food-contact service unless the specific additive package and colorant purity are verified for that end use.