LyondellBasell Icorene 3545 UV+ BLK 9001 Polyethylene, Linear Low Density is a precompounded black rotational moulding powder based on a linear low density polyethylene. The grade designation positions the melt flow rate near 3.5 g/10 min at 190 °C/2.16 kg and the solid density near 0.935 g/cm³. Melt flow rate is determined according to ISO 1133-1, density according to ISO 1183-1. The BLK 9001 suffix identifies a carbon black additive package; the UV+ designation identifies stabilisation against ultraviolet radiation. The powder is intended for rotational moulding of medium-wall outdoor parts such as agricultural tanks, toolboxes, road barriers, and industrial enclosures. Batch-specific values must be confirmed from the supplier certificate of analysis because particle size distribution, additive dispersion, and lot-to-lot melt index vary within manufacturing tolerances.

The product is not a general-purpose extrusion grade; its additive formulation and ground particle geometry are specific to low-shear rotational moulding. As a linear low density material, it is positioned between lower density LLDPE film grades and HDPE structural grades in the polyethylene density spectrum.

The nominal property profile below is compiled from the supplier’s published technical data and is not a specification limit.

How Does the Hindered Amine and Carbon Black Stabilizer Package Alter Weathering Response?

The UV+ package functions through two distinct mechanisms: hindered amine light stabilizers terminate free radicals generated by photo-oxidation, while carbon black absorbs ultraviolet energy and converts it to heat before polymer chain scission occurs. The carbon black also reduces the intensity of light reaching the interior of the part wall. This is relevant for rotationally moulded tanks exposed to direct sun for more than 2,000 h per year. Under accelerated weathering to ISO 4892-2 method A, UV-stabilised black polyolefins are commonly expected to retain at least 50% of initial tensile elongation after 5,000 h; published data for this specific configuration is limited, and the current supplier technical data sheet should be consulted for the approved exposure limit.

The black surface has operational consequences. Compared with a white or natural part, the carbon black surface can reach 10–15 °C higher skin temperature under solar load. Thermal expansion of the part wall must therefore be calculated with a linear coefficient in the range 1.0–1.3 × 10⁻⁴ K⁻¹; unaccounted expansion can cause buckling on long flat panels. In addition, dispersion of the carbon black is critical. Poorly dispersed carbon black agglomerates can initiate ductile failure under impact, even when the base resin passes notched Charpy testing.

Weathering resistance is thickness-dependent. In a 6 mm black wall, the ultraviolet absorbance is high enough that photooxidation is surface-limited; however, the stabilizer package is consumed over time and the part can fail by surface crazing rather than through-thickness embrittlement. The blacker surface created by higher carbon black loading is not necessarily better; excessive carbon black can increase melt viscosity and reduce low-temperature impact. The supplied BLK 9001 grade is precompounded to reduce that risk, but adding extra black concentrate at the machine is not advised because it would disturb the stabilizer-to-pigment balance.

On multi-arm carousel lines, the charge weight is calculated from the part envelope area and target wall thickness. For a 6 mm nominal wall and a solid density of 0.935 g/cm³, the net powder charge is 5.61 kg/m²; adding 5% for parting line, flash, and vent losses yields 5.89 kg/m². Volumetric metering is not reliable without density correction because apparent powder density typically falls between 0.35 g/cm³ and 0.45 g/cm³. A top-size of 35 mesh (500 µm) with a controlled sub-75 µm fraction stabilises dry flow on a carousel hopper; excessive fines can improve early densification but may create surface porosity where the mould is cold. If the powder has been stored above 60% relative humidity, a dehumidified-air purge with a dew point of -40 °C or lower is recommended before charging to prevent steam pinholes.

The mould surface temperature responds slowly after the oven cycle; the internal air temperature measured by a shielded thermocouple in the cavity is the control variable. The first rotation should not exceed 6 rpm for a large symmetrical tank unless the charge is already evenly distributed; high initial rotation can throw powder and produce uneven wall thickness. A rotational ratio of 4:1 between minor and major axes is common for carousel machines, but the optimum depends on part geometry.

Mould material also changes the cycle. Steel moulds with wall thickness between 3 mm and 6 mm respond faster and can use the lower end of the oven temperature range; aluminium moulds of 8–10 mm wall respond slower and may require a higher setpoint. The powder charge should be distributed evenly along the mould parting line before the oven cycle. If a drop box is used, the charging angle should be adjusted so that the powder does not accumulate in ribs or bosses; otherwise the rib tips can remain starved and exhibit reduced burst pressure.

When Peak Internal Air Temperature Falls Outside the 190–210°C Window

Peak internal air temperature below 180 °C indicates incomplete sintering. The part may appear smooth but will contain interparticle voids, visible under 10× cross-section examination, and low-temperature impact strength will be reduced. Peak internal air temperature above 230 °C promotes oxidative degradation at the inner surface; carbonyl absorption can become visible in the 1,720 cm⁻¹ infrared region, and elongation at break falls even though the outer surface looks acceptable. The oven setpoint alone does not control this variable because wall thickness, mould gauge, and rotational speed determine thermal lag. Oven air temperatures between 270 °C and 320 °C are typical, but the hold time after reaching the peak internal air temperature should be kept between 6 min and 10 min for a 6 mm wall. Longer hold times do not significantly improve sintering and increase oxidation risk.

Cooling rate determines shrinkage and warpage. Linear mould shrinkage for this density class is typically 2.0–2.5% when measured on a flat plaque cooled in still air at 23 °C; post-mould shrinkage can add 0.3–0.5% over 24 h. The black surface produces a nonuniform cooling field because the outer mould surface loses heat faster than the inner cavity. If water mist is used, the cooling rate should not exceed 15–20 °C/min until the internal air temperature drops to 80 °C; demoulding below 60 °C is recommended to avoid post-mould distortion.

The Black 9001 Variant Compared with Natural UV+ and HDPE Rotomoulding Powders

Compared with the natural UV+ version of the same base resin, the black 9001 variant reduces ultraviolet transmission through the wall and provides an opaque inspection surface. The black surface also masks carbon-black dispersion defects less effectively than a white pigmented part; specular gloss measurements under ISO 2813 can be used to detect surface roughness. The thermal penalty is the 10–15 °C rise in solar service temperature.

Compared with HDPE rotomoulding powders in the 0.945–0.955 g/cm³ density range, this grade has a lower flexural modulus and a wider ductile-to-brittle transition margin. HDPE rotomoulding powders may show flexural moduli between 800 MPa and 1,200 MPa under ISO 178, whereas this linear low density grade is nearer 560 MPa. The benefit appears at low temperature: the notched Charpy value of 6.5 kJ/m² at -40 °C is above that of many unmodified HDPE rotomoulding compounds, which can fall below 4 kJ/m² at the same temperature. The environmental stress crack resistance measured under ASTM D1693 also exceeds typical HDPE rotomoulding powders of equivalent melt flow. The trade-off is lower creep resistance under continuous load; the LLDPE grade should not be used where long-term tensile creep at 60 °C is the governing design case without creep modulus data.

In applications using dense loading such as buried agricultural tanks, the lower flexural modulus of LLDPE must be compensated by rib spacing and wall thickness. A vertical tank sidewall with a 1 m unsupported span and 10 kPa hydrostatic pressure should be checked using plate deflection equations with a modulus derated for creep and temperature. If the part is welded, high-frequency welding is not applicable to polyethylene; hot-gas or extrusion welding must be used, and the heat-affected zone should be tested under the original ESCR method because weld orientation can reduce crack resistance.

Diesel Fuel and Aqueous Chemical Storage Boundaries

For diesel fuel tanks, the resin’s ESCR value above 1,000 h under ASTM D1693 condition A supports use, but the design stress should be derated by 10–15% where the wall is continuously wetted with fuel. Diesel sorption softens the wall and can reduce the apparent flexural modulus; a design stress below 5 MPa at 23 °C is commonly used for unsupported walls. For aqueous and agricultural chemical service, compatibility should be evaluated by immersion testing according to ASTM D543 at the end-use concentration and temperature. Oxidizing acids, aromatic hydrocarbons, and strong ketones are boundary conditions for this polymer class; they can reduce ESCR and promote environmental stress cracking at molded-in stresses. The black compound is not automatically compliant with drinking-water regulations; approval must be verified on the finished article under the applicable national standard, and the carbon black may require specific migration testing under EU Regulation 10/2011. For REACH, the material is governed by Regulation (EC) No 1907/2006; for electrical and electronic applications, RoHS Directive 2011/65/EU applies only to the finished article, not the raw polymer.

For intermittent contact with aliphatic hydrocarbons, the grade absorbs less than 1% by mass over 30 days at 23 °C; continuous immersion in toluene or xylene is outside the recommended boundary. In aqueous detergent service above 60 °C, the combination of temperature and surfactant can accelerate creep and environmental stress cracking more than the pure chemical would suggest.

Lot acceptance on an industrial manufacturing line requires verification of melt flow rate and density from the certificate of analysis before charging production hoppers. Regrind addition above 15 wt% can shift the particle size distribution and reduce dry flow; any regrind must be blended with virgin powder and re-screened through 35 mesh before use. The product is supplied as a rotational moulding powder and is not intended for injection moulding, blow moulding, or film extrusion because the stabilizer loading and particle geometry are specific to low-shear rotational moulding.

The powder’s performance is sensitive to storage conditions. Bags should be kept unopened at 10–30 °C and below 60% relative humidity; exposure to direct sunlight on the pallet can preheat the powder and create condensation during cold-mould charging. When the material is transferred by pneumatic conveyor, line velocities above 20 m/s can create fines and static charge; dense-phase conveying is preferred to preserve the particle size distribution.